Ecology and Development Series No. 10, 2003 - ZEF

Impacts of human use on the forest vegetation5.4.2 Population structure of treesSome tree species (Type I population structure group) are less affected by disturbance dueto management of the forests for coffee production. Species with such population structureare considered as being in good regeneration condition (Demel 1997). It appears that thechange in vegetation structure and the light conditions under the managed forests do notaffect the ability of their seeds to germinate. These are large canopy trees, which are alsoimportant as shade trees in the forests managed for coffee production. Hence, they are lesstargeted during the thinning of trees and clearing of understorey vegetation, unless there isa higher density of their stems than required for shade. The tree species in Type II appear tobe pioneer species, whose seeds require disturbance for germination. The number of maturestems of Cordia africana, which belongs to this group, decreased in the managed forestcategories compared to the undisturbed forests, and finally disappeared from the oldestmanaged forest type (SEMIFOR-PLAN) (Table 5.7). This can be due to two possiblereasons: (1) broad-leaved deciduous tree species like Cordia are considered as unsuitablefor shade and are gradually replaced by legumes or other broad-leaved evergreen treespecies, and (2) Cordia is highly hunted for its quality timber.The tree species in the Type III appear to be shade-tolerant, and cannot regeneratein gaps created under disturbed forest conditions. The trees in this group are also notrepresented even in the higher height classes of the vegetation of the managed forestcategories, probably because they are not useful trees for shade in coffee production.5.4.3 The forest structureThere is a clear difference in the structure of the forest vegetation between the undisturbedforests and the forests managed for coffee production. It appears that forests are convertedfrom complex and continuous-structured vegetation in undisturbed forests to two-layeredvegetation in the managed forests. The two distinguishable layers in managed forests are:the canopy layer of shade trees and the coffee stand layer. The high degree of decline in theabundances of plants in the lower height classes in the managed forest (Table 5.10), therelatively lower decline in abundances of trees in the higher height class and canopy cover(Table 5.7 and 5.10), and the very high increase in the proportion of matured coffee trees93