Sorting through Missouri's wide variety of oaks

Missouri is over 30 percent forested, and oaks are among our most important and abundant trees. Oaks provide food for wild animals in the form of acorns, especially for deer, wild turkeys and squirrels. Oaks belong to the so-called hardwood trees, in contrast to the cone-bearing needle trees, and are a most important source for lumber. The lumber we cut from oak trees is important to Missouri's economy; it is used for making barrels, furniture, cabinets and flooring.

Oaks also shape the landscape of much of Missouri, provide shade to homes and streets and serve as historical markers.

The oaks form a large group (genus) of worldwide distribution. Most are trees, but some are shrubs. One estimate calls for 450 species in the world; another, more modest, calls for 275. In North America, north of Mexico, there are about 54 species, of which 20 are growing wild in Missouri.

This abundance of American oak species compares with just three to five in all of Europe. When the glaciers covered much of the northern hemisphere during the last two million years, our oak species found favorable conditions further south; their European relatives, however, were trapped by mountain ranges lying east to west, blocking their growth to the south.

Identification problems

To begin with, oaks hybridize readily. While one speaks commonly of hybrid sterility, our oaks have viable hybrids-hybrids with seeds that produce trees.

The amazing variability in the leaf shapes of certain species is confusing. This forces us to accept certain basic leaf shapes for identification, through we know full well that differing shapes are common.

The leaves of young trees often vary totally from the mature shape. They can be huge, an assist by nature to form an enlarged chlorophyll factory, but not conducive to identification.

No wonder Julian Steyermark, author of Flora of Missouri, said that in identifying oaks, it must be kept in mind that as many characteristics as possible -- leaves, twigs, winter bud, range, bark and site must be taken into consideration.

Oak characteristics

Oaks have separate male and female flowers on the same tree. Male flowers are pollen-bearing stamens on catkins; females are rounded-to-pointed, knoblike and usually on short spikes in leaf axis. Pollination is by wind, requiring huge amounts of pollen.

The fruit, the acorn, takes one or two years to reach maturity. The combined fruits of oaks, hickories, walnuts and beeches sustain deer, raccoon, squirrels, chipmunks, possum, mice and fox. Turkey and quail also eat acorns as do waterfowl.

Acorns are attacked by a host of insects; because of that, only an occasional one will produce a new tree. Most oaks take more than 30 years before they produce acorns.

Joe Garvey is a forestry supervisor with the Missouri Department of Conservation.