Agriculture Reference
In-Depth Information
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), Díaz 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 precipi-
tation. 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.
In any case, our goal in this closing chapter is not so much to discuss the influence
of leaf longevity and foliar habit on ecosystem function, but rather the obverse - to
highlight work in ecosystem ecology that may help improve theory for leaf longevity.
Through perspectives drawn from ecosystem function, we basically turn the discus-
sion of leaf longevity back to the Chabot and Hicks' (1982) seminal review, with a
focus on better accounting the costs of foliar construction and defense in predicting
variation in leaf longevity. The relatively limited treatment of these factors in the
initial cost-benefit models for leaf longevity (Kikuzawa 1991, 1995a,b, 1996)
leaves room for improvement in our understanding of leaf longevity as a key factor
in foliar function.
Leaf Turnover and Leaf Longevity in the Ecosystem
The most direct connection of leaf longevity to ecosystem function is through leaf
turnover because this turnover rate essentially defines a storage term for materials
in the system as well as an indication of system productivity. Not surprisingly,
there is a positive correlation between leaf longevity and mean retention time of
