Old-Growth Forests

Have you ever walked in an old-growth forest?  Probably not, as in the Eastern United States, almost all of that majestic forest was clear-cut by 1920.  However, before Europeans arrived in North America that old growth forest stretched totally unbroken, from Florida to Maine and west to the Great Plains, as the virgin forest map for 1620 depicts below.

Do you even know for sure what makes a forest “old growth”?  Again, probably not, for if you asked 100 scientists, you might get 100 different answers.

In her book “Among the Ancients, Adventures in the Eastern Old-Growth Forests” Joan Maloof explores some of the last remaining stands of old-growth in the eastern United States.  The characteristics of each stand vary depending on the climate and soils where it grows. This makes a precise definition of old-growth not possible.  Joan perhaps best describes “old growth” when she says that “old-growth forests are places that have been left alone for a very long time”.  She goes on to say “The reason definitions are so difficult is that every forest is different.”

As the eastern United States was settled in the 1700s and 1800s the forest began to be clear-cut for agriculture and lumber.  Yet by 1850, vast portions of the forest remained, even here in northwestern Pennsylvania

As the population in the eastern United States swelled in the late 1800s and into the 1900’s, development finally took its toll on the forest.  By 1920, vast areas were clear-cut to the point that few tracts of virgin forest remained.  In Pennsylvania, nearly the entire state was harvested for its timber.  Old-growth forests finally met their match after thriving for 12,000 years after the Laurentide ice sheet retreated.

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 lesser species.  The hemlock is particularly fond of the steep banks of Falls Run Gorge, but along those banks, you will find wonderful specimens of all the others too.  Sheltered from severe weather by being in the Gorge, the trees reach for the skies to great heights.

But how old are these trees?  They seem stately, but these are long-lived species.  Hemlock and white pine can live 500 years, oak and beech for 300 years, 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 approximately 190 years old.

Howard Falls red oak estimated at 190 years old

It is possible that some of the mature trees along and in the gorge were spared the lumbermen’s axes due to the inaccessible terrain.  Nonetheless, much of the surrounding area was clear-cut, probably in the late 1800s-early 1900s, and the land used for timber or farming. In the orthoimagery data map from Pennsylvania Spatial Data Access (PASDA), we can see “scars” left from farming in the forest east of the gorge.

Aerial image of the Falls Run Gorge via PASDA

So, while the gorge itself contains relatively mature trees, the supporting landscape vegetation is well along in re-establishing a diverse forest community. We hope to dive deeper into these aerial images in a later blog.

Christian Wirth et al, “Old-Growth Forest Definitions: a Pragmatic View” analyzed 118 studies where the ages of old-growth forests were reported. Summarized in the following figure, they found that transition to “old-growth” for a temperate forest typically begins at around 200 years, and is achieved at 300 years and beyond.

Within the Falls Run Gorge, that transition to old-growth is well underway.  Trees there are estimated to be 100-150 years old. Another 100 years and they can be rewarded with “old growth” status.  The supporting woodland landscape will need another 200 years.

Here at Howard Falls, we are committed to ensuring that will happen.  Along the way, we hope to re-introduce American Chestnut to the forest.  Until the Chestnut blight of the early 20th century, it was a dominant tree in the eastern US and it rightly belongs here.  The root system of a stump here at Howard Falls continues to send up new growth. Unfortunately, it’s killed off by the blight before reaching maturity. We have recently obtained blight-resistant seedlings from the American Chestnut Foundation and can’t wait to share their journey with you.

Future blogs will continue to explore the age and diversity of our forest community at Howard Falls.  It is a unique place, once again undisturbed, and returning to its full potential. 


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