Land use transitions and vegetation dynamics in the Rwizi catchment, Uganda

Abstract

Land use transitions and vegetation dynamics are critical to the ecological and biogeochemical processes in catchments. They are proxies of the catchment health and integrity and knowledge on them can facilitate planning and interventions for sustainable environments. Whilst Rwizi drainage catchment is reported to be highly degraded, there is paucity of knowledge pertaining to land use transitions and vegetation dynamics. This study therefore assessed land use transitions and vegetation dynamics on short to medium temporal scales in Rwizi drainage catchment. The objectives of the study were; (i) determine land use transitions (ii) assess the spatio-temporal vegetation dynamics and (iii) determine the drivers of land use cover change. Land use transitions were determined from multi-temporal satellite imagery data using the Terrset Land Use Change Modeler (LCM). In the modeling, Markovian processes were employed to analyze the pattern and trend of transitions. Vegetation dynamics were assessed using the Normalized Differential Vegetation Index (NDVI). Phonological profiles of vegetation along selected transects within the catchment were taken to identify the variations of different factors. Temporal NDVI values were correlated to precipitation to elicit lags and variations. In order to identify drivers of land use and land cover change a cross-sectional survey was undertaken among the selected respondents and the data obtained was subjected to a logistic regression analysis. Results show an increase inbuilt up areas and farmlands from 0.95% to 10% and 2% to 35% respectively between 1985 and 2015. This led to decrease in forest area and woodlands from 15% to 2% and 13% to 1% respectively in the same study period. Well defined dry and wet seasonal variations in vegetation phenology were observed, with NDVI peak values increasing in the second growing season except for the year 2005 where it decreased by about 1.2 percent. For grasslands, the NDVI peak values increased in the second growing season by 1.3%, 1.05%, 6.48% and 6.5% in 2001, 2005, 2009, and 2014 respectively. Crop production, level of education, occurrence of bush fires, livestock increase and farm land size were the major socio-economic drivers (p<0.05) of land use and land cover change identified. The study concludes that the Rwizi drainage catchment is experiencing drastic changes in land use and land cover with the conversions mainly occurring in the woodlands, forests to farmlands and built up areas. Further, precipitation and elevation have an influence on vegetation growth and distribution within the Rwizi drainage catchment. Agriculture was found to be the main factor of land use change, therefore interventions that modernizes farming and limits its horizontal expansion would address the identified issues.