From our THI headquarters south of Livingston, Mont. thick, black smoke has been seen billowing from the Pine Creek Fire. The 12,000-acre blaze will be recorded during a fire season that’s already five times Montana’s normal level for acres burned. As crews work to douse the blaze, at least seven Paradise Valley drainages are under threat. Like 85 percent of our nation’s fires, the Pine Creek Fire was likely human caused.
The increase in human-caused fires, whether accidental or prescribed, combined with fire suppression activities, have an impact on natural plant communities. Fire is a natural process in many forests and prairie environments that allows these ecosystems to mature and undergo a process called vegetative succession. In fact, many plants are adapted to withstand fire conditions, and either colonize quickly after a burn, or have special adaptations that require intense heat in order to release seeds.
However, in some heavily-developed areas, hotter, catastrophic fires may be more common due to fire suppression activities, which allow fire fuel loads to build. In other areas, frequent prescribed burns or frequent accidental burns may have slowed succession, preventing natural plant communities from maturing.
Whatever the case, healthy, diverse, streamside vegetation and wide, lush floodplains can buffer the effects of wildfire and protect water quality by having the ability to reseed and recover more quickly than streams devoid of vegetation. Roots of woody vegetation can hold the soil, reducing siltation to streams.
How does fire impact streams?
Natural, low intensity fires can provide improved aquatic habitat through increased channel complexity and are an important part of a healthy stream ecosystem. Short-term impacts however, or long-term impacts from high-intensity fires may need to be mitigated to protect water quality and aquatic life.
Following a wildfire event, ash and burnt organic matter fall into the water, raising nutrient concentrations and using-up dissolved oxygen. Water may be blackened, cloudy and scummy from ash, affecting visibility for fish and possibly clogging gills. During this period fish kills are possible. Reptiles, frogs and river mammals that have survived the fire may also be further disturbed during this period. If fire suppression was attempted, fire suppressant chemicals that have entered the stream may cause fish kills or affect nutrient concentrations. Extreme heat can cause soils to become hydrophobic, reducing water infiltration, increasing runoff, and limiting natural regeneration of vegetation.
Other 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, insects, plants, and algae. Increased water temperatures and greater fluctuations in temperature ranges reduce dissolved oxygen. Reduced ground cover and streamside vegetation mean less filtration capacity and higher amounts of sedimentation and organic debris entering the stream. Stream banks that are unprotected by vegetation and roots are more likely to erode, increasing sediment load, which can, if left untreated, lead to changes in riverbed structure and water quality. Overhanging vegetation no longer offers cover against predators for fish and aquatic insects or larvae, nor supplies terrestrial insects and organic matter to the stream.
If left untreated, longer-term effects may include the formation of debris jams from dead trees falling into streams, altering water flow patterns and even creating permanent changes to the stream channel. Nutrient concentrations can remain high for a number of months, possibly as a side-effect of changed nutrient cycling or decomposition of woody debris. Without treatment, sediment movement can take years to recover to pre-fire conditions. Fire damaged streams can benefit greatly from low-cost treatments that restore native vegetation, giving nature a boost in the recovery process.