🪵Invasive Trees in Washington State: Identification, Removal & Expert Advice

An invasive tree is a non-native species that spreads beyond where it was planted and disrupts natural ecosystems. Unlike native trees, invasive species often produce large amounts of seed, spread through root suckers, or rely on birds and waterways to establish new populations. As they spread, they can crowd out native vegetation, reduce biodiversity, alter wildlife habitat, and become increasingly difficult to remove.

Not every fast-growing tree is invasive. Many native species, such as Red Alder and Bigleaf Maple, naturally colonize disturbed areas and play an important role in forest recovery. Proper identification is the first step in determining whether a tree is beneficial or should be managed.

Some of the most common invasive or invasive-concern tree species found in Washington include Tree of Heaven, English Holly, Black Locust, Norway Maple, Cherry Laurel, and Mimosa Tree. Each spreads differently—some through seeds carried by birds or wind, while others produce aggressive root suckers that allow new trees to emerge from underground root systems.

The species found on your property will depend on your location, surrounding vegetation, and previous landscaping. Early identification can make removal much easier before the tree establishes a larger seed bank or root system.

Small seedlings and young saplings can often be removed by homeowners if they are identified early. However, larger invasive trees frequently require specialized equipment and follow-up management to prevent regrowth.

Species such as Tree of Heaven and Black Locust commonly produce vigorous root suckers after being cut down. Simply removing the trunk may result in multiple new shoots appearing nearby. Large trees may also present hazards related to falling limbs, nearby structures, overhead utilities, or difficult access.

If you're unsure about the species or the safest removal method, having an ISA Certified Arborist evaluate the tree can help prevent unnecessary work and recurring infestations.

Tree of Heaven spreads aggressively through both seeds and underground root suckers. When the tree is cut without proper follow-up treatment, the remaining root system often responds by producing numerous new shoots around the original stump.

These sprouts can emerge several feet away from the original tree, making the infestation appear larger after removal. Because of this growth habit, effective management often requires a planned removal strategy rather than simply cutting the tree down.

Early intervention usually results in less regrowth and lower long-term removal costs.

No. Fast growth alone does not make a tree invasive.

Many native Pacific Northwest species are considered colonizing trees, meaning they naturally establish after storms, fires, logging, or other disturbances. Species such as Red Alder, Bigleaf Maple, Black Cottonwood, and Pacific Willow help stabilize soil, provide wildlife habitat, and prepare disturbed sites for mature forest development.

Invasive trees differ because they continue spreading aggressively, outcompete native vegetation, and often require active management to prevent long-term ecological damage.

Yes. English Holly has become a significant invasive concern in many parts of Western Washington. Birds readily consume its berries and disperse seeds into forests, parks, and natural areas where dense stands of holly can develop beneath the forest canopy.

Over time, these thickets reduce native plant diversity and make forest restoration more difficult. Although English Holly is still commonly found in older landscapes, many property owners now choose to remove volunteer seedlings and replace mature trees with native alternatives that better support local wildlife.

It depends on the tree's location, size, and condition.

Norway Maple has become an increasing concern because it escapes cultivation, produces abundant seedlings, and creates dense shade that limits native forest regeneration. In natural areas or along forest edges, removal is often recommended to help preserve native ecosystems.

Healthy landscape trees may not require immediate removal, but homeowners should monitor for volunteer seedlings and consider native replacement species when the tree eventually reaches the end of its lifespan.

Invasive trees use several methods to establish new populations.

Some species produce seeds that are carried by birds, while others rely on wind or waterways to spread. Trees such as Tree of Heaven and Black Locust also produce underground root suckers, allowing new trees to emerge several feet from the original trunk.

Many invasive species begin as ornamental landscape trees before escaping into nearby forests and open spaces. Identifying and managing invasive trees before they mature can greatly reduce future spread.

Many beautiful native trees provide shade, seasonal interest, and valuable wildlife habitat without becoming invasive.

Excellent alternatives for Washington landscapes include:

Vine Maple (Acer circinatum)

Oregon White Oak (Quercus garryana)

Western Red Cedar (Thuja plicata)

Serviceberry (Amelanchier alnifolia)

Choosing native species helps support pollinators, birds, and healthy forest ecosystems while reducing long-term maintenance concerns.

Yes. If you're unsure whether a tree is invasive, an ISA Certified Arborist can identify the species, evaluate its condition, and explain whether removal or management is recommended.

Often, a few clear photos of the leaves, bark, flowers, fruit, and the overall tree are enough for an initial identification. For larger or potentially hazardous trees, an on-site evaluation may be recommended to assess structural condition, nearby hazards, and the most effective removal strategy.

Professional identification helps ensure beneficial native trees are preserved while invasive species are addressed before they become more difficult and expensive to manage.