Effects of Fire on Aquatic Systems

Mill Creek, Bitterroot National Forest, MT Terrestrial and aquatic systems are intimately linked. Much of the rain or snow that falls onto the forests of the Northern Rockies ultimately finds its way into associated streams, ponds, rivers, and lakes. Changes in the nature of forested lands caused by fire can have strong repercussions on the quantity and quality of water in these watercourses and water bodies.

Fire-caused changes in the quantity and quality of water yield from forested lands have both short- and long-term effects on aquatic creatures. Immediate changes in water temperature and chemistry can kill fish and other animals. Enduring changes in the physical and chemical attributes of catchments and watercourses have longer-term effects on populations of aquatic biota. In general, fire effects depend largely on the pre-fire condition of these systems, the pattern and severity of forest fire, patterns of post-fire precipitation, and the nature and speed of post-fire vegetation changes in the affected forests.

A myriad aquatic invertebrates reside in our forest streams. Common insects, for example, include various species of mayflies, stoneflies, caddisflies, true flies, and beetles. These and other invertebrates are important food for most other creatures in these systems, including frogs and fish. Amphibians native to northern Idaho and western Montana forests include boreal toad, Rocky Mountain tailed frog, Columbia spotted frog, long-toed salamander, and Idaho giant salamander (Maxell 2000). Common fish of this region include species of salmon and trout (salmonids).Three native salmonids that spend their entire lives in fresh water and do not migrate to the ocean (although they often migrate from streams to rivers) are bull trout, westslope cutthroat trout, and mountain whitefish. Native anadromous salmonids (fish that migrate from the ocean to spawn in streams) include Chinook salmon and steelhead. In the Selway and Salmon River basins, the low gradient sections of these two rivers, together with their larger tributaries, provide key spawning and rearing habitat for bull trout, westslope cutthroat trout, steelhead, and Chinook salmon.

In the following sections we describe what's known about the immediate, short-term, and long-term effects of fire on water quality and quantity and on populations of aquatic invertebrates, amphibians, and fish in the northern Rocky Mountains:

The immediate effects of forest fire on aquatic systems
Short-term effects of forest fire on aquatic systems
Long-term effects of forest fire on aquatic systems


Maxell, B. A. 2000. Management of Montana's amphibians: a review of factors that may present a risk to population viability and accounts on the identification, distribution, taxonomy, habitat use, natural history, and the status and conservation of individual species. Report to USDA Forest Service Region 1, Order No. 43-0343-0-0224. Available online at http://www.isu.edu/~petechar/iparc/Maxell_Mgmnt.pdf.

Return to Fire Effects