. The changing Illinois environment : critical trends : technical report of the Critical Trends Assessment Project. Man; Pollution; Environmental protection; Ecology; Environmental impact analysis. FORESTS Under current global trade patterns, with weak restric- tions on importation of plant material, exotic insect pest introductions are likely to continue. Some of these pests will become established, causing both ecological and economic effects on the forests of Illinois. FOREST CONSERVATION Numerous types of land are used to preserve biological diversity in Illinois forests (for example, stat
. The changing Illinois environment : critical trends : technical report of the Critical Trends Assessment Project. Man; Pollution; Environmental protection; Ecology; Environmental impact analysis. FORESTS Under current global trade patterns, with weak restric- tions on importation of plant material, exotic insect pest introductions are likely to continue. Some of these pests will become established, causing both ecological and economic effects on the forests of Illinois. FOREST CONSERVATION Numerous types of land are used to preserve biological diversity in Illinois forests (for example, state parks and nature preserves). One major concern for conserva- tion of this biological diversity is undesired changes in community composition among forests through time. Early settler records suggest that most northern and central Illinois upland forests were open mature forests dominated by oaks and hickories (Anderson 1991). The abundance of oak-hickory forest was maintained through occasional fire (Anderson 1991). After European settlement, forests that were not logged began to change as a result of fire suppression. These changes continue today, as witnessed by the rapidly increasing amount of sugar maple and beech forest types within the state (Figure 11). This transition from oak-hickory forests to sugar maple forests has dimin- ished overall forest quality by reducing species diversity (Wilhelm 1991). From an economic perspective, this shift in community composition toward sugar maple is also viewed unfavorably because sugar maple is a lower value timber product than either oaks or hickories. With respect to other conservation efforts, recent evidence suggests that clear-cutting of forests erodes the habitat's ability to maintain populations of wild- flowers (Duffy and Meier 1992). Clear-cutting causes severe damage to the understory herb layer, and it appears that this herbaceous flora does not recover during a typical growth cycle between cutting events. A recent tren
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