Did you know there are over 400 species of oaks?
Some are large and some are small. Some are deciduous and most are evergreen. Oaks in this part of the country have two distinguishing characteristics:

• They are large, stately, deciduous trees that can live several hundred years and appear indestructible.
• In some respects they are actually very delicate.

While oaks can tolerate brutally harsh winters and long, hot summers, they are extremely intolerant of any soil disturbance anywhere near their root zone. The root zone may reach three times the branch spread.

Two oaks that are common in Riverwoods are the white oak and the red oak. Unlike many other oaks, they have adapted to heavy, damp clay soil.

The white oak is the state tree of Illinois. The tree tolerates all but shallow, dry soil, and prefers damp, well-drained soil. It is a slow-growing tree, and probably the largest of the native oaks. It can reach 110 feet in height, with an equal spread. The leaves are long with 3 or 4 pairs of pronounced rounded lobes. There isn’t anything white about the white oak. Its bark is gray, and sometimes develops a horizontally-ringed appearance as the tree ages. Its fall foliage varies from brown to red.

The red oak is a relatively quick-growing oak, which can achieve up to 80 feet in height. It is noted for its spectacular fall leaf color. The leaves are large, and pointed.The red oak has relatively shallow roots. Because of its shallow roots, it is even more susceptible to construction and drought damage than other oaks. Also it is somewhat more susceptible to oak wilt disease than other oaks in this area. It is adaptable to most soil types, and prefers well-drained sites.The red oak, like other oaks, grows best in full sun. The red oak’s bark is gray with "ski run" flat vertical plates. Its fall foliage is typically bronze to bright red and on mature trees, will remain on the tree throughout the winter.

Most oaks require full sun and most require deep, well-drained soil. Because their roots are delicate, most oaks can be transplanted only when very young, when the trunk is less than about 3 inches in diameter at chest height. You may think that the oak trees are in the shady woodland, but the leaves of the oak canopy are at the top of the forest, open to the sun.

Oak trees reproduce through acorns, which at some times of the year can sound like hail on the roof of a nearby house. Acorns are an important source of food for area wildlife, including squirrels, woodpeckers, deer, chipmunks and raccoons. Having an ample supply can be critical to their survival.

With sun, seedlings can grow several feet in a year. Seedlings, new twigs and saplings are favored by deer, however, so oak saplings in Riverwoods are rare. Transplanted saplings should be protected. Unfortunately, oak trees are also targeted by gypsy moths, so trees should be examined regularly. If gypsy moths or larvae are discovered, the Village should be notified.

Besides the white oak, other oaks commonly found in Riverwoods are swamp white oaks and bur oaks. Both are natives of Riverwoods.
The swamp white oak is a rapidly growing tree that can reach 70 feet in height, and can live several hundred years. Its leaves turn orange-brown or dark red in the fall. It is also known as the bicolor oak, because its leaves are glossy-green on the top surface and silver-gray on the under surface, much like the silver maple. As the name suggests, it does best in areas that periodically collect water.

The bur oak is also an impressive tree in full maturity, when it tends to be widely spreading with a huge trunk, deeply furrowed bark and gnarled limbs. It is very cold-hardy, drought-tolerant, and adaptable to many soils, including thin soils and heavy clay hardpan. Unlike the swamp white oak, the bur oak prefers well-drained soil and is intolerant of flooding. It is slow-growing, and one of the more difficult oaks to transplant. Its leaves are leathery, up to a foot long, and turn yellow-brown in the fall. The bur oak grows to about 80 feet in height in this area. It has the largest acorns of any native oak. Bur oaks can live to be several hundred years old.

In general, oaks are more difficult to transplant than other trees, and are likely to survive only if their trunk is less than about 3 inches in diameter at chest height. The red oak is more tolerant of transplanting than other oaks. Transplanted saplings should be protected from deer.

Other oak trees may sometimes be found in local nurseries, including the willow oak, pin oak, post oak and Hill's oak. The willow oak is easily recognized by its narrow leaves, which resemble willow tree leaves. It grows to about 60 feet in height, and its leaves turn brownish-yellow in the fall. The willow oak is tolerant of heat and drought, and is very popular along the east coast of the U.S. It is not native to the Riverwoods area, however, and cold-tolerance is limited. Pin oaks are native to Illinois, and although some may be found in our area, it is more common farther south in the state. Pin oaks are in the same family as red oaks, but their leaves are much more deeply lobed and their branches droop towards the ground. Hill's oaks may reach 75 feet in height. They are in the pin oak family and have the pin oak's characteristic drooping branches. This makes the Hill's oak a good choice as a screen. Post oaks are also small to medium trees that grow up to 60 feet. They are in the same family as the white oak, swamp oak and bur oak, with rounded lobed leaves, but are smaller than the other species and fit well in a landscaped area.