Simon’s project is concerned with the isolation of the Blue Mountains World Heritage Area as well as the issue of internal barriers and the effects this has on the native fauna as a prelude to efforts towards increasing the connectivity of the area with protected habitat to the north, south and west. An introduction to the project is available here.
Along with many others over the Anzac Day long weekend, I visited the Blue Mountains to enjoy some fresh air and beautiful scenery. The great majority of visitors coming from Sydney use the major transport corridor running across the mountains – the Great Western Highway or the neighbouring railway for those taking the train. As important as this route is to our needs, there is perhaps little thought given to the effect this corridor has on the World Heritage values of the area.
An historic route
The Great Western Highway is perhaps Australia’s most historic road. Its initial construction opened up the vast interior of the continent to the settlers previously confined to the coast. Many of the towns that are situated along the route such as Wentworth Falls, Lawson and Blaxland are named after the early European explorers who discovered that a path across the ridges of the mountains was possible.
Today the Great Western Highway is a major four-lane road with the railway, isolated by fencing on each side, often alongside. Unsurprisingly, considering the early importance of this road, the major settlements within the mountains are strung out along the route meaning that there is an urban belt stretching east-west across the ridge tops. There can’t be too many World Heritage Areas that are effectively cut into two by such a band of linear infrastructure and urban development.
The barrier effect
My research aims to consider both the external and internal connectivity of the Blue Mountains but it is the internal barriers to animal movement that I considered first. My early research has highlighted how roads can act as barriers to animal movement, affecting migration and home ranges possibly leading to altered social structures. The barrier effect can also alter patterns of gene flow with subsequent genetic drift and isolation (Taylor and Goldingay, 2010). As a consequence, roads have been described as the most destructive force driving habitat fragmentation (Van der Ree et al., 2011).
A number of studies from around the world have demonstrated the barrier effect of roads on species across many classes. Behavioural studies which demonstrate which species show an aversion to crossing roads and the factors that may decrease this inhibition are particularly valuable but few studies of this kind have been completed in Australia and studies that assess the impact of roads on gene flow are rarer still (Taylor and Goldingay, 2010).
Although the full consequences of roads for animals remain poorly understood (Beyer et al., 2016), Road Ecology is a growing field that has been attempting develop and assess solutions to the barrier effect of roads for some years. Even in Australia, which my research has shown to be behind much of the rest of the world, there have been some animal crossing structures built to help overcome these barriers. These include glider poles and rope bridges across the Hume Highway in NSW to help dispersal of arboreal mammals. In Brisbane a vegetated overpass crossing the Compton Road has been shown to be used by a range of animal groups.
Although such developments are welcome, it begs the question as to why more has not been done in a World Heritage Area listed for its natural values. The Great Western Highway has just been through a major upgrade over many years with the focus on easing traffic flow and safety. Only one animal underpass was created at Boddington Hill with little apparent assessment of its likely effectiveness either before or after construction.
Furthermore, the NSW Government commissioned an independent review of further upgrades proposed between Katoomba and Lithgow after community members raised environmental, cultural, social and economic concerns. The resulting report makes no mention of animal crossings in its recommendations. Retro-fitting animal underpasses or overpasses is likely to be difficult and costly so the lack of action on animal crossings during the upgrades seems like a lost opportunity.
How are other World Heritage Areas addressing the issue?
Like the Blue Mountains, Banff National Park in Canada is part of a World Heritage Area that is also bisected by a four-lane road – the Trans-Canada Highway. A key difference is that when this highway was expanded to four lanes, 23 animal crossing structures (overpasses and underpasses) where constructed at the same time and there have been numerous studies since that have highlighted their effectiveness (Clevenger and Sawaya, 2010). Meanwhile, in the World Heritage listed Wet Tropics of North Queensland it has become commonplace to include animal crossing structures across roads during major projects (Goosem, 2012). These include canopy bridges for arboreal species and underpasses for ground-dwellers.
In order to qualify for World Heritage status certain integrity conditions must be met. A synthesis of the Blue Mountains qualification notes that the area’s size and pristine condition will allow ecological processes to continue. However, little is known about how much of a barrier roads are in the area and whether they partially fragment it into smaller functional units. This may become more important if fires become more frequent and more intense as the climate changes.
In addition, the area is home to 40 threatened vertebrate taxa which may be more vulnerable to the potential fragmentation effects of roads than more common species. Road Ecology studies and mitigation efforts are becoming more common around the world but the Blue Mountains seems to be lagging behind. If animal crossing structures are going up outside of our protected areas surely it is appropriate to have similar structures in a World Heritage Area?
Beyer, H. L., Gurarie, E., Borger, L., Panzacchi, M., Basille, M., Herfindal, I., Van Moorter, B., R Lele, S. and Matthiopoulos, J. (2016) ”You shall not pass!’: quantifying barrier permeability and proximity avoidance by animals’, Journal of Animal Ecology, 85(1), pp. 43-53.
Clevenger, A. P. and Sawaya, M. A. (2010) ‘Piloting a Non-Invasive Genetic Sampling Method for Evaluating Population-Level Benefits of Wildlife Crossing Structures’, Ecology and Society, 15(1).
Goosem, M. (2012) ‘Mitigating the impacts of rainforest roads in Queensland’s Wet Tropics: Effective or are further evaluations and new mitigation strategies required?’, Ecological Management and Restoration, 13(3), pp. 254-258.
Taylor, B. D. and Goldingay, R. L. (2010) ‘Roads and wildlife: impacts, mitigation and implications for wildlife management in Australia’, Wildlife Research, 37(4), pp. 320-331.
Van der Ree, R., Jaeger, J. A. G., Van der Grift, E. A. and Clevenger (2011) ‘Effects of roads and traffic on wildlife populations and landscape function: road ecology is moving towards larger scales’, Ecology and Society, 16(1).