Before European settlement, forests covered about 13.8 million acres, or 38%, of Illinois. Between 1820 and 1920, nearly 80% of our woodlands were eliminated. Since the 1920s, we have seen a reversal of this trend. Woodland habitat has increased in the last seventy years, largely the result of increased planting and natural succession in abandoned pastures. Current estimates indicate some 4.6 million acres of forested land statewide.

Despite the continuing increase in woody habitat, Illinois wildlife that depend on this cover face three problems:

Table 4.1 "Deciduous Woodland Restoration Guide"

Changing Species Composition and Structure

As scientists have learned how ecosystems function, one fact has become clear: fire played a historically important role on much of the Illinois landscape. Many natural communities, including savannas and some forests, were actually fire dependent; they needed periodic fire to maintain community composition and diversity. After settlement, suppression of this natural process played a major role in altering the composition and reducing the diversity of our woodlands. Oak-hickory forest, the dominant community type on Illinois' uplands, is gradually being replaced in many areas-largely because of lack of fire-by shade-tolerant species, such as maple and ash, that are less valuable to wildlife. Research has also shown that the lack of fire and altered river hydrology (human-magnified floods and artificial water levels) have changed the composition of many bottomland forests.

The process of reforestation has also resulted in a different forest composition. Many of these newer successional forests established this century grew on abandoned agricultural lands. At present, these areas are often dominated by less desirable invader species such as honeylocust, box elder, and silver maple and by non-natives such as white mulberry and European buckthorn. Woodlands composed primarily of these species are nearly devoid of hard mast (acorns and nuts) and often lack snags (standing dead trees) and older trees with cavities. They also have a comparatively low value for timber products.

Another type of woody habitat that has nearly disappeared from the Illinois landscape is the open-canopy savanna. Savannas were a different habitat than forests; they were often the transition community between prairie and forest. Savannas had their own wildlife communities, ones that didn't entirely overlap with those of the forest or prairie. For example, bluebirds and flickers preferred savanna as their primary home. Initially, savannas were cleared for cropland because they were easier to cut off than dense forest. Some became forests due to fire suppression. Most recently, home builders have been attracted to the remaining savannas because of their idyllic open-shade settings.

Non-native plants have also changed the composition of the understory and forest-floor plant communities, usually to the detriment of wildlife. Many non-native woody and herbaceous plants are very aggressive once they get a foothold. Species such as Japanese honeysuckle, garlic mustard, and the bush honeysuckles (Tartarian and Amur) invade forests, smothering or shading out nearly all other plants, including woodland wildflowers, shrubs, and small trees. Climbing euonymus can climb and smother even large trees. The loss of diversity of native plants reduces the variety of natural nesting sites and food, and there is evidence pointing to a corresponding reduction in the diversity of insects, an important component of the food chain.

Exotic plants often gain a foothold in forested areas that have had some human disturbance, such as grazing or logging. And lack of fire may allow the plants to spread; some of these exotics cannot withstand burning like many fire-adapted native plants.

Changing Size and Interspersion

Although forest acreage is increasing, Illinois has about 9.5 million fewer acres of woods today than in 1820. The reduced acreage has spawned other problems, primarily a change in the size and connectedness of the remaining woodlands. Our existing forest tracts are smaller and, for the most part, more isolated from each other. Many woodland wildlife species, including some of our most colorful songbirds, cannot reproduce successfully in smaller forests. And smaller animals, such as salamanders, mice,;and lizards, that cannot travel long distances eventually disappear if their habitat is too small and there are no nearby populations to bring in "fresh" genes.

Woody fencerows and windbreaks, which have played an important role in linking fragmented woodlands, have decreased significantly since the 1970s. Agricultural policies that promoted intensive farming were largely responsible. These fencerows not only provided corridors from one woodland to another, they also provided valuable habitat for edge-loving species and stopover points for many migratory birds.

Changing Age

Much of the recent increase in forested acreage is due to abandonment of pastures and new planting efforts. Coupled with continued reversion of mature forests to younger growth or early successional forests through logging, the result is a significant amount of young forest.

Forests commonly referred to as "old growth" are in very short supply in Illinois. This type of forest is characterized by a diversity of age classes, including a canopy of very old trees, 125 to 300 years old. To be considered old growth, a forest would have been relatively undisturbed by logging or grazing for one hundred years or longer, with the exception of an occasional tree cut for firewood or perhaps lumber. Large-diameter trees are important to the survival of some wildlife species, such as the pileated woodpecker. The Illinois Natural Areas Inventory found only 11,600 of the state's existing 4.3 million forested acres to be older, relatively undisturbed forest.

Mature forests are still relatively plentiful in Illinois, but this, could change if timber demands increase or the sale of mature woodlands for homesites continues at its current pace. Mature forests are those that may have been selectively logged during the last century but currently have recovered and typically support a wide range of tree age classes. Trees 60 to 100 years old are scattered throughout a mature forest.

It can take centuries to develop a truly mature, full functioning forest ecosystem. The multiple layers that develop support a diversity of wildlife. Yet a sizeable forest ecosystem can be eliminated in a matter of days! Because it is the slowest of all habitat types to recreate, think carefully before converting forest to another habitat type. Remind yourself how long it takes a tree to grow when you're cutting one down.