2005 THE MICHIGAN BOTANIST 13 THE ROLE OF FIRE IN GREAT LAKES ALVAR LANDSCAPES Judith Jones1 and Carol Reschke2 1Author for correspondence. Winter Spider Eco-Consulting, R.R. #1 Sheguiandah, Manitoulin Island, Ontario P0P 1W0 Canada E-mail: [email protected] . 2The Natural Resources Research Institute University of Minnesota 5013 Miller Trunk Highway Duluth, Minnesota 55811 E-mail: [email protected] ABSTRACT The role of fire in alvar landscapes in the Great Lakes region of the United States and Canada was examined through the notes of the original land surveyors, through field work which looked for burn evidence, and through a comparison of alvars on two sets of aerial photographs taken 40 to 45 years apart. The results show that alvars existed in all regions of the Great Lakes prior to settlement of the area by European immigrants. Also, fire can create alvars and has done so in the last 150 years. Some alvar community types correlate strongly with past burning while others correlate with no burning. Some community types show noticeable change in a 40 year period while others show lit- tle or none. Although the presence of burn evidence is common, fire is shown to be infrequent in alvar landscapes, with some communities experiencing fire return intervals of at least 200–500 years. In these communities, fire is not the primary factor maintaining the open condition. The history of Great Lakes alvars is shown to be diverse and complex. Controlled burning is not recommended for all sites or all alvar community types. INTRODUCTION “Alvar” is a Swedish word used for the grasslands on the island of Oland, in the Baltic Sea. The word is now commonly applied to natural, open, ecosystems which occur on shallow soils over flat limestone bedrock, and which have a dominant cover of grasses and sedges or low shrubs often with less than 25% cover of trees. The underlying bedrock may be exposed and appear as a natural “pavement” with plants growing from cracks or deep crevices. Most alvar ecosystems occur only around the Great Lakes in North America and in the Baltic region of Europe. Alvar ecosystems are globally rare and contain many species and communi- ties that are rare on a global or province/state-wide basis (Oldham 1999; Gross- man et al. 1998; Bakowsky 1996). The different types of alvar (vegetation com- munities) in the Great Lakes region have recently been distinguished based on compositional and structural differences (Brownell and Riley 2000, Reschke et al. 1999; Lee et al. 1998; Bakowsky 1996). Several recent studies have brought attention to the alvar ecosystems found around the Great Lakes (Brownell and Riley 2000; Reschke et al. 1999; Catling and Brownell 1998, 1999; Schaefer and Larson 1997; Gilman 1995; Belcher et 14 THE MICHIGAN BOTANIST Vol. 44 al. 1992; Belcher 1992). Despite the thoughtful design of these works, assump- tions have still been made about the history and origin of Great Lakes alvars, be- cause, for the most part, these topics have not been studied. Specifically, because evidence of burning is found on many alvars, many people assume all alvars need fire to remain in an open state (Brownell and Riley 2000; Catling and Brownell 1998). The fact that alvars are open in a region where most of the natural landscape is forested has led to a number of hypotheses on how alvars originate and remain open. Drought, a seasonal cycle of drought and flooding, and fire have all been proposed as factors maintaining open conditions. The shallow soils charactieris- tic of alvars (usually <10 cm in the Great Lakes region) limit water holding ca- pacity, and the nearly level, exposed bedrock limits drainage, leaving alvars often in conditions of either extreme saturation or drought. Stephenson and Herendeen (1986) studied patterns of drought on Drummond Island, Michigan alvars and found that drought was keeping trembling aspen (Populus tremu- loides Michx.) from getting established in alvar grasslands. Reschke (1995) stud- ied soil moisture regimes and evidence of fire at Chaumont Barrens in New York. She found that a seasonal cycle of summer drought and fall-spring satura- tion (or flooding) was strongly correlated with presence of alvar shrubland veg- etation, but not with alvar grasslands. Catling and Brownell (1998) claim that the majority of alvars have burned and suggest that burning may have resulted in higher species diversity at the Burnt Lands Alvar in eastern Ontario. On the other hand, Schaefer and Larson (1997) found no difference in alvar community structure between alvars burned 70 years ago and those apparently never ex- posed to fire. Many alvars do in fact show extensive evidence of burning; however, other alvars very similar to the burned ones present no burn evidence at all (data below). Speculation about alvar fire history leads to assumptions about the use- fulness of fire as a management tool for alvars, but prior to this study no exami- nation had been made of whether most alvar sites and community types had in fact burned in the past. This paper focuses on the history of Great Lakes alvars and attempts to clarify the role of fire in different alvar community types. For this work, the history of Great Lakes alvars was examined in a number of ways to investigate three main questions: 1) Did Great Lakes alvars exist before the time of settlement by European immigrants or were they opened up as a result of recent human distur- bance? 