Impact of Aspect on Stand Density and

Species Frequency in Gordon Gulch

Brian Owens IIUniversity of Colorado, Boulder

BACKGROUND

How Aspect May Play a Role in Tree-Stand Composition -Tree Species in an area is determined by the

microclimate created by a factor such as Aspect.

North-facing = Cooler Temperatures, less direct sunlight, higher retention of moisture (dominated by dense forests that contain Lodgepole Pine Pinus contorta, Douglas Fir Pseudotsuga menziesii)

South-facing= Warmer Temperatures, more direct sunlight, more evapotranspiration (dominated by sparsely dense stands that contain primarily Ponderosa Pine Pinus ponderosa)

RESEARCH QUESTION and HYPOTHESIS

• Does two separate aspects change the make-up of a stand of trees in terms of species frequency and overall stand density?

Hypothesis The overall stand density and species frequency of the two

separate aspects will be significantly different from one another. North will contain a higher density of trees as well as more species due to the fact that more species tend to thrive in the montane at cooler, more moist conditions.

Null The make-up of the two separate stands will exhibit no

significant difference from one another in terms of frequency and density.

Area of Research

Gordon Gulch=a small catchment of 2.74 km² located

roughly 5 km northeast of Nederland, Colorado. The catchment lies at an elevation of 2500 to 2700m.

Buraas. 2009

METHODS

Point Quarter Method2 sites on North-facing slope2 sites on South-facing slope -5 randomly selected points in each site • Each point represented the center of the 5x5 meter

measurement area. • From the center, a compass was used to define four

quadrants. • In each of these quadrants, measured the distance to

the closest tree from the center point, and determined the species.

Sites

• Sites on North Facing Slope had a dense, dark feel and look to it.

• 2638m Elevation 21˚ Slope (roughly 38% slope)

• Sites on South Facing Slope had an open, sunny (light) look and feel to it.

• 2588m Elevation 23˚ Slope (roughly 42% slope)

RESULTSNORTH FACING SLOPE4 Species=-Lodgepole Pine Pinus contorta -Douglas Fir Pseudotsuga menziesii -Engelmann Spruce Picea engelmannii -Ponderosa Pine Pinus ponderosa

Points (1-5 Site 1, 6-10 Site 2)

Species 1 2 3 4 5 6 7 8 9 10#points w/ Species

Total for Species

LP 4 3 2 4 2 2 4 3 2 4 10 30

DF 0 0 0 0 2 2 0 1 0 0 3 5

ES 0 0 0 0 0 0 0 0 2 0 1 2

PP 0 1 2 0 0 0 0 0 0 0 2 3

RESULTS

SOUTH FACING SLOPE2 species=-Lodgepole Pine Pinus contorta-Ponderosa Pine Pinus ponderosa

Points (1-5 Site 1, 6-10 Site 2)

Species 1 2 3 4 5 6 7 8 9 10#points w/ Species

Total for Species

PP 3 3 2 4 4 2 4 3 4 4 10 33

LP 1 1 2 0 0 2 0 1 0 0 5 7

RELATIVE FREQUENCY

LodgepoleEngelmann

Doug. firPonderosa

0102030405060708090

88.25

69.4

62.7

59.2

25.1

23.75

DENSITY OF SPECIES

NorthSouth

SPECIES

TREE

S PE

R HE

CTAR

E²

North South0

50

100

150

200

250

300

279.55

48.85

Density of North vs. South

ASPECT

Tree

s per

Hec

tare

²

Discussion

Research proved the hypothesis to be correct. There is a difference between North vs. South facing slopes in both species frequency as well as the stand density. --Reject the null hypothesis

Background research was backed up --North-facing aspect= dominated by more species

in a dense fashion --South-facing= dominated by less species as is

sparsely dense in its make-up

SOURCESBuraas, E., 2009, Getting water into the ground and to the channel, Gordon Gulch, Colorado (unpublished undergraduate thesis): Williams College, 102 pages. (IMAGE)

Gabet, E.J., 2000, Gopher bioturbation: Field evidence for non-linear hillslope diffusion: Earth Surface Process and Landforms 25, p. 1419-1428.

Kittel, Timothy. "Biogeography Lecture." Vegetation Ecology. MRS Colorado, Nederland. 1 July 2013. Lecture.

Long, J. N., Shaw, J.D., 2005, A density management diagram for even-aged ponderosa pine stands: Western Journal of Applied Forestry, (20)4, p.205-215.

Lotan, J. E., Critchfield, W. B., 1990, Pinus Contorta ssp. murrayana - Lodgepole pine forest: Silvics of North America, v. 1, p. 302-313.

Oliver, W. W., Ryker, R. A., 1990, Pinus Ponderosa – Ponderosa Pine: Silvics of North America, v. 1, p. 836-856.

Peet, R.K., 1978, Forest vegetation of the Colorado Front Range: Patterns of species diversity: Vegetation, Vol. 37, p. 65-78.