The Effect of Land use/cover change on Biomass Stock in Dryland Areas of Eastern Uganda. A case study of Olio Sub-county in Soroti District

Abstract

Drylands occupy 44% of Uganda's land surface and provide livelihood to a cross-section of both rural and urban folks. However in the face of population pressure, drylands are increasingly in the path of conversion and degradation. This study therefore, performed an assessment of the effect of land use/cover change on biomass stock in olio sub-county from 1973 to 2001. A series of systematically corrected Orthorectified Landsat imageries of 1973, 1986 and 2001 obtained from the Landsat website were used. The images were analysed using unsupervised approach in Integrated Land and Water Information System version 3.3 and validated using field observations and historic memories of village elders. Findings indicate that land use/cover change is driven by small-scale farming. Between 1973-1986 significant declines were identified among small-scale farming (23.2%), grasslands (8.7%) and large scale-farming (9.9%). Further, declines were also registered between 1986-2001 in Bushland (12.1%), woodlands (13.9%) and wetlands (8.2%) while dramatic gains were registered in small-scale farming by 19.4%. These declines led to losses in the available biomass stock by 2001 within bushlands, wetlands and woodlands loosing 29.1 million tons, 669.1 metric tons and 87.3 million tons respectively. We conclude that small-scale farming by resource poor farmers is rapidly transforming the vegetation landscape. Therefore, there is need for increased use of remote sensing and GIS to quantify change patterns at local scales for essential monitoring and assessment of land use and or/cover change effects and human interference on the landscape. @JASEM Uganda's drylands cover 44% of the country (84,000 km 2). They are the second most fragile ecosystems in the country after the highlands (NEMA, 2007). These environments provide livelihood to both rural and urban folks and are very important food production zones. The current land use/cover change (LUCC) patterns are threatening the stability of these ecosystems; this is because LUCC that once required centuries now take place within a few decades. This is largely attributed to the dare dependence on primary resources (Ademiluyi et al; 2008). However, land use has been a component of human-driven global change that has been occurring for the longest period of time. Imperatively, land-cover change associated with agriculture has had an enormous impact on the structure and functioning of ecosystems (Paruelo et al; 2001). These changes have increased the rate of species extinction, not only by replacing natural ecosystems but also by changing the disturbance regime. Further LUCC have a potential of triggering local and regional consequences including loss of soil fertility, soil erosion, reduction of biological diversity, hydrological changes, climatic alteration and a modification of the atmospheric composition. These have all attracted attention in the recent past but one very basic effect of LUCC on biomass stock has eluded attention. Historically, the driving force for most LUCC is population growth (Ramankutty et al; 2002b) although there are several other interacting factors involved (Lambin et al; 2001). LUCC detection at micro level allows for the identification of major processes of change (Fasona and Omojola, 2005) and can also facilitate quantification of change effects. The effects of LUCC are less well studied thus there is a need to understand LUCC and its effect on the overall ecosystems (Lambin et al; 2003). It is within this background that this study sought to determine the effect of LUCC on biomass stock.