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Issue link: https://read.dmtmag.com/i/57838
I n Oregon and Washington where I have lived for the past 25 years, I would nominate Himalayan blackberry (Rubus discolor), Scotch broom (Cytisus scoparius), and English ivy (Hedera helix) as the top three woody invasive weeds. These not only crowd out natives, but are widespread, dif- ficult to control, thrive in sun and persist in shade, and with the first two, rapidly fill disturbed areas. While the first is no longer planted, a few varieties of broom are still planted and English ivy even more so. Both Himalayan blackberry and ivy invade intact native forest, and, growing in from the edges, the blackberry can cover small wetlands and creeks. The broom requires more sun and is adapted to dominate after a forest fire; it, and the blackberry, also increase fire risk: thickets of blackberry contain many dead canes intermingled with low tree limbs, and the broom will burn green because it contains flammable oils. I once thought that ivy "pulling down trees" was a myth, but ivy can break limbs and small trees because of its weight. This is not to say that these plants have no positive qualities: Himalayan blackberry has tasty fruit and is both prime bird-nesting habitat and a good pollen and nectar source, scotch broom is a nitrogen-fixer, and all three have some utility for erosion control. However, landslide risk may actually increase if deeper-rooted trees that also would transpire more water have been crowded out on steep slopes. Eradication usually takes several years because of remaining roots and seed. Some combination of mechanical control, herbicide application, mulching, and re-planting natives may be used depending on the location and objectives. Local volunteers are sometimes organized to hand-clear public green spaces and re-plant natives; this can work, but requires follow-up. In sensitive areas like stream banks and wetlands, mechanical control plus heavy mulching and re- planting natives can be effective without herbicide use. On one project I was involved in along a creek in eastern Oregon (the "dry side" of the state) we treated a heavy infestation of Himalayan blackberry and bigleaf periwinkle (Vinca major) without using herbicide because of proximity to the creek. After cutting and removing the blackberry and periwinkle, sheets of cardboard were laid down and buried with 4 inches (10 cm) of ground yard waste mulch; the area was then planted with native trees and shrubs right through the mulch and cardboard. Survival was excellent the following year, with very little weed growth. www.urban-forestry.com While none of these three invasives is a new arrival, they continue to spread into new areas, and can make sudden jumps following disturbance. If you wish to see one of the largest scotch broom "planta- tions" anywhere, drive along Interstate 5 near Castle Rock in southern Washington, where it covers exten- sive piles of ash dredged from the Toutle River after the eruption of Mt. St. Helens in 1980. Mitigation has begun on the piles; that would be worth a look. —David M. Braun, Braun Arboricultural Consulting LLC, Hood River, Oregon invasive species that we encounter in the Pacific Northwest. Although I fervently wish for a way to eradicate troublesome plants such as English ivy (Hedera helix), clematis (Clematis vitalba), Himalayan blackberry (Rubus discolor), holly (Ilex sp.), English laurel (Prunus laurocerasus), and Japanese knotweed (Polygonum cuspidatum), I am not waiting around for a magic bullet. Instead, within our office we have focused on education and understanding when and how to attempt to control or eradicate invasive plants on our clients' properties. O On smaller residential sites, I have learned to look for opportunities to eradicate the problem plant within a defined area. For instance, it is much easier to work within a space contained by infra- structure, where the plant you are dealing with is not immediately present but waiting to invade again. This situation is very common here in the Seattle area with many properties adjacent to parks, greenbelt areas, or neighboring properties that are often overrun with ivy, blackberries, or other nasty invasives. Another way that we have made progress with eradication of invasive species is by building relationships with contractors that specialize in ecological restoration. These specialists have extensive experience and know what works and how to accomplish it. Having experience and knowledge is especially important when working on difficult sites such as steep slopes. We find that when people realize there are professionals that can help with the work, they are more likely to act on our recommendations. Also, teaching people simple facts about invasive plants serves to get them interested in beginning to control the plant and sparks their awareness of the problem. 25 ver the years that I have been inspecting trees and landscapes, I have had to come to terms with some of the