It’s easy to think of forests as peaceful, unchanging places. In reality, this isn’t the case, because forests are much more dynamic than they may seem. In fact, forests are shaped by change, and many forest ecosystems depend upon it.
In the aftermath of a major change or disturbance like wildfire or human clearing of land, hardy pioneer species such as shrubs and grasses are the first to move back into the area, creating an open and highly productive patch of land known as early successional habitat, sometimes called young forests. Early successional habitat is created and maintained by disturbance. Without it, the grasses, shrubs and young stands of trees that characterize it will give way to older, denser forests, and the species that depend on these young habitats will no longer thrive.
Katie Greenberg is a research ecologist and research unit project leader at Bent Creek Experimental Forest, which is part of the U.S. Forest Service’s Southern Research Station. She says many species, including some species of conservation concern, rely on early successional habitat for food and shelter.
“Birds will bring their young families there to forage,” said Greenberg.
Early successional habitat can have up to 20 times more fruit than mature forest, from species like blackberry and pokeweed, or even from sprouts of forest trees like dogwood or black cherry. Young birds learn to forage in these productive areas, which contain shrubs and abundant stump sprouts of trees that provide places to nest and hide from predators. Greenberg says indigo buntings, bluebirds, bobwhites and chipping sparrows are just some of the bird species that favor early successional habitats.
But, one “size” of early successional habitat may not fit all. Some species prefer grass-dominated habitats, whereas others prefer shrub-dominated habitats, or may have other “specs” such as elevation or the presence of snags (dead trees) for nesting. Other species, including game species such as black bear and ruffed grouse, also find food in these open patches. Also, if some standing trees remain in the new forest openings, most of the bird species associated with mature forest will also use the stands.
Among the bird species that prefer young forests is the golden-winged warbler, a diminutive silver-gray songbird with lively streaks of yellow on its head and wings. The golden-winged warbler lives in patchy landscapes where areas of open habitat abut sections of more mature forest. The birds nest in open, shrubby areas until their chicks begin to fledge, at which point they move into more thickly forested areas where the fledglings are protected from predators like hawks.
Natural disturbance like wildfire and burning by Native Americans and European settlers likely promoted the kinds of patchy landscapes favored by the warbler, until fire suppression and land development got in the way. With humans preventing the disturbances that once created and maintained these landscapes, not enough open habitat was created for the warbler to nest, and the species suffered a sharp decline.
“Diverse habitat structures lead to a diversity of wildlife,” said Greenberg. “If your forest consists of only mature habitat, then you won’t get species that require early successional habitats. If it’s only early successional habitats, then species that favor mature forest won’t thrive there.”
If the goal is to create biodiversity, then having a wide variety of habitats for species to live in is key. The best strategy for biodiversity may be “if you build it, they will come.” Instead of targeting each individual species for protection, create a diverse landscapes with different habitats for a diversity of species, and the rest will follow.
In many forests, including some national forests, the amount of young forest habitat has declined over the past several decades. Several factors, including fire suppression, reduced timber harvesting and agriculture have reduced the availability of early successional habitats.
The good news is that, with help from scientists like Katie Greenberg, we are learning more and more about the benefits of young forest habitat and how we can create more of it.
For more information, email Cathryn Greenberg at firstname.lastname@example.org.