Wow! Pennsylvania is full of trees!

Posted: October 23, 2013

As reported in the recent USDA Forest Service forest inventory publication, trees and forests still dominate Pennsylvania’s landscape, but there are changes: total forestland is holding stable, but land being converted is going more and more to unrecoverable uses; invasive pests, diseases, and plants are significant threats; and adequate forest regeneration to establish the next generation of trees is absent on many sites.

Literally Pennsylvania means Penn’s Woods. A grant from King Charles II to William Penn in March 1681 established the colony founded on Quaker principles for religious freedom. Sylvania is a Latin word that means “forest land.” Penn recognized the value of the Pennsylvania forests and, shortly after receiving the grant as payment of debt owed his father, issued his Charter of Rights. In this document he ordered colonists to leave one acre of trees for every five acres of land cleared.

As reported in the recent USDA Forest Service forest inventory publication, trees and forests still dominate Pennsylvania’s landscape. In the past statewide forest inventories conducted by the US Forest Service were periodic -- every 10 to 15 years. Starting in 2004 the data are collected annually and reported on a five year cycle. The most recent 2012 report on Pennsylvania’s Forests (2009 data) provides useful insights into the health and condition of the state’s woodlands.

Pennsylvania’s forest land area is stable, with some parts of the state gaining while others are losing forest cover. This has been the case since the mid-1960s as the forest recovered from heavy cutting in the late 1800s and early 1900s. Land use patterns suggest that the forest land area stability is a function of offsetting of development in the southern tier as agriculture declines in the northern tier counties. The amount of forest cover has relatively constant at about 59 percent or about 16.7 million acres.

Most of this forest land, about 71 percent, is held privately by individuals, families, partnerships, and other entities not in the business of harvesting and using trees. A recent Penn State study estimated there are 738,000 individual private ownerships in the state. Most of these ownerships are small parcels; oftentimes, they come with the home. In fact, about 420,000 of these ownerships are smaller than 10 acres, and about 25 percent of the private forest is in ownerships of less than 20 acres. Statewide there are only about 25,000 privately owned forest tracts larger than 100 acres in size. This study and others suggest that the average size of our privately owned forest is decreasing.

Just how many trees are there in Pennsylvania’s forests and woodlands? First, forest, by the USDA Forest Service definition, has to be at least an acre in size, with a minimum width of 120 feet (fencerows and narrow strips don’t count), have tree cover of at least 10 percent, and not be maintained as lawn. Using this as the basis for the count, there were an estimated 8,168,796,257 trees one inch and larger measured at diameter breast height (a foresters term for measuring the diameter 4.5 feet above the ground abbreviated DBH) growing in our woodlands. In absolute terms, this is about 3.4 percent fewer trees than we had in 2004. Most of these trees (68.2%) were 4.9 inches or smaller DBH, trees 5 and up to 11.9 inches DBH represented about one of four trees (25.6%), and the remaining trees were 12 inches and larger (6.2%).

While the number of trees might have dropped a small amount, the estimated volume of trees growing in the state increased. Between 2004 and 2009, the average volume per acre of Pennsylvania forest increased by 60 cubic feet from 2,138 to 2,198 cubic feet. If you consider this from a cordwood perspective, that means that the average acre of woodlands in the state now holds about 27 cords of wood and increased in volume by just under a cord in the five years between inventories. A cord, by the way, measures 4 feet X 4 feet X 8 feet and contains 128 cubic feet of volume, but only about 80 cubic feet of this volume is actually wood. Hence, if you are familiar with the cord measure, you might have questioned this math.

From a removal perspective, Pennsylvania is still growing more wood than it uses. Forest industry harvests trees for many uses and it is a major part of the state’s rural economy. The 2009 data finds that the growth to remove ratio is 2:1 for timberland – the forest is growing twice as much than is harvested. Specifically, the overall growth-to-removals for public and private ownerships were 2.7:1 to 1.8:1 respectively. Stocking, a measure of the number and size of trees on an acre, is changing most on privately held timberland.

Not everything is rosy. Sixty-seven percent of the forest land lost during the inventory period, which was primarily offset by agricultural abandonment, was converted to essentially nonreversible uses. Landowner study data finds that much of this loss is the result of parcelization, the process by which land areas are increasingly divided into smaller parcels. This affects habitat and management options and drives further parcelization, which threatens many forest values.

The report conveys concerns about potential impacts from non-native insects and diseases that are increasingly affecting forests. Among these are gypsy moth, hemlock wooly adelgid, emerald ash borer, Asian long-horned beetle, thousand cankers disease, sudden oak death, and the list goes on. Added to this are the rapid invasion and expansion of non-native exotic plants that are filling our old fields and woodlands with aggressive competitors. That list, too, is long and growing.

A truly problematic concern is the continuing failure to establish adequate tree regeneration (the next generation of trees) in woodlands disturbed by harvesting and other events. Using guidelines developed by the USDA Forest Research Lab near Warren, Pennsylvania, the 2009 inventory assessed adequacy of tree regeneration. When there was canopy disturbance sufficient to initiate and sustain seedling growth and development, only four of ten acres had sufficient desirable regeneration to replace the overstory. Desirable species are those important to product manufacturing and wildlife (e.g., oaks, maples, ashes, hickory). If the list of species was expanded to all commercial species (i.e., add birch, beech, blackgum, elm, black locust, aspen), only half the forest is in good shape. If the list expands to include all woody species (e.g., sassafras, invasive ailanthus, dogwood, striped maple), the situation only improves to 54%.

Forest regeneration issues are not new to the state. Repeatedly, research has pointed to regeneration concerns caused by white-tailed deer, competing plants (e.g., ferns, grass, beech, striped maple) and to this list we now a host of exotic species, and acid deposition. On the horizon are concerns about changing climate conditions and parcelization that make it easier for competing plants to gain access to woodlands and may reduce our ability to manage deer populations.

The 2012 Pennsylvania’s Forests report sheds some light on opportunities and concerns related to keeping our forests healthy and working – providing social, economic, and ecological benefits to all citizens. Clearly, it is important for woodland owners to practice stewardship if we are to continue to meet the needs of future generations. William Penn understood the importance of forests and admonished colonists to use the resource wisely. We should do no less.

If you wish to review the Pennsylvania’s Forests 2009 report, visit

The Pennsylvania Forest Stewardship Program provides publications on a variety of topics related to woodland management. For a list of free publications, call 800 234 9473 (toll free), send an email to, or write to Forest Stewardship Program, Natural Resources Extension, The Pennsylvania State University, 416 Forest Resources Building, University Park, PA 16802. The Pennsylvania DCNR Bureau of Forestry and USDA Forest Service, in Partnership with Penn State’s Department of Ecosystem Science and Management, sponsor the Forest Stewardship Program in Pennsylvania.