The Effects of Grazing Activity on the Hydrology of the Bogong High Plains, Australia.

Abstract

Stock have been grazed on the Bogong High Plains during the summer months every year for more than a century. Several severe droughts between the 1880s and 1920s resulted in abnormally large numbers of stock being depastured there in addition to the usual numbers, which contributed both to the degradation of the vegetation cover and an increase in erosion. In the 1940s, controls were placed on the number of stock permitted to graze the Bogong High Plains, and since that time total numbers 07 grazing stock have declined from 9000 cattle to just over 3000 cattle today. In this paper, historical hydrological data from the Bogong High Plains are examined to see if cattle grazing activities may be related to trends in the run-off of several streams in the subalpine and alpine zone. Long-term declining trends in both cattle grazing numbers and run-off variables were identified as statistically significant in one of the four catchments examined - albeit in the catchment with the longest run-off record. There was some evidence that the monthly run-off from three small catchments subject to differential grazing pressures supported a correlation between high grazing densities and large run-off volumes during the summer months, but this result was not substantiated by modelling daily storm hydrographs for those same months. All the hydrological data examined post-dates the period of major environmental degradation, which may have contributed to the moderate results obtained. The fact that run-off volumes declined between the 1940s and the 1980s suggests that there has been an improvement in the environmental conditions of the Bogong High Plains since grazing controls were introduced, but it is not certain whether full recovery has taken place, or ever will.