Case Study: Ecological corridors in ecological networks
This case study is part of the IUCN Guidelines for conserving connectivity through ecological networks and corridors illustrating initiatives around the world that are working toward maintaining, enhancing, and restoring ecological connectivity. See all case studies here.
Fragmentation of riparian protections throughout catchments, Oregon, USA
By Rebecca Flitcroft, USDA Forest Service, Brett Boisjolle, Massachusetts Department of Conservation and Recreation, and Mary Santelmann, College of Earth, Ocean and Atmospheric Sciences, Oregon State University
Key lesson
Maintaining functional habitat can require policy protections and voluntary restoration efforts, both guided by science; monitoring and evaluation are critical to ensure that the actions will indeed result in the desired outcome.
Context and challenge
Lotic and lentic environments provide lateral connectivity to floodplain and riparian ecosystems. They can be passages for movement of aquatic organisms to and from headwater areas and marine environments, and are important components of global biogeochemical cycles (Butman & Raymond, 2011). Riparian environments also provide critical buffers between human land uses adjacent to the water’s edge by filtering nutrients, retaining sediment and contributing biotic material that constitutes significant food inputs into freshwater food webs.
In many places, protection for freshwater taxa and their habitats is linked to the ribbon of riparian areas that flank rivers and lakes. Riparian protections, in turn, are often linked to land ownership, which changes along the length of a river, from its headwaters to the sea. However, this approach to conservation results in fragmented protections along the continuum of the river.
In coastal Oregon, USA, high-gradient headwater streams tend to be located within dense Douglas fir forest where the primary land use is timber harvesting. Downstream of these areas are low-gradient lowland areas that have been converted to agriculture, residential and urban development (Figure 1). Historically, these streams supported thriving populations of anadromous salmonids that found spawning and rearing habitats throughout the connected corridors of the river network. The extensive floodplain of the Coquille River was a highly productive area for coho salmon (Oncorhynchus kisutch). However, this and other flat floodplains were colonised quickly by European settlers and continue to be used for agriculture.
In recent decades, migratory anadromous salmonids, including coho salmon, have been listed as ‘threatened’ or ‘endangered’ under the US Endangered Species Act, making them critical drivers of restoration and habitat protection. Millions of dollars of public funds have been spent on restoration intended to enhance the habitat and population-scale survival of this species. However, fish abundance continues to be lower than historical levels.
Juvenile coho salmon (Oncorhynchus kisutch) © Adobe Stock
Approach
In coastal Oregon, riparian protection measures include a variety of approaches, from voluntary best management practices to legislated prescriptions (Boisjolie et al., 2017). The most rigorous protections are generally associated with extractive natural resource uses such as timber harvest or mining, while the least rigorous are linked with agricultural land uses. Policy approaches include prescriptive policies intended to eliminate pollution to waterways by specifying requirements for riparian areas and explicitly limiting certain management actions. For agricultural lands, outcome-based policy approaches are intended to minimise water pollution, allowing landowners discretion in land management so long as it does not negatively impact water quality standards. The efficacy of these approaches can be difficult to assess at a catchment scale. Prescriptive approaches may constrict dynamic ecosystems to meet an ideal target condition, while outcome-based policies and a reliance on voluntary efforts can create gaps in protective efforts.
Protective efforts influence habitat conditions in time and space. Consequently, the variability in protective efforts has strong implications for the conservation of riparian ecological corridors. Overcoming fragmented riparian protections can be aided by:
- Legislative efforts;
- Restoration incentives;
- Collaborative restoration projects;
- Conservation designations;
- Technical assistance; and
- The formulation of collaborative governance bodies to address habitat and/or ecosystem degradation.
Understanding the extent of variable protective efforts can inform multi-agency policy responses for species recovery or conservation priorities. Developing an understanding of the mosaic of protective efforts can help identify and quantify gaps in them.
Figure 1. Historically, river systems of the Pacific Northwest connected a diverse array of freshwater and wetland habitats. Over time, development has reduced stream complexity and fragmented landscapes coincident with anthropogenic land uses such as agriculture, timber harvesting or residential development. Figure from Penaluna et al., 2017.
Examples of ecological corridors
For the Coquille River system, maps of riparian policy protections were overlaid with the distribution of coho salmon and areas of high intrinsic potential to support them (Figure 2). The maps show that the majority of riparian areas within the distribution of this fish are managed for agriculture, followed by timber harvesting. Further, areas with high intrinsic potential to support coho salmon are mostly located in agricultural areas. This shows a mismatch between riparian protection of coho salmon streams (which is determined by land ownership) and the location of habitats appropriate for different life stages of these highly migratory fish (which is determined by the hydro-geomorphic context of the river).
Figure 2. Coho salmon in the Coquille River Basin have historically utilised low-gradient floodplain areas. On the modern landscape, these areas are often associated with agricultural land uses. © Rebecca L. Flitcroft
Results
Policies intended to protect riparian areas and coho salmon are more specific and enforceable in areas these fishes are less likely to occupy (Boisjolie et al., 2019). This gap in protections has led to the development of voluntary incentives for stream restoration actions and the management of working lands in the Coquille Basin. By mapping protections, their fragmentation along the continuum of the river network can be identified, allowing for targeted restoration or additional protection work. Tracking the effects of voluntary riparian protections, prescribed protections, voluntary approaches to stream restoration and collaborative landscape management are critical in evaluating the success of freshwater recovery throughout the river network. A broader perspective on identifying and quantifying fragmentation, as well as connectivity, is necessary if protections are to be effective for highly migratory fishes that must access habitats throughout a river system.
References
Boisjolie, B.A., Flitcroft, R.L., and Santelmann, M.V. (2019). ‘Patterns of riparian policy standards in riverscapes of the Oregon Coast Range.’ Ecology and Society 24:22.https://doi.org/10.5751/ES-10676-240122.
Boisjolie, B.A., Santelmann, M.V., Flitcroft, R.L., and Duncan, S.L. (2017). ‘Legal ecotones: a comparative analysis of riparian policy protection in the Oregon Coast Range, USA.’ Journal of Environmental Management 197:206–220. https://doi.org/10.1016/j.jenvman.2017.03.075.
Butman, D. and Raymond, P.A. (2011). ‘Significant efflux of carbon dioxide from streams and rivers in the United States’. Nature Geoscience 4:839–842. https://doi.org/10.1038/ngeo1294.
Penaluna, B.E., Olson, D.H., Flitcroft, R.L, Weber, M.A., Bellmore, J.R., Wondzell, S.M., Dunham, J.B., Johnson, S.L., and Reeves, G.H. (2017). ‘Aquatic biodiversity in forests: A weak link in ecosystem services resilience’. Biodiversity and Conservation 26:3125–3155. https://doi.org/10.1007/s10531-016-1148-0.