Hemlock (White Pine) – Northern Hardwood Forest

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System: Terrestrial
Subsystem: Forest
PA Ecological Group(s): Appalachian-Northeast Mesic Forest

Global Rank:G4G5 rank interpretation
State Rank: S4

General Description

This community has at least 25% combined relative cover of eastern hemlock (Tsuga canadensis) and/or white pine (Pinus strobus). Component hardwood species include sugar maple (Acer saccharum), American beech (Fagus grandifolia), yellow birch (Betula allegheniensis), black cherry (Prunus serotina), red maple (Acer rubrum) and sweet birch (Betula lenta). These forests occur on mesic sites, often north-facing, sometimes rocky and steep. This type is fairly widespread in northern Pennsylvania. Rosebay (Rhododendron maximum) may be locally abundant. Other common shrubs include witch-hazel (Hamamelis virginiana), striped maple (Acer pensylvanicum), and viburnum species (Viburnum spp.) The herb layer is usually sparse and reflects a northern affinity, with species such as common wood sorrel (Oxalis montana), violets (Viola blanda, V. sororia, V. rotundifolia), starflower (Trientalis borealis), Canada mayflower (Maianthemum canadense), partridge-berry (Mitchella repens), teaberry (Gaultheria procumbens), and ground pine (Lycopodium obscurum, L. dendroideum, L. hickeyi).

Rank Justification

The Hemlock (white pine) – Northern Hardwood Forest is fairly widespread throughout Pennsylvania; occurring mainly in the northern tier and central Pennsylvania. Some examples of this type are mapped at several hundred acres. Eastern hemlock and white pine are currently under threat by insect pests and this type may transition do a strict northern hardwood forest type in the event these tree species disappear from the local flora.

Identification

  • Associate hardwood trees include sugar maple, American beech, and yellow birch
  • At least 25% cover of eastern hemlock and/or white pine
  • Herbaceous layer is usually sparse and reflects a northern affinity
  • Rosebay may be locally abundant

* 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:

Central Appalachian-Northeast Hemlock – Northern Hardwood Forest (A3302)

Representative Community Types:

Hemlock - Transitional Northern Hardwood Forest (CEGL006639)
Central Appalachian Hemlock - Northern Hardwood Forest (CEGL006206)

NatureServe Ecological Systems:

None

NatureServe Group Level:

Appalachian-Northeast Mesic Forest (G742)

Origin of Concept

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

Gawler, S. C. 2018. Central Appalachian Hemlock - Northern Hardwood Forest (CEGL006206). NatureServe Explorer [web application]. NatureServe, Arlington, Virginia. Available https://explorer.natureserve.org/. (Accessed: March 10, 2022).

Neid, S. L, Gawler, S. C., Fleming, G. P., and Faber-Langendoen, D. 2015. Hemlock - Transitional Northern Hardwood Forest (CEGL006639). NatureServe Explorer [web application]. NatureServe, Arlington, Virginia. Available https://explorer.natureserve.org/. (Accessed: March 10, 2022).

Pennsylvania Community Code*

FB : Hemlock (white pine) – Northern Hardwood Forest

*(DCNR 1999, Stone 2006)

Similar Ecological Communities

This type can be very similar to the Hemlock (White Pine) Forest type, which typically has less of a hardwood component (maple, birch, beech with less than 25% relative cover) and more hemlock and white pine (over 75% for either/combination of relative cover for these species). The Hemlock (White Pine) – Red Oak – Mixed Hardwood Forest is also similar but has more red oak in the canopy and subcanopy, and often supports mountain laurel (Kalmia latifolia) in the shrub layer.

