Hemlock (White Pine) red oak mixed hardwood forest

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

Global Rank:G4 rank interpretation
State Rank: S4

Hemlock (White Pine)  red oak mixed hardwood forest
Hemlock (White Pine) red oak mixed hardwood forest, PNHP

General Description

Conifers such as eastern hemlock (Tsuga canadensis) and white pine (Pinus strobus) may be scattered, locally abundant, or may dominate the subcanopy. Red oak (Quercus rubra) is usually present, often dominant/codominant, most often with red maple (Acer rubrum), black oak (Quercus velutina), white oak (Q. alba), bitternut hickory (Carya cordiformis), sweet bitch (Betula lenta), white ash (Fraxinus americana), American beech (Fagus grandifolia), and tuliptree (Liriodendron tulipifera). Shrubs include maple-leaved viburnum (Viburnum acerifolium), shadbush (Amelanchier arborea), ironwood (Carpinus caroliniana), hop-hornbeam (Ostrya virginiana), witch-hazel (Hamamelis virginiana), and spicebush (Lindera benzoin). Herbaceous species include false Solomon’s-seal (Maianthemum racemosum), Solomon’s seal (Polygonatum biflorum), teaberry (Gaultheria procumbens), Canada mayflower (M. canadense), and may-apple (Podophyllum peltatum).

Rank Justification

This type is widespread throughout Pennsylvania but not common. It is presently mapped at about 1.3% of public land, with some of the largest occurrences being over 200 acres. Invasive insect pests for the eastern hemlock and white pine are serious threats to this type. Some tree species in this type may experience range shifts due to climate change, which would alter this type.


  • At least 25% canopy cover from hemlock or white pine
  • More oak and hickory species than other hardwoods
  • Herbaceous layer is typically sparse
  • Species composition reflects a northern affinity and can be slightly richer than Hemlock (white pine) – Northern Hardwood Forests

* 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:


Representative Community Types:

Red Oak - Hemlock - Mixed Hardwood Forest (CEGL006566)

NatureServe Ecological Systems:

Appalachian (Hemlock) – Northern Hardwood Forest (CES202.593)

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.

Sneddon, L. A. 2006. Red Oak - Hemlock - Mixed Hardwood Forest (CEGL006566). NatureServe Explorer [web application]. NatureServe, Arlington, Virginia. Available https://explorer.natureserve.org/. (Accessed: March 2, 2022).

Pennsylvania Community Code*

FR : Hemlock (white pine) - Red Oak - Mixed 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 an oak/northern 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) – Northern Hardwood Forest is also similar, but has less red oak/hickory in the canopy and subcanopy, and often has a less diverse shrub and/or groundcover layer. The Red Oak – Northern Hardwood Forest may also be similar to this type; however the Hemlock (white pine) – Red Oak – Northern Hardwood Forest will have greater cover of hemlock and white pine comparatively.

Fike Crosswalk

Hemlock (white pine) – Red Oak – Mixed Hardwood Forest

Conservation Value

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).


Eastern hemlock (Tsuga canadensis) forms a significant component of Hemlock (white pine) – Red Oak – Mixed Hardwood Forests. 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 this type in Pennsylvania. Eastern hemlocks are also affected 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 (Peters et al., 2020). It is currently spread throughout Pennsylvania. Wide-spread hemlock mortality could result in replacement by white pine in some forests, or a transition to mixed deciduous-conifer forest. Hemlock (white pine) – Red Oak – Mixed 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). Climate change models are showing mixed results with red oak and have shown both the possibility that it could remain stable or become more common. With component conifer and hardwood species potentially moving north, Hemlock (white pine) – Red Oak – Mixed Hardwood Forests could become less common in a changing climate, and potentially transition to Red Oak – Mixed Hardwood Forests, which lack high relative cover from hemlock and white pine. Throughout much of its range, Hemlock (white pine) – Red Oak – Mixed 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) – Red Oak – Mixed Hardwood Forest is found in the shale gas region in Pennsylvania. Development of the shale gas region may result in additional fragmentation throughout range in Pennsylvania, and could negatively impact forest interior birds who depend on this conifer-dominated community type. Invasive plant species such as garlic mustard (Alliaria petiolata) and Japanese barberry (Berberis thunbergii), among others, are also a threat to this type. LDD (Lymantria dispar dispar) also poses a significant threat to the health of oak forests, however annual surveys and spray programs continue throughout the state. The spotted lanternfly (Lycorma delicatula) is newly established in Pennsylvania and has been found to lay eggs and feed on a number of common hardwood trees in Pennsylvania but has not been found to cause tree mortality (Barringer & Ciafré, 2020).


