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Rabbits

Apart from the past impact of domestic sheep, cattle and horses, the main introduced grazing species is now the rabbit. Rabbits were not of concern in our Research Woodland in the 1980s, as the groundcover was much more open and there was little cover for rabbits to allow populations to build up. By 1991 however the impact of rabbits, particularly diggings and dunghills were obvious enough for us to have the fenced, rabbit exclosure plots set up.

Rabbits: exclosure plot observations

In pre-European times grazing and browsing animals included wallabies, kangaroos, possums, bandicoots, as well as birds and invertebrates. Present today, though in smaller numbers are some Swamp wallabies and Wallaroos. We have seen no signs of bandicoots or possums, and we have no idea of what changes have occurred as far as bird and invertebrates are concerned.

Our initial expectations were that in the fenced rabbit exclosure plots there would be obvious establishment and growth of species grazed by rabbits elsewhere, in particular of lilies and rarer herbs. However these expectations were not met.

In general, the appearance of the fenced plots has remained similar to surrounding unfenced areas. Native plant species richness in fenced plots did not differ significantly from unfenced plots over an 8 year period (see Figure  below). Annual recordings were made in November.

However for exotic species, though there was no difference at 4 years, there was a significant difference at 8 years with 40% more exotic species within the fenced plots (see Figure below).

One plot showing a marked response to the absence of grazing is Plot 10. Plot 10 becomes dominated by dense growth of the exotic grasses *Lolium perenne and *Bromus catharticus in spring, particularly in wet years, with the herbage dying off in summer; the dead grass cover preventing establishment of native species later in the season. *Lolium perenne was widespread and common in all plots at the beginning of the monitoring, having presumably been encouraged as a pasture species. However by the early 1990s it had disappeared from most plots, but was still present in two of the fenced plots 5 years later. It would appear that rabbit activity helped remove *Lolium perenne but that in their absence, and with the right weather conditions, it can dominate the groundlayer.

Our general observations are that rabbit browsing appears to be random, but some native species, particularly Calotis lappulacea and Stackhousia viminea, are heavily affected at certain times. There are only a few plants of Calotis lappulacea in the woodland; these are clustered and were severely chewed by rabbits during dry conditions in 2002. Some were covered with wire netting to protect them. Unprotected plants were eaten down to ground level, some plants subsequently died. All fruits on these plants were eaten. Seed survived on protected plants but no new seedlings have been observed. Inflorescences are commonly chewed off Stackhousia viminea, and while this does not kill the plant it does not allow for seedling recruitment.

A prominent rabbit activity is digging holes 5-10 cm deep, probably associated with digging for roots. It is more noticeable in dry periods. There does not appear to be any particular concentration on particular species, though the digging is generally in open areas, as though the rabbits are using tracks. This digging provides localised patches of bare soil that may be colonised by seedlings of native and exotic species.

Some rabbit activity tends to concentrate droppings on bare soil areas that become small dunghills. Seedings of some species appear to recruit in these sites, particularly Solanum prinophyllum, *Solanum nigrum  in autumn. With winter rainfall, seedlings of Cotula australisCrassula sieberiana, *Lepidium species and *Stachys arvensis are common.

Asterisk * indicates exotic species naturalised at the Australian Botanic Garden.


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