Mitigating the Impacts of Roads as a Climate Change Adaptation Strategy
Introduction
Climate has changed throughout the history of our planet and species have adapted and persisted over time (Noss 2001). Unlike previous periods of climatic change, though, many species’ ability to adjust has been severely constrained by anthropocentric alterations of many ecosystems, such as habitat loss and fragmentation. It is these additional environmental stressors that make climate change such a challenge for biodiversity conservation. But while humans have inflated the conservation challenges associated with climate change, we can also help to alleviate them.Roads are a ubiquitous feature across North America that have greatly modified aquatic and terrestrial ecosystems. In this paper we discuss how forest roads and their associated impacts are compounding the threats of climate change on fish and wildlife and how decommissioning and upgrading some forest roads can improve ecosystem resiliency and foster species’ ability to adjust to changing environmental conditions.
Climate change impacts on fish and wildlife
There is high certainty that air temperature is increasing around the world (CCSP 2008). In general, stream temperatures are expected to rise as a result of increased air temperatures and decreased thermal mixing from snowmelt (Mote et al. 2003). As stream temperatures rise, it is likely that several streams and rivers that currently support salmonids and other cold-water species may become inhospitable, as critical temperature thresholds are breeched (Keleher and Rahel 1996). Such changes are likely to alter distributions, as fish adapted to cool and cold water must migrate in search of more suitable water temperatures (Eaton and Scheller 1996). Furthermore, extreme fluxes in stream temperature may produce thermal barriers that impede fish migration and constrict their range (Bartholow 2005).Climate change is also predicted to alter stream flows (both peak and low), but impacts will vary based on elevation and snowpack contributions (Hamlet and Lettenmaier 2007). Reduction of summer and fall stream flows and consequent reductions in the length of the overall stream network during the summer dry season are also likely to limit food and habitat availability for juvenile rearing. Increased forest die-back resulting from fire and/or pathogens may further increase stream temperatures by reducing streamside vegetation cover, but also may increase summer low flows in the short-term due to decreased uptake of water by vegetation (Potts 1984); however, the magnitude and duration of such effects is not well understood.
An increase in climatic variability is also predicted, resulting in more frequent, extreme storms and increasing intensity of precipitation (Groisman et al. 2005). Increases in high-intensity precipitation and winter flooding pose several significant risks to fish. For example, increased flooding can scour salmon redds, destroying the eggs (Lisle 1989). High flows can also flush rearing juvenile salmonids downstream before they are ready to migrate, potentially disrupting their biochemical and physiological development (Shirvell 1994). Another likely outcome of increased flooding and heavy precipitation is an increase in mass-wasting events (e.g., landslides). Such incidents increase the amount of fine sediment in streams, which has been strongly and negatively correlated to salmonid health, growth, and survival (Newcombe and MacDonald 1991).
Wildlife also face threats driven by temperature and precipitation patterns and changes in disturbance regimes, including changes in food availability, habitat, and distribution of competitors and prey (Janetos et al. 2008). For example, grizzly bear (Ursus arctos horribilis) food sources may be dramatically altered. In the Greater Yellowstone Ecosystem, grizzly bears depend on winter-killed carrion as a key springtime food. However, recent modeling exercises have predicted a decline of winter-killed carrion due to a substantial reduction in late winter snowpack (Wilmers and Getz 2005). Additionally, climate change is predicted to reduce the availability of the highly-nutritious white-bark pine (Pinus albicaulis) seeds by accelerating the rate of the white pine blister rust fungus (Cronartium ribicola) spread, competitive replacement by lodgepole pine (Pinus contorta), and increasing frequency of stand-replacing wildfires (Koteen 2002).
Intersection of roads and climate change
Climate change is exacerbating the many human-caused impacts that are already leading to species decline. One of the most common and far-reaching anthropogenic features on the landscape is roads. Roads can affect aquatic systems by increasing stream peak flows by impeding water infiltration and expanding the drainage network (Wemple et al. 1996), increasing surface runoff carrying sediment to streams (Sugdon and Woods 2007), and triggering landslides from culvert or road failures that transport large amounts of sediment and debris to streams (Swanston 1991). Roads can also block or disrupt natural transport of materials such as large wood into streams (Furniss et al. 1991), which is critical to salmonid survival because it increases in-stream habitat complexity and provides off-channel areas of refugia during high flow events (Bilby and Bisson 1998).Several studies have also documented deleterious impacts of roads on terrestrial wildlife. One simple, but major impact of roads on wildlife is that they facilitate human access. For example, roads allow access to remote grizzly bear habitat resulting in avoidance of roads by bears (Mace et al. 1999). In the context of climate change, roads can also adversely affect wildlife habitat by fragmenting landscapes, altering wildlife movement, and acting as a vector for invasive species and plant pathogens (Trombulak and Frissell 2000). Cumulatively, the presence of roads often leads to avoidance and a reduction in available habitat.
Road decommissioning and upgrading as a climate change adaptation strategy
The impacts of climate change and roads on aquatic and terrestrial systems will likely be intensified by their interactions and cumulatively pose more serious threats to many species than either would alone. One adaptation strategy that directly impacts resiliency of many species is decommissioning and upgrading of forest roads. When roads are decommissioned the old roadbeds are ripped and often recontoured to enhance water infiltration (Switalski et al. 2004). Additionally, culverts are removed and natural stream connections and transport processes are restored. This practice lessens risks associated with landslides, erosion of fine sediment, and intensification of peak flows (Madej 2001).Decommissioning and upgrading roads and thus reducing the amount of fine sediment deposited on salmonid redds can increase the likelihood of egg survival and spawning success (McCaffery et al. 2007). In addition, this would reconnect stream channels and remove barriers such as culverts. Decommissioning roads in riparian areas may provide further benefits to salmon and other aquatic organisms by permitting reestablishment of streamside vegetation, which provides shade and maintains a cooler, more moderated microclimate over the stream (Battin et al. 2007).
For wildlife, road decommissioning can reduce the many stressors associated with roads. Road decommissioning restores habitat by providing security and food for wildlife. Preliminary results suggest that black bear (Ursus americanus) use decommissioned roads extensively in central Idaho (A. Switalski in prep.). In addition to providing early successional foods, such as huckleberries, decommissioned roads when seeded with native species can reduce the spread of invasive species (Grant et al. in review).
One of the most well documented impacts of climate change on wildlife is a shift in the ranges of species (Parmesan 2006). As animals migrate, landscape connectivity will be increasingly important (Holman et al. 2005). Decommissioning roads in key wildlife corridors will improve connectivity and be an important mitigation measure to increase resiliency of wildlife to climate change.
Conclusion
While climate change is the greatest threat of our age, we have the ability to help fish and wildlife adapt to predicted changes. Roads are a major stressor in the environment and decommissioning and upgrading them has the potential to increase ecosystem resiliency.Adam is Wildlands CPR’s Science Coordinator and Liane is the Ellsworth Creek Ecologist for The Nature Conservancy.
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