People need clean water. In the western United States, almost all municipal water—the stuff we city-slickers use—comes from forests. About 70% of these same forests are also actively managed for timber harvest. Thus far, municipal water quality has been sustained while other forest uses, logging and recreation for example, have also been sustained. With a growing population in the West, can we keep it up?

Fish need clean, cool water. Fish and other aquatic animals, are not limited to the forested reaches of waterways. Salmon, for instance, use waterways to travel from the highest reaches, the often-forested mountains where adults spawn, all the way to the oceans where juveniles grow to adulthood. Because animals like salmon use all stretches of waterways, it will take more than forest-covered mountains to keep our streams healthy for them. Every stretch of river—whether in the mountains, in agricultural valley-lands, in the city, or along the coast— is important in maintaining water quality, forested or not!

Trees play an important role in our waterways. Fish need cool, oxygen-rich water in order to survive and stay healthy. Trees help shade waterways, keeping the water temperature down and the dissolved oxygen high. Also, sediments washed into waterways from adjacent land can coat the bottom of streams where fish lay their eggs, suffocating them before they can hatch—tree roots can stabilize river banks, reducing erosion of sediments into the stream. Tree roots can also regulate the flow of water in the ground—this water can move more slowly through the soil, giving microorganisms like fungi and bacteria a chance to degrade pollutants before they reach the waterway! Similarly, tree leaves—both green leaves in the tree canopy and fallen leaves on the forest floor—absorb the impact of raindrops, protecting easily eroded soil surfaces.  

Because trees can play such an important role in maintaining water quality, many times we can often minimize water quality problems by "buffering" a waterway from harmful impacts. In some cases we do this by leaving borders of trees and understory vegetation; we call these "buffer strips".

Buffer strips are successfully used to reduce negative impacts on riparian areas in a variety of circumstances. In fact, one can see them along streams in agricultural, urban, and forested areas.  They are used as filters for animal waste-rich waters that percolate from pasture. They are used as live barriers to keep livestock away from sensitive areas like easily eroded streambanks They are used to provide myriad benefits to forested areas adjacent to fish-bearing streams—trees are still harvested from upslope stands, but the valuable services of streamside trees and other plants are maintained.

As you can see, trees and other plants are important factors in water quality.  Woody vegetation like trees offer something else that few other plants can however; large woody debris. Woody debris in streams creates slow spots in fast-moving water where fish can rest. It creates pools where fish can grow and escape predation. Woody debris becomes both home and food for insects that make up a fish's diet. It also provides fish the physical cover needed to avoid predators. And, as mentioned before, it can serve as a filter for pollutants and sediments by acting as a biological "scrub-brush" for the water!

Salmon Habitat