The leaf mass/number trade‐off of Kleiman and Aarssen implies constancy of leaf biomass, its density and carbon uptake in forest stands: scaling up from shoot to stand level

Abstract

Summary 1. Kleiman & Aarssen (2007) propose that the regression slope of the mean individual leaf mass across species vs. the number of leaves does not differ significantly from -1.0, based on logtransformed experimental data for tree shoots (i.e. isometric trade-off ). A quantitative model is set out here that explains the mechanism of isometric trade-off of leaf mass/number across species. 2. From Kleiman and Aarssen's result for the leaf mass/number trade-off in trees, the constancy of leaf biomass density per unit volume of shoot is derived theoretically. This constancy may scale up to the tree crown level, assuming proportionality of total shoot volume and crown volume, and also up to the canopy at stand level, based on the observed proportionality between crown depth and tree height. 3. On the basis of the constancy of leaf biomass density, the constancy of leaf biomass in a fully closed forest stand is analysed, since tree height tends to a limit as tree age increases due to hydraulic constraints. The resulting constancy of leaf biomass is consistent with previous reports for actual forest stands. 4. The allometric scaling theory of Enquist and colleagues suggests that metabolic rates of an entire organism scale as the 3/4 power of mass, so that scale-up is important: indeed, scaling up may be related to tree physiology and ecosystem carbon balance. The present scaling model from shoot to forest stand level is consistent with the work of Enquist and colleagues. The scaled-up result of leaf biomass constancy indicates that carbon uptake by forest stands may be almost constant if the mean leaf photosynthetic rate remains constant after closure of the forest canopy. 5. Synthesis. By analytically explaining the mechanism of the leaf mass/number trade-off at shoot level proposed by Kleiman and Aarssen, it is predicted that leaf biomass and carbon uptake are constant in fully closed forest stands, by scaling up the constancy of leaf biomass density from shoot to canopy level. The present analysis provides the theoretical basis for leaf biomass constancy in forest stands.

The leafing intensity premium hypothesis tested across clades, growth forms and altitudes

“…Deciduous species, on the other hand, conformed to the isometric trade‐off in a very accurate manner. It is thus stated that, per unit of crown volume, leaf biomass should remain relatively constant across deciduous species, which has been demonstrated by Ogawa (2008) for trees. However, why should the rate of decrease in leafing intensity as LM increases be different between deciduous and evergreens?…”

“…The recurrent prevalence of a cross‐species correlation among traits informs on very relevant ecological aspects, from species autecology to ecosystem functioning (Westoby et al. 1995; see Ogawa 2008, for relevance of the leaf size–number trade‐off to ecosystem level carbon balance). However, more in‐depth investigations are needed to assess adaptive significance of trait correlations and their evolutionary routes.…”

“…2008). In addition, the few empirical studies performed so far have conformed to the pattern of inverse and isometric relationship between leaf size and leafing intensity (Ogawa 2008; Yang et al. 2008).…”

Density effects on the growth of self-thinning Eucalyptus urophylla stands

“…Ogawa (2008) also demonstrated constant leaf biomass in mature forest stands after canopy closure. As self-thinning occurs, unoccupied space is produced.…”

Theoretical analysis of the interrelationships between self-thinning, biomass density, and plant form in dense populations of hinoki cypress (Chamaecyparis obtusa) seedlings

“…Because the above reformulation of the self-thinning exponent in mature forest is applied to the present seedling population, the results obtained in this study provide guidance in forest management practices and the modeling of growth and yield. Ogawa (2008) also demonstrated constant leaf biomass density in mature forest stands after canopy closure. Constant leaf biomass density might therefore be a common feature of both seedling (Fig.…”