Suchergebnisse

Degradation of natural resources has become a serious challenge in rangelands, bearing negative impacts on the pastoral ecosystems, livestock production and livelihoods. In Namibia, the driest country of sub-saharian Africa 45 per cent of the national land area can only be used as rangeland. Many Namibians are pastoralists, whose livelihoods mainly depend on natural rangeland vege-tation and water resources. 43 per cent of Namibia�s land surface is used by 90 per cent of the population under communal land tenure. This socio-economic importance makes the sustainable use of the rangeland essential. Furthermore northern Namibia will be heavily affected by climate change. Integrating local and scientific environment perception, decision-making proc-esses of the local land users and the impact of land use practices on vegetation dynamics into ecological research becomes increasingly important in today�s complex web of social, ecological and political changes. This thesis develops an integrated approach focusing on ecological aspects in a social-ecological rangeland system in Northwestern Namibia. Firstly I developed a methodological approach for the synthesis of local eco-logical knowledge (LEK) and scientific knowledge. I found that to local live-stock herders, woody species are more important than herbaceous species, what does not correlate with species� ecological performance in the grazing area. I hypothesise that reliability of forage resources in times of scarcity is important in local perception. This shows that integrating LEK on ecological items into ecological research helps to identify criteria, or indicators for local management decisions. In the second step I matched local knowledge and local management decisions. In dealing with scarce and variable natural resources it is crucial to acquire a functional understanding of the interactions between management strategy and the mechanisms which buffer the variability of rainfall. I differentiated between abiotic buffers (key resource areas) and biotic buffers (storage tissue and stockpiled forage). The two biotic buffer mechanisms can be managed via herd mobility. I analysed how mobility is connected to the supply of the eco-system goods �water� and �forage�. I related the mobility decisions of local herders to the biotic and abiotic buffers of pastures used to see if they made use of pastures with key resource properties. In the communal areas, the main decision factor for mobility was permanent water availability and herders mainly follow short-term management objectives. Their set of options may be limited by influences that go beyond ecological conditions, such as land pres-sure, a non-adapted institutional framework and limited options for sustaining their livelihoods. This section shows that to grasp the essential elements of range management it is important to understand user objectives in deciding when and where to move in times of scarce resources. Reliability, which is perceived as an important criterion for the quality of for-age resources, has a lot in common with the concept of key resources, which are defined as forage resources available in times of resource scarcity. While other authors have a descriptive approach to the reliability of key resources, I functionally defined them as biotic and abiotic buffers. In contrast to a com-mon view in rangeland science decision-making of local pastoralists does of-ten not reflect the availability of key forage resources but of the second essen-tial resource for livestock, such as drinking water. In the third step I evaluate the overall impact of the grazing practices on the vegetation and how to indicate ecological thresholds. Direct measures for sys-tem shifts are difficult to obtain, due to multiple factor controls that operate at diverse spatial and temporal scales. Consequently, there is a need for the de-velopment of indicators to determine if an ecosystem is approaching a thresh-old. I aimed to identify potential early-warning indicators and long-term indi-cators for crossing a degradation threshold in a semi-arid African savanna. I identified indicators for changes in a rangeland ecosystem on different levels. Long-term indicators were identified as the structural shift from grassland to woodland indicating a major shift in the supply with grazing resources, that indicate major ecological restructuring on a functional level symptomatic of land degradation. Furthermore early warning indicators, the ratio between annual and perennial grasses were characterised. The local range use strategy may not be adaptive, but seems to be the only possible adaptation of local users to the current ecological and socio-economic situation because options for action are restricted. Since the starting point for the analysis of social-ecological system functioning is the sustainable provision of ecosystem services and the maintenance of livelihoods, this integrated analysis is important to conceptualize the effects of environmental variability, the supply of ecosystem services, and to connect this to management rules. Progress in rangeland ecology can be achieved by integrating local knowledge, local decision-making processes with regard to their drivers and the impact of land use and environmental variability on the natural resources. If integrated analysis is to meet the challenges facing rangelands, users and scientists, the-ory and application have to be linked by a common set of objectives in which monitoring could become a vital tool in the quest for sustainable rangeland use.