Bigleaf maple in Washington and Oregon yards

Size, speed and the sprouting habit

OSU’s Landscape Plants database lists bigleaf maple at 50–75 feet, occasionally 100, with the largest leaves of any maple at 20–30 cm across and a shallow root system. The USDA Forest Service silvics manual says most mature trees run about 50 feet tall and 20 inches in diameter, with big ones reaching 100 feet and 36–48 inches, and ages of 200 years or more. Open-grown trees, the yard version, carry “rounded crowns supported by short, branching boles”: a wide, low-forking tree rather than a single tall trunk.

It grows fast and it does not stay cut. The silvics manual records seedlings reaching 3 to 6 feet in one season, stump sprout clumps 17 feet tall with 21-foot crowns in three years, and as many as 67 sprouts around a single stump; OSU puts the sprout growth at over 3 meters in a year. That is why a maple “removed” ten years ago is now a five-trunk tree, and why the stump decision is part of the removal decision (see below).

Included bark and co-dominant stems

Those short, branching boles are the structural problem. When two trunks of similar size grow up side by side from one fork, the bark between them gets folded into the union instead of forming a connected ridge of wood. Arborists call the fold included bark and the pair co-dominant stems. The union has little wood holding it together, it collects water and decay, and as each trunk adds weight the fork is levered open.

On a bigleaf maple each trunk is often as thick as a whole tree, over a roof, and loaded with moss and licorice fern: the silvics manual notes that maples heavy with rain-soaked epiphytes are more prone to windthrow than clean ones.

What to look for: a tight V between trunks with a seam or crack running down from it, bark pushed up like a lip, water staining or fungal fruiting below the fork, and a trunk that has started to lean away from its partner. What to do: have a certified arborist assess the union; the choices are usually a reduction cut to lighten the weaker stem, a cable or brace between the stems, or removal of one stem. That assessment is described on tree risk assessment, and the pruning options on crown thinning and reduction.

Two outside references put numbers on it. A Mississippi State University Extension risk worksheet (P3717, 2025), used here only as a general principle, rates a co-dominant union with included bark as a moderate likelihood of failure and the same union with a crack or decay as high, and it names maples among the trees prone to weak joints. And the USDA Forest Service’s pruning guide gives the young-tree fix: keep side branches no more than one-half to three-quarters of the trunk’s diameter where they attach, and where two stems are competing, removing some lateral branches from one slows it enough for the other to become dominant. That is cheap at 15 years and impossible at 60.

Bigleaf maple decline: what the research found

Washington DNR began fielding reports of dying maples in 2011 and started investigating that year; calls jumped in 2015 and 2016. The field study that followed, by the University of Washington with DNR (Betzen, Tobin, Ramsey, Ettl and Omdal), was published in Forest Ecology and Management on September 16, 2021. Its findings, from DNR’s summary:

DNR’s drought fact sheet adds the yard-scale symptom list, “partial to entire crown dieback, discoloration and reduced size of the leaves, crown thinning, and death,” and notes that affected trees had shown no recovery by the end of 2018, with seven of the previous ten years warmer than average in Washington. ODF has no separate Oregon program for maple decline; its guidance for drought-stressed hardwoods is the same: water, mulch, no fertilizer, and remove severely weakened trees.

For a maple with small leaves and a thinning top, the research points to the same care as western redcedar dieback: deep summer watering (DNR: slowly, over many hours), a 2–4 inch chip mulch kept off the trunk (Trees for Seattle), no fertilizer during drought, and no heavy pruning while the tree is stressed.

Sidewalk, foundation and sewer roots

The silvics manual describes “a shallow, widespreading root system well suited to the shallow or saturated soils on which it often grows.” OSU’s database is blunter: bigleaf maple is “probably not suitable as a street tree.” The roots are shallow enough to lift sidewalks and driveways and wide enough to find a cracked clay sewer lateral on a 1950s lot. Whether any of that justifies removal is covered in the legacy guide the impact of tree root damage on your property; roots do not break sound pipes, they exploit broken ones.

