Understanding impacts of water supplementation in a heterogeneous landscape
Date
2011-03-11
Authors
Farmer, Helen
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Abstract
Artificial water provision is a contentious management issue in southern African
savanna conservation areas. Supplementation of permanent water leads to higher
herbivore population sizes which can generate greater profits. However, water
supplementation can lead to detrimental effects on soils and vegetation surrounding
waterpoints. Currently, the impact of artificial waterpoints across properties is
understood in terms of the piosphere model: concentric circles with differing
degradation levels, focused on waterpoints. Southern African savannas are highly
heterogeneous so the suitability of a homogeneity based approach in management is
questionable. Provision of water currently follows a relatively high degradation risk
strategy on many properties so a sound basis for management is essential.
This study assessed the general applicability of the piosphere model by testing the
relationship between distance to water and ecological variables (soil functionality and
herbaceous and woody vegetation). 23 variables were tested across 22 waterpoints
from five properties within the Great Limpopo Transfrontier Conservation Area.
Statistical approaches used matched those of previous piosphere studies but only 14%
of tests were significant. Although utilisation gradients were found for some variables
and some transects, there was no generally applicable pattern. This means that results
from previous piosphere studies cannot be transferred to unsampled waterpoints or
scaled up across properties. The level of heterogeneity in southern African savannas
disrupts the piosphere pattern to such an extent that the model does not form an
appropriate basis for management.
In order to develop an alternative approach to understanding the functionality of
properties which takes into account both water supplementation and heterogeneity,
the influence of a range of environmental and management variables on degradation
and species composition were tested using ordinations. The best explanation of
variation was a combination of environmental and management variables. Broader
scale variables such as natural and artificial water availability were more important
than finer scale variables such as distance to water. These results were used to
develop a basic approach to evaluating property functionality.