Vegetation Cover Changes in Selected Pastoral Villages in Mkata Plains, Kilosa District Eastern Tanzania
Arid and semi-arid savannah ecosystems of Tanzania are subjected to increasing pressure from pastoral land-use systems. A spatial temporal study involving analysis of satellite imageries and range surveys was carried out to determine the effects of high stocking levels on savannah vegetation cover types in Mkata plains. The GIS data sources include MSS satellite image of 1975, Landsat TM images of 1991 and 2000. Information obtained during community mapping and timeline trend analysis with local communities formed a local knowledge integrated into GIS analysis. Ground- truthing was based on 2000 satellite imagery sub-scenes. The main vegetation covert types in the study area include: wooded grassland (23.5%), bush grassland (20.12%), bush land (15.15%), woodland (11.65%), open grassland (5.2%), and cultivation area (18.64%). Net area cover changes between 1975 and 2000 include: 4 X increase in bush land, – 66.7% loss of open grassland and + 95.3% increase of wooded grass lands. Land cover change detection matrix indicates that the main land cover changes involved conversion to cultivation area (33.0%) and succession progression towards woody vegetation cover types (+33.4%). The rangelands were overstocked, in poor range condition and declining trend. There was a strong negative correlation (r = - o.87932) between stocking levels and size of open grassland and perfect correlation (r = 1) between stocking level and woody grassland cover types. It was concluded that increasing stocking levels has significantly contributed to conversion to woody cover types and loss of open grasslands. It was recommended to develop state-transit-models in order to predict the likely system response to policy interventions and to integrate control fire regimes and livestock mobility in range management strategy for the area.
Key words: Savannas, pastoralism, herbivory, vegetation cover change, Mkata plains.