Tree species diversity promotes aboveground carbon storage through functional diversity and functional dominance

Abstract

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.

An individual‐based forest model to jointly simulate carbon and tree diversity in Amazonia: description and applications

“…, Mensah et al. ), and with our sensitivity analyses. Also, the complementarity effect on AGB was strongly correlated to the dispersion of species maximal heights, as expected from a better canopy packing and complementarity of light niches due to heterogeneity in tree heights (Poorter et al.…”

Determinants of Aboveground Biomass across an Afromontane Landscape Mosaic in Kenya

“…The results are in line with [19] and [70], as slope also explained more of the variation in AGB in the Afromontane landscape mosaic. In this study, larger AGBs are limited to steep slopes (<37 degrees), compared with shallow and steepest slope in [20] and [71]. The steepest slopes and hilltops are covered by bare rocks, and they do not have enough nutrients and soil to hold high biomass forests.…”

Drought can favour the growth of small in relation to tall trees in mature stands of Norway spruce and European beech

“…Many current silvicultural guidelines strive for more heterogeneous stands (Utschig et al 2011;Pretzsch and Zenner 2017) as they may provide many ecosystem goods and services Poorter et al 2015;Mensah et al 2016;Dieler et al 2017) better than monocultures. The finding that small trees benefit in relation to tall trees from dry years and on dry sites (see also Pretzsch and Biber 2010) means that structural heterogeneity, as aimed at by many modern silvicultural guidelines, is easier to maintain on poor dry sites.…”