Bigleaf Maple (Acer macrophyllum)

Oregon maple, large-leaf maple, broadleaf maple

• General Characteristics
• Biology & Management
• Harvest & Utilization
• Wood Properties
• Related Literature
• Oregon Producers and Users of Bigleaf Maple

This information was originally published in Hardwoods of the Pacific Northwest, S.S. Niemiec, G.R. Ahrens, S. Willits, and D.E. Hibbs. 1995. Research Contribution 8. Oregon State University, Forest Research Laboratory

General Characteristics

Bigleaf maple is second to red alder among native hardwood species in abundance and in commercial importance in the Pacific Northwest. It is the only western maple that reaches commercial size, yet its potential as a commercial species has not been fully recognized.

Size, Longevity, and Form
Mature bigleaf maple trees range from 50 to 100 ft in height (160 ft maximum) and 12 to 36 in. in DBH (133 in. maximum). Bigleaf maple is moderately long-lived; some individuals may reach 300 years of age. Height growth becomes negligible after 50 to 70 years. In forest stands, maples often develop clear (50 to 70 percent of total height), well-formed stems with narrow crowns. Open-grown trees have broad, rounded crowns on short, branching boles. The root system of bigleaf maple is shallow and spreading on wet or shallow soils.

Geographic Range
Bigleaf maple is native to the Pacific Northwest at low to middle elevations from San Diego to Vancouver Island (lat 33 to 51°N). It usually grows from near the Pacific Ocean to a maximum of 186 miles inland.

Timber Inventory
Substantial volumes of bigleaf maple occur in every subregion of the Northwest (Appendix 1, Table 1). Maple is most abundant in the Puget Sound region of Washington and the Northwest region of Oregon. About 18 percent of the total hardwood volume in the Pacific Northwest is bigleaf maple.

Biology and Management

Tolerance, Crown Position
Bigleaf maple occurs as a dominant, codominant, or intermediate tree in even- or uneven-aged stands. It is quite tolerant and commonly establishes in forest understories, where it can persist for long periods. Maple in the understory can quickly respond to release when openings are created in the overstory. It also has the capacity to grow rapidly and maintain dominance under favorable conditions in the open sun.

Ecological Role
Bigleaf maple increases in abundance during intermediate to late stages of succession. It can follow willow and alder in riparian succession. On drier upland sites, bigleaf maple can replace oaks and Pacific madrone in the absence of significant disturbance.

The abundance of bigleaf maple also increases after disturbance in stands with an established maple component. Basal sprouts stimulated by cutting or burning can dominate other vegetation in the new stand. Removal of overstory trees can stimulate rapid growth on bigleaf maple in the understory.

Associated Vegetation
Bigleaf maple is commonly found in association with almost all other tree species in its range. The greatest abundance of bigleaf maple is in the foothills of the Cascade and Coast ranges. Its most common association are Douglas-fir, grand-fir, red alder, Sitka spruce, western redcedar, western hemlock, Pacific dogwood, and Pacific madrone. Common shrub and herb associates include serviceberry, salal, red huckleberry, devil’s-club, Pacific rhododendron, thimbleberry, salmonberry, vine maple, and hazel. Herbaceous associates include maidenhair fern, western swordfern, ladyfern, red woodsorrel, false lily-of-the-valley, prince’s-pine, spreading sweetroot, and twinflower.

Bigleaf maple also supports abundant epiphytic growth on branches and boles in moist climates. Common epiphytes are licorice fern, club moss (Selaginella oregano), and other mosses (Hylocomium splendens, Leucolepis menziesii, Isothecium stoloniferum, and Neckera menziesii) and lichens (Cladonia, Nephroma, and Crocynia spp.).

Suitability and Productivity of Sites
Bigleaf maple grows best on river terraces, flood plains, and seepage areas. Good performance is also common on upland sites if soils are deep and moisture is abundant. Bigleaf maple will establish and grow on a wide variety of sites, including relatively harsh, dry areas in southwestern Oregon; however, growth and stem form may be poor. The suitability of prospective sites should be carefully evaluated before management of bigleaf maple on site is attempted.

