324Lab2 2011 - ESR 324 Environmental Systems II Lab 2...

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2 ESR 324 Environmental Systems II Lab 2 Winter 2011 Vegetation Distribution in a Forested Watershed Where: TBA, Portland State University, and field sites in the West Hills TA - Tues: Matthew Duveneck ( [email protected] ; office TBA) TA – Thurs: Sarah S. Holman ( [email protected] ; office TBA) Instructor: Alan Yeakley (725-8040; [email protected]) Introduction Plant species vary in their responses to environmental factors. A given species will have a unique set of tolerances to environmental variables, such as light, temperature, moisture, and nutrients. At the community level, these differences in tolerances will cause various species to have competitive advantages, depending on the nature of those environmental factors. For example, tree species that are very tolerant of low light conditions, such as western hemlock ( Tsuga canadensis ) may proliferate in shady areas, such on north facing slopes. On the other hand, western hemlock is also very in tolerant of low moisture conditions, so one would expect that this species would have less survival success in drier areas, such as up on ridgetops. In this laboratory, we will examine the distribution of tree species with respect to terrain properties. Terrain distributes several major environmental variables, including light, temperature and moisture. Steep slopes tend to be drier. Ridgetops tend to be drier due to drainage. Orographic lifting, however, may offset drainage by increasing rainfall with elevation. Temperature drops with elevation. Sunlight intensity and duration varies with aspect (i.e. the angle of the slope plane with respect to north). Solar radiation is greatest for south facing slopes in the Northern Hemisphere. Soil depth and nutrient concentrations typically decrease with elevation, although this relationship can be quite complex depending on hillslope geomorphology.
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This note was uploaded on 01/12/2012 for the course ENVIRONMET 321 taught by Professor Dr.j.alanyeakley during the Winter '11 term at Portland State.

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324Lab2 2011 - ESR 324 Environmental Systems II Lab 2...

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