Bob Leverett leads the way into an Ancient Forest Lisha Kill Forest Preserve Niskayuna, NY PHOTO: DYarrow 12/1/01

Old growth experts and enthusiasts use a scientific approach that assesses specific physical features that are characteristic of old growth. Their belief is that one definition is too broad for the East's many different forest types—from subtropical baldcypress swamps on the Gulf Coast whose dominant trees reach 1000 years of age and 200 feet tall, to spruce-fir boreals forest of high latitudes and altitudes where 100-year-old trees are already ancient survivors, yet rarely over 50 feet tall.

Amid this complexity of wide ranging diversity, old growth experts agree this overlooked class of forests share certain characteristics in common. Leaders who have studied these woodlands firsthand have formulated specific criteria that can be used to define, evaluate and rank these rare and unique natural resources. While trees supply the living pillars of the forest superstructure, the forest is a complex biological community of plants, animals, insects, and microbes in which the greatest depends of the least. These features are also useful to gather data for effective comparison and long-term study of ancient forests.

Current consensus concentrates on 14 characteristics that can be applied to describe and measure an ancient forest community. These criteria, if not too rigidly defined or dogmatically applied, provide a basis for classification and ranking. Few forests will qualify under all 14 criteria; most forests will contain a few, but not all of, these features. Numbers for one feature -- how old, how tall, how thick, how deep, how many, what percent, etc. -- varies from forest type to forest type.

Old Growth Beech Saratoga Spa State Park Saratoga Springs, New York PHOTO: DYarrow 3/9/02

Old Growth Criteria
Trees of Advanced Age Trees of Mixed Ages Tree Species Diversity Canopy Structure Uneven Snags Treefall Topography Understory Diversity Coarse Woody Debris Ferns, Mosses, Lichen and the like Fungi, Mushrooms and Decay Human Disturbance is Minimal

Change is one quality old-growth forests share in common. Ecologists once believed old-growth is a climax state where a balance of renewal and destruction mean the forest changes little for thousands of years. But forests are dynamic; composition, age structure and overall character change over short time periods. One survey is little more than a single frame in a movie -- one snapshot in a steady, endless sequence of changes.

A deepening concern today is how our ancient forests will change to adapt to the oncoming era of climate change. Global warming will require species to migrate and shift their domains in a few decades. More frequent extreme weather events will strike catastrophic disturbances on forests of greater magnitude and frequency.

The Ancient Forest Palmaghatt Kill, Minnewaska State Park 300-500 year old hemlocks PHOTO: DYarrow 4/13/02

Advanced Age of Trees

A sizable percent of mature trees are old for their species and growing conditions.

Ideally, 50 percent of mature trees are at least half the maximum age for those species, and a few approach the maximum ages attainable. At least two Pennsylvania Eastern Hemlock stands have trees dated over 900 years. However, 350-450 years is a more common age maximum for Hemlock.

Mixed Ages of Trees

Virgin, open, park-like conditions with as few as five large, mature trees per acre.

In natural forest evolution, random disturbances create uneven age distributions. Ideally, old-growth will exhibit a wide range of ages. Older trees may be either thickly or sparsely distributed. The number of older trees per acre can vary greatly even within the same tract; 40 to 60 old trees per acre isn't unusual.

Tree Species Diversity

Representative Species Distribution: Many forest types exist in the East: boreal, northern hardwood, oak-hickory, southern hardwood, Appalachian cove are the broad classes. Within them, many sub-classes exist. Most have what are called "indicator species." But forest types overlap, and it can be hard to determine the natural composition of a specific site. Light-loving species (Paper Birch, Bigtooth Aspen, White Ash, Black Cherry) usually take over after a large disturbance

Coarse Woody Debris

Downed Logs and woody debris highly conspicuous. Moss species growing near one another. A mosaic of fungi, lichens and mosses that's visually striking and contrasts markedly with sparser distributions in younger forests. Yet, some old-growth exhibits little understory vegetation and a rather barren floor.

Treefall Topography

Pits and mounds created by windthrow mounds in varied stages of erosion indicates a forest hasn't had significant human impact for a long time. Uprooted trees produce cradles that persist several hundred years; logging and pasturing smooth out windthrow mounds.

Human Disturbance

Absence of Human Disturbance: Old trees alone aren't sufficient to identify old-growth. Selective logging and other human actions may damage a stand's natural integrity. Consequently, most old-growth definitions adopted by scientists prohibit past human activity. Cut stumps, old rock walls, apple trees, unmistakably indicate human intrusion, and, if widespread, are inconsistent with the idea of old-growth. Multiple trunks and root sprouts are good indicators of cutting. Northern Red Oak and Red Maple are prolific stump sprouters.

Analysis of an area's history may produce circumstantial evidence. For instance, absence of a particular species may be the result of selective logging. With no direct evidence of human interference, and all other old-growth characteristics present, an area can be considered old-growth. The prevailing perception is that virgin forest is supposed to be visually spectacular. Old-growth is supposed to have big trees.

Dwarf Ancient Pitch Pine Schunemunk Mountain Orange County, New York

Size, Age and Appearance of Eastern Old-Growth

Remnant stands of Eastern old-growth bear scant resemblance to the Pacific Coast old-growth conifers. Eastern trees are mere infants compared to the great trees of the Pacific Northwest. Further, the wide variety of forest communities in the East differ markedly in physical characteristics and appearance.

Within a forest, or even within the same stand, tree size for comparably aged trees can vary widely. Red Spruce is a case in point. In higher altitudes of New Hampshire's White Mountains, spruce may reach 70-foot heights and 6-foot circumference. Red spruce in favorable areas of New York Adirondacks may exceed 100-foot height and 8-foot girth. Great Smoky Mountain Red Spruce exceed 135-foot height and 10-foot girth (one reached 162 feet height). The national champion Red Spruce, located in the Smokies, measures over 14-foot girth and 123 feet high.

Site conditions and genetics of trees that make up a stand in an area must be taken into consideration. Girths and heights achieved by vigorous second growth in favorable may exceed the sizes of the largest trees in an adjacent old-growth area.

Ancient Yellow Birch Schunemunk Mountain Orange County, New York PHOTO: DYarrow 2/1/02

Recognizing Old-Growth Trees

Tree age and size doesn't correlate well, yet it's possible to develop sufficient skill to recognize age characteristics of particular species and thus identify old trees by sight alone.

Yellow Birch: Advanced age is very conspicuous as young, yellowish peeling bark is replaced by whitish-gray plates with a broken-up, shingle-like appearance, and are usually thicker on one side of the tree, particularly concave areas of the trunk.

Red Maple shows advanced age with brownish-gray bark strips that curl conspicuously outward. At a distance, some people confuse old Red Maple bark with Shagbark Hickory.

Tulip Poplar, when young, have unmistakable symmetry with elbow-like branches, spear-shaped crown, and slightly furrowed bark. With age, the Tulip Poplar changes shape and bark texture. Thick ridges and deep furrows develop, later flattening with extremely advanced age as outer bark is lost. Old crowns are broad and foliage clumped.

Eastern Hemlock is relatively easy to age by sight. Young bark is greenish-brown to brown; old bark is a noticeable rusty brown to almost reddish. Deeply furrowed bark, massive root structures and stubby branches are distinguishing marks of age.

White Pine old-growth specimens are easy to recognize. Bark is deeply furrowed. With truly great age, bark scales fall off, and the pine looks increasing "platy." Crowns usually flatten, and foliage is sparse and irregular.