Geomorphic influences on ground-flora and overstory composition in upland forests of northwestern lower Michigan

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Abstract
Ground-flora and overstory composition and abundance patterns in 76 upland forest stands were related to the glacial geomorphology of a five-county area in northwestern lower Michigan. Nine classes of landforms were identified based on parent material and surface configuration. Chi-squared analyses of standardized residuals indicated that spatial distribution patterns of the ground flora were significantly associated with glacial landform. Detrended correspondence analyses showed that specific overstory–ground flora assemblages recur in characteristic landscape positions. The Interlobate Moraine, a predominant landform in the northeastern portion of the study area, was characterized by a northern hardwood canopy, primarily sugar maple (Acersaccharum Marsh.), basswood (Tiliaamericana L.), and red oak (Quercusrubra L.), with herbaceous annuals, perennials, and ephemerals forming the ground flora. Other morainal and glaciofluvial landforms supported oak (Quercus spp.) overstories with a woody ericaceous or graminoid ground flora. Ground-flora and overstory composition were highly correlated, indicating that they respond similarly to variation in environmental and historical factors. Moisture availability, as evidenced by soil texture and the presence of subsurface textural discontinuities, appeared to be a predominant factor influencing species distribution patterns. Since moisture availability and related nutrient dynamics are functions of depositional and postglacial history, regional-scale geomorphic patterns constrain forest composition in a probabilistic manner.

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