Rock elm (Ulmus thomasii), often called cork elm because of the irregular thick corky wings on older branches, is a medium-sized to large tree that grows best on moist loamy soils in southern Ontario, lower Michigan, and Wisconsin (where a town was named for the elm).
It may also be found on dry uplands, especially rocky ridges and limestone bluffs. On good sites, rock elm may reach 30 m (100 ft) in height and 300 years of age. It is always associated with other hardwoods and is a valued lumber tree. The extremely hard, tough wood is used in general construction and as a veneer base. Many kinds of wildlife consume the abundant seed crops.
Of major concern is that this elm is susceptible to Dutch Elm Disease. It is now becoming a very rare tree on the edges of its range and its future is not certain.
The seeds and buds of rock elm are eaten by wildlife. Small mammals such as chipmunks, ground squirrels, and mice apparently relish the filbert-like flavor of rock elm seed and frequently eat the major part of the crop.
Rock elm wood has long been valued for its exceptional strength and superior quality. For this reason rock elm has been drastically over-cut in many localities. The wood is stronger, harder, and stiffer than any of the other commercial species of elms. It is highly shock resistant and has excellent bending qualities which make it good for bent parts of furniture, crates and containers, and a base for veneer. Much of the old-growth was exported for ship timbers.
3. The Range of Rock Elm
Leaf: Alternate, simple, elliptical ovate, 2 1/2 to 4 inches in length, doubly serrated, base inequilateral, dark green and smooth above, paler and somewhat downy beneath.
Twig: Slender, zigzag, reddish brown, often (when rapidly growing) developing irregular corky ridges after a year or two; buds ovate, reddish brown, similar to American elm, but more slender.