Patterns of Changes to Woody Vegetation near Resettlement Sites in Semi-arid Northwestern Ethiopia

Communal rangelands provide diverse ecosystem services to millions of pastoralists and agro-pastoralists. Resettling destitute communities into hitherto uninhabited communal rangelands and forests, a common practice throughout Sub-Saharan Africa, is a threat to the sustainable use of range and forest land resources. In order to understand the effect of resettlement on a semi-arid woodland in northwestern Ethiopia, satellite imagery of 23 resettlement villages taken over a period of fourteen years, and woody vegetation floristic data for three old resettlements, three new resettlements, two refugee camps and one protected area were analyzed using ANOVA and canonical correspondence analysis (CCA). The normalized differential vegetation index (NDVI) and canopy cover around all village types decreased with disturbance gradients, while the magnitude of change varied according to the type of settlement. Limited canopy cover was observed in refugee camps and new resettlements, compared to old resettlements and protected areas. Woody vegetation height class showed a J shaped distribution in all sites except refugee camps (RC), indicating a decline in vegetation. CCA showed that variables like site type, altitude and disturbance gradient significantly affected the diversity of woody species at the different sites. Comparison of individual species responses to disturbances indicated that low fodder value invaders like Dichrostachys cinerea, and many Acacia species were increasing in proportion and coverage at the expense of some multipurpose species including Tamarindus indica, Diospyros mespiliformis, and Pterocarpus lucens. In the absence of regulated vegetation use, resettlements result in a decline in overall vegetation cover and a shift in floristic diversity in favor of invasive species.     

CORRELATIONS BETWEEN DEM-DERIVED TOPOGRAPHIC INDICES AND REMOTELY-SENSED VEGETATION COVER IN RANGELANDS

The paper describes an attempt to relate patterns of vegetation cover with topography and a set of biological and grazing intensity variables in a mountain and piedmont area of arid central Australia. Vegetation cover, as measured by an index based on data from the Landsat satellite, can also be used as an erosion/deposition surrogate so the results have implications for distributed erosion models. A simple, analytically based erosion model derived from the continuity equation does not reproduce observed patterns of vegetation cover, and neither do various topographically based moisture indices. A regression approach shows that patterns of vegetation cover are related to topography but the most important predictors are biological ones, with percentage of bare ground upslope being the strongest. Tests with variable drainage area show that relationships between cover and topography, bare area upslope and grazing effects change systematically with basin size and that scale effects are present. Distributed erosion models are not yet capable of handling biological processes very well, yet these processes must be incorporated if erosion prediction is to be successful.     

Population and rangelands in Central Tibet: a GIS-Based Approach

This study focuses on the meso-regional pattern of rangeland ecotypes in Central Tibet in relation to population density. Data on rangelands derive from a recent land-cover GIS database of China based on the 1:1,000,000 Land Use Map of China. Specific kinds of grassland and steppe are analyzed in relation to 466 township-level enumeration units selected from China's 1990 census in the Tibetan Autonomous Region. This methodology offers a finer geographic resolution than in all other available research reports, and results in a more detailed understanding of the kinds of rangeland resources available to Central Tibetan communities. Systemic land cover patterns are mapped, and reveal the importance of local interactions between population and rangeland ecotypes. Alpine meadow and alpine steppe predominate above the cultivation limit at approximately 4,200 m. In the densely settled valleys below this limit, dry steppe and scrub grassland predominate.