Seasonal variability of pasture biomass and carrying capacity in Karamoja Sub-Region
Wabwire, Ambrose Buyinza
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Livestock in Karamoja defines the socio-cultural facets as the main financial capital and determinant of wealth, status, and resilience to climate variability shocks. However, pasture biomass for livestock is becoming a major issue of concern due to seasonal variations. Efforts have been made to quantify forage in this area before, although pasture biomass is very delicate especially under variable climate changes. This study was conducted in the cattle corridor of Uganda, (Karamoja region) a largely semiarid area to determine the seasonal variability of pasture biomass for grazers specifically cattle and sheep. The overall objective of the study was to determine the grazing carrying capacity of pasture biomass for livestock (grazers) in Karamoja Region and this was supported by three specific objectives which included: to Classify and quantify pasture biomass for grazers in Karamoja rangelands, to assess the spatial-temporal variability of pasture biomass quantity and to determine the carrying capacity of pasture biomass for cattle and sheep in Karamoja Region. The study has shown that the use of GIS/Remote sensing to complement field data is a dependable approach to quantifying pasture biomass and determining the carrying capacity of rangelands. The study adopted a quantitative research design and it employed pasture biomass quantification method using remote sensing. Carrying capacity was analyzed by gridding livestock and relating pasture stock with uptake by livestock. Field surveys, ground truthing and image processing were utilized in the study. The research materials employed consisted of landsat7 thematic mapper satellite images of 1987, 2002,2005,2009,2014 and 2016. Zonal statistics tool and raster calculator were used to compute carrying capacity with the formula CC = Forage Demand/Forage Supply per 1 km2 grid. The recode tool, and accuracy assessment tools in ERDAS were key in image classification and in merging of classes. Change detection across years and seasons was conducted in Ms excel. Data were tested for normality in SPSS. The Kruskal Wallis test was employed to establish variations in pasture quantity across seasons and years. Post hoc tests were strategic in determining variations between two seasons/years through pairwise comparisons. The study highlights the spatial and temporal variability of pasture quantity across selected years and seasons in the rangeland of the Karamoja region. Pasture biomass quantity in the dry season recoded 27.5kg/pixel compared to 46.1kg/pixel in the post dry, pre-wet 61.6kg/pixel and wet season recorded 77.2kg/pixel. This revealed an upward trend in pasture biomass production across seasons given the distribution of the climatic changes in the region. Annual pasture biomass production across the selected years in the four traditional seasons indicated 3673973 tones/km2 in Akamu, Akiceret 3509425 tones/km2, Akiporo 1844717tones/km2 and Atieth with 8935350 tones/km2 respectively. The carrying capacity across the four traditional seasons ranged between ≥15AUM/Km2in the dry season, ≥38 AUM/Km2 in post dry, Pre-wet season 24AUM/Km2 and ≥47 AUM/Km2in the wet season. Pasture biomass information during the dry season is not only important for grazing but also for determining the grazing decisions, range and pattern. During the dry season, grazers are mainly limited by grass quantity than quality. This study demonstrates that pasture biomass when quantified, are important for understanding grazing and feeding patterns of animals. The biomass monitoring system is crucial for planning and management of savanna ecosystems reminiscent of Karamoja region .The spatial and temporal variation in pasture biomass quantity is a strong gauge of pasture dynamics in the sub-region which is vital in supporting the herding decisions in the areas especially when choosing where to go and when to go. The concept of carrying capacity is useful for planning and decision-making purposes for pastoralist, calculations of the average productivity of land in terms of feed resources, and expected output of livestock. The ultimate validity of the CC concept rests on the recognition that biomass is governed by an interlinked set of environmental factors, which determine the upper and lower limits carrying capacity.