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Paving our understanding of how roads impact wildlife

Updated: Sep 1, 2022

By Balint Andrasi

Balint Andrasi was an MSc student at the University of Exeter’s Conservation Science and Policy course. His final year dissertation was supervised by Dr Kimberley Hockings and Dr Kristian Metcalfe. Balint is now based at the Natural History Museum of Luxembourg, where he carries out research on the diversity, distribution and genetics of wild bees and hoverflies.

What are the main threats to biodiversity? Although that may depend on the species and where they are found in the world, but generally I would say habitat loss, climate change, and invasive species. What often gets missed is how the expanding global road network is contributing to them all.

Roads are fundamental for humanity. They facilitate trade, connect communities across landscapes and cultures, and allow people to access medical care, among many other benefits. However when they are ill-planned they can also do the opposite, by threatening the wellbeing and safety of communities, biodiversity, the economy, and even a country’s sovereignty.

I was oblivious to the enormous effects of roads before I started my dissertation research as part of the University of Exeter’s Conservation Science and Policy course. The enormity of the problem is daunting. The implications of expanding global road networks has crept up on me and is probably creeping up on most of us.

For my dissertation, I was interested in finding research that established so called ‘road-effect zones’ or REZs, which refers to the areas next to roads that have reduced populations of wildlife. Even though there were many papers on how species respond to roads, very few actually quantified an REZ. A few estimations exist for some birds, reptiles and amphibians, but estimates for large, charismatic endangered species were nowhere to be found. With over 90 percent of Europe located within less than 10 km from a road, I doubt that the true extent of their impact on large-bodied European species like bears and wolves is even measurable.

I was amazed when there were no REZs for primates – one of the most diverse and speciose mammalian orders that are mostly found in the Tropics. We set out to measure the REZ for a critically-endangered great ape, the western chimpanzee (Pan troglodytes verus). The West African forest and savannah ecosystems they inhabit are changing rapidly, with networks of roads planned across the region. We wanted our research to inform the already established legal framework to protect great apes from infrastructural development. As our main findings, we estimated that chimpanzees are impacted by major roads up to 17.2 km away. In addition, minor roads – which extend for approximately five times the total length of major roads –reduce chimpanzee abundance up to 5.4 km away. Together, that leaves about 5 percent of the entire range of the western chimpanzee (over half a million km2) free from the direct impact of roads (Fig. 1).

Figure 1: Reproduced from Andrasi, B., Jaeger, J. A. G., Heinicke, S., Metcalfe, K., Hockings, K. J. Quantifying the road-effect zone for a critically endangered primate. Conservation Letters. 2021; 00:e12839. under a CC-BY 4.0 license. No modifications were made to the figure.

We hope that the results of our paper will be: 1) used by relevant bodies (policy makers, development planners and conservationists) to better avoid or minimise road impacts on chimpanzees, and 2) help raise awareness of the unprecedented challenge that comes with constructing roads sustainably. And when I talk about sustainability I say it in the most transdisciplinary sense possible, sustainably for economies, communities and environments.

We ran out of time to slow climate change. Are we running out of time for mitigating road impacts?

If you want to read more about this research, please check out our article just published in Conservation Letters:

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