Understory Vegetation and Seed Bank Response to the Restoration Efforts at Quincy Bluff and Wetlands Area, an Oak-Pine Barrens in Central Wisconsin

Abstract

The Wisconsin Department of Natural Resources (WDNR) has designated barrens communities as high priority for restoration. These communities are globally imperiled and support many endangered and threatened species. Many barrens are in various stages of degradation or are unmanaged. While some studies have demonstrated rapid return of savanna and barrens communities with restoration of structure and fire, an intermediate term evaluation, completed in 1999, of management efforts at the Quincy Bluff and Wetlands Area (Quincy Bluff) demonstrated only small changes with harvesting and return of fire. This discrepancy in results may reflect the length of fire suppression and the degree of degradation at Quincy Bluff. Prior to initiating management, fire had been absent from Quincy Bluff for approximately 70 years, while other restoration sites have reported fire suppression of approximately 30 years. Located in Adams County, Wisconsin, Quincy Bluff is owned and managed by the WDNR and The Nature Conservancy (TNC). It consists of over 1500 ha of several community types including considerable oak‐pine barrens. The objectives of this study were to test the impact of prescribed fire, timber harvest, and the seed bank on understory plant diversity at Quincy Bluff. Thirty‐nine permanent transects were established prior to initiation of restoration efforts in five TNC management units and in the unmanaged WDNR property. Twenty‐six newly established, independent transects and the 39 previously established transects were monitored in 2010. Cover and presence of all living vegetation < 1 m tall; shrub and small tree cover and density; and tree cover, density, and basal area were determined. Soil samples were obtained for greenhouse analysis of the seed bank. Species richness and ground layer cover in 2010 were lowest in management units treated with prescribed fire alone and were 50 percent to 150 percent greater in units with substantial reduction in canopy cover and basal area. Structural changes resulted from timber harvest and/or a tornado that struck one management unit in 2004. To refine our assessment, utilizing a literature review, we generated a list of species likely to be indicators of barrens vegetation. In 2010 these barrens indicator species had the largest percent cover in the control unit; however, cover of barrens indicator species declined in all units. In units with reduced canopy cover and basal area barrens indicator species richness increased by two or three species and declined or remained the same in the other units. Frequent fires eliminated shrubs and small trees. Greenhouse analysis of the seed bank demonstrated low species richness and produced few germinants of any restoration value. Barrens, if left unmanaged, degrade to closed canopy forests with low species richness and low ground layer cover. Frequent fires over 17 years were ineffective at reducing canopy cover or basal area and understory species richness remained low. Manipulation of the tree structure through timber harvest and/or natural processes (i.e. tornado) increased understory species richness; however, species determined to indicate barrens communities decreased in relative cover, while richness increased marginally. These results further suggest that the resiliency of this system may be exceeded by the long period without management and seven decades of fire suppression.