Transcript Document

The Effects of Cliffs and Stream Banks
on the Species Richness of a
Dry River Bed
See-U 2001
Eli Pristoop
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
Stream 1
STUDY SITES
Stream 3
Stream 2
No Cliff
Cliff
No Cliff
Cliff
No Cliff
Cliff
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
S
Riparian Zone
A
M
P Stream
5 Meters
L
E
Riparian Zone
A
R
E
A
Cliff Site
Sampling Area
Stream Bank
Stream
Sampling Area
Cliff
Stream
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
Erigeron divergens
Ambrosia deltoidea
Erigonium abertianum
Artemesia
Fraxinus velutina
Asteracae
Gilia sp.
Ayenia pusilla
Gnaphalium sp.
Baccharus salicifolia
Lepidium lasiocarpum
Robinium neomexicana
Baccharus sarothroides
Lichen
Rumex
Bouteloua curtipendula
Mimosa biuncifera
Salix goodingii
Bromus rubens
Moss
Stachys cocinnea
Celtis spinosa
Nolina microcarpa
Sisymbrium irio
Chenopodium
Opuntia engelmanii
Vigueira annua
Cirsium neomexicanum
Oxalis sp.
Prosopus velutina
Cynodon dactylon
Panicum sp.
Daucus pusilla
Phlaris canariensis
Descuriana pinnata
Populus fremonti
Eragrostis curvulaVar. Chloromelas
+
Species 1-41
Species
MethodsAllCont’d
Figure 1
Species per meter squared for cliff and no cliff by stream
0.8
species (# found)/m^2
0.7
0.6
0.5
no cliff
0.4
cliff
0.3
0.2
0.1
0
stream 1
stream 2
stream 3
Figure 2
Non-Parametric Mann-Whitney
Test Based on Species per m^2
Test Statisticsb
Mann-Whitney U
Wilcoxon W
Z
Asymp. Sig. (2-tailed)
Exact Sig. [2*(1-tailed
Sig .)]
species/m^2
.000
6.000
-1.964
.050
a
.100
a. Not corrected for ties.
b. Grouping Variable: CLIFFED
Figure 3
species richness (#
found/m^2)
Stream width vs species richness
0.8
0.7
0.6
0.5
no cliff
0.4
cliff
0.3
0.2
0.1
0
3
4
5
6
Stream width (m)
7
8
Figure 4
Cliff height sampled vs species
richness
species
richness(#
found/m ^2)
0.8
0.7
0.6
0.5
0.4
0.3
2
2.5
3
3.5
4
4.5
5
5.5
maximum height sampled (m above ground)
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
SEE-U
2001
Thanks to Tim and
Gwen for Advice,
Erika for
Identifications and
Map Guidance, and
James for Statistics
Help
Thanks to J.C. for
Helping Collect
Samples and
Finding the
Rattlesnakes
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 along
riverbanks. Journal of Biogeography. 18(5) 533-541.