Impacts of sand mining on species diversity of vascular plants in Lwera wetland, central Uganda

Abstract

Wetlands provide enormous socio-economic and environmental benefits but they are threatened by various degradation activities of which sand mining is one of the most rampant and devastating in Uganda. This study was conducted in Lwera wetland in Central Uganda to assess the impacts of sand mining activities on the diversity and distribution of vascular plants. The objectives were: (i) To characterize the sand mining sites; (ii) To determine the species diversity of vascular plants; and (iii) To assess the Spatial Turnover (β diversity) of vascular plants in the sand mined areas. The wetland was stratified in four zones based on the density of pits: 1). High pit zone: 2). Medium pit zone; 3). Low pit zone; and 4). Virgin zone. In each zone, four plots of 200m by 200m were established. In each plot, five subplots of 1m by 1m were established giving a total of 80 quadrats. Plant species diversity was determined in these subplots. Characteristics of sand mined sites were determined within three sand mined zones out of the four. The results show that the high pit zone had a pit density of 0.248 while the low pit zone had a pit density 0.109. The average pit size ranged from 13, 314.2m2 in the low pit zone to 2, 144.8m2 in the high pit zone. A total of 75 species belonging to 25 families and 60 genera was recorded. The plant forms included the Herbs-39 spp., Climbers-9 spp., Grasses-9 spp., Sedges-7 spp., Shrubs-8 spp., and Creepers-3 spp. Plant diversity was highest in the High pit zone (Shannon-Wiener diversity index-H1 = 2.57); and lowest in the Virgin zone (H1 = 1.7). The turnover was highest in the paired zones of high pit zone and Virgin zone (β1-J =80%) indicating that the similarity of plant species in the two zones was relatively low. Pit area (F = 6.710, df = 1, p = 0.005), Zone (mined vs unmined, F = 5.12, df = 1, p = 0.005) and pit density (F = 2.829, df = 1, p = 0.005) influenced the distribution of wetland species. Environmental variables induced by sand mining played an important role in influencing plant species diversity and though, this seems positive to the biological integrity of the sand mined sites, it is assumed that some ecologically and socio-economically valuable wetland plant species were lost. There is therefore a need to develop a strategy for sustainable use and management of wetlands for sand mining.