6 . Boreal Forest

The boreal forest biome occupies 13 x I06km1. It comprises approximately 25% of the world's forest land (Olson et al. 1983; Apps et al. 1993) and includes 2.6 x 106km1 of peatlands (Gorham 1991). Changes in the extent or functioning of the boreal forest wuld substantially modify global climate through (1) release of its large stocks of soil carbon (Post et al. Boreal forests have also been implicated as the "missing sink" for atmospheric carbon dioxide (Ciais et al. 1995). For these reasons, there has been considerable interest and speculation about future changes in the extent, structure , and functioning of the boreal forest. The functioning of the boreal forest is more tightly tied to its species composition than to climate. For example, in Alaskan white spruce forests there is virtually no change in soil carbon across the entire latitudinal range of boreal forest (July mean temperature from 10 to lS°C) (Michaelson et al. 1996). whereas there is a greater than twofold range in soil carbon between conifer and hardwood stands on north and south aspects of the same hill (Van Cleve et al. 1983), due largely to differences in the effects of different plant species on soil temperature and nutrient cycling (Flanagan and Van