Scrub Oak Shrubland

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System: Terrestrial
Subsystem: Shrubland
PA Ecological Group(s): Central Appalachian – Northeast Pine – Oak Rocky Woodland

Global Rank:G4 rank interpretation
State Rank: S4

General Description

This community type occurs either on sandy soils or on thin soils over bedrock. Conditions are dry; soils are acidic. It most commonly occurs on rocky ridgetops in eastern Pennsylvania on the Pocono Plateau. Scrub oak (Quercus ilicifolia) is the dominant shrub species, although low shrubs like low sweet blueberry (Vaccinium angustifolium), lowbush blueberry (V. pallidum), teaberry (Gaultheria procumbens), sheep laurel (Kalmia angustifolia), black huckleberry (Gaylussacia baccata), Appalachian sand cherry (Prunus pumila var. susquehanae), dwarf chestnut oak (Quercus prinoides), and sweet-fern (Comptonia peregrina) sometimes occur beneath the taller shrub stratum. Tree species may occur as scattered individuals or as small patches of woodland. Characteristic tree species include quaking aspen (Populus tremuloides), chestnut oak (Quercus montana), and pitch pine (Pinus rigida). Herbs include northern oatgrass (Danthonia compressa), bracken fern (Pteridium aquilinum), cow-wheat (Melampyrum lineare), little bluestem (Schizachyrium scoparium), common hair grass (Deschampsia flexuosa), and orange-grass (Hypericum gentianoides). This community type may occur as part of the Ridgetop Acidic Barrens Complex.

The Scrub Oak Shrubland occurs most commonly within the Pocono Plateau, from Schuylkill County east to the Delaware Water Gap. There are also mapped occurrences in the Central Appalachians from Center County south to Bedford and Fulton Counties. These shrublands may represent a different community entirely and be more representative of the Pitch Pine – Scrub Oak Woodland or represent sites where frequent or recent disturbance has removed the tree layer. The Scrub Oak Shrubland community also includes most of what is referred to as Sand Barrens. Sand barrens in Pennsylvania are found primarily in Huntingdon and Centre counties. Sand barrens are areas of sandy (Morrison series) infertile soils that form extensive, gently rolling expanses of mostly scrub oak with occasional patches of blueberries (Low Heath Shrubland) and grassy frost pockets (Little bluestem – Pennsylvania Sedge Opening).

Rank Justification

This community type typically occurs in small- to medium-sized patches as a part of the Ridgetop Acidic Barrens Complex, however, can also occur in large patches. This community type is threatened by development and recreation and is vulnerable to forest succession without active management.

Identification

  • Greater than 25% shrub cover
  • Less than 10% tree cover (woody species > 5 m tall)
  • Scrub oak is the dominant shrub species
  • Occurs on dry, sandy, acidic soils

* 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:

Ridgetop Bear Oak Barrens (CEGL006121)

NatureServe Ecological Systems:

None

NatureServe Group Level:

Central Appalachian - Northeast Pine - Oak Rocky Woodland (G906)

Origin of Concept

Fike, J. 1999. Terrestrial and palustrine plant communities of Pennsylvania. Pennsylvania Natural Diversity Inventory. Pennsylvania Department of Conservation and Recreation, Bureau of Forestry, Harrisburg, PA. 86 pp.

Largay, E. and S. C. Gawler. 2006. Ridgetop Bear Oak Barrens (CEGL006121). NatureServe Explorer [web application]. NatureServe, Arlington, Virginia. Available https://explorer.natureserve.org/. (Accessed: January 14, 2022).

Pennsylvania Community Code*

KA : Scrub Oak Shrubland

*(DCNR 1999, Stone 2006)

Similar Ecological Communities

The Scrub Oak Shrubland may occur alongside others in the Ridgetop Acidic Barrens Complex. The barrens types represent a group of communities with open-canopies found on high elevation ridgetops and summits (350m – 670m), where low soil moisture, shallow soils, high wind velocities, frequent fires, and usually a history of cutting have limited tree growth.

The Scrub Oak Shrubland is most similar to the Low Heath Shrubland, but it is not clearly dominated by scrub oak and has a greater cover of heath species in the shrub layer. The Little Bluestem – Pennsylvania Sedge Opening has similar species composition but will have less than 10% shrub cover, and it may occur in small openings amongst the shrub dominated types. If the tree cover (>5 m tall) is greater than 10%, see the Pitch Pine – Scrub Oak Woodland as it has a similar understory species composition.

