copyright 2006, francisco javier gonzalez gonzalez
TRANSCRIPT
VEGETATION CHANGES AFTER 12 YEARS IN FOUR PRIVATE
RANCHES UNDER SHORT-DURATION AND CONTINUOUS
GRAZING SYSTEMS IN CHIHUAHUA, MEXICO
by
FRANCISCO JAVIER GONZALEZ GONZALEZ, B.S., M.S.
A DISSERTATION
IN
LAND-USE PLANNING, MANAGEMENT AND DESIGN
Submitted to the Graduate Faculty of Texas Tech University in
Partial Fulfillment of the Requirements for
the Degree of
DOCTOR OF PHILOSOPHY
Approved
Mukaddes Darwish Chairperson of the Committee
Michael Galyean
Eduardo Segarra
Mark Wallace
Accepted
John Borrelli Dean of the Graduate School
August, 2006
Copyright 2006, Francisco Javier Gonzalez Gonzalez
ii
ACKNOWLEDGEMENTS
First, and foremost I would like to thank God because with him anything is
possible. I also express my gratitude to Dr. Mukaddes Darwish, chair of my
graduate committee for the opportunity she gave me to work with her, for her
support and encouragement to me, and for her example. To the other members
of my committee, Drs. Mark Wallace, Mike Galyean, and Eduardo Segarra, thank
you for this collaboration and your contribution in helping ensure that this work
was completed. I especially thank Drs. Galyean and Segarra for their support
through the tough times.
My deepest gratitude to the Consejo Nacional de Ciencia y Tecnologia
(CONACYT) and the Instituto Nacional de Investigaciones Forestales Agrícolas y
Pecuarias (INIFAP) for their financial support during the entire period of study.
My sincere gratitude is extended to Ing. Jesus Almeida, Lic. Federico
Terrazas, my friends Jaime Jeffers and Ing. Carlos Prado for permitting this study
to be conducted on their ranches.
Also I thank the following people for their help before and during the study:
Ing. Octavio Nuñez for his help in conducting the field work; and Drs. Alicia
Melgoza, Santos Sierra and Jorge Jimenez for their advice in organizing and
analyzing the data.
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I thank the following friends for their support, friendship and prayers:
Rogelio and Diana Carrera; Alejandro and Beatriz Meza; Gerardo and Beatriz
de la O, and all the people who helped me with their prayers.
Special thanks to Ing. Antonio and Enriqueta Chavez for their friendship
and moral support during all these years.
Also, thanks must be given to Dr. Sherman Phillips for his invaluable help
in editing this document and his friendship.
I express my appreciation to the Texas Tech Graduate School staff for
their fairness and financial support during the last year, especially to Drs. Ralph
Ferguson and John Borelli.
Finally I must thank my wife Bertha, my daughter Palmira, and my sons
Octavio and Eduardo for their incredible encouragement, support, and love
during all this time, because without them this work would have not been
completed.
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TABLE OF CONTENTS
ACKNOWLEDGEMENTS ii
ABSTRACT v
LIST OF TABLES vi
LIST OF FIGURES viii
LIST OF ABBREVIATIONS AND ACRONYMS ix
CHAPTER
I. INTRODUCTION 1
II. LITERATURE REVIEW 7
Short-Duration Grazing 8
Vegetation Changes 17
Cover 18
Forage Production 20
Density 23
III. VEGETATION CHANGES AFTER 12 YEARS IN FOUR
PRIVATE RANCHES UNDER SHORT-DURATION AND
CONTINUOUS GRAZING IN CHIHUAHUA, MEXICO. 27
Introduction. 27
Material and Methods 28
Results 38
Discussion 60
IV. CONCLUSIONS AND RECOMMENDATIONS 71
LITERATURE CITED 77
v
APPENDIX
A. VEGETATION SAMPLING TABLES 86
B. STATISTICAL ANALYSIS OUTPUTS 105
C. GLOSSARY 119
vi
ABSTRACT
With the objective to evaluate the vegetation changes over 12 years in
four ranches under Short-Duration (2 ranches) and Continuous (2 ranches )
grazing systems, a vegetation survey study was conducted in the fall of 1993,
1994, and 2005. Vegetation information was collected related to herbaceous
basal cover and shrub aerial cover, grass forage production, and plant density.
Vegetation was divided by functional groups to facilitate the analysis. The
perennial grasses functional group was the most consistent and reliable
functional group over time. Annual grasses and annual and perennial forbs were
important in the first year but tended to disappear in later years. Short-Duration
grazing had a higher perennial basal cover than the traditional system (P=0.059).
However, the magnitude of the decrease was greater in Short-Duration than in
Continuous grazing. A difference in forage production was found between
grazing systems (P=0.006). Ranches under continuous system had the highest
and the lowest production. The presence of Lehmann lovegrass in one of the
ranches under Continuous grazing accounted for a large proportion of forage.
A severe drought in 5 out of 12 years affected the response of vegetation,
and the effect of grazing system was likely diminished by the drought. Short-
Duration stocking rates were greater than those used in Continuous grazing.
Nevertheless, due the range condition in the Continuous treatment, the stocking
rates were also considered high. The stocking rates and drought conditions
affected the vegetation response of the grazing systems evaluated in this study.
vii
LIST OF TABLES
3.1 Basal cover (%) of perennial grasses in four ranches under two different grazing systems in Chihuahua, Mexico. 40 3.2 Basal (grasses and forbs) and aerial (shrubs and suffrutescents) cover (cm) of species present in sampled transects categorized by functional groups in Ranch 1. 42 3.3 Basal (grasses and forbs) and aerial (shrubs and suffrutescents) cover (cm) of species present in sampled transects categorized by functional groups in Ranch 2. 44 3.4 Basal (grasses and forbs) and aerial (shrubs and suffrutescents) cover (cm) of species present in sampled transects categorized by functional groups in Ranch 3. 46 3.5 Basal (grasses and forbs) and aerial (shrubs and suffrutescents) cover (cm) of species present in sampled transects categorized by functional groups in Ranch 4. 49 3.6 Basal cover (%) of by functional groups in four ranches under Short Duration (SD) and Continuous (CG) grazing management in Chihuahua Mexico. 52 3.7 Eigenvectors and weighed averages for the significant components resulted from a PCA conducted in 1993 and 2005 for vegetation changes in ranches with different grazing systems. 54 3.8 Forage production (kg DM/ha) in four ranches managed under Short Duration (SD) or Continuous (CG) grazing systems in Chihuahua, Mexico. 58 4.1 List of species sampled in Fall 1993; Cover (cm/1200 cm) length Ranch 1 87 4.2 List of species sampled in Fall 1994; Cover (cm/1200 cm) length Ranch 1 88 4.3 List of species sampled in Fall 2005; Cover (cm/1200 cm) length Ranch1 89
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4.4 List of species sampled in Fall 1993; Cover (cm/1200 cm) length Ranch 2 90 4.5 List of species sampled in Fall 1994; Cover (cm/1200 cm) length Ranch 2 91 4.6 List of species sampled in Fall 2005; Cover (cm/1200 cm) length Ranch 2 92 4.7 List of species sampled in Fall 1993; Cover (cm/1200 cm) length Ranch 3 83 4.8 List of species sampled in Fall 1994; Cover (cm/1200 cm) length Ranch 3 94 4.9 List of species sampled in Fall 2005; Cover (cm/1200 cm) length Ranch 3 95 4.10 List of species sampled in Fall 1993; Cover (cm/1200 cm) length Ranch 4 96 4.11 List of species sampled in Fall 1994; Cover (cm/1200 cm) length Ranch 4 97 4.12 List of species sampled in Fall 2005; Cover (cm/1200 cm) length Ranch 4 98 4.13 Ranch 1 list of species sampled ; Density (plants/m2) 99 4.14 Ranch 2 list of species sampled ; Density (plants/m2) 100 4.15 Ranch 3 list of species sampled ; Density (plants/m2) 101 4.16 Ranch 4 list of species sampled ; Density (plants/m2) 102 4.17 Forage production (kg DM/ha): Ranch1 103 4.18 Forage production (kg DM/ha): Ranch 2 103 4.19 Forage production (kg DM/ha): Ranch 3 104 4.20 Forage production (kg DM/ha): Ranch 4 104
ix
LIST OF FIGURES
3.1 Localization of Chihuahua State in Mexico. 29 3.2 Pasture distribution and vegetation type in Ranch 1. 30 3.3 Pasture distribution and vegetation type in Ranch 2. 31 3.4 Former pasture distribution and vegetation type in Ranch 3. 32 3.5 Former pasture distribution and vegetation type in Ranch 3. 34 3.6 Rainfall pattern (mm) of four ranches under Short Duration (SD) and Continuous (CG) grazing management in Chihuahua, Mexico. 39 3.7 Perennial grasses basal cover (%) in four ranches under Short Duration (SD) or Continuous (CG) grazing management in Chihuahua, Mexico. 53 3.8 Principal component analysis of functional groups associated with management system at four ranches in Chihuahua, Mexico in 1993. 56 3.9 Principal component analysis of functional groups associated with management system at four ranches in Chihuahua, Mexico in 2005. 57
x
LIST OF ABBREVIATIONS AND ACRONYMS
AU. Animal Unit
AUM Animal Unit Month
AUY. Animal Unit Year
ANPP-N. Above Ground Net Primary Production Nitrogen
CETES. Certificados de la Tesorería de la Federación (Mexico).
CONACYT. . Consejo Nacional de Ciencia Y Tecnología
CG Continuous Grazing COTECOCA Comisión Técnico Consultiva Para la determinación de los
Coeficientes de Agostadero cwt. hundred weight (per 100 pounds)
DM Dry matter.
FIRA. Fideicomiso Instituido en Relación a la Agricultura
GLM General Linear Model
ha hectare.
HILF High Intensity Low Frequency
HRM. Holistic Resource Management
INIFAP. Instituto Nacional de Investigaciones Forestales Agrícolas y Pecuarias
Km . kilometers
ROT Rotation grazing System
SDG. Short–Duration Grazing
SL Season-Long
1
CHAPTER I
INTRODUCTION
Natural resources have been affected by human use, and vegetation is
one of the components most disturbed by this activity. The introduction of
domesticated animals in America, as well as in other places worldwide, has
replaced the grazing impact that native wildlife had for centuries on natural
vegetation. Many plant species had adapted to grazing by native animals
because they evolved together; however, plants are susceptible to domestic
grazing, and whole plant communities have been changed or replaced by other
communities because of this new grazing pressure (Stoddart et al., 1975).
Destructive livestock grazing in the western US occurred in the late 1800s
and early 1900s; however, it was largely arrested by WW II, when more intensive
management practices were applied to the majority of rangelands (Pieper, 1999).
This situation was aggravated with the invention and use of barbed wire.
Barbed-wire fences helped confine free-roaming animals to a specific piece of
land. Variable grazing rates by native herbivores were replaced by years of
season-long heavy grazing by livestock beginning in the late 1800s (Miller et al.,
1999).
Grazing animals affect plants both directly and indirectly. Direct effects of
grazing are those associated with alterations of physiology and morphology
resulting from defoliation and trampling. Grazing also influences plant
2
performance indirectly by altering the microclimate, the soil properties, and the
plant’s competitive interactions. Over time, the combined direct and indirect
effects of grazing on plant growth and reproduction become manifest in plant
population dynamics (Archer and Smeins, 1991).
Livestock grazing has played a role in decreasing the amount of fuel for
wildfires, altering nutrient distribution, acting to create patchiness at landscape
levels for many animal species, and disrupting cryptogamic crusts.
Nevertheless, domestic livestock grazing at conservative levels seems to be
sustainable (Pieper, 1999). As previously stated, many rangeland communities
were subjected to grazing, and therefore, the effect of grazing is an integral part
of the ecosystem. The discontinuation of grazing on rangelands has often been
based on the belief that decreasing or removing livestock will solve any existing
rangeland problem and rapidly return these lands to near pristine condition
(Vallentine, 2001). However, removing all livestock grazing would not return
rangelands to a pristine condition. In many cases the changes would be subtle,
and in the long run, they might even be negative in terms of biodiversity and
other desirable characteristics (Pieper, 1999).
Even under protection from large herbivores, vegetation is dynamic and
fluctuates in response to other controlling factors such as climate. The effect of
grazing by domestic livestock is variable. It is extremely difficult to generalize
because of differences in climate, resistance of various species to grazing,
3
stocking levels, composition of vegetation, grazing season, and many other
factors.
Despite the current development of sophisticated analytical techniques,
separation of grazing impact from climatic impact remains difficult (Holecheck,
1998).
1.1 Justification
For many decades, continuous grazing was practiced by ranchers in the
Western US. Because of this practice, detrimental effects on range condition
were observed in many areas in North America. Continuous grazing has often
been criticized as being detrimental to vegetation; however, the major cause of
deterioration has commonly been heavy grazing and/or poor distribution of
grazing (Vallentine, 2001).
This situation of decreasing range condition resulted in an early attempt at
grazing methods development. The primary objective of most grazing
management practices is to maximize livestock production per unit area of
rangeland, while maintaining a sustainable forage resource (Heitschmidt and
Walker, 1983). The inclusion of grazing deferment and rest were the first
practices implemented as grazing methods, which allowed vegetation recovery.
Rotational stocking methods have been recommended as a way to
enhance vegetation, livestock, and wildlife production. Theoretically, benefits
from rotational stocking results from control of selective grazing (Taylor et al.,
4
1997). Historically, an array of special grazing techniques has been collectively
referred to as “grazing systems.” These techniques vary from simple to complex,
and are available to further fine tune the management of grazing. “Special
grazing technique” is a generic term employed to include both grazing methods
and grazing systems. A grazing system is defined as a specialization of grazing
management based on rotating grazing animals among two or more grazing land
units (paddocks), while defining systematically recurring periods of grazing and
non-grazing. A grazing system will generally include one or more grazing
methods in addition to rotating grazing (Vallentine, 2001).
One innovative way to implement range management was promoted by
Allan Savory in Zimbabwe, Central Africa, in 1960. Inspired by the grazing habits
of wild animals in his home country, Savory developed a theory regarding the
way domestic animals could be managed to improve both animal and vegetation
performance. This new grazing management philosophy was named Holistic
Resource Management (HRM). One of the tools that include the HRM is the
Short-Duration grazing (SDG), which consist in the division of pasture in a large
number of paddocks, in order to rotate the livestock through all pastures, the
rotation is more rapid during growing season and slower during the mature stage
and dormancy, the length of grazing and rest depend on the number of
paddocks.
During the1980s, HRM resulted in controversial discussions because the
principles on which it was based are unusual, and to a certain degree, they
5
contradict many of the traditional range management guidelines. Much was
published regarding the evaluation of HRM on soil, vegetation, animal response,
and so on. The majority of these evaluations concur that HRM or SDG, which it is
also termed, instead of improving the animal, soil and vegetation measurements,
produces a detrimental effect on the measurements evaluated. The most
negative results obtained were observed in arid and semiarid environments. The
predominant vegetation under these situations is more fragile and sensitive to
mismanagement compared with more humid conditions. Most adverse effects
found were related to soil infiltration rate caused by soil compaction and
decrease in individual animal performance resulting from an increase in carrying
capacity.
Despite the adverse results obtained in most studies where HRM was
evaluated, some philosophical principles on which it is based are quite
interesting, mainly those that encourage the range manager to maintain a
frequent monitoring of soil, vegetation, and animal conditions. The establishment
of annual, monthly, and daily plans that may be redirected at any time depending
on monitoring results, is not a common practice in the majority of the grazing
system programs. However, the most interesting aspect of HRM is that some
ranchers, no matter what they expected in terms of vegetation response to
increased carrying capacity, perceive benefits in other aspects. For example,
they now practice a more opportunistic destocking during forage shortages.
Moreover, they are now more aware of the detrimental effect of
6
overgrazing and its negative effect on range condition. This effect increases
during drought periods such as those experienced in State of Chihuahua during
the past 14 years. Some ranchers who initiated the use of HRM were forced to
destock the ranches and use lower stocking rates because of the severe drought.
Nonetheless, because they invested a large amount of money in infrastructure,
some of them still practiced the HRM, but at lower stocking rates.
Many studies conducted by other people to evaluate the SDG lasted two
or three years, some were monitored for five or six years, but only few were
conducted for ten or more years. Determination of vegetation changes through
the implementation of range management practices is a process that takes time,
particularly when great climatic variation occurs. For this is the reason, one
objective of this study was to evaluate vegetation changes on some ranges that
have been managed under the HRM for more than a decade.
1.2 Objectives
To examine vegetation changes on private properties after 12 years.
To measure vegetation changes on private ranches that practiced Short-
Duration grazing compared with those that utilized Continuous grazing.
7
CHAPTER II
LITERATURE REVIEW
Barbour et al., (1989) described grasslands as herbaceous communities
dominated by graminoides (grasses, sedges, and rushes) but with forbs (non-
graminoid herbs) present and sometimes seasonally dominant. Trees are absent
except for local sites, such as along water courses or among rock outcrops.
Grasslands are dominated by annual grasses, perennial bunch grasses, or
perennial sod-forming grasses. Annuals are most abundant on dry, overgrazed,
or disturbed sites. Annual warm-season types germinate in spring or summer
and complete a much shorter life cycle in a matter of weeks, rather than months.
They do not reproduce vegetatively with runners or rhizomes. Six-week grama
(Bouteloua barbata, in the desert grassland), is such an annual.
Perennial bunch grasses, such as purple blue grama (Bouteloua gracilis)
produce tillers, and the continuation of that process for many years result in a
large clump a decimeter or more in diameter. Bunch grasses alone do not
generally produce a community with 100% cover, the spaces between clumps
can be seasonally filled by forbs and other grasses. Perennial sod-forming
grasses, such as big bluestem (Andropogon gerardii) in the tall-grass prairie,
spread laterally by rhizomes. New shoots and roots arise from nodes on the
8
rhizomes in such number that a turf results. Top soil is thoroughly penetrated
and held together by the fibrous root system, and a continuous sward of shoots
covers the surface. Sod-formers are more resistant to grazing than bunch
grasses because they have so many more growing points. Some sod-formers
are less aggressive than others, producing only short rhizomes, and some
produce rhizomes only under certain environmental conditions (Barbour et al.,
1998).
Forbs are also an important component on many grasslands. Forbs are
nongrass-like plants with tap roots, generally broad leaves with netlike veins, and
solid non-jointed stems. Shrubs, which are a minor component of most
grasslands, have woody stems that branch near base, and long, coarse roots.
Stems remain alive during dormant periods, which is different than most grasses
and forbs, with which the above-ground parts die back to the crown during winter
or during the dry season (Holecheck et al.,1998). More specific descriptive
terminology will be provided in the appendix section.
2.1 Short Duration Grazing
Grazing is the process by which some animals acquire their food needs to
meet their intake and nutritional requirements. Grazing in most natural
ecosystems is as much as part of the system as is the need for forage by grazing
animals. Most native rangeland evolved under animals grazing plants and plants
tolerating grazing (Vallentine, 2001).
9
Although, not native to western rangelands, livestock function similarly to
native herbivores in that they harvest plants, defecate, urinate and are involved in
nutrient cycles. In addition, livestock compete with and complement other
herbivores in rangeland ecosystem, and they may stimulate primary production
or depress it (Pieper, 1999).
Grazing management involves the regulation of this consumptive process
by humans, primary through the manipulation of livestock, to meet specific,
predetermined production goals (Briske and Heistchmidt, 1991).
Since SDG emerged as a new way to handle grazing animals, and
because it sounded too good to be true, many researchers were prompted to
evaluate this new paradigm in grazing management under different regimens.
The responses of vegetation to the SDG use vary, and many times these
variations are associated with climatic conditions. Weather interacts with grazing
treatments, species, and the combined effects of other factors, indicating the
dominant effect of weather, particularly precipitation, on changes in herbaceous
basal area (Teague et al., 2004). Nevertheless, a major concern is the failure of
SDG, as well as other grazing systems at high stocking rates (Pitts and Bryant,
1987; Pieper and Heischmidt, 1988). Stocking rates have much greater potential
than grazing systems for altering frequency and intensity of defoliation and
subsequent changes in botanical composition of range plant communities (Hart
et al., 1993).
