Acer rubrum
Acer rubrum, the red maple, also known as swamp maple, water maple, or soft maple, is one of the most common and widespread deciduous trees of eastern and central North America. The U.S. Forest Service recognizes it as the most abundant native tree in eastern North America. The red maple ranges from southeastern Manitoba around the Lake of the Woods on the border with Ontario and Minnesota, east to Newfoundland, south to Florida, and southwest to East Texas. Many of its features, especially its leaves, are quite variable in form. At maturity, it often attains a height around. Its flowers, petioles, twigs, and seeds are all red to varying degrees. Among these features, however, it is best known for its brilliant deep scarlet foliage in autumn.
Over most of its range, red maple is adaptable to a very wide range of site conditions, perhaps more so than any other tree in eastern North America. It can be found growing in swamps, on poor, dry soils, and almost anywhere in between. It grows well from sea level to about. Due to its attractive fall foliage and pleasing form, it is often used as a shade tree for landscapes. It is used commercially on a small scale for maple syrup production and for its medium to high quality lumber. It is the state tree of Rhode Island. The red maple can be considered weedy or even invasive in young, highly disturbed forests, especially frequently logged forests. In a mature or old-growth northern hardwood forest, red maple only has a sparse presence, while shade-tolerant trees such as sugar maples, beeches, and hemlocks thrive. By removing red maple from a young forest recovering from disturbance, the natural cycle of forest regeneration is altered, changing the diversity of the forest for centuries to come.
Description
Though A. rubrum is sometimes easy to identify, it is highly variable in morphological characteristics. It is a medium to large tree, reaching heights of and exceptionally over in the southern Appalachians where conditions favour its growth. The leaves are usually long on a full-grown tree. The trunk diameter often ranges from ; depending on the growing conditions, however, open-grown trees can attain diameters of up to. The trunk remains free of branches until some distance up the tree on forest grown trees, while individuals grown in the open are shorter and thicker with a more rounded crown. Trees on poorer sites often become malformed and scraggly. Generally the crown is irregularly ovoid with ascending whip-like curved shoots. The bark is a pale grey and smooth when the individual is young. As the tree grows the bark becomes darker and cracks into slightly raised long plates. The tallest known living red maple is near Sevierville in the Great Smoky Mountains National Park, with a height of, and the largest known is near Armada, Michigan, with a height of and a bole circumference, at breast height, of.The leaves of the red maple are deciduous and arranged oppositely on the twig. They are around long and wide with three to five palmate lobes and a serrated margin. The sinuses are typically narrow, but the leaves can exhibit considerable variation.
The twigs are reddish in colour and somewhat shiny with small lenticels. Dwarf shoots are present on many branches. The buds are usually blunt and greenish to reddish in colour, generally with several loose scales. The lateral buds are slightly stalked, and in addition, collateral buds may be present, as well. The buds form in fall and winter and are often visible from a distance due to their large size and reddish tint. The leaf scars on the twig are V-shaped and contain three bundle scars.
The flowers are generally unisexual, with male and female flowers appearing in separate sessile clusters, though they are sometimes bisexual. They appear in late winter to early spring, from December to May depending on elevation and latitude, usually before the leaves. The tree itself is considered polygamodioecious, meaning some individuals are male, some female, and some monoecious. Under the proper conditions, the tree can sometimes switch from male to female, male to hermaphroditic, and hermaphroditic to female. The red maple begins blooming when it is about 8 years old, but this varies from tree to tree: some trees begin flowering when they are 4 years old. The flowers are red with 5 small petals and a 5-lobed calyx, usually at the twig tips. The staminate flowers are sessile. The pistillate flowers are borne on pedicels that grow out while the flowers are blooming, so that eventually the flowers are in a hanging cluster with stems long. The petals are lineal to oblong in shape and are pubescent. The pistillate flowers have one pistil formed from two fused carpels with a glabrous superior ovary and two long styles that protrude beyond the perianth. The staminate flowers contain between 4 and 12 stamens, often with 8.
The fruit is a schizocarp of 2 samaras, each one long. Prior to dehiscence, the wings of the fruit are somewhat divergent at an angle of 50 to 60°. They are borne on long slender pedicels and are variable in colour from light brown to reddish. They ripen from April through early June, before even the leaf development is altogether complete. After they reach maturity, the seeds are dispersed for a 1- to 2-week period from April through July.
