Fine-scale tree spatial patterns are shaped by dispersal limitation which correlates with functional traits in a natural temperate forest

Questions Studying the spatial distribution of tree species is fundamental to understanding the ecological processes governing forest dynamics. Habitat filtering and dispersal limitation are two key processes in the emergence of intraspecific aggregation in natural forest communities. The contributions of these ecological processes vary among species, communities, ontogenetic stages (i.e. juveniles and adults) and spatial scales. In this study, we investigated the ecological processes underlying species spatial distributions in two ontogenetic stages and determined how these processes are linked to species functional traits. Location A naturally established 2.4-ha temperate forest located on a limestone hill in SW Belgium. Methods Trees >= 1.3 m were exhaustively censused and mapped, and environmental variables and functional traits were collected. We applied spatial point pattern modelling to explore the processes underlying species distributions. First, point process models simulating complete spatial randomness, habitat filtering and non-habitat clustering processes were fitted to observed species point patterns. The analyses were conducted for juveniles and adults both separately and together. The most parsimonious model for each species/ontogenetic stage was selected based on three summary statistics. Secondly, we investigated the links between functional traits and the parameters of the spatial models. Results (a) Dispersal limitation plays a central role in the formation of intraspecific aggregation in this forest, alone or in combination with habitat filtering. (b) Distributions of juveniles are less influenced by habitat filtering than distributions of adults. (c) Dispersal differ substantially among species and interspecific differences in clustering characteristics are explained by seed mass, wood density and maximum height. Conclusions Dispersal limitation can be of major importance in shaping temperate forests. Coupling spatial point pattern modelling and functional traits is an efficient way to understand mechanisms of species assemblages at fine spatial scales in temperate forests.