There are no established guides or site-index curves for estimating the productivity of a site for bigleaf maple. Good potential for growth of bigleaf maple on a site is indicated by the following:

• Top height of existing mature trees is 80 to 100 ft
• Rapid juvenile height growth of >3 ft per year
• Sustained height growth from age 15 to 30 of 1 to 2 ft per year
• Continuing diameter growth on mature trees.

Climate
Bigleaf maple is commonly found across a wide range of climates, from the cool, moist (temperate rain forest) conditions of the Olympic Peninsula to warm, dry (Mediterranean) conditions of southwestern Oregon. Within its range, precipitation varies from 22 to 260 in. (560 to 6600 mm) annually, and from 2 to 46 in. (50 to 1170 mm) during the growing season. Average temperatures range from a minimum of 28°F (January) to a maximum of 81°F(July). Where maple is most prolific, the climate is mild and humid, with moderate precipitation during the growing season.

Bigleaf maple can grow on relatively hot, dry areas, such as upland sites in southwestern Oregon. Maple tolerates moisture stress as low as -20 bars (-2 MPa, nocturnal), which is a low value for broadleaved deciduous trees. Planted maple seedlings are susceptible to heat-girdling and sunscald on the lower stem, however.

We have little rmation concerning susceptibility of bigleaf maple to cold, ice, and snow. A low tolerance to cold and snow is indicated by the absence of maple at higher elevations and by its narrow coastal range. Cold temperatures probably limit the northern occurrence of bigleaf maple.

Elevation
Bigleaf maple usually grows at low to middle elevations (near sea level to 3000 ft) in the central part of its range. In southern California, it may be found from 3000 to 7000 ft; at the northern end of its range it seldom occurs above 1000 ft in elevation.

Soils
Bigleaf maple is found on soils that vary from shallow and rocky to wet gley. Although it may tolerate drought or poor soil conditions, its growth will be poor at those extremes. It grows best on deep, well-drained soils with abundant moisture, conditions that occur most commonly on river terraces, flood plains, and seepage areas.

Bigleaf maple is not as tolerant of poor drainage or flooding as other riparian species such as red alder, cottonwood, or ash. Bigleaf maple appears to be somewhat tolerant of wet conditions, as indicated by its shallow, spreading root system and its common presence in wet areas. Flooding for more than 2 months during the growing season will kill maples of all ages.

Bigleaf maple does not seem to require high soil fertility, based on its competitive success over a range of soil nutrient conditions. One study indicates a high sensitivity to toxic boron in the soil. Maple is considered to be a soil-building species; leaves and litter contain relatively high concentrations of macro- and micro-nutrients.

Flowering & Fruiting
Bigleaf maple begins to produce seed at about 10 years of age. Maple is polygamous, bearing both male flowers and perfect flowers in one cylindrical raceme. The flowers appear before the leaves in early spring. The greenish-yellow flowers are pollinated by insects within 2 to 4 weeks after bud-burst.

Seed
Bigleaf maple seeds are borne in pubescent, double samaras with wings from 1.4 to 2 in. long. Seeds are triangular or oval in shape and 0.16 to 0.47 in. long. There are from 2700 to 4000 seeds/lb. Seeds ripen early in September and October, and are dispersed by the wind from October through January. Many seeds may remain on trees during this period.

Seed should be collected from healthy, well-formed trees. If the outplanting site is known, parent trees should be selected from nearby locale that has conditions similar to the outplanting site. Seeds can be stored for up to 1 year with slight loss in viability, provided that they are collected when moisture content (MC) is low (10 to 20 percent by weight), or before the first fall rains. If seed are collected later, at higher MC, they should not be dried. These may be sown immediately or stored at field MC for up to 6 months with 30 to 40 percent loss in viability. Seeds should be stored in airtight containers at 34°F.

Bigleaf maple seeds are typically sown in fall, soon after collection. Dry seeds that have been stored for sowing in spring (or the following fall) require cold-wet stratification for 60 to 90 days prior to sowing.

