Tropical forests provide a variety of ecosystem services on the local and global scale. However, intact rainforests have been in peril over the last decades due to severe dieback of trees, probably due to changing environmental conditions. Most insights in the responses of vegetation to climate depend on short-term records (annual or decadal-scale), yet short-term sensitivities do not necessarily translate into long-term responses (centennial or millennial-scale). As such, a long-term perspective of linkages between climate and vegetation dynamics is imperative to accurately predict the 21st century fate of Earth’s rainforests. Therefore the general ambition of this FED-tWIN research profile is to improve our understanding of long-term tropical forest sensitivity and resilience to climate change, by comparing multi-timescale records of the best possible natural archives of forest dynamics: wood and fossil charcoal. This profile will focus on the Congo Basin, which represents the World’s second-largest contiguous area of rainforest and plays a major role in global biogeochemical and climate cycles, while it has been largely underrepresented in long-term studies due to a lack of ground-based data.
The major long-term objective is to improve our understanding of past climate-biodiversity-carbon interactions in the Congo Basin at four different timescales. To facilitate comparison among the timescales, the multi-timescale dataset will be geographically integrated by a network of permanent forest inventory plots. These plots are demarcated rectangles or squares of median size 1 ha where each tree is mapped, tagged and repeatedly measured according to standard protocols. The FED-tWIN researcher will consolidate and expand the network of plots located in the inner Congo Basin and will confine all research activities to these plots. Objectives and methodology per timescale include:
• seasonal scale: untangle feedbacks between biogeochemical fluxes and forest dynamics, by comparing fluxtower measurements with high-resolution measurements of tree growth;
• decadal-scale: analyse impact of environmental change on carbon fluxes and floristic composition over the last few decades (1980’s-1920’s), using repeated tree diameter measurements in the plots;
• centennial-scale: determine the timing of recent major forest disturbances by estimating tree-age distributions of light-demanding tree communities, using growth-ring records;
• millennial-scale: detect long-term shifts in species and functional composition, by radiocarbon dating and identifying fossil charcoal fragments sampled from soil profiles dug around the plots.
The ambition of the first two years is to reconstruct millennial-scale vegetation shifts in Salonga National Park, which was the last area occupied by Bantu-speaking farmers who gradually occupied Central Africa during the last three millennia. Fossil charcoal from SNP older than 1000 BP will likely represent traces of a natural drought-induced fire regime, providing clear insights in natural vegetation responses to climate change. The major hypothesis is that African rainforests are resilient to long-term and severe climate change, by shifting their species and functional composition in favour of drought-tolerant species. To do so, the FED-tWIN researcher will compare past (fossil charcoal) and present (inventories) characteristics of species communities.
Finally, a second long-term objective is to improve predictions of future climate-biodiversity-carbon interactions, by integrating insights from the multi-timescale dataset, into existing ecosystem and climate models.