10
Many aspects of SDG have been evaluated, from soil characteristics
(Weltz and Wood, 1986; Chanasyk and Naeth, 1995; Weigel et al., 1990) to plant
defoliation (Aiken and Springer, 1998; Guillen et al., 1998; Taylor et al., 1997;
Pierson and Scarnecchia, 1987), animal diets (Ortega et al., 1997; Hirschfeld et
al., 1996; Taylor and Kothmann, 1990; Kirby et al.,1986; Nelson et al., 1989),
cattle nutrition (Olson et al., 1989; Pitts and Bryant, 1987; McCollum and Guillen,
1998), animal performance (Volesky et al., 1990; Aiken, 1998; Bertelsen et al.,
1993), vegetation response (Taylor et al., 1997, White et al., 1991; Guillen et al.,
1991; Palmer et al., 1990; Hart et al., 1993; Dormaar et al., 1989), and many
other more specific vegetation, animal, and soil characteristics.
Although every aspect is important when evaluating a grazing system, the
vegetation issue is probably of major concern because all other concepts are
directly or indirectly interrelated to vegetation. As established previously,
diminishing range condition was the trigger that initiated the development of the
first grazing strategies. Grazing systems have been developed as a means of
increasing rangeland productivity by increasing carrying capacity (Pitts and
Bryant, 1987), and SDG is purported to sustain higher stocking rates through
increased forage production and utilization compared with other grazing systems
(Savory, 1983).
Results found in literature regarding the SDG are quite interesting,
because they seem contradictory. However, the major concerns with SDG are
the large investments in infrastructure, high stocking rates utilized, and pasture
11
size. In addition, outcomes in vegetation aspects and animal performance are
varied and highly dependent on climatic condition and vegetation types.
In a study conducted by Dormaar et al. (1989), it was found that range
condition decreased when the stocking rate was increased two- to three-fold
above that recommended on a festuca grassland in western Canada. Over five
years, Ralphs et al. (1990) conducted an experiment near Sonora, Texas, where
four stocking rates were used to determine whether the standing crop could be
maintained with a graze length of 3 days and 51 days of rest. Ralphs et al.
(1990) found little change in frequency and composition of short-grasses, but
mid-grass frequency and composition both declined. This decline was greater for
the fall than in the growing season, and inversely proportional to stocking rate.
Taylor et al. (1997) continued the previously mentioned study five more years,
and found that the tendency was the same: curly-mesquite (Hilaria belangerii)
increased in all treatments, and decreased in the livestock exclosure. Sideoats
(Bouteloua curtipendula) and other mid-grasses decreased under all stocking
rate treatments and increased with livestock exclusion.
Continuous grazing is considered the benchmark when any grazing
system is evaluated, and SDG is not an exception. In many instances no
differences were found when SDG has been compared with continuous grazing,
and many times the performance of continuous grazing was superior (Angell,
1997; Bryant et al., 1989)
12
Research comparing rotational with continuous grazing has generally
concluded that the effects of rotational grazing per se on defoliation patterns are
weak or absent. However, research on rotational grazing systems has invariably
been carried out using small paddocks, usually less than 25 ha, and often less
than 5 ha. In addition, research areas are specially chosen to be as uniform as
possible. Both factors significantly decrease the variability that causes patch
selection and the associated deterioration in large paddocks (Norton, 1998). In a
study conducted in Vernon, Texas, where the size of the pastures used as
replications ranged from 1,295 to 2,131 ha, the conclusion was that when
summer growing conditions were favorable, rotational grazing treatment resulted
in greater increases of perennial herbaceous basal areas and a lower proportion
of bare ground than the continuously grazed treatment. Although, rotational
grazing did not prevent deterioration in basal areas and bare ground with the
series of four drought years, it decreased the rate of deterioration (Teague et al.,
2004).
Decreased pasture size and distance to water may be responsible for the
alleged benefits of intensive time-controlled rotation grazing systems.
Comparisons were made on cattle gains and activity, distance traveled, and
forage utilization on a time-controlled rotation system with eight, 24-ha pastures,
on two 24-ha pastures grazed continuously (season-long), and on one 207-ha
pasture grazed continuously, stocked at the same rates. Utilization on the 207-
ha pasture, but not on the 24-ha pasture, decreased with distance from water. At
13
distances greater than 3 km from water in the 207-ha pasture, utilization was
significantly less than on adjacent 24-ha pasture at distances of 1.0 to 1.6 km
from water. Cows on the 207-ha pasture traveled farther (6.1 km/day) than cows
on the 24-ha rotation pasture (4.2 km/day), which in turn traveled farther than
cows on the 24-ha continuously grazed pasture (3.2 km/day). Grazing system,
range site, slope, and weather had minimal effect on cattle activity patterns.
Intensive rotation grazing systems are unlikely to benefit animal performance
unless pasture size and distance to water are decreased (Hart et al., 1993).
The stocking rate on semi-permanent heavily grazed patches is much
greater than the intended stocking rate of the paddock as a whole (Kellner and
Bosch, 1992). This leads to a progressive deterioration characterized by
replacement of taller perennial by shorter perennial grasses, followed by annual
grasses, and finally bare ground (Teague et al., 2004).
The vegetation response of SDG and continuous grazing at the same
stocking rates were similar in a tallgrass prairie (Guillen et al.,1998). Similarly,
after a four-year evaluation, Angell (1997) found no difference between high
stocked SDG and continuous grazing in crested wheatgrass tiller density.
However, they found that Wyoming sagebrush densities increased under high
SDG, but not under low stocking, and that SDG was similar to continuous
grazing.
Declining grassland productivity is a major concern in southern temperate
Australia. Continuous grazing is thought to be a primary contributor to this
14
decline, which is associated with the loss of perennial grasses. Dowling et al.
(2005) reported a comparison between continuous grazing and time-controlled
grazing with sheep and cattle using a paired-paddock design at 5 locations.
Throughout the sites there were a few consistent differences between
management treatments. Basal cover was greater on the time-controlled grazing
than continuous for most of the experimental period at three sites, but the initial
values were also higher (Dowling et al., 2005).
The practice of continuous grazing using low animal density in a
tobosagrass [Hilaria mutica (Buckl.) Benth.] rangeland in the northern
Chihuahuan Desert resulted in non-uniform forage utilization (Senock et al.,
1993). Stocking smaller tobosa rangeland paddocks with high numbers of cattle
for short periods of time may facilitate more uniform forage utilization. Two
grazing periods in each of two consecutive years were monitored to investigate
the frequency with which tobosa tillers were defoliated and the intensity of
defoliation (change in height) in relation to grazing pressure under high-density
seasonal rotational and low-density seasonal continuous grazing. Percentage of
tillers defoliated in the rotational treatment was always greater than 75%, and
always less than 30% in the continuous treatment. The probability that a tiller
would be grazed at least once in the rotational treatment was more than twice as
great as in the continuous treatment; however, within the rotational treatment,
the probability of multiple grazing events (greater than or equal to 2) of an
individual tiller was less than the probability of a tiller being grazed only once. In
15
general, high-density rotation grazing promoted more uniform forage utilization of
tobosa than low-density continuous grazing (Senock et al., 1993).
In a 6-year study conducted by Biondini and Manske (1996) the effects of
a twice-over rotation grazing system (ROT) and a season-long grazing system
(SL) were conducted to compare the effects with long-term grazing exclosure
(NG) in relation to: 1) species composition and basal cover; 2) above ground
net primary production (ANPP) and above ground N uptake (ANNP-N); 3) rates
of litter and root decomposition and N release; 4) soil N mineralization and
immobilization; 5) above ground C and N flow; and 6) grazing intensity (GI) and
animal performance. Species composition was more responsive to grazing than
were C and N flows. The differences in this case were found between grazed
and non-grazed treatments, but not between the two grazing treatments . No
broad patterns of change were detected in total plant basal cover as a result of
grazing patterns or drought. Changes in species composition were highly
dependent on range site. The most consistent pattern involved Bouteloua
gracilis, which had higher relative cover in the grazed treatments than in the non-
grazed treatments.
Results from this study indicated that in the grasslands of western North
Dakota: 1) the recommended stocking rate may be too conservative; 2) rotation
grazing may allow for higher stocking rates than season-long grazing without a
major effect on animal performance; 3) rainfall is more important than grazing or
grazing systems in the control of the ecosystem-level variables measured ; 4)
16
species composition is affected by drought and grazing (but not by grazing
systems), but the responses are highly dependent on range site; and 5) drought
and grazing tend to increase the relative composition of warm-season grasses
and forbs (Biondini and Manske, 1996).
From 1989 to 1993, Cassels et al. (1995) evaluated a grazing system and
stocking rate effect on forage standing crop of tall grass prairies in north-central
Oklahoma. Pastures were dominated by big bluestem [Andropogon gerardii
Vitman], little bluestem [Schizachyrium scoparium (Michx.) Nash], indiangrass
[Sorghastrum nutans (L.) Nash], and switchgrass [Panicum virgatum L.].
Rotation units were arranged with either a short duration rotation or continuous
grazing system and stocking rates ranging from 127 kg animal live weight/ha to
222 kg live weight/ha. Yearling steers grazed the units from late April to late
September. Herbage standing crop was sampled in July and September. Total,
live and dead standing crops did not differ significantly between the 2 grazing
systems in July. Total standing crop was significantly higher in the rotation units
in September (3,600 vs. 3,020 kg/ha). Dead standing crop was also greater in
the rotation units in September (1,950 vs. 1,570 kg/ha, P<0.05). The authors
suggested that the difference in standing crop between systems was due, in part,
to decreased forage intake by the livestock. Grazing system did not interact with
either stocking rate or year. Stocking rate had significant effects on total live and
dead standing crops at both sample dates. Higher standing crop at the end of
the grazing season in the rotation units would mean greater soil protection,
17
suggesting a lower effect on plant vigor. However, if the higher standing crop
was a result of lower forage intake, one would expect livestock weight gains to
decline. The assumption of a decrease in forage intake mentioned above is
questionable based on results found by Hirschfeld et al. (1996) and Soltero
(1987), who found that the forage intake by livestock grazing native grasslands
was higher under SDG than under continuous grazing.
2.2 Vegetation Changes
Allen-Diaz and Bartolome (1998), critiqued the classical succession
theory, which is still widely applied, which suggests that rangeland systems are
best described as predictable linear sequences of plant communities,
sequentially changing in an orderly response to control variables such as
grazing, fire, precipitation, and competition. But the development of models for
nonlinear, nonequilibrium plant community dynamics as an alternative; like the
State Transition proposed by Westoby et al. (1989), were plant communities may
change from discrete states and a set of discrete transitions between the states,
instead of follow a single continuum.
Moreover, Buttolph and Coppock (2004) mentioned that management
recommendations intended to decrease rangeland degradation and increase
livestock productivity often assume equilibrium conditions, wherein vegetation
and herbivore dynamics are tightly coupled and that recent research in Africa,
18
Asia, and North America, however, suggests that the dynamics of some arid
systems are driven more by precipitation, a non-equilibrium factor.
Ellis and Swift (1988), stated that plant production and composition in
many arid ecosystems depend more on climate than on herbivory. Nevertheless,
high stocking rates increase the effect of adverse weather conditions such as
severe droughts, and exert an additional detrimental effect on more desirable,
less defoliation-resistant species.
2.2.1 Cover
Continuous and reversible vegetation dynamics prevail within stable
vegetation states. Discontinuous and nonreversible dynamics occur when
thresholds are surpassed and one stable state replaces another (Briske et al.,
2005). Heavy grazing often results in a dramatic decrease of plant diversity,
vegetation cover, primary production (Fensham, 1998), and other soil aspects.
When degradation occurs as a result of intensive herbivory, Kraaij and
Milton (2006) stated that, it initially affects plant population demography. Once
this is initiated, diversity and productivity start to decline. Thereafter, a reduction
in perennial plant cover facilitates the establishment of ephemeral and weedy
species, which ultimately ends with the loss of vegetation cover. When
vegetation communities have been highly abused through heavy and prolonged
stocking rates and grazing use, the resiliency of those communities is difficult to
perform. The change and damage caused to vegetation is such that the return to
19
pristine vegetation is practically impossible, and a new vegetation assemblage
takes place. As was pointed out by Westoby et al. (1989) when he described the
mechanisms that produce the complex ecosystem communities’ dynamics.
In a grazing experiment conducted by Zhao et al. (2005) during 5 years in
a sandy rangeland in Inner Mongolia, continuous heavy grazing resulted in a
considerable decrease in vegetation cover and canopy height. Vegetation cover
in the heavy grazing plot was 58.6% less than that of the no grazing plot the first
year and 88% lower the fifth year. The vegetation cover increased slightly over
the study period in the light grazing and moderate grazing plots.
Range condition decreased under SDG system in a fescue grassland
(Dormaar et al.,1989) from 50 to 39%, whereas the range condition increased
within a grazing exclosure from 51.6 to 56.2%, during a 5-year period.
Graminoids increased from 58.1 to 65.7% within the exclosure, whereas the
grazed areas values changed from 64.4 to 65.7%. Fescue was a desirable
species that decreased under grazing treatment (1.3 to 0.7%); however, it
increased when the grass was excluded from grazing (1.6 to 6.0%). Other less
desirable species such as Carex, Koeleria, Bouteloua, and Poa, increased in
both treatments, but were slightly higher under the SDG system (Dormaar et
al.,1989).
Differences in plant species abundances in response to cattle grazing and
protection were measured at 15 sites in productive, semi-natural Mediterranean
grasslands in Israel by Noy-Meir et al. (1989). Perennial species with long
20
growing seasons increased somewhat more frequently under grazing protection,
and their total cover was greater in protected grassland. Grazing response was
significantly associated with growth form: increases under grazing protection
were mostly tall erect plants; increases under grazing treatment were mostly
small prostrated or rosette plants; and plants with intermediate responses were
mostly erect plants of medium height. Ungrazed grassland was dominated (60 to
80% cover) by tall perennial and tall annual grasses. Tall and medium legumes
were also prominent (15 to 30% cover). Under light to moderate grazing their
coverage decreased (35 to 50%) to the benefit of a wide range of growth form
and families. Under heavy grazing, tall perennial and tall annual plants
combined, covered 20 to 35 %, with two species accounting for the greatest
percent. One grazing resistant and one unpalatable plant, and small, prostrated,
annual rosette crucifers and thistles remained abundant.
2.2.2 Forage production
Some speculation regarding the herbivory optimization hypothesis
suggested that grassland may show an increase in productivity due to the
grazing process (McNaughton and Bardget, 1979). Nonetheless results have
been varied and contradictory, and even no responses have been reported.
Frank et al. (2002) reported a 21% increase in the above annual net primary
productivity due to grazing in a grassland, whereas Milchunas and Lauenroth
(1993) found a decrease in the above ground production.
21
Results reported by Taylor et al. (1993) of the effects of SDG and high-
intensity, low-frequency grazing systems showed that ANPP (grass + forbs)
increased for both grazing treatments in 4 years. Total ANPP varied significantly
among years but not between grazing systems. Total grass production averaged
128 g/m2 for the SDG treatment and 154 g/m2 for the HILF. Therefore, Taylor et
al. (1993) rejected the hypothesis that grazing systems increase ANPP.
In an experiment conducted by Zhao et al. (2005) in a sandy rangeland in
Mongolia, the standing crop biomass decreased significantly with increased
grazing intensity. The standing crop biomass decreased slightly but not
significantly with grazing time in both the heavy and moderate grazing
treatments. Conversely, it increased significantly with grazing time in the light
grazing treatment. The non-grazing treatment increased from early to mid-term
and showed a decreased trend thereafter. These authors assumed that this
might be due mainly to litter accumulation, which restricted plant growth.
Regarding the effects of grazing exclosure, Walker (1989) cited by West (1993),
mentioned that ungulate grazing is an important process in many rangeland
ecosystems. If grazing is excluded, biodiversity may increase in the short term
but decrease long-term because the system itself changes, and in the future, the
rangeland may be less able to withstand other disturbances such as drought and
fire. West et al. (1984), advised that if manager expectations of pathways and
time scales for vegetation recovery following a disturbance were unfounded, then
much time and potential rangeland productivity could be lost waiting for changes
22
that may never or very slowly materialize. In a study conducted by West et al.,
(1984) in the Tintic valley in west central Utah, the total standing crop did not
increase following 13 years of rest from livestock grazing. The average standing
crop from 1963-64 (grazed) to that of 1980-81 (ungrazed) was compared.
Authors emphasized the fact that the lack of change was even more
dramatic because the data from 1954-64 represent the residual herbage
following grazing during May-June, and the precipitation during 1980 was the
highest of the entire sequence. Nevertheless, herbage was considerably less
than the average (226 kg/ha) during the 1956-64 period. The standing crop of
many perennial grasses decreased over the 13 years of rest. In contrast,
cheatgrass apparently increased during the rest period.
In 1982, Dormaar et al. (1989) established a SDG system on 972 ha in a
fescue grassland at Fort McCleod, Alberta, Canada, that consisted of 17
pastures. Stocking rates varied from 3 to 2.3 AUM/ha over the five-year study.
Forage production fluctuated from 570 kg/ha in 1983, then decreased to
approximately 340 kg/ha in 1984 to 85, increasing again in 1986 to 784 kg/ha.
Forage utilization averaged 83% on the entire period.
Two grazing studies were conducted by Pitts and Bryant (1987), in which
continuous grazing and SDG were compared. The stocking rates used were
similar at the beginning, but in the second year, stocking rate was increased to
twice the continuous stocking rate in SDG, and in the third year, decreased to 1.5
times the continuous stocking rate. Standing crop was low on both CG and SDG
23
during the first 2 years of the study because of low rainfall. Greater standing
crop on SDG than CG in Year 2 was attributed to two relatively unpalatable
forage species. In the last two years of the trial, when adequate rainfall occurred,
forage availability was less under the SDG regimen. Changes in standing crop of
different grass species occurred during the 4-year study, but changes were
similar for both CG and SDG.
Stocking rate seems to be the most important factor that drives forage
availability; however, climatic conditions, mainly frequency and occurrence of
rainfall, are dominant in forage production fluctuation. Milchunas and Lauenroth
(1993) found a trend for decreased above ground production with grazing,
suggesting that the results at any given locality were influenced by moisture
availability and the evolutionary history of grazing.
2.2.3 Density.
The effects of grazing on changes in species composition of plant
communities have been extensively discussed in the literature. Cyclic changes
in plants densities throughout several years have been reported by many
researchers. However, the direct effect of grazing and climatic influences is often
confounded, making it difficulty to distinguish between them.
In 1956, 2 areas of mixed grassland and oak woodland at the Hopland
Research Extension Center of the University of California were fenced to exclude
sheep. The variation in density of perennial grasses through time among
24
grassland transects was striking. The overall pattern of change showed a
decrease by 1979, with a return to original density by 1991. In several plots, non-
native annuals dominated by 1979. By 2000, perennial grass density was
greater than in 1979, but still lower than 1959. For example, the dominant
species purple needlegrass was less abundant in 2000 (≈1.2 plants/m2) than in
1958 (≈1.8 plants/m2). After more than 40 years without livestock grazing, the
density of native perennial grasses was lower in open grassland than when
transects were established, but considerably greater than in 1979 (≈0.8 pl/m2)
(Merenlender et al., 2001).
Landsberg et al. (2002) conducted a study of native plant communities in
an arid rangeland region of South Australia to explore how rangeland grazing
affects native plant diversity at local and regional scales. Six transects were
spread across a large region, four transects were established within a
commercial sheep-grazed paddock, and two transects were established outside
in similar land that had never been developed for pastoralism. Transects were
established at 1, 4 ,7, and 10 km from the nearest water point in the paddock,
and the outside (at more than 10 km distance) on undeveloped sites. Nearly 200
species were recorded, but distribution was patchy, with more than 30% of
species present at less than 105 of sites. At a regional level, pastoral
development had a predominantly negative effect on the abundance of species.
Sixteen species were less abundant within paddocks than in areas that
had never been developed, and only one species was more abundant. The local
25
trend was more positive than the regional trend, in that significantly more species
showed trends of increasing abundance with increasing proximity to watering
points and associated grazing activities. Based on these results, Landsberg et
al. (2002) concluded that pastoral development enhanced richness of plant
species at local scales (by providing opportunity for more species to establish),
but that it had the potential to decrease richness at a regional scale by removing
the most grazing-sensitive species from the regional species pool.
