What old growth actually looks like

Ask most people to picture old growth and they describe a cathedral: huge straight trunks, an open floor, quiet and tidy. Real eastern old growth is close to the opposite: cluttered with dead wood, uneven in every direction, full of holes in the canopy and lumps in the ground, and many of its oldest trees are not its biggest. Old growth is a structure, not an age, and once you know the structure you can recognize it in a ten-acre woodlot as readily as in a national park.

Old growth is a structure, not an age

A forest that grew back on an abandoned pasture a century and a half ago is old, but it is usually not old growth: its trees are all about the same age and size, and they have not yet begun to die in numbers. Old growth is what a forest becomes once the first generation starts to fall apart and the trees underneath start to take its place. The signs are consistent from Maine to the Gulf coast:

• Trees of many ages and sizes mixed together, from seedlings to giants.
• Big old trees with broken tops and huge limbs, often with only part of the crown still living.
• Standing dead snags, often the largest trunks in the stand.
• Large fallen logs in every stage of decay, from fresh to moss-covered mounds you can push a stick through.
• Pit-and-mound topography: the hollows and humps left where windthrown root plates tore out of the ground and rotted back into it. A floor that rolls like a rumpled blanket is old ground.
• A broken canopy with light gaps where trees have fallen, and dense young growth filling them.
• A rich understory and deep litter and duff, with lichens and mosses on bark and rock.

An untouched forest has all of this; a forest cut once long ago and left alone can have most of it. The structure is what counts, and it takes centuries of trees living, dying and falling in place.

How to spot an old tree

Old trees carry their age on the outside, and researchers who core them have written down what to look for. The best-known list, drawn from eastern hardwoods over 250 years old, includes:

• Balding bark. Old oaks, hickories and gums lose their sharp bark ridges and turn smooth, plated or flaky, especially near the base and high up.
• Low taper and twist. An old trunk stays nearly the same thickness a long way up, and often spirals or curves rather than running straight.
• Buttressed, hollow or lumpy bases, with cavities where old limbs tore out.
• Reiterated crowns: small new crowns sprouting from big broken limbs, so the tree looks like a candelabra.
• Stag-headed tops: dead limbs poking above the living crown like antlers.
• Very slow growth. On a stump or a core, the rings are packed so tightly that a decade can fit under a fingernail.

Size is a poor guide. Most of the oldest trees ever dated in the East are smaller than you would expect, because slow growth on a harsh site is what lets a tree live so long, and hollow trunks and shelf fungi are not the end of the story. A stunted, twisted black gum in a swamp or a post oak on a ledge is a likelier ancient than the fat oak on the lawn.

How little is left, and where it hides

The most thorough survey of eastern old growth put the total at well under one percent of the region’s forest, much of it in small, scattered pieces. What survives was hard to reach or not worth cutting: steep slopes and ravines, boulder fields and ridge tops, swamps and river islands, mountain coves the railroads never reached. A few groves were saved on purpose, among them Joyce Kilmer in North Carolina, Cook Forest in Pennsylvania, Congaree in South Carolina, and large tracts in the Adirondacks and the Great Smoky Mountains.

Much of the rest is unknown and unmarked: town watersheds, the back corners of farms, cemeteries and church lots, property lines nobody wanted to argue over, ridges where the trees were too crooked to bother with. If you own woods on rough ground, walk them with the list above in mind.

Why it matters

• Carbon. Old forests keep storing carbon for centuries, in the biggest trees and in soil that has been building under undisturbed litter the whole time. Cutting resets both.
• Habitat. Hollow trees and snags house owls, wood ducks, flying squirrels, bats and the woodpeckers that dig the holes everyone else uses. Big rotting logs feed fungi, beetles and salamanders that cannot live on twigs.
• Genetics. An old tree has survived every drought, ice storm and hard winter of the last few centuries on that ground. Its seed is the proven local strain, which is why we collect from known parent trees rather than wherever seed is cheapest.
• Water. Deep duff and pit-and-mound ground soak up rain and release it slowly, which is why streams out of old forests run clear when others run brown.

Growing old growth back

No one can make old growth in a lifetime, but any second-growth woodland can be pushed that way, and the first steps are mostly about stopping things.

• Leave the dead wood. Snags, fallen tops and logs are the structure you are trying to build. Do not tidy them up or burn them.
• Stop cutting the biggest trees. Taking the largest and best-formed trees, the way most private woodlots have been logged for two centuries, removes exactly the ones that would have become giants. If you must cut, cut the small and the poor and leave the best.
• Remove invasives. Vines and shrubs from elsewhere choke regeneration and keep the understory from ever forming.
• Protect regeneration from deer. Where deer are dense, nothing reaches head height without a fence or a cage, and a forest with no young trees has no future.
• Let the gaps work. When a tree falls, the light it lets in is the point. If nothing native comes up, plant local seedlings there.
• Be patient. The first hollow trees, the first big snags, the first shade-grown seedlings under the canopy arrive in decades; the rest takes generations. The woods you leave alone today are the old growth of a century from now.