Acer rubrum - WikiHQ

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. 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. 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. 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. 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. 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 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. 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.

Ecology

Red maple's maximum lifespan is 150 years, but most live less than 100 years. The tree's thin bark is easily damaged from ice and storms, animals, and when used in landscaping, being struck by flying debris from lawn mowers, allowing fungi to penetrate and cause heart rot. The maple shoot borer, Proteoteras aesculana, is a serious pest of maples being raised in cultivation. The caterpillars tunnel into the shoots, weakening them; if a central shoot dies, the tree forks, though one of the branches may take over as the leading shoot.

Due to the species' very wide range, there is significant variation in hardiness, size, form, time of flushing, onset of dormancy, and other traits. Generally speaking, individuals from the north flush the earliest, have the most reddish fall colour, set their buds the earliest and take the least winter injury. Seedlings are tallest in the north-central and east-central part of the range. In Florida, at the extreme south of the red maple's range, it is limited exclusively to swamplands. The fruits vary geographically with northern individuals in areas with brief, frost-free periods producing fruits that are shorter and heavier than their southern counterparts. As a result of such variation, there is much genetic potential for breeding programs with a goal of producing red maples for cultivation. This is especially useful for making urban cultivars that require resistance from verticillium wilt, air pollution, and drought.

Allergenic potential

The allergenic potential of red maples varies widely based on the cultivar. The following cultivars are completely male and are highly allergenic, with an OPALS allergy scale rating of 8 or higher:

'Autumn Flame' ('Flame')
'Autumn Spire'
'Columnare' ('Pyramidale')
'Firedance' ('Landsburg')
'Karpick'
'Northwood'
'October Brilliance'
'Sun Valley'
'Tiliford'

The following cultivars have an OPALS allergy scale rating of 3 or lower; they are completely female trees, and have low potential for causing allergies:

Cultivation

Red maple's rapid growth, ease of transplanting, attractive form, and value for wildlife (in the eastern US) has made it one of the most extensively planted trees. In parts of the Pacific Northwest, it is one of the most common introduced trees. Its popularity in cultivation stems from its vigorous habit, its attractive and early red flowers, and most importantly, its flaming red fall foliage. The tree was introduced into the United Kingdom in 1656 and shortly thereafter entered cultivation. There it is frequently found in many parks and yards.

Red maple is a good choice of a tree for urban areas when there is ample room for its root system. Forming an association with arbuscular mycorrhizal fungi can help A. rubrum grow along city streets. It is more tolerant of pollution and road salt than sugar maples, although the tree's fall foliage is not as vibrant in this environment. Like several other maples, its low root system can be invasive and it makes a poor choice for plantings near paving. It attracts squirrels, who eat its buds in the early spring, although squirrels prefer the larger buds of the silver maple.

Red maples make vibrant and colourful bonsai, and have year around attractive features for display.

Cultivars

thumb|upright|[[Acer × freemanii 'Jeffersred' cultivar in Toronto]]

Numerous cultivars have been selected, often for intensity of fall colour, with 'October Glory' and 'Red Sunset' among the most popular. Toward its southern limit, 'Fireburst', 'Florida Flame', and 'Gulf Ember' are preferred. Many cultivars of the Freeman maple are also grown widely. Below is a partial list of cultivars:

'Armstrong' – Columnar to fastigate in shape with silvery bark and modest orange to red fall foliage.
'Autumn Blaze' – Rounded oval form with leaves that resemble the silver maple. The fall colour is orange red and persists longer than usual.
'Autumn Flame' – A fast grower with exceptional bright red fall colour developing early. The leaves are also smaller than the species.
'Autumn Radiance' – Dense oval crown with an orange-red fall colour.
'Autumn Spire' – Broad columnar crown; red fall colour; very hardy.
'Bowhall' – Conical to upright in form with a yellow-red fall colour.
'Burgundy Bell' – Compact rounded uniform shape with long lasting, burgundy fall leaves.
'Columnare' – An old cultivar growing to with a narrow columnar to pyramidal form with dark green leaves turning orange and deep red in fall.
'Gerling' – A compact, slow growing selection, this individual only reaches and has orange-red fall foliage.
'Northwood' – Branches are at a 45 degree angle to the trunk, forming a rounded oval crown. Though the foliage is deep green in summer, its orange-red fall colour is not as impressive as other cultivars.
'October Brilliance' – This selection is slow to leaf in spring, but has a tight crown and deep red fall colour.
'October Glory' – Has a rounded oval crown with late developing intense red fall foliage. Along with 'Red Sunset', it is the most popular selection due to the dependable fall colour and vigorous growth. This cultivar has gained the Royal Horticultural Society's Award of Garden Merit.
'Redpointe' – Superior in alkaline soil, strong central leader, red fall colour.
'Red Sunset' – is also a recipient of the Award of Garden Merit. The other very popular choice, this selection does well in heat due to its drought tolerance and has an upright habit. It has very attractive orange-red fall colour and is also a rapid and vigorous grower.
'Scarlet Sentinel' – A columnar to oval selection with 5-lobed leaves resembling the silver maple. The fall colour is yellow-orange to orange-red and the tree is a fast grower.
'Schlesingeri' – A tree with a broad crown and early, long lasting fall colour that is a deep red to reddish purple. Growth is also quite rapid. The original tree grew at the home of Barthold Schlesinger in Brookline, Massachusetts.
'Shade King' – This fast growing cultivar has an upright-oval form with deep green summer leaves that turn red to orange in fall.
'V.J. Drake' – This selection is notable because the edges of the leaves first turn a deep red before the colour progresses into the centre.

Other uses

thumb|upright=0.5|Red maple may be used for [[maple syrup|syrup, but its short harvest season reduces its commercial viability.]]

In the lumber industry Acer rubrum is considered a "soft maple", a designation it shares, commercially, with silver maple (A. saccharinum). In this context, the term "soft" is more comparative, than descriptive; i.e., "soft maple", while softer than its harder cousin, sugar maple (A. saccharum), is still a fairly hard wood, being comparable to black cherry (Prunus serotina) in this regard. Like A. saccharum, the wood of red maple is close-grained, but its texture is softer, less dense, and has not as desirable an appearance, particularly under a clear finish. However, the wood from Acer rubrum while being typically less expensive than hard maple, has greater dimensional stability than that of A. saccharum, and machines and stains more readily. Thus, high grades of wood from the red maple can be substituted for hard maple, particularly when it comes to making stain/paint-grade furniture. Red maple lumber contains a greater percentage of "curly" (aka "flame"/"fiddleback") figure, prized by musical instrument/custom furniture makers, as well as the veneer industry. As a soft maple, the wood tends to shrink more during the drying process than with the hard maples.

Red maple is used for the production of maple syrup, though the hard maples Acer saccharum (sugar maple) and Acer nigrum (black maple) are more commonly utilized. One study compared the sap and syrup from the sugar maple with those of the red maple, as well as those of the Acer saccharinum (silver maple), Acer negundo (boxelder), and Acer platanoides (Norway maple), and all were found to be equal in sweetness, flavour, and quality. However, the buds of red maple and other soft maples emerge much earlier in the spring than the sugar maple, and after sprouting, chemical makeup of the sap changes, imparting an undesirable flavour to the syrup. This being the case, red maple can only be tapped for syrup before the buds emerge, making the season very short.

References

External links

NRCS: United States Department of Agriculture Plants Profile and map: Acer rubrum
Acer rubrum images from Vanderbilt University
Portrait of the Earth, Winter ID photos