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

For this model the broader concept of the mixed mesophytic forest has been split. This model is specific to the mesic and dry-mesic forests of the loess bluff and plain. The distribution of these forests is determined by the interaction of topography and fine textured soils. Within the type, local variability in topography and moisture determine the dominant canopy. Drier sites occur along the bluff tops and on the loess plain. Mesic sites occur in protected areas. Loess deposits make the fertility and the local topography of this area distinct (Natureserve 2005, Braun 1950, Miller and Neiswender 1987). The geology of the area is mapped as the Jackson Formation (Hardeman 1966). Vegetation Description Most stands are co-dominated by American beech (Fagus grandifolia) with or without white oak (Quercus alba). The mesic end of the gradient may not include oaks at all, but instead show dominance by Fagus grandifolia, yellow poplar (Liriodendron tulipifera), or sweet gum (Liquidambar styraciflua). In the southern bluffs cherrybark oak (Quercus pagodifolia) is an important canopy dominant. There is a recognized species shift from north to south, with southern magnolia (Magnolia grandiflora) occurring in the southern loess bluffs and dropping out in the north. Disturbance Description Fire frequency and severity in this PNVG is classified as Fire Regime Group III, with infrequent, low intensity surface fires and rare mosaic or replacement fires. The mean fire return interval (MFI) is about 35 years with wide year-to-year and within-type variation related to moisture cycles, degree of sheltering, an