* limited to sites with higher soil calcium
Vascular plant nomenclature follows Rhoads and Block (2007). Bryophyte nomenclature follows Crum and Anderson (1981).

International Vegetation Classification Associations:

USNVC Crosswalk:

None

Representative Community Types:

Northern Mixed Mesophytic Forest (CEGL005222)
Central Appalachian-Piedmont Rich Cove / Mesic Slope Forest (Twinleaf - Blue Cohosh Type) (CEGL008412)
Upper Piedmont-Northern Blue Ridge Basic Mesic Hardwood Forest (CEGL006816)
Central Appalachian Rich Cove Forest (CEGL006237)
Central Appalachian Rich Cove Forest (Tuliptree - Northern Red Oak - Cucumber-tree Type) (CEGL008510)

NatureServe Ecological Systems:

South-Central Interior Mesophytic Forest (CES202.887)

NatureServe Group Level:

Appalachian - South-central Interior Mesic Forest (G020)

Origin of Concept

Fike, J. 1999. Terrestrial and palustrine plant communities of Pennsylvania. Pennsylvania Natural Diversity Inventory. Harrisburg, PA. 86 pp.

Pennsylvania Community Code*

MM : Mixed mesophytic forest

*(DCNR 1999, Stone 2006)

Similar Ecological Communities

There is considerable overlap between the Mixed Mesophytic Forest associations and the more commonly occurring Northern Hardwood Forest, Sugar maple – Basswood Forest, and Tuliptree – Beech – Maple Forest. The Mixed Mesophytic Forest differs from these and other hardwood forest types in the diversity of the canopy and richness of the spring flora, many of which have an affinity to calcareous geology. The abundance of yellow buckeye and pawpaw is often a key indicator, along with the species-rich vernal flora. There is considerable overlap between the Mixed Mesophytic Forest and Rich Hemlock – Mesic Hardwood Forest, which also is found on lower slopes and coves of creeks and rivers in Southwestern Pennsylvania. The Mixed Mesophytic Forest community type is dominated by hardwood tree species. Forests greater than 25% cover of eastern hemlock (Tsuga canadensis), are classified as the Rich Hemlock – Mesic Hardwoods Forest. The Sugar Maple – Basswood Forest is less species-rich than this type, has a much broader range, and soils are considerably more acidic (pH 5.5-6.5). Outside of the Western Appalachian Plateau, forests with prevalence of tuliptree, American beech, white ash, sugar maple, and basswood occurring may be more correctly typed as Sugar Maple – Basswood Forest, particularly belonging to the USNVC’s CEGL006237. Less diverse forest communities with less than 25% cover of eastern hemlock most likely belong to the Northern Hardwood Forest community type.

Fike Crosswalk

Mixed Mesophytic Forest

Conservation Value

Occurring from the western portion of the Mid-Atlantic south to Tennessee, this community is more common outside Pennsylvania – where it is limited to southern Western Pennsylvania (Allegheny, Fayette, Washington, Beaver, Butler, Indiana, and Greene Counties). The richest, most diverse examples of this type occur in protected concave topographic positions. This community type supports a number of rare and vulnerable plant species and the community itself is also an element of conservation concern (S1). There are only two occurrences of this type in the PA Natural Heritage Program database. Neither site is considered “old growth,” but similar to sites in West Virginia, it has recovered well and supports a diversity of large overstory trees due to high site productivity. Other sites in Pennsylvania may support this community. The forests of Greene and Washington Counties are a mosaic of low-density residential development, mine-lands, and agriculture, many small patches of lower slope cove forest in a somewhat precarious position as they are somewhat disconnected from other patches. This is also true for Mixed Mesophytic Forests of Pennsylvania’s Piedmont. This forest type is much more common to the south, and forest patches exist in a fragmented landscape of farmland and development.

Threats

There exists very little protected land within the range of the Mixed Mesophytic Forest community in Pennsylvania and much of the remaining acreage which is formally protected is not of high quality. Most stands represent second-growth forests in some stage of recovery and a majority of the higher quality sites remain threatened by future timber harvests. Timber harvest activities disturb the rich forest floor, disrupt the canopy, and introduce invasive plants. Invasive plant species, including garlic mustard (Alliaria petiolata) and tree of heaven (Ailanthus altissima), and others, are the most serious threat to this forest type. Climate change may also impact Mixed Mesophytic Forests. Several species that are currently present in the overstory, such as sugar maple, eastern hemlock, or black cherry, could become less common in future climate scenarios (Peters et al. 2020, Shortle et. al 2015 ). Forest pests/pathogens have already impacted tree species in this community type, including emerald ash borer (EAB; Agrilus planipennis), hemlock wooly adelgid (HWA; Adelges tsugae), and beech bark disease. The Asian long-horned beetle (Anoplophora glabripennis), while not known from this region, has been known to infest many of the overstory trees of this forest type and may decimate the hardwood forests of this region.

 

Overharvesting of American ginseng, goldenseal, and ramps has been cited as a threat to Mixed Mesophytic Forest patches on rich lower slopes. Soil disturbance and introduction of invasive pests, such as jumping worms (Amynthas agrestis) from harvesting wild plants may further impact the quality of Mixed Mesophytic Forest occurrences.

Management

The steep lower slopes and coves that support this forest type are often protected by the relative difficulty of access. However, timber harvesting activities should be limited in forest stands of this type because of the steepness of the slope and the potential for further spreading invasive plants. Management of invasive plant species is encouraged. Also, management of white-tailed deer will limit over-browsing.

Range Map

Pennsylvania Range

Mixed Mesophytic Forests of the Western Allegheny Plateau (CEGL005222) are found in the USEPA’s Western Allegheny Plateau Ecoregion (USEPA Level III Ecoregion 70)

 

The very rich Mixed Mesophytic Forest (CEGL008412), limited to mid-to lower slopes in Southwestern Pennsylvania (Greene and Washington Counties) in USEPA’s Western Allegheny Plateau Ecoregion (USEPA Level III Ecoregion 70) (PNHP Data)

 

The Mixed Mesophytic Forest subtype occurring in the Piedmont Ecoregion (CEGL008510) is limited to USEPA’s Northern Piedmont Ecoregion (USEPA Level III Ecoregion 70)

Global Distribution

This type is found primarily in the Western Allegheny Plateau, Cumberland Plateau, and Northern Piedmont regions of the United States, ranging from southern Pennsylvania and eastern Ohio south to West Virginia and Tennessee, with outliers in Indiana (USNVC 2019).

Braun EL. 1950. Deciduous forests of eastern North America. Blakiston, the University of California.

Dyer JM. 2006. Revisiting the Deciduous Forests of Eastern North America. BioScience 56:341.

Fike J. 1999. Terrestrial & palustrine plant communities of Pennsylvania. Available from http://www.naturalheritage.state.pa.us/Uplands.aspx (accessed April 16, 2018).

Muller RN. 1982. Vegetation Patterns in the Mixed Mesophytic Forest of Eastern Kentucky. Ecology 63:1901.

Peters MP, Prasad AM, Matthews SN, Iverson LR. 2020. Climate change tree atlas, Version 4. U.S. Forest Service, Northern Research Station and Northern Institute of Applied Climate Science, Delaware, OH. Available from https://www.fs.fed.us/nrs/atlas/tree/.

USNVC. 2019. United States National Vegetation Classification Database, V2.03. Federal Geographic Data Committee, Vegetation Subcommittee, Washington DC. Available from http://usnvc.org/.