Potential Natural Vegetation Group (PNVG): Rapid Assessment Reference Condition Model

This type occurs principally on moraines composed of well-to-moderately-well-drained heterogeneous soils with inherently high moisture and nutrient availability. Vegetation Description Structurally, these uneven-aged forests were characterized by large volumes of coarse, woody debris lying beneath multi-storied canopies of different-aged cohorts, with supercanopies composed of trees centuries old (Tyrell and Crow 1994). The dominant tree species are among the most moisture and nutrient-demanding species in the eastern U.S.A., and their distribution is confined to glacial landforms underlain by fertile soils (Woods 2000, Whitney 1986). Composition of the ground flora and understory varies along a moisture-nutrient gradient, and typically consists of high densities of shade-tolerant tree species and mesophilic herbaceous species including blue cohosh, yellow violet, sweet cicely, various ferns, and ginseng. In the mid-1800’s, there were 5.8 million acres of northern hardwood ecosystems in the Upper Peninsula of Michigan (Cleland 2004a, ongoing R-9/SRS/MTU study). Sugar maple, hemlock, yellow birch, balsam fir, cedar in swales, spruce, and beech were the dominant late-successional species recorded along section lines by GLO surveyors (figure 1). Early-successional aspen and white birch comprised only 2.0 % of the GL