Wet Uplands

Description

From: http://www.naturalheritage.state.pa.us/Community.aspx?=16029

This describes a group of wetland forests that are dominated by a mixture of conifers and hardwood species. The substrate is usually mineral soil or muck over mineral soil. There is generally some groundwater enrichment in these systems. Eastern hemlock (Tsuga canadensis) contributes between 25% to 75% of the canopy. Other conifer species that may occur with hemlock include eastern white pine (Pinus strobus), red spruce (Picea rubens), and tamarack (Larix laricina). The most common hardwood species are yellow birch (Betula alleghaniensis), red maple (Acer rubrum), black ash (Fraxinus nigra), blackgum (Nyssa sylvatica), and gray birch (Betula populifolia). Rosebay (Rhododendron maximum) often forms a dense understory; other shrubs include highbush blueberry (Vaccinium corymbosum), winterberry (Ilex verticillata), swamp azalea (Rhododendron viscosum), and witherod (Viburnum cassinoides). Herbaceous species include cinnamon fern (Osmunda cinnamomea), sedges (e.g., Carex trisperma, Carex prasina, Carex leptalea), violets (Viola spp.), skunk-cabbage (Symplocarpus foetidus), false hellebore (Veratrum viride), sensitive fern (Onoclea sensibilis), partridge-berry (Mitchella repens), gold-thread (Coptis trifolia), Canada mayflower (Maianthemum canadense), crested wood fern (Dryopteris cristata), and purple-stemmed aster (Symphyotrichum puniceum). The bryophyte layer is usually well developed and may be dominated by sphagnum.

Disturbance Description
Non-Fire Disturbance: This system is dominated by long-lived, mesic species that form multi-layered uneven-aged forests over time. Canopy dynamics are dominated by single and multiple disturbances encouraging gap phase regeneration (Abrams and Orwig 1996). Larger disturbances include windthrow, insect attack and ice storms. Although stand-replacing wind events are rare, small to medium blowdown events are more common and occur at greater frequency on the plateau and exposed side slopes (Ruffner and Abrams 2003). Localized insect and disease outbreaks can create small to medium canopy gaps.

Running the VDDT model resulted in 0.9% disturbance (fire and/or wind, weather, stress) annually, consistent with disturbance rates documented by Runkle (1981, 1985) and others. Wind, weather, stress alone resulted in 0.7% disturbance annually.

Fire Regime Description: Historically, this system was probably only subject to occasional fires. Fires that did occur may have been catastrophic and may have lead to even-aged stands of pine and hemlock (NatureServe 2007).
Due to the predominance of cool, moist site conditions, surface and replacement fires are extremely rare, occurring at 700-1000yr intervals. Most protected sites are essentially fire free. The principal cause of fuel formation leading to fire in northern hardwood ecosystems is broad-scale, storm-driven windthrow of catastrophic proportions (Hough 1963, Runkle 1982).

The reference state is a combination of several vegetation associations of the following systems as described by NatureServe (2007):
• High Allegheny Wetland (CES202.069) represented by Picea rubens - Acer rubrum / Ilex verticillata Swamp Forest (CEGL006556).
• North-central Appalachian Acidic Swamp (CES202.604) represented by Tsuga canadensis / Rhododendron maximum / Sphagnum spp. Swamp Forest.
Due to the heterogeneity and the broadness of this provisional ecological site, the plant communities listed are not intended to cover every situation nor the full range of conditions and species. There are no transition pathways designated between the communities in the reference state because the differences in vegetation are more controlled by landscape position or inherent soil fertility than management or disturbance.

Submodel