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Changing Conditions of the Forest
The ability of nonfederal forests to provide a variety of benefits to the nation's citizens depends on the biological and physical conditions of these forests. For example, the U.S. Department of Agriculture's (USDA) Forest Service has identified potentially deteriorating and serious conditions of the nation's forests, which may be of concern when considering the future sustainability of forests, including nonfederal forests (Box 5-1). These conditions include loss of biological diversity, diminished water quality, effects of global climate change, and increased timber mortality. An assessment of these ecological trends and conditions is provided in this chapter. In addition, the effects of management intensity, forest fires, air pollution, climatic change, insects and disease, alien plants, and watershed characteristics on forest conditions are discussed.
Issues Involving Forest Condition
The term "forest" encompasses an enormous diversity of forest types and structures. The United States contains some of the most magnificent and biologically diverse forests of the world (Box 5-2). The particular kind of forest that occupies an area is determined by the interactions of several elements: the frequency and intensity of natural and anthropogenic disturbances, local environmental variability, and the available gene pool. Interactions among these elements
influence the species composition and structure of the vegetation and the nature of the ecological processes that characterize a particular forest ecosystem.
Forestland area in the United States (737 million acres) is about two-thirds of the forested area present during the 1600s (Darr 1995). Since the seventeenth century, approximately 124 million acres of forests have been converted to other uses, primarily agricultural. More than 75 percent of this conversion has occurred in the last century (Darr 1995). Noss and Cooperrider (1994) estimated that roughly half of the conterminous United States was forested at the time of European settlement. Forest area decreased between the late 1700s and World War I, stabilized at less than one-half of its presettlement area after the war, and today has been recovered in large part in the Southeast, Northeast, and Upper Great Lakes regions, mainly on private land. Only about 15 percent of the original forests remain, mostly in Alaska; the structure and composition of other forests appear to differ from pre-European settlement forests. Even where forest cover has returned, for example in the Northeast, residential development has intruded on recovering forest areas and reproductive success of neotropical migratory bird species remains low (Friesen et al. 1995).
Forest management has notable effects on animal biodiversity. Populations of certain game species, such as white-tailed deer (Odocoileus hemionus virginianus,
Biodiversity is one of several indicators used to assess the ecological health and sustainability of forests. Among the suggested definitions of biodiversity are:
The variety of life and its processes; it includes the variety of living organisms, the genetic differences among them, the communities and ecosystems in which they occur, and the ecological and evolutionary processes that keep them functioning, yet ever changing and adapting (Noss and Cooperrider 1994).
The variety and abundance of species, their genetic composition, and the communities, ecosystems, and landscapes in which they occur. It also refers to ecological structures, functions, and processes at all of these levels. Biological diversity occurs at spatial scales that range from local through regional and global. (Society of American Foresters 1990).
The variety of organisms considered at all levels, from genetic variants belonging to the same species through arrays of species to arrays of genera, families, and still higher taxonomic levels; includes the variety of ecosystems, which comprise both the communities of organisms within particular habitats and the physical conditions under which they live (Wilson 1992).
a forest-edge species), have increased greatly, largely as a result of more forest cover of early successional forests and a reduction in natural predators. In this case, high deer population levels are affecting changes in plant species composition and success of reforestation efforts. Forest management also often has resulted in the simplification of forest structure and composition, most notably where older forests have been replaced by even-aged stands (Noss 1993). Many of the remaining old-growth forests that are currently susceptible to fragmentation resulting from forest management activities are located on public lands (Robbins et al. 1989, Norse 1990, Henjum et al. 1994).
The potential of nonfederal forestlands to contribute to the maintenance of biodiversity is great, given their extent, variety, potential management flexibility, and that they are the primary forest category subject to conversion to nonforest uses. The critical role of nonfederal forests was made evident in the first Habitat Conservation Plan for the northern spotted owl (Murray Pacific Corporation, Wash.) and Florida's statewide wildlife conservation plan (Cox et al. 1994).
