What is an old-growth forest? As the question implies, it is an old forest with trees of great age. But where does one begin the old-growth clock? What clues lie on forest floors and in wispy treetop canopies? These topics and others related to old forests were discussed on March 31 when Dr. David Orwig, senior ecologist and forest ecologist at the Harvard Forest located in Petersham, gave a presentation hosted by the Marion Natural History Museum.
Orwig’s work has taken him deep into Massachusetts’ few remaining old-growth forests, including the Harvard Forest, Bish Bash, Wachusett and Mount Greylock. He said most older forests in our region are around 65 to 95-years old with the average being 80 to 85 years of age. Studies have shown that once colonial settlements took hold, virgin forests began to fall. By the early 1800s, 40% of forests in Massachusetts had been felled. Human impact has been profound, and still Massachusetts ranks 11th in the nation for woodlands with some 3,200,000 acres. Orwig said most of that acreage is either in private ownership or in conserved holdings.
Aging a forest requires a bit of detective work. Orwig said that the biggest tree isn’t necessarily the oldest tree. “We look at the condition of the canopy, the characteristics of the bark” and the scientists taking borings, he said.
Tattered canopy cover is an indication of age. This clue tells how a tree has been tossed and turned in storms over the ages. Many tree species mature into righteous elders with thick, pleated bark where once-smooth surfaces faced the sun. Orwig said these pleats or bark plates slough off the trees’ surfaces, adding to the rich organic material that feeds the soils.
“The forest is not a static environment,” he said.
The main physical clues when dating an area therefore are imperfect tree canopies, old root pits created by dead, falling trees that eventually become pits, and then mounds of organic material covered in bryophytes (moss.) Also, the absence of stonewalls and sawn tree stumps, a lack of human interference, can mean a forest is truly ancient.
Orwig noted that old-growth forests have been found on steep terrain of primarily hemlock trees. A stunning 90% of old-growth forests in Massachusetts are populated with hemlock. The reason this is the case, he explained, is the trees’ ability to survive in shady spaces. Other species found to a much lesser degree in these areas are Sugar Maple, Red Spruce, Yellow Birch and Ash.
Of those old-growth forests remaining in the state, Orwig said many people are surprised to learn that the Mount Wachusett area contains one. Known for its ski trails and other winter outdoor recreational activities, Wachusett Mountain resort’s trails are lined with guardians from the past. Established in 1899, it is the second oldest state reservation in Massachusetts, he said. Of special note, Wachusett contains a tree that has been dated to 1670 – a Northern Red Oak.
Beyond the beauty we mere mortals receive from forests, there are also the scientific realities. Forests are part of what makes our earth inhabitable. The production of oxygen from carbon makes trees a main contributing factor to the survival of humankind. The trees store carbon, which helps to cool the earth’s surface, and they are a main contributor to the biodiversity so critical to all life on our blue planet.
Hemlocks reign supreme over old-growth landscapes because they have lacked the commercial value placed on other species such as white pine.
“You won’t find many white pine in old-growth forests,” Orwig commented. And so that which humans have ignored ends up being the winner. “Hemlocks as old as 500 years have been found.”
Other tough old trees living long lives are Spruce at 400, Black Birch at 300, and Red and Yellow Oaks at 350 and up. But the oldest of all is the Tupelo tree or Black Gum, clocking in at over 555 years of age.
Like every story from the natural world, there seems to be a dark cloud. Such is the case for old-growth forests. Insects are quickly spreading throughout some old-growth spans, threatening these sentinels from the past. Orwig said ongoing study in how best to protect what remains includes looking at bio-control agents, enemies of the Emerald Borer and other invasive beetles. Their introduction may just make the difference.
Time is of the essence; there remains a mere .02% of all forests that can be classified as old growth.
To learn more, visit harvardforest.fas.harvard.edu and marionmusuem.org.
Marion Natural History Museum
By Marilou Newell