Two rules to know. In Portland, a street-tree maple needs a permit to remove at any size and a permit to prune anything beyond sucker shoots under half an inch; private trees are regulated from 12 inches DBH, and healthy trees 20 inches and up need the Type B permit with public notice (PCC 11.40). In Renton, bigleaf maple gets its own threshold: a landmark tree is 24 inches for most species but 30 inches for bigleaf maple, black cottonwood and red alder (RMC 4-11-200). Other cities are in Oregon tree removal permits and Washington tree removal permits.

When to prune a bigleaf maple

The USDA NRCS plant guide says pruning should be done in winter or early spring, and Portland’s guidance agrees that winter pruning of live branches drives vigorous spring growth without costing the tree its working leaves. The catch with maples is sap: this is the same species whose sap is tapped for syrup in late winter (USFS), so cuts made in February and March bleed. If that bothers you, Portland says limited pruning is fine in summer, after the leaves have hardened off, and it asks everyone to avoid pruning in spring when new leaves and buds are easily damaged.

Whatever the season, Portland’s cap is 20–25 percent of the canopy per cycle and topping is banned in the city, with fines or mandatory replacement. A topped bigleaf maple answers with a thicket of weakly attached sprouts, which is the included-bark problem multiplied by ten. The month-by-month picture for every species is in best time to trim trees in the Pacific Northwest, and the service page is tree trimming.

Unlike a Douglas fir, a spreading hardwood like this is what crown thinning is for, and the USDA pruning guide sets the limits a crew should work within: remove no more than one-quarter of the living crown at a time, spreading heavier work over successive years; do not strip the inner branches and leave foliage only at the tips (“lion’s tails”), which invites sunscald, sprouting and breakage; and make any reduction cut back to a side branch at least one-third the diameter of the limb removed. Its branch-size rule of thumb is simple: under about 2 inches, go ahead; 2 to 4 inches, think twice; over 4 inches, have a good reason.

Removal considerations

Reasons a bigleaf maple comes down: a failing co-dominant union over a target; decay in the trunk or union (the silvics manual lists Heterobasidion annosum, Fomitopsis pinicola and Armillaria root rot among its wood-rotting fungi); crown dieback that has gone past the point of recovery; and roots in conflict with a foundation or sewer after other fixes have failed. A thinning crown alone, in a hot dry summer, is a watering problem first.

The job itself is a rigging job more than a crane job. A spreading maple over a house is dismantled limb by limb and lowered, with the wide crown adding hours compared with a conifer of the same height. Modeled estimate, not quotes (method): a 50–80 ft maple models at $1,800–$3,600 in Oregon and $1,700–$3,400 in Washington, ×1.25 when the trunk is within 10 feet of a structure, before the stump. Current figures are on tree removal cost; the service page is tree removal.

Expect heavy wood. The USDA Forest Service’s FIA species reference table gives bigleaf maple a specific gravity of 0.44, close to Douglas fir’s, but green maple wood holds about 71 percent of its dry weight in water against about 35 percent for Douglas fir. Its dry-to-green weight factor of 1.75 works out to roughly 48 pounds per cubic foot of fresh-cut wood, heavier than fresh Douglas fir. Every limb lowered over a roof weighs more than it looks, and firewood rounds need a full dry summer before they burn well.

Plan for the stump. Because this species sprouts from the stump for years, a ground stump will send up shoots from the root flare; grinding below grade and removing the flare, or full excavation, is how you keep it from coming back. The choice is explained on stump removal vs grinding, with the modeled $150–$450 grinding range on stump grinding cost.

Next steps

1. Look at the forks after leaf-drop: tight V unions with seams, lips or cracks go on the arborist’s list.
2. Watch the leaves next June: undersized, shriveled leaves and a thin top mean drought stress; start deep watering and mulch.
3. Check your city’s threshold before any removal; a 30-inch maple is a landmark tree in Renton and a Type B permit in Portland.
4. Book structural pruning for winter and cosmetic work for late summer; never agree to topping.
5. Check the crew with L&I Verify in Washington or the CCB and LCB lookups in Oregon.

Other species pages are under trees.

The moss and ferns that coat bigleaf maple limbs are not parasites; see moss and lichen on trees for when heavy growth matters.