Impact of single species tree plantations on nutrient cycling in West Africa

摘要

This paper evaluates the impact of plantation monocultures of fast-growing exotic species and indigenous tree species on nutrient cycling in West Africa. The rates of nutrient uptake and recycling to the soil vary with tree species and ecological zones. In general, single species tree plantations immobilise soil nutrients faster and return less nutrients to the soil than native forest and savanna vegetation. Hence, they deplete soil nutrients. Plantations of an indigenous species, Terminalia ivorensis, exert less deleterious effects on soil nutrient status than exotics such as teak and gmelina. Owing to their effects in destabilising the nutrient cycle in forest and savanna ecosystems, the plantation monocultures of fast-growing tree species are not likely to be sustainable in the long term. The widespread adoption of plantation forestry as an alternative to the natural regeneration of native forests as a strategy for increasing the wood resources of humid tropics is, therefore, indicative of an uncritical acceptance of the view that monocultural tree plantations are sustainable. There is need for caution in the rush to convert native ecosystems, especially rain forests, into plantations of fast-growing exotic trees.