The Identification of Mesophytic Cove Sites in Pennsylvania

Location and Description

Mesophytic Cove Sites (MCS) are highly diverse hardwood-dominated stands that occur in sheltered and highly productive areas such as ravines, steep slope, and coves (areas protected by a concave topographic positions or headwater drainage) at mid- to lower elevation (1000-3600 ft). Soils in MCS are generally deep loams with a pH greater than 6.0. MCS with the richest species diversity have a pH between 7.0 and 8.0.

In Pennsylvania, MCS are limited to the southwest corner of the state (Allegheny, Fayette, Greene, Beaver, Butler, and Washington Counties; Figure 1) where a combination of rich soils, limestone geology, and climate support many species with a southern affinity.

Currently, work is being done by the Pennsylvania Natural Heritage Program to outline, define, and locate additional MCS-like sites in other parts of Pennsylvania. MCS are more commonly found outside of Pennsylvania, occurring from the western portion of the Mid-Atlantic states south to Tennessee. Forested coves are found throughout Pennsylvania; however, they lack species diversity (namely the southern species) required to be classified as an MCS. To be classified as an MCS, a stand requires a uniquely diverse overstory, midstory, and understory (see species list below).

Resource extraction (e.g., mining, farming, and ranching) and development have greatly impacted the MCS within their limited range in southwestern Pennsylvania. MCS that have been damaged have lost much of their uniquely diverse species community and productivity and are now dominated by early successional and/or seed-originated species like tulip poplar (Liriodendron tulipifera) and a mixture of non-native invasive shrubs. 

Protection and Management of High Conservation Value (HCV)

Mesophytic cove sites that remain are considered rare natural communities in Pennsylvania. As indicated above, these stands are functionally protected from human disturbance due to the steep topography, restricted entry points, and network of ephemeral and headwater streams present, which make active management of these stands difficult. Disturbance, specifically harvesting conducted in a manner that increases within-stand light levels and generates significant duff layer and soil disturbance, can cause the loss of diversity, which is the primary attribute of this HVC that must be protected. Management, particularly plans that include harvesting, must maintain the species diversity.

Given the limited disturbance that can be tolerated, along with the complex topography and hydrologic features present, significant planning and operational sophistication are required to successfully conduct harvesting in MCSs. Timber harvesting activities should be limited-especially on steep slopes to prevent the potential for spreading non-native invasive species and reduce soil erosion. The management of invasive plants and white-tailed deer in these highly vulnerable areas is encouraged.  

High-quality MCS sites are at risk from various threats. Timber harvesting within MCSs disturbs the rich forest floor, disrupts the canopy cover, and introduces and spreads non-native invasive species. Invasive plants such as knotweed (Reynoutria japonica), Oriental bittersweet (Celastrus orbiculatus), and tree-of-heaven (Ailanthus altissima) are serious threats to the diversity within these sites. Pests and pathogens such as emerald ash borer (Agrilus planipennis), hemlock wooly adelgid (Adelges tsugae), and beech bark disease have already impacted tree species within the forest communities of the MCSs and Asian long-horned beetle (Anoplophora glabripennis) has the potential to infest many of the overstory trees in this forest type if introduced to the region. Climate change may impact MCSs by reducing the occurrence of common overstory species such as eastern hemlock (Tsuga canadensis), basswood (Tilia americana), or sugar maple (Acer saccharum).

Bearing all of this in mind, it may be appropriate to give MCS a 100-yard buffer to ensure that they are protected and fully functioning.  

Sub-stands Aligned with MCS (Similar Ecological Communities)

There are areas within Pennsylvania with overlapping species characteristics of the MCS but which fall outside of the definition of cove sites. Sugar maple-basswood and tulip poplar-beech-maple forests in similar topographical positions extend beyond the range of the MCS region. While these stands are like MCS, they do not constitute an MCS because they lack canopy diversity and species richness.

The key indicator of an MCS is an abundance of yellow buckeye (Aesculus flava), pawpaw (Asimina triloba), and other relatively uncommon trees and shrubs. The herbaceous layer is lush and diverse, which is a key defining characteristic. Forest communities of cove sites in the Allegheny Mountains are often less diverse than those on the Allegheny Plateau.

There are also similarities between the MCS forests and the hemlock-mesic hardwood forest, which is found in the lower slopes of streams and rivers in Southwestern Pennsylvania. However, hemlock-mesic hardwood forest usually contains 25% or more relative cover of eastern hemlock. Rich northern hardwood forests composed of sugar maple and tulip poplar, red oak (Quercus rubra), and American beech (Fagus grandifolia) are often found within similar landforms (coves, protected lower slopes, and high floodplain terraces) and may be highly productive and diverse. However, they lack the species typical of the central and southern Appalachians and are currently considered to be separate from MCS.

