Benefit of permanent non-fire refugia for Lepidoptera conservation in fire-managed sites

Abstract

From the early 1990s through 2005, we conducted butterfly transect surveys annually at the same sites in three regions of Wisconsin. We compared specialist butterfly population indices at three sites where a permanent non-fire refugium (a unit kept unburned through cycles of rotational fire elsewhere in the site) was established during this study to indices at comparison sites (which had consistent management throughout this study) in the same region. At Crex Meadows (12,180 ha), all significant changes in specialist numbers skewed toward relatively higher abundance in the refugium (14 ha, last burned in 1988) during the later period (1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005) versus 10 comparison subsites (fire-managed in both periods) than expected from observations in the earlier period . The same pattern occurred in the refugium (4 ha) at Bauer-Brockway (125 ha), after the rest of that unit (9 ha) had its first management fire. Population trends were positive in these refugia, while the comparison sites usually had less favorable trends, or otherwise had similar trends. At Muralt Bluff (25 ha), regal fritillaries (Speyeria idalia) were more concentrated in the refugium (3 ha, last burned in 1991) during the earlier period but were more abundant in both periods in the refugium than the other units there (fire-managed in both periods). In the earlier period at Muralt Bluff, this species significantly declined, the opposite trend of comparison sites (which always had never-burned refugia), but significantly increased in the later period, similar to comparison sites. The refugium did not benefit Ottoe skipper (Hesperia ottoe), which declined significantly in the earlier period and was not recorded in the later period. Formerly burned units began functioning as refugia only >6-8 years after last fire and continued to increase in benefit for years after that. In fire-managed and fireprone sites, we recommend the creation of permanent non-fire refugia for Lepidoptera conservation, placed where the most specialists will benefit and managed unintensively (e.g. mowing) if needed.

Meta-analysis of survey data to assess trends of prairie butterflies in Minnesota, USA during 1979–2005

“…Burning usually began in a reserve before much butterfly surveying had occurred, most reserves were managed primarily with fire, and most surveys focused on sites after they were conserved (Wendt 1984;TNC 1988TNC , 1994Swengel 1996Swengel , 2001Swengel and Swengel 1997;Schlicht 2001Schlicht , 2003Nekola 2002). However, the pronounced declines of specialist but not common butterflies in this study is consistent with research that fire management is most unfavorable for specialist butterflies, compared to other butterfly species in prairies, and that other unintensive management types tend to be more favorable for specialist butterflies (Swengel 1998(Swengel , 2001Schlicht 2001Schlicht , 2003Swengel and Swengel 2007).…”

Paradoxes of Poweshiek Skipperling (Oarisma poweshiek) (Lepidoptera: Hesperiidae): Abundance Patterns and Management of a Highly Imperiled Prairie Species

“…Our five top sites tended to be more recently preserved, even more so tended to contain long or never-firemanaged habitat occupied by O. poweshiek throughout our study, and all had standing water in or next to them. Our analysis in Wisconsin of the benefit of a permanent nonfire refugium in core habitat for other prairie-specialist butterflies is consistent with this [43].…”

“…This likely contributes to the extreme range of variation in Figures 2-4: some fires occurred in areas of negligible relevance to the O. poweshiek population while others encompassed most or all core areas, while still burning only a portion of the site. At a minimum, these results strongly support the implementation in fire-managed sites of a permanent nonfire refugium [23,43] in core O. poweshiek habitat, with unintensive alternative management as suggested by Figure 2 (such as rotational haying or idling combined with brush-cutting).…”

“…The fluctuation evident in the coming summer surveys is unknowable at the time most land management occurs (e.g., cool-season burning and fall haying). Creating and maintaining permanent nonfire refugia managed without fire is one way to hedge against this risk in fire-managed sites, as this measure significantly benefits other specialized butterflies [23,43]. Greater variation and more frequent catastrophes (e.g., mortality from fire) are known to cause a greater risk of population extirpation than populations of the same average size that have less variability [51].…”

Replacing Hay-mowing with Prescribed Fire Restores Species Diversity and Conservation Value in a Tallgrass Prairie Sampled Thrice: A 59-Year Study

“…Maintenance of permanent non-fire refugia in several Midwestern tallgrass prairies has been successful in protecting fire-sensitive butterfly species within a fire-managed landscape (Swengel and Swengel 2007). Exclusions are typically created using a variety of ignition and holding techniques.…”