Chromolaena odorata thickets in forest recovery in southern Cameroon.
Background and aims - Every year, large areas of tropical forests are converted to agricultural lands by the slash and burn system of cultivation. Once crops have been harvested and in order to restore soil fertility, the land is abandoned for some years, opening the way to forest recovery. The different sequences in this process depend on the duration of the fallow period. Some steps of forest recovery are dominated by dense thickets of Chromolaena odorata, an invasive plant species in many tropical areas. This study aims to study its role in the course of secondary succession. Methods - The study was carried out in 144 post agricultural plots in southern Cameroon aging from six months to 35 years of age, situated along a phytogeographical gradient stretching from the coastal evergreen forest to the mixed forest in the hinterland. Floristic inventory involved recording all plant species and individuals of trees and shrubs of at least 5 cm diameter at breast height (dbh) in each plot. A multivariate analysis was performed to discriminate plant communities. Key results - Of the 144 plots studied, thirty aged from one to five years were forming a homogeneous plant community dominated by dense thickets of Chromolaena odorata. These thickets are distinctive with regard to their structure, species composition and dynamics. They hamper forest recovery and it is only when stems of Chromolaena odorata weaken and die that succession is sped up. The former vegetation cleared before the last cropping season, the vegetation type surrounding the fallows as well as the number of farming cycles in the same plots are factors influencing secondary succession in former agricultural lands.