Pictured left: Old-growth forest in the Opal Creek Wilderness, a wilderness area located in the Willamette National Forest in the U.S. state of Oregon, on the border of the Mount Hood National Forest. It has the largest uncut watershed in Oregon.
An old-growth forest (also termed primary forest, virgin forest, primeval forest, late seral forest, or in Britain, ancient woodland) is a forest that has attained great age (and associated structural features), and thereby exhibits unique ecological features. Old-growth forests tend to have more large trees and standing dead trees, multi-layered canopies with gaps resulting from the deaths of individual trees, and coarse woody debris on the forest floor.
Old-growth forests are often biologically diverse, and home to rare species, threatened species, and endangered species of plants and animals, such as the northern spotted owl, marbled murrelet and fisher, making them ecologically significant. Levels of biodiversity may be higher or lower in old-growth forests compared to that in second-growth forests, depending on specific circumstances, environmental variables and geographic variables. Logging in old-growth forests is a contentious issue in many parts of the world. Excessive logging can reduce biodiversity, affecting not only the old-growth forest itself, but also indigenous species that rely upon old-growth forest habitat. Fallen timber, or coarse woody debris, contributes carbon-rich organic matter directly to the soil, thus providing a substrate for mosses, fungi and for seedlings, and in creating microhabitats by creating relief on the forest floor. In some ecosystems, such as the temperate rain forest of the North American Pacific coast, fallen timber may become nurse logs, providing a substrate for seedling trees.
Plant species that are native to old-growth forests may someday prove to be invaluable towards curing various human ailments, as has been realized in numerous plants in tropical rainforests.
Old-growth forests were often given harvesting priority because they have the most commercially valuable timber, they are considered to be at greater risk of deterioration through root rot or insect infestation, and they occupy land that could be used for more productive second-growth stands. (Full article...)