Summary1. Studying the spatial pattern of plants may provide significant insights into processes and mechanisms that maintain species richness. We used data from a fully mapped 25-ha temperate forest plot at Changbaishan (CBS), north-eastern China, to conduct a community-wide assessment of the type and frequency of intra-and interspecific spatial association patterns. We analysed complex scale effects in the patterning of large trees of 15 common species. First, we tested for overall spatial patterning at 6, 30 and 50 m neighbourhoods and classified the types of bivariate association patterns at these spatial scales (analysis 1). We then explored small-scale (0-20 m) association patterns conditioning on the larger-scale pattern (analysis 2) and tested for positive large-scale (50-250 m) association patterns (analysis 3). 2. Analysis 1 provided ample evidence for non-random spatial patterning, and the type and frequency of spatial association patterns changed with scale. Trees of most species pairs co-occurred less than expected by chance and positive associations were rare in local neighbourhoods. Analysis 2 revealed a separation of scales in which significant small-scale interactions faded away at distances of 10-15 m. One third of all species pairs showed significant and mostly negative bivariate small-scale association, which occurred more often than expected by chance between species sharing attributes such as family, fruit type and habitat association. This suggests the occurrence of competitive interactions. Analysis 3 showed that only 8% of all species pairs co-occurred at large scales. 3. Comparison of our results with an analogous study conducted in the species-rich tropical forest at Sinharaja, Sri Lanka, revealed several structural similarities including the dominance of segregation and partial overlap in the overall patterning (analysis 1) and the separation of scales (analysis 2). However, species pairs at CBS showed considerably more significant negative small-scale associations (31% vs. 6% at Sinharaja). 4. Synthesis. The techniques presented here allow for a detailed analysis of the complex spatial associations in species-rich forests and have the potential to reveal indicative patterns that may allow researchers to discriminate among competing hypotheses of community assemblage and dynamics. However, this will require comparative studies involving a large number of plots.

SignificanceA focus in ecology is understanding the processes that govern ecosystem productivity and biodiversity. A multitude of co-occurring biological mechanisms shape these properties in plant communities, but the relative importance of specific processes remains ambiguous, such as competition among individuals and species for resources (bottom-up regulation) and the role of herbivory in controlling plant populations (top-down regulation). In this global synthesis of herbivore impacts on terrestrial plants, we find strong evidence that herbivores regulate most plant communities, but their positive effects on diversity may be contingent on a subset of animals and specific habitats. We conclude that the strength of top-down regulation in terrestrial ecosystems appears more variable and context-dependent than in aquatic systems.

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