Refining Species Traits in a Dynamic Vegetation Model to Project the Impacts of Climate Change on Tropical Trees in Central Africa

Marie Dury,Louis François,Alain Hambuckers,Adeline Fayolle,Lenni Mertens,Hans Verbeeck

doi:10.3390/f9110722

Marie Dury, Louis François + Show 4 more

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https://doi.org/10.3390/f9110722

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Abstract

African tropical ecosystems and the services they provide to human society suffer from an increasing combined pressure of land use and climate change. How individual tropical tree species respond to climate change remains relatively unknown. In this study, we refined the species characterization in the CARAIB (CARbon Assimilation In the Biosphere) dynamic vegetation model by replacing plant functional type morpho-physiological traits by species-specific traits. We focus on 12 tropical tree species selected for their importance in both the plant community and human society. We used CARAIB to simulate the current species net primary productivity (NPP), biomass and potential distribution and their changes in the future. Our results indicate that the use of species-specific traits does not necessarily result in an increase of predicted current NPPs. The model projections for the end of the century highlight the large uncertainties in the future of African tropical species. Projected changes in species distribution vary greatly with the general circulation model (GCM) and, to a lesser extent, with the concentration pathway. The question about long-term plant response to increasing CO2 concentrations also leads to contrasting results. In absence of fertilization effect, species are exposed to climate change and might lose 25% of their current distribution under RCP8.5 (12.5% under RCP4.5), considering all the species and climatic scenarios. The vegetation model projects a mean biomass loss of −21.2% under RCP4.5 and −34.5% under RCP8.5. Potential range expansions, unpredictable due to migration limitations, are too limited for offsetting range contraction. By contrast, if the long-term species response to increasing [CO2] is positive, the range reduction is limited to 5%. However, despite a mean biomass increase of 12.2%, a positive CO2 feedback might not prevent tree dieback. Our analysis confirms that species will respond differently to new climatic and atmospheric conditions, which may induce new competition dynamics in the ecosystem and affect ecosystem services.

Highlights

African tropical forests experience increasing pressure under the influence of land use and climate change, resulting in substantial area reduction and degradation
Whereas previous studies used morpho-physiological traits of plant functional types (PFT; [72]), we looked for characteristics of individual species in an attempt to refine the simulations (Table 2)
Substitution of PFT morpho-physiological traits by species-specific ones has an important impact on species net primary productivity (NPP) with significant differences (p < 0.01) in mean simulated NPP for eight species (Figure 1)

Summary

Introduction

African tropical forests experience increasing pressure under the influence of land use and climate change, resulting in substantial area reduction and degradation. The reduction of forest cover at landscape level may alter tree species composition and functionality [14], for instance, by the replacement of highly specialized taxa by more common local species taking advantage of the proliferation of fire-degraded, drier or more illuminated areas as observed in the Neotropics [15,16]. Such degradations of forest cores are much subtler than the deforestation and degradation observed around cities, they will considerably alter ecosystem services (ES) in the future

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