Individual study: Maintaining early successional habitat for the endangered Karner blue Lycaeides melissa samuelis by cutting and herbicide application along powerline corridors in the Hudson Valley Sand Belt, New York, USA
Forrester J.A., Leopold D.J. & Hafner S.D. (2005) Maintaining critical habitat in a heavily managed landscape: Effects of power line corridor management on Karner blue butterfly (Lycaeides melissa samuelis) habitat. Restoration Ecology, 13, 488-498
The Karner blue butterfly Lycaeides melissa samuelis (a federally listed species considered Endangered throughout its range), historically occupied barren and savannah ecosystems in the northeastern and midwestern USA. In New York state, it now occurs primarily on managed, early-successional sites such as power line corridors (management of which maintains early-successional habitats by regular cutting of woody species). Blue lupine Lupinus perennis, the sole larval food plant, has been suggested to be the most limiting factor for the butterfly in the east of its range. This study compared the effects of several vegetation-management methods on blue lupine populations and associated communities of nectar species for Karner blues. Methods evaluated differed in frequency and type (herbicide or mechanical).
Study sites: Twenty-four sites within 14 separate power line corridors were selected. These were located in the 'Hudson Valley Sand Belt' in Warren, Saratoga, Schenectady, Albany and Washington Counties, New York. The soils, elevations (60–120 m) and slope (0–20°) of the sites were fairly similar. The study sites excluded any with known Karner blue butterfly Lycaeides melissa samuelis populations (as required by law to avoid potential detrimental impacts).
Experimental design and treatments: Treatments evaluated in the study were vegetation management techniques practiced at the time in power line corridor management. A randomized design with six management treatments was used:
1) annual mowing each autumn (1995 to 2002) to cut all woody vegetation within a site (n = 3)
2) mowing on a 4-year interval, beginning autumn 1995 and repeated autumn 1999 (n = 3)
3) brushsaw or chainsaw cutting of woody vegetation as close to the ground as possible, autumn 1995 (n = 8)
4) brushsaw or chainsaw cutting followed by herbicide application to stumps, autumn 1995 (n = 3)
5) high-volume hydraulic stem–foliar application of herbicide, autumn 1995 (n = 4)
6) low-volume backpack foliar herbicide application, autumn 1995 (n = 3). Initially four sites were to be untreated controls, but after analyses of pre-treatment data, these sites were brush cut to minimize the heterogeneity of sites and combined with four sites previously selected for cutting, resulting in eight replicates. Herbicide treatments were a mix of glyphosate and imazapyr.
Sampling: Permanent line transects and vegetation plots were established and sampled in the pre-treatment 1995 growing season. Following initial treatments (autumn 1995), the plant community and blue lupine Lupinus perennis populations were monitored annually (May–August) to 2002 growing season. Transects were established across the width of the power line corridor (10–43 m). The number of transects (3–68), distance between each (1–20 m), and length of area treated (106–2,932 m) varied according to corridor dimensions and blue lupine density. Blue lupine clumps were sampled by line–intercept during the flowering period (mid-May-early June). Length, width, average and maximum height, number of stems and flowering spikes, and percent cover were recorded. One site was removed from analysis because pre-treatment data were not collected.
Characteristics of the plant community were monitored in permanent quadrats established within the same area as the transects. Cover of woody vegetation greater than 1 cm diameter at breast height was estimated within 10, 25-m² plots within each treated corridor. Nested 1-m² subplots were established to measure the cover of herbaceous and woody vegetation less than 1.4 m tall.
Treatment effects: The species with the greatest cover across all sites regardless of treatment included: little bluestem Schizachyrium scoparium, Tartarian honeysuckle Lonicera tatarica, American dewberry Rubus flagellaris, and scrub oak Quercus ilicifolia. The most frequently occurring species (which mostly increased following treatment) were: little bluestem (100%), American dewberry (88-96%), Black oak Q.velutina (92-96%), whorled loosestrife Lysimachia quadrifolia(92-96%), sedges Carex spp. (79-100%) and goldenrod Solidago spp. (79-96%).
Blue lupine and plant community responses did not significantly differ among the treatments applied to the power line corridors. Total plant and woody cover were significantly higher in brush cut sites versus sites that were mowed annually or intermittently. Overall, treatment resulted positive changes over time, including an increase in blue lupin, nectar-providing flowers and species richnesss.
Blue lupine response: Blue lupine cover, clump size, and density of stems per clump increased following the application of treatments in general.
Plant community response: The average number (increasing from 13 to 17 by 2002) and cover (from 18% to a maximum of 30% in 1998) of nectar species e.g. black raspberry Rubus occidentalis, common cinquefoil Potentilla simplex, goldenrod and American dewberry, increased following treatment. Though the cover of nectar species appeared to be more suppressed by broadcast foliar herbicide than other treatments, this was not statistically significant.
Non-native plant response: The percentage of non-native species temporarily increased (from 16 to 21%) following treatment but declined to a level (18%) similar to pre-treatment as woody cover increased. In particular, the frequency of non-native species e.g. Tartarian honeysuckle, red sorrel Rumex acetosella and spotted knapweed Centaurea maculosa increased, although their cover increased minimally in most cases. Total herbaceous and woody plant cover (<1.4 m tall) reached a maximum midway through the study, but remained higher in 2002 than prior to treatment (from 71 to 85% from 1995 to 2002).
Species richness: Species richness changed from 28 to at least 40 species over the duration of the study. As some individuals could not be identified, species were grouped into genus (e.g. Solidago spp.) causing an underestimation of species richness.
Conclusions: Results indicate that blue lupine and plant community responses did not significantly differ among the treatment types applied to the power line corridors, other than total plant and woody cover being higher in brush cut sites. Additional responses to treatment may exist but were too small to be detected in this study. Overall, the management treatments evaluated achieved the goal of halting or reversing succession by reducing woody cover and promoting more numerous and vigorous blue lupine populations, thus maintaining critical habitat for Karner blues and other species reliant on early successional habitat. In addition, after mangement, Karner blues were observed at two sites (within the same corridor) where they previously had not been observed.
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