The promise of "trait-based" plant ecology is one of generalized prediction across organizational and spatial scales, independent of taxonomy. This promise is a major reason for the increased popularity of this approach. Here, we argue that some important foundational assumptions of trait-based ecology have not received sufficient empirical evaluation. We identify three such assumptions and, where possible, suggest methods of improvement: (i) traits are functional to the degree that they determine individual fitness, (ii) intraspecific variation in functional traits can be largely ignored, and (iii) functional traits show general predictive relationships to measurable environmental gradients.

Département de Biologie Université de Sherbrooke Sherbrooke QC J1K 2R1 Canada

Department of Forest Resources University of Minnesota St Paul MN 55108 USA Hawkesbury Institute for the Environment University of Western Sydney Penrith NSW 2751 Australia

Environmental Research Institute and School of Science University of Waikato Private Bag 3105 Hamilton 3240 New Zealand

FdB Institute of Botany Academy of Sciences of the Czech Republic Dukelská 135 379 82 Třeboň Czech Republic Department of Botany University of South Bohemia Na Zlaté Stoce 1 370 05 České Budějovice Czech Republic

Institut de Recherche en Biologie Végétale Université de Montréal 4101 Sherbrooke Est Montréal QC H1X 2B1 Canada

Systems Ecology Department of Ecological Science FALW VU University De Boelelaan 1085 1081 HV Amsterdam The Netherlands

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