Fragmented fauna habitats – the value of remnant vegetation plots

A quick look at the Perth metropolitan area in Google Earth will show numerous small plots of vegetation surrounded by housing and industrial development. Similarly, the Wheatbelt contains many remnant plots of native vegetation surrounded by farming land (Plate 1). The value of many of these remnant patches of vegetation should be self-evident as they are the last remaining refuge for the fauna that once inhabited a much larger area. Where the clearing of vegetation has occurred on a large scale, remnant plots can provide important fauna habitat (How et al. 1996, Smith et al. 1996, Smith et al. 1997, Berry and Berry 2008). Some of these remnants support conservation significant fauna (e.g. Isoodon obesulus fusciventer in the greater Perth metropolitan area) and provide foraging habitat for conservation significant birds that move through the landscape (e.g. Calyptorhynchus latirostris).

Often, few if any of these remnant plots will support the complete fauna assemblage that was present prior to the disturbance. For example, Smith et al. (1997) made the point that even relatively large remnants with diverse vegetation did not always support all of the species expected to be found in the district and How et al. (1996) reported numerous remnant vegetation plots in the Perth metropolitan area that supported herpetofauna species that were not present in other plots where they probably once existed. There is generally a strong positive correlation between remnant size and species richness (Kitchener et al. 1980a, Kitchener et al. 1980b, How et al. 1996, Smith et al. 1996, Smith et al. 1997). It follows then that there is generally a higher loss of species over time from smaller remnants and habitat patches.

Of particular importance for remnant plots is that once a species becomes locally extinct, there is little opportunity for recruitment from other remnant patches (Smith et al. 1996). Also because many of these areas are particularly small, they can only support a few individuals for each species making them more susceptible to local extinctions.

Plate 1. Remnant plots of vegetation in the Western Australian wheatbelt

On one hand there is a case that fauna surveys of remnants, particularly those that represent a small fraction of what once existed, are not required as the habitat and the fauna assemblage are sufficiently important that they should be protected. However, to develop a strong case for the protection of these remnants it is often necessary to indicate what fauna are present and what fauna are present in adjacent remnants to demonstrate the consequence of a loss of a remnant.

As a general rule, small remnants do not support the larger-bodied species, particularly carnivores nor do they support small-bodied species that require large home ranges. Large-bodied species typically require large home ranges and access to an abundant prey source. In smaller remnant plots, once the resource is depleted there are limited opportunity for recruitment and replenishment of this prey source. However, there are examples, where this principle appears not to apply. For example, we know of remnant plots of vegetation in the wheatbelt that are quite small that continue to support a small population of Varanus giganteus, and others in the south-west that support a small population of Morelia spilota imbricata. In both circumstances, without a survey, these species could easily go undetected and be lost during a vegetation clearing program.

Given the ecological importance of remnants there is a strong case for having a near complete list of species for each habitat type and a good indication of their relative abundance. Although some of these areas are quite small, extensive surveys are required to achieve this objective (Smith et al. 1997, Berry and Berry 2008). Smith et al. (1997) for example, trapped remnant vegetation plots in the wheatbelt that had previously been surveyed by a team from the Western Australian Museum, and commented on the number of species that they caught that were not recorded in the earlier Museum survey.

Because in most cases the fauna assemblage in remnant plots will have been diminished by disturbances in adjacent areas, it cannot be assumed that two nearby remnants with similar vegetation will support the same fauna assemblage. Therefore, to understand the ecological significance of the fauna in remnants, it will be necessary to undertake an appropriate fauna surveys.

What would be the consequences of the government amending the existing legislation in its push to reduce red/green tape and to make life easier for land developers if it enabled upto 5ha of native vegetation to be cleared without the need to seek approval, as it has recently done for farmers?

References

Berry, P. F. and O. F. Berry. 2008. Herpetofauna of four remnant bushland isolates in the City of Nedlands, Perth. Western Australian Naturalist 26:27-41.

How, R. A., M. S. Harvey, J. Dell, and J. M. Waldock. 1996. Ground Fauna of the Urban Bushland Remnants in Perth, Report to the Australian Heritage Commission NEP Grant N93/04. Perth.

Kitchener, D. J., A. Chapman, J. Dell, and B. G. Muir. 1980a. Lizard assemblage and reserve size and structure in the Western Australian wheatbelt- some implications for conservation. Biological Conservation 17:25-62.

Kitchener, D. J., A. Chapman, and B. G. Muir. 1980b. The conservation value for mammals of reserves in the Western Australian Wheatbelt. Biological Conservation 18:179-207.

Smith, G. C., G. W. Arnold, S. Sarre, M. Abensperg-Traun, and D. E. Steven. 1996. The effect of habitat fragmentation and livestock grazing on animal communities in remnants of gimlet Eucalyptus salubris woodland in the Western Australian wheatbelt. II. Lizards. Journal of Applied Ecology 33:1302-1310.

Smith, G. T., J. Leone, and C. R. Dickman. 1997. Small terrestrial vertebrate communities in remnant vegetation in the central wheatbelt of Western Australia. Western Australian Naturalist 21:235-249.