An experimental framework to identify community functional components driving ecosystem processes and services delivery

Abstract

Summary1. There is a growing consensus that the distribution of species trait values in a community can greatly determine ecosystem processes and services delivery. Two distinct components of community trait composition are hypothesized to chiefly affect ecosystem processes: (i) the average trait value of the species, quantified by community-weighted mean trait values (CWM; related to the mass ratio hypothesis) and (ii) the degree to which trait values differ between species in a community, quantified by different indices of functional diversity (FD; related to non-additive community effects). The uncertainty on the relative effect of these two components is stimulating an increasing number of empirical studies testing their effects on ecosystem processes and services delivery. 2. We suggest, however, that the interdependence between CWM and FD poses a challenge on disentangling their relative importance. We present a framework that allows designing experiments to decouple and assess the effects of these two community functional components on ecosystem processes and services. To illustrate the framework, we focused on leaf litter decomposition, as this is an essential process related to important ecosystem services. Using simulations, we applied the framework for plant leaf litter traits (litter nitrogen and phenolic content) that are related to litter decomposition. 3. CWM and FD generally showed a hump-shaped relationship (i.e. at more extreme CWM values, communities can have only low FD values). Within this relationship, we showed that it is possible to select quasi-orthogonal combinations of CWM and FD that can be treated statistically. Within these orthogonal CWM and FD combinations, it is also possible to select species assemblages controlling for other community parameters, such as total biomass, total density and species richness. 4. Synthesis. The framework provides a novel approach for designing experiments to decouple the effects of CWM and FD of communities on ecosystem processes, which otherwise cannot be easily disentangled. To apply the framework and design proper experimental layouts, it is essential to have a priori knowledge of the key traits by which species affect ecosystem processes and service delivery.

Going Back to Basics: Importance of Ecophysiology when Choosing Functional Traits for Studying Communities and Ecosystems

“…If response and effect traits overlap or correlate to each other, directional changes in community composition due to environmental filtering is expected to have strong consequences for ecosystem processes (Suding et al 2008;Webb et al 2010). Second, different aspects of community trait composition (i.e., the distribution of trait values of species in a community) can affect ecosystem processes (de Bello et al 2010;Dias et al 2013a). Ecosystem processes and properties are mainly determined by the mean effect trait value of the species present in the community, weighted by their relative abundance (the so-called community-weighted mean trait value -CWM; Garnier et al (2004)).…”

“…Alternatively, functional diversity (the degree of dissimilarity in trait values between coexisting species -see Villéger et al (2008)) promotes non-additive effects on ecosystem processes, that is, effects not predictable from singlespecies results due to antagonistic or synergistic interactions among species (Heemsbergen et al 2004). The prevalence of each of these two aspects on ecosystem functioning is likely to depend on the ecosystem process of interest (Mouillot et al 2011;Dias et al 2013a).…”

“…Striking progress has been made on conceptual (Lavorel & Garnier 2002;Webb et al 2010) and methodological (Cornelissen et al 2003;Villéger et al 2008;Dias et al 2013a) aspects linking species traits to community and ecosystem responses. However, the first step for using a trait-based approach deserves much more attention.…”

A Review of Strong Evidence for the Effect of Functional Dominance on Carbon Stocks in Natural Forest Ecosystems

“…Several earlier studies conducted in different terrestrial ecosystems have suggested that plant functional trait effects may primarily be attributed to the mass ratio hypothesis (CWM effects) rather than to divergence effects (FD effects) (Mokany et al, 2008;Laughlin, 2011;Lavorel et al, 2011), sometimes due to correlation between these two FTD indices (Dias et al, 2013). Still, most recent studies have also strongly supported the mass ratio hypothesis, while poorly or no support for the niche complementarity hypothesis regarding FTD-C stocks relationship in natural forest ecosystems.…”

Integrating ecological engineering and ecological intensification from management practices to ecosystem services into a generic framework: a review

“…Ultimately, these ecosystem functions are the foundation of ecosystem services (Costanza et al 1997;Días et al 2013) through the integration of direct effects and indirect processes in the food web, which is the third interaction within the proposed framework. They can control the level of delivery of a target ecosystem service (Lange et al 2015).…”