Details That Matter: The Spatial Distribution of Individual Trees Maintains Forest Ecosystem Function

This paper shows that the processes controlling tree-scale spatial heterogeneity in forests have large effects on system-level properties such as standing crop, and on community-level properties such as successional species turnover. A mean field version of the forest simulation model SORTIE is developed in which horizontal spatial heterogeneity is eliminated while vertical structure is retained. The mean-field model maintains only approximately one half the standing crop and looses successional diversity approximately twice as fast as the full spatial model. Data from natural stands support the spatial model. A partial differential equation limit of the mean-field simulator is also derived. The results are set in the context of ongoing efforts to develop models intended to predict the biosphere's response to global change. The importance of processes governing fine-scale spatial heterogeneity implies that biospheric models will agree with nature only if they are phenomenological (e.g. fitted to data) at large scale, or if spatial scaling rules are discovered that allow one to derive system-level properties from individual-level processes.