This community often co-occurs with several other types in the Ridgetop Acidic Barrens Complex:

  • Dry Oak – Rocky Woodland 
  •     
  • Red Spruce Rocky Summit (rare; confined to high elevations) 
  •    
  • Scrub Oak Shrubland 
  •    
  • Low Heath Bedrock Outcrop (confined to high elevation)  
  • Little Bluestem – Pennsylvania Sedge Opening  
  • Pitch Pine – Heath Woodland  
  • Pitch Pine – Scrub Oak Woodland

The communities that create the Ridgetop Acidic Barrens Complex form a mosaic that are related by successional stage. The herbaceous types occur more sporadically throughout shrubland, woodland, and forest types based on time since fire, clearcutting, or other disturbance. The arrangement of different types within a site, and the pace of succession, is also determined by differences in environmental variables such as aspect, soil depth, elevation, exposure, and microclimate. In general, the physiognomy becomes more open at higher elevations and on southern exposures. Where fires are frequent, pitch pine will typically be present. In the absence of fire, other pines (white pine, Virginia pine, shortleaf pine, or Table Mountain pine) may accompany or replace pitch pine, or pine may be absent altogether. Frost pockets may play a role in maintaining open areas; this is especially true of the Little Bluestem – Pennsylvania Sedge Opening type. Long-term fire suppression may cause the distinctive vegetation of the herbaceous openings to give way to more mesic species typical of the surrounding forests at lower elevations.  

The forest types that most typically surround these communities are the Dry Oak – Heath Forest and Pitch Pine – Mixed Oak Forest.

Fike Crosswalk

Scrub Oak Shrubland

Conservation Value

Acidic barrens communities can host a number of rare plant species and an exceptional diversity of rare butterflies, moths, and other insects. Barrens communities can arise as a result of a variety of human-induced and natural disturbances; many have their origin in the 19th or 20th century, while others have persisted longer through a combination of periodic human-induced disturbance dating to pre-settlement times and edaphic factors (Copenheaver et al., 2000; Kurczewski, 1999; Latham, 2003; Motzkin & Foster, 2002). Latham (2003) suggests that the diversity and presence of rare plant species in barrens is correlated with the overall age of the barrens, with newer barrens less likely to host rare plants. Animal diversity appears to be less sensitive to age; perhaps because many of these species are highly mobile.

Both plant and lepidopteran species can be sensitive to successional stage and time since disturbance; some require very open, grassy areas, while others can also inhabit shrublands and woodlands with partial shade. The species of conservation value are not necessarily indicator species for the community type, and may also occupy other types of habitat, but barrens sites are one of the habitats important for their conservation.

Species of great conservation value that are associated with barrens include many species of Lepidoptera (moths and butterflies) which have barrens plants as hosts, plants that can withstand the acidic, thin soils, and vertebrate species who thrive with hot, dry conditions. Examples of invertebrates that can be found in barrens include waxed sallow moth (Chaetaglaea cerata; G3G4/S2S3), twilight moth (Lycia rachelae; G5/S2?), and flypoison borer moth (Papaipema sp. 1; G2G3/S2S3). The timber rattlesnake (Crotalus horridus; G4/S2S3) and eastern hognose snake (Heterodon platirhinos; G5/S3S4) can utilize barrens. A few plant species that are associated with barrens include variable sedge (Carex polymorpha; G3/S2), dwarf iris (Iris verna; G5/S1), and sand blackberry (Rubus cuneifolius; G5/S1).

Threats

The primary threats to acidic barrens communities are succession and fire suppression. Many of the unique species that inhabit these barrens are most successful in the early stages of succession, such as grasslands and open shrublands, and are therefore particularly vulnerable to the effects of succession over the long-term. Pitch pine are known to not germinate and establish well without fire.

Spongy moth (Lymantria dispar) outbreaks also threaten barrens, which often have a strong component of oak species in the tree and shrub layers. However, spongy moth control agents can also threaten the unique butterfly and moth species that inhabit barrens.

Studies across a number of sites in New England and Pennsylvania demonstrate that many barrens are disturbance-dependent ecosystems that, in the absence of disturbance, move through succession to forest rapidly (Copenheaver et al., 2000; Kurczewski, 1999; Latham, 2003; Motzkin & Foster, 2002). These studies have observed similar patterns of barrens succession to forest, sometimes even mesic forest, in recent decades.

