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AimGlobal forests and their structural and functional features are shaped by many mechanisms that impact tree vital rates. Although many studies have tried to quantify how specific mechanisms influence vital rates, their relative importance among forests remains unclear. We aimed to assess the patterns of variation in vital rates among species and in space and time across forests to understand and provide a baseline for expectations of the relative importance of the different mechanisms in different contexts.Location21 forest plots worldwide.Time period1981-2021Major taxa studiedWoody plantsMethodsWe developed a conceptual and statistical framework (variance partitioning of multilevel models) that attributes the variability in growth, mortality, and recruitment to variation in species, space, and time, and their interactions, which we refer to asorganising principles(OPs). We applied it to data from 21 forest plots covering more than 2.9 million trees of approximately 6,500 species.ResultsDifferences among species, thespeciesOP, were a major source of variability in tree vital rates, explaining 28-33% of demographic variance alone, and in interaction withspace14-17%, totalling 40-43%. Models with small spatial grain sizes (quadrats at 5 × 5 m) retained most of the spatial OP, but a large proportion of variance remained unexplained (31-55%). The average variability among species declined with species richness across forests, indicating that diverse forests featured smaller interspecific differences in vital rates.Main conclusionsDecomposing variance in vital rates into the proposed OPs showed that taxonomy is crucial to predictions and understanding of tree demography. Our framework has a high potential for identifying the structuring mechanisms of global forest dynamics as it highlights the most promising avenues for future research both in terms of understanding the relative contributions of mechanisms to forest demography and diversity and for improving projections of forest ecosystems.

The relative abundance patterns of tropical trees have been of interest since the expeditions of Alfred Russel Wallace, but little is known about how differences in relative abundance relate to reproductive patterns. Flowering is resource-dependent and fitness differences as well as differences in the quality of the abiotic and biotic neighborhood may contribute to the variation in reproductive status responsible for population-level flowering patterns. This variation determines the density and distance between flowering conspecifics and may alter relative abundance extremes among species during reproduction, factors known to influence pollination success. We collected flowering status data for a guild of twenty-three co-occurring tree species that flower in the understory of the Korup Forest Dynamics Plot in Cameroon. We examined how the occurrence and location of reproductive events were related to spatial patterns of adult abundance, focal tree size, neighborhood crowding, and habitat, while accounting for the influence of shared ancestry. Across species, the probability of flowering was higher for individuals of rarer species and for larger individuals but was unrelated to neighborhood crowding or habitat differences. Relative abundance extremes were reduced when only flowering individuals were considered, leading to a negative relationship between plot abundance and flowering probability at the species level that was not structured by shared ancestry. Spatially, flowering conspecifics tended to be overdispersed relative to all adult conspecifics. Rare species are predicted to suffer Allee effects or reduced fitness due to the difficulty of finding mates at low densities and frequencies. Here, however, rare species appear to maximize the size of their mate pool, compared to abundant species. If this partial ‘leveling of the playing field’ during reproduction is typical, it has consequences for our understanding of biodiversity maintenance and species coexistence in tropical forests.