Black Wattle (Acacia mearnsii De Wild.) in Rwanda’s Forestry: Implications for Nature Conservation

Abstract

Invasive species pose a serious threat to the conservation of biodiversity. Forestry is the most important driver of the introduction and spread of invasive woody plant species after horticulture. Nearly 450 invasive tree species have been recorded worldwide, amounting to more than half the world’s total invasive woody flora. Australian-native Acacia mearnsii De Wild. is one of world’s top invasive alien tree species related to forestry. The negative impacts of alien species spilling over into conservation areas because of forestry are increasingly being recognized, and we examined the context and timing of this Australian species’ arrival in Rwanda. The role of A. mearnsii in Rwanda’s colonial and postcolonial forestry and the species’ threat to biodiversity conservation are also investigated. The results suggest that A. mearnsii (a) was introduced into Rwanda between 1903 and 1918, with the earliest formal record dating back to 1941; (b) was a major forestry tree species until the late 1960s when its use in forestry declined significantly; and (c) demonstrates a comparatively higher occurrence and potential of regeneration within the understory of Eucalyptus plantations within the Congo-Nile ridge buttress; Bufundu and Bushiru; and Budaha, Ndiza, and Buberuka agro-bioclimatic zones. More recently, A. mearnsii has invaded national parks and forest reserves above 1,600 m of altitude. The most significant case was recorded at Nyungwe National Park (NNP), East Africa’s largest montane rainforest. A study of biomass and spatial patterns of this species in specific ecosystems, such as NNP, is strongly recommended in order to uphold effective conservation practices.