# Road barrier effect

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{{Short description|Effect of roads and railways on the movement of wildlife}}
{{Redirect|Barrier effect}}

The '''barrier effect''' of roads and highways is a phenomenon usually associated with [landscape ecology](/source/landscape_ecology), referring to the barrier that [linear infrastructure](/source/Linear_infrastructure_intrusions) like [roads](/source/roads) or [railways](/source/railways) place on the movement of animals. Largely viewed as a negative process, the barrier effect has also been found to have several positive effects, particularly with smaller species.<ref name="positive-effects">{{cite journal |last1=Downing |first1=R.J. |last2=Rytwinski |first2=T |last3=Fahrig |first3=L |date=2015 |title= Positive effects of roads on small mammals: a test of the predation release hypothesis |journal=Ecological Research |volume=30 |issue=4 |pages=651–662 |doi= 10.1007/s11284-015-1264-4}}</ref> To reduce a road or railway's barrier effect, [wildlife crossings](/source/wildlife_crossings) are regarded as one of the best mitigation options, ideally in combination with wildlife fencing.<ref name="positive-effects"/> The barrier effect is closely linked to [habitat fragmentation](/source/habitat_fragmentation) and [road ecology](/source/road_ecology).

thumb|Highway 10 in Quebec, Canada

==Effects on wildlife==

===Negative effects===

====Roads====
Both existing roads and the construction of new highways act as barriers for many species, fragmenting the surrounding habitat to such a degree that [connectivity](/source/Landscape_connectivity), or the ability for an animal to travel to all areas of its [home range](/source/home_range), is made practically impossible.<ref>{{cite journal |last1=Dupras |first1=J |last2=Marull |first2=J |last3=Parcerisas |first3=L |last4=Coll |first4=F |last5=Gonzalez |first5=A |last6=Girard |first6=M |last7=Tello |first7=E |date=2016 |title= The impacts of urban sprawl on ecological connectivity in the Montreal Metropolitan Region |journal=Environmental Science & Policy |volume=58 |pages=61–73 |doi= 10.1016/j.envsci.2016.01.005|hdl=2445/102826 |hdl-access=free }}</ref> Generally, animals with a higher [vagility](/source/vagility), or ability to travel long distances, are more severely impacted by roads compared to species with smaller home ranges.

====Railways====
{{Main|Railroad ecology}}
While very few studies have analyzed the effect of railways on animal movement, their presence across landscapes in most areas of the world suggests that they likely pose a significant barrier for many species. Most studies relating to this sub-field focus on animal use of [drainage culverts](/source/culverts) underneath railway networks. For example, Rodriguez et al. (1996) found that nearly 80% of culverts in their study received visits by both [mammals](/source/mammals) and [reptiles](/source/reptiles).<ref>{{cite journal |last1=van Rodriguez |first1=A |last2= Crema |first2=G |last3=Delibes |first3=M|date=1996 |title= Use of non-wildlife passages across a high speed railway by terrestrial vertebrates |journal=Journal of Applied Ecology |pages=1527–1540 |hdl=10261/43513 |hdl-access=free }}</ref>

====Land-use types====
Although few studies have analyzed the effect of land type on animal movement, those that exist have found man-made clearings and [agricultural land](/source/agricultural_land) to be strong barriers for many species who may only travel within forested landscapes.<ref>{{cite journal |last1=Laurance |first1=W.F. |last2=Lovejoy |first2=T.E. |last3=Vasconcelos |first3=H.L. |last4=Bruna |first4=E.M. |last5=Didham |first5=R.K. |last6=Stouffer |first6=P.C. |last7=Gascon |first7=C |last8=Bierregaard |first8=R |last9=Laurence |first9=S.G. |last10=Sampaio |first10=E |date=2002 |title= Ecosystem decay of Amazonian forest fragments: a 22‐year investigation |journal=Conservation Biology |volume=16 |issue= 3|pages=605–618 |doi= 10.1046/j.1523-1739.2002.01025.x|doi-access=free }}</ref>

