Let’s not plant any trees here.
That was my first thought as I looked out across a 15-acre field of invasive Scotch broom, Himalayan blackberries and a few old fruit trees at a natural area along Baker Creek in rural Washington County. This thought would not have occurred to me 10 years ago, because as a forester, I was focused on trees in my restoration work.
Then I began to learn about the decline in Pacific Northwest songbirds, which rely on the youngest, pre-forest stage of a forest. This stage, referred to as the early seral phase, is composed of forbs, grasses, shrubs and abundant standing and fallen dead wood. Conifers might be present, but they are often small seedlings and isolated older trees. This ephemeral habitat exists for a relatively short period of time – decades instead of centuries – then evolves into complex forests.
Songbirds forage, breed and shelter in the large swathes of open, low-growing grasses and shrubs that comprise seral habitat. Some scientists now consider seral habitat to be one of the rarest in the Pacific Northwest, in part due to forest management policies. As a result, some iconic songbirds, such as rufous hummingbirds, orange-crowned warblers and black-headed grosbeaks, have seen their numbers decline 2 to 4 percent a year. Restoration projects that create seral habitats may help our native songbirds make a comeback.
Most habitats experience major disturbances, such as wildfires or windstorms, which can create the conditions for shrub-dominated landscape to take root. Current policies emphasize putting out wildfires, which limits one effective way that nature uses to create early seral habitat.
The Oregon Forest Practices Act requires the rapid replanting of trees in harvested areas. On federal lands, the emphasis is on old-growth forests, and most disturbed land is replanted with trees. Although there are many good reasons to plant trees, this emphasis on planting trees – along with development – has reduced the seral habitat many songbirds depend on.
Metro manages more than 17,000 acres of natural areas, most of which are not in pre-forest condition. With songbirds in mind, every time we acquire a new site, we look for opportunities to start restoration as close to the beginning of a forest as possible. That means I choose native grasses, forbs and shrubs with just a few conifer seedlings in my planting mix to create some of the conditions of early forests. In the spring, these brushy habitats fill with the chapel-like call and response of birdsongs as chats and flycatchers, sparrows and hummingbirds stake their territories, find mates, breed and feed.
Along Baker Creek, we’ll remove invasive plants and fill in the open ground with native shrubs. By picking shrubs that bloom at different times and that produce different flower shapes, fruits, seeds and nuts, we are creating a cafeteria of variety and providing a source of food and shelter for many months each year.
At McCarthy Creek Natural Area, a former tree farm near Forest Park, we found a few places where the conifer tree planting done by the former owner failed. Hooray! In these areas, we interplanted with shrubs and thinned some of the remaining trees so they wouldn’t shade out the native oceanspray, baldhip rose, red-flowering currant and Oregon grape. The trees will come, establishing slowly from the adjacent forest: willows and red alder, black cottonwood, Douglas fir and western red cedar.
What is early seral now won’t stay that way. It will be a forest again someday, but I hope not too soon.