Fike Crosswalk

Hemlock (white pine) – Northern Hardwood Forest

Conservation Value

Very few state-listed plants are found in Hemlock (white pine) – Northern Hardwood Forests. However, a number of breeding birds prefer hemlock- or white pine-dominated forests, or forests with a strong hemlock/white pine component, including black-capped chickadee (Poecile atricapillus), blue-headed vireo (Vireo solitaries), black-throated green warbler* (Setophaga virens), blackburnian warbler* (Setophaga fusca), brown creeper* (Certhia americana), Canada warbler* (Cardellina canadensis), dark-eyed junco (Junco hyemalis), hermit thrush (Catharus guttatus), magnolia warbler (Setophaga magnolia), northern flicker (Colaptes auratus), Swainson’s thrush* (Catharus ustulatus), winter wren* (Troglodytes hiemalis), and wood thrush* (Hylocichla mustelina; Sargent et al., 2017). *SGCN species

Threats

Eastern hemlock forms a significant component of Hemlock (white pine) – Northern Hardwood Forest. Hemlock woolly adelgid (HWA; Adelges tsugae) has resulted in significant hemlock mortality, and continued loss of hemlock could drastically alter the distribution and abundance of Hemlock (white pine) – Northern Hardwood Forests in Pennsylvania. Eastern hemlocks are also afflicted by the elongate hemlock scale (Fiorinia externa). This exotic pest tends to co-occur with HWA and has been found to cause tree death within 10 years (McClure, n.d.). Additionally, white pine is affected by white pine blister rust (Cronartium ribicola), which causes stem and branch cankers that result in tree mortality (Iverson et al., 2008). It is currently spread throughout Pennsylvania. Widespread hemlock mortality could result in replacement by white pine in some forests, or a transition to mixed deciduous-conifer forest. Hemlock (white pine) – Northern Hardwood Forests could experience significant changes to the composition or distribution in a changing climate. Some authors have suggested that species that are currently dominant in our northern hardwood forests spectrum, such as eastern hemlock, sugar maple, red maple, or black cherry, could become less common in both high and low emissions scenarios (Iverson et al., 2008). With component conifer and hardwood species potentially moving north, Hemlock (white pine) – Northern Hardwood Forest could become less common in a changing climate. Invasive plant species that threaten Hemlock (white pine) – Northern Hardwood Forests include garlic mustard (Alliaria petiolata) and Japanese barberry (Berberis thunbergii), among others. Throughout much of its range, Hemlock (white pine) – Northern Hardwood Forests may have experienced forest fragmentation from roads, shallow gas development, and habitat conversion. Furthermore, part of the range of the Hemlock (white pine) – Northern Hardwood Forest is found in the shale gas region in Pennsylvania. Development of the shale gas region may result in significant, additional fragmentation throughout the Hemlock (white pine) – Northern Hardwood Forest range in Pennsylvania and could negatively impact forest interior birds who depend on this conifer-dominated community type.

Management

Hemlock trees infested with HWA can be treated, but treatment is expensive (Forest Health Fact Sheet: Hemlock Woolly Adelgid, n.d.). As with any terrestrial forest management, forest conditions at a given location may require a specific plan to achieve management goals. Private landowners can consult with service foresters at the Pennsylvania Bureau of Forestry for more information on sustainable forest management practices that are best suited for their property. Management of invasive species is encouraged. Also, management of white-tailed deer could improve hardwood regeneration in forests experiencing a high level of herbivory.

Research Needs

Potential range shifts (north) for hemlock, sugar maple, cherry, birch, and beech, all of which are components of the Hemlock (white pine) – Northern Hardwood Forests, could result in a change in distribution and abundance of this community type in a changing climate (Bauer et al., 2016; Shortle et al., 2015). It is possible that oaks could replace some hardwood species in a changing climate and the relative abundance of oaks in Hemlock (white pine) – Northern Hardwood Forests should be assessed in contemporary examples of this community type to provide a baseline for oak occupancy in Pennsylvania forests.

