Vegetation forms the most important natural interface between the atmosphere and the land surface. Consequently, land degradation is therefore often associated with vegetation change. The changes take place both on short and long term. The long term changes are generally studied under land cover change. The short term changes concern the seasonal and inter-annual variations.
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 significantly differs between the zones, dominated by croplands (see table and pie charts below). Implications are that high intensive cultivation zones such as Eastern Uganda, the Lake Victoria Crescent and the Highlands are running out options for further lateral expansion and production intensification is imminent.
|
Land Cover/ Zone (%) |
1 – Lake Victoria |
2 – Eastern |
3 – Eastern & |
4 – Cattle |
5 – Northern |
|
A – Croplands |
59 |
79 |
58 |
31 |
45 |
|
B – Wood & shrub lands |
7 |
4 |
10 |
26 |
40 |
|
C – Forest lands |
13 |
0 |
12 |
1 |
0 |
|
D – Grasslands |
14 |
5 |
17 |
36 |
14 |
|
E – Wetlands |
4 |
10 |
1 |
2 |
1 |
|
F – 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.
Land cover change statistics for Uganda is 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 harmonize the various data sets, to arrive at more reliable conclusions on trends in dominance of vegetation types and their respective area losses & gains.
A first quick analysis for Uganda seems to suggest, substantial losses in forest, shrub and savannah grasslands in favour of cropland expansion, between 2000 -2013.
III. Vegetation Dynamics
Vegetation dynamics for Uganda is being analysed using NDVI time series derived from the MODIS Terra satellite from 2000 to 2017. Two dynamic map animations (hyperlinks) are included below, demonstrating the large variations of growth and growing seasons, ranging from evergreen areas, bimodal and mono-modal climate systems. Periods of drought are easily recognized from the non-green locations. Changes vary from long to short term as analysed and displayed below.
IV. First insights in Net Primary Production & Carbon Assimilation
Net primary production represents the actual carbon assimilation rates (gC/m2) and carbon stocked in Uganda’s vegetation growth. Annual total may vary from xxx kg/m2 for croplands up to xxx Kg/m2 for forested areas.
Land Management is one of the key factors that determine the carbon losses/ exit from these locations thereby ultimately affecting how much is left for storage in the soils to contribute to a healthy soil system, including soil fauna as well as water & nutrient retention capacities.
V. Occurrences of fires/ burning
Fire can be considered as an agent of change. Many long term vegetation changes are invoked through burning. Although fires & burning are also natural phenomena, by far the largest amount of burning is human induced.
Modis satellite imagery was analysed for 2016 to show on a 2 weekly basis, where and when fires act as active agents of change. Implication of fires can be natural bush fires, activities of hunting, slash & burn practices, forest clearing or wetland reclamation, burning of crop residues.
Recommendations
Further analysis to more strongly underpin the various correlations and explore drivers that may exist, will assist planners and policy makers to prioritise, indentify limits to the Ugandan resources base and make timely corrections, to avoid declines and potential crises. This will better facilitate agricultural agencies and extension workers in the field, to identify new hotspots of degradation, for timely on-the-ground interventions and improved awareness.
