Why shade matters: Earth week special

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The Green/Duwamish and Central Puget Sound Watershed covers much of southern King County. In fact, it covers 450 miles. It is home to chinook, chum, coho, pink and steelhead salmon.

Map of the watershed0411WRIA9LocalActionMap.jpg

Since 2005, local governments in the watershed have carried out restoration projects to protect a healthy watershed ecosystem for both people and fish as part of the work of the Puget Sound Partnership. View King County’s interactive Tree Planting map.

Elissa Ostergaard has helped plan stewardship efforts in the Green/Duwamish and Central Puget Sound Watershed. She sat down  with our blog to discuss why planting trees along rivers, streams and other water bodies is so important for restoring healthy fish and wildlife populations.

Q: Why do trees along rivers and streams matter?

A: Fish need cold water to thrive. When the water gets above 65 or 70 degrees, fish start having problems with diseases and can even die. Cold water holds more oxygen which fish need to breathe. When water gets warm it causes fish stress, and it makes them more susceptible to pathogens or toxics that are in the water. We plant trees close to rivers and streams because we’re creating shade to try to make the water as cold as possible.

Warm water can be a physical barrier to migration for fish, and it can cause them to be less healthy or even die. Maybe the young fish won’t be able to make it out of the system. Maybe the adult fish won’t be able to make it back to their spawning ground. Migration is a big need for salmon.

8657985931_79f19c5cf7_zOtter release at Green River Natural Area.

Q: What are other benefits to planting trees along streams and rivers?

A: Trees also affect the microclimate – the humidity and air temperature in the vicinity of the stream. For example, trees drop leaves, a shower of insects, and aged branches into the streams that will become food for insects that live in the water. A native trees hosts a diversity of native invertebrates and insects that become fish food. Chinook salmon, which are listed as threatened under the Endangered Species Act are very opportunistic feeders. They love bugs of any kind. If it’s an aquatic bug they’ll eat it; if it’s a terrestrial bug they’ll eat it.

The other thing that trees along streams do is that they filter the air pollution. The leaves will capture the pollution that’s coming in with the rain and trap those particles, absorbing them. They also capture raindrops as they’re falling and slow it down so there is less erosion and sediment. They help aerate the soil: meaning that they make the soil better for filtering pollutants that may be running off from the roads nearby.

Q: What progress King County and WRIA 9 has made in restoration efforts?

A: Since chinook were listed in 1999 as threatened, local jurisdictions have come together to help fund salmon recovery. We’ve completed over 50 habitat improvement projects. We’ve set back miles of levees. We’ve planted miles of streambank. We have created off-channel and side-channel habitats which is where young fish will be able to go when it’s flooding to rest, feed and grow.

The trees that we plant along the sides of the rivers will eventually fall in, and that really helps the habitat become more complex. Water is forced to flow around branches, creating pools and eddies of slower water which make it easier for fish to get out of that main flow to be able to eat and rest.

Q: What happens when an area is restored?

A: An area that we target for restoration may have a history of farming, industrial use or had a levy put in. Usually the first thing that we do is to help restore the natural river processes – where the river can naturally meander back and forth along the channel migration zone. We might want to carve out some of that bank and soften it. We might move a levee further back.

Sometimes the sites are contaminated. We will do testing to figure out what the contamination levels are and how to dispose of material, haul the material out and that also helps create a shallower area where water can inundate and flood. That helps reduce the pressure of potential flood waters downstream.

We’ll plant native plants. Sometimes there are a lot of invasive plants growing that we’ll rip out to plant native trees and a variety of native shrubs that’s going to help with casting shade and long-term forest succession. We may also put in recreational amenities too to help people enjoy nature like a viewpoint, trail or boat ramp.

Great video highlighting the beauty, diversity and fragility of our watershed and the people who live in it.

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