1993 Proceedings of the Midwest Oak Savanna Conferences
ENHANCING HABITAT FOR THE KARNER BLUE BUTTERFLY: RESTORATION OF THE OAK-PINE BARRENS IN SOUTHWEST MICHIGAN
Mary L. Rabe
The oak-pine barrens of southwestern Lower Michigan have been eliminated or severely degraded by past logging and farming and by recent fire suppression policies. Restoration of oak-pine barrens is critical to improving habitat for the federally endangered Karner blue butterfly (Lycaeides melissa samuelis Nabokov). Portions of the Allegan State Game Area and the Manistee National Forest contain the largest known Karner blue populations in Michigan and provide opportunities for integrating endangered species protection with traditional multiple use management.
The General Land Office surveys (1830s) were used to characterize the species composition, tree size, and stand density for several sites and to make comparisons with current conditions. Since European settlement, white oak and white pine at low stand densities have been replaced by white oak and black oak with much higher stand densities. White pine persists only in the understory. Maps and data derived from the surveys are being utilized to establish realistic targets for restoration efforts.
Historically, the federally endangered Karner blue butterfly (Lycaeides melissa samuelis Nabokov) occurred at scattered sites within a band extending from eastern Minnesota, across portions of several Midwestern states and Ontario, through New England to New Hampshire. They are now believed to be extirpated from Ohio, Pennsylvania, Massachusetts, and Ontario. Recent surveys have shown that some of the most secure of the remaining populations in the Midwest occur in Michigan and Wisconsin (Clough 1992).
Karner blue butterflies have been recorded in 9 southern Michigan counties. Seven counties (Allegan, Lake, Monroe, Montcalm, Muskegon, Newaygo, and Oceana) have supported at least one population in the past 10 years, although no individuals have been observed in Monroe County since 1986. Records for two counties, Wayne and Ottawa, consist of specimens only (Nabokov 1943 and Shapiro 1969, respectively). Records for four other counties (Barry, Kalamazoo, Van Buren, Washtenaw) have been reported either verbally or in correspondence (Robert Derig, Cornell Univ., 1992, pers. comm.), but exact locations and documenting specimens are unknown. These four counties fall within the geographic range of the butterfly, although the appropriate habitat has been severely altered (Wilsmann, Status of the Karner Blue Butterfly in Michigan, in press).
The Karner blue butterfly has 2 generations per year. First generation larvae hatch from eggs in mid to late April. Larvae feed on wild lupine (Lupinus perennis L.) for about 3 weeks. First generation pupae, usually found on lupine plants or nearby litter, occur in late May and last for 8-11 days. First generation adults emerge in late May or early June. Adults typically live about 5 days. First generation adults lay eggs on lupine leaves, petioles, or stems. Second generation adults typically fly from mid-July into early August. There are usually 2-8 times more individuals in the second brood.
One of the key habitat requirements for Karner blue is the presence of wild lupine (Opler and Krizek 1984), the only plant on which the developing larvae feed. In Michigan, lupine typically flowers from mid-May to early July. Butterfly weed (Asclepias tuberosa L.) is one of many flowering plants that can serve as a nectar source for the adult butterflies. High nectar plant diversity may be important to ensure that food is available during both flight periods.
In Michigan, the areas occupied by Karner blue are situated on broad outwash channels or sandy lake plains. Typically, these sites are characterized by droughty soils and relatively flat topography that once supported dry prairies, woodlands and/or barrens dominated by oak and pine. Past land use has had a profound impact on the distribution and abundance of oak-pine woodlands and barrens in western Lower Michigan. Most of these areas were farmed briefly, then abandoned. Many abandoned parcels reverted to public ownership, where fire suppression, and eventually, intensive timber and wildlife management were the rule. As a result, these areas remain either as old fields or closed-canopy, white oak-dominated forests.
Today, most Karner blue populations are found in old fields, gas pipelines, or powerline corridors that arelocated within areas that were once dominated by oak-pine woodlands or barrens. The largest of these populations is located on the Allegan State Game Area (S.G.A.), in Allegan County, located in southwestern Michigan, and on portions of the Manistee National Forest, located further north in Oceana, Montcalm, Newaygo, Lake, Muskegon, and Mecosta counties.
The focus of initial restoration efforts for the Karner blue butterfly has been within the 20,000 hectare Allegan State Game Area. Sizeable Karner blue populations remain scattered across the game area. Public ownership provides a good potential for protection as well as management and restoration. Two management units (each approximately 2500 acres) have been established on the game area where efforts to monitor Karner blue populations and restore the oak-pine barrens are in progress.
