Illinois Natural History Survey - University of Illinois

Fire, Savanna Restoration, and Avian Populations in Midwestern Oak Forests

Periodic disturbance is an important determinant of the structure and composition of midwestern oak forests. Closed canopy forests develop without disturbance. Areas subject to disturbance by low intensity fires, however, tend to maintain relatively open canopy conditions and are known as either savannas (very open) or woodlands (moderately open). Fire suppression in the twentieth century has caused the widespread development of closed- canopy forests and encroachment by mesophytic, often non- native, plant species. Accordingly, midwestern oak savannas are viewed as one of the more threatened habitats/ecosystems in North America and in need of restoration.

Animal communities have likely responded to these recent changes in forest habitat, but few data exist. No bird species are found only within savannas, but regional declines of many species associated with "open" habitats are worrisome. In 1994, a study was initiated to examine how periodic disturbance by fire and savanna restoration affect the community structure, reproductive success, and foraging ecology of birds in Illinois. Results from several treatment (i.e., burned) and control sites in central Illinois indicate that savanna restoration has significant effects on the structure of local bird communities. Species such as the Red- headed Woodpecker, Baltimore Oriole, and Eastern Wood- Pewee were more common in savannas, but others such as the Scarlet Tanager and Wood Thrush decreased significantly. Many of the species responding favorably utilize aerial foraging maneuvers that are typically associated with open habitats.

Data from over 800 nests indicated that, for several species, reproductive success was markedly greater in savanna or restored habitats than in closed- canopy forests. This result was a surprise because most data from Illinois reveal extremely low nesting success owing to habitat fragmentation and associated high rates of nest predation or parasitism.

Therefore, the effects of savanna restoration on birds are largely positive. The mechanism for enhanced nesting success in savannas or woodlands is unknown at this time; nor is it known if this result will be consistent in different ecological settings such as urban versus agricultural landscapes. An important question for future studies is the relationship (if any) between the size of a restored savanna and viability of constituent bird communities.

Jeffrey D. Brawn, Center for Wildlife Ecology

Congested nonburned savanna beginning to lose its open structure.

Dense maple understory growing in unburned savanna area.

A healthy, open savanna following a prescribed burn.

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