Tree board highlights rapid spread of English holly, urges early control and public outreach
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Summary
The board reviewed research indicating English holly is expanding rapidly in Puget Sound–area urban forests and recommended early, targeted removal of large, seed-producing trees plus public education to limit spread.
Dave Olmstead, a Lake Forest Park tree board member, presented findings from a study of English holly in Saint Edward State Park, saying the species "is proliferating and spreading rapidly" and warning that delay will increase removal difficulty.
Olmstead summarized the study's key findings: sampled plants ranged from 1 to 46 years old; trees older than 10 years had low mortality and accelerating biomass accumulation; and both local vegetative expansion and long-distance seed dispersal—primarily by birds—are driving exponential increases in number and canopy area with doubling times of about five to six years. "Projecting past spread patterns forward suggests that holly has the potential to soon become a prominent species both in number and canopy extent, likely at the expense of native plant diversity and forest structure," he said.
The study recommended that control or elimination of English holly be an explicit management goal in forests managed for native biodiversity, and Olmstead told the board that a holly control plan should prioritize the removal of large, fruiting (female) trees and focus efforts in invasion-prone areas. He added that spatially explicit modeling of invasion risk could help prioritize work.
Board members and residents described on-the-ground experience removing holly and methods to prevent regrowth. One resident said seeds from female trees can germinate widely: "If you have a female, those seeds end up everywhere," and described finding many seedlings in a small area. Several speakers described recurrent resprouting after cutting; Olmstead and other participants recommended painting a systemic herbicide on freshly cut stems to move chemical control into roots and reduce resprouts.
The board reviewed terminology and regulatory context: Washington allows a "Class 3" noxious-weed designation for feral (wild) holly but exempts holly grown commercially or as ornamental plantings from that listing, a distinction Olmstead noted when discussing outreach to private property owners.
The board approved sending an essay summarizing these findings and recommendations to the city newsletter as a tree-board submission. Members said outreach to private landowners is essential and discussed coordinating control work with stewardship groups and the King Conservation District.
The board asked staff to keep holly control on the work plan and to explore field-oriented control pilot sites and outreach material that explains safe cutting and herbicide application practices. Olmstead said residents seeking application advice should consult local nurseries for the most appropriate, labeled products and follow product instructions.
Ending: The board will follow up on holly outreach and control planning at future meetings and will share the newsletter essay with stewardship partners and the city communications team.
