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• association with many conifer and other hardwood species. Aspen provide desirable <br />scenic value, the diversity of plants growing under aspen supply critical wildlife habitat, <br />valuable grazing resources, protect soils from erosion, and help maintain water quality. <br />These features make aspen a crucial component of many Western landscapes. <br />At the continental scale, aspen has several physiological characteristics that <br />permit it to attain great geographic amplitude. Lieffers and others (2001) outline the <br />following important adaptive traits of aspen: 1) among the wide ranging genus Populus <br />spp. (cottonwoods, poplars, aspen) aspen seems to have a very high stress tolerance. <br />Usually high stress tolerance is associated with slow growing species and those with a <br />limited reproduction strategy; 2) aspen appear to rely on vegetative reproduction via <br />root suckering more than other Populus species. These authors assert that the passing <br />of extensive root systems between generations enhances tolerance to absorb climate <br />stress (DesRochers and Lieffers 2001); 3) Aspen also has the ability to adapt leaf size <br />to xeric and mesic conditions (that is, smaller leaves for drier sites). Aspen's smaller leaf <br />size could keep the leaf surface slightly cooler allowing earlier shut down of stomata, <br />thus tempering water stress during drought; 4) aspen seem to tolerate cold temperature <br />and short growing seasons better than most hardwoods (Pearson and Lawrence 1958); <br />5) leaf fluttering may be an adaptive advantage in cooling leaf surfaces of many <br />Populus species and, 6) aspen appear to have a higher photosynthesis capability than <br />other Populus spp. which is comparable to that of high yield poplar hybrids. Aspen <br />photosynthesizes well in low light (for example, competitive situations) and even mature <br />bark is capable of photosynthesis, which helps to ameliorate respiration during periods <br />of high insolation (before spring leaf -out) (Pearson and Lawrence 1958). <br />Photosynthesizing bark may help aspen recover from injuries and infestations (Jones <br />and Schier 1985; Lieffers and others 2001) and may allow aspen to photosynthesize at <br />low levels during the winter giving the tree a photosynthetic "boost" prior to leaf -out <br />(Pearson and Lawrence 1958; Shepperd and others 2004). As leaf chlorophyll <br />increases during the summer, bark chlorophyll decreases causing bark to become <br />whiter (Strain 1964). <br />Although aspen does produce abundant crops of viable seed (McDonough <br />1979), it primarily reproduces vegetatively by root suckering throughout most of its <br />2 <br />