Barbara Bowen

During the late 19th and early 20th centuries, frustrated pastoralists in South Australia, New South Wales and Queensland fenced their properties to stop the Australian dingo (Canis lupus) killing their livestock. Eventually links formed between individual fences, creating a continuous barrier now covering over 5000 km. Known variously as the Dingo Fence ‘Dingo Barrier Fence or ‘Wild Dog Fence it is of wire mesh standing 1.8 in high, with a further 30cm buried. There is a 5 m wide cleared buffer on each side and the entire structure is well maintained. On the New South Wales side of the fence where sheep are the main livestock, dingoes are controlled and numbers are low, whereas on the South Australian side dingoes are tolerated alongside cattle husbandry. Unintentionally, the fence initiated a large-scale experiment, allowing biologists to assess the biological consequences of removing a large predator. Alan Newsome and his colleagues from the Commonwealth Scientific and Industrial Research Organisation (CSIRO) studied vertebrate abundances on either side of the fence by counting animal tracks at stock watering points. One striking finding was that the introduced predator the red fox (Vulpes vulpes) was present on both sides, but in higher numbers in the absence of dingoes. Dingoes eat foxes and drive them away, explaining the differences in fox numbers across the fence. Foxes threaten several native Australian mammals (see Chapters 2 and 16), including many borrowers and diggers important in soil turnover, nutrient cycling and dispersing plants. It may be that, by regulating fox numbers, dingoes are protecting native fauna that in turn modify the environment to the benefit of many soil organisms. The case of the Dingo Barrier Fence shows how relationships between organisms determine the range and relative abundance of species.

The condition of the tuart tree (Eucalyptus gomphocephala), a coastal southwestern Australian woodland species, has declined dramatically within parts of its distribution over the last decade, particularly within Yalgorup National Park. Prior to the park being gazetted in 1968, some of the woodlands were used for cattle grazing. Frequent, light, understorey burns were carried out to encourage grass fodder growth. Earlier, Aboriginal use is believed to have involved a similar regime to facilitate hunting and access. Since gazettal, the majority of the park has either been excluded from fire, or burnt infrequently by wildfire and prescribed fire. Consequently, from 1968 to the present, most fires are thought to have been more intense due to increased fuel loads. Alterations in disturbance patterns (particularly fire) elsewhere, have been linked with vegetation changes (composition and structure) and in some instances, declining tree health. For tuart woodland, it has been proposed that increased abundance and vigour of the lower storey peppermint tree (Agonis flexuosa) and a decline in the health of tuart trees are consequences of reduced fire frequency. Sample plot data from the mid – late 1970s and photographs from 1957 are contrasted with the 2003/2004 situation to describe changes in tuart woodland. Declining tuart health, changes in the health and abundance of some understorey species (for example, fewer Banksia attenuata) and a shift towards peppermint dominance are revealed. The contribution of changing fire regimes to these trends is explored. While a link between fire and changes to the woodland may be established, factors underlying the loss of tuart dominance remain to be determined. An integrated research project is in progress to examine the range of decline factors.