Does the altitude affect the stability of montane forests? A study in the Kahuzi-Biega National Park (Democratic Republic of the Congo)

To understand the functioning of montane forests, this study was conducted in the highlands of the Kahuzi-Biega National Park in the Democratic Republic of the Congo. The relationship between the altitude and the floristic stability of woody layers and regeneration capability of canopy species after many years of disturbance was studied. Ten 1-ha plots were established from 1935m to 2760m a.s.l. In each plot we inventoried the trees >= 10cm of diameter at breast height (DBH), separating a canopy layer (10% of the tallest trees) and an understorey layer (all the other trees). In each plot, we nested a 0.1 ha subplot to inventory the saplings between 1 and 10 cm DBH. We found that the Jaccard index of dissimilarity between the understorey layer and the canopy layer decreases with the altitude. The proportion of species which are well represented in the three layers increases with the altitude. The number of pioneer species decreases with the altitude while that of non-pioneer and shade tolerant species increases. These findings suggest that altitude influences the stability of highland forests, higher altitude being more stable than lower ones in the case of this study.