Early View (EV): 1-EV Predicting current and future spatial community patterns of plant functional traits Anne Dubuis, Leila Rossier, Julien Pottier, Loïc Pellissier, Pascal Vittoz and Antoine Guisan A. Dubuis (anne.dubuis@unil.ch), L. Rossier, J. Pottier, L. Pellissier, P. Vittozand and A. Guisan, Dept of Ecology and Evolution, Univ. of Lausanne, Biophore building, CH-1015 Lausanne, Switzerland. JP also at: INRA, Grassland Ecosystem Research Unit (UREP), 5 Chemin de Beaulieu, FR-63100 Clermont-Ferrand, France. AG also at: Faculty of Geoscience and the Environment, Univ. of Lausanne, CH-1015 Lausanne, Switzerland. Community-level patterns of functional traits relate to community assembly and ecosystem functioning. By modelling the changes of diferent indices describing such patterns – trait means, extremes and diversity in communities – as a function of abiotic gradients, we could understand their drivers and build projections of the impact of global change on the functional components of biodiversity. We used fve plant functional traits (vegetative height, specifc leaf area, leaf dry matter con- tent, leaf nitrogen content and seed mass) and non-woody vegetation plots to model several indices depicting community- level patterns of functional traits from a set of abiotic environmental variables (topographic, climatic and edaphic) over contrasting environmental conditions in a mountainous landscape. We performed a variation partitioning analysis to assess the relative importance of these variables for predicting patterns of functional traits in communities, and projected the best models under several climate change scenarios to examine future potential changes in vegetation functional properties. Not all indices of trait patterns within communities could be modelled with the same level of accuracy: the models for mean and extreme values of functional traits provided substantially better predictive accuracy than the models calibrated for diversity indices. Topographic and climatic factors were more important predictors of functional trait patterns within com- munities than edaphic predictors. Overall, model projections forecast an increase in mean vegetation height and in mean specifc leaf area following climate warming. Tis trend was important at mid elevation particularly between 1000 and 2000 m a.s.l. With this study we showed that topographic, climatic and edaphic variables can successfully model descrip- tors of community-level patterns of plant functional traits such as mean and extreme trait values. However, which factors determine the diversity of functional traits in plant communities remains unclear and requires more investigations. Functional traits provides better generality in understanding and predicting the formation and structure of plant commu- nities as well as ecosystem functions than approaches based on species identity alone (Keddy 1992a, b, Diaz and Cabido 2001, Hooper et al. 2005, McGill et al. 2006). Functional traits are defned as any morphological, physiological or phenological features measurable at the individual level that afect individual performances (Violle et al. 2007). By con- trasting trait values for individual species to the ones aggre- gated at the community level (Diaz et al. 2007), functional traits are supposed to enable the refnement of predictions of communities composition along environmental gradients (Shipley et al. 2006, Douma et al. 2012), but also to bring more understanding in the modifcation of ecosystem func- tioning (Lavorel and Garnier 2002, de Bello et al. 2010, Van Bodegom et al. 2012). Refned predictions of communities in space as well as a better insight in the evolution of ecosys- tem functioning are highly desirable in the current context of global changes (Nogues-Bravo and Rahbek 2011). Yet, few studies have investigated whether measures of aggregated traits at the community level can be modelled and predicted in space (Pellissier et al. 2010b, Sonnier et al. 2010b). Tere are three main expressions of the distribution of trait values at the community level, which consider the mean (or median), the extremes in trait values or their diversity. First, the mean of the trait values weighted by the respec- tive abundance of each species (community weighted mean; CWM; Garnier et al. 2004) has been used to functionally characterize plant communities in diferent environments (Cornwell and Ackerly 2009, Venn et al. 2011) so as to ulti- mately better understand community assembly (Ackerly and Cornwell 2007). When used to study ecosystem functions, CWM refects the mass ratio hypothesis (Grime 1998), which proposes that the dominant trait value in the com- munity has the greatest impact on ecosystem functioning. Second, extremes in trait values are simply measured by taking either minimum/maximum or some quantiles (e.g. 5th and 95th) of the distribution of trait values in the com- munity. Tese values may refect interesting fltering efects (Keddy 1992a, b), showing which limiting trait value allows a species to be included in a community in a given environ- ment. To our knowledge, extreme values of functional traits have not yet been investigated in this context. Tirdly, the diversity of trait values (or functional diversity) quantifes Ecography 36: 001–011, 2013 doi: 10.1111/j.1600-0587.2013.00237.x © 2013 Te Authors. Ecography © 2013 Nordic Society Oikos Subject Editor: Jens-Christian Svenning. Accepted 12 March 2013