Conducting general improvements of infrastructure can provide a useful opportunity to incorporate wildlife connectivity. However, given that there are also many other factors to consider, decision-making about connectivity needs to move fast and mesh well with existing cost and feasibility workflows. Connectivity models don’t always consider practical and social factors such as implementation cost, stakeholder perspectives, or competing land use interests.
A recent study at the Department of Energy (DOE) Oak Ridge Reservation in eastern Tennessee sought to integrate salamander connectivity into existing plans for culvert replacement and upgrades to benefit both management and conservation goals.
Wade, B.S., Carter, E.T., Derolph, C.R., Byrd, G., Darling, S.E., Hayter, L.E., Jett, R.T., Herold, J.M. and Giffen, N.R. 2023. Advancing wildlife connectivity in land use planning: a case study with four‐toed salamanders. The Journal of Wildlife Management: e22456.
Wetlands in the area are used by four-toed salamanders, a species of conservation concern in many states. Four-toed salamanders can be difficult to detect, so breeding sites were identified using prior observations and habitat suitability models, in addition to field surveys.
Researchers also collected field and remotely-sensed landscape data, and identified likely paths and barriers for salamander movement. Detailed data on roads and culverts were obtained in collaboration with the Oak Ridge National Laboratory (ORNL) and the United States Army Corps of Engineers. LiDAR technology was used to assess terrain roughness. Many of the landscape features assessed (such as ground saturation and presence of particular predators) were calibrated by relevance to four-toed salamanders for a species-specific approach.
Using this wealth of data, the researchers compared combinations of possible management strategies. These included removing barriers, creating buffer zones around culverts via native plantings and reduced mowing, and/or replacing culverts with open bottom culverts (which are easier for wildlife to move through). DOE and ORNL facilities and operations staff participated in a cost assessment process based on their expert knowledge. Researchers compared the culvert scenarios using Circuitscape and measured the percent increase in connectivity per million USD and per square meter of land modified.
The study found that the strategy of replacing current culverts near barriers on primary roads with open-bottom culverts and buffer vegetation performed best when considering connectivity, cost, and land modification effort. This strategy would increase connectivity similar to what was modeled for scenarios that required the removal of 40% more barriers or modifying 20% more culverts. Removing barriers also significantly increases connectivity; however, barrier removal was the most expensive and least feasible strategy. Providing buffer zones without installing open-bottom culverts is less expensive but requires much more land modification to see similar connectivity returns.
This study sought to incorporate connectivity planning into an existing decision-making framework for the DOE that didn’t consider wildlife management outside of regulatory components. It provides a great example and a great outcome: the recommended management strategy provided only slightly less connectivity returns than the ecologically ideal scenario of barrier removal, but for less than 20% of the total cost.
Another take-away from this study is the importance of existing, accessible, and fine-scale environmental data. The authors emphasize that the availability of such data allowed for rapid assessment of landscape scenarios without delaying managers. Additionally, this study highlights the value of a stakeholder engaged process. The strategy that emerged from this research was one that was practical and cost effective to implement without sacrificing connectivity. The best wildlife crossings are the ones that will actually be built.
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