OBJECTIVES




Range Ecology
(Dr. Anja Linstaedter)

 

Approach

We investigate degradation processes in savanna related to land management., using concepts and methods of range ecology.

 

Issue Degradation

Degradation is the long-term or permanent loss of economic value - in respect of rangeland, therefore, the irreversible reduction of stock production.
Degradation is no absolute. It is a concept variously interpreted according to the interests of different user groups. Descriptions of the extent to which a pasture has been degraded are almost invariably subjective. Ecologists recently have come to the conclusion that environmental changes, thus also droughts and processes of degradation, only become „environmental problems“ as a result of their economic and cultural context.

See paper by Bollig & Schulte (1999) for a discussion of contrasting perceptions of degradation in African savannas:

 

Issue Sustainability

Savannas are ecosystems highly threatened by degradation. This process is the main reason for the accelerated economic vulnerability both of subsistence and commercially orientated land use systems. We therefore ask which aspects of range management ensure sustainability.

Good criteria for a sustainable land use systems in savannas are:

    1. protection of natural resources
    2. risk minimization
    3. maintenance of productivity
    4. economic viability
    5. social acceptance

      (after SNYMAN 1998)

A sustainable land use is best described with respect to its goals and to the processes and management measures to achieve them. We concentrate our investigations on two cases of subsistence orientated land use and two cases of commercially orientated land use in a Namibian savanna. These case studies represent the broad range of range management approaches and related economical objectives in Southern Africa. One form of land use (Communal Conservancy) is promoted by government within the context of CBNRM (Link). It aims to counteract overexploitation and degradation of natural resources. At the same time, it intends to create an assured income for rural poor.

Method Monitoring

From an ecological point of view, the question of sustainabity can hardly be answered from analyses of the current state. It is practically impossible to investigate causal relationships occurring during vegetation changes by means of empirical snapshots of moments in time. Such relationships can only be studied by the direct documentation of temporal variability and directional changes, ideally by regular monitoring of permanent plots. Furthermore, permanent plots provide the opportunity of extrapolating beyond the actual scope of the monitoring period and to predict future environmental scenarios (e.g. caused by a recombination of ecological factors). Lastly, such direct field studies can be used to evaluate ecological models.

Detailed information on our methods of monitoring

 

Method Grazing Exclosures

A further essential tool of range ecology are grazing exclosures. On arid and semiarid ranges grazing exclosures provide information about the regenerative power of the pastures and about the structure of vegetation not affected by grazing. The dynamics of savanna vegetation are still not fully understood. The dynamic processes in savannas under pastoral land use are particularly complex. They are characterised by interactions between rainfall, soil conditions, history of land use and the actual land use pressure. A fundamental understanding of these multiple interactions is indispensable for identifying or developing adequate forms of land management.

Detailed information on our grazing exclosures

 

Common economic traits of a successful land management: Flexibility

Range degradation is not a continuous, but an episodic process. Variables such as rain fall are driving forces for ecological change. They are impossible to control by management. In event-driven ecosystems man can never control variability via a single biological variable, e.g. the stocking rate. Static management systems inevitably promote the risk of degradation, because they can rarely adapt to crisis situations - if at all, they do so very slowly.

The best possible manner of range utilisation is not to attempt to predict the unpredictable future but to continuously adapt to the ever-changing environment. A basic common feature of successful forms of land use in highly variably environments thus is „opportunistic“ or „flexible“ management such as pastoral nomads in Africa have applied for thousands of years. However, the criterion „opportunism“ evaluates the success of a land use mainly from the human perspective. First and foremost a successful land use system adequately guarantees the survival of the herds of the user in a highly variable environment. Consequently such a system is only indirectly based on the conservation of natural resources.

 

Common ecological trait of a successful land management: Near-natural disturbance regime?

A considerable discrepancy exists between the economic significance of savannas and the relative lack of knowledge about savanna ecology. We still discuss the so-called “savanna problem”, that is how grass and tree layer can coexist without competitive exclusion. Today many ecologists postulate that savannas, on the level of several criteria, are event-driven systems in which certain disturbances play an important role in maintaining a savanna-like vegetation structure. Considering this role of disturbances, it can be postulated that an ecologically sustainable land management in savannas implies a disturbance regime with ceratin similarities to the natural disturbance regime. Hence our project also focuses on the significance of anthropogenic disturbances for ecosystem functioning and sustainability.

Our study of basic principles of a successful (sustainable) range management is done in close co-operation with the two Junior Research Groups: