Understanding processes underlying spatial distribution of tree species is fundamental to studying species coexistence and diversity. This study modeled point patterns of tree distribution, expressed by Cartesian coordinates of individual trees within a mapped forest stand, for the purpose of identifying processes that may generate spatial patterns of tree communities. We used four primary point pattern processes (homogeneous Poisson process, inhomogeneous Poisson process, homogeneous Thomas process, and inhomogeneous Thomas process) to model tree distribution in two stem-mapped forests in Taiwan, Republic of China. These four models simulate spatial processes of habitat association and seed dispersal, allowing us to evaluate the potential contribution of habitat heterogeneity and dispersal limitation to the formation of spatial patterns of tree species. The results showed that the inhomogeneous Thomas process was the best fit model and described most of the species studied, suggesting that spatial patterns of tree species might be formed by the joint effects of habitat associations and dispersal limitation. The homogeneous Thomas process that models the effect of dispersal limitation was the second best model. We also found that the best fit models could be predicted by species attributes, including species abundance and dispersal mode. The significant traits, however, differed between the two study plots and demonstrated site-specific patterns. This study indicated that the interactive operation of niche-based (habitat heterogeneity) and neutral-based (dispersal limitation) may be important in generating spatial patterns of tree species in forest communities.

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Questions:Quantifying tree species persistence through recurrent disturbances is of crucial importance for understanding forest dynamics in typhoon-prone regions.We ask the following: (a) What are the major determinants of dominant tree survival in frequently typhoon-disturbed forests? (b) Are survival determinants different between small and large trees?Location: A subtropical old-growth forest located in Fushan, Taiwan (24°45′34″N, 121°33′58″E), with frequent typhoon disturbances.Methods: Data were from three consecutive censuses of a 25-ha permanent forest plot that censused trees ≥1 cm in diameter every five years. The survival of three dominant tree species was modeled using generalized additive model and boosted trees with abiotic and biotic predictors. We evaluated model performance using validation data obtained from the two available census intervals.Results: Model validations showed that multi-stemming and tree size enhanced the survival of large and small trees, respectively. For the most dominant species, multi-stemming had a consistently positive effect on survival irrespective of diameter classes. Abiotic factors and conspecific density had little effect on tree survival. Furthermore, evaluating model performance based on the data used in the model construction (i.e., training data) overestimated the predictive ability of survival models. Conclusions:We showed that the survival determinants for the three most dominant species at Fushan changed from tree size for small trees to multi-stemming for large trees. The results suggest that the dominant species in this frequently typhoon-disturbed forest have the stature and architectural traits to persist, and thereby maintain their dominance and shape the forest physiognomy. Our approach illustrates how datasets from different census periods can be used in model validation to better assess model performance. K E Y W O R D Sdevelopmental change, Fushan Forest Dynamics Plot, life history strategy, mortality, multistemming, sprouting, subtropical forest, survival, tree size, typhoon disturbance 430 |