Distribution and habitat
Acer rubrum is one of the most abundant and widespread trees in eastern North America. It can be found from the south of Newfoundland, through Nova Scotia, New Brunswick, and southern Quebec to the southwest west of Ontario, extreme southeastern Manitoba and northern Minnesota; southward through Wisconsin, Illinois, Missouri, eastern Oklahoma, and eastern Texas in its western range; and east to Florida. It has the largest continuous range along the North American Atlantic Coast of any tree that occurs in Florida. In total it ranges from north to south. The species is native to all regions of the United States east of the 95th meridian. The tree's range ends where the mean minimum isotherm begins, namely in southeastern Canada. A. rubrum is not present in most of the Prairie Peninsula of the northern Midwest, the coastal prairie in southern Louisiana and southeastern Texas and the swamp prairie of the Florida Everglades. Red maple's western range stops with the Great Plains where conditions become too dry for it. The absence of red maple from the Prairie Peninsula is most likely due to the tree's poor tolerance of wildfires. Red maple is most abundant in the Northeastern US, the Upper Peninsula of Michigan, and northeastern Wisconsin, and is rare in the extreme west of its range and in the Southeastern US.In several other locations, the tree is absent from large areas but still present in a few specific habitats. An example is the Bluegrass region of Kentucky, where red maple is not found in the dominant open plains, but is present along streams. Here the red maple is not present in the bottom land forests of the Grain Belt, despite the fact it is common in similar habitats and species associations both to the north and south of this area. In the Northeastern US, red maple can be a climax forest species in certain locations, but will eventually give way to sugar maple.
A. rubrum does very well in a wide range of soil types, with varying textures, moisture, pH, and elevation, probably more so than any other forest tree in North America. Its wide pH tolerance means that it can grow in a variety of places, and it is widespread along the Eastern United States. It grows on glaciated as well as unglaciated soils derived from granite, gneiss, schist, sandstone, shale, slate, conglomerate, quartzite, and limestone. Chlorosis can occur on very alkaline soils, though otherwise its pH tolerance is quite high. Moist mineral soil is best for germination of seeds.
Red maple can grow in a variety of moist and dry biomes, from dry ridges and sunny, southwest-facing slopes to peat bogs and swamps. While many types of tree prefer a south- or north-facing aspect, the red maple does not appear to have a preference. Its ideal conditions are in moderately well-drained, moist sites at low or intermediate elevations. However, it is nonetheless common in mountainous areas on relatively dry ridges, as well as on both the south and west sides of upper slopes. Furthermore, it is common in swampy areas, along the banks of slow moving streams, as well as on poorly drained flats and depressions. In northern Michigan and New England, the tree is found on the tops of ridges, sandy or rocky upland and otherwise dry soils, as well as in nearly pure stands on moist soils and the edges of swamps. In the far south of its range, it is almost exclusively associated with swamps. Additionally, red maple is one of the most drought-tolerant species of maple in the Carolinas.
Red maple is far more abundant today than when Europeans first arrived in North America. It only contributed minimally to old-growth upland forests, and would only form same-species stands in riparian zones. The density of the tree in many of these areas has increased six- to seven-fold, and this trend seems to be continuing. One of the primary factors for this appears to be a loss of forest management that comes in several forms. First, a loss regular prescribed burns, such as those performed by Native Americans who would use the burns to enhance acorn and other seed harvesting. Second, continued heavy logging and a recent trend of young, shrubby forests recovering from past human disturbances.
Because it can grow on a variety of substrates, has a wide pH tolerance, and grows in both shade and sun, A. rubrum is a prolific seed producer and highly adaptable, often dominating disturbed sites. While many believe that it is replacing historically dominant tree species in the Eastern United States, such as sugar maples, beeches, oaks, hemlocks and pines, red maple will only dominate young forests prone to natural or human disturbance. In areas disturbed by humans where the species thrives, it can reduce diversity, but in a mature forest, it is not a dominant species; it only has a sparse presence and adds to the diversity and ecological structure of a forest. Extensive use of red maple in landscaping has contributed to the surge in the species' numbers as volunteer seedlings proliferate. Finally, disease epidemics have greatly reduced the population of elms and chestnuts in the forests of the US. While mainline forest trees continue to dominate mesic sites with rich soil, more marginal areas are increasingly being dominated by red maple.