|
Ivanhoe Nature Preserve is one of the few remaining tracts of native landscape left northern Lake County, Ind. More than 270 species of native plants and 50 resident species of butterflies, including many habitat restricted species, live there. It is the only known existing site in the state for columbine duskywings — a butterfly.
 |
|
Lupine and puccoon in bloom at Ivanhoe
© Paul Labus |
Plight Brings Attention
In the early 1990s, a small population of Karner blues still occupied the 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.
The butterfly's endangered species status helped bring attention and funding. In 1996, the Conservancy and its partners — 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.
Karner Blue Disappears from Preserve
Unfortunately, two separate wildfires in the spring of 1996 consumed the majority of habitat occupied by Karner blues at Ivanhoe. 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.
 |
|
Staff member Mike Norris looking for Karner blues
© Paul Labus | 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 Conservancy’s work: The restoration continued with re-introduction of Karner blue as the goal.
Planning for Re-introduction: Opening up the Land
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 percent canopy cover to around 45 percent cover, which means that about 75 percent 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 predominantly was poison ivy and bracken fern.
At the time, the Conservancy 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, an aggressive prescribed fire program was started to reduce regeneration of woody species and stimulate the growth of prairie and savanna plants on the restored ridges.
Changes in the Land
The addition of fire and light brought rapid change to the system. The soil supported suppressed rootstocks of plants, and to the Conservancy’s 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. 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 also are fire-suppressed and will require intensive canopy thinning to create suitable habitat for Karner blues. Management at some of these sites already is under way. In addition, it may be necessary to create stepping stone habitat patches to facilitate dispersal between preserves. Over the next 10 years, the Conservancy plans to have five to seven new demes of the species re-established on about 500 acres of additional dune and swale habitat in the system, creating a self-sustaining metapopulation.
| 
