introduction - Pennsylvania Natural Heritage Program

(Aralia nudicaulis), Canada mayflower (Maianthemum canadense), and partridgeberry (Mitchella repens).Mesic ravines and valleys typically have a stronger component of yellow birch and hemlock. In the northernplateau portion of Clearfield County, these communities are typical, while oak-heath communities similar tothose described for the Central Appalachian Mountains are found at higher elevations and on dry slopes.The original Western Allegheny Plateau forests appear to have been dominated by white oak (Quercus alba),with shagbark hickory (Carya ovata), red maple (Acer rubrum), shingle oak (Quercus imbricaria), scarlet oak(Quercus coccinea), chestnut oak (Quercus montana), black oak (Quercus velutina), red oak (Quercus rubra),American chestnut (Castanea dentata), and black cherry (Prunus serotina) present in various mixtures.In Clearfield County the less-disturbed forests tend to resemble the type characteristic of the ecoregion they fallwithin, but also display features of adjacent ecoregional types, especially following along the lines oftopographic transitions. For example, the forests of the southern part of the county tend to contain a morediverse mixture of canopy trees, including species such as tulip poplar (Liriodendron tulipifera), green ash(Fraxinus pensylvanica), swamp white oak (Quercus bicolor), and cucumber magnolia (Magnolia acuminata),which have a more southerly distribution—and these species can also be found following the valleys thatextend north of the West Branch into the High Allegheny Plateau. Conversely, forests with more northernspecies such as yellow birch (Betula allegheniensis) and wild sarsaparilla (Aralia nudicaulis) are found athigher elevations in the lower half of the county as well. In the southeast corner of the county, shingle oak(Quercus imbricaria), typical of Western Allegheny Plateau forests, is an important component of relativelyundisturbed forests and reaches the northeast edge of its range.Wetland CommunitiesWetlands provide essential habitat for many plant and animal species, as well as valuable ecosystem servicessuch as water filtration and flood control. The ecological character of a wetland is influenced by local soil type,disturbance history, bedrock composition, and hydrological regime. Types of wetlands range from forestedseeps where groundwater saturates the surface only when heavy precipitation raises the water table, to openmarshes that are continuously flooded, to low areas along streambanks that are flooded during high waterevents, to beaver meadows where the water level fluctuates over relatively long periods of time. Some types ofwetland, such as those that are created by beaver dams, develop very quickly, and major changes can beobserved in their character over mere decades. However, other types of wetland, such as sphagnum bogs, formextremely slowly, their present-day condition resulting from slow ecological processes operating over manythousands of years.In the landscape of Clearfield County, wetlands occur naturally at the headwaters of streams, in the floodplainsof streams and rivers, in areas where groundwater intercepts the surface of the ground (seepages and springs),and in beaver-impounded areas. Each of these settings provides different habitat values for native biodiversity.Wetlands resulting from excavations and impoundments are also present in the landscape; although they mayprovide habitat for typical wetland species, they were not included in this study because artificially createdwetlands typically do not host as rich or distinctive an assemblage of native species as do natural wetlands.Headwaters wetlandsThese wetlands occur in broad depressions high in a watershed where precipitation accumulates beforecoalescing into a stream channel. They may also be fed by groundwater seepage. The underlying surfacegeology is predominantly sandstone, providing little mineral enrichment, and the wetlands appear to rangein pH from somewhat acidic to highly acidic. Vegetation is usually patchy with vegetation structureresponding to slight variations in elevation. Shrubs tend to occupy higher zones, graminoids (grass-likeplants) occupy semi-saturated areas, while sphagnum and other emergent species occupy low, hydric areas.The historic condition of these wetland areas is somewhat uncertain, as there are no known descriptionsfrom before the original forests were logged in the late 1800s. Many of the wetlands contain large whitepine or hemlock stumps, indicating they were once forested; however, very little tree regeneration can beobserved in the wetlands today. Removal of the forest canopy may have elevated the water table, thus12