The transcribed field notes of the General Land Office (GLO) surveys were used to characterize the approximate presettlement vegetation on both the east and west management units of the Allegan S.G.A. Surveys for Allegan Co. were completed during the early 1830s, prior to the logging era and intensive agricultural development. Surveyors established a grid system of township, range, and section lines. At least 2 "witness" trees were blazed at each section corner and half mile post. The distances and directions of these trees from the corners were recorded along with their species and estimated diameter (Caldwell 1990). Placement of corners and selection of witness trees was systematic. Forest composition, tree density, and tree basal area can therefore be approximated using the survey notes (Cottam and Curtis 1947, Anderson and Anderson 1975, Leitner et al. 1991). Forest composition was determined based on all tree species recorded within the area interpreted to include oak-pine barrens. Tree density and dominance were calculated using the witness tree data, and average tree diameters from all trees recorded, by species.
At the time of the original GLO survey in 1832, scattered white pine (Pinus strobus) dominated the barrens of what is now the east management unit, but white oak (Quercus alba) and black oak (Quercus velutina) were also present (Table 1a). Eighty three percent of the overstory trees were white pine, while just thirteen percent were white oak. The barrens were open, averaging only 3 to 4 trees per acre, and the combined basal area was approximately 6 to 7 square feet/acre.
The west unit at Allegan S.G.A. was characterized by co-dominance of white oak (48%) and white pine (44%) (Table 1b). Both trees/acre (2.18) and combined basal area/acre (1.91), were even lower than on the east unit.
Clearly, both of these areas were open, with witness trees located as much as 100 yards apart. Based on surveyors' written descriptions and bearing tree data, some of the barrens appear to have contained scattered prairie-like openings.
Both units are located along the southern edge of the Kalamazoo River. Native American occupation and land management along the river may have been partially responsible for the open barrens present at the time of European settlement.
The GLO survey records from parts of the Manistee National Forest that today contain degraded habitat for Karner blue butterflies were compared with data from Allegan. This was done to help establish whether any pattern in past Karner blue habitat may be evident from the survey record. These data indicated a similar forest composition to that seen at Allegan S.G.A. (Table 2). White pine (37%) and white oak (37%) were the dominants, but there were significant amounts of black oak (21%). Stand density was low (7.54) as was basal area (8.25 square feet/acre).
ORIGINAL VEGETATION DETERMINED FROM THE G.L.O. SURVEY NOTES OF 1831-2 FOR PORTIONS OF ALLEGAN STATE GAME AREA
ORIGINAL VEGETATION DETERMINED FROM THE G.L.O.
|NEWAYGO UNIT: SPECIES COMPOSITION, DENSITY, BASAL AREA IN SQ. FT. PER ACRE||SPECIES||PERCENT||TREES
|WHITE PINE||37%||2.79||4.87||WHITE OAK||37%||2.79||2.49|
|BLACK OAK||21%||1.58||0.76||RED MAPLE||02%||0.13||0.06|
Numerous Native American trails were noted along the Muskegon River. Native American fire management was probably at least partially responsible for the prairie and open barrens recorded by surveyors in 1838.
Today, as a result of many years of fire suppression, Allegan S.G.A. is dominated by well stocked oak stands of pole or saw log size (basal area 60-70 square feet/acre). White oak and black oak are now the overstory dominants. White pine persists as a subdominant and is sometimes common in the understory, but is rarely seen as an overstory dominant. This ten-fold increase in basal area since the 1830s has resulted in stands that are too dense for wild lupine to flower, and many are so densely stocked that no lupine persists. Within this landscape of closed-canopy forest, flowering lupine within each management unit can be found scattered along roads, powerlines, or gas line corridors. Where lupine persists under closed-canopy or near closed-canopy oak forest, it generally does not flower.
Numerous openings remain today, often in frost pockets located in natural depressions, and in those areas that were converted to agriculture and then abandoned. The old fields were typically located where there was a concentration of white pine at the time of European settlement. Following logging, attempts were made to farm the sandy soils. These attempts typically failed, as the sandy soils began to blow and drift following plowing. Even where there was no blowing, productivity was low and the lands were soon abandoned. While some of these openings were planted to red pine (Pinus resinosa) since the 1940s, other old fields are now covered with young trees and herbaceous vegetation. Young trees, often black cherry (Prunus serotina), sassafras (Sassafras albidum), or small oaks, are most common scattered across the openings. Herbaceous vegetation is dominated by a mix of exotic and native grasses, sedges, and forbs. Scattered colonies of wild lupine often provide adequate habitat for Karner blue, but the organic-poor soils are drought prone, resulting in early senescence of lupine during drought years. This early senescence may result in higher mortality of Karner blue larvae.
