The limited importance of size-asymmetric light competition and growth of pioneer species in early secondary forest succession in Vietnam

Abstract

It is generally believed that asymmetric competition for light plays a predominant role in determining the course of succession by increasing size inequalities between plants. Size-related growth is the product of size-related light capture and light-use efficiency (LUE). We have used a canopy model to calculate light capture and photosynthetic rates of pioneer species in sequential vegetation stages of a young secondary forest stand. Growth of the same saplings was followed in time as succession proceeded. Photosynthetic rate per unit plant mass (P mass: mol C g−1 day−1), a proxy for plant growth, was calculated as the product of light capture efficiency [Φmass: mol photosynthetic photon flux density (PPFD) g−1 day−1] and LUE (mol C mol PPFD−1). Species showed different morphologies and photosynthetic characteristics, but their light-capturing and light-use efficiencies, and thus P mass, did not differ much. This was also observed in the field: plant growth was not size-asymmetric. The size hierarchy that was present from the very early beginning of succession remained for at least the first 5 years. We conclude, therefore, that in slow-growing regenerating vegetation stands, the importance of asymmetric competition for light and growth can be much less than is often assumed.

Trade‐off between light interception efficiency and light use efficiency: implications for species coexistence in one‐sided light competition

“…The higher total leaf area per unit plant mass (LAR) of shorter species compensated for their lower light capture per unit leaf area (Hirose & Werger 1995). Similar patterns were observed in very young secondary forest (van Kuijk et al 2008;Selaya et al 2008). These results indicate that size-symmetric competition may occur under one-sided light competition, which clearly contradicts the general notion that light acquisition is by definition size asymmetric (Weiner 1990).…”

“…The lower LUE P in taller individuals was partly due to the saturating nature of light-photosynthesis relationship; photosynthetic rates often saturate at 500-1000 lmol m À2 s À1 PPFD, while the top canopy leaves receive light levels that were higher than this saturation point. Similar studies comparing LUE p among species in very young secondary tropical forests obtained varying results with LUE p either higher in taller than shorter species (Selaya & Anten 2010), or not related to stature (van Kuijk et al 2008). All these studies, however, share two important short-comings.…”

The relative importance of above- versus belowground competition for tree growth during early succession of a tropical moist forest

“…Test statistics on the relationship between neighborhood competition and sapling growth in Table 3 Plant Ecol (2012) 213:25-34 31 2008). Overall growth in the Vietnam site was much slower than in our site and the Bolivian site (van Breugel et al 2006;Kuijk et al 2008;Selaya et al 2008). The intensity and the degree of size-asymmetry in competition may thus, as hypothesized by Schwinning and Weiner (1998) and Wilson (1999), change along a gradient of site productivity.…”

“…However, it has also been argued that, even if competition is mediated by light, the degree of asymmetry may differ depending on crown allometry of competing trees and canopy structure of the stand (Kikuzawa and Umeki 1996), which may result from species differences (Uriarte et al 2004(Uriarte et al , 2005Selaya et al 2007;Kuijk et al 2008;Uriarte et al 2010).…”

“…In the humid tropics, aboveground biomass can accumulate very rapidly during the first years of secondary forest succession (Swaine and Hall 1983;Uhl 1987;van Breugel et al 2006;Fonseca et al 2011), with the leaf area index (LAI) and understory light levels approaching old-growth values within just few years (Uhl 1987;Saldarriaga and Luxmoore 1991;Selaya et al 2007;Kuijk et al 2008). This finding has led to the commonly held assumption that competition for light plays a predominant role in the early phases of succession in humid tropical forest ecosystems.…”