Parallel functional and stoichiometric trait shifts in South American and African forest communities with elevation

Marijn Bauters,Dries Van Der Heyden,Miro Demol,Landry Cizungu,Hans Verbeeck,Pascal Boeckx,Cys Taveirne,Stijn Bruneel

doi:10.5194/bg-14-5313-2017

Marijn Bauters, Dries Van Der Heyden + Show 6 more

Open Access

https://doi.org/10.5194/bg-14-5313-2017

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Abstract

Abstract. The Amazon and Congo basins are the two largest continuous blocks of tropical forest with a central role for global biogeochemical cycles and ecology. However, both biomes differ in structure and species richness and composition. Understanding future directions of the response of both biomes to environmental change is paramount. We used one elevational gradient on both continents to investigate functional and stoichiometric trait shifts of tropical forest in South America and Africa. We measured community-weighted functional canopy traits and canopy and topsoil δ15N signatures. We found that the functional forest composition response along both transects was parallel, with a shift towards more nitrogen-conservative species at higher elevations. Moreover, canopy and topsoil δ15N signals decreased with increasing altitude, suggesting a more conservative N cycle at higher elevations. This cross-continental study provides empirical indications that both South American and African tropical forest show a parallel response with altitude, driven by nitrogen availability along the elevational gradients, which in turn induces a shift in the functional forest composition. More standardized research, and more research on other elevational gradients is needed to confirm our observations.

Highlights

A good understanding of the future response of tropical forest ecosystems to global change is required because of their vital role in global biogeochemical cycles and ecology
Canopy and topsoil δ15N signals decreased with increasing altitude, suggesting a more conservative N cycle at higher elevations. This cross-continental study provides empirical indications that both South American and African tropical forest show a parallel response with altitude, driven by nitrogen availability along the elevational gradients, which in turn induces a shift in the functional forest composition
Contrary to latitudinal gradients or elevational gradients in the higher-latitude zones, they are not complicated by changes in seasonality, and with careful interpretation can offer great insights into tropical forest functioning (Körner, 2007; Malhi et al, 2010; Sundqvist et al, 2013)

Summary

Introduction

A good understanding of the future response of tropical forest ecosystems to global change is required because of their vital role in global biogeochemical cycles and ecology. Elevational transects have been postulated as a viable and useful setup to assess long-term ecosystem responses to environmental changes, and serve as an empirical tool to assess future trajectories of forest ecosystems under global change (Malhi et al, 2010; Sundqvist et al, 2013) This has invoked research efforts on transects in South America, but no such studies have been carried out in central African forests, leaving the second-largest continuous block of tropical forest understudied. Recent work has shown that African and South American tropical forest currently show important differences in structure (Banin et al, 2012) and species richness and composition (Slik et al, 2015) These differences call for cross-continental empirical research in both the Amazon and the Congo basins (Corlett and Primack, 2006), and in this context we can raise questions about the universality of tropical forest biogeochemistry and functioning across both continents, and subsequently their response to future global change scenarios.

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