The Effects of Grazing by Kangaroos and Rabbits on the Vegetation and the Habitat of Other Fauna in the Tidbinbilla Nature Reserve, Australian Capital Territory.

Abstract

Exclosures established in 1979 at 3 grassland sites in the Tidbinbilla Nature Reserve kept out kangaroos and rabbits, kangaroos only or rabbits only, at each site. The occurrence of some plant species changed over time in all treatments as a result of natural plant succession, but other changes were caused mainly by grazing by the grey kangaroo [Macropus giganteus]. The 3 sites were different floristically mainly in the percentage cover of Themeda australis, Bromus molliformis, Hypochoeris radicata and Trifolium spp. The frequency of occurrence of moss, Haloragis tetragyna, Rumex acetosella, B. molliformis and Trifolium spp. also differed between sites. Compared with ungrazed plots, exclosures grazed by kangaroos had decreased percentage cover of Glycine clandestina, Aira caryophyllea and Haloragis tetragyna whereas moss species increased. Bothriochloa macra, which occurred only at 1 site, increased on plots grazed by kangaroos and produced a significant site-treatment interaction. The plots grazed by kangaroos had increased frequency of occurrence of dicotyledonous seedlings, A. caryophyllea, Danthonia sp. and H. radicata. Since 1982-83, the frequency of occurrence of G. clandestina, Lomandra filiformis and Verbascum thapsus decreased where the grey kangaroo grazed. New species recorded in 1986, that appeared only in sites grazed by the grey kangaroo, included B. molliformis, Eriochilus cucullatus, Trifolium campestre, Luzula sp. and Silene gallica. Species such as Hibbertia obtusifolia, Plantago lanceolata, Lactuca serriola, Conyza bonariensis, Danthonia sp. and Hydrocotyle laxiflora were not present on plots grazed by the grey kangaroo. Height of Acrotriche serrulata, dicotyledonous seedlings, G. clandestina, H. laxiflora, Hypericum gramineum, H. radicata, L. filiformis, Poa sp., Sorghum leiocladum and T. australis was reduced markedly in plots grazed by the grey kangaroo, although grazing did not always appear to be the reason. The reduction in the height of the vegetation made the areas unsuitable for stubble quail (Coturnix pectoralis) and Richard's pipit (Anthus novaeseelandiae), and also affected certain invertebrates.