Regeneration from Seed
Most bigleaf trees produce seed every year, although the amount may vary greatly from year to year. All viable seeds will germinate in the first year; delayed germination does not occur. Seeds germinate well on both mineral and organic substances. Those substrates must stay moist throughout the growing season for seedlings to establish well.

Germination and establishment rates are best under partial shade. Natural rates of establishment are low under dense shade or in clearcuts. Good conditions for natural regeneration occur when overstory conifers are thinned out by natural self-thinning or silvicultural thinning. Dense brush and understory vegetation inhibit natural regeneration.

Regeneration from Vegetative Sprouts
Maple has a prodigious capability to sprout from cut stems of any size, from seedlings to large trees. Sprouts provide a reliable means of regeneration from existing trees. Unmanaged sprout clumps produce too many stems and poor stem quality. Management may greatly improve the quality of stems from sprouts of bigleaf maple.

Regeneration from Planting

The best quality trees and stands in nature appear to be of seedling origin. There have been very few efforts to plant bigleaf maple in the wild. Although some forest nurseries are producing bigleaf maple on a trial basis, commercial supplies of maple seedlings are not consistently available. To ensure a supply of maple seedlings, arrangements must first be made for collection of seed and for production of seedlings at a qualified nursery. Very large ( 3 to 6 ft tall) nursery seedlings may be produced in one year.

Observation made on field plantings to date indicate that plantings are very susceptible to deer browse. Planted seedlings are sometimes prone to forking and poor form, particularly after they have been browsed or physically damaged. To maintain stem quality in plantations, seedlings may need to be protected from deer, planted in high densities, and correctively pruned.

Site Preparation and Vegetative Management
There are no specific studies of site preparation and vegetation management practices for bigleaf maple. The outstanding performance of bigleaf maple cultivated in nurseries and back yards indicates great potential for management of seedlings in the field. Control of competing vegetation should improve on the low rates of establishment and slow growth observed for maple in the presence of dense understory vegetation. Little or no site preparation is required with maple regenerating from stump sprouts.

Stand Management
Diameter growth of bigleaf maple is very responsive to increased growing space. Management should target a spacing regime that produces optimal growth while maintaining the benefits of crowding in young stands or clumps. Moderate crowding is necessary to reduce branching and forking and induce self-pruning. A dense canopy of bigleaf maple will also suppress competing understory vegetation, reducing the need for other vegetation management treatments.

Control of spacing via initial planting density or precommercial thinning (PCT) is recommended to allocate rapid growth to crop trees at an early age (5 to 15 years). To maintain moderate crowding, stands should not be opened too much initially. Intermediate thinning (for pulpwood, firewood, PCT) may be needed to maintain diameter growth. Bigleaf maple can continue to grow in diameter and respond to released growing space for at least 30 to 40 years.

Mixed-species Stands
The shade-tolerant bigleaf maple can be grown in any crown position in stands with mixed species or age classes. Management of mixed stands is complex; stands may require periodic treatments to maintain the growth of diverse components. Bigleaf maple stump sprouts must be controlled or thinned to prevent the early suppression of associated seedlings. Later treatments may be needed to maintain growth of bigleaf maple when intermixed conifers ultimately reach their superior height.

Delayed establishment of bigleaf maple seedlings in conifer plantations is a sensible strategy, since maple naturally establishes and grows under partial cover. Thinning and vegetation management may be needed to maintain adequate space for the growth of bigleaf maple. With even-aged mixtures or short (less than 10 years) delays in bigleaf maple establishment, maple sawtimber can be harvested at the same time as associated conifers.

Because this species tends to establish in patches or clumps, it may be sensible to manage bigleaf maple in monospecific patches in mixture with other trees. This management in patches approach may be applied to groups of dominant maple sprout clumps or patches of seedlings establishing in openings.

