How Can I Tell if My Woods are Old Growth?

How Can I Tell if My Woods are Old Growth?

Old-growth forests, sometimes simply called “old growth,” are just that: really old woods. Accordingly, they are marked by the presence of exceptionally old, typically large-diameter trees that are living, dying, and dead. For most forest types in our region, this likely means there are trees exceeding 150 years old and some may be as old as 200 (white pine), 250 (sugar maple), or 400 years (hemlock).

If you do have an old growth forest, consider yourself very lucky indeed, as truly old forests are exceedingly rare in the northeast. Most of our forests have been cleared for agriculture and cutover one or more times over the last few centuries. And although much has re-grown, and despite a strong history of conservation and good management since, trees in the secondary forests we see today are much younger and therefore significantly different from those that existed previously.

By most accounts, less than 0.5 percent of the current forestland in the northeast is old growth and no region in the eastern deciduous and mixed forest zone has more than 1.1 percent old growth. With a couple of notable exceptions in northern New Hampshire and Maine, most of the last remaining northeastern old-growth forests are small and isolated, restricted mostly to inaccessible steep land and wetlands. Still, if you have some particularly large-diameter trees in your woods, say, in excess of 25–30 inches, and there is little evidence of human intervention or large-scale natural disturbance, they just might qualify.

Because tree growth rates vary so much by species and growing conditions, diameters can be misleading. Thus, there is no good substitute for measuring the actual age of a tree. Fortunately, you do not have to cut down your prized old tree to determine its age by counting the annual growth rings on its stump. You can instead count the rings in a cross-section of the stem extracted as a pencil-sized core from the standing tree using a forester’s tool known as an increment borer. Ask any second-grader who’s had a visit from a local forester and they’ll confirm that it works like magic.

Except when it doesn’t. No, it is not foolproof. In very large, very old trees, the innermost rings of wood tend to be decayed and this makes an accurate estimate of the tree’s age impossible. But fear not. Even without an increment borer you can judge whether your woods are old growth by other means. In fact, the alternative approach involves a more complete understanding of the characteristics of old forests – most of which can be observed while simply walking through your woods and requiring no specialized equipment.

First, accept that old forests comprise trees of many ages and sizes. Sure, to be actual old growth, there must be some exceptionally old ones, but even the oldest woods contain many more young and middleaged trees than old ones. If you’ve got a range of tree diameters and at least a few lunkers in the mix, keep walking and looking, you might be on to something special. Next, look up at the canopy. Truly old forests have an uneven canopy with many scattered, small gaps owing to tree crowns breaking and falling here and there over an extended period of time. Young forests tend to have fewer large trees and fewer canopy gaps.

If your woods are truly old-growth, you will also notice an abundance of dead trees, both standing as “snags” and on the ground as “woody debris.” Importantly, in old growth this accumulated dead wood exists in many sizes and in varying stages of decay, reflecting the full range of ages and sizes of the living trees accumulated on the site over many years. This diversity of dead wood provides habitat for a wide range of animals – from insects to salamanders – as well as critical germination seedbeds and nutrient cycling for forest regeneration. In old growth you will also notice a greater abundance and diversity of herbs, lichens, and fungi, all of which support life forms and processes under-represented in younger forests.

Lastly, truly old forests will exhibit “pit and mound” microtopography, which reflects where trees were toppled by windthrow long ago but have decomposed, leaving only the pit, where the trees used to be rooted and mounds of soil that used to contain the roots.

Beyond all the good ecological science describing them, chances are you’ll just know it when you’re in an old-growth forest. All of those attributes add up to make a very different kind of forest, and when you’re in one, it is a difference you can feel.

Michael Snyder, a forester, is Commissioner of the Vermont Department of Forests, Parks and Recreation.

  1. Art Wilder → in Norridgewock, ME
    May 01, 2012

    I think the age given for White Pines (“maybe as old as 200”) is a little low. In 2004 I cored a group of five White Pines in a forested wetland about 60 miles north of here near the Kennebec; they showed ages of from 217 to 330 years.The tree centers were deteriorated but the ages were based on the rings counted; had to use magnification.

  2. Bruce Phillips → in United States
    May 21, 2012

    Well, yippee-ca-yay!  I was actually interested in this article until the author called “blow down”, “WINDTHROW”!
    Just like the new fad of calling a FARM, a CSA. (Community Supported Agriculture for you old schoolers).  Changing the names of things, or making up new ones like WINDTHROW, seems to validate these peoples sense of importance or knowledge or something. I’m sick of the jargon!
    By the way, SAW LUMBER out of an increment bored tree, and tell me that that process does no damage to the trees inherent value as lumber, or its NATURAL lifespan. Woods grow, oh, wait….I mean FORESTS. Humans use the trees at all stages of their lives for many many things, and have for millennia. Likely will continue to as well. I don’t need someone to tell me if a tree is “OLD” or not. As a responsible land owner, (and logger) I don’t cut the “Big Boys”. We all know they both act as “seeders” and are beautiful, majestic, homes to a myriad of life. And that the hearts are often rotted. But then again, nowhere in the article did this SPECIALIST tell me that the trees were beautiful, and majestic. Maybe they really are not. Sure hope someone else graduates college so they can tell me the facts .  All sarcasm aside, sell these stories in NYC, NOT in the northeast woods. You keep romanticizing our lives up here, and more twerps will come and tell us what we can and must do with them. Land and its usage included.

  3. dave → in corinth
    May 21, 2012

    I hear you with your frustration about jargon, Bruce. I hate it when people use the word “community” to mean anything other than the town they live in. Every time I hear the phrase “ecosystem services” my eyes glaze over and I want to hit my head against the wall.

    But why not make your point without sarcasm? And why take words as a personal insult? We’re on the same team here.

  4. Joe Zorzin → in Massachusetts
    May 29, 2012

    Those interested in old growth should check out The Native Tree Society, and it’s bulletin board at

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