The Response of Rabbit Populations and Vegetation to Rabbit Control on a Calcareous Shrubby Grassland in Central Australia

Abstract

The effect of rabbit control methods on rabbit populations and subsequent changes in vegetation were assessed over 2 years on a calcareous shrubby grassland in central Australia. Warren ripping and fumigating decreased mean population levels to four rabbits per kilometre of spotlight transect, and 1080 poisoning decreased mean levels to 9 km-1, compared to the untreated levels of 20 km-l. Release of European rabbit fleas did not have any significant effect on rabbit populations. In the untreated rabbit populations, 68% of the fluctuation in numbers was accounted for by total rainfalls in the previous summer and the previous winter, and by a forage greenness rating. Experimental control of rabbits combined with exclosures indicated that grazing by high numbers of rabbits reduced the frequency of Enneapogon spp. at one site whereas levels rose in all other sites during the two years of good rainfall. The frequency of several species, such as Chenopodium cristatum, Phyllanthus rhytidospermus and Portulaca oleracea, was highly correlated with rabbit density in the previous year, suggesting that rabbit grazing promotes their increase. Grazing'by rabbits alone depressed standing biomass in the following season by 300 kg ha-1 from a maximum 1200 kg ha-1 within the exclosures. Cattle grazing further decreased biomass by 150 kg ha-1. Seedlings of Acacia kempeana were almost absent in those areas open to rabbit grazing, but they were reasonably dense where rabbits were excluded. However, the vegetation response over the 2 years of experiment was due mainly to seasonal changes rather than rabbit control, and does not justify the expense of rabbit control at this stage. Substantial improvement in vegetation composition over the longer term may alter this conclusion.