Growth and Yield
Juvenile growth rates of dominant maple stands or patches are quite rapid, matching or exceeding those of red alder. Yields of about 4500 ft3 per acre were estimated for 70-year-old stands of pure bigleaf maple in British Columbia. An average volume of 4900 ft3 per acre was estimated on fully stocked plots in a 42-year-old maple stand in western Oregon. Gross annual volume growth on these plots was about 140 ft3 per acre. On these plots, height growth after 45 years already appeared to be very slow (no measurable growth in 3 years). A rotation age of 40 to 50 years may be feasible in managed stands.

Interactions with Wildlife
Damage caused by deer and elk is probably the most important factor affecting the height and form of bigleaf maple seedlings and sprouts. The foliage and young stems of bigleaf maple are preferred browse for elk and deer, and these animals often use saplings for rubbing antlers. Seedlings and saplings are often clipped by mountain beaver. Birds and rodents feed on bigleaf maple seeds. Predation by rodents and invertebrates is a major cause of seedling mortality. Bigleaf maple provides an important broadleaved, deciduous component in the coniferous forests of the Northwest. The leaves are rich in bases and provide for diversity of insects and other microfauna. The understory vegetation associated with maple can be quite different from that in adjacent conifer forests. A variety of birds and mammals may benefit from these distinct attributes of food and habitat.

Insects and Diseases
Young, undamaged trees are generally free of serious disease or decay. Old or damaged trees commonly have serious defects caused by wood-rotting fungi, which invade through stem and branch wounds. Root pathogens (Armillaria spp.) and butt rots also attack older trees. The verticillium wilt (Verticillium albo-atrum) can be a serious problem for ornamental trees and it sometimes kills bigleaf maple in the forest.

Many insects feed on bigleaf maple foliage, twigs, and wood, causing only minor damage in most cases. The carpenter worm (Prionoxystus robinae) can cause serious damage in living trees of all sizes. Roundheaded borers often damage the wood of dead and dying trees. Powderpost beetles (Ptilinus basalis) may rapidly infest dead trees or lumber that is improperly stored.

Genetics
In genetics research, the major interest is in cultivars for ornamental uses. A red-leaved variety of bigleaf maple (Acer macrophyllum Pursh forma rubrum) has been found in northern California. Another variety with triple samaras (Acer macrophyllum Pursh var. kimballi Harrar) is occasionally found in Washington.

Harvesting and Utilization

Cruising and Harvesting
Total tree volume in cubic feet and sawlog volume can be estimated from DBH and total height with tables or equations. Log grades developed by the Forest Service for eastern hardwoods and modified by Oregon State University appear to separate log values to the point that it may be worth grading logs for marketing. Generally, logs are priced on the basis of diameter and length specifications developed by local log buyers.

Product Recovery
Sawlogs generally have a minimum diameter of 7 to 10 in. Lumber is graded with the special NHLA rules for bigleaf maple; grades include Selects and Better, No. 1 Shop, No. 2 Shop, No. 3 Shop, and Frame. Unlike the standard NHLA grading rules, these grasdes are generally based on the best face of the piece. Grades can be applied to rough, surfaced, green, or dry lumber; in practice, lumber is usually dried and surfaced before grading. One mill study conducted with NHLA standard grades rather than modified red alder and maple grades found a percentage recovery of No. 1 Common or Better green lumber from bigleaf maple logs (80 percent and 58 percent for grade 1 and 2 logs, respectively) that is quite good compared to other hardwoods (Appendix 1, Table 2).

There are also specialty markets for figured wood from bigleaf maple, although there are no standard grades. Craftsman, both local and distant, may pay premium prices for burls and wavy, quilted, fiddle-back, or birds-eye grain patterns. This figured material is utilized for thin-sliced, decorative veneers for furniture and architectural paneling.

Wood Properties

Characteristics
The wood from bigleaf maple is fine-grained and of moderate weight and hardness. The sapwood is reddish-white, sometimes with a grayish cast; the heartwood is light pinkish-brown. The wood is without any characteristic odor or taste. The growth rings on the end grain are not very distinct; on the radial and tangential surfaces, however, the growth rings (diffuse porous) and are moderately small to medium in size. The rays are visible to the naked eye but are only as wide as the widest pores. Although much of the wood is straight-grained, some highly figured wood that includes wavy, quilted, fiddle-back or birds-eye grain patterns is also produced.

