I look at a lot of farm properties for landowners, and it is not uncommon to find that some of the woodlands they now have were cleared for farming a few decades ago. Before chemical fertilizer and lime was readily available, per acre yields for farm crops were much lower and so more land was needed to farm. This was not a problem as most farms had large families with a built in labor force. But over the years the land eroded, kids left the farm, and the farmer got older. So slowly the steeper, rougher fields or field edges were let go, and the forest reclaimed them. There are indicators you can look for to tell if a forest was once a field.
One obvious indicator is rock piles in the old field woodland where farmers were constantly picking them up out of the field. There are some species of trees that are geared to jump onto open areas quickly and grab the sunlight before everybody else. Foresters refer to them as pioneer species: the first to immigrate to a new area. Probably the most common pioneer tree we have is Virginia pine, which often forms pure stands on old field sites. Pines must have full sunlight to grow, and so their survival tactic is to seed into fields from birds or the wind and put on height growth quickly to stay ahead of competitor trees. Eventually the pine crowns grow together and “close canopy” as we call it, darkly shading the forest floor and capturing all of the sunlight, leaving other species in the dust. Yellow poplar, red-cedar, and shortleaf pine are other trees that often form pure stands or in a mixture. Other trees you’ll often see in old field forests are sassafras, sourwood, red maple, dogwood, and hickory.
Some old fields have had two generations of trees due to insect attack. They started out as pine stands, which were killed off by the southern pine beetle back in the 1970s and again in the 1990s. The site was then taken over by shade tolerant hardwoods that were growing under the pines as seedlings and saplings, such as sourwood, dogwood, sassafras, and red maple. You will often see the decaying bodies of pine trees lying on the ground beneath the hardwoods.
One other indicator of an old field site is that the trees are uniform in size, with the same height and similar diameters. This is because they all germinated around the same time. Many old fields were abandoned over the last 40-60 years, and so most of the trees are pole timber size with diameters of 4 to 10 inches. The trees are usually pretty crowded with lots of stems per acre.
Management of an old field forest for timber or wildlife depends on the landowner’s objectives and tree species present. To help figure all this out, contact your local state forester.