Forest Fragmentation and Habitat Isolation
Fragmentation of forests and other habitats is considered one of the greatest threats to biodiversity worldwide (Ehrlich and Ehrlich 1981; Harris 1984; Diamond 1984; Wilson 1988, 1992; Soule 1991a,b; Noss and Cooperrider 1994). Primary
effects of fragmentation include reduction in remaining habitat area, alteration of the microclimate of the fragment site, and increasing isolation from other remnant patches (Saunders et al. 1991). Effects of increased fragmentation and isolation on biodiversity have been detected in several taxa in a variety of settings.
Numerous studies of breeding birds in small urban woodlots and woodlots of the eastern United States have shown severe population declines, particularly of neotropical migrants, between the late 1940s and the late 1980s. Although the specific ecological mechanisms responsible are poorly understood, the studies attributed the decreases, in part, to forest fragmentation (Finch 1991). In areas where large forest tracts have been fragmented into smaller isolated parcels, forest-interior species reproduce less successfully, resulting in population declines and local extirpations (Finch 1991). Robbins et al. (1989) found that 75 percent of the forest neotropical migrants experienced population declines between 1978 and 1987 in eastern deciduous forests, apparently caused by loss of wintering habitat in the tropics and fragmentation of breeding habitat. In the West, where fragmentation has been studied less, resident bird species appear to be more susceptible to fragmentation effects than neotropical migrants (Rosenberg and Raphael 1986, Sharp 1996). These effects include increased vulnerability of nests situated along forest edges and small forest fragments to predation and brood parasitism from brown-headed cowbirds (Molothrus ater) (Gates and Gysel 1978, Wilcove 1985, Yahner and Mahan 1996). Severe effects have been observed on nonfederal lands in Oregon where cutting intensities have been high (Sharp 1996). Birds in highly fragmented landscapes have less pairing success than birds in less fragmented areas (Gibbs and Faaborg 1990, Vilard et al. 1993). These isolated habitats might function as population "sinks," attracting birds to areas where reproductive success is comparatively low.
Populations of many organisms exist as metapopulations (subpopulations) linked to one another through dispersal (Harrison 1994). Although even less information is available on the demographics of metapopulations, dispersal among metapopulations is believed to play a key role in maintaining genetic variability and would be expected to be adversely affected by fragmentation of large forest tracts (Harrison 1994). Such fragmentation affects the population in addition to the recruitment necessary to prevent population extirpation (Donovan et al. 1995).
Rare and Endangered Species Habitat
Increasing attention is being paid to continued losses of whole types of ecosystems, beyond changes or losses of individual species, and possibilities of at least their partial restoration. For example, freshwater ecosystems in California and old-growth forests in the Pacific Northwest are being altered faster than most tropical systems and stand to lose as great a proportion of their species (Noss et al. 1995). Biodiversity at this scale can be affected by losses in total area through
conversion to other uses and by reductions in structure or composition. If the latter is sufficiently severe, it could be considered as habitat loss.
In some cases, conversion of original forests has been extensive. For instance, using satellite image analysis, Beebe (1991) found only one unharvested watershed of more than 30,000 acres in the coastal temperate rainforest region of Oregon and Washington. Similarly, Henjum et al. (1994) reported that 75 to 90 percent of the late-seral and old-growth forest patches that remain east of the Cascades in Oregon and Washington are less than 100 acres in size, and that no patches on three national forests in Oregon are larger than 5,000 acres.
Types of original forest ecosystems that have suffered extensive losses in the United States were grouped into three categories: critically endangered (more than 98 percent reduction), endangered (85 to 98 percent reduction), and threatened (70 to 84 percent reduction) (Noss et al. 1995, Noss and Peters 1995). Of six types of habitat suffering the greatest losses, most (30 percent) were forests, of which 15 percent were forested wetlands. (Noss and Peters 1995). Most of the habitat losses have occurred in the South, Northeast, Midwest, and California; these areas also have the highest proportions of nonfederal forests in the United States. The 10 most endangered forest types are southern Appalachian spruce-fir forest, longleaf pine forest and savanna, southeastern riparian forests, Hawaiian dry forest, California riparian forests and wetlands, old-growth eastern deciduous forests, old-growth Pacific Northwest forests, old-growth white pine forests, old-growth ponderosa pine forests, and southern forested wetlands. Each has experienced dramatic reductions in area, is highly fragmented, contains relatively high numbers of endangered species, and faces continued threats from a variety of sources (Noss and Peters 1995). For instance, the Southeastern longleaf pine wire-grass (Aristida stricta) community, perhaps the most reduced forest type in the United States, contains 27 federally listed and 99 candidate species. The former include 18 plants, 4 reptiles, 4 birds, and 1 mammal; the latter include 70 plants, 10 insects, 4 amphibians, 7 reptiles, 4 birds, and 4 mammals (Noss et al. 1995).