Weight
Bigleaf maple weighs about 47 lb/ft3 when green, and 34 lb/ft3 when dried to 12 percent MC. The average specific gravity is 0.44 (green) or 0.51 (ovendry).

Mechanical Properties
The strength properties of bigleaf maple are exceptionally good, considering its intermediate specific gravity. While it is not as strong as the eastern hard maples, it performs better in most tests than the soft maples. Bigleaf maple is suitable for most furniture design applications, and the lower grades perform well as pallet stock. It holds nails well and is not likely to split with nailing. See Appendix 1, Table 3, for average mechanical properties for small clear specimens.

Drying and Shrinkage
Under properly controlled conditions, bigleaf maple can be successfully kiln-dried in a short time with a minimum of degrade. The most prevalent drying defects are end checks and collapse, or mold growth that causes stained wood. The average green MC is 72 percent (ovendry basis.)

The radial shrinkage (green to ovendry) is 3.7 percent and the tangential shrinkage value is 7.1 percent. These values are the same as those of black cherry, and are better than those of red alder (radial 4.2 percent, tangential 7.3 percent) and Oregon white oak (radial 4.4 percent, tangential 9.0 percent). See Table below for an appropriate kiln schedule for 4/4, 5/4, and 6/4 lumber.

Machining
Bigleaf maple wood retains many of the favorable machining (planning, shaping, boring, and turning) characteristics of the eastern hard maples, while allowing for greater production feed rates because of its lower density. Best results for planning were obtained with hook angles of 20°. As with other fine-grain, hardwoods, surface scratching associated with sanding (swirls and cross-grain) can be a problem, although not to the same degree as with the hard maples.

Adhesives
There appear to be no reliable test results available that deal directly with the newer synthetic adhesives, but communication with local users indicates that bigleaf maple performs satisfactorily with good quality joints if conditions are well controlled. The glue line can be visible when darker resins are used because of the wood’s light color.

Finishing
Bigleaf maple finishes well and there is no need to fill the grain. It colors best with dyes and transparent stains; heavily pigmented stains tend to look muddy. With careful color selection, the straight-grained wood can be stained to resemble cherry. Figured bigleaf maple is exceptionally beautiful when clear-coated.

Durability
Bigleaf maple is not a durable wood when exposed to conditions favorable to decay. When properly seasoned, the wood is relatively stable and is not apt to split or surface check in use.

Uses
Bigleaf maple is used for furniture, veneer, paneling, hardwood plywood, musical instruments, moulding, pallets, turnery, pulpwood, and firewood.

Related Literature

BASTENDORFF, K.M., and A. POLENSEK. 1984. Strength and stiffness of red alder and bigleaf maple pallet materials. Forest Products Journal 34(7/8):51-56.

FRIED, J.S., J.R. BOYLE, J.C. TAPPEINER II, and K. CROMACK Jr. 1990. Effects of bigleaf maple on soils in Douglas-fir forests. Canadian Journal of Forest Research 20:259-266.

FRIED, J.S., J.C. TAPPEINER II, and D.E. HIBBS. 1988. Bigleaf maple seedling establishment and early growth in Douglas-fir forests. Canadian Journal of Forest Research 18:1226-1233.

MINORE, D., and J.C. ZASADA. 1990. Bigleaf maple. P. 33-40 in Silvics of North America, Volume 2, Hardwoods. R.M. Burns and B.H. Honkala, coords. USDA Forest Service, Washington D.C. Agriculture Handbook 654.

NADKARNI, N.M. 1984 Biomass and mineral capital of epiphytes in an Acer macrophyllum community of temperate moist coniferous forest, Olympic Peninsula, Washington State. Canadian Journal of Botany 62:2223-2228.

WOLLIN, A.C., and J.R. PFEIFFER. 1955. Oregon maple log and lumber grading. Oregon Forest Products Laboratory, State Board of Forestry and School of Forestry, Corvallis. Report No. G-4. 21 p.