In the northern Chihuahuan desert, Nash et al. (1999) evaluated the
response of annual plant communities to grazing. They concluded that
disturbance by grazing livestock resulted in only small changes in annual plant
communities and that it was very different from the effects of intensive livestock
grazing on perennial vegetation. This might be the reason why in most degraded
perennial grass communities, the remnant vegetation after a severe drought or
prolonged overgrazing is mostly annual grasses and forbs.
Conclusions;
• Grazing is a process that has played an important role in the
grassland development over the time.
• Overgrazing practiced during late 1800s and early 1900s resulted
in a severe deterioration of vegetation in many grasslands in
western United States and Northern Mexico.
26
• Continuous grazing was the most commonly grazing method
utilized, and overgrazing of most desirable species and a non
uniform utilization was a common denominator under this grazing
scheme.
• More grazing systems were developed in an attempt to improve
ranges condition. Rotational grazing systems became a very
popular strategy in grazing management to solve the overgrazing
problem.
• Short-Duration grazing was very popular in the 1980s based on the
premise of improved grazing distribution, improved soil infiltration,
and a two to three-fold increase in carrying capacity, among others
benefits.
• Results on SDG studies are contradictory, but most of them did not
observe any advantages compared with continuous grazing;
however, the major concerns were related to the use of high
stocking rates that were not sustainable and the fact that no soil
improvement was achieved.
• In general, most of the literature agreed that stocking rates were
more determinant on vegetation response than grazing system
effects, particularly when environmental conditions were adverse.
27
CHAPTER III
VEGETATION CHANGES AFTER 12 YEARS IN FOUR
PRIVATE RANCHES UNDER SHORT-DURATION AND
CONTINUOUS GRAZING IN CHIHUAHUA, MEXICO
3.1 Introduction
The cattle industry in northern Mexico has been identified for many years
because of extensive grazing. Erratic rainfall and other weather conditions limit
land use to grazing in most of the region. In the State of Chihuahua, rangelands
suitable for grazing have been well identified. According to COTECOCA (1978),
eighteen native and one introduced vegetation types within sixty-four rangeland
sites were recognized, and estimated stocking rates ranged from 8.5 to 60.0
ha/AUY.
Because of overgrazing and desertification processes, carrying capacity in
many ranches in Mexico has actually decreased (Manzano and Navar, 2000). In
addition, property size has decreased through time because of both population
increase and increased production costs (Molinar et al., 1998). Under this
situation, in the late 1980s and early 1990s, some ranchers, searching for
alternatives that could improve or ameliorate the critical condition of their ranch
enterprises, thought that SDG would be the solution to their crisis. Stocking rate
increases and range condition improvement were the most attractive aspect of
this practice. Short duration grazing is a system that enables more rigid control
28
of animal distribution with the use of numerous smaller pastures, thereby
concentrating livestock and permitting time-controlled grazing. It has been
proposed that short duration grazing will allow conventional stocking rates to
double or triple, regardless of range condition at the time of implementation
(Dormaar et al.,1989; Savory, 1983). However, is well known that most changes
in vegetation that have occurred in native rangelands that have been related to
grazing effects through years, specifically where heavy, continuous grazing has
been practiced, takes year to reversed.
Over time, many people were disappointed by the SDG results and
returned to their traditional CG. Others still believe in the benefits of this
particular grazing system and continue practicing and managing their ranches
using SDG. Based on these observations, the present study was proposed to;
1) evaluate vegetation changes on private ranches as a result of different grazing
management after 12 years, and 2) Measure the differences in vegetation cover,
forage production, and density on four ranches in Chihuahua, Mexico two
managed under SDG and two under CG.
3.2 Material and Methods
3.2.1 Study Sites
Around 1990, several ranches implemented the HRM in Northern Mexico,
as illustrated in Figure 3.1. Among other reasons for implementing this system,
HRM was strongly promoted by various private and public agencies as FIRA
29
from Banco de Mexico that organized several symposium and field days.
Vegetation on four of these properties in Chihuahua, Mexico were measured in
1993.
Figure 3.1. Location of Chihuahua State in Mexico.
Ranch 1
Ranch 1 was a family operated ranch, located approximately 340 km NW
of Chihuahua City at 30o 26’ 42’’ lat N and 108o 11’ 30’’ long W, at approximately
1,500 m above sea level. The long-term annual rainfall average was 370 mm,
mean annual temperature ranges between 16 to 18oC, with 200 frost-free days.
At this property, 9,731 ha were managed under HRM. Fifteen paddocks of
different sizes were established, ranging from 157 to 1,607 ha, as shown in
Figure 3.2.
Vegetation at this ranch was considered as mid-open grassland
(COTECOCA, 1978). Major vegetation species included desirable species such
as Bouteloua gracilis, B. eriopoda, B.hirsuta, B. curtipendula, and less desirable
Chihuahua City
30
species such as Digitaria californica, Setaria macrostachya, some species of
Aristida, and Lycurus phleoides. In 1993 the stocking rate was established at 7
ha/AUY. After 1994 to 2005, stocking rates were changed because of drought,
fluctuating as follow: 9, 11, 10, 11, 11, 15, 11, 11, 10, 10, 11, 16, and 15 ha/AU,
only cow/calf pairs were used.
Figure 3.2. Pasture distribution and vegetation type in Ranch 1.
Ranch 2
This ranch is located approximately 130 km NW Chihuahua City, between
29o 11’ 00’’ lat N and 106o 50’ 53’’ long W, at 2,000 m above sea level. Annual
long-term rainfall average was 440 mm with approximately 105 mm in the form of
snow. Mean temperature is 14 to 16oC, with 180 frost-free days. This rangeland
belongs to a larger area, but under this cell, only 2,868 ha were included and split
31
in four pastures (Figure 3.3), an average stocking rate of 6 ha/AUY was assigned
to this grazing unit.
Vegetation was described as a mid-open grassland in high valleys
(COTECOCA 1978). The characteristic species are Bouteloua gracilis,
Bouteloua hirsuta, Buchloe dactiloides, also, Setaria macrostachya, Bouteoua
curtipendula, Chloris latisquamea, Leptocloa dubia, Panicum obtusum, Panicun.
hallii, Lycurus phleoides, Aristida ternipes, Aristida. divaricata, Aristida orcuttiana,
Microchloa kunthii, and Leptoloma cognatum.
Figure 3.3. Pasture distribution and vegetation type in Ranch 2.
Ranch 3
This unit was located about 160 km north of Chihuahua City, between 29o
50’ 37’’ lat N and 106o 36’ 16’’ long W at 1,400 meters above sea level. Average
32
annual rainfall wass approximately 350 mm, with an annual mean temperature of
15 to 17 oC and 200 frost-free days. Approximately 1,531 ha were included
under the SDG. The area was divided in 16 equal size paddocks (Figure 3.4).
The initial stocking rate was approximately 12 ha /AUY, approximately 200 young
heifers of 250 kg that came from other ranch were allotted to these pastures in
January, and remained at this unit until December, when they were removed and
a new herd was brought the next year.
After 1999, all internal fences were removed, except one at the middle that
separates the pasture in two large paddocks. Thereafter, stocking rates were
Figure 3.4. Initial pasture distribution and vegetation type in Ranch 3.
decreased to 17 ha/AUY, and 40 female calves grazed 6 months (January
through June); followed by 65 nursing mature cows the next 6 months (July
33
through December), and the unit was split in two parts, with the same stocking
rate. Most common desirable species for this area included Bouteloua gracilis,
Bouteloua. hirsuta, Bouteloua chondrosoides, Bouteloua curtipendula, and
Buchloe dactiloides. Less-desirable species include; Bouteloua eriopoda,
Digitaria californica, Setaria macrostachya, Leptochloa dubia, Aristida pansa,
Aristida ternipes, Aristida. hamulosa, Aristida adscencionis, Aristida arizonica,
Lycurus phleoides, Eragrostis intermedia, Panicum obtusum, Hilaria mutica,
Eneapogon desvauxii. Invasive species were considered; Botriochloa barbinodis,
Botriochloa. saccharoides, Erioneuron pulchellum. Also several other plants
such; annual grasses, some annual forbs and also several toxic plants as;
Drymaria arenarioides, Solanum eleagnifolium, and Baileya multiradiata, and
shrubs species like Prosopis juliflora, Mimosa sp., Ephedra sp., Flourencia
cernua, and Larrea tridentate, were considered invaders as well.
Ranch 4
This private ranch is located 300 km NW Chihuahua City, between 30o 32’
28’’ lat N and 107o 33’ 16’’ long W, at 1,400 meters above sea level. Average
annual rainfall was 300 mm, with an average annual temperature of 16 to 18 oC
and a 210 frost-free days. Vegetation was classified as medium-tall shrubland
(COTECOCA 1978). Dominant species include Prosopis juliflora, and Fourencia
cernua, also Mimosa biuncifera, Koeberlina spinulosa, Ephedra trifurca, Opuntia
imbricata, Condalia spp, and Celtis pallida. The most important grasses were
34
Bouteloua eriopoda, Bouteloua trifida, Digitaria californica , Setaria macrostachya
Bouteloua gracilis, Lycurus phleoides, Aristida pansa, Aristida divaricata,
Botriochloa saccharoides, Hilaria mutica, Hilaria belangeri, and Scleropogon
brevifolius.
This grazing unit size was 2,600 ha, which included two grazing cells,
together forming a 13-paddock grazing unit (Figure 3.5). At the beginning of the
implementation of SDG, a stocking rate of 7 ha/AUY was assigned.
After several years of low rainfall, the internal paddocks were removed,
and a new stocking rate was initiated, with an average of 16 ha/AU. From 1993
to 2005 the stocking rates fluctuated as follow: 7, 7, 15, 16, 16, 18, 22, 21, 14,
14, 14, 14, and 23 ha/AUY. Initially cow/calf pairs were used, after 2001 only
stockers.
Figure 3.5. Initial pasture distribution and vegetation type in Ranch 4.
35
3.2.2 Management
Each ranch was managed by the owner or their land manager. Every
manager was trained in the HRM philosophy and/or had an advisor from the
HRM Center in Mexico. Researchers do not participate in the management of
these ranches. Personnel from the HRM Center argued that the needs of the
ranchers were different from that of technicians and researchers. Therefore, the
only research concern was to record vegetation changes on these ranches
through time.
Ranches 1 and 2 were managed under SDG for the entire period 1993-
2005, Ranches 3 and 4 started were under SDG from 1993-1998, but returned to
Continuous Grazing System (C) for the remaining 7 years 1998-2005
3.2.3 Sampling
The first vegetation sampling was conducted in Fall 1993, and the same
procedures were repeated in Fall 1994; and in late Fall 2005. Vegetation
variables evaluated were percentage of basal (herbaceous) and aerial (shrubs
and suffrutescents) cover, density (individuals/area), and forage production (kg
DM/ha). Two pastures on each ranch were randomly selected on which to
establish permanent transects. In each pasture a set of 12-m transects was
established at different distances from the center of the pastures or the source of
water. The distances among varied from 250 to 400 m depending of the shape
and the size of the pastures at each ranch.
36
3.2.4 Vegetation measurements
Permanent transects, 12-m long, were established in two pastures
(Canfield, 1941). The basal cover was measured using 12 m-long permanent
transects, plants were measured individually (Canfield, 1941), one end of each
transects was oriented toward the water source at the center of pastures and the
other to a reference point at the end of the pasture. Measurements were made
on the same transects in Fall 1993, 1994, and 2005. For grasses and
herbaceous plants, data collected were based on basal area, whereas for brush
and shrub-like plants, aerial coverage was recorded. The number of transects
varied among ranches, which occurred because not all transects established in
1993 were relocated in 2005, the number of transects surveyed varied from 9 to
10, except at one ranch, where all transects were located. Initially 18 transects
were located at each ranch but, some sticks were removed or missed, mainly by
the animals. In ranch 1 ten permanent transects were measured, in ranch 2
eighteen transects, in ranch 3 nine transects, and at ranch 4 nine transects were
relocated
To estimate grass forage production (kg DM/ha) a 0.25-m2 quadrats were
clipped (Cook and Stubbendieck, 1986). Four quadrats were randomly located
on each transect. Forage samples were clipped at approximately one inch above
soil surface, samples were oven dried until constant weight at 55 oC for 72 hours
37
to determine dry matter content. Twenty-four samples per pasture and 72
samples per ranch were collected.
To estimate grass and herbaceous vegetation density two 0.125-m2
quadrat were placed, one at each terminal end of each permanent transects.
Every individual plant within quadrat was counted. Most plants were identified to
species but, those that were not identified, a common name or any other
description was used to distinguish each species. Where shrubs occurred, a 3.0-
m diameter plot was located at each end of every permanent transect, to
estimate its density. To facilitate the vegetation analysis, the species were
divided into the following functional groups: shrubs, suffrutescents, perennial
grasses, annual grasses, perennial forbs, and annual forbs. Rainfall data were
collected from rainfall gauges located on each one of the ranches included in the
study.
3.2.5 Statistical Analyses
Perennial grass cover data were analyzed by analysis of variance with
repeated measurements (years) using the Proc Mixed procedure, Compound
symmetry was used as covariance structure, and basal cover from the initial year
was used as a covariate to adjust for antecedent conditions. The Shaphiro-Wilk
normality test was performed to evaluate the distribution of the data. LSMEANS
comparisons were made to asses the differences between the initial and final
perennial grasses basal cover distribution. To determine differences in forage
38
production, the Proc Mix procedure was used to run a Analysis of variance, with
repeated measurements, using initial survey as covariate (SAS/STAT, 2004). In
order to contrast the importance of functional groups as a descriptor of the
vegetation variation in the first year with the to the last year, using management
system as ordination value, a Principal components multivariate analysis was
done.
3.3 Results
3.3.1 Rainfall
The timing of rainfall occurrences was very similar at all locations.
However, ranches under SDG management received a larger amount of rain
than those under traditional management. The general pattern across sites
showed 4-5 years that were equal or above average annual rainfall, and 5 to 7
years of severe drought conditions during this 12-year period. However, after
1994, precipitation was above average for only one or two years. Ranch 4, had a
lower amount of precipitation during the entire 12-year period (Figure 3.6). In
general, weather conditions were considered as a severe drought during a
considerable period of time during the evaluation period.
3.3.2 Cover
Initial basal cover (1993) was greater (P=0.0004) in SDG (23.2 ± .9 %)
than in CG (3.3 ± 1%). Because the initial basal cover was different between
39
treatments, the initial condition was used as covariate.
Statistical difference was found between years of sampling (P=0.0001),
the basal cover was greater in 1994 (11.4 ± .6%) than in 2005 (6.6 ± .6%).
Ranch 1 (SDG) Ranch 2 (SDG)
0
200
400
600
800
90 92 93 94 95 96 97 98 99 00 01 02 03 04 05
Years
Mili
mite
rs
Annual Mean
0200400600800
90919293949596979899000102030405
YearsM
ilim
eter
s
Annual Mean
Ranch 3 (CG) Ranch 4 (CG)
0
200
400
600
90919293949596979899000102030405
Years
Mili
mite
rs
Annual Mean
0
100
200
300
95 96 97 98 99 00 01 02 03 04 05
Years
Mili
met
ers
annual mean
Figure 3.6: Rainfall patterns of four ranches under Short Duration (SDG) and Continuous (CG) grazing management in Chihuahua, Mexico.
40
Treatments by year interaction was detected (P≤ 0.0002). Statistical
difference (P=0.0001) was found in 1994 between treatments, SDG showed a
greater basal cover (16.5 ± 1.1%) than CG (6.3 ± 1.5%). However, in 2005,
there was not statistical (P = 0.51) difference, SDG had (5.8 ± 1.1%) basal cover
and CG system had (7.4 ± 1.5%). In general, basal cover of perennial grasses of
the ranches that used the SDG system declined. The highest percent was found
in 1994 (16.5%) and then it tended to decline toward 2005 (5.8%). Statistical
difference (P < 0.0001) in percentage of perennial grasses basal cover was
found among years in ranches managed with the SDG treatment (Table 3.1).
Table 3.1: Basal cover (%) (± SEM) of perennial grasses in four ranches under two different grazing systems in Chihuahua, Mexico.
*Covariate Mean in a row with different capital letters were different (P<.0001) Mean in a column with different lower case letter were different (P<.0001) Mean in a column with the same lower case letter were similar (P>.05)
Treatment
Year Short-Duration Continuous Overall Mean
1993* 23.2 ± 0.9A 3.3 ± 1B
1994 16.5 ± 1.1Aa 6.3 ± 1.5Ba 11.4 ± 0.64a
2005 5.8 ± 1.1Ab 7.4 ± 1.5 Aa 6.6 ± 0.6b
41
The perennial grasses basal cover was lower in ranches managed under
CG system than under SDG. Despite the initial basal cover being lower on
ranches under CG management (3.3%), the adjusted values showed a slight
tendency to increase in 1994 (6.3%), and a slight increase was observed later on
toward 2005 (7.4%), the magnitude of changes over years was not significant
(P = 0.36).
Perennial grasses accounted for the greatest basal cover (cm) among all
the functional groups in Ranch 1, followed by the annual forbs (Table 3.2)
Bluegrama (Bouteloua gracilis) was the species with the highest basal cover
length among all the perennial grasses. Threeawn (Aristida spp) and
tobosagrass (Hilaria mutica) also contributed to the cover of perennial grasses in
1993, but less than blue grama. An overall decrease in amount of cover close to
40% was observed in perennial grasses by 2005. Comparatively, cover
decrease was higher for threeawn and tobosagrass than for blue grama. All
functional groups showed a tendency to decrease from 1993 to 2005. Within
annual grasses, only two species accounted for the basal cover but, just one
Bouteloua spp. (9 cm/1200 cm) was important in 2005, along with two species of
perennial forbs, Sida procumbens and Solanum eleagnifolium 2 cm/1200 cm
each in 1993 but both disappeared in 1994 and 2005. Of the annual forbs,
Heteroteca spp (40 cm/1200 cm) was dominant in 1993, with two others
unidentified forbs showing minor participation. In 1994 only one species of a
legume species was recorded with a 1.1 cm/1200 cm the rest were too small and
42
Table 3.2: Basal (forbs and grasses) and aerial (shrubs and suffrutecents) cover (cm/1200cm) of species present in sampled transects,
categorized by functional groups in Ranch 1.
Year SPECIES 1993 1994 2005 SHRUBS Mimosa spp 3.2 Subtotal PERENNIAL GRASSES Bouteloua gracilis 213.7 177.0 104.2 Aristida adcensionis 45.1 21.9 0.9 Hilaria belangeri 6.7 4.3 2.0 Panicum spp 0.5 0.1 Hilaria mutica 17.1 17.2 Botrhiocloa barbinodis 0.9 2.2 Bouteloua curtipendula 9.3 10.6 11.1 Bouteloua hirsuta 11.1 14.1 3.9 Lycurus phleoides 9.4 13.8 1.9 Schizachirium spp. Mulhenbergia spp, 1.4 4.0 Bouteloua eriopoda Subtotal 313.3 263.0 128.1 ANNUAL GRASSES Aristida annual Chloris annual 0.4 Eragrostis annual 9.0 Bouteloua annual Subtotal 0.0 0 9.4 PERENNIAL FORBS Guillemina spp 0.9 Sida procumbens 1.9 Hoffmansegia spp. Solanum eleagnigolium 2.0 0.2 0.1 Dalea spp 0.6 Malva spp 0.3 Leguminose 0.5 Subtotal 5.4 0.5 0.6 ANNUAL FORBS Hairy forb 4.7 Heteroteca spp 40.2 Grindelia spp Compositae 0.4 1.2 Annual Forb 8.7 0.3 3.3 Argemone mexicana 0.2 Cyperacea 0.4 Tronadorcillo 0.2 Spharalcea spp 0.4 Ceniza 3.3 Paronichya spp
43
Table 3.2: Continued Species
Aphanosteohus spp 11.0 Gnaphalium canescens 3.0 Hypericum spp 2.3 Euphorbia spp 0.2 Leguminose 1.1 Cebollin Compositae 2 1.9 Subtotal 74.4 2.0 6.4
Cover is the average in 1200 cm transects.
two not previously reported annual forbs were found in 2005, but both were found
in a very low coverage.
