Impacts of the European Rabbit (Oryctolagus cuniculus) on Eucalyptus regeneration in Box-Gum Grassy Woodland

Abstract

Insufficient natural regeneration in an issue affecting modified landscapes around the world. Loss of tree cover due to a lack of regeneration has a detrimental effect on both biodiversity and agricultural productivity in these landscapes. Insufficient Eucalyptus regeneration is an established problem in Box-Gum Grassy Woodland, a threatened ecological community in south-eastern Australia. The European Rabbit (Oryctolagus cuniculus) is known to prevent recruitment of many species of woody perennials across a range of ecosystems. Its distribution overlaps with that of Box-Gum Grassy Woodland. Despite this, there have been very few studies on the effects of grazing by the European Rabbit on Eucalyptus regeneration in this ecological community. I investigated the impact of the European Rabbit on regeneration of Yellow Box (Eucalyptus mellidora) and Blakely's Red Gum (E. blakeyi) in Box-Gum Grassy Woodland in a Canberra nature reserve. One hundred and fifty seedlings of Yellow Box and Blakely's Red Gum were planted across a range of rabbit densities. Fifty of these seedlings were caged, representing zero rabbit density. At the location of each seedling I recorded potential explanatory variables representing three factors that may affect the impact of the European Rabbit on the survival of Eucalyptus seedlings: rabbit density, total availability of food and competition with other herbivores. The survival of planted seedlings was assessed after 6 weeks. I also measured the abundance of naturally occurring Eucalyptus seedlings at 100 sites in a retrospective study to assess longer-term impacts of rabbit grazing. Planted seedlings at zero rabbit density (caged seedlings) had a significantly higher probability of survival than uncaged planted seedlings, although this difference was minor. There was a significant association between rabbit density (as measured by rabbit diggings) and the survival of planted seedlings; however, seedling survival was only negatively associated with rabbit density at sites with a high cover of forbs. Rabbit density was also negatively associated with the abundance of naturally occurring Eucalyptus seedlings. This effect was greatest at sites with high grass cover. A high density of the other major herbivore at the site, the Eastern Kangaroo Grey (Macropus giganteus), did not drive rabbits to consume more seedlings. Although this study did not provide compelling evidence that the European Rabbits impacts Eucalyptus regeneration in Box-Gum Grassy Woodland, it does suggests that the rabbit presents a potential threat and rabbit control should be considered as part of restoration efforts in this ecological community. Show more