exotic herbivore species grazing effect on plant life module 5 see-u 2001 biosphere 2 center, az...
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Exotic Herbivore Species Grazing Effect On Plant Life
Module 5
SEE-U 2001 Biosphere 2 Center, AZ
Adam Nix
Eli Pristoop
J.C. Sylvan
Yuko Chitani
Mei Ying Lai
Lily Liew
Asma Madad
Prof. Tim Kittel, TA Erika Geiger
IntroductionA community is all associated
species within a given area. A variety of factors act to structure communities — factors as varied as weather fluctuations and natural disasters, to exotic species introductions, to the natural tension between producers and consumers. Whether or not the plant is killed, however, herbivory has the potential to dramatically alter plant and animal communities.
In this study the question at hand was, how grazing effects a community? What is the effect of herbivory on plant community diversity and species abundance? It is important to find out the influences that cattle grazing has on sonoran desert land. Understanding the functioning of communities is essential to conserve endangered ecosystems and the species therein. The only way to accumulate data on this is to measure the percent of plant life forms.
Methods
Three different sites were chosen to represent the varying intensity of herbivory on plant communities: area 1 experienced little or no grazing by cattle. Area 2, which was fenced off, experienced moderate grazing by cattle; 64 head of cattle ranged this area for a period of 3 months prior to this study. Area 3, also fenced off, was highly utilized by neighboring ranchers as rangeland. Observation indicated that this area had experienced a high intensity of cattle grazing. The line intercept sampling was used to determine the aerial cover of species (as oppsed to basal cover) on a 50-meter line within the three sites. The distance of the line to the fence of each respective site was also recorded. The line was then divided into 10-meter sections. Working in pairs, we identified each intersecting species and their coverage.
Sample bags were labeled with: site, location on the 10-meter sections from which it was collected, specie name, and lifeform. 6 GPS readings were taken at the three sites, at the beginning and end of the line. The data was then put into Excel.
We selected four other species that were representative of the changes in the percent cover over the three areas: Boraginaceae Family #1, Calliandra eriophylla, Hilaria belangeri, Opuntia engelmanni
Absolute percent cover measures the specie’s proportion in respect to the length of the line sampled (50m).
Relative percent cover measures the specie’s proportion in respect to the total length of all species sampled (>50m).
Herbacious Woody Succulent
Grass Forb Tree Shrub
Annual Perennial Annual Perennial Broad-leaf
Micro-fyllous
Borad-leaf
Micro-fyllous
Plant Lifeform Classification
Bunch grass
Sod-forming
Draught deciduous
Draught deciduous
Draught deciduous
Draught deciduous
Cold deciduous
Cold deciduous
Cold deciduous
Cold deciduous
Evergreen Evergreen Evergreen Evergreen
Sarcostemma cynanchoides sp. Hartwegii, a vine, was classified as a perennial forb.
ResultsRESULTS
1) Plant coverage: Area 1 (ungrazed) > Area 2 (moderately grazed) > Area 3 (heavily grazed). The percent coverage of annual forbs dropped from 55% relative coverage in Area 1 to 52% in Area 2 to only 14% in Area 3 (see fig. 1, 2, 3).
2) As total plant coverage diminished, relative and absolute % values achieved parity (see fig. 3).
3) Overall bare ground increased from Area 1< 2 < 3 (see fig. 4, 9).
4) Four species represent the changes in the percent cover over the three areas: Boraginaceae Family #1, Calliandra eriophylla, Hilaria belangeri, Opuntia engelmanni. While some species displayed a decrease in percent cover, others tended to increase (e.g. succulents increases from Area 1 (9.2%) to Area 2 (16.5%) and Area 3 (24.2%)) (see fig. 9).
5) Species diversity remains constant over three areas (see fig. 10).
6) Lifeform diversity also remains constant over three areas (see fig. 10).