Similar trends to Ranch 1 in cover length were observed for Ranch 2. A
general decreasing tendency in cover length in all categories from 1993 to 2005
was noticed. Within the perennial grasses functional group, again blue grama
accounted the highest basal coverage. Threeawn and wolftail (Lycurus
phleoides) contributed a lesser proportion compared with blue grama (Table 3.3).
In 1993, length of cover of the rest of herbaceous strata was very limited; among
annual grasses only one species of Eragrostis (0.7 cm/1200 cm) was barely
recorded. Within perennial forbs, four species with equal proportions were noted,
but total amount were small (7.7 cm/1200 cm). With respect to annual forbs, two
non-identified species accounted for the major amount of cover, but in low
quantities (4 and 9.5 cm/1200 cm). In 1994, a slight increase was observed in
perennial forbs cover: Dalea spp increased to 5 cm/ 1200 cm in cover, and two
new species showed up, Drymaria arenarioides and Zinnia spp., but, in a very
small amounts (3.2 and 1 cm/1200 cm respectively). Contribution to basal cover
44
Table 3.3: Basal (forbs and grasses) and aerial (shrubs and suffrutecents) cover (cm/1200 cm) of species present in sampled transects, categorized by functional groups in Ranch 2. Year SPECIES 1993 1994 2005 SHRUBS Mimosa spp. 52.1 50.3 56.9 Condelia spp 3.3 Subotal 52.1 15.2 60.3 PERENNIAL GRASSES Bouteloua gracilis 178.2 153.7 76.5 Aristida spp 22.9 18.7 5.1 Lycurus phleoides 22.7 22.1 1.8 Microchloa kuntii 4.1 4.2 2.2 Mulhenbergia spp 2.5 2.9 0.67 Elyonurus barbiculmis 3.3 Schizachirium spp. 4.4 7.1 2.2 Bouteloua hirsute 8.6 1.7 0.2 Botriochloa barbinodis 0.0 Subtotal 243.5 213.6 88.8 ANNUAL GRASSES Eragrostis annual 0.7 0.7 Bouteloua annual 0.0 Panicum annual 0.3 Aristida annual 0.1 Chloris annual 0.0 Subotal 0.7 0.3 1.0 PERENNIAL FORBS Dalea spp. 1.7 5.0 0.1 Drymaria arenarioides 3.2 Yerbaniz 2.0 0.9 Guillemina spp 0.6 Zinnia spp 1.0 Perennial Forb 1.6 Croton spp 2.5 Subtotal 7.7 10.7 0.1 ANNUAL FORBS Red forb 4.0 0.8 0.2 Annual Forb 0.4 0.5 Hairy forb 0.2 Forb 2 2.3 Lepidium spp 1.4 Vigueria spp 6.1 Forb 3 0.1 Little strawberry 1.2 Cyperacea 0.1
45
Table 3.3: Continued Species Big forb 9.5 2.6 Star forb 0.9 0.3 Gnaphalium canescens 0.1 Composite 0.8 Eringium spp. 0.1 Grape weed 1.9 Subtotal 17.2 15.2 0.9
Cover length is the average in 1200 cm transects.
of perennial and annual forbs in 2005 was much less than in 1993 and 1994 or
they had disappeared. A new species of genus Bouteloua, Aristida, and Chloris
annual grasses were recorded but, only in traces.
Mimosa spp. was the only species that accounted for shrub aerial cover in
1993 (52 cm/1200 cm). In 2005, Condelia spp was also noted but in a small
amount (3.3 cm/ 1200 cm). Mimosa spp. coverage remained stable across time
with a slight decrease at the end (57 cm/ 1200 cm).
In Ranch 3, basal cover of perennial grasses performed differed from that
of Ranches 1 and 2, in that cover increased from 1993 through 2005. Lehmann
lovegrass (Eragrostis lehmanniana) and threeawn (Aristida spp.) were the
species with the greatest amount of coverage. Both species had similar values
in 1993; nevertheless, in 2005, Lehmann lovegrass increased more than two-fold
in the amount of cover, whereas threeawn decreased approximately 60% in its
basal cover length (Table 3.4). Blue grama also contributed to the coverage of
perennial grasses in this ranch in 1993, but only in small way, remaining
unchanged through 2005.
46
Table 3.4: Basal (forbs and grasses) and aerial (shrubs and suffrutescents) cover (cm/1200 cm) of species present in sampled transects, categorized by functional groups in Ranch 3. Year SPECIES 1993 1994 2005 SHRUBS Acacia angustissima 3.8 0 1 Ephedra sp. 9.8 5.3 0 Prosopis sp. 69.8 61.1 70.7 Mimosa spp. 0.0 0.0 0.0 Condelia spp. Subtotal 83.3 66.4 71.7 SHRUBS-LIKE Menodora like 7.0 Xantocephalum sarotrae 1.8 Subtotal 8.8 0 0.0 PERENNIAL GRASSES Eragrostis lehmanniana 19.2 10.7 49.8 Bouteloua gracilis 8.3 4.7 8.7 Mulhenbergia porteri 1.3 Botrichloa barbinodis 3.8 Setaria macrostachya 2.4 5.6 Digitaria californica 0.8 0.6 3.1 Cenchrus incertus 0.7 Eneapogon desvauxii 0.3 0.2 Panicun obtusum 0.6 0.0 Aristida spp 16.4 10.4 6.3 Sporobolus airoides 0.8 Panicum halli Subotal 53.9 33.9 68.1 ANNUAL GRASSES Bouteloua curtipendula (annual) 0.1 Eragrostis annual 1.4 1.4 Aristida annual 15.2 2.2 Bouteloua annual 4.3 0.4 Panicum annual 6.7 0.6 Chloris annual 4.8 Mulhenbergia annual 0.8 Subtotal 33.2 2.8 2.0 PERENNIAL FORBS Sida procumbens 10.3 18.2 0.1 Legume 0.3 Calcomeca 0.1 Hoffmansegia spp 22.7 2.6 0.3 Forb perennial 6.3 Zinnia spp 6.9 1.0
47
Table 3.4: Continued Species Forb 2 Croton potsii 0.6 2.7 Coldenia spp Cassia spp 1.3 Solanum eleagnifolium 0.6 0.2 Subtotal 47.0 26.3 0.3 ANNUAL FORBS Evolvolus spp 7.4 3.9 0.3 Annual forb 1 0.2 Composite 0.6 Hairy forb Cotton forb 0.1 Curly forb 1.9 Amaranthus spp 1.1 Eringium spp. 0.3 Cebollin Subtotal 10.9 4.4 0.6
Coverage is the average in 1200 cm transects.
Perennial forbs accounted for the second largest amount of cover in 1993
of herbaceous functional groups at Ranch 3. Immediately below perennial
grasses; Hoffmansegia spp., was the species responsible for the major amount
of cover. In 2005, however, a dramatic decrease in coverage occurred in this
group of plants to the point that they were just barely recorded. The same pattern
occurred with annual grasses; some species of the Aristida genus were the most
common within this functional group, followed by Panicum, Bouteloua, and
Chloris.
Within annual forbs, Evolvolus spp., was the predominant plant at Ranch
3. Shrubs constituted part of the plant (aerial) coverage at this ranch; however,
their contribution was limited. The aerial cover length of shrubs varied from 83
cm out of 1200 in 1993 to 71 cm/ 1200cm in 2005. Mesquite Prosopis spp. was
48
the predominant species in this group. Other species, Acacia angustissima and
Ephedra spp. were also recorded in 1993, but they were not important in 2005.
In fact, one species (Ephedra spp.) was not recorded the last year.
Vegetation characteristics in Ranch 4 were quite different from the other
three ranches. Perennial grasses were not the dominant group at this ranch. Its
basal cover length was only 27 cm out of 1200 cm in 1993, and it almost
disappeared in 2005 (1.9 cm/ 1200 cm).
Arizona cottontop (Digitaria californica) and Plains bristlegrass (Setaria
macrostachya) were the most significant species in the perennial grasses
functional group with 8.1 and 5.6 cm/1200 cm respectively (Table 3.5). Broom
snakeweed (Gutierreza sarotrae), a very common short-lived half-shrub in the
Chihuahuan desert landscape that is highly influenced by winter moisture, was
an important species at Ranch 4. In 1993, this species accounted 202 cm/1200
cm out of 1200, the highest cover length (aerial); however, it is not surprising that
it decreased to 31.2 cm/1200 cm in 2005.
Although basal cover of perennial forbs was greatest among all the
herbaceous groups in 1993, even more than perennial grasses, the cover length
noted for this group is considered small (40 mm/1200 cm). In 2005, the cover
determined for this group was even smaller than the first year.
Among the annual grasses two Bouteloua and one Panicum species
were recorded in a very small amounts the first year, accounting only 9.7
cm/1200 cm over all annual grasses, and disappeared by 2005.
49
Table 3.5: Basal (forbs and grasses) and aerial (shrubs and sufrutecents) cover (cm/1200 cm) of species present in sampled transects, categorized by functional groups in Ranch 4. Year SPECIES 1993 1994 2005 SHRUBS Budleja scordioides Parthenium incanum 32.2 31.1 Ephedra sp. 11.1 Prosopis sp. 72.3 95.2 76.2 Mimosa spp 6.1 Flourencia cernua 29.3 21.9 54.0 Atriplex spp 0.6 Condalia spp Subtotal 140.0 148.8 141.3 SUFFRUTECENTS Xantocephalum sarotrae 202.6 94.2 31.2 Agave spp 3.6 Subtotal 202.6 94.2 34.8 PERENNIAL GRASSES Lycurus phleoides 0.7 Bouteloua gracilis 2.4 3.3 0.2 Bouteloua eriopoda 0.8 0.7 0.8 Botrichloa barbinodis 0.3 Setaria macrostachya 5.6 1.1 0.4 Digitaria californica 8.1 2.3 Erioneuron pulchellum 1.0 Eneapogon desvauxii 1.6 Aristida adscencionis 3.6 Aristida spp 3.7 0.7 0.4 Subotal 27.7 8.1 1.9 ANNUAL GRASSES Eragrostis annual 3.0 Aristida annual 0.6 Bouteloua barbata 1.4 Panicum annual 2.0 Chloris annual 0.3 Bouteloua aristirioides 2.9 Subtotal 9.7 0.0 0.6 PERENNIAL FORBS Sida procumbens 5.0 0.8 Legume 0.7 Solanum eleagnifolium 0.2 Hoffmansegia spp 0.1 0.2 Verbena spp Zinnia spp 2.3 0.4
50
Table 3.5: Continued Species Legume2 0.3 Dichondria argentea 1.1 0.2 5.4 Guillemina spp 0.4 Legume 3 27.7 Legume 4 0.7 Cassia spp 0.3 1.7 Subtotal 38.0 2.1 8.0 ANNUAL FORBS Evolvolus spp 0.3 Annual forb 1 0.2 White forb Ddysodia spp 0.9 Tronadorcillo Cabezuela Vigueria spp 8.8 Hybiscus spp Amaranthus spp Red forb 0.8 White flower forb Big forb 0.3 Salsola spp 0.1 Subtotal 0.9 0.0 10.6
Cover is the average in 1200 cm length transects.
Within perennial forbs only Sida procumbens and a none identified
legume species were important in 1993, and disappeared later on. Dichondra
argentea was the only perennial forb species present in 2005. Annual forbs were
almost absent in 1993, and were present in only a very small amount in 2005;
Vigueria spp. was the plant with the larger coverage in 2005.
Shrub aerial coverage remained steady over the years, with 140 and 141
cm out of 1200 cm for 1993 and 2005, respectively; including mesquite and
tarbush (Flourencia cernua), and a browse species mariola (Parthenium spp.) as
the major contributors in this group.
51
In Ranches 1 and 2 (SDG), perennial grasses were the functional group
with the largest percentage of coverage. Annual forbs were another group that
contributed to basal coverage during 1993. In 2005, however, the amount of its
coverage was less than 1%. In these two SDG ranches, shrubs were present
only at Ranch 2. Aerial cover of shrubs was relatively small, fluctuating from 4%
in 1993 to 5% in 2005 (Table 3.6).
Vegetation cover in Ranch 3 followed a different trend than that in Ranch
4. In Ranch 3, the largest herbaceous strata coverage was formed by the
perennial grasses and perennial forbs. Although they were the major proportion,
it was small. Basal cover in 1993 was 4.5 and 3.5%, whereas in 2005, it was 5.6
and 0.03% for both perennial grasses and forbs, respectively. Aerial cover of
shrubs was only 7% in 1993 and 6% in 2005, so their contribution was
considered not relevant, taking in account that the value correspond to canopy
cover.
In Ranch 4, the basal cover of herbaceous plants was very limited.
Perennial forbs had the greatest value, but it barely passed 3% in 1993. In 2005
no herbaceous group was larger than 1%. Shrubs-like plants showed the largest
aerial cover in 1993 (16%); however, they declined drastically in 2005 (2.9%),
whereas the shrubs functional group remained more stable, accounting for 12%
through time.
Initial basal cover was greater in ranches managed under SDG system
than in the traditional CG system (P=.0004); however, the difference in basal
52
Table 3.6: Basal cover (%) by functional groups in four ranches under Short Duration (SDG) and Continuous (CG) grazing management in Chihuahua, Mex. (2006). Ranch/ Basal cover (%) Functional Group 1993 1994 2005 Ranch1 (SDG) Perennial Grasses 26.1±1.9 21.92±2 10.68±2.8 Annual Grass 0.00 0.00 0.78±0.3 Perennial Forbs 0.45±0.2 0.04±0.1 0.05±0.1 Annual Forbs 6.20±2.3 0.17± 0.53±1.4 Ranch 2 (SDG) Shrubs 4.34±2.5 4.19±2.3 5.02±1.6 Perennial Grasses 20.29±1.2 17.80±1.3 7.40±1.5 Annual Grasses 0.06±.03 0.02±.02 0.09±0.01 Perennial Forbs 0.64±0.2 0.89±0.3 0.01±0.16 Annual Forbs 1.44±0.8 1.27±0.7 0.08±0.3 Ranch 3 (CG) Shrubs 6.94±3.4 5.54±2.8 5.97±3.2 Shrubs-like 0.73±0.6 0.00 0.00 Perennial Grasses 4.49±1.2 2.90±0.8 5.68±0.9 Annual Grasses 2.77±0.7 0.23±0.6 0.17±0.5 Perennial Forbs 3.92±1 2.19±0.9 0.03±0.9 Annual Forbs 0.91±0.4 0.37±0.2 0.05±0.2 Ranch 4 (CG) Shrubs 11.67±3.5 12.40±3.6 11.78±3.5 Shrubs-like 16.88±3.2 7.85±3.1 2.90±2.9 Perennial Grasses 2.31±.5 0.68±0.4 0.16±0.4 Annual Grasses 0.81±0.2 0.00 0.05±0.9 Perennial Forbs 3.17±1.6 0.18±1.1 0.67±0.4 Annual Forbs 0.07±0.1 0.00 0.88±0.4
53
cover was smaller in 2005 that at the beginning of the study (Figure 3.7). In
general the trend for perennial grass basal cover was to decrease in the four
ranches independently of the treatment, except in Ranch 3 (continuous), where
an increase in basal cover was observed by 2005.
26.0+1.9
21.9+2
10.6+2.8
20.3+1.2
17.7+2
7.3+1.54.5+1.2 2.9+.885.6+.96
2.3+.5 0.6+.44 0.16+.40
5
10
15
20
25
30
1993 1994 2005
Ranch 1 SD Ranch 2 SD Ranch 3 C Ranch 4 C
Figure 3.7: Perennial Grasses Basal Cover (%) in four ranches, under Short- Duration (SDG) or Continuous (CG) grazing management in Chihuahua, Mexico.
According to the results of the principal component (PC) analysis using
grazing system as the ordination value, in 1993 PC 1 explained 42% of total
variation (Table 3.7). Perennial grasses basal cover accounted as the most
important predictors of vegetation variation in ranches managed under SD
Year
Bas
al C
over
(%)
54
grazing system (-0.5638), and annual forbs basal cover seemed to the second
major source of variation (-0.2778) as shown in Figure 3.8. With regard to
ranches that used traditional CG management as grazing system, annual
grasses (0.4232) and perennial forbs (0.4341) basal cover were the most
important variables describing the vegetation variation in this grazing system
(PC1; Figure 3.8). Principal Component 2 (PC2) explained only 16.9% of the
Table 3.7: Eigenvectors for the significant components resulting from a principal component analysis conducted in 1993 and 2005 for vegetation changes in ranches with different grazing systems. Eigenvectors 1993 2005 Variable PC1 PC2 PC1 PC2 Shrubs 0.3159 -0.4898 0.321 -0.5879Shrubs-like 0.3701 -0.2872 0.5769 0.2963Perennial Grasses -0.5638 0.0138 -0.543 0.2733Annual Grasses 0.4232 0.5505 0.1016 -0.3498Perennial Forbs 0.4341 0.3868 0.5084 0.3791Annual Forbs -0.2787 0.4739 0.019 0.475 Component Variation explained Cumulative variation
PC1 0.4216 0.4216
PC2 0.169
0.5906
PC1 0.3072 0.3072
PC2 0.19350.5006
variation, annual grasses (0.5505) and shrubs (-0.4898) were the variables that
produced the highest variation in both grazing systems.
In 2005, only 30% of total variation was attributable to PC1; perennial
grass basal cover (-0.543) not only was the most important variable describing
the variation of vegetation in ranches managed under SDG system, but also
55
accounted for a smaller amount for variation in the ranches with CG
management. Nevertheless, suffrutescents aerial cover (0.5769) was the
variable that caused the major variation in continuous grazing (Figure 3.8).
Principal Component 2 accounted for 19% of total variation. Annual forbs
cover (0.475), and shrubs aerial cover (-0.5879) were important in both SDG and
CG management.
In 2005, the variable that had the major influence in PC2 in SDG managed
ranches was annual forbs basal cover; however, both the shrubs aerial cover
and annual grass basal cover were responsible for the greatest variation in the
two ranches that used the traditional CG system management.
3.3.3 Forage Production
Ranches managed under SDG had a greater (P = 0.006) forage
production (634 ± 56 kg DM/ha) than those managed under CG grazing (339 ±
57 kg DM/ha). Also, statistical difference was found (P=0.08) between initial
forage production of treatments. In 1993 the forage production was greater in
ranches managed under SDG (1098 ± 232 kg DM/ha) than in those under CG
grazing (795 ± 232 kg DM/ha). Because the difference in initial forage production
in the treatments, the forage production was adjusted by the initial condition. In
general, forage production was slightly greater in 1994 (521 ± 50 kg DM/ha) than
in 2005 (453±50 kg DM/ha); however, no statistical difference (P = 0.28) among
years of sampling was found, Table 3.8.
56
Prin2 ‚ 4 ˆ ‚ 2 ‚ ‚ A.Grasses(.55) ‚ ‚ ‚ 3 ˆ ‚ ‚ ‚ ‚ ‚ 1 ‚ 2 ˆ ‚ ‚ ‚ 2 ‚ ‚ 1 2 ‚ 2 1 ˆ 2 ‚ ‚ 1 ‚ 1 1 2 ‚ 1 ‚ 1 2 ‚ 2 2 0 ˆ P.Grasses(-.563) 1 1 2 P.Forbs(.434) A.Grasses(.423) ‚ 11 1 1 1 ‚ 111111 1 ‚ 2 ‚ 1 2 ‚ 2 ‚ -1 ˆ 1 2 ‚ ‚ ‚ 2 2 ‚ 2 2 ‚ 1** -2 ˆ ‚ Shrubs(-.489) Šƒƒˆƒƒƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒƒˆƒƒ -3 -2 -1 0 1 2 3 4 Prin1 NOTE: 4 obs hidden.
