Roads as corridors, for better and worse

By Tomasz Sienicki [user: tsca, mail: tomasz.sienicki at gmail.com] - Photograph by Tomasz Sienicki, CC BY 2.5, https://commons.wikimedia.org/w/index.php?curid=13377

Railways, roads, and other linear structure have the potential to help spread invasive plants in multiple ways. Credit: Tomasz Sienicki

Highways, interstates, railroads, two-lane and dirt roads – all have the potential to act as corridors for not just people, but plants and animals as well. That includes both rare or threatened species in need of connectivity, as well as invasive species looking to spread out. Two new studies provide evidence for how linear infrastructure can act as corridors in contrasting ways.

Roads and railroads are common transportation highways that enable invasive plants to spread via increased edge habitat, increased disturbance, and increased opportunities for “hitchhiking” on vehicles. This ability to spread could potentially interact with landscape context at multiple scales.

A new study looks at invasive plants across the eastern United States in over 44,000 plots from the USDA Forest Service Forest Inventory and Analysis (FIA) program. It compares their presence with the presence of roads and railways, along with the land use types and ecological provinces within which plots were located.

Invasive plants, such as this kudzu, can be found across the eastern United States near transportation corridors. Credit: Jud McCranie

The results show that invasive plant richness was highest on plots nearest to roads and railways regardless of landscape context. In contrast, the rate of decay for invasive richness- i.e. how quickly invasive species become absent as you move away from the linear structure – was influenced by both land use and ecological province, with richness declining fastest on plots associated with development. This means that while these transport corridors definitely encourage the spread of invasive plants, the extent to which they do so is highly context dependent.

While roads have the potential to spread invasive species, they also have the potential to connect pollinators. Road verges (the habitats immediately adjacent to roads) cover large areas of land and can support numerous small patches of flowers, grasses, and other plant life important to pollinators. Given the growing concern over pollinator declines, active management of road verges may be useful in conserving pollinators and keeping populations connected.

Unmowed road verges can act as corridors for pollinators to move between larger habitat patches. Credit: Gilles San Martin

A recent global review summarizes the current research on how road verges act as corridors for pollinators. It also discusses the potential negative impacts of roads, and highlights how appropriate management can enhance road verges to support pollinators.

The synthesis of 140 studies reveals that it’s well established that road verges are hotspots for flowers and pollinators, and that strategic management can enhance road verges for pollinators. Traffic and road mortality are shown to have negative impacts on pollinators, but the benefits of road verges likely outweigh these costs. Key management recommendations for improving road verges include creating high quality habitats on new and existing road verges, reducing mowing frequency, and reducing the impacts of street lighting.

Resources

Ward, S.F., Taylor, B.S., Hamil, K.A.D., Riitters, K.H. and Fei, S. 2020. Effects of terrestrial transport corridors and associated landscape context on invasion by forest plants. Biological Invasions 22: 3051-3066.

Phillips, B.B., Wallace, C., Roberts, B.R., Whitehouse, A.T., Gaston, K.J., Bullock, J.M., Dicks, L.V. and Osborne, J.L. 2020. Enhancing road verges to aid pollinator conservation: A review. Biological Conservation 250: 108687.

Urban power lines act as corridors for both native and invasive plants (December 2015)

Small-scale connectivity makes a big impact for some species (June 2020)

State	Year	Policy	Description
New Hampshire	2026	SB592	Enables regional, conservation, and energy resource planning for habitat strongholds and wildlife corridors
New Hampshire	2019	SB200	Requires the New Hampshire Department of Transportation to consider fish and wildlife crossings and mitigation measures in all future road and culvert projects
New Hampshire	2016	SB376	Requires the fish and game department to identify existing and needed wildlife corridors connecting wildlife habitats in the state and to make recommendations for legislative changes

State	Year	Policy	Description
Maine	2023	LD258	Appropriates $7.5 million to Department of Transportation to improve roadways with potential adaptations for wildlife
Maine	2023	LD1881	Establishes compensation fee program relating to fish and wildlife habitats and associated corridors, including compensation paid by solar energy development
Maine	2023	LD508	Requires Department of Environmental Protection to review its permitting laws concerning climate change, habitat connectivity, ecological resilience, and coastal environments

State	Year	Policy	Description
New Jersey	2025	S3618	Directs state agencies to develop a Wildlife Corridor Action Plan
New Jersey	2024	S3916/A5486	Expands eligibility for existing wildlife fencing programs by including farmers leasing farmland
New Jersey	2007	NJAC7:13	Requires the state to incorporate wildlife crossings or a natural bank for terrestrial threatened and endangered species and/or species of concern when a new bridge or culvert project would cause habitat fragmentation

