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Data from: Structural complexity and large-sized trees explain shifting species richness and carbon relationship across vegetation types

Citation

Mensah, Sylvanus; Salako, Valere; Seifert, Thomas (2020), Data from: Structural complexity and large-sized trees explain shifting species richness and carbon relationship across vegetation types, Dryad, Dataset, https://doi.org/10.5061/dryad.pvmcvdnhr

Abstract

1. It is prominently claimed that enhancing forest diversity would play a dual role of nature conservation and climate regulation. While the idea is intuitively appealing, studies show that species richness effects on aboveground carbon (AGC) are not always positive, but instead unpredictable especially across scales and complex terrestrial systems having large-diameter and tall-stature trees. Previous studies have further considered structural complexity and larger trees as determinants of AGC. Yet it remains unclear what drives differential diversity-AGC relationships across vegetation types.

2. Here, we test whether structural complexity and large-sized trees play an influential role in explaining shifting diversity-AGC relationships across vegetation types, using a 22.3 ha sampled dataset of 124 inventory plots in woodlands, gallery forests, tree/shrub savannahs and mixed plantations in West Africa.

3. Natural vegetation had greater species richness and structural complexity than mixed plantations, as expected. In addition, AGC was highest in gallery forests and mixed plantations, which is consistent with favorable environmental conditions in the former and high stocking densities and presence of fast-growing species in the latter. Significant interaction effects of species richness and vegetation on AGC revealed a vegetation-dependent species richness-AGC relationship: consistently, we found positive species richness-AGC relationship in both mixed plantations and woodlands, and nonsignificant patterns in gallery forests and tree/shrub savannah. Further, there was a vegetation-dependent mediation of structural complexity in linking species richness to AGC, with stronger positive structural complexity effects where species richness-AGC relationships were positive, and stronger positive large-sized trees’ effect where species richness-AGC relationships were neutral.

4. Our study provides strong evidence of vegetation-dependent species richness-AGC relationships, which operated through differential mediation by structural complexity of the species richness and large trees’ effects. We conclude that even higher species richness in diversified ecosystems may not always relate positively with AGC, and that neutral pattern may arise possibly as a result of larger dominant individual trees imposing a slow stand dynamic flux and overruling species richness effects.

Methods

The dataset consisted of floristic information (tree species names, tree density, and diameter at breast height – DBH and tree height) from 124 plots, established using a stratified random sampling scheme across  gallery forest, woodland, savannahs and mixed plantations in Benin, West Africa. Plot size was approximately 0.18ha. In each plot, all individuals with diameter ≥ 5 cm were measured and identified at species level.