Figure 3.8: Principal components analysis of functional groups associated with management system as an ordination value at four ranches in Chihuahua, Mex. in 1993. ** 1 Short-Duration 2 Continuous
57
Prin2 ‚ 3 ˆ 2 2 ‚ ‚ ‚ A.Forbs(.475) ‚ ‚ ‚ 2 ˆ ‚ ‚ ‚ ‚ ‚ ‚ 1 ˆ 1 ‚1 1 ‚ 1 1 1 2 ‚ 1 1 1 2 ‚ 1 ‚ 2 1 2 ‚ 2112 2 0 ˆP.Grasses(-.543) 111 1 Suffrutescents(-.576) ‚ 1 11 ‚ 1 2 ‚ 1 2 ‚ 2 ‚ 1 ‚ 2 -1 ˆ ‚ ‚ 1 ‚ ‚ 2 ‚ ‚ 2 -2 ˆ ‚ ‚ 1 ‚ 1 ‚ 2 ** ‚ ‚ Shrubs(-.587) -3 ˆ ‚ ƒƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒƒƒ -2 -1 0 1 2 3 4 5 Prin1 NOTE: 4 obs hidden. Figure 3.9: Principal components analysis of functional groups associated with management system as an ordination value in at four ranches in Chihuahua, Mex. in 2005. ** 1 Shorth-Duration 2 Continuous
58
A treatment by year interaction was found (P=0.001), the forage
production in ranches managed under SDG had a lower production in 1994 (815
± 70 kg DM/ha) than in 2005 (453 ± 70 kg Dm/ha), whereas the CG managed
ranches showed an opposite trend, with a lower production obtained in 1994
(228 ± 70 kg Dm/ha) than in 2005 (451 ± 72 kg DM/ha).
In 1994, statistical difference (P = 0.0002) in forage production was found
between SDG and CG grazing systems, whereas in 2005, no statistical
significant difference was found (P = 0.98).
Table 3.8: Forage production (kg DM/ha) in ranches managed under Short- Duration (SDG) or Continuous (C) grazing systems in Chihuahua, Mexico.
Treatments
Year Short-Duration Continuous Average***
1993*† 1098±232a 795±232b
1994 815±70Aa 228±70Ab 521±50A
2005 453±70Ba 451±72Ba 452±50A
Mean** 634±56a 339±57b
*Initial (1993) means with different lower case letters within a row are statistically different(P=0.08) **Treatments means with different lower case letters within a row are statistically different(P=.05) ***Years average with same capital letter are statistically similar (P=0.28) Means within treatments with different capital letter within same column are statistically similar (P≤0.03) Means within year with different lower case letter same row are statistically different (P=0.002) Means within years with same lower case letter in same row are statistically similar (P=0.98) †Covariate
59
The fact that a treatment by year interaction was detected suggests that
the variation in forage production was a result of variation in rainfall patterns over
the period of study or other factor, and cannot be attributed only to the difference
of grazing management effect.
3.3.4 Density
In general, a decreasing pattern was observed from the beginning to the
end in plant density at all four ranches. Blue grama was the most abundant
species in Ranches 1 and 2, increasing from 1993 to 1994, but decreasing
drastically by 2005. The same pattern as blue grama was shown by threeawn
and side oats in Ranch 1 and 2. Microchloa kuntii, the second most abundant
species presented a linear trend, decreasing from 1993 to 2005. In Ranch 3,
threeawn was the most abundant species in 1993, followed by Lehmann
lovegrass. By 2005, threeawn almost disappeared, whereas density of Lehmann
grass increased two-fold.
In Ranch 4, some species of annual grasses; Panicum spp, Erafrostis
spp, and Bouteloua aristiroides, along with threeawn were the most abundant
species in 1993. However, in 2005, the density of all species was very low, with
some species even disappearing. There was a huge population of broom snake
weed in 1993, but in 2005 a tremendous reduction in plant density of broom
snakeweed was observed (see table 4.16 in Appendix).
60
3.4 Discussion.
Perennial grasses basal cover (%) was the most consistent and reliable
variable on which to base the criteria to evaluate the vegetational changes.
Teague (2004) mentioned that when monitoring sustainable use, basal area are
between the most sensitive indicator. Nash (2006) concluded that changes in
annual communities in the Chihuahuan Desert response to livestock grazing
intensities differ from that on perennial vegetation. Taylor (1997) recommended
the monitoring of grazing use on preferred plants. In a study conducted by White
et al. (1991) perennial grasses showed the most dependable cover data, other
forbs species were present in rather small quantities in all pastures; but did not
exhibit a consistent trend in pastures.
Perennial grasses basal cover in SDG was different from the CG system
at the beginning of the study (P = 0.0004), but not at the end of the period of
evaluation (P = 0.51). Dowling et al. (2005) found no consistent differences in
response in perennial grasses basal cover percentage in 5 sites evaluated in
grassland components in southeastern Australia. Basal cover was greater on
time controlling grazing management compared with continuous grazing, but
initial values was also greater, except that they did not find management by
time interaction, as was noted in the present study..
All four ranches showed a decrease in basal cover toward the last year
evaluated, except for Ranch 3. At this ranch, the presence of an exotic species
(Lehmann lovegrass) produced a change in the observed pattern for the other
61
species, showing an increase in basal cover in last year of evaluation. Lehmann
lovegrass is a very aggressive, introduced species that has been invading open
spaces in desert rangelands, often replacing native species. Smith and Schmutz
(1975) noted this situation in a desert grassland range in Arizona. Additionally,
McClaran and Anable (1992) mentioned that livestock grazing is not necessary
for Lehmann lovegrass to spread, but that its relative abundance was greater at
higher grazing intensities.
Perennial grasses basal cover in ranches managed under SDG showed a
greater decline (P = 0.0001) than with traditionally managed ranches were basal
cover of perennial grasses remained stable (P = 0.36). This response could be
attributed to the fact that higher stocking rates were used under the rotational
systems compared with the traditional CG system, although coverage was
greater since the beginning, and remained greater in ranches managed under
SDG system no statistical difference was found (P = 0.98) on the last year of
evaluation (2005). Nonetheless, the magnitude of the decrease in perennial
grasses basal cover was greater in SDG than in traditionally managed CG
ranches.
The average stocking rates used in SDG systems were greater than those
used in CG managed ranches; however, in the present study, the range condition
of traditionally managed ranches was poorer than in the SDG ranches,
particularly in Ranch 4. This situation can be seen in Table 4.6. Initial perennial
grasses basal cover was 4.5 and 2.6% in Ranches 3 and 4 respectively,
62
compared with 26 and 20 % in Ranches 1 and 2, respectively. Although, the
higher stocking rate used in SDG system seemed to have more effect on
vegetation than grazing system.
A considerable amount of literature supports the statement that stocking
rate influences vegetational changes more than the grazing system (Heady,
1961; Van Poolen and Lacey, (1979); Angell, (1997); Pitts and Bryant, (1987);
Guillen et al., (1998)).
The major species in ranches under SDG management was blue grama,
which is widely recognized because of its grazing and drought resistance (Fair et
al., 2001). However, its basal coverage decreased in these four ranches.
Perhaps the grazing intensity and the magnitude of drought were so intense, that
this species was not capable of maintaining its cover size and/or recuperating in
a short period of time. This perception is supported by the decrease observed in
density of blue grama in the quadrats sampled at the same places.
An analysis in global range environments was conducted by Milchunas
and Lauenroth (1993). They concluded that changes in species composition
were primarily a function of ANNP, and the evolutionary history of grazing on the
site, with level of consumption being third in importance. These three variables
explained >50% of the variance in the species response of grasslands or
grasslands-plus-shrublands to grazing, even though methods of measurement or
grazing systems varied among studies. Sensitivities of changes in dominant
species were greater to varying ecosystem-environmental variables than to
63
varying grazing variables, from low to high values. The response of shrublands
was different from that of grasslands, both in terms of species composition and
the dominant species. Species dissimilarity of grazed vs. ungrazed shrubland
was less than for grassland, and increases in dominants in grazed areas were 9
times more likely in shrublands compared with grasslands Guillen and Sims
(2006) found that basal cover of grass species did not respond to the stocking
rate in a single direction in a 20-year study, but exhibited continuous variation
according to rainfall patterns. The effect was more evident during dry years.
With regard to environmental factors that interact with vegetation changes;
Vetter (2005) noted that the current paradigms in ecology and range
management describing the equilibrium models that support the importance of
biotic feedback such as density-dependent regulation of livestock population and
the feedback of livestock density on vegetation composition, cover and
productivity, and management are centered on carrying capacity, stocking rates,
and range condition assessment. Conversely, the non-equilibrium paradigm
suggests that rangeland systems are driven by stochastic abiotic factors,
essentially rainfall, resulting in a highly variable primary production, and that the
livestock population is rarely in equilibrium with its fluctuating resource base.
The decrease in perennial grasses basal cover was caused mainly by two
factors: high stocking rates and the low amount rainfall that occurred in several
years within the study period, regardless of grazing system. This finding agrees
with the conclusions expressed by Herbel and Anderson (1959) after they
64
evaluated the response of true prairie vegetation on major Flint Hills range sites
to different grazing treatments. They compared heavy, moderate, and light
season-long stocking, and deferred-rotation at a moderate stocking rate. The
major factors influencing changes in plant composition were the stocking rates
and the variation in weather conditions from abundant moisture before mid 1951
to severe drought that remained through 1955.
The amount of rainfall received over the study period varied considerably
(Figure 3.6), but the most remarkable aspect was the number of years in which
the precipitation was less than 80% of the annual average; precipitation less
than 75% is considered to reflect severe drought conditions. An extreme
situation in vegetation condition occurred in Ranch 4, where even before the
evaluation period, the drought was critical and becoming worse over time.
Despite a decrease in stocking rate in some years, the adverse rainfall conditions
that prevailed across the time (Figure 3.6) aggravated the situation.
Biondini et al. (1998) did not find differences among non-grazing,
moderate grazing, and heavy grazing treatments, in a Poa pratensis dominant
species, mixed-grass prairie in North Dakota in terms or absolute basal cover
and absolute density; however, they found a significant positive correlation
(r2=0.77) with annual precipitation. Their conclusion about the mixed-grass
prairie was that climatic variation, in particular droughts, control major trends in
plant species composition and production, with grazing playing a secondary role.
65
O’connor (1994), also reported similar conclusions, and agreed that
rainfall variability had more influence on species abundance than grazing
intensity.
The forage fluctuation observed in all ranches could be considered more a
result of rainfall than a grazing effect. The trend observed in forage production
was similar to perennial grasses basal cover. Both are closely influenced by
rainfall conditions, but forage production is probably more sensitive to
environmental changes than is basal grass cover.
In 2005, the greatest and the least forage production values were
measured at the ranches with traditional management. In Ranch 4, the range
condition was becoming worse because of the impact of grazing and adverse
environmental conditions that prevailed during the entire study period. Forage
production was limited to only 100 kg DM/ha, whereas in Ranch 3, the presence
of Lehmann lovegrass resulted in a greater response in forage production in
2005 than was noted for Ranch 4.
In general, forage production was low, and the small amount of
precipitation during some years over the study period was the cause of this
response. Nonetheless, the last year (2005) was at or slightly above average.
Vegetation did not respond and thereby result in a substantial increase in
forage production, mainly due to the decrease in perennial vegetation basal
cover, as well as a reduction in plant density. Unfortunately, the lack of
intermediate samples taken between 1994 and 2005 did not allow the
66
establishment of a more clear tendency through time. Beck and McNeeley
(1991) reported a close relationship (r2= 0.53) between plant biomass and
precipitation in the Chihuahuan desert rangeland over 20 years. In a study
conducted by Heitschmidt et al. (1987), with two different stocking densities in a
rotational grazing system, no differences were found in ANNP between the
treatments, but variation among years was evident. In general ANNP was
greater in the paddocks with highest stocking density. Total standing crop had
two peaks, one of them occurred because of an increase in annual broomweed
herbage production.
Van Poolen and Lacey (1979) compiled results from reliable studies
regarding comparison of grazing systems and stocking rates separately. They
reported that rotational grazing versus continuous grazing increased herbage
production by 13%. While decreasing from heavy to moderate stocking rates,
the increment in herbage production fluctuated around 35% compared with 28%
with a change from a moderate to a light stocking rate.
Socio-economic factors.
The changes in vegetation observed in the ranches evaluated were not
merely the result of mismanagement of rangelands by the owners. The origin of
the problem is more complex than simply an overstocking practice. A brief
67
analysis will be done to explain some of socio-economic factors that contributed
to exacerbating the rangeland deterioration in the ranches evaluated.
Historically, the uncertainty in land ownership has contributed to
overstocking or overgrazing of rangelands. The landlord tried to make more
profits from the land because the threat of loosing part of their land by the
government expropriation from ranchers that owned a larger amount of land than
that allowed by law, which started in the 1930s and continued through the early
1990s, and was latent in many instances. The lack of security in land ownership
contributed to exploitative land use (Molinar et al., 1998). All people that faced
this situation tried to run as many cattle as possible, as they wanted to obtain as
much value from the land as they could before they lost it. Under these
circumstances, the land degradation was aggravated every year.
The financial crash of the Mexican economy in 1994 and the drought that
started the same year and lasted for approximately 10 years also influenced
landowners choices and the concomitant vegetative results..
During the late 1980s and early 1990s, an aggressive program from the
Central Mexican Government promoted the implementation of an innovative
grazing system (Savory system or SDG), with the aim of improving the efficiency
of the ranch enterprises nationwide. Doubling carrying capacity was the magnet
which drew the government and landowners to the program. Large amounts of
investment were needed to implement the system; however, the low interest
rates offered by financial institutions at that time to promote the program resulted
68
in several ranches implementing the system. The expectancy of some ranchers
of doubling the ranch carrying capacity in a short period of time, and
subsequently increasing profits, would allow them to easily overcome the debt
situation and could be able to afford the debt contracted.
A common practice for many years was to obtain credits early in the year
to finance most of the ranch variable costs and to repay them the end of the year
after calf crop was sold. This practice worked for many years because the
interest rate fluctuation was more stable, and the constant slide of Mexican peso
allowed the debt on the contracted loans to be paid because the Mexican calf
market is strongly tied to prices in dollars. This situation seemed to put them in
even better shape. Unfortunately after 1994, the Mexican economy passed a
tremendous crisis, and sometimes the interest rates rose above 100%, making in
many instances the debts of many ranchers non-payable.
An important aspect in ranches’ economy is cattle price. Feeder prices at
1994 were below $100.00/cwt until 1999 (180 kg average live weight), and as
low as $66.00/cwt in 1996, decreasing the gross income tremendously. In
addition to the economic situation, the environmental conditions faced by the
rancher were the worst in many years. The precipitation pattern in the 4 ranches
evaluated during the 1994 to 2005 period showed 5 to 7 years out of 12 with
severe drought.
Holecheck (1998) pointed out that climatic and financial conditions are
among the greatest risks in range livestock production. In arid and semiarid
69
environments, recurrent droughts are well recognized and expected. Smart et al.
(2005) cited 14 times out of 95 years that a severe drought occurred in the Great
Plains. Holecheck (1996) made reference of 3 out of 10 years are characterized
by less than 75% of precipitation in the growing season in several parts in New
Mexico. Many Mexican ranchers in Chihuahua as well as some of the New
Mexico land owners (Holecheck, 1996) were forced to liquidate more than 50%
of their cattle inventories due to lack of forage with giveaway prices for cattle
after Fall 1994.
Cattle sold during droughts are often discounted in the marketplace
because of increased supply, decreased demand, poor livestock condition, and
untimely marketing. Market value of livestock may be depressed below book
value or balance sheet value, which causes problems with net-worth statement
and potentially with lenders (Dunn et al., 2005).
Profitability of ranches in Chihuahua State is critical, and it varies among
the geographical locations in the state. Martinez-Nevarez (2002) evaluated 154
ranches in the state of Chihuahua. The average size was 4500 ha, with a base
of 185 mother cows. Most ranches showed losses in their operations, and the
benefit/cost ratio was 0.95 on average, the investment return was -5.4%, the
break even calf crop selling price was $1.00 in 158 kg average weight. A 20-year
financial projection suggested that the average net present value was close to -
$290,000.00 and the internal rate of return was 2.79 points lower than the
Mexican discount rate (CETES).
70
Thus, the critical financial situation, the prolonged drought, the previous
range condition, and the declining cattle market, collectively contributed to an
overuse of the limited forage resources, thereby hastening the decline in basal
cover of the perennial grasses and the deterioration in the range condition. In
some cases, these changes allowed for an increase in less desirable species or
an increasing bare soil.
Shoop and McIlvain (1971) suggested that an extra supplementation or
feed complement can be profitable until the plant and soil resources are badly
damaged, or until a series of drought years combined with low or dropping cattle
prices “terminate” the business or put it in a subsistence level. Thus, energy
supplementation was performed by most of the ranchers for many years, until the
point of no return, when the extended drought plus the overstocked ranges finally
showed up in the most vulnerable resource, the vegetation. This ultimately
resulted in a decrease in basal coverage, forage production, density of plants,
and, of course, land deterioration.
71
CHAPTER V
CONCLUSIONS AND RECOMMENDATIONS
5.1 Conclusions
This study evaluated the effects of grazing systems on vegetation
changes in private ranches. Short Duration Grazing was compared with
traditional Continuous Grazing system.
The question implicit in the initial objectives was which is the best grazing
management practice? This question was posed with the aim that it would lead
to identification of more efficient and sustainable grazing management practices
to enable decision making that would be more suitable and operating under
different environmental conditions. In the present study, basal and aerial cover,
forage production, and plant densities of present vegetation were surveyed, while
rainfall was recorded. This took place at four ranches managed under either
short-duration or continuous grazing systems in Chihuahua, Mexico.
Initial condition (1993) in basal cover was different between ranches under
SDG and CG. The perennial basal cover was greater in SDG ranches than in CG
managed ranches
Higher decline tendency was observed in SDG managed ranches
compared with CG, however, after the values were adjusted due the difference in
initial condition, no difference was found between treatments in the last year of
the evaluation period (2005).
72
Forage production showed a similar performance to that observed in basal
cover. The initial forage production (1993) was greater in SDG than in CG
system managed ranches. Also a decline in forage production was observed in
both treatment but, the magnitude of the difference was greater in SDG
compared with CG. No difference in forage production was found at the end of
the evaluation period (2005).
The decline in basal cover and forage production were definitely
influenced by the low precipitation received during the evaluation period. Even
though, the forage production could be considered more sensitive to climatic
conditions.
The greatest decline observed in basal cover and forage production in
SDG compared to CG, is most probably in response to the higher stocking rates
used in SDG.
The presence of lehmann lovegrass in one of the ranches under CG
affected the response of the vegetation in this treatment.
Grazing systems effects were not separable from the environmental
conditions and high stocking effects during the time of study. This finding agrees
with works found in the literature review .
The financial and market conditions indirectly increased the pressure on
rangelands. Given the economic situation prevailed during study period,
ranchers were unable to decrease stocking rates because cows rather than
73
range are visualized as the product. This resulted in more attention being
focused on retaining large number of animals instead of increasing vegetation.
As Shoop and McIIvan (1971) cited previously said, the extended drought
plus the overstocked ranges finally showed up in the most vulnerable resource,
the vegetation.
5.2 Management Implications
The implementation of SDG does not provide any vegetation improvement
compared with traditional CG when high stocking rates are utilized in SDG.
However, the vegetation response could be improved, however, at lower stocking
rates.
The use of high stocking rates when an undesirable, unpalatable, and
aggressive grass species is present, such as Lehmann lovegrass, will favor the
spread out of this species; aggressive species will increase its coverage and
density, often replacing highly desirable species. This displacing process would
likely occur under any grazing system when high stocking rates are used.
The amount of money required to construct a large number of
intermediate fences is substantial. Thus, return on these investments will require
many years.
In ranches that actually have the infrastructure established and are
continuing under the SD grazing system, a reduction in stocking rates is
imperative. Otherwise, the deterioration of vegetation deterioration will continue
74
with each passing year. Lowered income by a decrease in the number of grazing
cattle will be compensated by a reduction in supplemental feed during dry
seasons, which most ranches in Chihuahua experience so far for 5 to 6 months
every year. This would also decrease the risk under the recurrent periods of
severe droughts. Moreover, an improvement in production variables is expected
under moderate stocking rates, as well as an improvement in range condition. In
years with more favorable environmental conditions, producers could purchase
stocker cattle or raise their own stocker cattle as an alternative to maintaining a
larger cow herd, considering that stocker cattle are more readily transformed into
cash.
