Table 1. - Annual estimates, uncertainty, and change.

Figure 1. - Area of forest land and timberland by year.

Figure 2. - Area of forest land of the top six forest types

by stand-size class.

Pennsylvania’s Forest Resources, 2007 Research Note NRS-88

This publication provides an overview of forest resource attributes for Pennsylvania based on an annual inventory 

conducted by the Forest Inventory and Analysis (FIA) program at the Northern Research Station of the U.S. Forest 

Service. These annual estimates, along with web-posted core tables, will be updated annually. For more information, 

please refer to page 6 of this report.

1

Note: When available, sampling errors/bars provided in 

Figures and Tables represent 68 percent confidence intervals

Estimate 

(2007)

Sampling 

error (%)

Change(%) 

since 2004

Area (1,000 acres) 16,616 0.7 0.3

Number of live trees > 1-inch 

diameter (million trees) 8,312 1.6 -1.7

Dry biomass of live trees > 

1-inch diameter (1,000 tons) 1,005,743 1.0 3.6

Net volume of live trees > 

5-inch diameter (1,000,000 ft3

) 35,072 1.1 3.8

Annual net growth of live trees > 

5-inch diameter (1,000 ft3

/year) 847,645 3.2 N/A

Annual mortality of live trees > 

1-inch diameter (1,000 ft3

/year) 320,175 5.5 N/A

Harvest removals of live trees > 

1-inch diameter (1,000 ft3

/year) 416,848 9.5 N/A

Other removals of live trees > 

1-inch diameter (1,000 ft3

/year) 26,853 45.0 N/A

Timberland Estimates

Area (1,000 acres) 16,067 0.8 0.2

Number of growing-stock trees 

> 5-inch diameter (million trees) 6,935 1.8 -1.9

Dry Biomass of live trees > 

1-inch diameter (1,000 tons) 972,400 1.1 3.4

Net volume of live trees > 

5-inch diameter (1,000,000 ft3

) 33,894 1.2 3.6

Net volume of growing-stock 

trees (1,000,000 ft3

) 31,870 1.2 3.1

Annual net growth of growingstock trees (1,000 ft3

/year) 740,655 2.9 N/A

Annual mortality of growingstock trees (1,000 ft3

/year) 232,092 6.1 N/A

Harvest removals of growingstock trees (1,000 ft3

/year) 351,909 9.6 N/A

Other removals of growing-stock 

trees (1,000 ft3

/year) 59,262 34.8 N/A

Forest Land Estimates
Table 2. - Top 10 species by statewide volume estimates 2007.

2

Figure. 3. - Area of forest land by major owner group (2007) and size of family forest landholding (2006).

1 Red maple 6,529 2.6 5.0 15,287 3.9 8.7

2 Black cherry 3,606 4.2 2.2 11,169 5.6 2.7

3 Northern red oak 3,390 3.9 7.0 12,987 4.6 8.2

4 Chestnut oak 2,590 4.2 5.0 6,742 5.1 9.6

5 Sugar maple 2,559 4.7 2.1 7,078 6.0 2.7

6 Eastern hemlock 1,750 5.9 1.5 4,935 6.9 3.6

7 White ash 1,695 5.1 5.2 5,177 6.8 6.7

8 White oak 1,637 5.2 1.4 5,329 6.7 3.9

9 Yellow-poplar 1,528 7.9 7.1 6,205 9.0 9.4

10 Sweet birch 1,436 4.7 3.2 2,679 6.6 8.8

Other hardwoods 6,809 2.3 1.8 17,875 3.3 4.9

Other softwoods 1,543 6.6 8.0 4,845 7.7 11.3

All species 35,071 1.1 3.8 100,310 1.7 6.4

Change 

(%) 

since 

2004 

Volume of live 

trees on forest 

land 

(1,000,000 ft3

)

Change 

(%) 

since 

2004 

Volume of sawtimber 

trees on timberland 

(1,000,000 bdft)

Rank Sampling 

error 

(%)

Sampling 

error 

(%)

Species

Private forest land - 71 percent of all forest land. 

Public forest land - 29 percent of all forest land. 

Nonforest
Continuous Improvement Process for Volume, Biomass, and Carbon Estimation

Implementation of the annual inventory requires ongoing evaluation of existing methods and implementation of 

improved system components as they become available. Recently, significant changes were made to the 

methods for estimating tree-level volume and biomass (dry weight) for Northeastern states, and the calculation of 

change components (net growth, removals, and mortality) was modified for national consistency. These changes 

have focused on improving the ability to report consistent estimates across time and space--a primary objective 

for FIA.

Tree-level Volume Estimation

As the remeasurement phase of the annual inventory began, it became apparent that the 5-year measurement 

cycle was limiting the ability to track changes in volume over time because “noise” in the system outweighed the 

actual “signal” of the ecosystem. Sources of noise include: measurement variability, field protocol changes, field 

crew cohort changes, definition changes, processing algorithm changes, and model error. This noise impacts 

estimates of volume, biomass, carbon, and associated change component estimates.

