No abstract

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.

No abstract

Regeneration niches for tree seedlings are defined as possessing the biotic and abiotic requirements to successfully replace adults. However, two critical discrepancies obscure our understanding of the role of regeneration niches in forest community assembly: a weak association between seedling assemblages and environmental factors, and an uncoupling between seedling and adult‐tree assemblages. However, understory plants, which may interact with microenvironments and seedlings, may be a better spatial descriptor of regeneration habitats. To test this, the spatial variations of seedling assemblages in a montane cloud forest of Taiwan were analyzed in terms of their association with neighborhood assemblages of understory plants, the shrub layer, and overstory trees, as well as environmental variables. We found that the understory plant spatial structure contributed most in explaining spatial variations of the seedling assemblages (especially for widespread Lauraceae and patchy Fagaceae) and facilitated the identification of patches of different regeneration habitats for specific seedling assemblages. Moreover, among these regeneration patches, tall herbs affected seedling density and diversity differently. We found segregation between tall herbs and Lauraceae seedlings, indicating that tall herbs shape seedling assemblages and uncouple the association between seedling and adult stages. However, positive covariations between seedlings/tall herbs and between seedlings/adults were found for Fagaceae and Pentaphylacaceae in different regeneration patches, suggesting that positive, neighboring effects and dispersal limitation may cause the patchy distribution of seedling assemblages and affect their coupling with adults. Thus, the understory plant spatial structure shapes seedling assemblages and provides a better link to spatial associations with regeneration habitats.

In spite of high population density of Taiwan and rapid economic development, the evergr@n broad-leaved forests continue to cover abolt 32Vo of the Taiwan Island. The forests occur from sea level to about 2,500 m, and support a diverse flora and a spectrum of four major forest types. The evergreen broad-leaved forests of Taiwan occur from sea level to about 2,500 m. These forests are usually referred to as the lauro-fagaceous forests (Kudo & Sasaki, 1931). They show much variation in zonation patterns due to overlapping of the tropical and temperate zonation types (Ohsawa, 1993). Most of the forests in lowlands have been cleared for agriculture and industry and only a few modified remnants are left. However, in relatively undisturbed forests in the mountains, there are many lianas, eprphytes and fems and a great variety of trees and shrubs. The dominant tree species include evergreen members of Fagaceae, Lauraceae, Theaceae, Symplocaceae and other broad-leaved evergrcen species. The flora of Thiwan is relatively well known. The composition and distribution of plant communities are known only incompletely because of the complexity and divenity of the vegetation and the dfficulty of access in the mountain regions. The purpose of the present account is to compare and interpret the forest complexes of the evergreen broad-leaved forcsts in Taiwan. The second aim of this paper is to review the forest nranagement and conservation status for the past three