The relative contribution of external vs. internal aggregation mechanisms for determining community structure and its manifestations has been the subject of a continuous debate, but few attempts have been made to examine their single and joint effects in a compound process model. In this study, we tested four a priori hypotheses on the relative importance of habitat heterogeneity and dispersal limitation on the species area relationship and distance decay curve in two 25ha plots of temperate forests in the CBS (China) and National Forest in Wisconsin. Model selection favored the hypothesis that integrated habitat heterogeneity and internal clustering. For the CBS, which shows weak topographic structuring, models were consistent with data only if soil factors were included into assessment of habitat heterogeneity. At the Wabikon we could not test soil variables, but inclusion of topographic variables substantially improved the fit of the distance decay curve. In general, the results of the SAR agreed with those of the distance decay curve, but the latter was sensitive to positive habitat mediated species associations. The SAR distinguished among competing hypotheses for the community of large trees at CBS, where species exhibited only weak clustering. This result adds to our understanding of the ecological processes underlying the spatial diversity structure in natural forest communities.