Old Growth Forests
Ever wondered how old that tree really is? Did you believe it when you were told that all timber in the south was cut down at the turn of the century leaving no trees standing today over 100 years old?
Contrary to popular belief, our Southern Appalachian forests and mountains harbor old-growth trees and forest communities that are 300+ years old. The Southern Appalachian Forest Coalition (SAFC) has been inventorying these sometimes hard-to-locate giants, with a goal of permanent protection and conservation. These rare forests provide habitat for a growing list of species and harbor important climatic, geological, and biological links to the past.
Characteristics of Old-Growth
Forest Trees of Great Age
For a forest to be old-growth there should be a number of trees of great age. Unfortunately, there is no definitive agreement as to how old constitutes "great age," but a reasonable criterion might be trees exceeding at least 50% of the projected maximum attainable age for that species. Because of small-scale natural disturbances, there may not be any trees at the maximum attainable age at all. Thus, on a very dry, low-quality site, trees may not have the same impressive diameter structure that they would on a moist, high-quality site.
Uneven-Aged Canopy Structure
Eastern old-growth forests are generally characterized by trees of all ages and diameters. They typically exhibit a reverse age distribution, whereby younger stems are at a much higher density than older stems. The shape of the age distribution often (but not always) parallels that of the diameter distribution. The age/diameter structure is driven largely by small-scale natural disturbances and differential shade tolerance among species.
Downed Logs
Course woody debris should be a prominent component of the forest floor. These downed logs should also be from multiple size classes and in various states of decay, suggesting that they are the result of long-term processes and not one single disturbance event. These logs contain much of the nutrients present in a stand, are important in maintaining forest hydrology, and function as important wildlife habitat.
Standing Snags
Standing dead trees are another prominent element of the old-growth forest. Snags indicate that trees have reached natural mortality in place and have not been selectively removed. Snags perform many of the same ecological functions as do logs and are a vitally important component of the ecosystem. They are particularly important for a variety of species of wildlife.
Treefall Gaps
Old-growth stands typically exhibit many small blowdowns of one to several trees. These blowdowns create a mixed overstory and markedly change the understory microenvironment.
Pit and Mound Topography
The microtopography of old-growth soil surfaces is often dominated by a rolling topography produced by windthrown trees. When the trees are thrown, their root mat and associated soil is ripped up from the forest floor, creating a pit or depression. As the root ball decays, the soil is loosened and falls into a mound adjacent to the pit. These pits and mounds are important in forest nutrient cycling and understory diversity, but are generally absent from human-disturbed forests.
Undisturbed Soils
Old-growth forests typically have a soil which is high in organic matter, with a thick organic layer and considerable numbers of ferns, mosses, and fungi. Not having experienced heavy logging equipment, horses, dragged logs, or grazing livestock, the soils will not be compacted.
Diversity of Plants and Animals
In addition to the abundance of ferns, mosses, and fungi, old-growth forests often have an increased diversity of understory herbs. This may not be the case in some old-growth stands of softwoods because of the decreased light and highly acidified soils, but it is generally the case in most old-growth hardwood forests. In addition to plants, there may be a variety of animals which are associated with old-growth stands because of their structural elements. Certain species of salamanders, soil invertebrates, small mammals, songbirds, and black bear are often found in much greater abundance in old-growth stands compared to younger stands.
Little or No Evidence of Human Disturbance
Stands with obvious signs of human disturbance cannot likely be classified as old growth. Stumps, mechanical bole damage, logging roads, skid trails, and yarding areas can provide direct evidence of logging. Evidence of livestock grazing might come from tree bole scars left from fencing, or small pens or corral areas for holding roaming stock. Past agricultural or homesite land is generally indicated by old plow furrows, piles or walls of rock, remnants of a house foundation or chimney, an abandoned cistern, or cultivated plant species.