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The Karner Blue
Restoration Project
Ivanhoe Nature Preserve is one of the few remaining tracts of native landscape left in the urban industrial complex that covers northern Lake County, Indiana. A series of 13 linear sandy beach ridges alternate with long narrow wetlands in parallel bands to form the unique dune and swale topography that characterizes the preserve. Xeric black oak savanna, prairie, sedge meadow and open marsh form a mosaic of natural community types at this small (130 acres) but incredibly rich site. Ivanhoe supports over 270 species of native plants and over 50 resident species of butterflies, including many habitat restricted species. It is the only known extant site for columbine duskywings (Erynnis lucilius) in the state.
The history of Karner blue in this area is poorly documented. However, it was probably once a common species that functioned as a metapopulation composed of several sub-populations shifting across the dune and swale landscape in response to the wildfires that created and sustained open savanna and prairie habitats. Over time, the widespread destruction of habitat throughout the region reduced the native landscape to a series of small isolated natural areas. Karner blue was subsequently divided into discrete populations restricted in range to the remnant natural areas. As development increased, the natural areas became smaller and more isolated, virtually eliminating ecological interaction between sites. Faced with less and less available habitat, the populations diminished. Eventually local extinctions occurred with no hope of recolonization.
In the early 1990s, a small population of Karner blues still occupied Ivanhoe Nature Preserve. However, past fire suppression had allowed woody vegetation to encroach on the open savanna and prairie habitat patches that the butterfly needs to survive; as a result their available habitat had been reduced to less than 15 acres. TNC used the plight of Karner blue to focus restoration efforts at the site. The butterfly's endangered species status brought the necessary attention and funding, while its ecology supplied a conceptual model to use in restoring pre-fire suppression dynamics to the dune and swale. In January of 1996, the Conservancy, in cooperation with the U. S. Fish and Wildlife Service and the U.S. Environmental Protection Agency, began an aggressive effort to thin canopy cover and restore fire to the system.
Unfortunately, in the spring of 1996 two separate wildfires at Ivanhoe consumed the majority of habitat occupied by Karner blues. A prolonged period of cold damp weather during late spring caused a drop in Karner blue populations throughout northwest Indiana. The combination of fire and bad weather drastically reduced the butterfly's numbers, and within one year it disappeared from the preserve. This event was a sobering lesson, confirming that prairie and savanna habitats had degraded to the point that specialized species such as the Karner blue were indeed vulnerable to local extinction. It also underscored the importance of the work that had begun at the site. We continued the restoration with re-introduction of Karner blue as the goal.
Most of the work involved chainsaw crews and herbicide application, with "restoration artists" re-sculpting a pre-fire suppression landscape. The first step was to reduce the coverage of shrubs and saplings in the under story. Next, larger trees were cut to create gaps in the canopy. Several ridges were reduced from 100% canopy cover to around 45% cover, which means that about 75% of the trees and shrubs were cut and removed. This left primarily the larger, open grown black oaks, some younger regeneration, and ground cover that was predominantly poison ivy and bracken fern.
At the time, we had no idea how resilient the system would be. The plan was to assess the restored areas over the following two growing seasons and determine how to best supplement the herbaceous community. At the same time, we began an aggressive prescribed fire program to reduce regeneration of woody species and stimulate the growth of prairie and savanna plants on the restored ridges. The addition of fire and light brought rapid change to the system. The soil supported many suppressed rootstocks of open grown plants, and to our surprise, several prairie and savanna grasses and forbs appeared the following spring. Within two growing seasons, the plants where setting seed and species such as lupine quickly began an ecological expansion that continues today. All told, about 80 acres at Ivanhoe now support high-quality dune and swale, with oak savanna scattered throughout the restored habitats. Equally important, three discrete habitat patches were created to shelter vulnerable species from an all-consuming wildfire event in the future.
Success at Ivanhoe will be one milestone in the long process of re-establishing a true metapopulation in the dune and swale system. Most of the nearby natural area remnants are also fire-suppressed, and will require intensive canopy thinning to create suitable habitat for Karner blue. Management at some of these sites is already under way. In addition, it may be necessary to create stepping stone habitat patches to facilitate dispersal between preserves. Over the next 10 years, we hope five to seven new demes of the species can be re-established on about 500 acres of additional dune and swale habitat in the system, creating a self-sustaining metapopulation.
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