Relationships between livestock management and the ecological condition of riparian habitats along an Australian floodplain river.
Abstract
Grazing by introduced ungulate livestock is a major form of land use over large parts in Australia. Due to the tendency of stock to concentrate around water, riparian zones and wetlands are heavily impacted by grazing. However, little is known about how effects on riparian habitats vary spatially and with management regimes. We investigated how livestock affected riparian habitats on the Murrumbidgee River in south-eastern Australia. Floodplain vegetation in this area is dominated by the native river red gum (Eucalyptus camaldulensis), and the riparian zone was therefore defined as the area which was vegetated (or would have been prior to clearing) with this species. A rapid appraisal index of the ecological condition of floodplain riparian habitats was developed. This measured habitat continuity and extent, vegetation cover, bank stability, soil structure, quantity of fallen debris, dominance of natives vs. exotics, and the presence of indicative species. The method could be readily adapted for use on other floodplain rivers with extensive riparian habitats. Riparian condition was scored at 138 sites along 620 km of the Murrumbidgee River on private properties (n=77), in State Forests (n=27) and on Crown Land (n = 34). Riparian condition declined significantly with increasing grazing intensity and also with distance upstream in the upper half of the floodplain. Stocking rate, distance upstream, relative periods of paddock rest and grazing, proportion of bank accessible to stock, and the presence of off-river water in the paddock, accounted for 76% of the variance in riparian condition. Most riparian habitats on the Murrumbidgee River and other rivers in the Murray-Darling Basin are privately owned. Thus exclusion of the grazing industry from the riparian zone was not practical. However, lowered stocking rates, particularly in the upper parts of the catchment, resting of paddocks to allow recovery from grazing, and the provision of off-river watering points could all be used to improve riparian habitats. Exotic plants are ubiquitous, occurring even where grazing has been excluded for many years. Thus restoration of riparian habitats will require weed removal even in areas not used by livestock.