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Orange–Senqu River Basin Transboundary Diagnostic Analysis
Land degradation as a result of overgrazing, which is often accompanied by the invasion of alien species, is common to all the biomes in the basin. It generally renders the land less productive, reduces biodiversity and affects water balance. Land ownership issues are strongly related to land degradation and frequently stand in the way of sustainable land management and development in rural areas. These issues include the lack of land tenure rights, limited management control over natural resources and either a lack of, or a failure to implement appropriate rural development and agriculture policies. It is becoming increasingly evident that for many areas the biggest threat to the terrestrial and aquatic environments is poverty and lack of development rather than development itself. A shortage of land and associated resources leads to non-sustainable land management practices, the direct causes of degradation. Any solution to land degradation requires intervention to help create alternative off-farm livelihoods and/or to organise and encourage rational urbanisation, which will ultimately make the provision of social services less costly. While land degradation is taking place throughout the basin, the degradation of the river’s headwaters deserves special attention in view of the close linkages between the terrestrial and aquatic ecosystems in these areas. Degradation of the terrestrial environment translates rapidly into degradation of the aquatic environment, impacting the downstream environment and users. The main transboundary impacts of degradation of the Lesotho highlands relate to changes to the hydrological regime. In particular, increased levels of soil erosion, reduced infiltration and loss of wetland storage are translated into reduced base flow, increased levels of flooding and higher sediment loads. Land degradation is also a concern in south-western Botswana, which is dominated by linear, vegetated dunes. With the advent of borehole technology in the 1960s, wells were replaced by boreholes and many pans have become ringed by sizeable human settlements. This has made the pans less accessible to wildlife, and overgrazing of livestock around the pans and livestock watering boreholes has led to loss of vegetation and remobilisation of the dunes. Invasive alien plants
Alien invasive species are species introduced from another geographical location that establish themselves, grow and propagate. They often have adverse economic, environmental, hydrological and ecological effects on the habitats they invade and the indigenous vegetation found there. Large numbers of species are found in the higher-rainfall areas of the basin, especially in the Vaal and upper Orange–Senqu sub-basins. Invasions are particularly severe along the rivers in the basin. A number of species are problematic, but the most frequently recorded invasive alien is Salix babylonica (weeping willow), followed by Prosopis glandulosa (mesquite). These plants are closely associated with overall ecosystem degradation. Other relevant factors associated with the spread of invasive plants in the basin include changes in hydrological regime, reduced flows and poor water quality. Each of these contributes to the alteration of the natural ecosystem, disturbing natural habitat and creating a niche for alien species to take hold and proliferate. Along the Orange River, the proliferation of invasive alien plants is estimated to reduce river yield by as much as 13% in the upper catchment and 7.8% in the lower catchment. Effective clearing could reclaim these water resources for other uses. Numerous factors operating in the catchment may limit or even counteract restoration actions in specific reaches invaded by alien plants. Restoration should therefore be planned and implemented in an integrated way, respecting both the