  Understanding the main determinants of species coexistence across space and
time is a central question in ecology. However, ecologists still know little
about the scales and conditions at which biotic interactions matter and how
these interact with the environment to structure species assemblages. Here we
use recent theory 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 species-rich competition theories and large-scale species
distribution data analysis.
