W. Wallace Covington
School of Forestry
Northern Arizona University
Flagstaff, AZ 86011
Margaret M. Moore
School of Forestry
Northern Arizona University
Flagstaff, AZ 86011
William A. Niering
Department of Biology
Connecticut College
New London, CT 06320
Joan L. Walker
USDA Forest Service
Southern Research Station
Clemson University
Clemson, SC 29634-1003
This extended abstract presents an overview of a paper being developed for the interagency Ecologically Based Stewardship source book. For the sake of brevity we use ecological restoration of western conifer forests as the example for this abstract. However, in the full paper we will use examples from throughout North America, discussing not only forest ecosystems but also tundra, woodlands, grasslands, shrublands, deserts, wetlands, and aquatic systems.
The paper will deal with the science and practice of ecological restoration in the context of adaptive ecosystem management. Ecological restoration has as its goal the restoration of degraded ecosystems to more closely emulate conditions which prevailed before disruption of natural structures and processes, i.e., environmental conditions which have influenced native communities over recent evolutionary time. Humans are seen as vital to the restoration process. A central objective of ecosystem restoration is developing mutualistic human:ecosystem interactions so that biodiversity and human habitats are sustained. The goals of ecological restoration are compatible with ecosystem management goals. Ecological restoration has always involved partnerships between researchers and practitioners, consistent with the adaptive management approach of ecosystem management.
Ecosystem restoration is related to rehabilitation, reclamation, and bioremediation, although the goals of ecosystem restoration, restoration of natural conditions, are generally more ambitious. Nonetheless, all share to a greater or lesser extent some of the same techniques and can be viewed as closely allied.
Ecosystem restoration consists of a broad variety of practices designed to restore natural ecosystem structure and function. Historical analysis, paleoecological techniques, retrospective ecological analysis, and dendrochronology, along with other techniques, are used to determine the natural structure and function of the ecological system to be restored. Once goals and performance measures are clearly defined, the next step is to clearly define (diagnose) the ecosystem pathology, clearly specify assumptions about ecosystem dysfunction, and specify a set of alternative treatments for restoring ecosystem health.
Ecosystem health refers to the health of ecosystems in their entirety, including humans as members of ecosystems. Taking this metaphor a bit further, we can define ecosystem medicine as the science and art of dealing with the health of ecosystems, including the prevention, alleviation, and cure of diseases, where disease is defined as dysfunctions such that natural ecosystem structures and processes become disrupted. Among the most common symptoms of ecosystem pathology are unnatural irruptions or crashes of native species, disruption of natural disturbance regimes, degradation of ecosystem productivity, and invasion by exotic species. In a sense, ecosystem restoration as an ecosystem health discipline is analogous to general practice in the field of human medicine.
Ecosystem restoration should not be construed as a fixed set of procedures, nor as a simple recipe for ecosystem management. Rather, it is a broad intellectual and scientific framework for developing mutually beneficial human:wildland interactions compatible with the evolutionary history of native ecological systems. Ecosystem restoration consists not only of restoring ecosystems, but also of developing mutualistic human uses of wildlands which are in harmony with the natural history of these complex ecological systems.
The concept of the evolutionary environment is central to understanding ecosystem restoration. The term evolutionary environment is used to refer to the environment in which a species or groups of species evolved--the environment of speciation. Over evolutionary time species not only adapt to their evolutionary environment, but they may also come to depend upon those conditions for their continued survival.
To illustrate ecosystem restoration procedures, we will now turn to the example of western conifer ecosystems.
The evolutionary environment of western forest ecosystems is dominated by natural disturbance regimes (e.g., fires, predation, defoliation), which have varied in kind, frequency, intensity, and extent. These disturbance regimes served as natural ecological checks and balances on populations and insured spatial and temporal habitat diversity.
Natural fire regimes were particularly important in shaping the communities present at the time of Euro-American settlement. Exclusion of natural fires in the forests and woodlands of the West, coupled with global climatic fluctuations and increases in atmospheric carbon dioxide concentrations, has led to tree population irruptions, dead fuel accumulations, and landscape fuel continuity to such an extent that the niches of some species of plants, animals, and microbes have become threatened. In many cases, the natural functioning (e.g., successional processes, recycling processes) of these ecosystems has been severely impaired. Parallel declines in resource conditions for humans have occurred to a greater or lesser extent in all types.
As a result of increased tree densities in the ponderosa pine type, the increase in late successional species in the mixed conifer climax type, and the increasing landscape homogeneity in all types, catastrophic resetting of these systems by either large crown fires or large insect and disease epidemics is certain. And the resulting homogenous landscapes will tend to be self-perpetuating unless something is done to restore more nearly natural conditions.
Ecosystem restoration and management can remedy these problems and prevent wide-scale collapse of existing ecological systems. Ironically, this is especially true for wilderness areas and nature reserves where unnatural tree densities often exceed that of surrounding wildlands.
The general trajectory seems unequivocal. Continued climate changes coupled with fire regime disruption are likely to lead to continued high tree seedling establishment (especially of shade-tolerant species), intensified competition among established trees, further deterioration of tree vigor, and increased tree mortality from insects, disease, and drought. Thus, we should anticipate an acceleration of historical changes in western conifer ecosystems including increased fuel accumulations, lengthened fire seasons, and intensified burning conditions, all contributing to larger and more catastrophic wildfires. The threats to human lives and resource values are great.
Given current trends, scientifically based ecosystem restoration of western conifers is essential. In the case of ponderosa pine ecosystems, restoration might involve the retaining all trees which predate Euro-American settlement, thinning of most trees which postdate fire regime disruption, raking heavy fuels from the base of the trees to be retained, removal of exotic species, revegetation with native herbaceous and shrub species, and prescribed burning to emulate the natural fire regime.
There has been a lot of wishful thinking from different quarters that there might be some simple solution to ecosystem health problems, that thinning, prescribed fire, wildfire, bark beetles, or tree diseases alone will restore natural conditions. Although this may be true under specific circumstances of site, ecosystem condition, and disturbance environment, it is likely that the more general case is that these individual disturbances, in isolation, will result in only partial restoration of some individual ecosystem components. It is more probable that some combination of management actions and natural recovery processes will be necessary for restoration of western conifer ecosystems.
Given the diversity of human needs and wide variety of goals for federal lands and waters, it seems unlikely that vast areas will be restored to natural conditions. In fact, keeping some areas in a some-what artificial state may be desirable. Areas dedicated to wood fiber production, livestock grazing, non-native sportfishing, or other human habitat uses might fall into this category, with the caveat that it is generally safer to manage in harmony with natural tendencies. Such departures from managing within the range of natural range of variability should be made judiciously.