Nonfederal forestlands, therefore, have a critical role to play in biodiversity conservation. Conservation planning and programs should incorporate all owners across the various landscapes, which together support the nation's biodiversity.
Forest Management Intensity
The intensity with which management practices are applied can have implications for the sustainability of nonfederal forests. Timber (solid wood) harvests from U.S. federal lands have decreased during the past 10 years and will continue to be substantially lower than harvests between World War II and about 1990 (Table A-19). The reduction in harvests is a result of changes in policies governing national forests, for example, the move toward ecosystem management (Box 5-3)
(Jensen and Everett 1994), and the depletion of remaining old-growth stands, which are high in volume and biomass relative to other forests but are comparatively low in their rate of biomass accumulation (Harmon et al. 1990). In the short term (for example, 5 years), increased rates of timber harvesting from private forestlands, primarily in the South, might make up the shortfall.
One way to increase wood flow from forests is to increase removals of biomass from each site. However, the effect of this action is debatable. Recent reviews conclude that increased removals of nutrients in the biomass will likely reduce long-term yields (Mann et al. 1988, Johnson et al. 1988, Dahlgren and Driscoll 1994). The shortening of cutting cycles will have similar effects. A potential reduction in long-term yields suggests that other forest management activities might be intensified so that higher yields from all lands could be expected to last indefinitely. Other ways to make up for the shortfall in wood are to (1) increase use of small log utilization technology and engineered wood, (2) increase use of composites to substitute for solid-wood products, (3) increase wood recycling, (4) increase area of private land devoted to timber production, (5) decrease use of (decrease demand for) timber products, and (6) increase use of wood substitutes such as plastics and steel studs. Demand does not appear to be declining, but most of the other changes are likely to occur to some extent. However, they are not expected to make up for the potential shortfall (USDA Forest Service 1995). An additional constraint to shifting the timber harvest from federal to private lands is that many industrial private forestlands in the southern United States already are heavily devoted to producing pulp fiber for paper production, and nonindustrial forestlands of the region are decreasing in area (Table A-3).
What does ''increased management intensity" mean? Although the specifics will vary greatly from one forest area to another and from one ownership to another, in general it means that fossil-fuel inputs are increased, possibly through additional labor, machinery use, fertilizers, pesticides, or even irrigation, to increase tree growth and, hence, timber removal per acre. The average stocking (volume of timber) per acre on industrial forestlands is already almost 40 percent greater than the national average for all forests (Powell et al. 1993), primarily reflecting investments in management intensity. Most timber-stand improvement is occurring on nonfederal forestlands, 70 percent on industrial lands alone. Long-term forecasts are for more management changes on industrial lands, but for small changes on nonindustrial forestlands (Haynes et al. 1995). Currently, only 20 percent of nonindustrial private landowners have a written management plan for their forests (Birch 1996).
Under any definition of "sustained yield management," increases in yield resulting from more intensive management should offset the additional inputs, and wood harvested over multiple harvest intervals should at least remain constant. One recent change in management practice that is viewed as positive according to most criteria is the enhanced training of loggers and the adoption of "reduced-impact harvesting," whereby residual trees and other aspects of long-term ecosystem functioning are minimally affected by logging operations (MacKay et al. 1996).
