The oak-hickory forest is typical of the Appalachian forest system, of which Illinois is the westernmost fringe, and the oaks are the dominant tree in it. The oak is long-lived and has commercial value as hardwood--two of the reasons why the white oak, or Quercus alba, was adopted as Illinois' official state tree.
While the majority of Illinois' oak trees are young and small, roughly two-thirds of Illinois forests dominated by oaks in 1985 were older than 60 years. Oaks are still by far the largest contributor (8.83 billion board feet, or 51.2%) to the volume of Illinois' commercial forest, in spite of the fact they comprise only 12.2% of its trees. In many places these aging trees are not regenerating naturally. Grazing deer take a toll. Fires no longer clear the forest understory of the oak's competitors. More shade in the forest understory means that oak seedlings, which need sun to grow, are being overwhelmed by shade-tolerant trees like maples. When the overstory is removed (by cutting, windthrow, or disease) the maples are positioned to rapidly exploit the opening. The result is "maple takeover," the process by which the oak-hickory forest is replaced not by younger oak and hickory trees, but by different tree species.
Disease and insect infestations also are changing the ecology of the oak-hickory forest. A serious outbreak of gypsy moths in Illinois appears to be inevitable, in spite of state and federal control programs underway since the early 1980s. By the late 1990s the moth is expected to infest Chicago Forest Preserves and then move downstate.
Excerpted from The Changing Illinois Environment: Critical Trends. Summary Report. Illinois Department of Energy and Natural Resources and the Nature of Illinois Foundation. 1994.
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