Trends

Hemlock (white pine) – Northern Hardwood Forests account for 2.7% of mapped forested acreage on public lands and the majority of this acreage is found in the North Central Appalachians. Some historical data noted that hemlock had a strong presence in Allegheny National Forest around the time of European settlement (Lutz, 1930; Marquis, 1975). Marquis (1975) suggested white pine forests (which would be similar to the Hemlock (white pine) Forest classification) occurred in small patches across the landscape, and were less common than Hemlock-beech forests (similar to our Hemlock (white pine) – Northern Hardwood Forests classification). Other authors (Day, 1953; Lobeck, 1927) have suggested that white pine-dominated forests were most common in abandoned clearings, and in river terraces where sandy soil was common. Other component species of the Hemlock (white pine) – Northern Hardwood Forest, including beech, maple, birch, and white pine, accounted for about 88% of species observations, suggesting mixed stands of hemlock, white pine, and hardwoods were probably very common before European settlement.

Range Map

range map

Pennsylvania Range

The Hemlock (White Pine) – Northern Hardwood Forest is found in the following USEPA Level III (Level IV) Ecoregions: Northern Allegheny Plateau (60), Erie Drift Plain (61), North Central Appalachians (62), Ridge and Valley (67), Central Appalachians (69), Western Allegheny Plateau (70) and Eastern Great Lakes Lowlands (83).

Global Distribution

Maryland, New Jersey, New York, Pennsylvania, West Virginia, Connecticut, Massachusetts, Rhode Island, Virginia; Ontario

Bauer, A., Farrell, R., & Goldblum, D. (2016). The geography of forest diversity and community changes under future climate conditions in the eastern United States. Ecoscience, 23, 41-53.

Day, G. M. (1953). The Indian as an ecological factor in the northeastern forest. Ecology, 34, 327-346.

Forest Health Fact Sheet: Hemlock Woolly Adelgid. (n.d.). Pennsylvania Department of Conservation & Natural Resources. https://elibrary.dcnr.pa.gov/GetDocument?docId=1738100&DocName=sf-FrstHlthFactSheet-HWA.pdf

Iverson, L. R., Prasad, A. M., Matthews, S. N., & Peters, M. (2008). Estimating potential habitat for 134 eastern US tree species under six climate scenarios. Forest Ecology and Management, 254(3), 390-406.

Lobeck, A. K. (1927). A popular guide to the geology and physiography of Allegany State Park. New York State Museum Handbook.

Lutz, H. J. (1930). Original forest composition in northwestern Pennsylvania as indicated by early land survey notes. Journal of Forestry, 28(8), 1098-1103.

Marquis, D. A. (1975). The Allegheny hardwood forests of Pennsylvania. Gen. Tech. Rep. NE-15. Upper Darby, PA: US Department of Agriculture, Forest Service, Northeastern Forest Experiment Station. 32 p., 15.

McClure, M. S. (n.d.). Elongate Hemlock Scale (NA-PR-01-02; Pest Alert). United States Department of Agriculture Forest Service. https://www.forestpests.org/acrobat/EHScale.pdf

Sargent, S., Yeany III, D., Michel, N., & Zimmerman, E. (2017). Forest Interior Bird Habitat Relationships in the Pennsylvania Wilds, Final Report for WRCP-14507. Audubon Pennsylvania, National Audubon Society.

Shortle, J., Abler, D., Blumsack, S., Britson, A., Fang, K., Kemanian, A., Knight, P., McDill, M., Najjar, R., Nassry, M., Ready, R., Ross, A., Rydzik, M., Shen, C., Wardrop, D., & Yetter, S. (2015). Pennsylvania Climate Impacts Assessment Update. The Pennsylvania State University, University Park.

Cite as:
Braund, J., E. Zimmerman, A. Hnatkovich, and J. McPherson. 2022. Pennsylvania Natural Heritage Program. Hemlock (White Pine) – Northern Hardwood Forest Factsheet. Available from: https://naturalheritage.state.pa.us/Community.aspx?=16067 Date Accessed: April 24, 2024

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