USDA Forest Service

Pacific Southwest Research Station

 
Pacific Southwest
Research Station

800 Buchanan Street
Albany, CA 94710-0011
(510) 883-8830
United States Department of Agriculture Forest Service. USDA logo which links to the department's national site. Forest Service logo which links to the agency's national site.

Research Topics Fire Science

Fire and riparian areas

Two scientists stand in a stream taking measurements.
Field scientists obtaining stream measurements for the Kings River Experimental Watershed research program within the Bull Creek drainage, Sierra National Forest. U.S. Forest Service photo by Carolyn Hunsaker.

Riparian areas (areas on or near the bank of a river, or other body of water) are transition areas between terrestrial and aquatic ecosystems and are typically highly productive areas. They also have an important function through buffering the effects of fires and other watershed disturbances on aquatic ecosystems.

Due to higher levels of moisture, riparian areas next to streams and rivers can disrupt the spread of fire within a landscape and often burn at lower severity. However, in the absence of periodic fire, riparian areas may accumulate fuels rapidly due to their high productivity, leaving them vulnerable to high-intensity fire during dry fire seasons.

Management considerations

Riparian areas that are vulnerable to uncharacteristic high-severity fire (due to unnaturally high fuel levels, tree densities, and seasonal dry conditions) may benefit from upland fuel reduction treatments to promote resilience to wildfire across the landscape. Furthermore, treatments that reduce tree density and allow more light to reach the forest floor can have positive effects on understory plant diversity and aquatic productivity in some riparian areas, for example those riparian areas with aspen trees and other key hardwoods that provide important habitat for wildlife species.

Studies on prescribed fire in Sierra Nevada riparian areas have found relatively benign impacts on riparian vegetation or function. The characteristic hardwood species common to riparian areas tend to bounce back quickly from fire (and other disturbances. Information about the effects of combined mechanical treatments and prescribed fire treatments is still relatively limited, which suggests a need for experimental treatments and additional study (see Kings River Experimental Watersheds on the Sierra National Forest). However, fire historically also burned through riparian areas, and some forms of active management may offer greater long-term resilience than a broad hands-off approach.

Water and Aquatic Ecosystems

fire
Post-fire conditions within a high severity burn patch after the King Fire. U.S. Forest Service photo by Eric Knapp.

Water, riparian areas, and aquatic ecosystems have high social, cultural, and ecological values in California. National forests in the Sierra Nevada are a major source of water supply, hydropower, and recreational activity for much of California.

Erosion associated with wildfires that are similar in size and frequency to those with which streams naturally evolved is important for maintaining stream productivity and biodiversity. However, severely burned hillslopes are more likely to generate water and sediment that can lead to flooding, stream channel erosion, and debris flows, which can pose short-term threats to people and infrastructure and longer term threats to aquatic habitat. Significant increases in sedimentation rates may negatively affect sensitive aquatic organisms and reservoir water quality and capacity.

Management considerations

Aquatic ecosystems that are already degraded, have limited connectivity due to dams and other barriers that restrict movement of aquatic organisms, or harbor small populations of organisms or rare species may be especially vulnerable to losses and effects following fires. Before and after fires, managers should focus on promoting the natural passage of organisms, water, and sediment along streams, while also mitigating undesirable movement of sediment and water from road systems and other developed areas into streams.

Efforts to promote a fire regime that results in fewer uncharacteristically large and severe wildfires can help maintain resilience of aquatic systems. Forest restoration treatments that reduce tree densities could also increase water available to soils, groundwater, and streams due to reduced transpiration (forest water use) and increased snowpack.

Publications:
  • Hunsaker, C.T.; Long, J.W.; Herbst, D.B. 2014. Watershed and stream ecosystems. In: Long, J.W.; Quinn-Davidson, L.; Skinner, C.N., eds. Science synthesis to support socioecological resilience in the Sierra Nevada and southern Cascade Range. Gen. Tech. Rep. PSW-GTR-247. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 265-322. Chap. 6.1.
  • Hunsaker, C.T.; Long, J.W. 2014. Forested riparian areas. In: Long, J.W.; Quinn-Davidson, L.; Skinner, C.N., eds. Science synthesis to support socioecological resilience in the Sierra Nevada and southern Cascade Range. Gen. Tech. Rep. PSW-GTR-247. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 323-340. Chap. 6.2.
  • Long, J.W.; Pope, K. 2014. Wet meadows. In: Long, J.W.; Quinn-Davidson, L.; Skinner, C.N., eds. Science synthesis to support socioecological resilience in the Sierra Nevada and southern Cascade Range. Gen. Tech. Rep. PSW-GTR-247. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 341-372. Chap. 6.3.
  • Pope, K.L.; Long, J.W. 2014. Lakes: recent research and restoration strategies. In: Long, J.W.; Quinn-Davidson, L.; Skinner, C.N., eds. Science synthesis to support socioecological resilience in the Sierra Nevada and southern Cascade Range. Gen. Tech. Rep. PSW-GTR-247. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 373-390. Chap. 6.4.