PARENT SESSION
Poster Session 35: Restoration Ecology.

Thursday, August 5 Presentations from 5:00 PM to 6:30 PM, Exhibit Hall A 1.

Ecological restoration of tall grass oak savanna establishes mosaics of trees and herbaceous vegetation.

Brudvig, Lars^*,1, Asbjornsen, Heidi¹, ¹ Iowa State University, Ames, IA, USA

ABSTRACT- Tall grass oak savanna of midwestern North America is one of the rarest ecosystems in the world, occupying only 0.02% of its pre-settlement range. Recently, much interest in restoring degraded tall grass oak savanna remnants has been generated and many restoration efforts exist. Land managers have typically generated restoration plans from definitions of tall grass oak savannas based on overstory canopy cover, which range from 10-80% cover and lend little guidance. It is accepted, though, that tall grass oak savannas are characterized by mosaics of scattered oak trees and a dense herbaceous understory. As many restoration efforts have focused primarily on the overstory stratum, little is known about the effectiveness of restorations at creating vegetation mosaics. These conditions should be a high priority, as mixed-light canopy mosaics provide suitable habitat for a suite of rare herbaceous plant species and encourage oak regeneration in tall grass oak savannas. To better understand the prevailing ecology, the restoration of degraded tall grass oak savanna remnants in central Iowa was initiated in 2002. The restoration plan entailed mechanical removal of encroaching trees and periodic prescribed burns. Under and overstory vegetation and canopy cover data were collected prior to restoration efforts and one and two years after efforts began. These data were collected in two actively restored and two unthinned/unburned control savanna remnants. The density of understory vegetation was greater in actively restored areas than controls and pre-restoration conditions. Mechanical tree removal resulted in spatially variable light conditions, ranging from highly shaded areas similar to controls, to areas with no canopy cover. Additionally, a strong inverse correlation was seen between canopy cover and density of the herbaceous understory, where decreased canopy cover resulted in increased density of understory vegetation. These mixed-light conditions may provide suitable habitat for species with varying light requirements ranging from full sun to heavy shade. These results indicate that restoration of tall grass oak savannas involving the reduction of overstory canopy cover to 10-40% can successfully produce a mosaic of trees and herbaceous vegetation.

Key words: savanna definition, Quercus, mixed light