Tree species diversity under pastoral and farming systems in Kilosa District, Tanzania
Loss of tree diversity through improper land use practices such as overgrazing and poor farming practices in tropical areas and other natural ecosystems is one of today's most worrying environmental problems. This study was conducted to assess the impact of farming and pastoralism on tree species diversity in two forests each owned and managed by pastoral and farming communities in Kilosa District. Household survey solicited information on perceptions of local communities on drivers that influenced tree stocking and diversity of their forests. A forest inventory was conducted involving twenty circular in each system plots laid along two transects. In each plot, trees and shrubs with DBH > 5 cm were measured for DBH and height. A total of 48 different species were recorded out of which 75%were tree species and 25% shrubs species. The forest under pastoral system had a Shannon - Wiener Index (H’) of 3.13 as opposed to farming system with an index of 2.05. Average stocking for the forest under pastoral system was 235 stem ha-1, whereas that of farming system was 209 stem ha-1. Basal areas of 13m2ha-1 and 6m2 ha-l were recorded for forests under pastoral and farming systems respectively. Standing volume showed the same tendency where 216m3ha-1 was recorded from the forest under pastoral system as opposed to 100.12 m3ha-1 from the other forest. The high loss of species diversity and stocks particularly in the forest under farming system were attributed to anthropogenic disturbances including cutting trees for farm expansion, charcoal making and house construction. Although the assessment on the community perception on the loss of tree diversity in the area showed conflicting interests between the two societies each blaming activities of each community as major causes of forest degradation. This calls for more enforcement of rules and regulations and tree planting in degraded areas predominantly in the farming communities. The study further revealed that the existing tensions over land resource ownership between the two communities of farmers and pastoralists may be contributing factors of unsustainable use of tree species and other forest resources. It is recommended that interventions should be done to settle conflicts over land resource ownership and management between the two villages as well control proliferation and dominance of Acacia nilotica as a way to improve pasture and improve species diversity in the area.
Key words: Tree stocking - rules and regulations - anthropogenic disturbances
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