===Positive effects===
12% of studies analyzing the effects of roads on animals have found positive effects, indicating that some species benefit from the presence of roads.<ref>{{cite journal |last1=Fahrig |first1=L |last2= Rytwinski |first2=T |date=2009 |title= Effects of roads on animal abundance: an empirical review and synthesis |journal=Ecology and Society |volume=14 |issue= 1|pages=21 |doi= 10.5751/es-02815-140121|doi-access=free |hdl=10535/2475 |hdl-access=free }}</ref> The [predation release hypothesis](/source/predation_release_hypothesis), suggesting that roads may indirectly cause increases in abundances of animals whose [predators](/source/Predation) are negatively affected by road,<ref name="positive-effects"/> is often attributed to most positive effects of roads on animals.

==Mitigation measures==

===Driver behavior===
Studies have found that reducing the speed at which drivers travel along the road produces less [noise](/source/Roadway_noise), potentially reducing the road's barrier effect.<ref>{{cite journal |last1=van Langevelde |first1=F |last2= van Dooremalen |first2=C |last3=Jaarsma |first3=C.F.|date=2009 |title= Traffic mortality and the role of minor roads |journal=Journal of Environmental Management |volume=90 |issue= 1|pages=660–667 |doi= 10.1016/j.jenvman.2007.09.003}}</ref> The reduction in noise coming from the highway is assumed to make the road surface less intimidating for animals, potentially allowing crossings to take place. This increase in crossings, however, may result in a subsequent increase in [animal-vehicle collisions](/source/Roadkill).

===Animal movement===
[[File:WildlifeCrossingRoad38IsraelOct092022 02.jpg|thumb|right|A wildlife overpass built over [Highway 38](/source/Highway_38_(Israel)) in Israel]]

[Wildlife crossing](/source/Wildlife_crossing)s, such as wildlife [overpasses](/source/Overpass) or [underpasses](/source/Subway_(crossing)), are generally seen as the most effective [mitigation](/source/mitigation) measure to help make roads more passable for wildlife while increasing both driver and animal safety. To funnel wildlife towards these crossings, many studies have called for a combination of both wildlife crossings and exclusion [fencing](/source/Fence), making the crossings under or over the road the only available path for wildlife.<ref>{{cite journal |last1=Olsson |first1=M.P. |last2= Widen |first2=P |date=2008 |title= Effects of highway fencing and wildlife crossings on moose Alces alces movements and space use in southwestern Sweden |journal=Wildlife Biology |volume=14 |issue= 1|pages=111–117 |doi= 10.2981/0909-6396(2008)14[111:eohfaw]2.0.co;2|doi-access=free }}</ref><ref>{{cite journal |last1=Yanes |first1=M |last2= Velasco |first2=J.M. |last3= Suarez |first3=F |date=1995 |title= Permeability of roads and railways to vertebrates: the importance of culverts |journal=Biological Conservation |volume=73 |issue= 3|pages=217–222 |doi= 10.1016/0006-3207(94)00028-O }}</ref> With a combination of both wildlife crossings and suitable lengths of fencing, the barrier effect of roads is expected to decrease, allowing animals to access both sides of the road and therefore allowing for important life cycle processes including [migration](/source/Animal_migration) and [mating](/source/mating).<ref>{{cite journal |last1=Beben|first1=D |date=2012 |title= Crossings for animals–an effective method of wild fauna conservation |journal=Journal of Environmental Engineering and Landscape Management |volume=20 |issue= 1|pages=86–96 |doi= 10.3846/16486897.2012.662753|doi-access=free }}</ref>

==References==
{{reflist}}

Category:Landscape ecology
Category:Transport and the environment

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Adapted from the Wikipedia article [Road barrier effect](https://en.wikipedia.org/wiki/Road_barrier_effect) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Road_barrier_effect?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.