Sugar Maple

The Sugar Maple Acer saccharum is a prominent tree in the hardwood forests of eastern North America. It is the largest American maple, reaching heights of 30-37 m tall.

The leaves are deciduous, 8-15 cm long and equally wide with five palmate lobes. The basal lobes are relatively small, while the upper lobes are larger and deeply notched. In contrast with the angular notching of the Silver Maple, however, the notches tend to be rounded at their interior. The fall color is often spectacular, ranging from bright yellow through orange to fluorescent red-orange.

The flowers are in corymbs of 5-10 together, yellow-green and without petals; flowering occurs in early spring after 30-55 growing degree days. The fruit is a double samara with two winged seeds, the seeds are globose, 7-10 mm diameter, the wing 2-3 cm long. The seeds fall from the tree in autumn.

It is closely related to the Black Maple, which is sometimes included in this species but sometimes separated as Acer nigrum. The western American Bigtooth Maple (Acer grandidentatum) is also treated as a variety or subspecies of Sugar Maple by some botanists.

Sugar Maple is also often confused with Norway Maple, though they are not closely related within the genus. Sugar Maple is most easily identified by clear sap in the leaf petiole (Norway Maple has white sap), orange fall color (Norway Maple is a simple yellow), and shaggy bark on older trees (Norway Maple bark has small grooves). Also, the leaf lobes of Sugar Maple have a more triangular shape, in contrast to the squarish lobes of the norway maple.

Ecology

The Sugar Maple is an immensely important species to the ecology of many forests in North America. Pure stands are common, and it is a major component of many forest types. It often forms associations with the American Beech, forming the beech-maple forest type, common in northern areas. Other associations include Sugar Maple-Yellow Birch (which is most important beyond the northern limit of beech), Sugar Maple-American Basswood, Sugar Maple-White Ash and Sugar Maple-Ironwood-Red Oak. Sugar Maples engage in hydraulic lift, drawing water from lower soil layers and exuding that water into upper, drier soil layers. This not only benefits the tree itself but also many other plants growing around it.

Sugar Maple is among the most shade tolerant of large deciduous trees. Among north American maples its shade tolerance is exceeded only by the Striped Maple, a smaller tree. Like other maples, its shade tolerance is manifested in its ability to germinate and persist under a closed canopy as an understory plant, and respond with rapid growth to the increased light formed by a gap in the canopy.

Human influences have contributed to the decline of the sugar maple in many regions. Its role as a species of mature forests has led it to be replaced by more opportunistic species in areas where forests are cut over. Sugar maple also exhibits a greater susceptibility to pollution than other species of maple. Acid rain and soil acidification are some of the primary contributing factors to maple decline.

In some parts of Eastern North America, particularly near urbanized areas, the Sugar Maple is being displaced by the Norway Maple. The Norway Maple is also highly shade tolerant, but is considerably more tolerant of urban conditions than the Sugar Maple, making it a natural replacement in those areas heavily disturbed by human activities.

Cultivation and uses

Sugar Maple is one of the most important Canadian trees, being (with Black Maple) the major source of sap for making maple syrup; Black Maple being regarded as slightly better. Many maples can be used as a sap source for maple syrup, but none of the others are as good as these two.

The wood is one of the hardest of the maples, and is prized for furniture and flooring. Bowling alleys and bowling pins are both commonly manufactured from sugar maple. Trees with wavy wood grain, called "birdseye maple", are especially valued.

The Sugar Maple is a favorite street and garden tree, because it is easy to propagate and transplant, is fairly fast-growing, and has beautiful fall color; however, its intolerance of pollution and compacted soils common to inner city conditions make it a frequent victim of maple decline. It also has some of the most dense shade to be found in shade trees. The shade and the shallow, fibrous roots may interfere with grass growing under the trees. Deep well-drained loam is the best rooting medium, although Sugar Maple can grow well on sandy soil which does not become excessively dry. Poorly drained areas are unsuitable and the species is especially short-lived on flood-prone clay flats. Its salt tolerance is low and it is very sensitive to boron.

Cultivars

'Apollo' - columnar.
'Arrowhead' - pyramidal crown.
'Astis' (Steeple^®) - heat-tolerant; good in southeastern USA. Oval crown.
'Bonfire' - fast-growing.
'Columnare'
'Fall Fiesta' - tough-leaved, colorful in season.
'Green Mountain' - durable foliage resists heat and drought.
'Legacy' - tough, vigorous and popular.
'Monumentale' - columnar.
'Newton Sentry' - very narrow.
'Sweet Shadow' - lacy foliage.
'Temple's Upright' - columnar.
'Unity' - very hardy Manitoba cultivar.

Sugar Maple is the State Tree of New York, Vermont, West Virginia and Wisconsin. Its leaf is also featured on the Canadian Flag.

References

Horton, J. L., & Hart, S.C. (1998). Hydraulic lift: a potentially important ecosystem process. Trends in Ecology and Evolution 13 (6): 232-235.
Canham, C. D. (1989). Different Respones to Gaps Among Shade-Tollerant Tree Species. Ecology 70 (3): 548-550.
Brisson, J., Bergeron, Y., Bouchard, A., & Leduc, A. (1994). Beech-maple dynamics in an old-growth forest in southern Quebec, Canada. Ecoscience (Sainte-Foy) 1 (1): 40-46.
Duchesne, L., Ouimet, R., & Houle, D. (2002). Basal Area Growth of Sugar Maple in Relation to Acid Deposition, Stand Health, and Soil Nutrients. Journal of Environmental Quality 31: 1676-1683.
Godman, Yawney and Tubbs. Sugar Maple
Acer saccharum
Acer saccharum images at bioimages.vanderbilt.edu

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Ecology

Cultivation and uses

References