Forest community structure may be influenced by seedling density dependence, however, the effect is loosely coupled with population dynamics and diversity in the short term. In the long term the strength of conspecific density dependence may fluctuate over time because of seedling abundance, yet few long‐term studies exist. Based on 11 years of seedling census data and tree census data from a 25‐ha temperate forest plot in Northeast China, we used generalized linear mixed models to test the relative effects of local neighborhood density and abiotic factors on seedling density and seedling survival. Spatial point pattern analysis was used to determine if spatial patterns of saplings and juveniles, in relation to conspecific adults, were in accordance with patterns uncovered by conspecific negative density dependence at the seedling stage. Our long‐term results showed that seedling density was mainly positively affected by conspecific density, suggesting dispersal limitation of seedling development. The probability of seedling survival significantly decreased over 1 year with increasing conspecific density, indicating conspecific negative density dependence in seedling establishment. Although there was variation in conspecific negative density dependence at the seedling stage among species and across years, a dispersed pattern of conspecific saplings relative to conspecific adults at the local scale (<10 m) was observed in four of the 11 species examined. Overall, sapling spatial patterns were consistent with the impacts of conspecific density on seedling dynamics, which suggests that conspecific negative density dependence is persistent over the long term. From the long‐term perspective, conspecific density dependence is an important driver of species coexistence in temperate forests.

No abstract

& Key Message Deterministic processes drive functional and phylogenetic temporal changes of woody species in temperate forest, depending on successional stage and tree size classes. The dominant influential factors changed from abiotic (especially topographic factors) to biotic (e.g., basal area), with both increasing successional stage and tree size, suggesting that deterministic processes shifted from habitat filtering to biotic interactions. & Context Disentangling how deterministic and stochastic processes govern the temporal change of community composition is critical for understanding community assembly and predicting long-term ecosystem change. However, rare studies have examined the distinctive imprint of these two processes on functional and phylogenetic temporal changes of woody species in temperate forests. & Aims The objectives of this study are to detect (1) the relative importance of deterministic vs. stochastic process in driving the functional and phylogenetic temporal changes at different successional stages and tree size classes in temperate forests and (2) the relative influence of abiotic vs. biotic factors on temporal change. & Methods We analyzed 10 years of detailed species composition, phylogenetic information, and 14 functional traits from 66 woody species in young-growth (5-ha) and old-growth (25-ha) forest plots in Northeast China. We devised a null model approach to determine the relative importance of deterministic and stochastic processes in driving functional and phylogenetic temporal changes. Then, we investigated the influence of abiotic (soil and topography) and biotic (basal area, stem density, and species richness) factors on temporal change using boosted regression tree (BRT) models. All analyses were conducted for different tree sizes (all trees, small trees [diameter at breast height (DBH) < 10 cm], and large trees [DBH ≥ 10 cm]).