COS 191-1 - Road-effect mitigation in times of rapid road construction across the planet: Modelling the fence-end effect and the FLOMS trade-off to determine effective fence-length
Current rates of road construction on the globe are unprecedented. More effective mitigation of the growing road impacts on wildlife populations is urgently needed. Wildlife fences are highly effective at reducing road mortality, often used in combination with wildlife passages. In contrast, measures that are less expensive than fencing (e.g., wildlife warning signs and reflectors), are ineffective, and wildlife passages do not reduce road mortality unless fences are present. Will a Few Long Or Many Short (FLOMS) fences be more successful? In theory, fencing many short road sections would require a shorter total amount of fence for the same predicted reduction in mortality than fencing a few long sections (Spanowicz et al. 2020, Cons. Biol. 34(5)). However, animals can move around the fence ends and often get killed there, which reduces the effectiveness of fencing. Mortality-reduction graphs can be employed to prioritize road sections for fencing, following an adaptive fence-implementation plan (Spanowicz et al., 2020). The “fence-end effect” makes the use of a few long fences more interesting, because animals are more likely to change course before arriving at the fence end. How long is long enough for a fence to be effective?
Results/Conclusions
We present a novel analytical model for predicting the fence-end effect as a function of fence length (L) and home-range size of the target species. We compare four variations of the model with empirical data. Effective fence-length is Leff= L–R in Model A, Leff= L–0.5×R in Model B, Leff= L–0.4521×R in Model C, and Leff= L–0.226×R in Model D, where R = radius of the home range of the species. The probability of fence success is PFS= 1–R/L in Model A, P<sub>FS = 1–0.5×R/L in B, PFS= 1–0.4521×R/L in C, and PFS= 1–0.226×R/L in D. We predict and compare the minimum length of wildlife fencing that can be expected to be effective for various species. We also present modifications for fences that are poorly maintained. The models are included in the mortality-reduction graphs to predict the effectiveness of any fencing configuration and to help planners design effective and efficient configurations of fencing. We compare mortality reduction graphs and proposed highway fencing maps for Highway 175 in Quebec for two species.
