Abstract
Biodiversity and ecosystem functioning (BEF) research has progressed from the detection of relationships to elucidating their drivers and underlying mechanisms. In this context, replacing taxonomic predictors by trait-based measures of functional composition (FC)—bridging functions of species and of ecosystems—is a widely used approach. The inherent challenge of trait-based approaches is the multi-faceted, dynamic and hierarchical nature of trait influence: (i) traits may act via different facets of their distribution in a community, (ii) their influence may change over time and (iii) traits may influence processes at different levels of the natural hierarchy of organization. Here, we made use of the forest ecosystem model ‘LPJ-GUESS’ parametrized with empirical trait data, which creates output of individual performance, community assembly, stand-level states and processes. To address the three challenges, we resolved the dynamics of the top-level ecosystem function ‘annual biomass change’ hierarchically into its various component processes (growth, leaf and root turnover, recruitment and mortality) and states (stand structures, water stress) and traced the influence of different facets of FC along this hierarchy in a path analysis. We found an independent influence of functional richness, dissimilarity and identity on ecosystem states and processes and hence biomass change. Biodiversity effects were only positive during early succession and later turned negative. Unexpectedly, resource acquisition (growth, recruitment) and conservation (mortality, turnover) played an equally important role throughout the succession. These results add to a mechanistic understanding of biodiversity effects and place a caveat on simplistic approaches omitting hierarchical levels when analysing BEF relationships. They support the view that BEF relationships experience dramatic shifts over successional time that should be acknowledged in mechanistic theories.
Highlights
Wood production and carbon storage by forests are of primary concern among the ecosystem services provided by terrestrial ecosystems
We present a dynamic and hierarchical framework for analysing biodiversity and ecosystem functioning (BEF) relationships that copes with the inherent complexity of natural ecosystems
We found an increase of the biodiversity effect in annual biomass change’ (ABC) with increasing species richness and saturation was reached with a richness of six species, which is consistent with the findings of Zhang et al [41]
Summary
Wood production and carbon storage by forests are of primary concern among the ecosystem services provided by terrestrial ecosystems. Tree species richness is declining due to, for example, the expansion of plantations or deforestation [4,5]. With this dramatic loss of species diversity, it is important to know how and to what extent plant diversity matters for the functioning of terrestrial ecosystems, especially the essential services of productivity and carbon storage [6,7]. Significant and mostly positive effects of various facets of biodiversity on a wide range of ecosystem functions have been reported from grasslands experiments [7,9] and to some extent from forests [10,11]. Experiments are far fewer and still young, their results are restricted to the very early and transient stages of a succession (‘BIOTREE’, since 2004: Scherer-Lorenzen et al [12], ‘BEF China’, since 2009: Bruelheide et al [13], since 2001: Potvin et al [14])
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