Acer rubrum

Did You Know?

• In the lumber industry, Acer rubrum is considered a 'soft maple', a designation it shares commercially with silver maple.
• Red maple lumber contains a greater percentage of 'curly' (also called 'flame' or 'fiddleback') figure, prized by musical instrument and custom furniture makers.
• The wood of red maple has greater dimensional stability than that of sugar maple and machines and stains more readily.

Description

Acer rubrum is a medium to large tree, reaching heights of 27 to 38 m, with exceptional individuals over 41 m in the southern Appalachians. Trunk diameter typically ranges from 46 to 88 cm, but open-grown trees can reach up to 153 cm. The bark is pale grey and smooth on young trees, becoming darker and cracking into slightly raised long plates with age. The leaves are deciduous, arranged oppositely, and measure 5 to 10 cm long and wide with three to five palmate lobes and serrated margins.

The sinuses are usually narrow, though leaf shape varies considerably. Twigs are reddish and somewhat shiny with small lenticels, and dwarf shoots are present on many branches. Buds are blunt, greenish to reddish, and often visible from a distance due to their large size and reddish tint. Leaf scars on the twig are V-shaped with three bundle scars.

The tallest known living red maple, at 43.59 m, is near Sevierville in the Great Smoky Mountains National Park, while the largest known, near Armada, Michigan, has a height of 38.1 m and a bole circumference of 4.95 m.

Distribution and habitat

Acer rubrum, the red maple, claims the largest continuous coastal range of any tree that also grows in Florida, stretching from southeastern Canada down to Florida and west to eastern Texas and Oklahoma. It is missing from most of the northern Midwest’s Prairie Peninsula, the coastal prairies of southern Louisiana and southeastern Texas, and the swamp prairies of the Florida Everglades, a gap likely tied to its poor tolerance for wildfires. The tree is most common in the northeastern United States, Michigan’s Upper Peninsula, and northeastern Wisconsin, while it becomes rare at the western edges of its range and in the Southeast.

In Kentucky’s Bluegrass region, red maple avoids open plains but appears along streams. It adapts to a broader variety of soil types, textures, moisture levels, pH, and elevation than any other North American forest tree, thriving on both glaciated and unglaciated soils derived from granite, gneiss, schist, sandstone, shale, slate, conglomerate, quartzite, and limestone. Very alkaline soils can cause chlorosis, but otherwise its pH tolerance is high. Moist mineral soil provides the best conditions for seed germination.

Ecology

Red maple's maximum lifespan is 150 years, though most live less than 100 years. Its thin bark is easily damaged by ice, storms, animals, and lawn mower debris, allowing fungi to cause heart rot. The tree produces roots suited to its site from a young age: in wet locations, seedlings develop short taproots with long lateral roots; on dry sites, they develop long taproots with shorter laterals. Mature trees have woody roots up to 25 m long, primarily horizontal in the upper 25 cm of ground.

Red maple is very tolerant of flooding, with one study showing no leaf damage after 60 days of flooding, and also tolerates drought by stopping growth and producing a second flush when conditions improve. It is one of the first plants to flower in spring, producing a seed crop every year with a bumper crop every second year. A single tree 5 to 20 cm in diameter can produce 12,000 to 91,000 seeds in a season. Seeds are epigeal and germinate in early summer if light, moisture, and temperature are sufficient; if densely shaded, germination may wait until the next spring.

Red maple increases significantly when associate trees are damaged by disease, cutting, or fire. One study found over 2,200 red maple seedlings per hectare taller than 1.4 m six years after clearcutting a 3.4 ha oak-hickory forest that originally contained no red maples.

Cultivation

Red maple is extensively planted due to its rapid growth, ease of transplanting, attractive form, and value for wildlife in the eastern US. In parts of the Pacific Northwest, it is one of the most common introduced trees. Its popularity stems from its vigorous habit, early red flowers, and flaming red fall foliage. It was introduced into the United Kingdom in 1656 and is now found in many parks and yards.

Red maple is suitable for urban areas with ample root space, especially when associated with arbuscular mycorrhizal fungi. It is more tolerant of pollution and road salt than sugar maple, though its fall foliage is less vibrant in such environments. Its low root system can be invasive and is a poor choice near paving. Squirrels eat its buds in early spring, though they prefer silver maple buds.

Red maples are used for bonsai and have year-round attractive features. Numerous cultivars have been selected, often for fall colour intensity, including 'October Glory', 'Red Sunset', 'Fireburst', 'Florida Flame', and 'Gulf Ember'. Examples of cultivars include 'Armstrong' (columnar with silvery bark), 'Autumn Blaze' (rounded oval with orange-red fall colour), and 'Autumn Flame' (fast grower with early bright red fall colour).