One common method of intensifying management is through planting genetically improved tree seedlings or cuttings, rather than relying on natural regeneration. This method ensures that little or no time is lost in the tree-growth cycle, assuming adequate success in establishment. In some cases, tree planting is accompanied by chemical or mechanical removal or suppression of competing vegetation. A measure of the changes expected from tree planting is the projected steady increase in planted area on private lands in the Southeast, South Central, and Pacific Northwest regions during the period 1990-2040 (Tables A-8 and A-9). The area of federal land that has been planted has consistently decreased in all regions through 1995 (Table A-6), a trend projected to continue. The tree-planting trends are also highly regional, the greatest decreases occurring on federal lands in the Pacific Northwest and the greatest increases occurring on industrial and nonindustrial private lands in the South (Table A-6). In addition, changes in incentive programs (for example, in the Conservation Reserve Program between 1986 and 1989) have led to intervals during which substantially greater numbers of acres have been planted, confusing the long-term picture.
Increased management intensity for tree-fiber production creates greater uncertainty, if not actual decline, in the delivery of other natural and societal benefits from forest ecosystems. Forests managed with greater attention to tree growth and harvest removals will be simpler in terms of structure (spatial heterogeneity within a stand) and biodiversity than unmanaged forests. For example, reductions in coarse woody debris, such as standing dead trees and downed logs,
and complex living vegetation structures, such as large older trees, have potentially negative consequences for some wildlife, especially specialist insectivores (Maser 1994). These reductions also decrease the long-term nutrient and organic-matter (carbon) storage of forest sites.
From 1990 through 1996, approximately 1.7 million acres of state and private forest and rangeland burned each year in the United States. Wildfires in nonfederal forests can result in immediate catastrophic losses, including loss of timber, wildlife habitat, recreational opportunities, and aesthetic values of land. Although the total area burned by wildfire has declined nationwide during this century, that statistic masks disturbing trends: the total area burned is increasing in the West, and the average severity of these fires is increasing (Agee 1993). Long-term wildfire trends are difficult to predict because of potential changes in climate, particularly altered patterns of precipitation.
Management of fire is paradoxical: long-term protection of resources through fire suppression results in fuel accumulation and associated risks to resources because the wildfires that do occur are more severe (Brown and Arno 1991). Many forest types evolved with wildfire as a natural periodic disturbance, and those types, sometimes called fire-dependent forests, benefit from the use of fire as well as its control. Fire should be recognized as an important ecological process to maintain the diversity and productivity of wildlands. It can be used as an effective management tool to maintain fuel loads at manageable levels, particularly in ecosystems where fire was historically frequent and low in intensity. Trade-offs between prescribed fire smoke and wildfire smoke might be necessary to defend prescribed burning because of the air-quality effects. In addition, proposed changes in EPA air-quality standards at the national level to restrict fine particulates (less than 2.5 micrograms) could have a major impact on open burning because much of the smoke produced by prescribed fires contains particles within this range. Strategies for managing fire effectively are expensive and require substantial technical assistance. Because the costs of mistakes can be high in terms of property and lives lost, fire management likely will be used more by large nonfederal-forest landowners, such as tribal landowners or cooperatives of private or public landowners, than by small nonindustrial-forest landowners.
Fire at the wildland and urban interface, defined as the zone, area, or line where structures and other human development meet or intermingle with undeveloped wildland or vegetative fuels (SAF 1990), will be a critical issue on nonfederal forestlands. Residents of these areas, which are located across all parts of the United States, benefit from a close association with wildlands, but also face the potentially substantial costs of property damage from wildfires. Such fires can move from residential communities into surrounding wildlands or from wildlands to intermingled residences. The problem is growing for two
reasons: (1) urban residents are moving in greater numbers to urban-interface property, and (2) accumulation of highly flammable fuels is increasing partly because of the success of past fire-suppression efforts.
Six of the 10 urban-interface wildfires with the highest losses of structures in California history have occurred since 1990; similarly increasing losses are occurring in Michigan, Florida, Colorado, and Washington. The problem is national, and it is growing. Many of the intermingled lands are privately owned, and fire protection for both structures and wildlands is the responsibility of state and local agencies. Federal agencies have long been requested to assist local forces in these crisis situations, even when there is no threat to federal lands. Priority has been given to scattered structures, resulting in considerable sacrifice of natural-resource values and the threat of loss of structures elsewhere. Substantial costs to all levels of government and insurance carriers are increasing, and urban-interface residents have suffered financial and emotional losses.
