The Conceptual Basis of LTER Studies in the Alaskan Boreal Forest

The boreal forest occupies 10% of the ice-free terrestrial surface and is the second most extensive terrestrial biome on Earth, after tropical forests (Saugier et al. 2001). It is a land of extremes: low temperature and precipitation, low diversity of dominant plant species, dramatic population fluctuations of important insects and mammals, and a generally sparse human population. The boreal forest is also a land poised for change. During the last third of the twentieth century, many areas of the boreal forest, such as western North America and northern Eurasia, warmed more rapidly than any other region on Earth (Serreze et al. 2000). This pattern of warming is consistent with projections of general circulation models. These models project that human-induced increases in greenhouse gases, such as carbon dioxide, will cause the global climate to warm and that the warming will occur most rapidly at high latitudes (Ramaswamy et al. 2001). If we accept the projections of these models, the climate of many parts of the boreal forest will likely continue to warm even more rapidly than it has in the past. The ecological characteristics of the boreal forest render it vulnerable to warming and other global changes. Because the boreal forest is the coldest forested biome on Earth, organisms are adapted to low temperatures, and many of its physical and biological processes are molded by low temperature. Permafrost (permanently frozen ground) is widespread and governs the soil temperature and moisture regime of a large proportion of the boreal forest. Yet permafrost temperatures are close to the freezing point throughout much of interior Alaska (Osterkamp and Romanovsky 1999), so only a slight warming of soils could greatly reduce the extent of permafrost. Low temperature and anaerobic soil conditions associated with permafrost-impeded drainage constrain decomposition rate, leading to thick layers of soil organic matter. Consequently, boreal soils account for about a third of the readily decomposable soil organic matter on Earth (McGuire et al. 1995). This represents a quantity of carbon similar to that in the atmosphere. Fire is another process that could rapidly return this undecomposed carbon from the organic layers of the soil to the atmosphere.