The degree to which climate factors influence the signal of isotopes and tree-ring width may vary between sites and species… © D. Colombaroli © H. Beeckman

To obtain information of climate fluctuations in the rainforest belt in the recent past, stem discs can be used to establish chronologies of tree ring widths and stable isotopes of C and O. A collection of Pericopsis stem discs from the Kisangani and Yangambi regions should allow the construction of 200+-year long time series of tree ring widths and stable isotopes.

Studying the paleoenvironmental signal from the lake Bambili (2200 m, Cameroon) © A.M. Lézine

Partners will reconstruct the long-term dynamics of forest vegetation and fire regimes in response to past climate variability (and human impact). Analyses are based on plant pollen and macroscopic (> 150 µm) charcoal preserved in high-quality lake-sediment archives from near the western and eastern periphery of the African rainforest (Cameroon and Uganda). Patterns of similarity and dissimilarity between these two regions’ histories of vegetation change and fire will allow identification of the more prominent climate-change events that must also have affected the central lowland rainforest block.

Reconstructing the history of fires through anthracology © H. Beeckman

Soil charcoal collections from the D.R.Congo, Cameroon and Uganda will be studied through analyses of stratigraphic distribution, ¹⁴C dating and botanical identification. The changes in tree species assemblage inferred from charcoal collected at different depths can then be interpreted as changes in local forest composition through time. Structural and chemical change which occurred during the charcoalification process should also reveal information on the intensity of paleofire event.

Soil carbon in Central Cameroon for deciphering Holocene tropical vegetation changes © B. Turcq

Analysis of ∂¹³C in ¹⁴C dated organic matter from soil profiles allows to reconstruct the local succession between forest and savannah habitat through time, because these ecosystems present very different ∂¹³C values. To identify periods of expansion or decline of the Equatorial forest, both at its margins and through gap formation within it, we will perform ∂¹³C analyses of organic matter from soil profiles in D.R.Congo, Cameroon and Uganda. The results are then used to validate vegetation reconstructions from model simulations (WP4).