USA — The 2008 fire season is proving to be another hot one a trend thats lasted nearly five years. According to the National Interagency Fire Center, last year wildfires scorched more than 9.3 million acres across the U.S. and 2008 may log high numbers again.
When evaluating the effects of recent wildfire, often the impacts to streams and rivers can be most worrisome. The high value of water, the ecological importance of riparian areas, and the prevalence of at-risk populations of fish require that these areas receive special consideration. Fortunately, proper approaches to stream restoration after a fire event can significantly lessen the recovery time, and help to prevent long-term, harmful effects.
Fire: Beneficial or harmful? Fire is a natural process in many forests and prairie environments that allows these ecosystems to undergo vegetative succession. However, over the past century, fire suppression policies throughout the U.S. have altered natural fire regimes, resulting in higher-intensity, and more frequent wildfires. The once rejuvenating effects of a more moderate fire regime with an abundance of habitat refuges, has been negated in many places by fire suppression, damming, and other impacts of development.
How does fire impact streams? Immediately following a wildfire, ash and organic matter fall into the water, raising nutrient concentrations and diminishing dissolved oxygen. Fish kills are possible, since water may be blackened and cloudy, possibly clogging gills and affecting visibility for fish. Reptiles, frogs and mammals that have survived the fire may also suffer further decline during this period. If fire suppression was attempted, fire retardant chemicals may impact water quality.
Short-term effects of fire on streams and rivers include an increase in the amount of light reaching the stream, which promotes changes in fish, insect, and plant communities. Increased water temperatures and greater fluctuations in temperature ranges affect dissolved oxygen levels. Reduced ground cover and streamside vegetation mean less filtration capacity and higher amounts of sedimentation and organic debris entering the stream. Stream banks left unprotected by vegetation and roots are more likely to erode, increasing sediment load, which can lead to changes in riverbed structure and water quality. Diminished overhanging vegetation means less cover against predators for fish and aquatic insects or larvae, and less terrestrial insects and organic matter for the stream.
If left untreated, longer-term effects may include the formation of debris jams from dead trees falling into streams can alter stream flows and trap sediments, and higher nutrient concentration from runoff can last for months to years.
Renewal and repair after fire Restoration treatments like Trout Headwaters EcoBluâ¢ can create aquatic conditions that are more resilient to fire. The most effective approach will promote diverse aquatic life and robust fish populations by addressing riparian health, floodplain function, channelization, chronic sediment input, accelerated erosion, and changes in natural flow regimes. Low impact, cost-effective treatments may include fish passage barrier removal, riparian vegetation recovery, road reclamation, and the mitigation of other identified disturbances. Fish survival tends to be high during fires if the watershed and in-stream habitat are healthy, and if fish are able to move freely upstream and downstream.
Many Western streams will face a natural disturbance like fire. Before next years fire season heats up, consider whether your streams are healthy. Are your riparian areas broad and lush? Are your streambanks stable with a good diversity of native grasses, forbs, shrubs and trees? Healthy, functioning riparian areas, floodplains and streams are a good hedge against any future fire threat.