The Affects of Elevation on Tree Growth along Niwot Ridge

Steven GriffinWinter Ecology, Spring 2013Mountain Research Station, University of Colorado, Boulder

Question: How does elevation affect the age

structure of subalpine forests along Niwot Ridge?

Hypotheses H1: The subalpine forest of Niwot Ridge

vary in age structure along an elevation gradient due to biotic and abiotic environmental conditions.

H0: The age structure of the subalpine forest on Niwot Ridge shows no variation along an elevation gradient.

Experiment Design Sample 50m transects of subalpine

forest at three sites between Niwot Ridge tree line and the CU MRS to determine approximate age structure

Data Collection: Intended Method: Incremental Tree BoresPerformed Method: Diameter at Breast

Height

Key Assumptions By Changing my research method from

tree cores to DBH, I am unable to make claims about the age structure of the subalpine forests.

DBH is a poor proxy for tree age, especially near timberline where growth is stunted by exposure

The DBH data collected provides an estimate of the size structure of Niwot Ridge’s subalpine forest

Statistical Analysis Tree data was classified into three

diameter ranges for statistical testing The Chi Square test was used to

compare the normalized distribution of trees against the size structure observed at each site

No statistical difference was found in the tree sizes

Results Treeline X-squared = 1.2915, df = 2, p-

value = 0.5243 Ribbon X-squared = 1.7249, df = 2, p-

value = 0.4221  Mountain Research Lab X-squared =

4.7538, df = 2, p-value = 0.09284

Conclusion Fail to Reject Null Hypothesis Given the small sample size and limited

scope of the sampling method, significant results are unlikely.

Although the numbers don’t support my hypothesis, I suspect that there is are significant differences between tree age, distribution and size by elevation

Discussion Much more research is required GIS & Satellite imagery can help map

forest geography Tree size is not an acceptable age proxy

at elevation

Take-Home Points Field work is HARD-Pick sites WISELY Its important to scrutinize data collection

methods and results to ensure appropriate claims are made and supported

Have a contingency plan Bring hand warmers

References:  "The Subalpine Ecosystem". National Park Service. Archived from the original on 2007-

08-09. Retrieved 2013-2-10.

Jørgensen, S.E. (2009). Ecosystem Ecology. Academic Press. ISBN 978-0-444-53466-8.

"Alpine Tundra Ecosystem". Rocky Mountain National Park. National Park Service. Retrieved 2011-05-13

Peet, R.K. (2000). "Forests and Meadows of the Rocky Mountains". In Barbour, M.G.; Billings, M.D. (2nd ed.). Cambridge University Press. ISBN 978-0-521-55986-7.

http://en.wikipedia.org/wiki/Pearson's_chi-squared_test