A handbook of protocols for standardised and easy measurement of plant functional traits worldwide

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 336 Introduction and discussion . . . . . . . . . . . . . . . . . . . . 336 The protocol handbook . . . . . . . . . . . . . . . . . . . . . . . . 337 1. Selection of plants and statistical considerations . . . 337 1.1 Selection of species in a community or ecosystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337 1.2 Selection of individuals within a species . . . . . . 339 1.3 Statistical considerations . . . . . . . . . . . . . . . . . . 339 2. Vegetative traits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341 2.1. Whole-plant traits . . . . . . . . . . . . . . . . . . . . . . . 341 Growth form . . . . . . . . . . . . . . . . . . . . . . . . . . . 341 Life form . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341 Plant height . . . . . . . . . . . . . . . . . . . . . . . . . . . . 342 Clonality (and belowground storage organs) . . 343 Spinescence . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343 Flammability . . . . . . . . . . . . . . . . . . . . . . . . . . . 344 2.2. Leaf traits. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345 Specific leaf area (SLA) . . . . . . . . . . . . . . . . . . 345 Leaf size (individual leaf area) . . . . . . . . . . . . . 347 Leaf dry matter content (LDMC) . . . . . . . . . . . 348 Leaf nitrogen concentration (LNC) and leaf phosphorus concentration (LPC) . . . . . . . . . 349 Physical strength of leaves . . . . . . . . . . . . . . . . . 350 Leaf lifespan. . . . . . . . . . . . . . . . . . . . . . . . . . . . 351 Leaf phenology (seasonal timing of foliage) . . . 352 Photosynthetic pathway . . . . . . . . . . . . . . . . . . . 353 Leaf frost sensitivity. . . . . . . . . . . . . . . . . . . . . . 355 2.3. Stem traits. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 356 Stem specific density (SSD) . . . . . . . . . . . . . . . 356 Twig dry matter content (TDMC) and twig drying time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 357 Bark thickness (and bark quality) . . . . . . . . . . . 358 2.4. Belowground traits . . . . . . . . . . . . . . . . . . . . . . . 359 Specific root length (SRL) and fine root diameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359 Root depth distribution and 95% rooting depth. 360 Nutrient uptake strategy . . . . . . . . . . . . . . . . . . . 362 3. Regenerative traits. . . . . . . . . . . . . . . . . . . . . . . . . . . . 368 Dispersal mode. . . . . . . . . . . . . . . . . . . . . . . . . . 368 Dispersule shape and size . . . . . . . . . . . . . . . . . 368 Seed mass. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369 Resprouting capacity after major disturbance . . 370 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 372 336 Australian Journal of Botany J. H. C. Cornelissen et al. Introduction and discussion This paper is not just another handbook on ecological methodology, but serves a particular and urgent demand as well as a global ambition. Classifying plant species according to their higher taxonomy has strong limitations when it comes to answering important ecological questions at the scale of ecosystems, landscapes or biomes (Woodward and Diament 1991; Keddy 1992; Körner 1993). These questions include those on responses of vegetation to environmental variation or changes, notably in climate, atmospheric chemistry, landuse and natural disturbance regimes. Reciprocal questions are concerned with the impacts of vegetation on these large-scale environmental parameters (see Lavorel and Garnier 2002 for a review on response and effect issues). A fast-growing scientific community has come to the realisation that a promising way forward for answering such questions, as well as various other ecological questions, is by classifying plant species on functional grounds (e.g. Díaz et al. 2002). Plant functional types and plant strategies, the units within functional classification schemes, can be defined as groups of plant species sharing similar functioning at the organismic level, similar responses to environmental factors and/or similar roles in (or effects on) ecosystems or biomes (see reviews by Box 1981; Chapin et al. 1996; Lavorel et al. 1997; Smith et al. 1997; Westoby 1998; McIntyre et al. 1999a; McIntyre et al. 1999b; Semenova and van der Maarel 2000; Grime 2001; Lavorel and Garnier 2002). These similarities are based on the fact that they tend to share a set of key functional traits (e.g. Grime and Hunt 1975; Thompson et al. 1993; Brzeziecki and Kienast 1994; Chapin et al. 1996; Noble and Gitay 1996; Thompson et al. 1996; Díaz and Cabido 1997; Grime et al. 1997; Westoby 1998; Weiher et al. 1999; Cornelissen et al. 2001; McIntyre and Lavorel 2001; Lavorel and Garnier 2002; Pausas and Lavorel 2003). Empirical studies on plant functional types and traits have flourished recently and are rapidly progressing towards an understanding of plant traits relevant to local vegetation and ecosystem dynamics. However, functional classifications are not fully resolved with regard to application in regional to global scale modelling, or to the interpretation of vegetation–environment relationships in the paleo-record. Recent empirical work has tended to adopt a ‘bottom-up’ approach where detailed analyses relate (responses of) plant traits to specific environmental factors. Some of the difficulties associated with this approach regard the identification of actual plant functional groups from the knowledge of relevant traits and the scaling from individual plant traits to ecosystem functioning. On the other hand, geo-biosphere modellers as well as paleo-ecologists have tended to focus on ‘top-down’ classifications where functional types or life forms are defined a priori from a small set of postulated characteristics. These are often the characteristics that can be observed without empirical measurement and only have limited functional explanatory power. The modellers and paleo-ecologists are aware that their functional type classifications do not suffice to tackle some of the pressing large-scale ecological issues (Steffen and Cramer 1997). In an attempt to bridge the gap between the ‘bottom-up’ and ‘top-down’ approaches (see Canadell et al. 2000), scientists from both sides joined a workshop (at Isle sur la Sorgue, France, in October 2000) organised by the International Geosphere–Biosphere Programme (IGBP, project Global Change and Terrestrial Ecosystems). One of the main objectives of the workshop was to assemble a minimal list of functional traits of terrestrial vascular plants that (1) can together represent the key responses and effects of vegetation at various scales from ecosystems to landscapes to biomes to continents, (2) can be used to devise a satisfactory functional classification as a tool in regional and global-scale modelling and paleo-ecology of the geo-biosphere, (3) can help answer some further questions of ecological theory, nature conservation and land management (see Table 1 and Weiher et al. 1999) and (4) are candidates for relatively easy, inexpensive and standardised Abstract. There is growing recognition that classifying terrestrial plant species on the basis of their function (into ‘functional types’) rather than their higher taxonomic identity, is a promising way forward for tackling important ecological questions at the scale of ecosystems, landscapes or biomes. These questions include those on vegetation responses to and vegetation effects on, environmental changes (e.g. changes in climate, atmospheric chemistry, land use or other disturbances). There is also growing consensus about a shortlist of plant traits that should underlie such functional plant classifications, because they have strong predictive power of important ecosystem responses to environmental change and/or they themselves have strong impacts on ecosystem processes. The most favoured traits are those that are also relatively easy and inexpensive to measure for large numbers of plant species. Large international research efforts, promoted by the IGBP–GCTE Programme, are underway to screen predominant plant species in various ecosystems and biomes worldwide for such traits. This paper provides an international methodological protocol aimed at standardising this research effort, based on consensus among a broad group of scientists in this field. It features a practical handbook with step-by-step recipes, with relatively brief information about the ecological context, for 28 functional traits recognised as critical for tackling large-scale ecological questions. BT