The relationship between phylogenetic diversity, trait diversity, and temporal biomass dynamics in tropical successional forests

Background/Question/Methods

Ecological theory predicts that community species richness may affect ecosystem function in multiple ways. Managers often seek to restore diversity and function, although selection of species for restoration may prove challenging in diverse systems. Maximizing niche complementarity of tree species may be one way to increase carbon storage and promote species coexistence. Niche complementarity may be associated with axes of phylogenetic and functional diversity (PD and FD), with each axis potentially representing different forms of niche diversity. We studied how PD and FD of trees in 100m²quadrats in one year predicted temporal aboveground biomass (AGB) change over the subsequent year. Our study sites were eight 1-ha Costa Rican lowland rainforest plots in secondary and old growth stands, monitored annually for 15 years. PD and FD were calculated as the shared phylogeny or trait dendrogram branch length of co-occurring species. We used linear mixed-models to test for correlations between PD and FD and changes in AGB calculated by allometric scaling. We controlled for local stem density because stem density and diversity may be correlated due to sampling.  We partitioned AGB change into growth gains, mortality losses, and net changes (i.e. change in total AGB), each having distinct implications for management.

Results/Conclusions

In general, PD and FD effects on AGB dynamics differed with stand age. PD had a significant positive effect on growth AGB gains in young stands (10-23 yrs), but had no effect later in succession. FD of three traits, specific leaf area (SLA), leaf density, and wood specific gravity, were positively correlated with growth gains in AGB, while AGB gains were reduced with greater FD of leaf area and leaf toughness. High PD and FD for multiple traits were associated with lower AGB losses to mortality, but only in early-successional stands. Overall, PD and wood specific gravity FD were positively related with net AGB change in early successional stands, while FD of nearly all leaf traits was negatively correlated with net AGB change in mid-successional (24-39 yrs) stands. Our findings indicate that managing PD and wood specific gravity FD may accelerate the recovery of AGB in restoration efforts via increased growth and lower mortality in diverse stands.