Did you know that 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 are deciduous – they shed their leaves in the winter. The same species in warmer climates may be evergreen.
Oaks in Riverwoods have two distinguishing characteristics:
They are large, stately, deciduous trees that can live several hundred years and appear indestructible, and 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. 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, i.e., when the trunk is less than about 3 inches in diameter at chest height. Oaks reproduce through acorns, which 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.
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. All saplings should be carefully protected to prevent browse damage. It is best to protect the trunks of all trees less than about 3 inches in diameter, to avoid girdling – the removal of a tree’s outer bark layer around the circumference of the tree when deer rub their antlers against the tree trunk.
Unfortunately, oak trees are also targeted by gypsy moths, so the Village should be notified of infected trees.
White Oak – Illinois State Tree
The White Oak is a large, stately tree that is common in Riverwoods … at least as a mature tree. Saplings are rare, primarily because of deer browse and canopy shading by faster-growing trees such as maples.
Unlike many other oaks, white oaks have adapted to the heavy, damp clay soil common in Riverwoods. They tolerate all but shallow, dry soil, and prefer damp, well-trained soil.
The white oak 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 of the white oak are similar to those of the pin oak – long with 3 to 4 pairs of pronounced lobes. The lobes on the white oak’s leaves are rounded, whereas the lobes on the pin oak’s leaves typically are more pronounced and sharply pointed.
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.
Pin oaks, unlike many other oaks, have adapted to the heavy, damp clay soil common in Riverwoods. They tolerate all but shallow, dry soil, and prefer damp, well-drained soil.
The pin oak, with its relatively shallow root system, is especially tolerant of wetter conditions. In fact, it does best in heavy, wet clay soil. It prefers the acidic soil of wooded areas, and is less tolerant than other oaks of the alkaline soil typical of many open areas in the Midwest.
Pin oaks are relatively fast-growing oaks, with a more upright appearance than other oaks. They can reach 100 feet in height. Pin oaks survive transplanting somewhat better than most other oaks, which means you can purchase larger specimens with greater assurance that they will survive (if you protect them from the deer).
The leaves of the pin oak are similar to those of the white oak – long with 3 to 4 pairs of pronounced lobes. The lobes on the white oak’s leaves are rounded, whereas the lobes on the pin oak’s leaves are more pronounced and sharply pointed.
The pin oak’s trunk is gray. Its fall foliage is typically bronze to bright red. The pin oak, like the red oak, is somewhat more susceptible to oak wilt disease than other oaks.
The pin oak is believed to have gotten its name from the pin-like spurs that sometimes appear on young shoots.
The bur oak is very cold-hardy, drought-tolerant, and adaptable to many soils, including thin soils and heavy clay hardpan, both of which are found in Riverwoods. It prefers well-drained soil and is intolerant of flooding. Plant it away from areas that collect water..
It is slow-growing, and one of the most difficult oaks to transplant. Its leaves are leather, 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.
(That’s an image of a bur oak leaf that appears at the bottom of the left hand column of the main pages of this site.)
The swamp white oak is a relatively rapidly-growing tree that can reach 70 feet in height.
Its leaves turn orange-green or dark red in the fall. The swamp white oak is also known as the bicolor oak because its leaves are glossy-green on the top surface and silver-gray on the underside, much like the leaves of the silver maple.
As its name suggests, the swamp white oak does best in areas that periodically collect water. It does not, however, tolerate constant flooding.
The swamp white oak can live several hundred years.
Red oaks are relatively quick-growing trees, which can achieve up to 80 feet in height.
The leaves are large, and pointed like the pin oak’s leaves, but shinier and fuller in the central area.
Red oaks, like other oaks, grow best in full sun. They are adaptable to most soil types, and prefer well-drained sites.
Like the pin oak, 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 like the pin oak, the red oak is somewhat more susceptible to oak wilt disease than other oaks in the Riverwoods area.