Recent studies on species coexistence suggest that density dependence is an important mechanism regulating plant populations. However, there have been few studies of density dependence conducted for more than one life-history stage or that control for habitat heterogeneity, which may influence spatial patterns of survival and mask density dependence. We explored the prevalence of density dependence across multiple life stages, and the effects of controlling for habitat heterogeneity, in a temperate forest in northeast China. We used generalized linear mixed-effects models to test for density-dependent mortality of seedlings and spatial point pattern analysis to detect density dependence for sapling-to-juvenile transitions. Conspecific neighbors had a negative effect on survival of plants in both life stages. At the seedling stage, we found a negative effect of conspecific seedling neighbors on survival when analyzing all species combined. However, in species-level analyses, only 2 of 11 focal species were negatively impacted by conspecific neighbors, indicating wide variation among species in the strength of density dependence. Controlling for habitat heterogeneity did not alter our findings of density dependence at the seedling stage. For the sapling-to-juvenile transition stage, 11 of 15 focal species showed patterns of local scale (<10 m) conspecific thinning, consistent with negative density dependence. The results varied depending on whether we controlled for habitat heterogeneity, indicating that a failure to account for habitat heterogeneity can obscure patterns of density dependence. We conclude that density dependence may promote tree species coexistence by acting across multiple life-history stages in this temperate forest.Electronic supplementary materialThe online version of this article (doi:10.1007/s00442-012-2481-y) contains supplementary material, which is available to authorized users.

Climate is widely recognised as an important determinant of the latitudinal diversity gradient. However, most existing studies make no distinction between direct and indirect effects of climate, which substantially hinders our understanding of how climate constrains biodiversity globally. Using data from 35 large forest plots, we test hypothesised relationships amongst climate, topography, forest structural attributes (stem abundance, tree size variation and stand basal area) and tree species richness to better understand drivers of latitudinal tree diversity patterns. Climate influences tree richness both directly, with more species in warm, moist, aseasonal climates and indirectly, with more species at higher stem abundance. These results imply direct limitation of species diversity by climatic stress and more rapid (co-)evolution and narrower niche partitioning in warm climates. They also support the idea that increased numbers of individuals associated with high primary productivity are partitioned to support a greater number of species. LetterClimate and the latitudinal tree diversity gradient 247 Figure 4 The effects of forest structural attributes on tree diversity derived from the within-forest plot structural equation modelling analyses. Panels a, b and c at the scale of 20 m 9 20 m, and panels d, e and f at the scale of 50 m 9 50 m. The effect of stem abundance on tree species richness showed a significant latitudinal trend at the scale of 20 m 9 20 m (panel b; P < 0.01, R 2 = 0.27). Standardised path coefficients AE 1 SE are shown; SE's are smaller than the size of the symbol for some forest plots. Colours indicate increasing absolute latitude from pink to turquoise.

Abstract. The main processes underlying the generation and maintenance of biodiversity include both local factors such as competition and abiotic filtering and regional forces such as paleoclimate, speciation and dispersal. While the effects of regional and local drivers on species diversity are increasingly studied, their relative importance for other aspects of diversity, notably phylogenetic and functional diversity is so far little studied. Here, we link data from large Chinese forest plots to data on current and Last Glacial Maximum (LGM) climate as well as local disturbance regimes to study their relative roles in determining woody plant phylogenetic and functional diversity in this important hotspot for woody plant diversity. Local disturbance was the best predictor of functional diversity as represented by maximum canopy height (H max ), probably reflecting the dominant role of competition for light in determining the forest H max structure. In contrast, the LGM-present anomaly in temperature was the factor with the strongest explanatory power for phylogenetic diversity, with modern climate also important. Hence, local contemporary and regional historical factors have highly contrasting importance for the geographic patterns of the functional (as represented by variation in maximum canopy height) and phylogenetic aspects of Chinese forest's woody plant diversity. Importantly, contemporary factors are of overriding importance for functional diversity, while paleoclimate has left a strong signature in the phylogenetic diversity patterns.

Aims Patterns of spatial community dissimilarity have inspired a large body of theory in ecology and biogeography. Yet key gaps remain in our understanding of the local‐scale ecological processes underlying species replacement and species nestedness, the two fundamental components of spatial community dissimilarity. Here, we examined the relative influence of dispersal limitation, habitat filtering and interspecific species interactions on local‐scale patterns of the replacement and nestedness components in eight stem‐mapped temperate forest mega‐plots at different ontogenetic stages (large versus small trees). Location Eight large (20–35 ha), fully mapped temperate forest plots in northern China and northern U.S.A. Time period 2004–2016. Major taxa studied Woody plants. Methods We combined decomposition of community dissimilarity (based on the Ružička index) and spatial point‐pattern analysis to compare the spatial (i.e., distance‐dependent) replacement and nestedness components of each plot with that expected under five spatially explicit null models representing different hypotheses on community‐assembly mechanisms. Results Our analyses revealed complex results. In all eight forests, spatial community dissimilarity was best explained by species replacement among local tree assemblages and by a null model based on dispersal limitation. In contrast, spatial nestedness for large and small trees was best explained by random placement and habitat filtering, respectively, in addition to dispersal limitation. However, interspecific interactions did not contribute to local replacement and nestedness. Main conclusions Species replacement is the predominant process accounting for spatial community dissimilarity in these temperate forests and caused largely by local‐scale species clustering associated with dispersal limitation. Nestedness, in contrast, is less prevalent and primarily associated with larger variation in local species richness as caused by spatial richness gradients or ‘hotspots’ of local species richness. The novel use of replacement and nestedness measures in point pattern analysis is a promising approach to assess local‐scale biodiversity patterns and to explore their causes.

1. Many leaf traits strongly vary with tree size and environmental factors, but the importance of these factors to intraspecific variations of leaf traits in forest trees has rarely been simultaneously evaluated.2. We measured needle longevity and specific leaf area (SLA) and nitrogen (N) content of every needle age (0-to 4-year old) for 65 individuals with 0.3-100 cm diameter at breast height (DBH) for an evergreen coniferous species, Pinus koraiensis Sieb. et Zucc., in Northeast China. We simultaneously evaluated the effects of tree size (DBH or tree height) and environment factors (light intensity, soil N content and water availability) on the needle longevity, SLA, foliage N content as well as the slopes of regressions of SLA and foliage N content against needle age.3. All of the studied leaf traits and slopes of regressions of SLA and foliage N content against needle age were significantly related to tree size. Tree height had a greater impact on SLA and area-based leaf N content (N area ), whereas DBH was more important for needle longevity and mass-based leaf N content (N mass ). The environment variables, light intensity, soil N content and water availability, were rather minor factors for trait variations compared with tree size. Significant influence of light intensity was found only on needle longevity, and soil N and water availability had no effects on the leaf traits.4. Our study clearly showed that tree size is an important driver of intraspecific variations in the key leaf traits of P. koraiensis in a natural forest. We also emphasize the importance of DBH or tree height varies depending on leaf traits, suggesting various mechanisms of size effects on the intraspecific variations in leaf traits. We suggest that ecological significance of leaf trait variations needs reconsideration incorporating tree size effect.