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:
- protection of natural resources
- risk minimization
- maintenance of productivity
- economic viability
- 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:
|