Quantification and characterization of encroach bushes targeted for conversion into livestock feed at Neudamm farm, Khomas region, Namibia
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Date
2020
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University of Namibia
Abstract
Bush encroachment is a serious problem in Namibia leading to significant reduction in livestock production and biodiversity. Harvesting encroacher bushes for conversion into livestock feed is a practice becoming more common. Every encroached area is unique in species composition and density of encroacher bushes and hence characterisation of such bushes is essential prior to laying out harvesting strategies. The main aim of this study was to determine the species composition and estimate the amount of feed-suitable biomass of the dominant species constituting encroacher bushes in Block G of Neudamm Farm. Landsat images (Landsat 5 TM and Landsat 8 TM) of the study site were used to stratify the area into low, medium and high bush density classes to assess how encroachment changed between 1989, 2000 and 2017. In the high bush density areas, bush densities, species composition, diversity and similarity were analysed in relation to site, topographical positions and soil properties. Data were gathered from 27 sample plots (2 x 50 m). There was a 14% increase in area covered by high bush density between 1989 and 2017. Senegalia mellifera had the highest density and biomass across all sites and at all topographical positions. Bush density differed significantly only between sites. Site 2 had significantly higher bush density than Sites 1 and Site 3. This higher bush density in Site 2 was contributed by presence of high numbers (in excess of 10000 plants/ha) of small sized trees and shrubs. Only Sodium had a negative correlation (Pearson correlation) with bush density at different topographical positions (p=0.3888), this could be because Na increases osmotic tension, by which water is held in the soil and as result the plant die-off. The total biomass of bushes varied significantly across sites (Kruscal Wallis Test, P=0.024 and biomass fit for animal feed varied significantly across Sites Kruscal Wallis Test, P=0.027). This variation is linked to variation in bush density since Site 2 which had the highest bush density also had the highest biomass. It is concluded that 4.8 tonnes/ha can be harvested by selectively removing S. mellifera. The study recommends harvesting of only S. mellifera as this would yield large amounts of uniform feed and preserve other rare species especially those being given special protection like Boscia albitrunca, Searsia lancea and Ziziphus mucronata. Similar studies are recommended for other areas where encroacher bushes are to be harvested.
Description
A thesis submitted in fulfillment of the requirements for the Degree of Master of Science (Environmental and Natural Resource Management)
Keywords
Bush encroachment, Senegalia mellifera, Species composition