The primary environmental variable that appears to regulate the function and, to some extent, the structure of Alaskan taiga ecosystems is soil temperature (Van Cleve et al. 1983, Van Cleve and Dyrness 1983). The structural and functional changes that occur in relation to changing soil temperatures are fairly well documented (Chapters 7, 10, and 12). These changes are generally described across a series of ecosystems going from aspen (Populus tremuloides Michx.) and balsam poplar (Populus balsamifera L.) to black spruce ([Mill.] B.S.P.). As yet, there have not been any in-depth studies within a single vegetation type to determine what ecosystem controls might be responsible for differing productivity found within that type.