Should linear assessments be treated as a special case in fauna assessments?

Linear corridors, in particular long linear corridors for railway lines, haul roads, pipe lines and power lines, should probably be treated as a ‘special case’ when assessing the potential impact on fauna. The EPA (2004) Guidance Statement No 56 on Terrestrial Fauna Surveys for Environmental Impact Assessment in Western Australia in its Table 3 provides a guideline that indicates that the scale and nature of impact is high when the disturbance area is >10ha in Group 1 bioregions, >50ha in group 2-3 bioregions and >75ha in group 4 bioregions. In linear corridors, vegetation clearing is often limited to a maximum width of a 100m for a rail line, 50m for a road and 30m for a pipe line, but because of its length, will almost always exceed the 75ha, and a Level 2 fauna assessment would be the normal expectation. Is a corridor that is 100m wide, in a spinifex meadow on red sandy soil in the Pilbara, in fauna habitat that stretches for thousands of hectares on either side of the corridor, an impact that is high in scale and nature and one that warrants the expenditure of hundreds of thousands of dollars on flora and fauna surveys?

It is highly probable that the flora and fauna in the corridor are similarly represented in the adjacent areas; so is their loss likely to be highly significant, even on threatened species? In most cases these corridors will cut through fauna habitat that will remain mostly intact in adjacent areas. The overall size of the area to be cleared or impacted can be large (e.g. railway line), however, at a local scale, the impact can often be quite low (i.e. only a small proportion of an existing habitat is impacted on) unless the corridor passes through a habitat that is scarce in the sub-bioregion.

So instead of the current approach, perhaps the fauna assessment should focus more on:

  • edge effects;
  • corridors that will facilitate pest fauna and flora movements; and
  • barriers to fauna movements.

All of which are difficult to assess based on field survey data.

Edge effects include disruption to ecological processes such as predation and dispersal (Paton 1994), altered animal movements (Oxley et al. 1974, Goosem 2001) and changes to the fauna assemblage structure (Laurance 1991, Temple 1998, Luck et al. 1999). The consequence is that the impact footprint will always be much larger than the cleared area (Strevens et al. 2008). But how much larger is largely unknown.

Transport corridors have a propensity to develop weed infestations which can impact on natural fauna habitats. Cleared corridors can also provide improved predator access to areas (e.g. dogs and cats).

Raised ballast rail line foundations, cleared linear areas and pipelines laid on the ground all provide barriers to fauna movement through the landscape. These linear barriers can also impede the movement of fires, which can have both positive and negative impacts.

corridors 1 corridors 2

Plate 1. Pipeline linear corridor

Plate 2. Rail line linear corridor

In the Pilbara, there are already two major rail lines leading south from Port Hedland, with a third under construction and a fourth in the planning stage. The existing rail corridors often run parallel to each other a couple of hundred metres apart. Should a fire burn the area between two elevated rail lines, then there are few opportunities for fauna in adjacent areas to recolonise these burnt areas and they can become sterilized as a result.

In most circumstances, a Level 1 desktop review and a non-trapping field survey will be sufficient to describe the major fauna habitats and to map areas likely to support threatened species. The focus of the field work should be on identifying and describing the risks of impacting on fauna assemblages, in particular conservation significant vertebrate species or threatened ecosystems. In most situations, because the impact on the habitat at a local scale will be low, there will be no need to undertake a generic fauna survey along the corridor.

For a field assessment, two survey methods are useful for long corridors, particularly in areas that are relatively inaccessible:

  • helicopters; and
  • all terrain vehicles (ATVs).

A reconnaissance assessment using a helicopter flying at a low altitude and at a slow speed is a cost-effective method to delineate those areas that should be subsequently searched on-the-ground and where habitat likely to support conservation significant fauna (e.g. Macrotis lagotis, Leipoa ocellata) should be mapped. It is our experience that the usefulness of this approach is appreciably enhanced by previous on-ground knowledge of the fauna habitats being viewed from the air. ATVs are particularly useful in undertaking fauna assessments on long linear corridors, particularly in areas of relatively rough terrain and dense vegetation (Plate 3 and 4). We have used and found ATVs to be cost-effective in assessing threatened species habitat on hilly slopes, mature spinifex meadows, grasslands, heath sand plains and mulga woodlands.

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Plate 3. ATV being used for habitat assessment

Plate 4. ATV being used for habitat assessment

ATV riders need appropriate personal protective equipment (PPE; gloves, glasses, helmet, boots, etc) and vehicles should be equipped with UHF radios, GPS, scrub guards and first aid kits. It is important that users of ATVs have the necessary training and experience before embarking of fauna surveys in rugged and remote locations.

References

Environmental Protection Authority. 2004. Guidance for the Assessment of Environmental Factors. Terrestrial Fauna Surveys for Environmental Impact Assessment in Western Australia No. 56. Perth.

Goosem, M. 2001. Effects of tropical rainforest roads on small mammals; inhibition of crossing movements. Wildlife Research 28:351-364.

Laurance, W. F. 1991. Edge effects in tropical forest fragments: application of a model for design of nature reserves. Biological Conservation 57:205-219.

Luck, G. W., H. P. Possingham, and D. C. Paton. 1999. Bird responses at inherent and induced edges in the Murray Mallee, South Australia. 1. Differences in abundance and diversity. Emu 99:157-169.

Oxley, D. J., M. B. Fenton, and G. R. Carmody. 1974. The effects of roads on populations of small mammals. Journal of Applied Ecology 11:51-59.

Paton, P. W. C. 1994. The effect of edge on avian nest success: How strong is the evidence? Conservation Biology 8:17-26.

Strevens, T. C., M. L. Puotinen, and R. J. Whelan. 2008. Powerline easements: ecological impacts and contribution to habitat fragmentation from linear features. Pacific Conservation Biology 14:159-168.

Temple, S. A. 1998. The edge of the cut: implications for wildlife populations. Journal of Forestry 96:22-26.

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