Relative vs. Absolute Percent Coverage by Lifeforms in Area 1
0%
10%
20%
30%
40%
50%
60%
Annual Grasses Perennial BunchGrasses
Annual Forbs Perennial Forbs MicrophyllousDeciduous
Shrubs
MicrophyllousDeciduous
Trees
Succulents
Lifeform
Pe
rce
nt
Co
vera
ge
relative %
absolute %
Fig. 1
Relative vs. Absolute Percent Coverage by Lifeform in Area 2
0%
10%
20%
30%
40%
50%
60%
Annual Grass Perennial BunchGrass
Annual Forbs Perennial Forbs MicrophyllousDeciduous
Shrubs
MicrophyllousDeciduous
Trees
Succulents
Lifeform
Pe
rce
nt
Co
vera
ge
relative %
absolute %
Fig. 2
Relative vs. Absolute Percent Coverage by lifeform for Area 3
0%
2%
4%
6%
8%
10%
12%
14%
16%
Annual Grass PerennialBunch Grass
PerennialSod-forming
Grass
Annual Forbs PerennialForbs
MicrophyllousDeciduous
Shrubs
MicrophyllousDeciduous
Trees
Succulents
Lifeform
Pe
rce
nt
Co
vera
ge
Relative (%)
Absolute (%)
Fig. 3
Fig. 4
Comparison of Absolute % Cover by Lifeform in Areas 1,2,3
0%
10%
20%
30%
40%
50%
60%
Annua
l Gra
ss
Pere
nnial
Bun
ch G
rass
Pere
nnial
Sod
-form
ing G
rass
Annua
l For
bs
Pere
nnial
For
bs
Microp
hyllo
us D
ecidu
ous
Shrub
s
Microp
hyllo
us D
ecidu
ous
Tree
s
Succu
lents
Bare
Groun
d
Lifeforms
Pe
rce
nt
Co
ver
Absolute % (1)
Absolute % (2)
Absolute % (3)
Fig. 5
Comparison of Relative % Cover by Lifeform Areas 1,2,3
0%
10%
20%
30%
40%
50%
60%
Annual Grass Perennial Bunch
Grass
Perennial Sod-
forming Grass
Annual Forbs Perennial Forbs Microphy llous
Deciduous
Shrubs
Microphy llous
Deciduous
Trees
Succulents
Lifeform
Pe
rce
nt
Co
ver
Relative % (1)
Relative % (2)
Relative % (3)
Relative vs. Absolute Cover Percentages in Area 1
0.00%
5.00%
10.00%
15.00%
20.00%
25.00%
Acacia
gre
ggii
Aristid
a te
rnipe
s va
r. ge
ntilis
Bothr
iochlo
a ba
rbino
dis
Boute
loua
hirsu
ta
Callian
dra
eriop
hylla
Daucu
s pu
sillus
= S
pecie
s H
Echin
ocer
eus
Erag
rost
is cu
rvula
Erige
ron
diver
gens
= S
pecie
s A
Gilia s
p.
Lept
ochlo
a du
bia =
Spe
cies
B
Micros
eris
linea
rifoli
a =
Specie
s D
Opunt
ia ph
aeac
anth
a
Pros
opis
velut
ina =
Mes
quite
Viguier
a lon
gifoli
a =
Specie
s F
BARE GROUND
Species
Pe
rce
nt
Co
vera
ge
Relative Cover (%)
Absolute Cover (%)
Fig. 6
Relative vs. Absolute Percent Coverage in Area 2
0.00%
5.00%
10.00%
15.00%
20.00%
25.00%
Ambros
ia co
nfer
tiflor
a
Borag
inace
ae F
amily
#1
Borag
inace
ae F
amily
#3
Boute
loua
curti
penb
ula
Callian
dra
eriop
hylla
Daucu
s pu
sillus
= S
pecie
s H
Echin
ocer
eus
Erag
rost
is cu
rvula
Eriog
onum
wrig
htii
Gnaph
alium
Lept
ochlo
a du
bia =
Spe
cies
B
Micros
eris
linea
rifoli
a =
Specie
s D
Opunt
ia en
gelm
anni
Opunt
ia sp
inosio
r
Pros
opis
velut
ina =
Mes
quite
Viguier
a lon
gifoli
a =
Specie
s F
LITTE
R, INCLU
DING D
EAD C
ACTI
Species
Pe
rce
nt
Co
vera
ge Relative Cover (%)
Absolute Cover (%)
Fig. 7
Relative vs. Absolute Percent Coverage in Area 3
0.00%
10.00%
20.00%
30.00%
40.00%
50.00%
60.00%
Am
bros
ia
Aris
tida
tern
ipes
Bor
agin
acea
e
Bou
telo
ua
Bro
mus
rub
ens
Dau
cus
pusi
llus
Elym
us
Erag
rost
is
Gilia
sp.