When a year at or above average rainfall show up after a severe drought ,
a decrease in stocking rate might prevent the continued reduction in perennial
grasses basal cover and forage production; however, when the deterioration is
too severe, the potential vegetation response is very limited, no matter he
grazing system used.
5.3 Recommendations for further studies.
In this study, the changes in basal and aerial cover, forage production,
and plant density were surveyed after 12 years in four private ranches under two
different grazing systems, SDG or CG. As in many other studies, the high
stocking rates used in SDG and the drought conditions minimized the effects of
the grazing system.
75
Many questions that were noy answered from this study remain and could
be integrated to future researches.
The most important aspects to evaluate in the implementation of future
studies on SDG could be considered:
The use of moderate stocking rates
The performance of grazing animals to low stocking rates
The economic analysis of the grazing system
The inclusion of more number and more homogeneous grazing units
Increase the number of year of evaluation
Use more than one herd in the grazing unit
Increase in grazing period in the growing season to 7-10 days
The use of moderate or proper stocking rates has not been tested under
SDG. Many researches initially agreed that HRM principles make sense, except
for the idea that carrying capacity could be increased two-fold and that hoof
action is beneficial.
Test the use of moderate stocking rates in combination with more than
one herd at a time, thereby splitting the stocking densities among more pastures,
mainly at times when grasses are more nutritious could be important.
In addition, the use of high stocking densities was justified under SDG
because it would promote soil water infiltration, but this was not proved in many
instances. Density problem could be avoided by spreading the animals into more
76
paddocks instead of grazing just one a time. Splitting herds should be more
desirable mainly during early growing stage by allowing the animals to have
access to more nutritional forage at the same time, decreasing grazing pressure
by other animals. Rotating the herds every 7 to 10 days at the same time with
multiple herds might be more suitable than every 2 to 3 days with a single herd.
In arid environments, it is not uncommon that vegetation completes a
cycle in a very short period of time depending on the rainfall pattern. Thus, at the
end of rotation after 28 to 30 days, the vegetation on the first pastures grazed will
be mature. At later stages when vegetation is more mature, the rotation could be
conducted as the system originally proposed, allowing the perennial plants
accumulate enough energy to form the buds that will promote the tillering next
year, ensuring persistence of perennial vegetation, mainly perennial grasses.
77
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85
APPENDIX
86
APPENDIX A
VEGETATION COVER (CM), DENSITY (PLANTS/M2), AND
FORAGE PRODUCTION (KG DM/HA)TABLES OF
SAMPLES TAKEN BY YEAR
BY RANCH
87
Table 4.1 List of species sampled in Fall 1993:Cover (cm/1200cm) lengthRanch 1 T1 T2 T3 T4 T5 T6 T7 T8 T9 T10
SPECIESSHRUBSMimosa spp 0 0 0 0 0 0 32 0 0 0Subtotal 0 0 0 0 0 0 32 0 0 0PERENNIAL GRASSESBouteloua gracilis 254 349 261 73 100 122 85 256 285 352Aristida adcensionis 64 5 6 0 14 66 92 32 86 86Hilaria belangeri 0 0 0 45 0 0 22 0 0 0Panicum sppHilaria mutica 0 0 0 171 0 0 0 0 0 0Botrhiocloa barbinodis 0 0 0 6 3 0 0 0 0 0Bouteloua curtipendula 0 0 0 0 70 9 0 0 14 0Bouteloua hirsuta 0 0 0 0 111 0 0 0 0 0Lycurus phleoides 0 0 0 0 0 40 0 32 22 0Schizachirium spp.Mulhenbergia spp,Bouteloua eriopodaSubtotal 318 354 267 295 298 237 199 320 407 438ANNUAL GRASSESAristida annualChloris annualEragrostis annualBouteloua annualSubtotalPERENNIAL FORBSGuillemina spp 0 0 9 0 0 0 0 0 0 0Sida procumbens 11 3 0 0 0 5 0 0 0 0Hoffmansegia spp.Solanum eleagnigolium 0 0 0 0 0 0 0 0 0 20Dalea spp 0 0 4 0 2 0 0 0 0 0Malva sppLeguminoseSubtotal 11 3 13 0 2 5 0 0 0 20ANNUAL FORBSHairy forb 0 0 0 0 0 0 0 0 0 47Heteroteca spp 13 0 12 0 9 0 294 0 39 35Grindelia sppCompositaeAnnual Forb 0 0 23 0 0 0 0 0 57 7Argemone mexicanaCyperacea 0 0 0 0 0 0 0 0 4 0Tronadorcillo 0 2 0 0 0 0 0 0 0 0Spharalcea spp 0 0 0 0 4 0 0 0 0 0Ceniza 0 0 24 0 9 0 0 0 0 0Paronichya spp.Aphanosteohus spp 0 0 0 0 0 14 0 96 0 0Gnaphalium canescens 0 30 0 0 0 0 0 0 0 0Hypericum spp 0 0 16 0 0 7 0 0 0 0Euphorbia spp 0 0 0 0 0 2 0 0 0 0LeguminoseCebollinCompositae 2Subtotal 13 32 75 0 22 23 294 96 100 89
88
Table 4.2 List of species sampled Fall 1994: Coverage (cm/1200cm) lenght Ranch 1 T1 T2 T3 T4 T5 T6 T7 T8 T9 T10
SPECIESSHRUBSMimosa sppSubtotalPERENNIAL GRASSESBouteloua gracilis 268 295 195 70 70 198 89 170 188 227Aristida adcensionis 54 3 3 0 5 43 38 11 42 20Hilaria belangeri 0 0 0 43 0 0 0 0 0 0Panicum spp 0 0 0 5 0 0 0 0 0 0Hilaria mutica 0 0 0 152 0 0 0 20 0 0Botrhiocloa barbinodis 0 0 0 22 0 0 0 0 0 0Bouteloua curtipendula 6 0 0 0 64 0 24 0 0 12Bouteloua hirsuta 0 0 0 0 128 3 0 0 0 10Lycurus phleoides 0 0 0 0 4 48 29 0 44 13Schizachirium spp.Mulhenbergia spp, 0 0 0 0 14 0 0 0 0 0Bouteloua eriopodaSubtotal 328 298 198 292 285 292 180 201 274 282ANNUAL GRASSESAristida annualChloris annualEragrostis annualBouteloua annualSubtotal 0 0 0 0 0 0 0 0 0 0PERENNIAL FORBSGuillemina sppSida procumbensHoffmansegia spp.Solanum eleagnigolium 0 0 0 0 0 0 0 2 0 0Dalea sppMalva spp 0 0 0 0 0 0 0 0 3 0LeguminoseSubtotal 0 0 0 0 0 0 0 2 3 0ANNUAL FORBSHairy forbHeteroteca sppGrindelia sppCompositae 0 0 0 4 0 0 0 0 0 0Annual Forb 0 0 3 0 0 0 0 0 0 0Argemone mexicana 0 0 2 0 0 0 0 0 0 0CyperaceaTronadorcilloSpharalcea sppCenizaParonichya spp.Aphanosteohus sppGnaphalium canescensHypericum sppEuphorbia sppLeguminose 0 0 0 0 0 0 6 0 5 0CebollinCompositae 2Subtotal 0 0 5 4 0 0 6 0 5 0
89
Table 4.3 List of species sampled Fall 2005: Cover (cm/1200cm) lengthRanch 1 T1 T2 T3 T4 T5 T6 T7 T8 T9 T10
SPECIESSHRUBSMimosa sppSubtotalPERENNIAL GRASSESBouteloua gracilis 198 177 77 3 144 113 0 95 33 202Aristida adcensionis 0 0 0 0 0 4 0 5 0 0Hilaria belangeri 0 0 0 20 0 0 0 0 0 0Panicum spp 0 0 1 0 0 0 0 0 0 0Hilaria muticaBotrhiocloa barbinodisBouteloua curtipendula 0 0 0 0 91 0 0 0 20 0Bouteloua hirsuta 0 0 0 0 15 12 0 12 0 0Lycurus phleoides 0 0 0 0 0 19 0 0 0 0Schizachirium spp.Mulhenbergia spp, 0 0 0 0 13 0 0 0 6 21Bouteloua eriopodaSubtotal 198 177 78 23 263 148 0 112 59 223ANNUAL GRASSESAristida annualChloris annual 0 0 1 3 0 0 0 0 0 0Eragrostis annual 0 0 16 0 0 0 74 0 0 0Bouteloua annualSubtotal 0 0 17 3 0 0 74 0 0 0PERENNIAL FORBSGuillemina sppSida procumbensHoffmansegia spp.Solanum eleagnigolium 0 0 0 0 0 0 0 0 1 0Dalea sppMalva sppLeguminose 0 0 0 0 0 0 5 0 0 0Subtotal 0 0 0 0 0 0 5 0 1 0ANNUAL FORBSHairy forbHeteroteca sppGrindelia sppCompositae 5 0 0 0 0 0 0 7 0 0Annual Forb 0 2 0 3 1 1 0 4 22 0Argemone mexicanaCyperaceaTronadorcilloSpharalcea sppCenizaParonichya spp.Aphanosteohus sppGnaphalium canescensHypericum sppEuphorbia sppLeguminoseCebollinCompositae 2 0 4 0 3 1 3 0 0 3 5Subtotal 5 6 0 6 2 4 0 11 25 5
90
Table 4.4 List of of species sampled Fall1993 :Cover (cm/1200cm) lengthRanch 2 T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 T12 T13 T14 T15 T16 T17 T18SPECIESSHRUBSMimosa spp. 0 0 168 435 335 0 0 0 0 0 0 0 0 0 0 0 0 0Condelia sppSubotal 0 0 168 435 335 0 0 0 0 0 0 0 0 0 0 0 0 0PERENNIAL GRASSESBouteloua gracilis 112 168 213 212 41 90 272 172 220 92 297 248 190 97 288 151 233 112Aristida spp 25 39 22 34 0 14 61 44 50 0 8 12 5 8 25 2 41 23Lycurus phleoides 27 4 8 7 7 65 0 22 1 83 20 28 24 55 0 29 0 29Microchloa kuntii 29 3 0 0 0 0 0 8 4 9 2 0 0 3 0 3 3 9Mulhenbergia spp 0 0 2 0 0 9 0 0 0 0 0 0 0 0 0 12 0 22Elyonurus barbiculmisSchizachirium spp. 0 0 0 11 11 0 0 0 0 0 0 0 0 0 0 58 0 0Bouteloua hirsuta 7 0 0 0 0 73 0 0 0 0 0 0 0 75 0 0 0 0Botriochloa barbinodis 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0Subtotal 200 214 245 264 59 251 333 246 275 184 327 288 219 238 313 255 277 195ANNUAL GRASSESEragrostis annual 0 1 6 0 1 0 0 0 0 0 0 0 0 0 0 0 0 4Bouteloua annualPanicum annualAristida annualChloris annualSubotal 0 1 6 0 1 0 0 0 0 0 0 0 0 0 0 0 0 4PERENNIAL FORBSDalea spp. 5 3 0 0 0 6 0 0 0 0 0 0 0 0 0 13 0 3Drymaria arenarioidesYerbaniz 0 0 5 31 0 0 0 0 0 0 0 0 0 0 0 0 0 0Guillemina sppZinnia sppPerennial Forb 3 3 13 0 0 0 0 1 0 0 5 0 0 0 0 0 0 3Croton spp 0 0 0 0 45 0 0 0 0 0 0 0 0 0 0 0 0 0Subtotal 8 6 18 31 45 6 0 1 0 0 5 0 0 0 0 13 0 6ANNUAL FORBSRed forb 24 0 0 0 14 0 0 0 0 0 0 0 34 0 0 0 0 0Annual ForbHairy forbForb 2Lepidium sppVigueria sppForb 3Little strawberryCyperaceaBig forb 0 0 0 0 0 170 0 0 0 1 0 0 0 0 0 0 0 0Star forb 0 16 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0Gnaphalium canescen 0 0 0 0 2 0 0 0 0 0 0 0 0 0 0 0 0 0Composite 0 0 0 0 10 0 0 1 0 0 0 0 3 0 0 0 0 0Eringium spp. 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0Grape weed 0 0 0 0 0 0 0 0 0 0 0 0 34 0 0 0 0 0Subtotal 24 16 0 0 27 170 0 1 0 1 0 0 71 0 0 0 0 0
91
Table 4.5 List of species sampled fall 1994: Cover (cm/1200cm) lengthRanch 2 T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 T12 T13 T14 T15 T16 T17 T18SPECIESSHRUBSMimosa spp. 0 0 190 458 258 0 0 0 0 0 0 0 0 0 0 0 0 0Condelia sppSubotal 0 0 190 458 258 0 0 0 0 0 0 0 0 0 0 0 0 0PERENNIAL GRASSESBouteloua gracilis 130 202 0 113 16 108 237 191 258 88 165 166 197 143 237 195 210 111Aristida spp 51 46 36 24 0 22 14 7 8 3 31 8 9 17 0 0 40 20Lycurus phleoides 20 24 0 16 7 75 0 28 5 56 29 25 25 57 0 11 4 15Microchloa kuntii 0 0 18 0 8 28 0 0 0 0 0 0 0 0 0 0 0 21Mulhenbergia spp 0 0 0 0 0 22 0 0 0 0 0 0 0 0 0 7 0 23Elyonurus barbiculmis 0 0 0 0 0 0 8 0 7 19 18 3 0 0 0 0 0 4Schizachirium spp. 0 0 0 5 13 0 0 0 0 0 0 24 0 0 0 86 0 0Bouteloua hirsuta 6 0 0 0 0 0 0 0 0 0 0 0 0 25 0 0 0 0Botriochloa barbinodisSubtotal 207 272 54 158 44 255 259 226 278 166 243 226 231 242 237 299 254 194ANNUAL GRASSESEragrostis annualBouteloua annualPanicum annual 0 0 0 0 0 2 0 0 0 0 0 0 0 0 0 0 0 3Aristida annualChloris annualSubotal 0 0 0 0 0 2 0 0 0 0 0 0 0 0 0 0 0 3PERENNIAL FORBSDalea spp. 0 0 14 3 64 0 0 0 0 2 0 0 0 6 0 0 0 1Drymaria arenarioides 4 8 0 0 14 26 0 0 0 0 3 0 0 1 0 0 0 2Yerbaniz 3 0 0 14 0 0 0 0 0 0 0 0 0 0 0 0 0 0Guillemina spp 0 10 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0Zinnia spp 0 0 18 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0Perennial ForbCroton sppSubtotal 7 18 32 17 78 26 0 0 0 2 3 0 0 7 0 0 0 3ANNUAL FORBSRed forb 5 9 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0Annual Forb 3 0 0 1 4 0 0 0 0 0 0 0 0 0 0 0 0 0Hairy forb 4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0Forb 2 5 0 0 0 31 5 0 0 0 0 0 0 0 0 0 0 0 0Lepidium spp 0 6 0 0 0 0 0 16 0 0 0 0 0 0 0 2 0 2Vigueria spp 0 0 0 0 109 0 0 0 0 0 0 0 0 0 0 0 0 0Forb 3 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0Little strawberry 0 0 0 0 0 0 0 0 0 0 0 0 22 0 0 0 0 0Cyperacea 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 0 0Big forb 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 47Star forbGnaphalium canescensCompositeEringium spp.Grape weedSubtotal 17 15 0 1 144 6 0 16 0 0 0 0 22 0 0 4 0 49
92
Table 4.6 List of species sampled Fall 2005:Cover (cm/1200cm) lengthRanch 2 T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 T12 T13 T14 T15 T16 T17 T18SPECIES SHRUBSMimosa spp. 0 0 210 502 298 15 0 0 0 0 0 0 0 0 0 0 0 0Condelia spp 0 0 0 0 0 60 0 0 0 0 0 0 0 0 0 0 0 0Subotal 0 0 210 502 298 75 0 0 0 0 0 0 0 0 0 0 0 0PERENNIAL GRASSESBouteloua gracilis 173 95 111 28 46 71 51 24 231 57 71 73 28 46 81 44 99 48Aristida spp 0 7 3 0 0 31 5 1 0 0 7 3 0 9 12 7 0 7Lycurus phleoides 0 0 0 0 15 2 0 15 0 0 0 0 0 2 0 0 0 0Microchloa kuntii 0 1 0 0 0 1 7 0 1 0 7 0 0 0 0 2 0 21Mulhenbergia 0 0 0 0 0 0 0 0 0 0 12 0 0 0 0 0 0 0Schizachirium spp. 0 0 0 0 9 0 0 0 0 0 0 31 0 0 0 0 0 0Bouteloua hirsuta 0 0 0 0 0 4 0 0 0 0 0 0 0 0 0 0 0 0Subtotal 173 103 114 28 70 109 63 40 232 57 97 107 28 57 93 53 99 76ANNUAL GRASSESEragrostis annual 0 0 0 0 0 0 0 0 2 0 0 3 2 0 0 4 0 3Bouteloua annual 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0Chloris annual 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 2 0 0Aristida annual 0 0 0 0 0 0 0 1 0 0 0 0Subotal 0 0 0 0 0 0 0 1 2 0 0 3 2 2 0 6 0 3PERENNIAL FORBSDalea spp. 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0Subtotal 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0ANNUAL FORBSRed forb 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2Annual Forb 0 5 0 0 0 0 0 0 0 0 0 0 0 1 3 0 0 0Star forb 4 0 0 0 0 0 1 0 0 0 0 0Subotal 5 5 0 0 0 0 1 0 0 0 0 0 0 1 3 0 0 2
93
Table 4.7 List of species sampled Fall 1993: Cover (cm/1200cm) lengthRanch 3 T1 T2 T3 T4 T5 T6 T7 T8 T9SPECIESSHRUBSAcacia angustissima 19 0 0 2 0 0 10 0 3Ephedra sp. 0 0 0 0 0 10 40 0 38Prosopis sp. 0 55 0 172 0 361 0 0 40Mimosa spp. 0 0 0 0 0 0 0 0 0Condelia spp.Subtotal 19 55 0 174 0 371 50 0 81SHRUBS-LIKEMenodora like 0 0 0 63 0 0 0 0 0Xantocephalum sarotrae 15 0 1 0 0 0 0 0 0Subtotal 15 0 1 63 0 0 0 0 0PERENNIAL GRASSESEragrostis lehmanniana 0 0 13 0 0 0 85 44 31Bouteloua gracilis 0 48 0 0 0 0 0 0 27Mulhenbergia porteri 0 0 0 0 0 0 2 3 7Botrichloa barbinodis 0 34 0 0 0 0 0 0 0Setaria macrostachya 0 8 0 4 0 10 0 0 0Digitaria californica 0 0 0 0 7 0 0 0 0Cenchrus incertus 4 1 0 0 0 0 0 0 1Eneapogon desvauxii 2 1 0 0 0 0 0 0 0Panicun obtusum 0 0 0 0 0 0 5 0 0Aristida spp 25 36 71 6 0 10 0 0 0Sporobolus airoidesPanicum halliSubotal 31 128 84 10 7 20 92 47 66ANNUAL GRASSESBouteloua curtipendula (annual)Eragrostis annual 0 0 0 0 9 0 0 0 4Aristida annual 14 10 9 11 42 13 5 12 21Bouteloua annual 3 10 0 4 0 2 0 1 19Panicum annual 0 6 13 18 20 3 0 0 0Chloris annual 1 0 2 1 20 17 0 0 2Mulhenbergia annual 7 0 0 0 0 0 0 0 0Subtotal 25 26 24 34 91 35 5 13 46PERENNIAL FORBSSida procumbens 18 1 0 32 42 0 0 0 0Legume 0 0 1Calcomeca 0 0 0 0 1 0 0 0 0Hoffmansegia spp 29 48 97 23 5 2 0 0 0Forb perennial 0 0 0 2 0 0 38 3 14Zinnia spp 5 0 0 0 56 0 0 0 1Croton potsii 5 0 0 0 0 0 0 0 0Cassia spp.Solanum eleagnifoliumSubtotal 57 49 97 57 104 2 38 3 16ANNUAL FORBSEvolvolus spp 19 32 0 16 0 0 0 0 0Cotton forb 0 0 0 0 0 0 0 0 1Curly forb 11 5 0 0 0 0 0 1 0Amaranths spp 0 0 0 1 6 3 0 0 0Eringium spp. 0 1 1 0 1 0 0 0 0Subtotal 30 38 1 17 7 3 0 1 1
94
Table 4.8 List of species sampled Fall 1994: Cover (cm/1200cm) lengthRanch 3 T1 T2 T3 T4 T5 T6 T7 T8 T9SPECIESSHRUBSAcacia angustissimaEphedra sp. 0 0 0 0 0 0 18 0 30Prosopis sp. 0 40 0 128 0 331 0 0 51Mimosa spp. 0 0 0 0 0 0 0 0 0Condelia spp.Subtotal 0 40 0 128 0 331 18 0 81SHRUBS-LIKEMenodora likeGutierreza sarotraeSubtotal 0 0 0 0 0 0 0 0 0PERENNIAL GRASSESEragrostis lehmanniana 3 0 8 0 0 0 46 29 10Bouteloua gracilis 0 12 0 0 0 0 0 0 30Mulhenbergia porteri 0 0 0Botrichloa barbinodis 0 11 0 0 0 0Setaria macrostachya 0 0 0 50 0 0 0 0 0Digitaria californica 0 0 0 0 2 3 0 0 0Cenchrus incertusEneapogon desvauxiiPanicun obtusum 0 0 0 0 0 0 0 0 0Aristida spp 12 30 19 22 0 11 0 0 0Sporobolus airoides 7 0 0 0 0 0 0 0 0Panicum halliSubotal 22 53 27 72 2 14 46 29 40ANNUAL GRASSESBouteloua curtipendula (annual)Eragrostis annualAristida annual 2 0 0 3 2 0 0 1 12Bouteloua annualPanicum annual 0 0 5 0 0 0 0 0 0Chloris annualMulhenbergia annualSubtotal 2 0 5 3 2 0 0 1 12PERENNIAL FORBSSida procumbens 32 1 0 23 108 0 0 0 0LegumeCalcomecaHoffmansegia spp 1 0 0 3 0 0 3 14 2Forb perennialZinnia spp 2 0 0 0 7 0 0 0 0Croton potsii 16 8 0 0 0 0 0 0 0Cassia spp. 10 0 0 0 0 0 2 0 0Solanum eleagnifolium 0 0 0 0 0 3 0 0 2Subtotal 61 9 0 26 115 3 5 14 4ANNUAL FORBSEvolvolus spp 7 21 0 0 3 4 0 0 0Annual forb 1Composite 2 0 1 2 0 0 0 0 0Subtotal 9 21 1 2 3 4 0 0 0
