Dry Matter Biomass Productivity and Composition of Grasses along Grazing Gradient in Fenced and Unfenced Grazing Areas of the Gaborone North, Botswana.

Abstract

Objective: The present study was aimed at assessing and comparing grass species composition and biomass productivity along fenced and unfenced grazing gradient. Methods: For each study area 2 × 1000 m transects radiating from the water points (borehole) were used and sampling plots of size a total of 15 quadrants of size 1 m2 were systematically placed along each transect at intervals of 50 m for the first 500 m and the last 500 m the spacing interval was increased by 100 m. The total biomass of the selected plots was clipped, weighed; oven dried at 65 ̊C for 48 h and weight again in order to express the weight by dry matter. Results: The grazing gradient in fenced area exhibited the highest dry matter biomass (P<0.05) for the grass species at 644.7 g/m2) as compared to the unfenced area at 155.9 g/m2. High-value species (341 g/m2) significantly dominated the dry matter biomass composition in the fenced gradients while in the unfenced it was dominated by medium value species (66.8 g/m2). Despite the fluctuation of biomass from one interval to another, logarithmic trend line estimations suggested an increasing plant biomass relative to the distance from the water point in both grazing gradients. Areas of high biomass were demonstrated at 900 m in both fenced (915 g/m2) and unfenced (433 g/m2) gradients. Dry matter biomass declined in areas close to and furthest from the watering points. The high biomass of the intermediate grass species dominated by E. rigidior suggests that it was highly unutilized. Conclusions: Our findings indicate that dry matter biomass productivity of fenced gradients was higher as compared to that of unfenced grazing area. Dry matter biomass in fenced was mainly composed of high value species especially U. trichopus Meanwhile E. rigidior mid value species contributed the largest share to the biomass in the unfenced gradient.