Volume estimation is critically important because individual tree volume estimates form the basis for biomass and 

carbon estimates. In the past, estimates of individual tree gross volumes (cubic foot and board foot) were 

estimated using equations based on field-measured diameters and lengths (bole and saw log). Net volume of the 

tree was computed by subtracting field-measured cull (Scott 1981, Scott 1979). Over time, it was found that noise 

in the measurements of tree lengths and cull outweighed the true signal. To ameliorate this, a taper model was 

used to estimate length (Westfall and Scott 2010). In addition, a model was developed for determining the percent 

of total tree volume represented by cull. The modeled length and cull estimates are used in conjunction with 

Scott’s volume equations; thus providing a consistent estimation procedure across the Northeast. In general, the 

new volume estimates will be higher because previous estimates were based on length measurements that 

included reductions based on merchantability, e.g., prior to 2007, the measurement of the top of the bole may 

have been below the 4-inch top due to form deficiencies that prevents use for pulpwood. In 2007, the 

merchantability limits were removed from the field protocols. In conjunction with the removal of merchantability 

limits, changes in cull measurements were implemented, such that net tree volume would continue to represent 

only the merchantable portion of the tree. The modeled lengths and culls are aligned with these new 

measurement protocols.

Component Ratio Method (CRM) for Biomass/Carbon Estimation

Biomass and carbon have become increasingly important to FIA clients as demand for bio-energy has increased 

and carbon sequestration has emerged as a vital component of climate change analyses. As such, a method for 

harmonizing volume, biomass, and carbon estimates was needed. Prior to implementation of the CRM method, 

volume and biomass were estimated using separate sets of equations. The CRM method is comprised of the 

following steps (Heath and others 2009):

• Conversion of sound-wood volume in the merchantable bole to biomass using species-level specific gravities 

(dry mass per unit of green volume)

• Calculation of bark biomass using a set of percent bark and bark specific gravities

• Calculation of biomass in tops and limbs as a proportion of merchantable bole biomass based on component 

proportions using equations from Jenkins and others (2003)

• Calculation of stump biomass using equations from Raile(1982)

• Summation of biomass components to obtain total aboveground biomass

Estimates of carbon are derived through simple conversion of the biomass variables. 

3
Continuous Improvement Process for Volume, Biomass, and Carbon Estimation

Change Component Estimation

Change components are perhaps the most important volumetric variables reported by FIA because they are 

indicative of sustainability (net growth-to-removals ratio) and forest health (mortality). To summarize, gross growth 

is equal to ingrowth (volume of trees reaching the 5.0-inch minimum diameter threshold for merchantable volume) 

plus accretion (growth of surviving trees that were above the threshold at previous measurement). Net growth is 

equal to gross growth minus mortality (volume of trees meeting the threshold at previous measurement that died). 

Removals are equal to the volume of trees meeting the threshold at the previous measurement that were 

harvested or on forest land that changed to nonforest land. Net change in inventory is equal to net growth minus 

removals.

The National Inventory Management System (NIMS) is the compilation system for all FIA estimates. 

Implementation of NIMS has included some adjustments to regional change-component algorithms to achieve 

national consistency. A new method, termed the “midpoint method”, has introduced some fundamental differences 

in methods (Westfall and others 2009). Essentially, the new approach involves growing trees to the midpoint of 

the inventory cycle (2.5 years for a 5-year cycle). Although the overall net change component is equivalent under 

the previous and new theory evaluations, estimates for individual components will be different. For ingrowth, the 

midpoint method produces a smaller estimate because volumes are calculated at the 5.0-inch threshold instead of 

using the actual diameter measurement, which may be larger. The estimate for accretion is higher because 

growth on ingrowth, mortality, and removal trees is included. As such, the removals and mortality estimates will 

also be higher than before.

4
Bechtold, W.A., Patterson, P.L., eds. 2005. The enhanced Forest Inventory and Analysis Program: 

national sampling design and estimation procedures. Gen. Tech. Rep. SRS-80. Asheville, NC: U.S. 

Department of Agriculture, Forest Service, Southern Research Station. 85 p.

Heath, L.S.; Hansen, M.H.; Smith, J.E.; Smith, W.B.; Miles, P.D. 2009. Investigation into calculating tree 

biomass and carbon in the FIADB using a biomass expansion factor approach. In: McWilliams, W.; 

Moisen, G.; Czaplewski, R., comps. 2008 Forest Inventory and Analysis (FIA) Symposium; 2008 October 

21-23; Park City, UT. Proc. RMRS-P-56CD. Fort Collins, CO: U.S. Department of Agriculture, Forest 

Service, Rocky Mountain Research Station. CD.

Jenkins, J.; Chojnacky, D.C.; Heath, L.S.; Birdsey, R.A. 2003. National scale biomass estimators for 

United States tree species. Forest Science. 49(1): 12-35.

