Tree of the Month: November – American Sweetgum
Written by Collin McMichael, Education Coordinator
The American sweetgum is a tree not often seen in central Texas. Native to the eastern portion of the state, this tree’s natural habitat is that of the swampy, deep, acidic soils of the Big Thicket National Preserve or Sabine National Forest. Oddly enough, those are not the only conditions this tree needs to thrive. Sweetgums are tolerant of many soil conditions and can even thrive in the thin, chalky firmament so callously referred to as soil in the Texas Hill Country, given enough water and proper mulching. While sweetgums are not as drought tolerant as many of the trees seen in the Austin area, mature trees can handle our most severe droughts with little human intervention. Sweetgums are worth the minimal amounts of water they require in the summers given their other favorable attributes.
American sweetgums can grow to 150 feet in ideal conditions, though in the Austin area they tend to be smaller, maxing out at around 40-50 feet. The bark is oddly reminiscent of alligator scales leading to its alternate name of “alligatorwood”. Branch protrusions, or wings, are evident on many specimens but not all. The leaves are star-shaped, bearing three to seven lobes and are three to five inches across bearing a striking resemblance to maples. Sweetgum seedpods are diagnostic as a character, and few people will forget the oddly spiky spheres they tend to drop in great numbers.
The American sweetgum, Liquidambar styraciflua, is the single American representative of a larger genus found mostly in Asian and the Middle East. The wood of the entire genus is prized for its beauty and in carpentry circles its known as “satin walnut” though there’s no close relation to walnut at all. The close, interlocking grain of the wood makes it ideal for applications such as veneers, barrels, wooden utensils, and even a cheap substitute for ebony when dyed black. The sap is also a commercially useful resin, as one might deduce from the name of the genus, and is collected by processing the bark. The trees themselves are highly regarded for ornamental purposes too for their star-shaped leaves and brilliant fall color. Fall color varies from tree to tree but is most often described as a “conflagration” as it ranges from brilliant oranges and buttery yellows to deep purples and vibrant reds among the more prized cultivars.
Sweetgums were once a favorite shade tree in North American cities due to its outstanding tolerance of urban conditions and moderate, orderly growth. Unfortunately, the trees reproductive habits have lately caused a decline in plantings as the spikey spherical seedpods can be a nuisance if planted over a walkway. Fewer sweetgums along with higher incidences of light pollution have both been cited as reasons for the paucity of Luna and Promethea moth sightings in American cities. Sweetgum, along with white oaks, are preferred host plants for these moth’s larvae though they are rarely, if ever, present in large enough numbers to constitute a problem.
Sweetgums are not commonly attacked by pests, other than the giant silkmoths, or disease, though there are cases of fungal diseases moving through stands. In the Austin area the most common ailment would probably be chlorosis, a response to reduced iron uptake in the roots due to improper soil pH, which manifests itself as a yellowing of the leaves. Chlorosis in sweetgums occurs most often in thin, basic soils denuded of their organic content. To guard against this physical response to less than ideal conditions, Sweetgums are best planted with an ample layer of mulch out to the drip line of the tree. Soil amendment with mature compost can be used in extremely poor sites when the tree is planted. Regardless of their reported reticence to regale northwest Austinites with rapid growth rates, I have personally witnessed a sapling dug up from the river muck along the Texas-Louisiana border and transplanted to the three-inch-deep regolith in the Anderson Mill area that has been absolutely chugging along for over a year now with no ill effects.
Sweetgums are an excellent choice for an urban shade tree, as long as they are planted in the correct environment. Due to their size and propensity to encumber pedestrians, it is ideal to plant them far enough away from buildings and high traffic areas, but close enough to human activity to watch over young trees for summer drought stress.