Abstract
Studies of northern circumpolar tree line have related tree distribution to numerous environmental controls, such as permafrost, moisture, heat, radiation, and frontal circulation patterns (Barry, 1967; Bryson, 1966; Hare and Ritchie, 1972; Hustich, 1966; Larsen, 1989). Recent modeling experiments indicate that the circumpolar tree line could be shifted north tens to hundreds of kilometers if anticipated magnitudes of global warming due to increases in atmospheric greenhouse gasses are realized (e.g., Emmanuel et al., 1985; Rizzo and Wiken, 1992). Detecting and migitating the negative impacts of such vegetation shifts requires an understanding of the dynamics of tree line-climate interrelations. In this chapter we review some of the data and current concepts regarding climate-vegetation dynamics at the circumpolar tree line. In an effort to evaluate the mechanisms responsible for forest development we review selected northern European and North American studies of northern forests, the tree line, and forest-tundra, and evaluate the dominant influences and processes of forest development at the forest edge. We synthesize this information to suggest how the tree line might react in real terms to future climate warming.