Data from: Tree species diversity promotes aboveground carbon storage through functional diversity and functional dominance

The relationship between biodiversity and ecosystem function has
increasingly been debated as the cornerstone of the processes behind
ecosystem services delivery. Experimental and natural field-based studies
have come up with nonconsistent patterns of biodiversity–ecosystem
function, supporting either niche complementarity or selection effects
hypothesis. Here, we used aboveground carbon (AGC) storage as proxy for
ecosystem function in a South African mistbelt forest, and analyzed its
relationship with species diversity, through functional diversity and
functional dominance. We hypothesized that (1) diversity influences AGC
through functional diversity and functional dominance effects; and (2)
effects of diversity on AGC would be greater for functional dominance than
for functional diversity. Community weight mean (CWM) of functional traits
(wood density, specific leaf area, and maximum plant height) were
calculated to assess functional dominance (selection effects). As for
functional diversity (complementarity effects), multitrait functional
diversity indices were computed. The first hypothesis was tested using
structural equation modeling. For the second hypothesis, effects of
environmental variables such as slope and altitude were tested first, and
separate linear mixed-effects models were fitted afterward for functional
diversity, functional dominance, and both. Results showed that AGC varied
significantly along the slope gradient, with lower values at steeper
sites. Species diversity (richness) had positive relationship with AGC,
even when slope effects were considered. As predicted, diversity effects
on AGC were mediated through functional diversity and functional
dominance, suggesting that both the niche complementarity and the
selection effects are not exclusively affecting carbon storage. However,
the effects were greater for functional diversity than for functional
dominance. Furthermore, functional dominance effects were strongly
transmitted by CWM of maximum plant height, reflecting the importance of
forest vertical stratification for diversity–carbon relationship. We
therefore argue for stronger complementary effects that would be induced
also by complementary light-use efficiency of tree and species growing in
the understory layer.