Farming Magazine - May, 2010

SUGARING

Maples of North America

By Tim Wilmot

At a recent meeting I was talking with some sugar makers from Indiana, when I was asked, “What does striped maple look like?” I had never really that the distribution of maple species is not uniform across the sugaring region, but, in fact, it isn’t. So here is a description of the maples native to North America.

Various sources list the number of North American maples, excluding transplants from other continents like Norway maple, at around 13, but that number is debatable. For example, sugar maple and black maple are often described as different species, but many botanists consider black maple to be a subspecies of sugar maple; a subspecies is not considered genetically different enough to be a separate species. In any case, while we know there are many more maples native to East Asia, there is indeed a broad distribution of maples in North America, and they can be found in all the lower 48 states.

Acer negundo, or boxelder, an odd maple since it has compound leaves like an ash, has the widest distribution of maples. It can be found from western New England to the Pacific Coast, and through the Rockies from Alberta to Guatemala. Not the most popular tree, and described by some as “trashy, poorly formed and short-lived,” it is a source of syrup for some sugar makers, presumably because nothing else of that tree size is available. Boxelder can thrive in a variety of soils, both wet and dry, and is valuable in shelterbelt plantings because of its cold and drought tolerance.

Acer rubrum, or red maple, is another species that can thrive on widely diverse sites, from swamps to dry ridges. Red maple ranges over all of eastern North America, from Newfoundland to Florida and from Minnesota and east Texas. The remaining common “soft” maple is Acer saccharinum, or silver maple, which has a range similar to red maple, but without the northern or southern extremes. Silver maple is primarily a floodplain species and can survive prolonged inundation that would kill sugar maple. Red maple is suitable for sugaring, while silver maple can be tapped for sap collection, but presumably like boxelder only because nothing better is available. We have heard descriptions of sap collecting from silver maples in Illinois, but one probably needs hip boots to visit floodplain trees in the spring.

Besides sugar maple and its subspecies, the remaining North American maple that is commonly a medium to large tree is Acer macrophyllum, or bigleaf maple. Appropriately named, the leaves of this species are often 12 inches across. Like Norway maple, the petioles have milky sap, and oddly, the seeds are covered with stinging hairs. Bigleaf, or Oregon maple, is an important hardwood of the Pacific Coast forest, where most big trees are conifers, and its range extends from Alaska to Southern California. The wood of this species is not as hard or strong as sugar maple, but it is used especially for piano frames. The sap can be made into syrup, although one source says it is of “lower quality” than syrup from sugar maple; also, freeze-thaw cycles are much more irregular on the Pacific Coast than in the East.

Acer saccharum, or the true sugar maple, ranges from Nova Scotia to western Kansas and well into the southern Appalachian mountains. Subspecies Acer nigrum, or black maple, has many similar qualities to the sugar maple except for its leaf shape (three-lobed instead of five), and is adapted to somewhat warmer and drier climates than the sugar maple. Thus, black maple is predominant in Iowa and rare in New England. It is described as somewhat slower growing than sugar maple, with leaves that drop earlier in the fall. Subspecies Acer barbatum, commonly known as Florida maple or southern sugar maple, is native to the South from the Carolinas to eastern Oklahoma and Texas. It has smooth, gray bark and leaves very similar in shape to the sugar maple, but they are whitish underneath. An understory tree of rich soils, Florida maple can apparently reach a large size, but such trees are unusual. It has been described as a source for maple syrup. Subspecies Acer leucoderm, or chalk maple, is a rare shrub or small tree with approximately the same range as Florida maple. Its leaves look like those of sugar maple, but are small, and yellow-green underneath and its bark is chalky gray. Both Florida maple and chalk maple, as well as bigleaf maple, are hardy only to zone 5.

The remaining five species are all shrubs or small trees, and only one is described as a possible source for maple syrup. The two eastern species are Acer spicatum, or mountain maple, and Acer pennsylvanicum, or striped maple. Striped maple, with white stripes on a green trunk, is often described as a nuisance species that can dominate an area after cutting, excluding other species. While it is commonly only 10 to 15 feet tall, I have seen specimens that are 6 to 7 inches in diameter and 30 to 40 feet tall; at this size they are not easily recognized as striped maple. Like mountain maple, a shrubby species that is often found near mountain streams, both are important foods for moose, deer and snowshoe hares. The range of striped maple is smaller, extending through the Appalachian mountains in the West, plus northern Michigan (but not to Indiana), and to Nova Scotia and New Brunswick in the East, while mountain maple is found west all the way to Saskatchewan.

Three species of small maples are confined to the western mountains and beyond. Acer glabrum, or Rocky Mountain maple, ranges not only in those mountains, where it is very abundant, but to the Pacific Coast of Oregon and Washington. This shrubby species has small three-to-five-lobed leaves and conspicuously purplish young stems. Acer grandidentatum, or bigtooth maple, the largest of these three maples, inhabits sunny, dry mountain slopes from Montana to New Mexico, and is known for its brilliant fall foliage. Although it is often less than a foot in diameter when mature, some references list it as a source for maple syrup. Finally, Acer circinatum, or vine maple, is not a vine, but a western shrubby species that often forms “impenetrable thickets” with its many twisted branches. Vine maple can be found from British Columbia to California. Its leaf shape is the model for the rank insignia of majors and lieutenant colonels in the U.S. army.

It is often reported that maples are found only in North America and the area around Japan and Korea, when, in fact, various species are also native to western Europe, the Mediterranean, including a small portion of North Africa, the Balkans, Turkey, Iraq, Afghanistan, the Himalayan Mountains and tropical Indonesia. Some of these species attain a very large size, and presumably all are capable of the same sap flow mechanism that causes sap to exude from wounds under certain conditions. Thus, it is primarily the weather, and our reliable seasons of freeze-thaw cycles, that are responsible for the location and the success of the maple syrup industry in northeastern North America.

The author is maple specialist with University of Vermont Extension and Proctor Maple Research Center in Underhill Center, Vt. Comment or question? Visit www.farmingforumsite.com and join in the discussions.