Upland forests occur throughout Illinois. They are classified according to soil moisture. They range from xeric
(extremely dry) through mesic (moderate soil moisture) to wet-mesic
(wet, but not flooded soil conditions).
The ground cover is comprised of a dense, scrubby layer of stunted trees and shrubs, rather than the prairie plants typical of barrens. These forests usually have few herbaceous plants in the understory. Post oak (Quercus stellata) and blackjack oak (Quercus marilandica) dominate the xeric upland forest.
In addition to blackjack oak and post oak, bur oak (Quercus macrocarpa), black oak (Quercus velutina), chestnut oak (Quercus montana), black hickory (Carya texana) and pignut hickory (Carya glabra) are characteristic. The scrubby understory is not so thick, and the herbaceous layer is better developed than in the xeric upland forest.
or Dry Upland?
The dominant species are white oak (Quercus alba), red oak (Quercus rubra), black oak (Quercus velutina), mockernut hickory (Carya tomentosa), and pignut hickory (Carya glabra). Ironwood (Ostrya virginiana) and flowering dogwood (Cornus florida) occur in the sub-canopy.
Dominant trees of mesic forests include red oak (Quercus rubra), sugar maple (Acer saccharum), and Beech (Fagus grandifolia).
Other characteristic trees include a variety of oaks, several species of hickory (Carya sp.), slippery elm (Ulmus rubra), basswood (Tilia americana), paw paw (Asimina triloba), hackberry (Celtis occidentalis), white ash (Fraxinus americana), and blue ash (Fraxinus quadrangulata). Southern Red Oak (Quercus falcata) occurs in mesic forests in the southernmost part of the state. The leaves of these trees are rich in nutrients at leaf fall and decompose quickly, adding nutrients to the soil.
changing makeup of the forest
Many mesic upland forests in Illinois have large oak trees with spreading branches, which indicate a formerly more open environment that was maintained by frequent ground fires. Whereas oaks are resistant to fires, sugar maple and other mesic trees are quite sensitive to fire. In particular, ground fires kill sugar maple seedlings and saplings.
In the absence of annual fires, sugar maple becomes increasingly dominant in the forest, replacing native oak trees in many places. Sugar maple can reproduce in the dense shade of a closed-canopy forest.
Seedlings of sugar maple often carpet the forest floor, (notice the maple saplings and sprouts in the panorama) where they can survive for years growing very slowly. When a gap in the forest canopy forms because a canopy tree dies, the sugar maple seedlings are well positioned to rapidly grow into saplings and to occupy the gap.
Oak trees do not have shade-tolerant seedlings that can persist in the understory. Oak seedlings survive only for a short time under heavy shade. They do not reach the sapling stage. Oaks must disperse their seed just after or at the same time as a gap appears in the canopy in order to regenerate. Becuase of this, they do not compete as well as species whose seedlings become established and can grow in the shade. These species have a head start on oaks and other shade-intolerant species.
Dilemma for the future
Today the conservation of groves presents us with a set of conflicting land management issues. On the one hand, introduction of controlled burning and perhaps removal of old-growth maples can favor the restoration of oak woodland and the continuance of an ecosystem that was widespread in the last century. This ecosystem is becoming increasingly endangered in spite of attempts to protect it in nature preserves.
On the other hand, especially if the change to sugar maple is far along, restoration to oak woodland may be difficult and potentially destructive to the natural biodiversity of the maple forests.
Copyright © 2000 Illinois State Museum