Modeling controls on pattern at alpine treeline
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Alpinetreeline, the transition zone between low-elevation subalpine forest and high-elevation tundra, is often characterized by discontinuous tree cover as the absolute elevational limit to tree survival is approached. Physiological stresses are most often considered to limit the upslope position of trees in alpine environments. This research investigates whether tree response to environmental stress alone can explain the discontinuous pattern of trees within the treeline ecotone. To accomplish this goal, a forest process model. Alpine Treeline Ecotone-BioGeochemical Cycles (ATE-BGC), is used to predict the location of the potential treeline ecotone for a treeline area in Glacier National Park, Montana. The model predicts that tree cover within the treeline ecotone could be much more continuous. Tundra aras capable of supporting trees are compared to locations where trees are currently growing with regard to elevation, slope, the amount of snow, insolation and soil moisture at the different locations. Comparisons are done between potential tree sites and actual trees sites in aggregate and also with the potential tree sites divided into groups with statistically similar characteristics. Some of the predicted treeline sites have significantly higher slopes than the locations where trees are growing; slope instability most likely inhibits tree growth at these sites. However, a large proportion of the sites where the model predicts that trees could be growing do not have conditions that are obviously inimical to tree survival. For those locations, a process other than physiological stress, probably reproduction, limits tree growth.
