Demography of Butterwort (Pinguicula vulgaris) on Beaver Island, Lake Michigan

Introduction:
Common butterwort (Pinguicula vulgaris L.) is a carnivorous member of one of five genera of the Lentibulariaceae, the family which also includes the bladderworts (Utricularia). In Northeastern North America the genus is represented by only P. vulgaris, though there are approximately 35 species worldwide, distributed in from Arctic to temperate regions of the Northern Hemisphere and in the Andes (Lloyd, 1942; Gleason and Cronquist, 1991). P. vulgaris is distributed circumboreal in North America and Eurasia, with a gap in distribution in north-central Siberia; a distribution map is given in Hultòn's Amphi-Atlantic Plants (1958). The plant grows normally in Boreal and Arctic regions, with a more southerly distribution in North America to the northern Great Lakes-St. Lawrence region and the Maritime areas of Canada. It reaches its southern limit in the Great Lakes region along the shores of Lakes Michigan and Huron on Beaver Island and the northern lower peninsula "mainland".

Site of Study:
Beaver Island is located in the northeastern Lake Michigan, in Charlevoix County, Michigan. On Beaver Island, there are only two known locations of Pinguicula, indicated on the map is shown in figure 1. As referred to in this study, site 1 is the northern Donnegal Bay area, on the northwest side of the island, and site 2 is located on the northeast side of the island. These two sites are located close to the shoreline, in swales between the beach area and the forest edge. Typical swale vegetation such as Carex spp., Potentilla anserina, Tofeldia glutinosa, Thuja occidentalis, Castelleja coccinea, Equisetum spp, Juncus balticus, Larix laricina, Parnassia glauca, Primula mistassinica, Rhyncospora alba, Picea glauca, and others were typical at both sites. In addition, site 1, Donnegal Bay, has large populations of the canioverous plants Drosera linearis and D. rotundifolia, as well as apparently declining population of Sarracenia purpurea. Though other, similar habitats exist on Beaver Island, the two sites remain the only known occurrences on Beaver Island.

Purpose of Study:
The purpose of this paper and the research project is to begin a long-term monitoring of the demographic conditions of the two known areas of Pinguicula on Beaver Island via continued examination of "representative" quadrats. Financial and time restrictions during the 1994 study limited the study to four quadrats, two at each site. Another purpose of the study in 1994 was to examine the spatial and size variations present in the Pinguicula communities.

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Conclusion
The two communities of Pinguicula vulgaris on Beaver Island are worthy of continued monitoring. This will contribute further understanding not only of the general ecology and demographic characteristics of P. vulgaris, but the local state of plants and communities present on Beaver Island, an area under increasing development pressure for vacation and retirement homes, as well as tourism-related industries. Though site 2, Little Sandy Bay, has recently been purchased by a Michigan conservancy group, and therefore is assumed relatively free from the threat of development, the future of site 1, Donnegal Bay, is uncertain. There has been an increased amount of home construction along the shoreline on Beaver Island in recent years, particularly along the areas on the northwest of the island. Numerous new surveying and planning signs were observed in the immediate area of site 1, and even if the exact site of Pinguicula communities is not built upon, the risk of substantial degradation of the communities is present. Degradation is a threat to these fragile plants from disturbances such as foot and vehicle traffic, alien species introduction, landscaping changes by new residents, and other human-related factors. At the the Little Sandy Bay site, motorized vehicle degradation was seen clearly, from small recreational-utility vehicles and passenger vehicles, was seen in several areas along the shoreline, and even within several meters of the Pinguicula communities. The former had been made repeatedly, to within days of the site study, while the latter was from a truck, and was likely over a year old, though the deep vehicle tracks were clearly visible and degrading to the local beach-shoreline plant communities affected.

During the initial field research for this project, several qualities of Pinguicula were observed which merit further attention. Questions raised include: