The Problem

Pacific Northwest forests are threatened on many fronts: disease, insects, droughts, and development. Catastrophic wildfires, recurring and intensifying, have certainly gotten our attention. However, the quiet spread of exotic (non-native) invasive plants has not received the same media attention, yet may have more lasting impacts. If we allow the relentless spread of invasives to become entrenched, we may not recover from the loss of biodiversity and productive habitat that sustains pollinators and other vital “eco-services.” Know that many invasive plants- cheatgrass, Scotch broom, gorse - create fire-prone conditions that can only be prevented, not cured.

West of the Cascades, both English holly and English ivy are germinating in normally weed-resistant forests. Ivy's slow, relentless spread can create monocultures devoid of diverse wildlife habitat, including for native pollinators. Within 100 years, English ivy covered 50% of forests near urban epicenters, and is now leapfrogging by bird into regional forests.  If we don't act soon, "ivy deserts" could become regionally established, beyond our control. This could inhibit tree regeneration, biodiversity, and resources we take for granted. 

Loss of forest diversity will affect quality of life, property values, the rate of landslides, bird populations, and fisheries - an indigenous resource still feeling the effects of colonial plant invasions. And loss of biodiversity will affect human health. Bird diversity is linked to forest health, and healthy bird populations are a check and balance on insect infestations. English ivy is habitat for rats, a known disease vector and predator of bird nests.

“The loss of biological diversity is an accelerating process with profound consequences for the ability of ecosystems to provide services to human societies. Ecosystem provision of services such as food production, water filtration, and protection against floods and droughts is reduced when biological diversity is lost. High biological diversity also is hypothesized to protect against human and wildlife diseases (Lyme disease, West Nile Virus, SARS, and Hantaviruses), and reduced disease spread or prevalence has been recognized as an ecosystem service.” (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2673579/)

The spread of invasive plants poses unacceptable risks. Prevention is our best option, and widespread cooperation is needed. Otherwise, the re-infestation rate of "seed  rain" will nullify control efforts, risking ecological health and our economy. Already, one quarter of this country’s agricultural gross national product is lost each year to foreign plant pests and the costs of controlling them.

English ivy climbing a tree. The added weight and sail effect may cause this tree to topple.

Count five ivy seedlings in this 2-sq ft photo of a restored urban forest, illustrating the need to simultaneously reduce invasive seedrain sources as broadly as possible.

European Hawthorne berries, tempting to birds, can spread as fast as holly.

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