Abstract
The Kruger National Park (KNP) has developed and refined a system of management called ‘strategic adaptive management’ (SAM), which rests on the concept of ‘threshold of potential concern’ (TPC). TPCs represent end-points in a continuum of change. When thresholds are reached – at which point concerns of negative impacts on biodiversity are raised – management options are explicitly considered and implemented. This paper describes the TPCs developed for monitoring and managing invasive alien species (IAS). More importantly, however, it describes the conceptual understanding, principles and hypotheses adopted as the foundations for setting these TPCs. In accordance with adaptive management practices, the TPCs will be revised as the ecological and conceptual understanding of invasions grows and information is gained through research in the KNP and elsewhere.Conservation implication: In accepting that species and systems are variable, and that flux is inevitable and desirable, these TPCs developed for invasive alien species specifi cally, provide end points against which monitoring can be assessed. Once a threshold is reached, the cause of the threshold being exceeded is examined and management interventions recommended.
Highlights
Objectives hierarchyTracks ecosystem change to which there is not always a clear management response Usual response
Hypothesis: An increase in the density of invasive species leads to a negative impact on indigenous biodiversity, whether in terms of composition, function or structure. This hypothesis has not, been tested in the Kruger National Park (KNP) and only arbitrary density values have been assigned as evaluation criteria far
This is a substantial challenge for an area the size of the KNP
Summary
Tracks ecosystem change to which there is not always a clear management response Usual response. The first invasive-species TPCs (Foxcroft & Richardson 2003) provided a list of various criteria for evaluation These included 1) a new distribution in the KNP or an increase in distribution, 2) an increase in density, 3) the rate of spread versus the rate of clearing, 4) impact on biodiversity and 5) outside alien threats (Foxcroft & Richardson 2003). The expansion and contraction of alien species are expected to occur through natural processes and disturbances, such as floods, droughts and the resulting change in succession (the acceptance of a flux paradigm), the total area of the invasion should not be allowed to increase above a stated maximum tolerable ‘ceiling’ level from the base scenario This level is currently set at 5% but it is an estimate and requires refinement. This hypothesis has not, been tested in the KNP and only arbitrary density values have been assigned as evaluation criteria far
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