Ecosystem Perspectives on Leaf Longevity

Abstract

As an integral part of the adaptive strategy for productivity at the level of individual plants, leaf longevity should scale up to impact flows of energy and materials at the ecosystem level. Consequently, leaf longevity and foliar habit consistently appear in enumerations of traits relevant to ecosystem function (Weiher et al. 1999; Lavorel and Garnier 2002; Cornelissen et al. 2003; Kleyer et al. 2008). The past decade has seen a flood of papers discussing linkages between various traits and ecosystem function: useful entry points to this literature include Lavorel and Garnier (2002), Diaz et al. (2004), Wright et al. (2005b), Quetier et al. (2007), and Suding and Goldstein (2008). Although leaf longevity and its foliar correlates clearly influence ecosystem processes (Thomas and Sadras 2001; Wright et al. 2005b; Cornwell et al. 2008), scaling up the effects of leaf longevity at the level of individual plants or species to the aggregate influence of species assembled in diverse communities across the landscape is not at all straightforward (Suding et al. 2008). Zhang and colleagues (Zhang et al. 2009) provide perhaps the best example of what is possible if one is willing to invest the effort. They followed leaf longevity on individual species in ten evergreen forests in eastern China for 5 years, calculating frequency-weighted mean leaf longevity for each forest, which was negatively correlated with mean annual temperature and positively correlated with mean annual precipitation. Very few ecosystem studies focus to this degree on leaf longevity per se at the level of individual species, or for that matter on any other species-specific traits. Some models of forest productivity incorporate an impressive amount of detail on individual species at the population level in the forest community (cf. Medvigy et al. 2009), but the focus typically remains on the forest as a whole, not the detailed analysis of individual trees and species that in aggregate decide the functional characteristics of the forest. It clearly is no easy task to assess how leaf longevity and associated traits at the species level scale up to affect ecosystem function.