About Us

Who We Are

The 4-County CWMA is made up of organizations from Clackamas, Multnomah, Washington, and Clark Counties. These four counties boast 3,727 square miles of wildlife, natural features, and recreational opportunities, as well as cities, towns, farms and forests. Our area includes parts of both Mt. Hood National Forest and Willamette National Forest, the beautiful Columbia River Gorge and a piece of the Cascade Range. Numerous local parks and wildlife refuges are found here, including Metro’s Oxbow Park and Portland Parks’ Forest Park, and the Ridgefield Wildlife Refuge and Tualatin River National Wildlife Refuge.

The area is also home to important watersheds that we rely on: the Bull Run and Clackamas Rivers provide drinking water to over a million people. Additionally, there are hundreds of miles of trails to hike and rivers to kayak, where you might find native animals such as beaver, bald eagle, elk, salmon, and bobcat, and native trees like Douglas-fir, Western red cedar, Western hemlock, and big leaf maple.

We’re Urban

Starting in the mid-1990s, ecologists began thinking about urban lands as ecosystems (pretty drastically changed ecosystems, but still…). Since then, our understanding of how plants and animals in cities interact has expanded, though we certainly haven’t learned everything. Some key themes in urban ecology include:

Patches and Parks

Research has demonstrated the habitat value of even small (backyard-sized) patches and parks. These often-overlooked places can provide food and shelter for all kinds of animals and insects, whether they’re from the Pacific Northwest or just passing through. The Backyard Habitat Certification Program is a home-grown organization advocating for these little patches across the Lower Willamette Valley.

Human Introduction

Many invasive plants have been introduced by well-meaning gardeners. Many of our member organizations have outreach programs that help homeowners know which plants to be wary of.

Cities as Transit Points

Given the number of outdoor enthusiasts in our cities and towns, the rest of Oregon and SW Washington look to cities to control their own invasive species… so everyone else doesn’t have to!

We’re Rural

Thanks to the miracle of Oregon’s urban growth boundary, the cities of the Lower Willamette Valley have been kept off some of the best farmland in the world. Rural properties are much larger than city lots and often serve as a source of income, posing unique challenges to farmers and rural residents when it comes to weeds.

Our partners work closely with these communities to keep their pastures, farms, and woodlots clear of harmful weeds and their livelihoods intact. We do this by working with private landowners to identify, prevent, and manage their weeds of concern on a large scale. It’s another way to protect the health of the soil and ensure the future productivity of the land.

We’re Forested

We’re familiar with the great forests of the Cascades. They anchor much of what we think of as “the Pacific Northwest”: rivers, skiing, hiking, birding, hunting, boating, and timber. Protection of these forests falls substantially to the federal agencies that own them.

But many Pacific Northwesterners may not be aware of the private forests scattered throughout the 4-County area. These smaller holdings, sometimes less than 10 acres, constitute an important piece of local ecology. Smaller patches sometimes provide patches of refuge but more often link each other, and larger patches, into habitat corridors, providing crucial connections for birds and other wildlife. But all forest patches also present an opportunity for forest invaders, like garlic mustard. Our collaboration with private landowners is critical for protecting our large forests and maintaining wildlife corridors.

What Management Looks Like

Given the range of landscapes, human activities and invasive plant responses, management can and will differ across the CWMA. In general, partner organizations follow some variant of Integrated Pest Management, or IPM. IPM is a philosophy of management that seeks to maximize effectiveness of treatment while minimizing unwanted side-effects. Practically speaking, this means avoiding one-size-fits-all approaches and paying more attention to a site’s specific requirements. Easier said than done, but here are some of the tools commonly used in pursuit of invasive control:


It almost goes without saying, but here we are. Preventing the arrival of an invasive species is by far the most cost-effective approach. It’s much easier to manage plants that aren’t there!

Early Detection / Rapid Response (ED/RR)

A stitch in time saves nine. Early detection means small patches, small crews, less or no herbicide, little soil damage, and no replacement plants. Given how fast some species move across the landscape, catching them early makes sense.


Overwhelmingly recommended for most species in urban settings, hand-pulling is impractical in many rural, agricultural, or forest settings. Hand-pulling may not be safe on slopes, and can damage soils when done across large areas. Hand-pulling can also create favorable conditions for regrowth of the target weed or other invasive plants. These waves of emerging plants may or may not be what you want.


Biocontrols are another useful tool, assuming the insects used are given sufficient background testing. However, biocontrols are assumed to miss a percent of a target species out in the world. For this reason, biocontrols are not a ‘silver bullet.’ They’re a last resort aimed at tolerating, not eradicating, a target species.

Why Collaboration Is Important

Collaboration is how we (try to) get things done in invasive species management:

  • avoid gaps–no stragglers slipping between efforts

  • avoid overlaps–no wasted effort and resources

  • minimize confusion–no chasing around to get answers

  • improve funding options–granting entities prefer to see efficient, combined projects

Given the different treatment agencies and their individual mandates, collaborating is an active process. Even activities that have been happening for years still require regular check-ins, to be sure old assumptions are still good assumptions.