Functional traits partially mediate the effects of chronic anthropogenic disturbance on the growth of a tropical tree

Understanding how trees mediate the effects of chronic anthropogenic disturbance is fundamental to developing sustainable forest management strategies. Several tree species in Africa are repeatedly defoliated at large scale by cattle breeders to feed livestock. The same tree species are also often debarked for medicinal purposes. These human-induced disturbances can lead to biomass loss and subsequent decline in tree growth. A recent study by Amahowe et al. published in AoB PLANTS investigated how plant functional traits can mediate responses to such disturbances in the tree species Afzelia africana.

Afzelia Africana tree
Intact adult Afzelia Africana tree in a protected area in Northern Benin. This individual was not pruned because it is located in a well-protected forest reserve where the local Fulani people do not have access. Image credit: I.O. Amahowe.

Amahowe et al. collected data on leaf mass per area, wood density and growth rate, and recorded history of human disturbances (debarking, pruning) on individual trees from 12 populations of A. africana in Benin (West Africa). They found that debarking did not affect stem growth and that tree response to debarking was independent of plant functional strategy. By contrast, they found that pruning reduced the absolute growth of trees; however, trees with low wood density were more strongly affected than trees with high wood density. Tree location also affected functional traits indicating that even classical conservation measures can affect tree ecology. Trees that are in protected areas where indigenous Fulani people do not have access, tended to have greater wood density. The results of this study emphasize the importance of plant functioning in the interplay between availability of leaves for resource acquisition and a resilience strategy for when foliage is disturbed, i.e. mobilizing stored resources in stem wood for new growth under severe disturbances. From a practical perspective, environmental education sessions should be implemented to enhance traditional healers’ and local communities’ awareness of sustainable debarking methods. Regarding sustainable pruning, this study highlights the importance of leaving significant foliage and branches on trees to allow photosynthesis and subsequently improve tree growth.

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