Is the wide distribution of aspen a result of its stress tolerance?

Populus tremuloides is distributed from drought-prone fringes of the Great Plains to extremely cold sites at arctic treeline. To occupy these conditio ns aspen appears to be more tolerant of stress than the other North America n species of the genus Populus. Cold winters, cold soil conditions during t he growing season, periodic drought, insect defoliation, and competition fr om conifers are typical stresses faced by aspen. Aspen is capable of high p hotosynthetic rates but has conservative use of water during high vapor pre ssure deficits. This paper examines photosynthesis, water relations, morpho logical characteristics and root growth, and carbon allocation strategies i n relation to the above stresses.