Effects of human activities to the composition of woody plant species of Ngarama south forest reserve in Kilwa district, Tanzania

This study assessed the effects of human activities on woody plant species composition of Ngarama South Forest Reserve (NSFR) in Kilwa District, Tanzania. Vegetation survey was carried out in 40 systematically established rectangular sample plots aligned in five transects across the entire forest of 2 070 ha. The information recorded in each plot included: species name, diameter at breast height (DBH), height of few selected woody species with diameter ≥ 5 cm and various indicators of human disturbance. Landsat TM and ETM+ images from year 1995, 2000 and 2011 were used to locate and quantify the land cover change in NSFR for the past 20 years. Inventory data were analysed by using Microsoft Excel and R software while Landsat images were analysed using ILWIS 3.0 academic software. About 126 plant species belonging to 34 families were identified. Out of these, trees contributed 63% (28 families) and shrubs 37% (17 families). Shannon-Wiener Index and Simpson Diversity Indices were 3.95 and 0.03 respectively. Moreover, a mean stem density of 667±19 stems ha-1 and basal area of 13.11±0.34 m2 ha-1 were obtained. There were 23 stumps (7±3 stems ha-1) with mean basal area of 0.24±0.09 m2 ha-1 of stumps removed as indication of ongoing anthropogenic disturbances in the forest. Other recorded indicators of disturbances were fire damage (50%), paths/roads (13%), pit sawing (8%), timber/planks/poles collection (8%), cultivation (5%) and forest clearing (8%). Although NSFR has fair species richness and well diversified, there was consistently negative change in forest cover, relatively to low stem density, mean tree height, mean DBH and basal area, an indication of the presence of human disturbance. Conservation measures such as improving governance and accountability are recommended as regards responsibility for intense management of the forest resources.