/ Prairie and Savanna in Southern Lower Michigan: History, Classification, Ecology
ï~~2008 THE MICHIGAN BOTANIST PRAIRIE AND SAVANNA IN SOUTHERN LOWER MICHIGAN: HISTORY, CLASSIFICATION, ECOLOGY Kim Alan Chapman1 and Richard Brewer Department of Biological Sciences Western Michigan University Kalamazoo, MI 49001 ABSTRACT Tallgrass prairie and associated savanna were at their continental boundary in southern Michigan when white settlers arrived and had largely disappeared before scientists could describe them. The historical extent of upland prairie, wet prairie and savanna in Michigan was estimated to be 930,000 ha (2.23 million ac), with savanna constituting 78 percent. In 1830 there were 54 separate locations of upland prairie in Michigan. Historical and modern sources were consulted to locate and visit 66 relict prairies and savannas in 1979-1980. Ordination of these 66 remnants identified several prairie and savanna communities (and a distinct fen community) which varied along three environmental gradients. A moisture gradient ranging from soils of low to high water-retaining capacity formed the series of sand prairie/oak barrens; oak openings; mesic prairie; wet prairie; and fen. A soil texture gradient separated mesic and wet prairies on loams and silt loams (with some sandy loams) from those on sandy loams and sands (with some loams). Soil texture differences generally corresponded to glacial parent material differences: coarser-textured soils were associated with glacial lake plains and to a lesser extent with outwash plains, while finer-textured soils were associated with outwash plains and moraines. A third but weak gradient divided oak openings on south- to west-facing hillsides from those on rolling to level ground. Summaries of species presence, indicator species, and environmental characteristics are provided for each community type (except fens, which were used solely for the purpose of ordinating stands). Michigan's extensive savannas defined much of southern Lower Michigan and were characterized by a complex interaction of fire, tree canopy cover, and herbaceous plant diversity. Soils, landscape setting, drought, and other disturbances influenced these interactions. The oak grubs found in Michigan's savannas and described by early writers are now understood as essential for perpetuating the tree canopy of fire-maintained savannas. These remnants represent less than 0.1% of Michigan's historical prairie and savanna acreage. In view of this loss any remnant should be protected, but especially the oak openings, which were a dominant ecological feature of southern Lower Michigan. Since oak openings existed on a large scale, small reserves are insufficient to represent former ecological processes and encompass the majority of animal and plant species characteristic of oak openings. Consequently, conservation groups and natural resource agencies should identify, protect, and restore large blocks of oak openings in southern Michigan, especially those that contain other prairie and savanna plant communities. KEY WORDS: tallgrass prairie, oak savanna, classification, ecology, environmental history INTRODUCTION Michigan's extensive prairies and savannas disappeared in the 1800s before scientists could fully describe them (Chapman 1984), yet early 20th century tCurrent address: Applied Ecological Services, 21938 Mushtown Road, Prior Lake, MN 55372, 952.447.1919, kim@appliedeco.com
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