Hemlock trees infested with Hemlock woolly adelgid (HWA; Adelges tsugae) 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 high levels 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) – Red Oak – Mixed 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). Oaks could replace some hardwood species with climate change, making red oak – dominated forest more common across the Commonwealth.


Hemlock (white pine) – Red Oak – Mixed Hardwood Forests account for just less than 1% of mapped forested acreage on public lands. The majority of this acreage is found in the North Central Appalachians (about 13,000 acres), followed by the Ridge and Valley (about 12,000 acres). Many studies (Abrams & Ruffner, 1995; Black et al., 2006; Johnson, 2013) have used historical vegetation records to determine that oak-dominated forests were common prior to European settlement. Some authors have suggested that red oak and other species, such as red maple and chestnut oak, may be replacing historically dominant species, such as white oak and American chestnut in the absence of fire or other disturbance in certain ecoregions (Abrams, 1992, 2003; Abrams & Nowacki, 1992; Abrams & Ruffner, 1995; Nowacki & Abrams, 2008; Signell et al., 2005). Other authors who have researched common trees prior to European settlement have concluded that eastern hemlock had a strong presence in the Allegheny National Forest, and hemlock-beech forests (similar to our Hemlock (white pine) – Northern Hardwood Forest classifications) were also common (Lutz, 1930; Marquis, 1975). Other component species of the Hemlock (white pine) – Red Oak – Mixed Hardwood Forest, including beech, maple, birch, white pine, and chestnut, accounted for about 88% of species observations in the Allegheny National Forest region historically. This suggests mixed stands of hemlock, white pine, and hardwoods were probably very common before European settlement. These species are typically sensitive to periodic fires, so it is possible that the Hemlock (white pine) – Red Oak – Mixed Hardwood Forest may have become more common as a result of fires suppression in the mid to late 1900’s.

Range Map

range map

Pennsylvania Range

The Hemlock (white pine) – Red Oak – Mixed Hardwood Forest is found in the following USEPA Level III (Level IV) Ecoregions: Northern Allegheny Plateau, Erie Drift Plain, Northern Central Appalachians, Northern Piedmont, Blue Ridge, Ridge and Valley, Central Appalachians and Western Allegheny Plateau.

Global Distribution

New Jersey, New York, Pennsylvania, Vermont

Abrams, M. D. (1992). Fire and the development of oak forests. BioScience, 42(5), 346–353.

Abrams, M. D. (2003). Where has all the white oak gone? BioScience, 53(10), 927–939.

Abrams, M. D., & Nowacki, G. J. (1992). Historical Variation in Fire, Oak Recruitment, and Post-Logging Accelerated Succession in Central Pennsylvania. Bulletin of the Torrey Botanical Club, 119(1), 19. https://doi.org/10.2307/2996916

Abrams, M. D., & Ruffner, C. M. (1995). Physiographic analysis of witness-tree distribution (1765–1798) and present forest cover through north central Pennsylvania. Canadian Journal of Forest Research, 25(4), 659–668. https://doi.org/10.1139/x95-073

Barringer, L., & Ciafré, C. M. (2020). Worldwide feeding host plants of spotted lanternfly, with significant additions from North America. Environmental Entomology, 49(5), 999–1011.

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.

Black, B. A., Ruffner, C. M., & Abrams, M. D. (2006). Native American influences on the forest composition of the Allegheny Plateau, northwest Pennsylvania. Canadian Journal of Forest Research, 36(5), 1266–1275

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.

Johnson, S. E. (2013). Native American land use legacies in the present day landscape of the Eastern United States. Ph.D. Dissertation. Pennsylvania State University.

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

Nowacki, G. J., & Abrams, M. D. (2008). The demise of fire and “mesophication” of forests in the Eastern United States. Bioscience, 58, 123–138.

Peters, M. P., Prasad, A. M., Matthews, S. N., & Iverson, L. R. (2020). Climate change tree atlas, Version 4. U.S. Forest Service, Northern Research Station and Northern Institute of Applied Climate Science, Delaware, OH. https://www.fs.fed.us/nrs/atlas/tree/

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.

Signell, S. A., Abrams, M. D., Hovis, J. C., & Henry, S. W. (2005). Impact of multiple fires on stand structure and tree regeneration in central Appalachian oak forests. Forest Ecology and Management, 218(1–3), 146–158. https://doi.org/10.1016/j.foreco.2005.07.006

Cite as:
Braund, J., E. Zimmerman, A. Hnatkovich, and J. McPherson. 2022. Pennsylvania Natural Heritage Program. Hemlock (White Pine) red oak mixed hardwood forest Factsheet. Available from: https://www.naturalheritage.state.pa.us/Community.aspx?=16068 Date Accessed: May 22, 2024

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