Among the important Karner blue habitats within the Allegan S.G.A. are the extensive linear openings provided by gas pipeline corridors. Lupines flower within the open pipeline corridor. The pipeline corridor provides a connection with other openings within the game area, allowing populations of Karner blue to move and may be extremely important in maintaining genetic diversity within the population.
Most of the oak-pine barrens within the Manistee National Forest also have converted to closed-canopy oak forest as a result of logging and later fire suppression. An area of open prairie in Newaygo County was noted in the GLO notes, but most of this prairie has closed in with the exception of a few small depressions. As at Allegan S.G.A., several fields were farmed following logging in the late 19th century. Most of these are now old fields or planted to pine plantations. As at the Allegan S.G.A., power-line right-of-ways provide corridors which help to connect existing Karner blue butterfly populations.
Management on the Allegan S.G.A. is beginning to consider oak-pine barrens restoration and management impacts on the Karner blue butterfly. From study of the GLO survey records, not only is it clear that portions of the game area were much more open in character than they appear today, but also the sizes and shapes of those openings were variable. Restoration efforts within the two management units will therefore attempt to recreate a mosaic of grasslands, barrens, woodlands, and closed-canopy forests with an overstory species composition similar to the presettlement condition. Priority sites for restoration include areas where restored openings may provide linkages between large existing Karner blue populations and others which are now relatively close by, but isolated by blocks of unsuitable habitat.
Prescribed burns are being used within each management unit to open forest canopies for lupine, nectar plants, and Karner blue. We know that historically the oak-pine barrens were maintained by periodic wild fires which swept across the area. As of yet, no accurate local estimate of presettlement fire frequency has been calculated. During 1993, field searches will be conducted for mature white oaks and white pines that may have been fence-row trees during the middle to late 1800s. If enough trees can be located, they may contain fire scars from presettlement wildfires sufficient to estimate local fire frequency.
Prescribed burns are generally concentrated in oak forests adjacent to openings with known lupine and Karner blue populations. Lupine is often common within the edges of oak forests, where light conditions may be inadequate for flowering. Prescribed burns expand the size of openings, thus increasing habitat for both lupine andKarner blue.
Good response from lupine and prairie vegetation has been seen following most burns. The native grasses and forbs which respond well to burns also provide important food and cover for wildlife, including white-tail deer and upland game birds.
Burning is still in the experimental stage and results are not entirely predictable. For example, one unit was burned twice resulting in an open understory, but two years later the overstory remains closed. For this reason, direct tree removal will be used to create openings of several shapes and sizes.
Another question yet to be answered involves the length of time wild lupine could have persisted under the closed-canopy forest, either as growing plants or in the seed bed. Following a wildfire in 1988, a large area of the burnt oak forest was salvage cut. No lupine, and thus far, no Karner blue were found in the clearcut. Apparently the oak forest had closed sufficiently to eliminate lupine prior to the 1988 wildfire. If lupine remained in the seed bed at this site, it is likely that the surge of growth in Pennsylvania sedge (Carex pensylvanica) effectively kept the lupine seeds from successfully germinating. The only lupine found in 1992 surveys of the area were along edges of existing openings. In another example, where long, narrow wildlife openings were bulldozed within a large block of closed-canopy forest in the 1960s, lupine populations are now large. Here, the lupine may have survived in the seed bed, and with the surface lightly scraped by the bulldozer, seeds were able to germinate.
Because our knowledge of the species and processes of Michigan's historical oak-pine barrens is limited, and there are many questions yet to be answered about their restoration. A monitoring plan is being established to track changes in the populations of Karner blue butterflies, wild lupine, and their various possible nectar sources. As time proceeds, additional species (both plant and animal) will be incorporated into the monitoring procedures to establish the best approaches to oak-pine barrens restoration.
Given this relatively large block of contiguous public lands, restoration efforts can and should be aimed at restoring the mosaic of prairies, barrens, closed-canopy forest, and wetlands that existed prior to European settlement. Prescribed burning can be used maintain this landscape, re-creating the effects of past wildfires. The re-creation of an ecologically functional landscape should ultimately minimize the effort needed to maintain the Karner blue and associated species by permitting natural processes and disturbance.
Oak-pine barrens restoration, through prescribed burning and selective tree removal is still in the experimental stages at the Allegan State Game Area. A monitoring plan is being established, focusing on the known populations of the Karner blue butterfly, its host plant, and numerous forbs which may serve as nectar sources. With further inventory work, other sensitive plant and animal species will be incorporated into monitoring procedures.
Current management goals for the Karner blue butterfly include:
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