Seattle could lose significant amounts of its parkland forests, estimated at up to 70% of tree canopy in 20 years, if we do nothing about English ivy that is strangling Bigleaf Maple and Alder that compose most of Seattle’s natural areas.
Seattle’s old growth forests were logged 150 years ago, so we’ve already lost most of our evergreen forests’ capacity to intercept winter rains and reduce polluted stormwater runoff. The deciduous trees that grew in their place are short-lived and fast approaching the end of their life cycle. Invasive plants, like English Ivy, Holly, Laurel, Himalayan Blackberry and Wild Clematis, are preventing the growth of new native trees.
Invasive weed infestations are estimated to spread (nationally) at a rate up to 14% per year (see U.S. Dept of Interior statement). However, intact forests can resist many weed invasions, but ivy and holly “seed rain” coming from private property, parks, and public right-of-ways can germinate and grow in any conditions – sun, shade, wet or dry. Seed rain’s quiet spread could leapfrog into millions of acres of national forests, forever altering ecosystems on which we depend.
The potential loss of forest diversity will affect quality of life, property values, the rate of landslides, ecological health, human health, and the health of Puget Sound (orcas & salmon are in decline). It’s well known that ivy plus a food source (bird seed, blackberries, unpicked fruit, and garbage) are rat habitat, and studies suggest that diseases spread more readily in ecosystems lacking diversity.
“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.”
Gambling with health risks on a regional scale is unacceptable. Prevention is our best option. The longer we wait, the more expensive it will be – for taxpayers, homeowners, and consumers. 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.
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