Diversity–biomass relationship across forest layers: implications for niche complementarity and selection effects
Forest stratification plays a crucial role in light interception and plant photosynthetic activities. However, despite the increased number of studies on biodiversity–ecosystem function, we still lack information on how stratification in tropical forests modulates biodiversity effects. Moreover, there is less investigation and argument on the role of species and functional traits in forest layers. Here, we analysed from a perspective of forest layer (sub-canopy, canopy and emergent species layers), the relationship between diversity and aboveground biomass (AGB), focusing on functional diversity and dominance, and underlying mechanisms such as niche complementarity and selection. The sub-canopy layer had the highest species richness and diversity, while the emergent layer had the highest AGB. Species richness–AGB relationship was positive for each forest layer, but stronger for sub-canopy layer than for canopy and emergent layers. Total AGB was strongly correlated with functional diversity, leaf and wood traits of species in the sub-canopy and canopy layers. This suggests that sub-canopy and canopy species are major drivers of stand diversity–AGB relationship, and that resource filtering by canopy or emergent trees may not reduce the strength of diversity–AGB relationship in the sub-canopy layer. We argue that complementary resource use by sub-canopy species that supports niche complementarity, is a key mechanism driving AGB in natural forests. Selection effects are most evident in emergent species and niche complementarity effects for sub-canopy and canopy species, supporting arguments that AGB is affected by sub-canopy species’ efficient use of limited resources despite competition from emergent species.
KeywordsEcosystem function Functional diversity Forest strata Species coexistence Structural equation modelling
This research was supported by the African Forest Forum through a research grant provided to the first author. We also acknowledge the “Consolidoc” financial support from the Research Division of Stellenbosch University. The authors are grateful to the two anonymous reviewers and the editor for their comments on the earlier versions of this article.
Author contributions statement
SM and TS originally formulated the idea. SM, TS and BdT conceived the sampling design. SM collected and analysed the data. SM wrote the manuscript with editorial support from BdT and TS.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
Research involving human and animal rights
This article does not contain any studies with human participants or animals performed by any of the authors.
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