Transcript Comparing vegetation on the NE and SW

Caleb Benson, Senior
Vegetation Ecology Summer 2013
CU Mountain Research Station
•Sub-alpine life zone (3000-3500m)
•Arapahoe pass physiogeography
•Northeast: Aspect 21 deg. & slope 15.5 deg
•Southwest: Aspect 208 deg. & slope 22.2 deg
•Comparing vegetation characteristics between
north and south facing slopes.
•South slopes are theoretically drier due to more
direct sunlight during the day leading to higher
evapotranspiration.
•“Westerlies redistribute snow, creating deep,
long-lasting snow fields on leeward (west) slopes
while leaving adjacent windward slopes snow
free” (Isard).
•This should lead to a greater diversity of
herbaceous, low-growing vegetation.
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Engelmann Spruce
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Sub-alpine Fir
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Shade tolerant
Low establishment rate
Longevity
Wet environments
Shade tolerant
High recruitment rate
Rapid height growth
Wet environments
South facing slope bear open scrub vegetation,
whereas north facing have evergreen woodlands.
Chamaephytes and Hemicryptophytes
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Hypothesis #1: Overall basal area of tree
species (P. engelmannii, A. lasiocarpa, P.
tremuloides, P. flexilis ) will be greatest on the
northeast slope.
Hypothesis #2: Canopy cover will be greater on
the northeast slope.
Hypothesis #3: Species diversity of
undergrowth vegetation will be greater on the
southwest slope.
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Northeast and Southwest facing slopes
Aspect and slope
Daubenmire plots
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10 per slope
Random and continuous
Number of Species
Percent Cover
•Bitterlich Variable
Radius Method
•Tree Density
•15 per slope
•Spherical Crown
Densitometer
•Canopy Cover
•10 per slope
•ANOVA
•Rows  Slopes
•Columns  Species
25
20
15
•Fail to reject
hypothesis #1 due to
very low p-values.
SW-Plot
10
NE-Plot
5
0
Fir
-5
Spruce
Aspen
Limber Pine
•Canopy Cover t-test
•Southwest Slope
•Mean = 0.699 (69.9%)
•SE = 0.063
•Northeast Slope
•Mean = 0.811 (81.1%)
•SE = 0.023
•P-value = 0.1221
• Reject hypothesis #2
•Undergrowth diversity
•T-test
•Southwest Slope
•Mean = 3.9 species per
plot
•SE = 0.79
•Northeast Slope
•Mean = 2.6 species per
plot
•SE = 0.31
•P-value = 0.1443
•Reject hypothesis #3
SW species: 16 total
NE species: 10 total
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Basal area greater on NE slope due to:
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Shade
Longer growing season
Fewer disturbances
Canopy cover greater due to greater leaf area
on NE slopes from limited sun light.
Species diversity greater on SW slope due to:
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Less canopy cover
Snow blankets causing shorter growing seasons
Recent disturbances
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Higher number of Daubenmire plots would
provide more significant data.
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Daubenmire uses 50 evenly spaced(1m) subplots per plot
(50x50m) to obtain an objective evaluation of the
undergrowth vegetation (Mueller-Dombois, 121).
Northeast slope  more moisture  greater tree
basal area
Larger basal area  greater canopy cover 
decreased species diversity
Larger basal area  increased competition 
decreased species diversity
Aplet, Gregory, and Richard Laven . "Patterns of Community
Dynamics in Colorado Engelmann Spruce-Subalpine Fir
Forest." Ecology. 69.2 (1988).
Armesto, Juan J., and Josέ A. Martίnez. "Relations between vegetation
structure and slope aspect in the mediterranean region of
Chile." The Journal of Ecology (1978): 881-889.
Isard, Scott A. "Factors influencing soil moisture and plant
community distribution on Niwot Ridge, Front Range, Colorado,
USA." Arctic and Alpine Research (1986): 83-96.
Kutiel, Pua. "LOPE ASPECT EFFECT ON SOIL AND VEGETATION
IN A MEDITERRANEAN ECOSYSTEM." Israel Journal of Botany.
41.4-6 (1992).
Mueller-Dombois, Dieter, and Ellenberg Heinz. Aims and Methods of
Vegetation Ecology. Caldwell: The Blackburn Press, 2002. Print.