Old Growth Is More Than Big Trees

August 2, 2008

What do you think of when you hear the words "old growth?" Most people visualize sunlight filtering through towering trunks of giant sequoias or redwoods or western hemlock growing in a majestic, ancient forest cathedral. Others hear an echo of 1980's controversies over Spotted owls and timber harvesting in the Pacific Northwest.

What about remaining "ancient forests" in New Hampshire?

While interest in western old growth forests has captivated the public for the past 20 years, popular understanding of remaining rare fragments of eastern old growth forest has lagged. Most people have never seen one. They're very hard to reach. If that weren't so, they'd have been logged long ago!

Old growth is rare in New Hampshire because disturbance to our forests is very common. The odds of finding new areas of primeval forest are slim and utterly dependent upon understanding the forest history of a site. Three centuries of intensive human activity on the landscape has included clearing for agriculture, logging for wood products and the development of roads, houses and human settlements. Destructive natural events including hurricanes, fires, ice storms, winter gales – even beaver activity and insect infestations occur in semi-regular cycles.

Respect Your Elders

How much old growth remains in the state? According to a pioneering 1986 study by Lee Carbonneau while an undergraduate at UNH, there were only 12 well-documented old growth stands at that time totaling 3,000 acres ranging in size from 2 acres to over 400 acres. Modest new areas of old growth have been discovered since 1986 including approximately 75 acres in Mount Sunapee State Park. With 83% or 4.8 million acres of the state cloaked in forest, 3,000 acres is a small percentage. The 1995 N.H. Forest Resources Assessment Report refers to a high percentage of public land in the state – fifty-five percent or 434,000 acres of the White Mountain National Forest – being in management classifications which preclude timber harvesting. Those forests, including high elevation tracts, are forecast to gradually revert to old growth conditions over the next 150 years based on a minimum climax age of 250 years.

While there is no generally accepted or universally applicable definition of old growth, most ecologists define "old growth" as the oldest generation, or "cohort," of trees in a mature climax forest – a late succession stage characterized by the presence of shade-tolerant trees able to reproduce in their own shade. In New Hampshire, spruce, hemlock, yellow birch, beech, sugar maple and black gum can qualify for old growth. White pines may live to more than 150 years but need disturbance to regenerate. Sugar maple and beech can live in excess of 200 years; yellow birch in excess of 300 years; spruce and hemlock for 400 to 500 years. Western sequoias and small Bristlecone Pines live from 2,000 to 3,000 years. Therefore, "old" is a relative term.

Areas of "undisturbed" forest in New Hampshire are actually best characterized by the presence of disturbances on a small, site-scale. Consider the fall of an old dead tree. Regardless of whether it makes any noise, the small natural event creates a canopy gap, which multiplied over hundreds of years and thousands of acres creates a more diverse forest than areas subjected to periodic larger disturbances. Envision a constantly shifting population mosaic where old trees shed dead limbs, young trees in the understory compete for sunlight beneath standing dead snags and where fallen rotting logs lie haphazardly on the forest floor. Forget the classic image of a towering even-aged cathedral of huge trees. In New Hampshire, natural disturbances create a wide diversity of structural tree ages, sizes, heights and diameters from seedlings and saplings to large mature trees as well as standing dead snags and fallen rotting logs. It is visual chaos. An old forest is always a "messy" forest.

Although there are no wildlife species in New Hampshire entirely dependent upon old growth, old forests do provide unique habitat for certain lichens and insects which reach their greatest diversity in old stands. Several interior forest birds and mammal species are more commonly associated with large diameter trees – living, dead and down – that provide important roost, den, nest and feeding sites.

Is It Old Growth?

We recently visited a potential old growth site on private land in an undisclosed location to document old growth forest or find visual evidence to disqualify it. At the landowner's request, the location remains undisclosed. The difficult access and adjacent fragile areas would be negatively impacted by visitors.

To determine whether a tract is a mature forest or qualifies as rare old growth, we needed to answer four questions. What is the human history? Which tree species and ages are present? Are the heights, diameters and presence of standing dead and large down rotting logs consistent with old growth? Is there any evidence of historical management activity including cellars, stonewalls, wire fence, cut stumps, skid trails, nearby roads or missing tree age classes that would disqualify the stand?

In the forest, the oldest trees are spruce, yellow birch and beech with an abundance of old trees. The oldest trees exhibit age characteristics including large prominent root structures, deeply furrowed or plated bark, trunks showing a twist that develops with age, long trunks free of lower branches, large thick limbs, flattened crowns with protruding dead limbs and the presence of "super-canopy" trees.

We used an increment borer to take age cores from smaller spruce and the rings were readily counted in the field. A small 12" spruce is 190 years old. The largest yellow birches of nearly 30" diameter are too big for the standard 11" increment borer we brought so no yellow birch cores were taken. The slow-growing hardwood cores must be mounted, sanded and stained for rings to be counted. That awaits another visit.

We found no evidence of any historical human activity in the remote stream valley. Most important: the access to the site is so problematic that written historical accounts from the turn of the century had local logging firms willingly selling their interests in the uncut tract which was said to contain primeval forest at that time in the early 1900's.

Old growth? You bet! One colleague remains unconvinced.