As the problem increases, the response capability of government is decreasing. Federal policy defined fire-protection priorities as (1) life, (2) property, and (3) resources. The 1995 Federal Wildland Fire Management Policy and Program Review redefined these priorities as (1) life, and (2) property and natural and cultural resources based on relative values to be protected, commensurate with suppression costs. That redefinition implies a cutting back of urban-interface structural protection by federal fire fighting forces and a shifting of cost to state and local agencies. The federal government would continue to be involved operationally in urban-interface fire fighting, hazardous-fuels reduction, cooperative fire prevention and education, and technical assistance. A major challenge is to develop a uniform national approach to hazard and risk assessment and fire prevention and protection in the urban and wildland interface.
A successful approach to wildfire prevention and control, urban-interface fire problems, and intelligent use of prescribed fire should shift the focus away from emergency fire fighting efforts to an emphasis on enhancing preventive approaches that are well-established as successful methods to avoid loss. Primary fuel-management approaches are reducing fuel in wildlands and around structures and decreasing the flammability of structures. Technical assistance can improve the implementation of these and other approaches and will complement fire prevention, fire suppression, and prescribed fire efforts.
In addition to changes in fire regimens for nonfederal forests in the United States, changes have occurred in the air quality and environmental conditions of these forests during the past decade, although the ecosystem consequences are harder to determine. Issues involving climate or air quality will be resolved only through the involvement of the federal, state, and local government, and the nongovernmental sector.
Some measures of air quality have demonstrated marked improvement since 1985, and in general, rural air quality over the United States has improved over the past decade. In both rural and urban areas, substantial progress has been made in reducing carbon monoxide and sulfur dioxide emissions and atmospheric concentrations. However, several major cities still have not complied with the ozone air quality standards of the U.S. Environmental Protection Agency. A major accomplishment has been the marked reduction in acid rain over forestlands of the northeastern United States (EPA 1994). However, reduced acidity, per se, might not accomplish as much as initially thought in terms of forest health. Chronic nitrogen additions might continue after SO4 concentrations (and hence pH) in rainfall have been reduced and might lead to nitrogen saturation of soils and increased cation leaching, conditions that emissions controls and sulfur reductions originally were designed to mitigate (Aber 1992).
Air quality definitely is affecting tree and forest health in many urban forests and in forests in airsheds surrounding large urban areas. These areas deserve special attention, because they vividly show the acute long-term effects of air pollution on trees and forests (for example, ozone damage to ponderosa pine trees in the San Bernadino Mountains outside Los Angeles; Miller and Evans 1974). These areas illustrate conditions that could become more common for forests in general. However, even chronic low-level exposure to ozone in rural ambient air may be negatively affecting forest productivity over much of the United States (Reich and Amundson 1985).
Urban forests are exposed to more altered environmental conditions than most rural forests. Concentrations of some agents, such as hydrocarbons, carbon dioxide, dust, or ozone, are higher in urban than in rural air. Major cities form what are known as "heat islands," where the temperature of the city center may be as much as 10° F higher than that of the surrounding countryside (Oke 1982, Lein 1989). The consequences of this temperature difference for tree health and forest dynamics are difficult to predict.
Trees and forests in urban areas can respond to changes in environmental conditions, but they also can contribute greatly to their amelioration. A study of metropolitan Atlanta showed that the urban forest has decreased by 65 percent since 1972. During the same period, average summer temperatures increased nine degrees more than those of the surrounding countryside (American Forests 1996). Increases in ambient temperatures might also contribute to Atlanta's ozone problem, and necessitate greater use of fossil-fuel energy to offset the increased environmental temperatures. In urban air, ozone is a highly reactive substance that breaks down on contact with most surfaces. Because trees have a higher surface area than other ground covers, provided primarily by leaves, they enhance the breakdown of ozone (Cavender and Allen 1991), even if they are damaged at high ozone concentrations. In addition, trees store carbon, filter particulates, absorb nitrogen from rain as NO3 in solution and from dry air as HNO3 vapor and NH4, and provide shade and other benefits,
thus contributing greatly to the general amelioration of poor environmental conditions.
