Ecosystem Dynamics

In keeping with its position between much warmer climate of the temperate zone and colder climate of the tundra, the boreal forest's indices of production are intermediate between those two ecosystem types. Annual net primary production in the boreal forest has been estimated at 7.5tha—1 yr—1 (range 4-20). This compares with 11.5 tha—1 yr—1 for temperate forest and 1.5tha—1 yr—1 for tundra ecosystems. Mean boreal forest litterfall is estimated to be 7.5tha— yr— compared with 11.5 and 1.5tha— yr— for the temperature forest and tundra, respectively. Because low temperatures slow decomposition, the rate of litterfall decomposition in the boreal forest, 0.21 tha~ yr~ , is also intermediate between 0.77 and 0.03 tha-1 yr-1 for the temperate forest and tundra. This means that it takes roughly 3 x (1/0.21) = 14 years for 95% of a pulse of litter to decompose.

Fire is an inherent factor in the ecosystem dynamics of the boreal forest. Lightning-caused fires occur on a given area at intervals of 20-100 years in drier areas to 200+ years in wetter areas such as floodplains. Because nutrients tend to be tied up in slowly decomposing organic matter, fire may be important for maintaining tree growth by releasing pulses of nutrients periodically. Many taiga plant species have adaptations to fires, such as serotinous cones and early sexual maturity of some conifers, and resprouting capacity of hardwood trees and many herbs and shrubs. Fires also reset the successional cycle, allowing shade-intolerant species like birch and aspen to invade.

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