Background
In our 2021 blog “Old Growth Forests,” we discussed how, here in Northwestern PA, the predominant trees in our forest at Howard Falls are Eastern Hemlock, hard and soft maple, red and white oak, cucumber magnolia, white ash, American beech, white pine, and a multitude of less common species. Sheltered from severe weather by being in or along the gorge, the trees often reach for the skies to great heights.
Most of these are long-lived species. Hemlock and white pine can live 500 years, oak and beech for 300 years, and maples for over 300 years. A Red Oak along the rim of the gorge measures over 4 feet in diameter, and we estimate it to be now approximately 200 years old.
In our 2022 blog “American Chestnut,” we described an 1891 visit by the Natural History Society of Erie, PA, where the forest here was described as “a splendid growth of birch, maple, chestnut, and numerous other forest trees,” and concluded that the American Chestnut is seemingly making a comeback in our forest.
Now we take a deeper look at Tsuga Canadensis, commonly known as Eastern Hemlock, and that deep look is for good reason. Walking along the Falls Run Gorge rim trail here at Howard Falls, one will quickly become aware of an innumerable number of Eastern Hemlock thriving in the well-drained but moist and shaded microclimate of the gorge. They are by far the most abundant species along that forest trail.
Eastern Hemlock Forests
Eastern Hemlocks grow on 19 million acres throughout the eastern U.S. They are the dominant tree species on over 2 million of those acres, ranging from the Southern Appalachians of Georgia and Alabama, north to Maine and the Canadian Maritimes, and as far west as Minnesota. Thus, Eastern Hemlock is considered a foundational species in the eastern forests because it is both locally abundant and regionally common, and its structure and functional characteristics create microclimates and habitats for a range of native species.
The Hemlock’s shallow root system excels along riparian corridors like our gorge here at Howard Falls, where the soil remains moist throughout the year. These shade-tolerant trees, with the ability to form dense canopies, provide refuge for fish and other wildlife. Cool and densely shaded in the summer, Hemlock stands provide important wildlife habitat, and cool streams sheltered by hemlocks are more likely to support abundant fish. During harsh northern winters, these dense stands of Hemlock likewise provide ideal shelter for white-tailed deer and other wildlife. Importantly too, their extensive root system slows soil erosion along the gorge.
In supporting biodiversity, Eastern Hemlock forests provide both food and habitat for more than 120 species, including, here at Howard Falls, Black Bear, Fisher, White-tailed Deer, Red Squirrel, Porcupine, Coyote, Turkey, Ruffed Grouse, Woodpecker, and a plethora of other birds and animals.
How old are Hemlock Trees
Eastern Hemlocks are remarkably shade-tolerant. A Hemlock growing in the deep shade of a mature canopy might only grow an inch in diameter every few decades. There are documented cases of Eastern Hemlocks measuring just 2 to 3 inches in diameter that are over 200 years old.
With the ability to be extremely slow growers, a Hemlock’s size is a highly inaccurate indicator of age. A 12-inch diameter tree could be anywhere from 50 to 150 years old. Thus, the standard “growth factor” formula used for trees, in which a multiple of the diameter approximates a tree’s age, is notoriously unreliable for Eastern Hemlocks due to extreme suppression in the forest understory. However, for open-canopy-growing trees on typical sites, a general rule of thumb is about 50 years for a 12-inch diameter at breast height (DBH) and 100 years for a 24-inch DBH.
Because of their delayed growth in early stages, hemlocks can easily live from 300 to over 800 years. The oldest known living specimen, located not far away in Tionesta, PA, is estimated to be over 650 years old.
Hemlock Form Groves
We have mentioned that Eastern Hemlock possesses the unique ability to persist for decades and even centuries in the near complete shade of the forest understory (where other trees would languish and falter), in anticipation of the inevitable disturbance that will provide light and space for it to shoot rapidly upwards to join the forest canopy.
Thus over time it has the power to remake the forest along riparian corridors in its own image, creating a monolithic hemlock ecosystem around itself, which differs significantly from adjacent mixed hardwood forest areas; and in which it and countless other understory plant and animal species thrive in dense hemlock groves.
The Hemlock Forest at Howard Falls
The Falls Run Gorge flows north through its Natural Heritage Area for approximately 3 miles until it reaches its confluence with Elk Creek. The first ¾ mile is through our property at Howard Falls, and the Eastern Hemlock is unquestionably the dominant tree for that entire length. It is simply the ideal environment for the species.
Sampling of a few 50′ segments of the gorge enables us to confidently estimate that there are more than 5,000 Eastern Hemlock lining each side of the gorge on the Howard Falls ¾ mile segment. This population includes every age, from mature trees to saplings.
As the gorge forms just below the Falls, Eastern Hemlock begin to dominate the landscape. Below our belvedere at the beginning of the western rim of the gorge below the Falls, a typical succession of Hemlock is present, from mature trees of over 115 feet height with diameters in the 2+ feet range, all the way down to saplings of less than 5 feet and an inch or two in diameter. Even lesser Hemlocks are visible in that understory, and over 50 hemlocks are easily counted from that vantage point.
On the eastern rim of the gorge, perhaps because it may get more sunshine, Hemlock are exceptionally prolific, dominating the slope and rim of the gorge, but only rarely extending into the surrounding upland landscape. Simply put, they love the moist, well-drained soils of the gorge environment. Occasionally, a Hemlock finds a welcoming spot in the surrounding landscape beyond the gorge and grows to exceptional size.
Further north along the rim, Hemlock have begun to take over that area, forming a dense, monolithic grove of Hemlock. In the grove, mature trees dominate the available sunlight, while lesser Hemlock patiently wait their day when a patch of sky will open for them.
Headed toward Old Growth
As our forest continues its journey toward old growth status, our Tsuga Canadensis will play a dominant role in shaping the forest ecosystem at Howard Falls. Undoubtedly, the well-established Hemlock grove along the gorge will continue to expand, crowding out other species, but likewise providing habitat for our native wildlife.
The progression will be slow — but relentless – and to be witnessed and appreciated by coming generations.
DDHoward
July 2026