The Effects of Cliffs and Stream Banks

on the Species Richness of a

Dry River Bed

Eli PristoopSee-U 2001

Introduction

In the Sonoran desert, riparian communities occupy only 5% of land but are responsible for 85% of overall species diversity (Brusca 2000).

There are a variety of factors such as stream grade and substrate heterogeneity that affect species richness within riparian communities (Hupp 1982) (Nilsson et.al 1989).

Within streams there are often sites with flat riparian zones on each side of the stream. (I will call these Type A sites)

There are also sites where one side of the stream is bordered by a cliff and the other side is bordered by a tall steep stream bank. (I will call these type B sites)

Within the type A sites water is more easily accessible to a larger area more conducive to plant growth

The increased disturbance in the type B sites and variable conditions within cliffs provide opportunities for a variety of types of species to grow.

 

Primary Question:

Will the type B sites have higher plant species richness than the type A sites close by on the same stream?

Secondary Question:

What general trends will be associated with high species richness?

Apacherian Scrub Savanna

Riparian Zone

Cañada del Oro

32.6° N 110° W Elevation 1070 m.

MAP 1: Sites in Relation to Biosphere 2 Campus

MAP 2: Closeup of Sites

STUDY SITESStream 1

No Cliff

Cliff

Stream 2

No Cliff

Cliff Cliff

No Cliff

Stream 3

Methods• Identified 3 separate sections of one stream

• Found 1 cliff site and 1 non-cliff site for each stream

• Within a stream sites within 100m of each other

• Measured stream width, stream grade, and grade perpendicular to stream for all sites

• Measured cliff and stream bank slope and height for cliff sites

• Calculated area for each site

• Collected all plant species within rectangular area 5 meters long for each site

• Non cliff sites collected all species in riparian zone; determined by vegetation type

• Cliff sites collected all species from cliff and stream bank opposite cliff

• Identified or labeled all species from each site

• Found total species per site

• Calculated species per meter squared for each site

• Compared species per meter squared between cliffs and non-cliffs on each stream

• Also evaluated how species per meter squared was affected by stream grade, grade

perpendicular to stream, stream width, % of site made up by stream, cliff height, and

aspect.

• Evaluated species per meter squared for cliffed and non-cliffed sites in a Non-Parametric

• Mann-Whitney Statistical Test

Non-Cliffed Site

Riparian Zone

SAMPLE

AREA

5 Meters

Riparian Zone

Stream

Cliff Site

Stream Stream

Stream Bank Cliff

Sampling Area Sampling Area

Results In terms of species per meter squared, within each stream, species richness was higher for the type B sites.

With the use of a non-parametric Mann-Whitney test, the disparity in species richness values was found to be statistically significant with a P value of .05.The site with the highest species richness was the site with the highest stream grade, highest grade perpendicular to the stream, and was north-facing.

For cliff sites richness increased with stream width and for non cliff sites it decreased with stream width.

Stream width was greater in all cliff sites than in any non-cliff site.

Among cliff sites richness decreased as cliff surface area and height above ground sampled increased

Plant Species

Acacia greggii

Ambrosia deltoidea

Artemesia

Asteracae

Ayenia pusilla

Baccharus salicifolia

Baccharus sarothroides

Bouteloua curtipendula

Bromus rubens

Celtis spinosa

Chenopodium

Cirsium neomexicanum

Cynodon dactylon

Daucus pusilla

Descuriana pinnata

Eragrostis curvulaVar. Chloromelas

Erigeron divergens

Erigonium abertianum

Fraxinus velutina

Gilia sp.

Gnaphalium sp.

Lepidium lasiocarpum

Lichen

Mimosa biuncifera

Moss

Nolina microcarpa

Opuntia engelmanii

Oxalis sp.

Panicum sp.

Phlaris canariensis

Populus fremonti

Robinium neomexicana

Rumex

Salix goodingii

Stachys cocinnea

Sisymbrium irio

Vigueira annua

Prosopus velutina

+

Species 1-41

Methods Cont’d All Species

Species per meter squared for cliff and no cliff by stream

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

stream 1 stream 2 stream 3

spe

cie

s (#

fo

un

d)/

m^

2

no cliff

cliff

Figure 1

Test Statisticsb

.000

6.000

-1.964

.050

.100a

Mann-Whitney U

Wilcoxon W

Z

Asymp. Sig. (2-tailed)

Exact Sig. [2*(1-tailedSig.)]

species/m^2

Not corrected for ties.a.

Grouping Variable: CLIFFEDb.

Non-Parametric Mann-Whitney Test Based on Species per m^2

Figure 2

Stream width vs species richness

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

3 4 5 6 7 8

Stream width (m)

sp

ec

ies

ric

hn

es

s (

#

fou

nd

/m^

2)

no cliff

cliff

Figure 3

Cliff height sampled vs species richness

0.3

0.4

0.5

0.6

0.7

0.8

2 2.5 3 3.5 4 4.5 5 5.5

maximum height sampled (m above ground)

spec

ies

rich

ness

(#

foun

d/m

^2)

Figure 4

Discussion•Presence of cliffs prevents spillage of water into riparian zone. This increases water level, stream power, and thereby, disturbance. Increased disturbance can uproot existing plant species and provide opportunities for more species to establish themselves. It can also increase seed dispersal.•The higher stream banks at the cliffed sites increase the number of flow regimes, which allows species with different tolerances of flooding to live there (Nilsson et.al 1989).•The geometry of cliffs present great differences in exposure to sunlight, slope, disturbance, and nutrient availability (Cooper 1997). This can create an “overlapping niche” situation in which a wide variety of species live in a very small area

•Possible bias as a result of not sampling flat areas opposite cliffs.

Discussion Cont’d Cliffs that are north-facing are usually richer than south-facing cliffs (Cooper 1997).

Species richness tends to increase with stream grade (Hupp 1982).

Greater stream width among cliff sites could be a result of increased stream power pushing stream bank side farther back

Decreasing richness with increasing area among cliffs could be a result of a species area curve, and or it could be related to increasing distance from groundwater and from maximum water level.

Conclusion

Topographical characteristics within cliff sites create microhabitats which increase plant species richness within a riparian zone.CAÑADA DEL ORO IS A NICE PLACE

Acknowledgements

Thanks to J.C. for Helping Collect

Samples and Finding the Rattlesnakes

Thanks to Tim and Gwen for Advice,

Erika for Identifications and Map Guidance, and James for Statistics

Help

SEE-U 2001

References Brusca, R. 2000. Subdivisions (Regions) of the Sonoran Desert. (Lecture Notes)Cooper, A. 1997. Plant species coexistence in cliff habitats. Journal of Biogeography 24(4) 483

-494 Hupp, C. R. 1982 Stream grade variation and riparian forest ecology along Passage Creek,

Virginia Bulletin of the Torrey Botanical Club. 109 (4) 488-499. Kearney, Thomas H. and Peebles, Robert H. 1960. Arizona Flora. University of California Press,

Berkeley. Nilsson, C. Grelsson, G. Dyensius, M. Johansson, M.E. and Sperens, U. 1991. Small rivers

behave like large rivers: effects of postglacial history on plant species richness alongriverbanks. Journal of Biogeography. 18(5) 533-541.