Changes in land use and fire suppression over the last century are at the root of these patterns of succession. Through meticulous efforts to identify historic land use and changes in vegetation over time, researchers have documented that barrens are correlated with areas that burned frequently; primarily from Native American use of fire and railroads. The cessation of these land use practices, and the advent of widespread, long-term fire suppression, is correlated with succession of grasslands and open shrublands to dense shrub thickets and forests. Charcoal production retards vegetation such that former hearths resemble barrens, but it appears the mechanism is a more profound and persistent alteration of soil chemistry.

This community type is threatened by development and recreation. Sites supporting this community are attractive locations for wind farm and communication tower sites. Hiking and other low impact recreational activities are usually confined to trails and are therefore not a major threat to this type. Illegal ATV activity may occur as sites supporting this type are often remote and difficult to patrol. ATV damage may facilitate invasion by non-native plants.

Management

It is important to develop a site-wide management plan at acidic barrens to maintain multiple successional stages. Fire is the optimal tool for barrens management. Where it is not feasible to use fire as a management tool, a combination of cutting and soil scarification can be used to mimic its effects.

Plans should also consider specific needs of barrens indicator species and rare species. To avoid severe reduction of lepidopteran populations, prescribed burning should not be undertaken across an entire site at once; in a given year, unburned areas should be left as refugia for these species.

Spongy moth control programs should balance maintenance of oaks and lepidopterans, using control agents specific to the spongy moth where possible, or leaving some untreated areas as refugia for native lepidopteran populations.

Recreation management, specifically management of illegal ATV activity, is needed at specific locations that harbor rare species.

Research Needs

Site-specific research into historical land management, fire frequency, and vegetation patterns has greatly enhanced understanding of barrens systems at other locations in the northeastern region, but very few Pennsylvania sites have been studied. The origins and timeline of many of our barrens sites in Pennsylvania remains unknown.

There is a need to adapt and/or develop management techniques specialized to this region and its species of concern. In some areas, barrens have completely succeeded to forest. Research should focus on identifying specifically where shrub and herbaceous barrens once existed, identifying characteristics of optimal restoration sites, and identifying successful management techniques for restoring the herbaceous and shrub component of barrens mosaics.

Trends

Barrens ecosystems have declined due to succession and fire suppression in recent decades. Rare species that are particularly dependent on open barrens habitats have also declined across Pennsylvania. 

Range Map

range map

Pennsylvania Range

The Scrub Oak Shrubland is found in the following USEPA Level III (Level IV) Ecoregions: North Central Appalachians (62), Ridge and Valley (67) and Central Appalachians (69).

Global Distribution

Connecticut, Massachusetts, New Jersey, New York, Pennsylvania

Copenheaver, C. A., White, A. S., & William A. Patterson III. (2000). Vegetation Development in a Southern Maine Pitch Pine-Scrub Oak Barren. Journal of the Torrey Botanical Society, 127(1), 19-32.

Illick, J. S., and Aughanbaugh, J. E. 1930. Pitch pine in Pennsylvania. Pa. Dept. Forests and Waters Res. Bul. 2.

Latham, R. E. (2003). Shrubland longevity and rare plant species in the northeastern United States. Forest Ecology and Management, 185(1-2), 21-39. https://doi.org/10.1016/S0378-1127(03)00244-5

Ordnorff, S., & Patten, T. (Eds.). (2007). Management Guidelines for Barrens Communities in Pennsylvania (p. 208). The Nature Conservancy.

Perles, S., G. S. Podniesinski, E. Eastman, L. A. Sneddon, and S. C. Gawler. “Classification and Mapping of Vegetation and Fire Fuel Models at Delaware Water Gap National Recreation Area: Volumes 1 and 2. Technical Report NPS/NER/NRTR—2007/076.” National Park Service, U.S. Department of the Interior. Philadelphia, PA, 2007.

Perles, S., M. Furedi, B. Eichelberger, A. Feldman, G. J. Edinger, E. Eastman, and L. A. Sneddon. “Vegetation Classification and Mapping at Upper Delaware Scenic and Recreational River. Natural Resource Technical Report. Technical Report NPS/NER/NRTR—2008/133.” National Park Service, U.S. Department of the Interior. Philadelphia, PA, 2008.

Schweitzer, D.F. & Rawinski, T.J. (1987) Northeastern pitch pine ⁄ scrub oak barrens. Eastern heritage task force. The Nature Conservancy, Boston, MA.

Cite as:
Braund, J., E. Zimmerman, A. Hnatkovich, and J. McPherson. 2022. Pennsylvania Natural Heritage Program. Scrub Oak Shrubland Factsheet. Available from: https://www.naturalheritage.state.pa.us/Community.aspx?=16086 Date Accessed: May 19, 2024

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