National Weather Service.  2011.  Mid Atlantic Winters.

National Weather Service.  2011.  Washington winters.

National-Park-Service US-DOI.  2009.  Curriculum Based Program: Once upon a time, life at the Peirce Mill Plantation.

NatureServe.  1994.  International Vegetation Classification: A Catalogue of Global Ecosystem Diversity.

NatureServe.  2014.  NatureServe Explorer: An online encyclopedia of life.

NatureServe.  2009.  NatureServe Explorer: An online encyclopedia of life. (issue)

Nerurkar JD.  1974.  Plant communities on a quartzite ridge in Chester County, Pennsylvania. Proceedings of the Pennsylvania Academy of Science . 48:101-106

NOAA.  2015.  Comparative Climatic Data For the United States Through 2015.

O'Connor JV.  1989.  Geology of Rock Creek Park South. American Geophysical Union Guidebook T-208.

Orwig DA, Abrams MD.  1994.  Contrasting radical growth and canopy recruitment patterns in Liriodendron tulipifera and Nyssa sylvatica: Gap obligate versus gap facultative tree species. Canadian Journal of Forest Research. 24:2141-2149

Overlease WR.  1978.  A study of forest communities in southern Chester County, Pennsylvania. Proceedings of the Pennsylvania Academy of Science 52:37-44.

Parsons J.  2008.  Plant Answers.

Patchen D.G., Avary K.L.  1986.  Harpers Ferry Water Gap. Centennial Field Guide. 6:201-206.

Patterson KD.  Submitted.  Personal communication.

Pavek D.  2002.  Endemic amphipods in our nation’s capital. Endangered Species Bulletin. 27(1):8-9

Penn State.  2006.  Deer-free Areas May Be Haven For Ticks, Disease.

Pennsylvania Department of Conservation and Natural Resources.  2008.  Forest Health Fact Sheet: Beech Bark Disease .

Perkey A, Wilkins B, Smith HC.  1993.  Managing wildlife crop trees. Crop tree management in eastern hardwoods.

Pfanz H.  2008.  Bark photosynthesis. Trees —Structure and Function. 22(2):137-138

Raven PH, Evert RF, Curtis HA.  1981.  The Biology of Plants.

Rawinski TJ, Hickman KN, Waller-Eling J, Fleming GP, Austin CS, Helmick SD, Huber C, Kappesser G, Huber Jr. FC, Bailey T et al..  1996.  Plant communities and ecological land units of the Glenwood Ranger District, George Washington and Jefferson national forests, Virginia.

Rawinski TJ, Fleming GP, Judge FV.  1994.  Forest vegetation of the Ramsey's Draft and Little Laurel Run Research Natural Areas, Virginia: Baseline ecological monitoring and classification.

Richter D, Spielman A, Komar N, Matuschka F-R.  2000.  Competence of American Robins as reservoir hosts for Lyme Disease Spirochetes. Emerging Infectious Diseases. 6:2 March-April 2000. pp 133-138

Riedman M, Nortrup M.  2014.  NCRN Resource Brief: American Chestnut Inventory, Harpers Ferry NHP.

Robichaud B, Buell MF.  1973.  Vegetation of New Jersey.