Our Puget Sound ecosystem is a special place, altered by Scotch broom

Puget Sound is a forested place. It is a forested place because the trees and other forest plants have adapted over the ages to the unique soils and climate that make up the growing environment of this place. The wild species of Puget Sound — from soil microbes to deer, goldfinches, eagles, salmon and orca whales — have in turn grown up with the forests and other natural communities of this part of the world. Together, these plants and animals — this biological signature — say very emphatically: HERE. This place right HERE. There is no other place on Earth like it.

This is the Salish ecosystem, or what is left of it, known to the original human inhabitants of Puget Sound. These resources of forest and sea are still fundamental parts of our regional economy and ultimately the reason why so many of us have been drawn to this part of the world in recent centuries.

Scotch broom alters our terrestrial ecosystems in dramatic, fundamental ways. While it cannot thrive in dense, shady forests, it grows vigorously in most environments with moderate to full sun. Scotch broom can outgrow young fir and madrone trees, form dense thickets that shade out native shrubs and wildflowers and provide excessive tinder for hot wildfires that further degrade invaded forests.

But beyond just winning the competition, Scotch broom changes the playing field. Scotch broom is a legume; like peas and beans it hosts bacteria on its roots that capture nitrogen from the atmosphere. Nitrogen is a plant necessity and naturally in short supply in our native soils. While we like the extra nitrogen that peas and beans bring to our gardens, nitrogen enhancement in the soils of natural areas has the effect of making these soils less favorable for our native forest plants (which are adapted to low-nitrogen soils) and more favorable for more Scotch broom as well as other weedy introduced plants.

Recognizing the threat that Scotch broom poses to our native habitats, the Washington state Noxious Weed Control Board has classified Scotch broom as a Class B noxious weed, meaning that landowner-control is required in parts of the state where it is not already highly abundant. In the Puget Sound region, where Scotch broom already exceeds this control threshold, our King County weed board still recommends control “wherever feasible.”

Through invasive species like Scotch broom, our footprint, already broad and heavy across the landscape, extends into areas we do not even directly use. Knowing this changes the way I see Scotch broom and other invaders. When I see broom flowering profusely across the landscape, I don’t see an attractive display of wildflowers. I see another example of how profoundly we have altered our ecosystems. I see part of the richness of the world slipping away, part of the vibrant uniqueness of our region smothering in drifts of broomy branches, showy alien flowers and unseen pulses of nitrogen in the soil.

For all its injuries, Puget Sound is still a magical place. And those of us here now will have to fight to ensure it remains so for the next generation. The place is worth fighting for, and I am grateful for the broom-pullers, bird-counters, land stewards and all others who are willing to do the hard labor to try to make this place whole again.

— Islander Jim Evans is an ecologist for The Nature Conservancy.

For more information

For more information about Scotch broom, visit the state’s Noxious Weed Control Board Web site at www.nwcb.wa.gov/weed_list/Class_B_weeds.htm and scroll down to Scotch broom. Or read about Scotch broom at the U.S. Forest Service Fire Effects Information System Web site: www.fs.fed.us/database/feis/plants/shrub/cytspp/all.html.

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