How to Tell if Forest is Primeval or a Replacement

Once upon a time, dense wilderness covered about a million acres, or nearly half, of the United States. This endless canopy of maples, oaks, firs, and pines shaded the forest floor for miles. By 1920, Americans harvested around 300 million acres of those first forests (called primary, virgin or primeval forests) before early conservation efforts could pump the brakes on the timber industry.

Since then, advances in sustainable forest management have returned the total acreage of American forests to (roughly) the same levels of 1910, but that’s only by sheer acreage. This new forest, also called second growth forest, differs substantially from the native tracts of trees and undergrowth that once covered half the country.

Surface contours are one of the easiest and most obvious clues. Trees that fall in primary or primeval forests often go violently. Trees uproot, leaving a rotting root ball above ground and a gaping hole in the forest floor (referred to as a “pit and mound” feature). Over centuries this leads to dramatic dips and swells in the topography. Second growth forests are generally level. Trees stumps are sawn only inches above ground or just yanked out, with the hole filled to level the surface.

As land was logged and then farmed, any trees demarcating the line between primary and secondary forests often adapted to the newly-plentiful sunlight over the cleared land. These trees would become obviously asymmetrical over time as the branches grew toward the sunny side and away from the shaded side. When looking at a forest, these older trees often retain that odd branching, or you might notice an odd amount of lumpy branch bases on one side. In some cases, if only a single line of trees marked a hedgerow, you’ll notice a conspicuous row of trees with widely-spread branches seemingly in the middle of wilderness.

Second growth forests often have an unusual amount of fast-growing tree species, such as dogwood, honeysuckle and buckthorn. Since these small trees (often called scrub trees in forest management) grow quickly in sunlight, they are able to thrive even when neighboring maples and oaks tower over them. If you’re in a forest where armies of dense, needling trees are growing among the larger, stately ones, chances are it is second growth.

The United States owes its very existence to its forests. Settlers in this country would not have survived without the timber resources of North America. These trees made homes, provided transportation, heat, and food. Settlers placed logs across swamp tracts to form corduroy roads. Timber made our first ships and, when boiled down, provided the pitch to make them waterproof. Trees made the rifle butts that tragically forced Native-Americans west, and wood pulp made the treaties the US government broke at a whim. Whether decades or centuries old, our country’s forests are an intricate part of America’s culture.

Want to Know More? 

The USDA compiled six decades of forestry data into U.S. Forest Resource Facts and Historical Trends, a 64-page pdf.

To understand the difficulty in defining “old growth” forests, read the report “Defining Old Growth: Implications for Management” which summarizes a joint project between The Nature Conservancy and the USDA Forest Service.

It’s difficult to imagine the forests of the United States in their most pristine shape, but the fine folks at Scientific American gave it a shot in their article “What America’s Forests Looked Like Before Europeans Arrived.“