Data from: A few large roads or many small ones? How to accommodate growth in vehicle numbers to minimise impacts on wildlife

Roads and vehicular traffic are among the most pervasive of threats to biodiversity because they fragmenting habitat, increasing mortality and opening up new areas for the exploitation of natural resources. However, the number of vehicles on roads is increasing rapidly and this is likely to continue into the future, putting increased pressure on wildlife populations. Consequently, a major challenge is the planning of road networks to accommodate increased numbers of vehicles, while minimising impacts on wildlife. Nonetheless, we currently have few principles for guiding decisions on road network planning to reduce impacts on wildlife in real landscapes. We addressed this issue by developing an approach for quantifying the impact on wildlife mortality of two alternative mechanisms for accommodating growth in vehicle numbers: (1) increasing the number of roads, and (2) increasing traffic volumes on existing roads. We applied this approach to a koala (Phascolarctos cinereus) population in eastern Australia and quantified the relative impact of each strategy on mortality. We show that, in most cases, accommodating growth in traffic through increases in volumes on existing roads has a lower impact than building new roads. An exception is where the existing road network has very low road density, but very high traffic volumes on each road. These findings have important implications for how we design road networks to reduce their impacts on biodiversity.

道路与机动车交通是对生物多样性最为普遍的威胁之一，因其会造成栖息地破碎化、提升野生动物死亡率，并为自然资源开发开辟新的区域。当前，道路上的机动车数量正快速增长，且这一趋势未来大概率仍将持续，进而给野生动物种群带来愈发沉重的生存压力。因此，当前面临的一项核心挑战在于：如何规划道路网络以容纳日益增长的机动车保有量，同时尽可能降低对野生动物的负面影响。然而，目前我们几乎缺乏可用于指导实际景观中道路网络规划决策、以降低其对野生动物影响的相关原则。为此，我们开发了一种量化方法，用以评估两种应对机动车数量增长的备选策略对野生动物死亡率的影响：其一为新增道路数量，其二为提升现有道路的交通流量。我们将该方法应用于澳大利亚东部的考拉（Phascolarctos cinereus）种群中，量化了两种策略各自对死亡率的相对影响。研究结果表明，在大多数场景下，通过提升现有道路的交通流量来应对交通增长，其对野生动物的影响要低于新建道路。唯一的例外情况是：当现有道路网络的路网密度极低，但单条道路的交通流量却极高时。上述研究发现对于我们如何设计道路网络以降低其对生物多样性的负面影响具有重要的指导意义。