Caleb Benson, Senior Vegetation Ecology Summer 2013 CU Mountain Research Station

Sub-alpine life zone ( m) 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.

 Engelmann Spruce  Shade tolerant  Low establishment rate  Longevity  Wet environments  Sub-alpine Fir  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

 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.

 Northeast and Southwest facing slopes  Aspect and slope  Daubenmire plots  10 per slope  Random and continuous  Number of Species  Percent Cover

Spherical Crown Densitometer Canopy Cover 10 per slope Bitterlich Variable Radius Method Tree Density 15 per slope

ANOVA Rows  Slopes Columns  Species Fail to reject hypothesis #1 due to very low p-values.

Canopy Cover t-test Southwest Slope Mean = (69.9%) SE = Northeast Slope Mean = (81.1%) SE = P-value = 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 = Reject hypothesis #3 SW species: 16 total NE species: 10 total

 Basal area greater on NE slope due to:  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:  Less canopy cover  Snow blankets causing shorter growing seasons  Recent disturbances

 Higher number of Daubenmire plots would provide more significant data.  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 (1988). Armesto, Juan J., and Jos έ A. Mart ί nez. "Relations between vegetation structure and slope aspect in the mediterranean region of Chile." The Journal of Ecology (1978): Isard, Scott A. "Factors influencing soil moisture and plant community distribution on Niwot Ridge, Front Range, Colorado, USA." Arctic and Alpine Research (1986): Kutiel, Pua. "LOPE ASPECT EFFECT ON SOIL AND VEGETATION IN A MEDITERRANEAN ECOSYSTEM." Israel Journal of Botany (1992). Mueller-Dombois, Dieter, and Ellenberg Heinz. Aims and Methods of Vegetation Ecology. Caldwell: The Blackburn Press, Print.