Raile, G.K. 1982. Estimating stump volume. Res. Paper NC-224. St. Paul, MN: U.S. Department of 

Agriculture, Forest Service, North Central Research Station. 4 p.

Smith, J.E.; Heath, L.S.; Skog, K.E.; Birdsey, R.A. 2006. Methods for calculating forest ecosystem and 

harvested carbon with standard estimates for forest types of the United States. Gen. Tech. Rep. NE343. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northeastern Research Station. 

216 p.

Scott, C.T. 1981. Northeastern forest survey revised cubic-foot volume equations. Res. Note NE-304. 

Broomall, PA: U.S. Department of Agriculture, Forest Service, Northeastern Forest Experiment Station. 2 p.

Scott, C.T. 1979. Northeastern forest survey board-foot volume equations. Res. Note NE-271. 

Broomall, PA: U.S. Department of Agriculture, Forest Service, Northeastern Forest Experiment Station. 2 p.

Smith, W.B. 2002. Forest inventory and analysis: a national inventory and monitoring program. 

Environmental Pollution. 116: 233-242.

USDA Forest Service. 2009. Forest inventory and analysis national core field guide, Vol. 1, field data 

collection procedures for Phase 2 plots, Ver. 5.0. Available at www.fia.fs.fed.us/library/field-guidesmethods-proc(verified July 2009). 

Westfall, J.A., Scott., C.T. (in press) Taper equations for commercial tree species in the Northeastern 

U.S. Forest Science.

Westfall, J.A.; Frieswyk, T.; Griffith, D.M. 2009. Implementing the measurement interval midpoint 

method for change estimation. In: McRoberts, R.E.; Reams, G.A.; Van Deusen, P.C.; McWilliams, W.H., 

eds. Proceedings of the Eighth Annual Forest Inventory and analysis symposium; 2006 October 16-19; 

Monterey, CA. Gen. Tech. Rep. WO-79. U.S. Department of Agriculture, Forest Service: 231-236.

FIA Program Information

McCaskill, G.L.; McWilliams, W.H.; Butler, B.J.; Meneguzzo, D.M.; Barnett, C.J.; Hansen, M.H. 2011. 

Pennsylvania’s forest resources, 2007. Res. Note NRS-88. Newtown Square, PA: U.S. Department of 

Agriculture, Forest Service, Northern Research Station. 6 p.

Citation for this Publication

5
The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, 

color, national origin, age, disability, and where applicable, sex, marital status, familial status, parental status, religion, 

sexual orientation, genetic information, political beliefs, reprisal, or because all or part of an individual’s income is derived 

from any public assistance program (Not all prohibited bases apply to all programs.) Persons with disabilities who require 

alternate means for communication of program information (Braille, large print, audiotape, etc.) should contact USDA’s 

TARGET Center at (202) 720-2600 (voice and TDD). To file a complaint of discrimination, write to USDA, Director, Office of 

Civil Rights, 1400 Independence Avenue, S.W., Washington, DC 20250-9410, or call (800)795-3272 (voice) or (202)720-

6382 (TDD). USDA is an equal opportunity provider and employer.

Contact Information

Pennsylvania Analyst: Will McWilliams(610) 557-4050 wmcwilliams@fs.fed.us

Data acquisition / web sites: Carol L. Alerich, 610-557-4068, calerich@fs.fed.us

Website: fiatools.fs.fed.us

Additional Pennsylvania Inventory Information

6

Ferguson, Roland H. 1955. The timber resources of Pennsylvania. Upper Darby, PA: U.S. Department of 

Agriculture, Forest Service, Northeastern Forest Experiment Station. 46 p.

Ferguson, Roland H. 1968. The timber resources of Pennsylvania. Res. Bull. NE-8. Upper Darby, PA: U.S. 

Department of Agriculture, Forest Service, Northeastern Forest Experiment Station. 145 p.

Considine, Thomas J.; Powel, Douglas S. 1980. Forest statistics for Pennsylvania, 1978. Res. Bull. NE-65. 

Broomall, PA: U.S. Department of Agriculture, Forest Service, Northeastern Forest Experiment Station. 88 p.

Alerich, Carol L. 1993. Forest statistics for Pennsylvania, 1978 and 1989. Res. Bull. NE-126. Radnor, PA: U.S. 

Department of Agriculture, Forest Service, Northeastern Forest Experiment Station. 244 p.

Widmann, Richard H. 1995. Forest Resources of Pennsylvania . Res. Bull. NE-131. Radnor, PA: U.S. 

Department of Agriculture, Forest Service, Northeastern Forest Experiment Station. 41 p.

McWilliams, William H.; Stout, Susan L.; Bowersox, Todd W.; McCormick, Larry H. 1995. Advance tree-seedling 

regeneration and herbaceous cover in Pennsylvania forests. Northern Journal of Applied Forestry. 12(4): 

187-191.

McWilliams, William H.; Cassell, Seth P.; Alerich, Carol L.; et al. 2007. Pennsylvania's forest 2004. Res. Bull. 

NRS-20. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station. 86 p.