Lepi
dium
Mac
haer
anth
era
Opu
ntia
Plan
tago
Sar
cost
emm
a
BA
RE
GR
OU
ND
LITT
ER,
Species
Pe
rce
nt
Co
ve
rag
e Relative Cover (%)
Absolute Cover (%)
Fig. 8
Comparison of Absolute Percent Coverages of 5 Selected Species for Areas 1,2,3
0.00%
10.00%
20.00%
30.00%
40.00%
50.00%
60.00%
BARE GROUND Boraginaceae Family#1
Calliandra eriophylla Hilaria belangeri Opuntia engelmanni
Species (excluding "Bare Ground")
Ab
so
lute
Pe
rce
nt
Co
vera
ge
Area 1
Area 2
Area 3
Fig. 9
Total Number of Collected Species and Total Lifeforms Present Under Different Grazing Treatments
0
5
10
15
20
25
30
35
Area 1: Ungrazed Area 2: Moderately Grazed Area 3: Heavily Grazed
Grazing Treatment
Nu
mb
er
of
Sp
eci
es
/Lif
efo
rms
Species
Lifeforms
Fig. 10
Plant Species Found at Sites• Acacia greggii• Ambrosia confertiflora• Androsace occidentalis• Aristida ternipes var. gentilis• Boraginaceae Family #1• Boraginaceae Family #2 = Species K• Boraginaceae Family #3• Bothriochloa barbinodis• Bouteloua curtipenbula• Bouteloua hirsuta
• Bromus rubens• Calliandra eriophylla • Chenopodium sp.• Daucus pusillus = Species H• Descurainia pinnata = Species E• Echinocereus• Elymus elymoides• Eragrostis curvula• Eragrostis intermedia• Erigeron divergens = Species A• Eriogonum wrightii• Gilia sp.• Gnaphalium
•Hilaria belangeri•Lepidium lasiocarpum•Leptochloa dubia = Species B•Lupinus concinnus(?)•Machaeranthera tagetina•Microseris linearifolia = Species D
•Opuntia chlorotica
•Opuntia engelmanni
•Opuntia phaeacantha
•Opuntia spinosior
•Plantago patagonica
•Prosopis velutina = Mesquite
•Sarcostemma cynanchoides ssp. Hartwegii
•Sisymbrium irio L.
•Tridens muticus = Species J2
•Triodanis perfoliata = Species J1
•Viguiera longifolia = Species F
•Species I
•BARE GROUND
•DUNG
•LITTER
DiscussionHow Does Grazing Affect
Plant Community Diversity and Species Abundance?
To answer this question, we studied three different sites: Area 1 an ungrazed range, Area 2 a moderately grazed range, and Area 3 a heavily grazed open range. From general observation, it was clear that the heavily grazed site had the least abundance of plants and a lot of bare ground between markings. It also took us considerably less time to sample the heavily grazed site than it did for the other two sites.
We measured the plant community’s overall richness of species by analyzing the number of species found and collected in each of the three areas. The possible sources of error include: misidentification of plants, inconsistency and inaccuracy in measuring technique, uncertainty in whether the lines sampled were representative of the different areas.
Conclusion
•Intense herbivory has an effect on the lifeform composition of the plant community.
•However, herbivory does not necessarily affect the biodiversity of the community.
In this exercise we learned:• Plant identification and classification• Relative and absolute percent coverages
Epple, Anne Orth. A Field Guide to the Plants of Arizona. Lew Ann Publishing Company, Mesa, Arizona. 1995.
Gould, Frank W. Grasses of the Southwestern United States. University of Arizona Press, Tucson. 1993.
Kearney, Thomas H. and Peebles, Robert H. Arizona Flora. University of California Press, Berkeley. 1960.
Niehaus, Theodore F. A Field Guide to Southwestern and Texas Wildflowers. Houghton Mifflin Co., New York. 1984.
Robbins, Travis, David Lancaster, Janna Lancaster and Dr. Tony Burgess. Biosphere 2 Centre Plant Field Guide. (Unpublished).
References
Thanks to Tim and Erika for their
expertise in plant identification.