Understanding the main determinants of species coexistence across space
and time is a central question in ecology. However, ecologists still
know little of the scales and conditions at which biotic interactions
matter and how these interact with the environment to structure species
assemblages. Here we use recent theoretical developments to analyze
plant distribution and trait data across Europe and find that plant
height clustering is related to both evapotranspiration and gross
primary productivity. This clustering is a signal of interspecies
competition between plants, which is most evident in mid-latitude
ecoregions, where conditions for growth (reflected in actual
evapotranspiration rates and gross primary productivities) are optimal.
Away from this optimum, climate severity likely overrides the effect of
competition, or other interactions become increasingly important. Our
approach bridges the gap between modern coexistence theory and
large-scale species distribution data analysis.