Impact of feral water buffalo

Abstract

Water buffalo were introduced into northern Australia from South-east Asia between 1826 and 1866. They became feral when early British settlements were abandoned. From these introductions they spread and occupied all major habitat types in the Northern Territory north of latitude 16 °S. There are no reliable historical estimates of population size. However, between the 1880s and 1956 buffalo were used intensively for hides and the large number of animals killed during that time almost certainly had a negative effect on population growth. Buffalo populations probably peaked around the middle of this century following the collapse of the hide industry and the ensuing reduction in harvesting. Since the 1980s buffalo numbers have declined dramatically as the result of an intensive effort to eradicate bovine tuberculosis of which feral buffalo and cattle are hosts. In Kakadu National Park buffalo populations declined from 5.6 to 1.2 animals km ⁻² between 1983 and 1988. Present population density is estimated at < 0.1 animal km⁻².

Buffalo have had major impacts on the biophysical environment of the Kakadu region. Overgrazing and trampling have resulted in a reduction of vegetation biomass, in some areas the complete removal of vegetation, and changes in species composition. Trampling, and the formation of pads and wallows have caused soil compaction. Vegetation loss and damage to the soil structure have contributed to accelerated soil erosion, particularly sheet erosion, tilling, piping and gullying. Buffalo induced erosion of levees flanking the freshwater reaches of rivers and those separating the tidal reaches from freshwater flood basins have resulted in changes to surface hydrology, including reduced retention of freshwater in flood basins and intrusion of salt water into freshwater swamps. The water quality of water bodies has suffered due to trampling, wallowing, grazing and the contamination by buffalo faeces and urine. The extent and intensity of impacts differed greatly between different landforms of the region. The uplands, which include the sandstone plateau of the Arnhem Land Escarpment were the least disturbed landform, while the most spectacular and intensive degradation of both land and vegetation was on the flood plains, particularly those in the lowland reaches of the South Alligator River. Flood plains and levees here are formed in silty and sandy alluvium which have areas of erodible duplex soils. The East Alligator and West Alligator River flood plains in contrast, are formed in sandy and clayey-sand soils and were much less severely degraded. The effects of buffalo on vegetation, soils and surface hydrology have also affected the native fauna. Changes in vegetation communities have caused magpie geese to change their nesting sites on the flood plains. Populations of dusky rats and other small vertebrates on the flood plains were also adversely affected by high densities of buffalo. The main reason probably related to the removal of vegetation cover which provided food and protection from predators.

While some studies point out that changes in the environment attributed to buffalo could have other reasons, such as fire, climate change or natural geomorphological processes, a large body of anecdotal evidence and photographic records seems to support research findings that buffalo at least contributed significantly to these changes.