95
Table 4.9 List of species sampled Fall 2005: Cover (cm/1200cm) lengthRanch 3 T1 T2 T3 T4 T5 T6 T7 T8 T9SPECIESSHRUBSAcacia angustissima 5 0 0 0 0 4 0 0 0Ephedra sp.Prosopis sp. 0 0 0 134 0 472 0 0 30Mimosa spp.Condelia spp.Subtotal 5 0 0 134 0 476 0 0 30SHRUBS-LIKEMenodora likeXantocephalum sarotraeSubtotal 0 0 0 0 0 0 0 0 0PERENNIAL GRASSESEragrostis lehmanniana 61 102 49 4 0 6 64 70 92Bouteloua gracilis 0 10 38 0 0 0 0 0 30Mulhenbergia porteriBotrichloa barbinodisSetaria macrostachyaDigitaria californica 0 0 0 25 2 1 0 0 0Cenchrus incertusEneapogon desvauxii 0 2 0 0 0 0 0 0 0Panicun obtusumAristida spp 12 9 1 18 8 0 9 0 0Sporobolus airoidesPanicum halliSubotal 73 123 88 47 10 7 73 70 122ANNUAL GRASSESBouteloua curtipendula (annual) 0 0 0 0 0 1 0 0 0Eragrostis annual 0 0 0 0 5 7 1 0 0Aristida annualBouteloua annual 0 0 0 0 4 0 0 0 0Panicum annualChloris annualMulhenbergia annualSubtotal 0.0 0.0 0.0 0.0 9.0 8.0 1.0 0.0 0.0PERENNIAL FORBSSida procumbens 1 0 0 0 0 0 0 0 0LegumeCalcomecaHoffmansegia spp 0.0 0.0 0.0 0.0 0 0 0 3 0Forb perennialZinnia sppCroton potsiiCassisa spSolanum eleagnifolium 0 0 0 2 0 0 0 0 0Subtotal 1 0 0 2 0 0 0 0 0ANNUAL FORBSEvolvolus spp 0 1 0 0 0 2 0 0 0Annual forb 1 1 0 0 0 1 0 0 0 0CompositeCotton forbSubtotal 1 1 0 0 1 2 0 0 0
96
Table 4.10 List of species sampled Fall 1993: Cover (cm/1200cm) lengthRanch 4 T1 T2 T4 T5 T6 T7 T8 T9 T10SPECIESSHRUBSParthenium incanum 0 0 21 120 0 70 0 79 0Ephedra sp.Prosopis sp. 0 0 0 0 290 174 0 187 0Mimosa spp 30 0 0 0 0 0 4 0 21Flourencia cernua 0 0 215 49 0 0 0 0 0Atriplex sppSubtotal 30 0 236 169 290 244 4 266 21.0SHRUBS-LIKEXantocephalum sarotrae 417 147 49 166 155 138 333 157 261Agave sppSubtotal 417 147 49 166 155 138 333 157 261PERENNIAL GRASSESLycurus phleoides 0 0 0 0 6 0 0 0 0Bouteloua gracilis 0 20 0 0 2 0 0 0 0Bouteloua eriopoda 0 0 0 0 7 0 0 0 0Botrichloa barbinodis 0 0 0 0 0 0 0 0 3Setaria macrostachya 0 0 8 0 6 11 4 14 7Digitaria californica 0 19 17 0 4 0 0 12 21Erioneuron pulchellum 0 0 0 3 0 6 0 0 0Eneapogon desvauxii 1 8 0 0 2 0 3 0 0Aristida adscencionis 7 6 1 0 10 1 2 3 2Aristida spp 5 5 9 0 0 2 0 0 12Subotal 13 58 35 3 37 20 9 29 45 ANNUAL GRASSESEragrostis annual 10 0 0 0 6 1 5 3 2Aristida annualBouteloua barbata 1 3 0 0 1 1 1 3 3Panicum annual 7 4 0 0 3 2 1 0 1Chloris annual 0 0 0 0 0 0 0 0 3Bouteloua aristirioides 0 0 0 0 0 0 18 5 3Subtotal 18 7 0 0 10 4 25 11 12PERENNIAL FORBSSida procumbens 15 3 9 6 4 0 8 0 0Legume 6 0 0 0 0 0 0 0 0Solanum eleagnifoliumHoffmansegia spp 0 1 0 0 0 0 0 0 0Zinnia spp 0 0 0 0 0 16 5 0 0Legume2 0 0 0 4 0 0Croton potsii 0 0 0Dichondria argentea 0 0 0 0 10 0 0 0 0Guillemina sppLegume 3 0 0 0 0 0 150 0 0 99Legume 4 0 0 0 0 0 0 6 0 0Cassia sppSubtotal 21 4 9 10 14 166 19 0 99ANNUAL FORBSEvolvolus sppAnnual forb 1Ddysodia spp 0 0 0 6 0 0 0 2 0Subtotal 0 0 0 6 0 0 0 2 0
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Table 4.11 List of species sampled Fall 1994: Cover (cm/1200cm) lengthRanch 4 T1 T2 T3 T4 T5 T6 T7 T8 T9SPECIESSHRUBSParthenium incanum 0 0 17 119 0 60 0 84 0Ephedra sp.Prosopis sp. 0 0 0 0 320 127 0 393 17Mimosa sppFlourencia cernua 0 0 121 76 0 0 0 0 0Atriplex spp 0 0 0 0 0 5 0 0 0Subtotal 0 0 138 195 320 192 0 477 17SHRUBS-LIKEXantocephalum sarotrae 309 59 5 116 0 81 214 64 0Agave sppSubtotal 309 59 5 116 0 81 214 64 0PERENNIAL GRASSESLycurus phleoidesBouteloua gracilis 0 19 0 0 11 0 0 0 0Bouteloua eriopoda 0 0 0 0 6 0 0 0 0Botrichloa barbinodisSetaria macrostachya 0 0 0 0 0 4 0 6 0Digitaria californica 0 0 5 0 5 4 0 3 4Erioneuron pulchellumEneapogon desvauxiiAristida adscencionisAristida spp 0 0 5 0 1 0 0 0 0Subotal 0 19 10 0 23 8 0 9 4 ANNUAL GRASSESEragrostis annualAristida annualBouteloua barbataPanicum annualChloris annualBouteloua aristirioidesSubtotal 0 0 0 0 0 0 0 0 0PERENNIAL FORBSSida procumbens 5 2 0 0 0 0 0 0 0Legume 0Solanum eleagnifoliumHoffmansegia sppZinnia spp 0 0 0 0 4 0 0 0 0Legume2Croton potsii 0 0 0 0 0 3 0 0 0Dichondria argentea 0 0 0 0 2 0 0 0 0Guillemina sppLegume 3Legume 4Cassia spp 0 3 0 0 0 0 0 0 0Subtotal 5 5 0 0 6 3 0 0 0ANNUAL FORBSEvolvolus sppAnnual forb 1Ddysodia sppSubtotal 0 0 0 0 0 0 0 0 0
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Table 4.12 List of species sampled Fall 2005: Cover (cm/1200cm) lengthRanch 4 T1 T2 T3 T4 T5 T6 T7 T8 T9SPECIESSHRUBSParthenium incanumEphedra sp. 0 100 0 0 0 0 0 0 0Prosopis sp. 0 0 182 0 87 0 200 0 217Mimosa sppFlourencia cernua 0 0 172 314 0 0 0 0 0Atriplex sppSubtotal 0 100 354 314 87 0 200 0 217SHRUBS-LIKEXantocephalum sarotrae 54 69 0 0 0 9 19 55 75Agave spp 0 0 0 0 0 0 0 0 32Subtotal 54 69 0 0 0 9 19 55 107PERENNIAL GRASSESLycurus phleoidesBouteloua gracilis 0 0 0 0 2 0 0 0 0Bouteloua eriopoda 0 0 0 0 7 0 0 0 0Botrichloa barbinodisSetaria macrostachya 0 0 0 0 0 0 0 0 4Digitaria californicaErioneuron pulchellumEneapogon desvauxiiAristida adscencionisAristida spp 0 0 0 4 0 0 0 0 0Subotal 0 0 0 4 9 0 0 0 4 ANNUAL GRASSESEragrostis annualAristida annual 1 0 0 0 0 0 0 0 4Subtotal 1 0 0 0 0 0 0 0 4PERENNIAL FORBSSida procumbensLegumeSolanum eleagnifolium 0 0 0 0 0 0 1 1 0Hoffmansegia spp 0 1 0 0 0 0 0 1 0Zinnia sppLegume2Croton potsiiDichondria argentea 0 49 0 0 0 0 0 0 0Guillemina spp 4 0 0 0 0 0 0 0 0Legume 3Legume 4Cassia spp 0 9 0 0 2 0 0 0 4Subtotal 4 59 0 0 2 0 1 2 4ANNUAL FORBSEvolvolus spp 0 3 0 0 0 0 0 0 0Annual forb 1 1 1 0 0 0 0 0 0 0Ddysodia sppVigueria spp 0 0 0 0 0 79 0 0 0Red forb 0 0 0 0 5 2 0 0 0Big forb 2 1 0 0 0 0 0 0 0Salsola spp. 0 0 0 0 0 1 0 0 0Subtotal 3 5 0 0 5 82 0 0 0
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Table 4.13 Ranch 1 -List of species sampled : Density (plants/m2) SPECIES 1993 fall 1994 Fall 2005 FallPERENNIAL GRASSESBouteloua gracilis 67.7 94.7 32.1Aristida spp 12.3 0.4Bouteloua curtipendula 1.0 3.7 0.8Lycurus phleoides 1.3 4.0 0.2Botriochloa barbinodis 0.3 0.7 0.2Bouteloua hirsuta 2.0 3.0 1.1Hilaria mutica 4.0 3.3 0.4Mulhenbergia spp 0.7Hilaria belangerii 1.7Scleropogon brevifolius 0.4ANNUAL GRASSESAristida annual 11.3Panicum annual 1.7 3.3 0.8Chloris annual 0.3Eragrostis annual 0.3 0.4Bouteloua annual 4.2PERENNIAL FORBSDalea spp 1.0Hoffmansegia spp 0.2Legume 0.7 0.3ANNUAL FORBSComposite 6.9Grindelia spp 0.3Argemone mexicana 0.3Heteroteca spp 11.7Tronadoycillo 0.7Composite 2 20.0 3.1Hierba wide leaf 0.4Grey forb 0.2Forb annual 1.3Woody forb 0.4SHRUBSMimosa biuncifera 1.0
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Table 4.14 Ranch 2 -List of species sampled : Density (plants/m2)SPECIES Fall 1993 Fall 1994 Fall 1995PERENNIAL GRASSESBouteloua hirsuta 5 1.0Bouteloua gracilis 31 78.3 34.67Elyonurus barbiculmis 1Lycurus phleoides 6.3 10.3 5.11Microchloa kunthii 26.3 16.0 0.67Aristida spp 0.7 10.0 4.44Mulhenbergia spp 1.0 0.7Schyzachirium cirratus 0.3 0.3Eneapoon desvauxii 0.3 0.3ANNUAL GRASSESEragrostis annual 2.7 2.00Panicum annual 0.3Chloris annual 0.22Aristida annual 1.0 0.22PERENNIAL FORBSDalea spp 1.0Forb perenne 3.7Dalea sp 2 0.7Gnaphalium spp 0.7Legume 1 0.3 0.46Zinnia spp 0.3Croton spp 1.3 3.7Yerbanis 0.3ANNUAL FORBSStevia serrata 0.7Forb wide leaf 1.3Forb 6.7 2.01Composite 0.7 2.7Star forb 0.3Drymaria arenarioides 0.3Haiy forb 8.3 0.7 0.07Strawberry forb 0.3forbannual 2 0.23Red forb 0.23SRHUBSMimosa spp 8.3 0.3 0.07
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Table 4.15 Ranch 3 -List of species sampled: Density (plants/m2)SPECIES 1993 FALL 1994 FALL 2005 FALLPERENNIAL GRASSESBouteloua gracilis 2 0.7 0.7Eragrostis lehmanniana 24.7 1.0 51.8Aristida spp 4.3 9 14.7Setaria macrostachya 0.3 1.6Panicum obtusum 0.3Mulhenbergia porteri 0.7Digitaria californica 0.3 0.3 0.4Sporobolus airoides 0.0 0.3Botriochloa barbinodis 0.2ANNUAL GRASSESPanicum annual 13 1 0.2Aristida annual 48.7 9.7Bouteloua annual 8.7 1.8Cencrus incertus 0.3Eneapogon desvauxii 0.3 0.2Eragristis annual 1.0 2.0PERENNIAL FORBSZinnia spp 0.7 0.7Croton spp 2.0 2.0 0.5Cassia spp 1.0 0.7Legume 6.7Hoffmansegia spp 34.0 1.0Sida procubens 16.7 7.7 0.4Soalnum eleagnifolium 0.2ANNUAL FORBSEuphorbia spp 37.7Enredadera 2.0Forb 0.3 0.3 1.1Evolvolus spp 0.7 0.3 0.4Amaranthus spp 2.7Eringium app 0.3Calcomeca 0.3Forb 0.3Drymaria arenarioidesVerbena sppEysenhardtia sppRed forbComposite 0.3Little onion 0.4SHRUBS plants/ha plants/ha plants/haMimosa biuncifera 0.3Condalia ericoidesEphedra trifurca 350.7Prosopis glandulosa 511.3 78.6Acacia gregii 37.7 39.3Legume shrub 0.03
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Table 4.16 Ranch 4-List of species sampled: Density (plants/m2)SPECIES 1993 FALL 1994 FALL 2005 FALLPERRENNIAL GRASSESAristida adcencionis 17.3Eneapogon desvauxii 2.3Digitaria californica 0.2 1.67Bouteloua gracilis 0.7 0.67Aristida spp 1.7 0.67Chloris virgata 0.4Setaria macrostachya 2.3Erioneuron pulchellum 1.1Botriochloa barbinodis 0.7Bouteloua eropoda 0.0 0.67 0.2ANNUAL GRASSESPanicum annual 20.2 0.2Eragostis annual. 23.8 2.2Chloris annual 4.4Bouteloua barbata 3.9 1.2Bouteloua aristirioides 27.7Aristida annual 1.00 2.1PERENNIAL FORBSCassia spp 0.67 1.5Solanum eleagniflium 0.2 0.2Dichondra argentea 0.7 0.4Legumes 2.2Legume 2 14.0Dysodia spp 0.3Calcomeca 0.3Croton potsii 0.7 0.33 0.9Guillemina densa 3.3Hoffmansegia spp 0.3 0.9Zinnia spp 0.7Sida procumbens 15.1 0.67Euphorbia spp 0.2ANNUAL FORBSForb 0.3 0.9Hybiscus spp 0.3Evolvolus spp 0.4 Ipomoea spp 0.2White flower forb 3.3Red forb 0.9Vigueria spp 0.2Tall forb 0.7SHRUBS SSHRUBS-LIKE plants/ha plants/ha plants/haEphedra spp 333 156 39Prosopis glandulosa 767 1334 416Yucca spp 33Flourencia cernua 333 511 472Parthenium incanum 367 747 157Atriplex canescens 33 118 39Koeberlina spinulosa 267Mimosa spp 1367 38Budleja scordioides 133Condalia ericoides 393Xantocephalum sarotrae 14500 11233 815Brickelia spinulosa
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Forage Production Samples Table 4.17 Forage Production Ranch 1 Forage Production (Kg DM/Ha)RANCH 1 FALL 1993 FALL1994 FALL2005Samples Pasture Pasture Pasture
4 7 8 4 7 8 4 7 8Sample 1 2220 720 1060 260 100 40 880 1075 40Sample 2 2640 460 400 240 60 120 270 290 222Sample 3 1770 460 1220 460 70 440 270 425 200Sample 4 1500 740 720 540 320 270 248 262 540Sample 5 730 1100 1340 700 280 270 185 340 970Sample 6 848 660 1420 440 220 640 248 700 335
1100 130 452Mean 1618 690 1037 440 175 272 394 515 350 Table 4.18 Forage Production Ranch 2 Forage Production (Kg DM/Ha)RANCH 2 FALL 1993 FALL1994 FALL2005Samples Pasture Pasture Pasture
1 2 3 1 2 3 1 2 3Sample 1 1080 290 1920 440 0 820 280 345 225Sample 2 1080 506 1740 592 520 220 675 565 590Sample 3 880 1730 1160 200 240 400 245 1092 608Sample 4 1380 880 906 360 360 500 225 542 325Sample 5 340 1144 1300 230 360 580 298 693 682Sample 6 660 453 1740 2080 580 1020 400 562 425Sample 7 1173 460Mean 903 882 1461 650 360 673 353 633 475
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Forage Production Samples Table 4.19 Forage Production Ranch 3 Forage Production (Kg DM/Ha)RANCH 3 FALL 1993 FALL1994 FALL2005Samples Pasture Pasture Pasture
2 12 16 2 12 16 2 12 16Sample 1 560 700 480 200 820 360 630 692 360Sample 2 920 1840 1080 320 310 440 685 431 1041Sample 3 700 2280 1320 120 280 60 1630 1305 1939Sample 4 660 740 1760 60 240 320 903 215 1315Sample 5 480 1140 540 40 520 60 1010 970 507Sample 6 460 1840 1233 100 0 885 653 435
Mean 630 1252 1233 140 434 206 932 957 711 Table 4.20 Forage Production Ranch 4 Forage Production (Kg DM/Ha)RANCH 4 FALL 1993 FALL1994 FALL2005Samples Pasture Pasture Pasture
1 2 8 1 2 8 1 2 8Sample 1 340 940 220 0 0 0 41 35 472Sample 2 600 300 360 0 0 0 60 203 95Sample 3 1780 820 160 0 0 0 60 119 121Sample 4 740 540 0 0 0 0 80 61 62Sample 5 1640 240 500 0 0 0 85 72 30Sample 6 500 280 160 0 0 0 30 0 5
Mean 933 520 206 0 0 0 59 81 130
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APPENDIX B
STATISTICAL ANALYSIS OUTPUTS
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BASAL COVER NORMALITY TEST ----------------------- trt=1 ----------------------------- The UNIVARIATE Procedure Variable: Experimental errors Test --Statistic--- -----p Value------ Shapiro-Wilk W 0.971806 Pr < W 0.0619 Kolmogorov-Smirnov D 0.092634 Pr > D 0.0752 Cramer-von Mises W-Sq 0.12934 Pr > W-Sq 0.0453 Anderson-Darling A-Sq 0.758379 Pr > A-Sq 0.0472 Quantiles (Definition 5) Quantile Estimate 95% 89.6597 90% 75.5065 75% Q3 33.2668 50% Median 11.6851 25% Q1 -35.2077 10% -67.4935 5% -110.3403 1% -192.4935 0% Min -192.4935 Extreme Observations ------Lowest----- ------Highest----- Value Obs Value Obs -192.493 15 89.6597 66 -170.315 43 108.0882 9 -160.315 41 129.6597 61 -133.340 63 139.0882 10 -110.340 60 146.0780 75
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------------------ trt=1 ----------------------------- The UNIVARIATE Procedure Variable: ee Stem Leaf # Boxplot 14 6 1 0 12 09 2 0 10 8 1 | 8 2570 4 | 6 24566 5 | 4 014558 6 | 2 011333468890067 15 +-----+ 0 471222335779 12 *--+--* -0 630765410 9 | | -2 732299310 9 +-----+ -4 88665186 8 | -6 47421 5 | -8 2 1 | -10 00 2 | -12 3 1 | -14 -16 00 2 0 -18 2 1 0 ----+----+----+----+ Multiply Stem.Leaf by 10**+1 Normal Probability Plot 150+ ++*+ | *+* | +*+ | **** | **** +*** | ****** | ****+ | **** | **** | **** | ***+ | **+ | ++* | +++ * |++++ | * * -190+* +----+----+----+----+----+----+----+----+----+----+ -2 -1 0 +1 +2
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-------------------- trt=2 ----------------------------- The UNIVARIATE Procedure Variable: ee Tests for Normality Test --Statistic--- -----p Value------ Shapiro-Wilk W 0.967636 Pr < W 0.1515 Kolmogorov-Smirnov D 0.095054 Pr > D >0.1500 Cramer-von Mises W-Sq 0.071719 Pr > W-Sq >0.2500 Anderson-Darling A-Sq 0.536992 Pr > A-Sq 0.1677 Quantiles (Definition 5) Quantile Estimate 75% Q3 14.29085 50% Median 1.88889 25% Q1 -11.70915 10% -43.15359 5% -51.70915 1% -57.48693 0% Min -57.48693 Extreme Observations ------Lowest----- -----Highest----- Value Obs Value Obs -57.4869 89 29.2908 123 -54.4869 88 40.9314 95 -51.7092 126 63.2908 129 -48.7092 125 63.5131 86 -44.4869 90 64.2908 122
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Variable: ee Stem Leaf # Boxplot 6 344 3 0 5 5 4 4 1 1 | 3 | 3 | 2 57889 5 | 2 001 3 | 1 8 1 | 1 0112244 7 +-----+ 0 689 3 | | 0 22223 5 *--+--* -0 42 2 | | -0 8775 4 | | -1 42111111 8 +-----+ -1 876 3 | -2 3 1 | -2 | -3 31 2 | -3 | -4 43 2 | -4 9 1 | -5 42 2 0 -5 7 1 0 ----+----+----+----+ Multiply Stem.Leaf by 10**+1
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Normal Probability Plot 62.5+ * * +* | ++ | + | ++ | *+ | ++ | ++ | ***** | +* | +*** | *** | ** 2.5+ *** | * | ** | **** | **++ | *++ + | ** | ++ | ++** | ++ * | * * -57.5+ * ++ +----+----+----+----+----+----+----+----+----+----+ -2 -1 0 +1 +2