2) To what extent is fire involved in the origin and maintenance of Great Lakes alvars, and do different alvar community types have different fire origins? 3) Do Great Lakes alvars remain always open or do they grow in to some ex- tent over an observable period of time? Vegetation history is difficult to examine directly, so an indirect approach of looking for correlations and empirical evidence is typically used (for example, Cronon 1983; Russell 1993). In this study, vegetation history is interpreted from 2005 THE MICHIGAN BOTANIST 15 correlations among vegetation composition, evidence of fire, and historical veg- etation patterns. METHODS To address the first question regarding the history of alvar vegetation, notes from the original land survey records were used to reconstruct the presettlement vegetation of extant alvar areas on the Bruce Peninsula, Carden Plain, and Manitoulin Island in Ontario, and in Jefferson County, New York. Similar work by Comer et al. (1995) for Drummond Island, Michigan and by Goodban (1995) for the Flamborough Plain, Ontario was also consulted. The original land surveys (Table 1) were done about 150 years ago to lay out the location of lots and roads so homesteaders could acquire land. The surveyors also wrote down characteristics of the land to help homesteaders choose prop- erty they had never seen and recognize it upon arrival. In this study, surveyors’ comments such as “prairie,” “plains,” “rocky barrens,” etc. were used to map the possible presence of alvars at the date of the survey. In addition, we consulted old newspaper clippings and 15 elderly local residents, ages 74–96 in 1996, who had lived adjacent to alvar areas since childhood, to look for any obvious events (fire, log- ging, etc.) that might have created the alvars and to try to establish dates for burns. To address the second question regarding the role of fire, the presence or absence of burn evi- dence was recorded in the field at 258 observation points, distributed among 67 sites. Sites were se- lected to sample the largest, best-known, and least anthropogenically disturbed alvars in each region, and to represent as many different kinds of alvar vegetation as possible. Multiple observation points were recorded at many sites to sample different vegetation communities or variations within com- munity types. Burn evidence recorded included presence of charcoal, burnt woody debris or stumps, and fire scars on trees. In addition, a scan was made at each observation point for eastern white cedar trees (Thuja occidentalis L.) that could be exceptionally old (Larson and Kelly 1991), and some of the trees located in this process were cored. Dating of cores was done by Claudia Schaefer, then at the Cliff Ecology Research Lab, University of Guelph, Ontario. Information from Schaefer and Lar- son (1997) on old trees from Bruce Peninsula, Ontario alvars was also incorporated. Finally, Timo- thy Lynham, a fire history expert from the Canadian Forest Service, Natural Resources Canada, Sault Ste. Marie, Ontario, was escorted to a few sites to provide insight on possible fire history scenarios for some alvars. Relationships between community type and presence or absence of burn evidence were tallied. Community types used here follow those described by Reschke et al. 1999. TABLE 1. Location and date of first survey of some Great Lakes alvar study areas. Survey Area Name Location Date Citations Jefferson County, New York 44° 01′N, 76° 00′W 1799 Gilman 1996 Brodhead 1799 a–d Bruce Peninsula, Ontario 1855 C. Schaefer 1996a St. Edmunds Township 45° 01′N, 81° 22′ W Carden Township, Ontario 44°38′N, 79° 00′W 1858 C. Schaefer 1996b Flamborough Plain, Ontario Beverly Township 43° 25′N, 80° 00′W 1797 Goodban 1995 Manitoulin Island, Ontario Dawson Township 45° 53′N, 83° 08′W 1879 Fitzgerald 1879a Robinson Township 45° 51′N, 82° 52′W 1879 Fitzgerald 1879b; Patten 1908 Burpee Township 45° 47′N, 82° 38′W 1878 Abrey 1878 Gordon Township 45° 52′N, 82° 28′W 1871 Bray 1871 Tehkummah Township 45° 37′N, 82° 02′W 1870 Fitzgerald 1870 Drummond Island, Michigan 46° 00′N, 83° 40′W 1845 General Land Office 1890 Comer et al. 1995 16 THE MICHIGAN BOTANIST Vol.