The consequences of global environmental changes include altered community structure and associated ecosystem processes and services (Balvanera et al. 2006; Diaz et al. 2007). Recent studies have underlined metrics beyond species richness to assess the relationship between biodiversity and environmental changes (Mayfield et al. 2005; Moretti et al. 2009; Villéger et al. 2010). The emerging perception is that conservation and restoration practices can be improved by considering the consequences of management activities for both taxonomic and functional trait diversity (Devictor et al. 2010; Mayfield et al. 2010), functional traits being the biological attributes of organisms that influence fitness and that shape ecosystem properties (McGill et al. 2006; Diaz et al. 2007; Suding & Goldstein 2008; Cadotte, Carscadden & Mirotchnick 2011).
The recent expansion in the use of functional traits to study basic and applied questions in ecology has benefited from many methodological advances, particularly for the measure of functional diversity and its comparison with standard indices of taxonomic diversity (Petchey & Gaston 2006; Villéger, Mason & Mouillot 2008; Mouchet et al. 2010). Functional diversity metrics complement taxonomic metrics (Petchey & Gaston 2002; de Bello et al. 2010) and are particularly sensitive in the face of species extinctions (Devictor et al. 2010). However, there is still no consensus about the relationships between functional diversity metrics and key ecosystem properties and processes (Mayfield et al. 2010; Cadotte, Carscadden & Mirotchnick 2011). The performance of functional diversity metrics remains excessively dependent on the a priori choice of traits (Lavorel & Garnier 2002; Lavorel et al. 2008; Mouchet et al. 2010). A comprehensive analysis of community responses to environmental change should therefore include not only measures of functional diversity but also a discussion of functional composition (Moretti et al. 2009).
Tropical forests represent a major reservoir of global biodiversity, with an estimated 15 000 tree species occurring in the Amazon region alone (Hubbell et al. 2008). Large tracts of forests are at risk from land use change, with more than a quarter of tropical forest area in South America currently under threat (Asner, Loarie & Heyder 2010). Recent attention has advanced our focus beyond deforestation to forest degradation (Foley et al. 2007; Putz & Redford 2008), especially logging, which impacts at least 15 000 km2 of Amazonian forests per year (Asner et al. 2005). Several authors have argued that the lack of decrease in tree species diversity they observed in selectively logged forests implies that logging activities are compatible with biodiversity conservation (Plumptre 1996; Cannon, Peart & Leighton 1998; Kariuki et al. 2006; Berry et al. 2008). These findings merit further evaluation given the ongoing development of metrics of functional diversity. To our knowledge no study has assessed how selective logging impacts both taxonomic and functional composition of tropical tree communities.
Here we examine the long-term impacts of selective logging on a tropical forest tree community via a comprehensive analysis of changes in taxonomic and functional diversity, evenness and composition. We inventoried 4140 stems representing 473 species that recruited into logging gaps and into adjacent undisturbed forest in permanent plots that were monitored for 20 years after logging, and we integrated one of the largest functional trait databases for tropical trees to address the following questions: (i) How does logging disturbance affect tropical tree community structure, in terms of diversity, evenness and composition? (ii) How do the taxonomic and functional responses of tree communities to logging differ? (iii) What guidelines can we give to timber harvesters to improve biodiversity conservation in selectively logged forests?
Our results underline the need to consider not only taxonomy and functional traits, but also measures of both diversity and composition, when describing the impacts of global changes on community structure.