Linking Tree Population Dynamics and Forest Ecosystem Processes

Summary

A new, empirically based, spatially explicit model (SORTIE) predicts that tree population dynamics in forests of southern New England are (1) nonequilibrial, (2) strongly dependent on species composition immediately following disturbance, and (3) highly spatially aggregated. The population dynamics predicted by SORTIE are the result of a clear set of physiological, morphological, and life-history traits of the individual tree species. However, those traits generally do not depend on or determine the species effects on productivity, hydrology, or nutrient cycling. As a result, idiosyncratic differences among tree species in traits such as litter quality predispose these forests to strong linkages between the relative abundance of tree species and spatial and temporal variation in forest ecosystem processes. It is clear that energetics and biogeochemistry place constraints on forest ecosystem processes, and that the rates of many ecosystem processes are strongly influenced by physical, environmental factors. However, in the absence of evidence of stronger control of tree population dynamics by ecosystem processes and physical factors, we conclude that the spatial and temporal dynamics of productivity, nutrient cycling, and hydrology in these forests will be largely driven by the interactions between microbes, plants, and animals—often acting in extremely local neighborhoods—that determine tree population dynamics. Thus, ecosystem dynamics in these forests should be characterized by the same nonequilibrial, spatially aggregated dynamics exhibited by tree population dynamics.