Temporally-explicit models of fire and forest

Pollen and charcoal data from varved sediments of Lake Ahvenainen, southern Finland, were examined through ordination analyses to determine temporal g roupings of vegetation. The ordination 'continually' changed throughout the pollen profile, indicating nonequilibrium system dynamics. However, tempor al associations that were stationary existed during the history of vegetati on change at Lake Ahvenainen, and these temporal associations were nested i n a hierarchy. Weighted averaging regression and calibration were used to m odel the relationship between fire and vegetation within each temporal asso ciation. Fire was significantly related to the vegetation for nearly all te mporal associations. Community dynamics within temporal associations were e xamined with cross-correlation analysis. Taxa were correlated with fire occ urrence (charcoal fragments) within the temporal associations and classic s uccessional recovery was confirmed. In addition, two temporal associations showed evidence of chaotic behavior. The long-term pollen-charcoal analysis supported three theories of system dynamics: (1) nonequilibrium long-term dynamics, (2) hierarchical structuring of temporally stationary association s, and (3) chaotic dynamics in stationary associations. These theories are not necessarily contradictory, but are scale dependent.