The effect of redistribution of artificial stock waters from a boredrain to pipes and troughs on the vegetation and soil resources was investigated from December 1994 to October 1998 in a sheep paddock in the semi-arid mulga woodlands of south west Queensland, eastern Australia. The study examined 1) the effect of changing water distribution on the distribution of understorey biomass, sheep, cattle and macropods at the paddock scale; 2) patterns m herbivores, vegetation and soil out from the boredrain and change through time following water redistribution; 3) patterns in herbivores, vegetation and soil out from the new troughs and change through time following water redistribution; and 4) the relative effects of native versus domestic stock on piosphere development out from a trough.
Landscape zone and season were major drivers of vegetation and soil dynamics and patterns in this mulga landsystem. At the paddock scale, biomass and woody cover patterns were consistent with historical grazing gradients out from the boredrain, semipermanent waters and previous and current fencelines. There was a high degree of temporal variability in herbivore distribution patterns, not just related to changing water distribution. The native herbivores which presumably have evolved in this system were more likely to be correlated with forage resources than water at the scale of this study. This is in contrast to sheep whose spatial selection of feeding sites was partly influenced by non alimentary factors such as distance to waters, winds and fences, but largely unexplained. While sheep distribution was no longer correlated with distance from the boredrain following piping at the paddock scale, there was no evidence that 1) herbivores were focusing grazing activities around new troughs and 2) that vegetation patterns have changed following water redistribution.
The boredrain had distinct gradients in vegetation and soil surface condition associated with it that persisted following rainfall and the lightening and then removal of domestic stock. Gradients in functional plant composition, diversity indices, grass cover and soil stability, revealed zones of reduced production potential parallel to the drain. Following closure of the drain herbivore activity rapidly declined, but there was little evidence of rehabilitation during three years of above average rainfall. Reassessment of the site at 5 yearly intervals over a period in excess of 20 years would better tell the story of change post-drain. Current data suggests the drain induced gradient will continue to persist for many years, providing a 'ghost of waters past'
In the first two and a half years following changeover from the boredrain to point waters, there was little change to the natural landscape patterns in soil and vegetation out from the southern troughs. Patterns in soil and vegetation around troughs initially reflected patterns of geomorphic zone and tree and shrub distribution. While there was an increase in stocking intensity immediately around the new troughs, there was little evidence of a vegetation and soil response to this increased stocking activity. However increased soil erosion and restricted shrub recruitment close to the troughs perhaps signal the beginnings of change out from the new troughs through time.
Comparison between prevailing total grazing pressure, kangaroo only grazing and no large herbivore grazing, found that removal of stock had the effect of dramatically increasing the rate of woody cover change over the period of the study. In contrast the proportion of unpalatable plants increased most at the highest stocking rate with both domestic and native herbivores present. Soil surface condition and plant species also responded to exclosure from domestic stock, indicating that resting paddocks has the potential to improve soil and vegetation condition providing macropod densities are at similar levels to when stock are present.
Given that the rehabilitation of degraded areas adjacent to boredrains is unlikely at least in the short term, and that little change has occurred out from new troughs, it is likely that there will be little net change in degraded land as a result of piping bores in mulga landscapes with the level of water availability of this study. Factors likely to influence piosphere development and ecological and management implications for the Boredrain Replacement Program are identified.