BACKGROUND RESEARCH

There are numerous factors that determine the elevation at which trees can grow (list collected from several sources):

Temperature	strongest factor globally
high temperature injury	not applicable for this subalpine/alpine study area
low temperature injury	freezing injury when some of the plant tissue water freezes winter temperature is the indicator for this
temperature and growth	trees need a certain degree of warmth to grow summer temperature is the indicator for this
Precipitation	second strongest factor globally
drought	not applicable for this subalpine/alpine study area
snow cover	accumulation of snow and duration of snow cover stongly influences altitudinal distributions
Solar radiation	influences temperature, and photosynthesis directly
Topography	locally, environmental factor strongly vary depending on the topography of the area
aspect	the direction the hillslope is facing determines the amount of solar radiation that is being received, and thus temperature, and the amount of evapotranspiration
slope	varying degrees of slope determine how strong the influence of aspect is exposed and steep slopes reduce the amount of top soil, and thus reduce the ability of tree roots to hold on to the ground
Latitude	influences temperature on a global scale is the main reason for the existence of a polar treeline
Soil	soil fertility might slightly increase the range of climatic environments a tree can grow in soil depth determines how well tree roots can hold on to the ground
Wind	influences temperature dispersal of seeds is subject to availability of wind as a carrier strong winds can cause seeds to be blown away at exposed places
Tree Species	factors influence different tree species in different ways dominant tree species in study area 92: mountain hemlock dominant tree species in study area 82: alpine fir

Jones writes: "The transition between trees and dwarf shrub vegetation in mountains is characteristically sudden, with many species at such a treeline showing characteristically stunted and gnarled growth (krummholz). In general the level of the treeline corresponds with that where the temperature of the warmest month is less than about 10 [degrees] C." Let's find out how this relates to the findings in the spatial analysis section. Treeline summer temperature should be at about 10 degrees at both study sites.

It has been studied that identifying correlations between ecological factors and plants is highly complex. Plant response to a changing environmental factor is usually not linear. And if two identified factors change simultaneously, the overall effect may not be a simple addition of the individual plant responses to those factors. It is a complex web of factors that determines plant ecology, and thus the altitude of treelines.

In summary, the strongest influencing factors towards treeline altitude are high summer temperatures and the amount of snow in the area. I am making this the focus of my spatial analysis.

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