Description

General: Maple Family (Aceraceae).  A native tree with a dense, spreading crown, to 25-37(-40) m in height; bark light gray to gray-brown, rough, deeply furrowed, and darker with age.  The leaves are deciduous, opposite, long-petioled, blades 5-11 cm long and about as wide, with 5 shallow, blunt or short-pointed lobes, edges coarsely toothed, dark green and glabrous above, whitish and more or less hairy below, turning intensely red, orange, or yellow in fall.  The flowers are small, greenish-yellow, in long-stalked, drooping clusters or racemes, each cluster with 8 to 14 flowers.  Most trees are either male or female (the species is essentially dioecious), but both kinds of flowers occur on some trees (technically monoecious), sometimes segregated on different branches.  The fruits are winged nutlets (samaras) in a pair, 2-2.5 cm long, clustered on long stalks, red to red-brown.  The common name refers to the use of the species for making sugar and syrup. 

Uses

Sugar maple is the only tree today used for commercial syrup production, as its sap has twice the sugar content of other maple species.  The sap, mostly collected in the spring, is concentrated by boiling or reverse osmosis, with about 35-40 liters of sap making 1 liter of syrup.  A single tree may produce 5-60 liters of sap per year.  Nights below freezing and days at higher than 5°C are needed to ensure good sap flow.  Sugar maple was the premier source of sweetener, along with honey, to Native Americans and early European settlers.  Native Americans also used sugar maple sap for sugar and candies, as a beverage, fresh or fermented into beer, and soured into vinegar and used to cook meat.

Sugar maple is widely planted as an ornamental or shade tree and many cultivars have been selected, based on variation in growth habit/crown shape, mature height, fall color, leaf shape, and temperature tolerance.  The leaves go from green to brilliant yellow, orange, and red in autumn, although there is much variation in fall color within the species.  Orange and reds seem to be more intense in New England types, while yellows are more pronounced further west.  Interior leaves may be yellow, while outer exposed leaves turn orange-red.  The species is best suited to larger sites where soil compaction is not a concern.  It also is sometimes used in shelterbelt plantings and has potential value for rehabilitation of disturbed sites.  

Sugar maple is an important timber tree valued for its hard, heavy, and strong wood, commonly used to make furniture, paneling, flooring, and veneer.  It is also used for gunstocks, tool handles, plywood dies, cutting blocks, woodenware, novelty products, sporting goods, bowling pins, and musical instruments.

White-tailed deer, moose, and snowshoe hare commonly browse sugar maple.  Red squirrel, gray squirrel, and flying squirrels feed on the seeds, buds, twigs, and leaves.  Porcupines consume the bark and can girdle the upper stem.  Songbirds, woodpeckers, and cavity nesters nest in sugar maple.  Although the flowers appear to be wind-pollinated, the early-produced pollen may be important to the biology of bees and other pollen-dependent insects because many insects, especially bees, visit the flowers.

Distribution

Sugar maple is widespread in mixed hardwood forests of the eastern United States.  It grows from Nova Scotia and New Brunswick westward to Ontario and Manitoba, North Dakota and South Dakota, southward into eastern Kansas into Oklahoma, and southward in the east through New England to Georgia. 

Adaptation

Sugar maple most commonly occurs in rich, mesic woods but also grows in drier upland woods.  It often grows in canyons, ravines, valleys, stream terraces, and streambanks, but it is occasionally found on dry rocky hillsides, at 500-1700 meters elevation.  It is a dominant or codominant in many northern hardwood and mixed mesophytic forests.  Common codominants include beech (Fagus grandifolia), birch (Betula spp.), American basswood (Tilia americana), northern red oak (Quercus rubra), white oak (Quercus alba), and yellow poplar (Liriodendron tulifera), but it also grows with various other hardwood species as well as conifers such as pine, spruce, fir, and eastern hemlock. 

 In the absence of disturbance, forests of jack pine, eastern white pine, eastern hemlock, yellow birch, or red pine are replaced by sugar maple and American basswood.  Because repeated disturbance by fire was common in eastern deciduous forests in pre-settlement times, succession to sugar maple-American basswood stands may have taken as long as 650 years in some locations.  Increases in sugar maple during the past 50 years in central and Great Lakes hardwood forests have been attributed to fire suppression. 

This species flowers in April-June, with fruiting occurring in June-October.  Fruits ripen about 12-16 weeks after flowering and begin to fall about 2 weeks after ripening.  Leaves generally drop just after seeds have fallen.  At the southern edge of the species' range, dead leaves tend to remain on the trees through much of the winter.  

Establishment

Minimum seed-bearing age for sugar maple is 30-40 years; maximum seed production is reached after about 60 years of age.  Seed is abundantly produced each year but peaks occur mostly from 2-5 years.  Seeds are dispersed in fall and germinate in spring. Seeds can remain viable for up to 5 years but few persist in the seed bank for more than one year.  Sugar maples can live for up to 500 years. 

References

Nesom, G. & Moore, L. (2006). Plant fact sheet for sugar maple (acer saccharum Marsh). Retrieved from http://plants.usda.gov/java/factSheet