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Schematic Plots | 150 + 0 | 0 | | | | 100 + | | | | | | | 0 50 + | | +-----+ | | | | | | *-----* +-----+ 0 + | + | *--+--* | | | +-----+ | | | | +-----+ | -50 + | 0 | 0 | | | | -100 + | | | | | | | -150 + | 0 | 0 | 0 -200 + ------------+-----------+----------- trt 1 2
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ANALYSIS OF VARIANCE WITH REPEATED MEASUREMENTS OF PERENNIAL GRASSES BASAL COVER INITIAL SURVEY USED AS COVARIATE
Basal Cover The Mixed Procedure Model Information Data Set WORK.FORAGE Dependent Variable y Covariance Structure Compound Symmetry Subject Effect rep(trt*ranch) Estimation Method REML Residual Variance Method Profile Fixed Effects SE Method Model-Based Degrees of Freedom Method Between-Within Class Level Information Class Levels Values trt 2 1 2 ranch 4 1 2 3 4 year 2 2 3 rep 18 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Dimensions Covariance Parameters 2 Columns in X 14 Columns in Z 0 Subjects 46 Max Obs Per Subject 2 Number of Observations Number of Observations Read 92 Number of Observations Used 92 Number of Observations Not Used 0 Iteration History Iteration Evaluations -2 Res Log Like Criterion
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0 1 504.02032189 1 1 502.83193946 0.00000000 Convergence criteria met. The Mixed Procedure Covariance Parameter Estimates Cov Parm Subject Estimate CS rep(trt*ranch) 2.7461 Residual 13.8130 Fit Statistics -2 Res Log Likelihood 502.8 AIC (smaller is better) 506.8 AICC (smaller is better) 507.0 BIC (smaller is better) 510.5 Null Model Likelihood Ratio Test DF Chi-Square Pr > ChiSq 1 1.19 0.2757 Type 3 Tests of Fixed Effects Num Den Effect DF DF F Value Pr > F trt 1 41 3.75 0.0599 ranch(trt) 2 41 2.47 0.0967 year 1 44 36.42 <.0001 trt*year 1 44 55.58 <.0001 ini 1 41 14.57 0.0004 Least Squares Means Standard Effect trt year Estimate Error DF t Value Pr > |t| trt 1 11.2194 1.0453 41 10.73 <.0001 trt 2 6.8747 1.3928 41 4.94 <.0001 year 2 11.4428 0.6434 44 17.78 <.0001 year 3 6.6513 0.6434 44 10.34 <.0001 trt*year 1 2 16.5747 1.1573 44 14.32 <.0001
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trt*year 1 3 5.8640 1.1573 44 5.07 <.0001 trt*year 2 2 6.3108 1.5243 44 4.14 0.0002 trt*year 2 3 7.4386 1.5243 44 4.88 <.0001 Differences of Least Squares Means Standard Effect trt year _trt _year Estimate Error DF t Value Pr > |t| trt 1 2 4.3447 2.2448 41 1.94 0.0599 year 2 3 4.7915 0.7939 44 6.03 <.0001 trt*year 1 2 1 3 10.7107 0.9933 44 10.78 <.0001 trt*year 1 2 2 2 10.2639 2.3811 44 4.31 <.0001 trt*year 1 2 2 3 9.1362 2.3811 44 3.84 0.0004 trt*year 1 3 2 2 -0.4468 2.3811 44 -0.19 0.8520 trt*year 1 3 2 3 -1.5746 2.3811 44 -0.66 0.5119 trt*year 2 2 2 3 -1.1278 1.2389 44 -0.91 0.3676
ANALYSIS OF VARIANCE WITH REPEATED MEASUREMENTS OF FORAGE PRODUCTION
Forage Production The Mixed Procedure Model Information Data Set WORK.FORAGE Dependent Variable y Covariance Structure Compound Symmetry Subject Effect rep(trt*ranch) Estimation Method REML Residual Variance Method Profile Fixed Effects SE Method Model-Based Degrees of Freedom Method Between-Within Class Level Information Class Levels Values trt 2 1 2 ranch 4 1 2 3 4 year 2 1 2
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rep 3 1 2 3 Dimensions Covariance Parameters 2 Columns in X 14 Columns in Z 0 Subjects 12 Max Obs Per Subject 3 Number of Observations Number of Observations Read 24 Number of Observations Used 24 Number of Observations Not Used 0 Iteration History Iteration Evaluations -2 Res Log Like Criterion 0 1 246.74455224 1 2 246.47819212 0.00007372 2 1 246.46970588 0.00000096 3 1 246.46960213 0.00000000 Convergence criteria met. Covariance Parameter Estimates Cov Parm Subject Estimate CS rep(trt*ranch) 8219.86 Residual 21843 Fit Statistics -2 Res Log Likelihood 246.5 AIC (smaller is better) 250.5 AICC (smaller is better) 251.3 BIC (smaller is better) 251.4 Null Model Likelihood Ratio Test DF Chi-Square Pr > ChiSq 1 0.27 0.6000
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Type 3 Tests of Fixed Effects Num Den Effect DF DF F Value Pr > F trt 1 8 13.42 0.0064 ranch(trt) 2 8 13.64 0.0026 year 1 9 1.30 0.2834 trt*year 1 9 23.02 0.0010 ini 1 9 3.67 0.0875 Least Squares Means Standard Effect trt year Estimate Error DF t Value Pr > |t| trt 1 634.33 56.4819 8 11.23 <.0001 trt 2 339.96 57.1446 8 5.95 0.0003 year 1 521.92 50.0521 9 10.43 <.0001 year 2 452.37 50.7988 9 8.91 <.0001 trt*year 1 1 815.33 70.7844 9 11.52 <.0001 trt*year 1 2 453.33 70.7844 9 6.40 0.0001 trt*year 2 1 228.50 70.7844 9 3.23 0.0104 trt*year 2 2 451.41 72.8811 9 6.19 0.0002 Differences of Least Squares Means Standard Effect trt year _trt _year Estimate Error DF t Value Pr > |t| trt 1 2 294.38 80.3474 8 3.66 0.0064 year 1 2 69.5435 60.9570 9 1.14 0.2834 trt*year 1 1 1 2 362.00 85.3282 9 4.24 0.0022 trt*year 1 1 2 1 586.83 100.10 9 5.86 0.0002 trt*year 1 1 2 2 363.92 101.60 9 3.58 0.0059 trt*year 1 2 2 1 224.83 100.10 9 2.25 0.0513 trt*year 1 2 2 2 1.9204 101.60 9 0.02 0.9853 trt*year 2 1 2 2 -222.91 87.0754 9 -2.56 0.0307
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ANALYSIS OF PRINCIPAL COMPONENTS 1993 Correlation Matrix Shrubs Nonsh PGrass AGrass PForbs Aforbs shrubs 1.0000 0.1382 -.4335 0.0931 0.2132 -.2001 Nonsh 0.1382 1.0000 -.5477 0.1386 0.2298 -.1982 PGrass -.4335 -.5477 1.0000 -.5642 -.4814 0.2688 AGrass 0.0931 0.1386 -.5642 1.0000 0.4652 -.1669 PForbs 0.2132 0.2298 -.4814 0.4652 1.0000 -.1555 Aforbs -.2001 -.1982 0.2688 -.1669 -.1555 1.0000 Eigenvalues of the Correlation Matrix Eigenvalue Difference Proportion Cumulative 1 2.52957310 1.51571697 0.4216 0.4216 2 1.01385614 0.14925262 0.1690 0.5906 3 0.86460351 0.03800371 0.1441 0.7347 4 0.82659980 0.27614764 0.1378 0.8724 5 0.55045216 0.33553688 0.0917 0.9642 6 0.21491528 0.0358 1.0000 Eigenvectors Prin1 Prin2 Prin3 Prin4 Prin5 Prin6 shrubs 0.315964 -.489807 0.578963 0.483857 -.063423 0.294817 Nonsh 0.370130 -.287243 -.770198 0.156433 0.071153 0.397185 PGrass -.563830 0.013842 0.104266 -.166062 0.273844 0.753967 AGrass 0.423224 0.550583 0.130670 -.206832 -.520875 0.431944 PForbs 0.434133 0.386854 0.149831 0.026072 0.799119 0.012328 Aforbs -.278707 0.473912 -.145605 0.818764 -.077600 0.011532
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ANALYSIS OF PINCIPAL COMPONENTS 2005 Correlation Matrix shrubs suffrut. PGrass AGrass PForbs Aforbs shrubs 1.0000 0.1076 -.3642 -.0640 0.0390 -.1349 Suffru. .1076 1.0000 -.3599 -.0414 0.5125 0.0011 PGrass -.3642 -.3599 1.0000 -.2113 -.2153 -.1174 AGrass -.0640 -.0414 -.2113 1.0000 0.0331 -.0767 PForbs 0.0390 0.5125 -.2153 0.0331 1.0000 0.0054 Aforbs -.1349 0.0011 -.1174 -.0767 0.0054 1.0000 Eigenvalues of the Correlation Matrix Eigenvalue Difference Proportion Cumulative 1 1.84295398 0.68205002 0.3072 0.3072 2 1.16090396 0.09614295 0.1935 0.5006 3 1.06476101 0.04035716 0.1775 0.6781 4 1.02440385 0.50461277 0.1707 0.8488 5 0.51979108 0.13260496 0.0866 0.9355 6 0.38718612 0.0645 1.0000 Eigenvectors Prin1 Prin2 Prin3 Prin4 Prin5 Prin6 Shrubs 0.321016 -.587929 -.427109 -.278738 0.409518 0.351379 Suffrut.0.576942 0.296304 -.108566 0.181930 -.485355 0.546706 PGrass -.543011 0.273396 -.201455 0.357891 0.353979 0.580020 AGrass 0.101647 -.349832 0.832876 0.215706 0.160401 0.318347 PForbs 0.508461 0.379124 0.001197 0.337611 0.629868 -.294986 Aforbs 0.019010 0.475059 0.267438 -.774991 0.221276 0.229916
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APPENDIX C
GLOSSARY
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Glossary Animal Unit (AU). One mature, non lactating bovine weighing about 1000 lb (454
kg) or its equivalent in other classes or kind of ungulate herbivores based in animal demand or quantitative forage dry matter intake; assumes a standard daily forage intake of 26 lb (12 kg) on an oven-dry basis.
Brush. Shrubs or small tree considered undesirable from the stand point of
planned use of the area, an undesirable noxious woody plant. Carrying capacity. All nutrient resources available on a given land area, including
not only pasturage but also harvested forage and other feedstuffs used to complement the grazing resources, thereby providing a means of summarizing a total ranch capacity or that allotted to a specific animal enterprise (best usage)
Cell (or cell grazing). A grazing arrangement comprised of numerous subunits
(i.e. paddocks), usually in a rotational grazing system, with a common central component provided with drinking water, animal handling facilities, and access between units.
Climax. The final or stable biotic community in a successional series; it is self
perpetuating and in equilibrium with the physical habitat. Continuous grazing. Allowing animals unrestricted and uninterrupted access to a
grazing land unit for all or most of the grazing season; includes yearlong, growing season, dormant season continuous grazing. Synonym. Continuous stocking.
Deferment. Nongrazing from the breaking of plant dormancy until after seed set
or equivalent stage of vegetative reproduction, accomplished either by delaying the beginning of spring grazing or discontinuing winter grazing early.
Deferred–rotation grazing. A multi unit, one herd grazing system in which
deferment is systematically rotated among the respective grazing land units.
Defoliation. The removal of plant leaves by grazing or browsing, cutting, chemical
defoliant, or natural phenomena such as hail, fire or frost. Dominant. Plant species or species group which has considerable influence or
control over associated plant species.
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Drought. Prolonged dry weather, generally when precipitation is less than ¾ of average for a considerable period of time; period during which plants suffer from lack of water.
Forage mass. The total dry weight of forage per unit area of land, usually above
ground level and at a defined reference level. Forage mass may include forage not accessible to a particular kind of grazing animal.
Forage production. The weight of forage that is produced within a designated
period of time on a given area; expressed as green, air-dry, oven-dry weight and may be qualified as annual, current year’s, or seasonal forage production.
Grazing. The act of eating forage from the standing crop comprised (1) foraging,
the search for forage; (2) defoliation, the removal of forage; and (3) ingesting the forage. Synonym. Herbivory.
Grazing Capacity. (a) The optimal stocking rate that will achieve the target level
of animal performance or other specific objective, while preventing deterioration of the ecosystem. Must consider both management objectives and management intensity to be accurate. (b) Total number of AUM’s produced and available or grazing per acre or from a specific grazing land unit, a grazing allotment, the total ranch, or other specified land area.
Grazing intensity. A general term expressing (1) the amount of animal demand
placed upon the standing crop of forage mass, and (2) the resulting level of plant defoliation made during grazing.
Grazing period. The length of time that grazing animals occupy a grazing area
without interruption. Heavy grazing. A comparative term which indicate that the stocking rate on an
area is relatively greater than that on other similar areas; sometimes erroneously used to mean overgrazing.
Herbaceous. Vegetative growth with little or not woody component; non-woody
component such as graminoids and forbs. Light grazing. A comparative term which indicates that stocking rate on an area is
relatively less than that on other similar areas; sometimes erroneously used to mean undergrazing.
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Native species. A species which is part of the original flora or fauna of the area in question
Nongrazing. The restriction or absence of grazing use on an area for a period of
time , ranging from a short period of a few days to a year or more. Overgrazing. Continued heavy grazing which exceeds the recovery capacity of
the forage plants and creates deterioration of the grazing plants. Overstocking. Placing so many animals on a grazing unit that overuse will result
If continued unchanged to the end of the planned grazing period. Paddock. (a) One of the multiple grazing units or subunits included in a rotation
grazing series. Patch. (a) A specific aggregation of forage plants. (b) A spatial foraging levels
defined as a cluster of feeding station separated from other potential feeding stations ; requires a break in a foraging for transit from one patch to another patch.
Range condition. Historically, the term has usually been defined in of two ways;
(a) a generic term relating to present status of a unit of range in terms of specific values or potentials, or (b) the present state of vegetation of a range site in relation to the climax (natural potential) plant community for that site.
Rest period. The length of time that a specific land area is allowed to rest (remain
ungrazed). Rotation grazing. A generic term applied to moving grazing animals recurrently
from one grazing unit (paddock) to another grazing unit in the same series (group); one of the basic components of grazing systems.
Short-duration to grazing. A rotational grazing system employing high stocking
density. One herd, commonly 5 to 12 paddocks, grazing periods of 3 to 10 days (less commonly 1 to 15), and two to several grazing cycles per year; the common “rotation grazing” of improved pastures but has also been applied to range.
Stocking density. Animal demand per unit area of land at any instant of time (i.e.,
AU/acre or AU/section of land); an animal/area ratio describing the relationship between the number of animals and the corresponding area of land at any instant of time.
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Stocking intensity. A general term referring to animal demand-grazing land area relationship.
Stocking rate. Animal demand (for forage) per unit area of land over a period of
time (i.e., AUM/acre or AUD/acre or their reciprocals); an animal/area ratio describing the relationship between number of animals and the corresponding land area being grazed over a specified period of time.
Trampling. Treading under foot. The damage to plants or soil resulting from the
hoof impact of grazing animals. Ungrazed. The status of grazing land and associated vegetation that is not
grazed by ungulates herbivores. Ungulate. A hoofed animal, including animals, but also horses, tapirs, elephants,
rhinoceroses, and swine. Utilization. The proportion of current year’s forage production (biomass) that is
consumed and/or destroyed by grazing animals; may refer to single plant species or to a portion or all of the vegetation.
Vegetative. (a) Non-reproductive plant part (leaf and stem) in contrast to
reproductive plant parts (flower and seed) in developmental stages of plant growth. (b) Plant development stages prior to sexual reproductive stage.
Voluntary intake. Ad libitum food intake achieved by an animal when an excess
forage or other feedstuff is available for consumption. Yearlong continuous grazing. A grazing method in which continuous grazing is
applied to yearlong grazing lands. 1
Terminology Source: Vallentine J.F.2002. Grazing Management.