Leaves of pioneer and later-successional trees have similar lifetime carbon gain in tropical secondary forest

Different life history strategies among tropical rain forest species are generally related to inherent trade-offs in leaf and crown, traits, with early-successional species having traits that facilitate high productivity but a relatively wasteful use of resources and shadetolerant later-successional species exhibiting the opposite strategy. But the degree to which these trait differences contribute to short- and long-term carbon gain of different species that coexist in natural forest has not been quantitatively scaled. We applied a canopy model in combination with measurements of canopy structure, mass distribution, and leaf photosynthesis to determine whole-plant daily photosynthesis (Ppl) of individuals of three short-lived pioneers (SLP), four later-successional species, and three lianas growing together in a 0.5-, 2-, and 3-yr-old secondary tropical forest stand. Whole-plant daily photosynthesis per unit leaf mass (Plfm) and aboveground mass (P m) were assumed to indicate daily returns on investment at the leaf and crown level. By integrating these calculations with measured leaf longevities, we determined the lifetime carbon gain per unit leaf mass. Vegetation height and leaf area index increased with stand age. Two of the SLPs, Trema and Ochroma, increasingly dominated the top of the vegetation. In the 0.5-yr-old stand, these species also had the highest Pm and P lfm values. Whole-plant daily photosynthesis per unit leaf mass tended to decline with stand age but much more strongly so in the later-successional species than in the SLP. Leaf longevity was not significantly correlated with individual leaf traits (e.g., specific leaf area or leaf N content) but was strongly and negatively correlated with Plfm in the youngest stand. Latersuccessional species had considerably greater leaf longevities than SLP. Lifetime carbon gain per unit leaf mass, however, was relatively similar between the different species. Thus due to the strong negative correlation that exists between daily leaf productivity (P lfm) and longevity, short-lived pioneers and later-successional species achieve similar lifetime carbon gain per unit leaf mass in natural secondary forest. This could help explain why the slower-growing latersuccessional species are able to persist during the first years of succession.