Analyzing soil charcoals to assess the naturalness of tropical forest

إنجليزي. For conservation biology and sustainable management, the natural character of tropical forest is a crucial issue. Its assessment is usually based on ecological proxies such as forest composition and structure. However the estimation made on this basis only considers short term processes at a local scale. In contrast the long term processes are appraised by palaeoecological proxies (such as pollen) at a regional scale. So as to assess the degree of naturalness of tropical ecosystems in a conservation perspective it is important to combine a long temporal scale as well as a fine resolution spatial scale. Such approaches using palaeoecological proxies have been recently tested in temperate Europe but little in tropical ecosystems. Nonetheless the long term preservation of the palaeoecological material and its broad presence in the environment are necessary conditions to fulfill. In this perspective soil charcoal appears to meet these requirements. In this paper we aimed at assessing the naturalness of tropical forest using soil charcoal from southeastern Cameroon. Fieldwork involving as well archaeology as botany was undertaken at 53 sites. We quantified charcoal in soil samples by layers of 10 cm taken from pits located in the center of plots of botanical inventory. Spatial projections were performed using statistics together with multivariate analyses. Radiocarbon dating allowed interpreting the temporal framework. Results showed the ubiquitous presence of charcoal at each site. Main charcoal peaks were interpreted as fields (slash-and-burn agriculture) in the vicinity of ancient villages. These practices shaped the forest over time which cannot be considered as natural anymore. This underlines the potential input of the use of palaeoecological material in conservation biology and sustainable management issues. Charcoal fragments are under taxonomical identification and may provide new insights on the long term history of forest composition.

Population dynamics of light-demanding trees and herbs in the dense forests of Central Africa in relationship with climatic and anthropogenic disturbances