Background/Question/Methods Studies of exotic invasion ecology have become dissociated from the rest of ecology, inhibiting the application of general ecological principles to the control of exotic species. To help unify invasion and general colonization theory, we used historic and modern plant community data from 82 upland forest stands in southern Wisconsin to evaluate how initial stand characteristics predicted patterns of native and non-native colonization into the understory.  We first tested the diversity resistance hypothesis and then broaden the debate on the influence of initial diversity on colonization by also examining the influence of both within and between stand heterogeneity, as well as estimates of empty niches derived from Beals smoothing and nested subset analyses. We then added variables to represent abiotic and landcover conditions. This allowed us to apply a propagule pressure, abiotic, and biotic (PAB) framework and partial Mantel tests to evaluate the relative importance of each group factors in accounting for historical patterns of native and exotic colonization.  Finally, we examined how the life-history traits affected how colonizing species respond to site factors in this PAB framework.  
Results/Conclusions Initial measures of richness give some support for the biotic resistance hypothesis though estimates of heterogeneity and the number of empty niches further improve our ability to predict exotic (but not native) colonizations.  In the unified PAB framework, propagule pressure explained similar levels of variation in both native and exotic colonization. Initial biotic conditions more effectively predicted exotic colonization while abiotic conditions more effectively predicted native colonization.  The functional traits of native colonizing species also affected their patterns of colonization. Native colonizers of stands in fragmented landscapes generally had life history characteristics similar to those of exotic colonizers (short generation times and heavy investment in small dispersed fruits).  These results suggest that more complete models provide insights into exotic species colonization dynamics and that functional traits provide a key for understanding patterns of exotic and native plant colonization.