Résumé
There is increasing evidence that intraspecific trait variation plays a
role in governing rates of ecosystem functioning. While wood traits such
as wood specific gravity (WSG) and wood carbon concentration (WCC) are key
drivers of forest aboveground carbon (AGC) stocks, the sources of
intraspecific variation in these wood traits and the consequences of this
variation on AGC are poorly known, especially in the tropics. Here, we
investigated intraspecific variation in wood specific gravity (WSG) and
wood carbon concentration (WCC) from 556 individual trees belonging to 15
species that well characterize different successional stages of seasonal
evergreen forests in Southeast Asia. Specifically, we tested the
contribution of individual or species characteristics (tree size, growth
rate and regeneration guilds) and local environmental conditions
(topographic wetness index and successional stages) to intraspecific
variation in WSG and WCC, and assessed the consequences of intraspecific
variation in these wood traits on AGC estimates in 14 permanent forest
plots established along a successional gradient in Khao Yai National park,
Thailand. We found that tree size was the main driver of intraspecific
variation in WSG and WCC as tree sizes increased from 10−100 cm in
diameter, WSG increased by 7.3%, while WCC increased by 2.4% in heartwood,
1.6% and 2.7% in sapwood without and with volatile carbon included. There
was no effect of the topographic wetness and other local environment
condition in wood traits led to a slight overestimation of AGC in young
secondary forests (+0.09 to +1.29%) and a small underestimation in older
forests (-0.86 to -2.87%), but overall AGC estimates (13 of 14 forest
plots) remained within error margins (the 95% interval). Our study
provides evidence that tree size variation translates into intraspecific
variability in wood traits, whereas local environmental conditions related
to topography successional stages had no effect on wood trait variability.
While size-dependent variation in WSG and WCC have largely been
undocumented and thus ignored in forest carbon assessment approaches, we
highlight that it has a limited impact on AGC estimates, indicating that
it does not invalidate current forest carbon stock estimation
approaches.