Soil charcoal to assess the impacts of past human disturbances on tropical forests.
The canopy of many central African forests is dominated by light-demanding tree species that do not regenerate well under themselves. The prevalence of these species might result from ancient slash-and-burn agricultural activities that created large openings, while a decline of these activities since the colonial period could explain their deficit of regeneration. To verify this hypothesis, we compared soil charcoal abundance, used as a proxy for past slash-and-burn agriculture, and tree species composition assessed on 208 rainforest 0.2 ha plots located in three areas from Southern Cameroon. Species were classified in regeneration guilds (pioneer, non-pioneer light-demanding, shade-bearer) and characterized by their wood-specific gravity, assumed to reflect light requirement. We tested the correlation between soil charcoal abundance and: (i) the relative abundance of each guild, (ii) each species and family abundance and (iii) mean wood-specific gravity. Charcoal was found in 83% of the plots, indicating frequent past forest fires. Radiocarbon dating revealed two periods of fires: "recent" charcoal were on average 300 years old (up to 860 BP, n = 16) and occurred in the uppermost 20 cm soil layer, while "ancient" charcoal were on average 1900 years old (range: 1500 to 2800 BP, n = 43, excluding one sample dated 9400 BP), and found in all soil layers. While we expected a positive correlation between the relative abundance of light-demanding species and charcoal abundance in the upper soil layer, overall there was no evidence that the current heterogeneity in tree species composition can be explained by charcoal abundance in any soil layer. The absence of signal supporting our hypothesis might result from (i) a relatively uniform impact of past slash-and-burn activities, (ii) pedoturbation processes bringing ancient charcoal to the upper soil layer, blurring the signal of centuries-old Human disturbances, or (iii) the prevalence of other environmental factors on species composition.
Service d'Évolution Biologique et Écologie, Faculté des Sciences, Université Libre de Bruxelles, Brussels, Belgium.
Jason
J
Vleminckx
Laboratoire de Foresterie des Régions tropicales et subtropicales, Unité de Gestion des Ressources forestières et des Milieux naturels, Gembloux Agro-Bio Tech, Université de Liège, Gembloux, Belgium; Laboratory of Wood Biology & Xylarium, Royal Museum for Central Africa, Tervuren, Belgium.
Julie
J
Morin-Rivat
Laboratoire de Foresterie des Régions tropicales et subtropicales, Unité de Gestion des Ressources forestières et des Milieux naturels, Gembloux Agro-Bio Tech, Université de Liège, Gembloux, Belgium.
Achille B
AB
Biwolé
Laboratoire de Foresterie des Régions tropicales et subtropicales, Unité de Gestion des Ressources forestières et des Milieux naturels, Gembloux Agro-Bio Tech, Université de Liège, Gembloux, Belgium; Laboratory of Applied Ecology, University of Abomey-Calavi, Cotonou, Benin.
Kasso
K
Daïnou
Laboratoire de Foresterie des Régions tropicales et subtropicales, Unité de Gestion des Ressources forestières et des Milieux naturels, Gembloux Agro-Bio Tech, Université de Liège, Gembloux, Belgium.
Jean-François
JF
Gillet
Laboratoire de Foresterie des Régions tropicales et subtropicales, Unité de Gestion des Ressources forestières et des Milieux naturels, Gembloux Agro-Bio Tech, Université de Liège, Gembloux, Belgium.
Jean-Louis
JL
Doucet
Laboratoire d'Écologie Végétale et Biogéochimie, Faculté des Sciences, Université Libre de Bruxelles, Brussels, Belgium.
Thomas
T
Drouet
Service d'Évolution Biologique et Écologie, Faculté des Sciences, Université Libre de Bruxelles, Brussels, Belgium.
Olivier J
OJ
Hardy
D000383:Agriculture; D002163:Cameroon; D002606:Charcoal / Q000032:analysis*; D005390:Fires; D065928:Forests; D005843:Geography; D006801:Humans; D055110:Radiometric Dating; D012987:Soil / Q000737:chemistry*; D014197:Trees; D014329:Tropical Climate
D012987:Soil; D002606:Charcoal