The vegetation of Offield Bog (Offield Family Nature Preserve, Emmet County, MI) floristic quality, community description and management implications.

Abstract

Offield Family Nature Preserve (OFNP), Emmet County, MI was purchased in Spring 2009 by the Little Traverse Conservancy (LTC). Located within OFNP is Offield Bog, a relatively small, acidic peatland (4800 m2) with shallow peat depths (average < 3 m). We found 48 plant species in 23 families in the peatland. Native species consisted of 94% of the flora. Ericaceous shrubs including Vaccinium angustifolium, Chamaedaphne calyculata, and Vaccinium myrtilloides had the highest mean percent cover in the understory. The tree dominants were determined using a point-center quarter method by measuring the diameter at breast height of individual trees. The overstory dominants were Picea mariana, Larix laricina, and Ilex mucronatus. We found that the muskeg-moat contained 4.4 species per m² while the heath community contained 3.0 species per m². We compared the species richness and Floristic Quality Index (FQI) of Offield Bog to five other peatlands of Cheboygan and Emmet County, Michigan (Bryant’s, Hogback, Linné, and Livingston Bogs as well as Orchis Fen). A X2 analysis showed a significant difference in species richness among the peatlands (p-value < 0.05). This result was due in part to the high species richness of Livingston Bog. When we removed Livingston Bog from the X2 analysis we found that the difference in species richness was not significant (p-value > 0.05) between the remaining peatlands. The six peatlands also were not significantly different in their FQI values (p-value > 0.05). Bog vegetation usually consists of specialist species that can tolerate the anoxic, acidic, inundated, and cold physical conditions of peat substrates. Therefore it is not surprising that the vegetation of Offield Bog has so many similarities to other peatlands in northern Lower Michigan. Exotic species such as Hieracium piloselloides, Hypericum perforatum, and Lonicera morrowi may be of some concern for future land management. We recommend that management entail conservation of the existing hydrology of Offield Bog and that impervious surfaces near the peatland be minimized.