Identification and Management

Identification Key

1. Harvest area is between 1000-3600 ft and contains a cove (concave sloped, headwater drainage) greater than 2 acres? If Yes go to #2. If No stop, MCS does not exist 
2. Is the cove located low to mid-slope? If yes go to #3. If No stop, upper slope too dry for MCS.  
3. Is the cove located predominately on an North or East facing slope? If Yes got to #5. If No, go to #4.  
4. Is the cove on lower slope of predominately South or West facing slope? If Yes go to #5. If No stop, mid to upper south and west facing slopes too dry for MCS to exist. 
5. Does the cove site shows signs of farming, extensive logging, or mining such as fencing, rock piles, outbuildings, numerous stumps, or mine refuse? If Yes stop, recent past land use would prohibit the stand diversity needed to be an MCS. If No, go to #6.
6. Are at least 50% of the species in each category present in the stand? If Yes go to #7. If No stop, overstory lacks the diversity to be an MCS.
7. Does tulip poplar make up less than 33% (1 out of 3) of the dominant or co-dominant overstory trees. If Yes go to #8. If No stop, the stand is too dominated by tulip poplar and/or maple and therefore lacks the diversity to be MCS.
8. Cove has a high potential to be a MCS. See Recommendations  

Management Recommendations

1. Wherever possible do not harvest a known MCS, and buffer the MCS by at least 100 yards to protect species diversity and maintain interior forest conditions.
2. Advise controlled the wood user and landowner of the MCS existence. The landowner and manager may work with interested conservation groups to may explore the options for protection of these sensitive areas like conservation easements.
3. MCS maybe harvested, as long as approximately 75% of the dominant overstory trees left evenly distributed across the cove. Four out of the 5 trees (80%) harvested should consist of tulip poplar or cucumber magnolia.
4. While harvesting, make efforts to limit damage to the unique native plant community. Take steps like limit roads, strategically place skid trails, and wash equipment prior to harvesting to protect the rich species diversity and limit introductions of invasive plants. 

Characteristic Species

Trees

• American beech (Fagus grandifolia)
• Basswood (Tilia americana)
• Black cherry (Prunus serotina) 
• Black walnut (Juglans nigra)
• Cucumber magnolia (Magnolia acuminata)
• Eastern hemlock (Tsuga canadensis)
• Northern red oak (Quercus rubra)
• Shagbark hickory (Carya ovata)
• Sugar maple (Acer saccharum)
• Tulip poplar (Liriodendron tulipifera)
• White ash (Fraxinus americana)
•  Yellow buckeye (Aesculus flava)

Shrubs 

• Bladdernut (Staphylea trifolia)
• Pawpaw (Asimina triloba)
• Redbud (Cercis canadensis)
• Spicebush (Lindera benzoin)
• Wild hydrangea (Hydrangea arborescens)
• Witch-hazel (Hamamelis virginiana) 

Herbs 

• American ginseng (Panax quinquefolius)
• Black cohosh/baneberry (Actaea racemosa)
• Bloodroot (Sanguinaria canadensis)
• Blue cohosh (Caulophyllum thalictroides)
• Dutchman's-breeches (Dicentra cucullaria)
• Goldenseal (Hydrastis canadensis)
• Maidenhair fern (Adiantum pedatum)
• Squirrel corn (Dicentra canadensis)
• Virginia and Carolina spring-beauty (Claytonia virginica, C. caroliniana)
• Wake-robin/red trillium (Trillium erectum)

• White trillium (Trillium grandiflorum)
• Wild ginger (Asarum canadense)
• Wild leek/ramps (Allium tricoccum)
• Wood/spotted geranium (Geranium maculatum)
• Yellow trout-lily/dog-tooth violet (Erythronium americanum) 

Note: This document was adapted from a similar document published by the Center for Forest and Wood Certification, University of Kentucky, Department of Forestry and Natural Resources 

References

Braun, E. L. 1950. Deciduous forests of eastern North America. Blakiston Co. PA. 596pp.

Comprehensive Report Ecological Systems- Southern and Central Appalachian Cove Forest.

Ecological Site F126XY002OH, Natural Resources and Conservation Services.

FSC US Controlled Wood Regional Meeting Report, Appalachian Region: Asheville, NC July 19, 2018.

Iverson, L., Prasad, A., Matthews, S., Peters, M. Estimating potential habitat for 134 eastern US tree species under six climate scenarios. Forest Ecology and Management 254 390-406.

Kalisz, P. 1986. Soil Properties of Steep Appalachian Old Fields. Ecology 67 No 4 1011-1023.

Keever, C. 1971. A Study of the Mixed Mesophytic, Western Mesophytic, and Oak Chestnut Regions of the eastern Deciduous Forests: Including a Review of the Vegetation and Sites Recommended as Potential Natural Landmarks.

Modeled extent of South-Central Interior Mesophytic Forest:  Ferree, C and M. G. Anderson. 2013. A Map of Terrestrial Habitats of the Northeastern United States: Methods and Approach. The Nature Conservancy, Eastern Conservation Science, Eastern Regional Office. Boston, MA.

Moore, A., Nowacki, G., Burk, A. Rapid Assessment Reference Condition Model, Mixed Mesophytic Hardwood- U. S. Forest Service.

Mueller, R. N. 1982. Vegetation Patterns in the Mixed Mesophytic Forest of eastern KY. Ecology 63 1901- 1917.

Pennsylvania Natural Heritage Program Data: Pennsylvania Natural Heritage Program. 2021.