Rabbits and the failure of regeneration in Australian arid zone Acacia



Three experiments are reported concerning the effect of rabbit grazing (Oryctolagus cuniculus L.) upon the recruitment of Acacia seedlings to populations in the South Australian arid zone.

In western myall woodland (Acacia papyrocaqsa Benth.) under prevailing rabbit and sheep densities, seedlings exposed to grazing by these two herbivores or to rabbits alone were severely pruned, whereas totally protected seedlings grew unchecked.

Seedlings of four Acacia species; A. papyrocarpa, A. oswaldii (F. Muell.), A. kempeana (F. Muell.) and A. burkittii (F. Muell. ex Benth.) were transplanted into four 50 m × 50 m rabbit-proof enclosures. Six rabbits were introduced into each enclosure and within 24 h half of the total seedling population had been grazed. This was at a seedling dry weight ratio of 1|150 000 of the total fodder on offer. In one of the enclosures no seedlings were eaten and there is evidence to suggest that a dense patch of grass had a buffering effect, reducing grazing pressure.

Small shoots cut from old Acacia and transferred to the ground throughout 1000 ha of western myall woodland were grazed rapidly near rabbit warrens and progressively less rapidly with increased distance from warrens.

The experiments demonstrated that even with the lowered post-myxomatosis population densities, rabbit grazing pressure would significantly affect recruitment in arid zone Acacia populations in the absence of stock.