Oregon's Most Common Invasive Tree Species: What to Remove
Oregon's most damaging invasive tree species include English holly, tree of heaven (Ailanthus), Russian olive, English laurel, Norway maple, and black locust (in some regions). These species outcompete native Oregon trees, reduce biodiversity, and can decrease property values. Oregon Tree Pros removes invasive trees and can recommend native replacements suited to your region.
Invasive Trees Threatening Oregon's Landscape
Oregon's native tree canopy — Douglas fir, Oregon white oak, big-leaf maple, Sitka spruce — is under pressure from non-native invasive species. Oregon Tree Pros' contractor network regularly removes invasive trees across all regions of the state.
Top Invasive Trees in Oregon
English Holly (Ilex aquifolium) The most widespread invasive tree in Western Oregon. Birds spread berries throughout forests, where holly forms dense understory thickets that prevent native regeneration. Found throughout the Willamette Valley, it's particularly aggressive in Forest Park and urban natural areas.
Tree of Heaven (Ailanthus altissima) Extremely aggressive — grows 3-6 feet per year and produces root suckers that can sprout 50 feet from the parent tree. Found in Portland, Salem, and urban areas throughout the Willamette Valley. Removal requires treating the stump to prevent regrowth.
Russian Olive (Elaeagnus angustifolia) Common in Eastern Oregon, particularly along waterways. Fixes nitrogen in soil, altering growing conditions for native cottonwood and willow. Oregon Tree Pros' Eastern Oregon contractors regularly clear Russian olive from riparian areas.
English Laurel (Prunus laurocerasus) Widely planted as hedging throughout Western Oregon, it escapes cultivation and invades natural areas. Can grow 20+ feet tall if left unpruned.
Norway Maple (Acer platanoides) Outcompetes native big-leaf maple with denser shade and earlier leafing. Common in older Portland and Eugene neighborhoods where it was planted as a street tree decades ago.
Black Locust (Robinia pseudoacacia) Spreads aggressively through root suckers. While it has some uses (fence posts, firewood), it can take over disturbed sites in Southern and Central Oregon.
Why Invasive Trees Are a Problem in Oregon
- Biodiversity loss: Invasive trees form monocultures that displace dozens of native species
- Habitat degradation: Native birds and insects depend on native trees for food and nesting
- Water usage: Some invasives (tree of heaven) consume more water than natives
- Fire risk: Dense invasive understory increases fire fuel loading — critical in fire-prone Southern and Central Oregon
- Property values: Properties with invasive tree infestations can see decreased values
Removal Strategies
For trees that don't resprout (holly, laurel): Cut and grind the stump. Standard removal process.
For trees that resprout (tree of heaven, Russian olive, black locust): Cut and treat the stump immediately with a systemic herbicide. Without treatment, these species will send up dozens of root suckers. Oregon Tree Pros contractors trained in invasive removal handle the entire process.
For large infestations: Land clearing services can handle multi-acre invasive removal. Oregon Tree Pros coordinates with native plant nurseries for restoration plantings.
Native Replacements
After removing invasives, consider replanting with Oregon natives:
- Western Oregon: Oregon white oak, Pacific dogwood, cascara, vine maple
- Central Oregon: Ponderosa pine, quaking aspen, mountain mahogany
- Eastern Oregon: Cottonwood, juniper (native species), mountain alder
- Coast: Shore pine, Sitka spruce, red alder
Oregon Tree Pros' arborist consultants can recommend the best native species for your specific property and growing conditions.
Frequently Asked Questions
The most problematic invasive trees in Oregon are English holly, tree of heaven (Ailanthus), Russian olive (Eastern Oregon), English laurel, and Norway maple. These species outcompete native trees, reduce biodiversity, and can decrease property values. Oregon Tree Pros removes invasive trees statewide.
Tree of heaven requires cut-and-treat removal — cutting alone causes aggressive resprouting from roots up to 50 feet from the stump. Cut the tree, then immediately apply systemic herbicide to the stump. Oregon Tree Pros contractors trained in invasive species removal handle the entire process to prevent regrowth.
Yes, English holly is considered one of Oregon's most damaging invasive trees, particularly in Western Oregon. Birds spread berries into forests where holly forms dense thickets that prevent native tree regeneration. Oregon Tree Pros recommends removal and replacement with native species.
In most Oregon cities, invasive species are exempt from tree removal permit requirements. Portland's Title 11 has exemptions for documented invasive species. However, always confirm with your city's urban forestry department. Oregon Tree Pros contractors check permit requirements as part of their service.
For Western Oregon: Oregon white oak, Pacific dogwood, vine maple. For Central Oregon: ponderosa pine, quaking aspen. For Eastern Oregon: cottonwood, native juniper. For Coast: shore pine, Sitka spruce. Oregon Tree Pros arborists recommend species matched to your specific site conditions.
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