State	Year	Policy	Description
New Mexico	2023	SB72	Appropriates money to new Wildlife Corridors Fund for implementation of wildlife crossing projects under New Mexico Wildlife Corridor Action Plan
New Mexico	2022	HB 2	Allocates funding for projects to reduce wildlife-vehicle collisions and allows the Department of Transportation and Department of Game to implement their Wildlife Corridors Action Plan
New Mexico	2019	SB 228	Requires the creation of a Wildlife Corridor Action Plan that includes comprehensive guidance to agencies for identifying, prioritizing and maintaining important areas for wildlife movement

State	Year	Policy	Description
Washington	2023	HB1216/SB5196	Requires Department of Ecology to prepare environmental impact statements for clean energy projects that consider impacts to habitat connectivity and wildlife migration corridors
Washington	2022	SB5689	Provides funding for US 97 Wildlife Crossing Improvements project
Washington	2019	SEO 1031.02	Recognizes the effect of roadways in creating barriers to wildlife movement, breeding, and migrations; the Washington State Department of Transportation will promote and support Practical Solutions and Planning and Environmental Linkages to integrate habitat connectivity and biodiversity plans; will make use of the highway prioritization map known as Habitat Connectivity Investment Priorities; and will corporate and coordinate with other agencies involved in wildlife habitat protection, specifically along highways

Connecting Science to Conservation

Roads as corridors, for better and worse

Resources

About the Author: Heather Cayton

State	Year	Policy	Description
California	2026	SB1250	Requires the Department of Transportation (Caltrans) to include wildlife connectivity corridors and needs into its infrastructure project planning
California	2024	AB1889	Requires counties and municipalities to conserve wildlife corridors when planning new developments
California	2023	AB1760	Calls for a statewide analysis of wildlife corridors and connectivity to support conservation planning and climate change adaptation activities.
California	2023	SB145	Outlines provisions for transportation-related environmental mitigation, including funding for wildlife corridors, property and credit purchases for mitigation, reporting requirements, and mandates for wildlife crossings along Interstate 15.
California	2023	SB101	Provides funding for wildlife corridors and open spaces, including projects to improve connectivity and reduce barriers between habitat areas.
California	2022	AB2344	Establishes a state program to address roads with high wildlife-vehicle collisions, authorizes Caltrans to develop standalone wildlife connectivity projects, mandates an inventory and prioritization system for critical areas, and requires integration of wildlife passage features into relevant road designs.
California	2022	AB1384	Requires agencies to address vulnerabilities in Safeguarding California Plans, including protecting and enhancing wildlife corridors
California	2021	SB790	Approves compensatory mitigation credits for wildlife connectivity actions
California	2021	AB1183	Establishes the California Desert Conservation Program to protect biodiversity, including the protection and enhancement of habitat connectivity
California	2021	AB128	Appropriates funding for wildlife crossing projects, including the Liberty Canyon crossing for mountain lions
California	2015	AB 498	Amends the California Fish and Game Code to encourage, wherever feasible, voluntary steps to protect the functioning of wildlife corridors
California	2014	AB1471	Provides funds to the Sacramento- San Joaquin Delta Conservancy, in part to protect and restore aquatic, wetland, and migratory bird ecosystems including corridors.
California	2008	AB2785	Orders Dept. of Fish & Wildlife to investigate, study, and identify key wildlife corridors and linkages within the state, and to make those areas public

State	Year	Policy	Description
Florida	2024	SB1638	Dedicates annual funding to land purchases, conservation easements, and trail maintenance within Florida Wildlife Corridor
Florida	2023	HB1379	Creates annual appropriation to acquire lands that complete certain linkages and are under high population stress within Florida Wildlife Corridor
Florida	2023	SB2500 sec.146	Provides funding to buy Ocala to Osceola (“O2O”) Wildlife Corridor
Florida	2021	SB976	Tasks state agencies with maintaining wildlife connectivity and designates Florida Wildlife Corridor as an existing physical, geographically defined area
Florida	2021	SB2500	Appropriates $300 million to acquire lands to conserve Florida Wildlife Corridor
Florida	2019	SB7068	Creates a "Multi-use Corridors of Regional Economic Significance Program" that includes protection of wildlife corridors as an intended benefit
Florida	2008	SB542	Amends Florida Forever Act statues to include goals of connecting linkage corridors
Florida	2001	SB1468	Amends Florida Forever Act to establish that land acquisitions should include complete landscape linkages and corridors
Florida	1999	S908	Creates Florida Forever Program, with increased protection of lands that protect threatened or endangered species and plans to create a statewide system of connected landscape linkages