I. Introduction
Vegetation forms the most important natural interface between the atmosphere and the land surface. Land degradation is therefore often associated with vegetation change, taking place on both short and long time scales. Long-term changes are generally studied under land cover change; short-term changes concern seasonal and inter-annual variation.
II. Land cover & land cover change
According to information generated from the National Biomass Study (MWE, 1999), land cover for the Sustainable Land Management (SLM) zones differs significantly between zones, dominated by cropland (see table below). The implication is that high-intensity cultivation zones such as Eastern Uganda, the Lake Victoria Crescent and the Highlands are running out of options for further lateral expansion — production intensification is imminent.
Land cover change statistics for Uganda are relatively scarce, due to inconsistent and incomplete vegetation map data over time, especially for backward analysis of more historical trends — this forms a major challenge. A mapping process has been put in place to update, backdate, improve and harmonise the various datasets, to arrive at more reliable conclusions on trends in dominance of vegetation types and their respective area losses and gains. A first quick analysis for Uganda suggests substantial losses in forest, shrub and savannah grassland in favour of cropland expansion, between 2000 and 2013.
| Land cover (%) | Lake Victoria Crescent | Eastern Uganda | East & South-western Highlands | Cattle Corridor | Northern Uganda |
|---|---|---|---|---|---|
| Croplands | 59 | 79 | 58 | 31 | 45 |
| Wood & shrub lands | 7 | 4 | 10 | 26 | 40 |
| Forest lands | 13 | 0 | 12 | 1 | 0 |
| Grasslands | 14 | 5 | 17 | 36 | 14 |
| Wetlands | 4 | 10 | 1 | 2 | 1 |
| Inland water bodies | 3 | 2 | 1 | 4 | 0 |
| Bare & built-up areas | 1 | 0 | 0 | 0 | 0 |
Source: National Biomass Data, analysed by NARL Kawanda GIS Lab.
III. Vegetation dynamics
Vegetation dynamics for Uganda are analysed using NDVI time series derived from the MODIS Terra satellite from 2000 to 2017. These show large variation in growth and growing seasons, ranging from evergreen areas to bimodal and mono-modal climate systems. Periods of drought are easily recognised from non-green locations, with changes varying from long to short term.
IV. First insights in net primary production & carbon assimilation
Net primary production represents the actual carbon assimilation rate and carbon stocked in Uganda's vegetation growth, which varies considerably between cropland and forested areas. Land management is one of the key factors determining carbon losses from these locations, ultimately affecting how much carbon is left for storage in soils — supporting a healthy soil system, soil fauna, and water and nutrient retention capacity.
V. Occurrence of fires & burning
Fire can be considered an agent of change — many long-term vegetation changes are driven by burning. Although fires and burning are also natural phenomena, by far the largest amount of burning in Uganda is human-induced. MODIS satellite imagery analysed for 2016 shows, on a two-weekly basis, where and when fires act as active agents of change. Implications of fire include natural bush fires, hunting activity, slash-and-burn practice, forest clearing, wetland reclamation, and the burning of crop residues.