Why maintain riparian buffers

stream shaded by forest riparian buffer
Forested riparian buffers help cool the water temperature in streams. Photo Andy Perleberg

Over Thanksgiving, I had the privilege to visit with family. There was a lot to be thankful for, not the least of which is my mother’s renewed health after a recent illness, and the bright eyes of our next generation shining from my young cousins. It turns out, all the things for which we are really thankful are those that allow us to all move forward together as a family and as a community.

In returning from a holiday to my professional community, these thoughts stay in my mind and I am filled with pride because we, as a community of foresters, move forward together. We have overcome so many technical challenges. Perhaps the most significant challenge we faced — protecting water quality — is resolved by maintaining forested riparian buffers. These buffers tie together the forestry community with everybody else in Washington State before any timber even reaches a mill. This practice protects water quality and salmon productivity while allowing our uplands to provide timber. These basic resources are all essential to a healthy, prosperous community.

But, how do forested buffers protect water quality and salmon populations? Well, it’s actually pretty simple. We tend to describe the ways that riparian forests provide clean water and productive fish habitat in terms of the ecological functions of these streamside forests, which are the mechanical ways that the forest interacts with streams.

Forested buffers intercept the loose soils that erode, or flow down the hillside when it rains and provide root strength in the slopes nearest streams to keep streambanks from eroding. Road use and timber harvesting often loosen soils in the uplands. Eroded soils, which are primarily mud, can fill in all the spaces between the cobbles, gravels, and larger rocks in a streambed. These are the only spaces where salmon eggs can incubate. When large amounts of mud flow into a stream, it’s possible to smother every salmon egg in the neighborhood, even downstream on other properties. Mud also prevents adult salmon from reproducing. Soils loosened from timber harvest activities can also erode slowly, leaving continuous source of soil particles in the water that must be cleaned before it is suitable for people to drink.

By maintaining shade over streams, we maintain water temperature. Cool streams are more important than they sound because high water temperatures stress fish, preventing adult salmon from surviving their challenging upriver journey and decreasing the survival rates of juvenile salmon. Warm streams also incubate bacteria and diseases that again must be treated before it is drinkable.

By providing litterfall and nutrients to streams, riparian forests supply the basic building blocks of a food web for salmon, especially for young salmon whose initial growth and survival depends on having great food in the form of small insects that decompose the litterfall and other raw nutrients. This food web extends into the Puget Sound and the Pacific Ocean where the salmon travel, feeding orca whales and countless other species. The food web that starts with riparian forests also feeds land-based species, like bears and people.

By providing large woody debris, riparian forests create the physical structure of instream habitat. The gravels, cobbles, and large rocks that I described above as being essential to salmon reproduction would all move downstream if the streams were straight, steep chutes. Instead, streams in the Pacific Northwest tend to be stepped with intermittent pools and riffles, resulting from changes in the slope of the streambed. This habitat is a result of wood that fell into the stream and blocked the downstream movement of gravels. As gravels build up behind a log in a stream, the slope of the streambed becomes more gradual. The pattern of small calm pools dotted along a stream with clean flowing water allows for the diverse habitat needs of fish. Salmon use pools to rest and feed. The riffles of slightly faster flowing water downstream of the logs provide well-oxygenated waters excellent for reproduction.

I am constantly amazed that forests provide such important resources like sustainable food and clean water. It’s an expensive practice to retain riparian forests during a timber harvest, but we cannot live without food and water. I’m thankful that we, as a community of foresters, have committed to responsible forest management. I’m thankful that we have the best information to protect public resources. I’m thankful for clean water and healthy food. I hope you take pride in every riparian area you protect because everybody in Washington, whether they know it or not, is thankful for clean water and healthy food.

Marty Acker, ESA Ecologist
NOAA, National Marine Fisheries, Washington State Habitat Office