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Aim The relative contribution of community functional diversity and composition
to ecosystem functioning is a critical question in ecology in order to enable better
predictions of how ecosystems may respond to a changing climate.However, there is
little consensus about which modes of functional biodiversity are most important
for tree growth at large spatial scales. Here we assessed the relative importance of
climate, functional diversity and functional identity (i.e. the communitymeanvalues
of four key functional traits) for tree growth across the European continent, spanning
the northern boreal to the southern Mediterranean forests.
Location Finland, Germany, Sweden, Spain and Wallonia (Belgium).
Methods Using data from five European national forest inventories we applied a
hierarchical linear model to estimate the sensitivity of tree growth to changes in
climate, functional diversity and functional identity along a latitudinal gradient.
Results Functional diversity was weakly related to tree growth in the temperate
and boreal regions and more strongly in the Mediterranean region. In the temperate
region, where climate was the most important predictor, functional diversity
and identity had a similar importance for tree growth. Functional identity was
strongest at the latitudinal extremes of the continent, largely driven by strong
changes in the importance of maximum height along the latitudinal gradient.
Main conclusions Functional diversity is an important driver of tree growth in
the Mediterranean region, providing evidence that niche complementarity may be
more important for tree growth in water-limited forests. The strong influence of
functional identity at the latitudinal extremes indicates the importance of a particular
trait composition for tree growth in harsh climates. Furthermore, we speculate
that this functional identity signal may reflect a trait-based differentiation of
successional stages rather than abiotic filtering due to water or energy limitation.
