Diversity enhances carbon storage in tropical forests

Abstract

Aim Tropical forests store 25% of the global carbon and harbor 96% of the world’s tree species, but it is not clear whether this high biodiversity matters for carbon storage. Few studies have teased apart the relative importance of forest attributes and environmental drivers for ecosystem functioning, and no such study exists for the tropics.

Location Neotropics

Methods We relate aboveground biomass (AGB) to forest attributes (diversity and structure) and environmental drivers (annual rainfall and soil fertility) using data from 144,000 trees, 2,050 forest plots and 59 forest sites. The sites span the complete latitudinal and climatic gradients in the lowland Neotropics, with rainfall ranging from 750 to 4350 mm/y. Relationships were analyzed within forest sites at 0.1 ha and 1 ha scale, and across forest sites along large-scale environmental gradients. We used a structural equation model to test the hypothesis that species richness, forest structural attributes, and environmental drivers have independent, positive effects on AGB.

Results Across sites, AGB was most strongly driven by rainfall, followed by average tree stem diameter and rarefied species richness, which all had positive effects on AGB. Our indicator of soil fertility (cation exchange capacity) had a negligible effect on AGB, perhaps because we used a global soil database. Taxonomic forest attributes (i.e., species richness, rarefied richness and Shannon diversity) had the strongest relationships with AGB at small spatial scales, where an additional species can still make a difference in terms of niche complementarity, whereas structural forest attributes (i.e., tree density and tree size) had strong relationships with AGB at all spatial scales. key plant functions. Vegetative traits were filtered more often than regeneration traits. Specific leaf area, life span, ramification, canopy height, leaf weight ratio, carbon investment into support tissue and pollination mode were the traits showing differences in the largest number of pair-wise comparisons. This is probably the first attempt to detect, on a quantitative, statistically conservative basis, consistent linkages between climatic factors and numerous plant traits, over a broad spectrum of environmental conditions and plant growth forms. We discuss the advantages and limitations of this approach in predicting vegetation structure and functioning under present environmental conditions, and those expected for the next century as a consequence of global change.