Identifying the tree species compositions that maximize ecosystem functioning in European forests

1. Forest ecosystem functioning generally benefits from higher tree species richness, but within richness levels variation is typically large, mostly due to the contrasting performances of
communities with different compositions. Evidence-based understanding of composition effects
on forest productivity as well as on multiple other functions has large practical relevance,
because forest managers are more likely to be concerned with the selection of species that
maximize functioning rather than with diversity per se.
2. Here we used a dataset of thirty ecosystem functions measured in stands with different species
richness and composition in six European forest types. First, we quantified whether the
compositions that maximize annual aboveground wood production (productivity) generally also
fulfill the multiple other ecosystem functions (multifunctionality). Then, we quantified the species
identify effects and strength of interspecific interactions, to identify the “best” and “worst”
species composition for multifunctionality. Finally, we evaluated the real-world frequency of
occurrence of best and worst mixtures, using harmonized data from multiple national forest
inventories.
3. The most productive tree species combinations also tended to express relatively high
multifunctionality, although we found a relatively wide range of compositions with high or low
average multifunctionality for the same level of productivity. Monocultures were distributed
among the highest as well as the lowest performing compositions. The variation in functioning
between compositions was generally driven by differences in the performance of the component
species and, to a lesser extent, by particular interspecific interactions. Finally, we found that the
most frequent species compositions in inventory data were monospecific stands and that the
most common compositions showed below-average multifunctionality and productivity.
4. Synthesis and applications. While a management focus on productivity does not necessarily
trade-off against other ecosystem functions, it matters considerably which particular tree species
and combinations are promoted. These identity and composition effects are essential in thecontext of developing high-performing production systems, for instance in forestry and
agriculture, and deserve much more attention in the analysis and design of functional
biodiversity studies if the aim is to inform ecosystem management.