Atmospheric carbon dioxide has increased monotonically worldwide during the past century and might continue to do so for decades to come. Some circumstantial evidence indicates that forests in the temperate zone are responding to increased atmospheric CO2 through increased carbon fixation and growth (Ciais et al. 1994). That is an area of intensive research, and it is not yet possible to conclude whether the effects of elevated CO2 will be positive, negative, or neutral for trees, forests, or forested ecosystems in the United States.
However, forest management in some areas might be affected by the perception, if not the reality, that trees might also contribute to environmental quality problems. That notion is primarily based on the fact that many trees emit volatile organic hydrocarbons (VOCs) known to interact with NOx produced during fossil-fuel combustion to generate ozone in the presence of light (Corchnoy et al. 1992). Chameides et al. (1988) determined that hydrocarbon emissions from pine forests in the southeastern United States could account for the fact that, although hydrocarbon and sulfur emissions from automobiles had been greatly reduced, NOx was still emitted in sufficient amounts to combine with biogenic hydrocarbons from pine forests so that ambient air concentrations of ozone in Atlanta had essentially not changed. It is important to note that many other plants besides trees also emit hydrocarbons and that very little quantitative information exists on this subject.
Trees present one other potential problem. Because many trees use high amounts of soil water to support their growth, their presence in marginally dry areas might be a drawback if less water is available for other valuable vegetation or humans. However, the water intake of different tree species (conifers versus hardwoods) varies considerably, and quantitative values for water consumption are surprisingly rare in the literature.
The collective benefits of trees, in terms of enhancing environmental quality, far outweigh their potential negative effects. Land management with a focus on environmental quality must include trees.
The expansiveness of nonfederal forests in the United States suggests that they have implications for issues involving carbon sequestration. Given that organic matter is approximately 50 percent carbon and that living trees accumulate more carbon in their biomass than they respire, mature forests contain more organic matter per unit of ground area than any other potential form of cover (United Nations 1992). For example, although closed-canopy forests are estimated to occupy only about one-third of the global land area, they contain about 90 percent of all the carbon in vegetation and 40 percent of all of that in soil. Thus, forest management has a great potential to positively affect carbon balances by sequestering carbon from the atmosphere. In the United States, 50
percent of the carbon in timberlands is estimated to be in the mineral soil of forests, 33 percent is in tree biomass, 10 percent is in woody debris, 6 percent is in the forest floor, and 1 percent is in understory vegetation (Turner et al. 1995). On the other hand, clearing forests and converting land to other uses annually release large amounts of carbon back to the atmosphere, especially in the tropics (IPCC 1996). Tree and forest management and carbon sequestering are therefore inextricably connected.
Currently, the United States is a net sink for atmospheric CO2, largely because of the recovery from earlier periods of extensive harvesting, agricultural conversion, and mis-management (Turner et al. 1995). About two-thirds of the carbon stored on timberland in the United States is stored on private forestland. Nonindustrial private forestlands offer the greatest opportunity for increasing terrestrial carbon storage in the United States, because of their availability (compared with land currently in cultivation) and underuse as illustrated by their low stocking density and volume estimates (Powell et al. 1993). Clearly, carbon storage on many nonindustrial private forestlands can be increased. The extent to which this can occur will depend on the motivation of landowners and the degree to which they take advantage of incentive programs.
The overall greatest potential for increasing biological carbon sequestration is through the forestation of areas currently without forest cover. Carbon sequestration policies and programs must focus on agricultural lands and marginally used lands. Fewer opportunities exist for sequestering additional carbon on currently forested lands, but conservation programs are important in maintaining current forests, stores of carbon—particularly in the remaining large, older forests—and rapid reforestation of cutover areas. Additional sequestration can also occur if wood is harvested using reduced-impact logging techniques and the wood removed from forests is used in longer-lived products.
Urban areas can also have an important role in carbon sequestration (Nowak 1994). Urban tree cover, biomass, and carbon storage can be expanded and fossil-fuel consumption can be reduced for additional carbon savings.
Forest Insects and Diseases
Forest insects and diseases at endemic levels are natural components of healthy forest ecosystems. They thin stands, provide food for wildlife, and control other biota. Epidemic levels of insects and diseases have occurred for millennia in U.S. forests and have caused substantial mortality in forests from the Northwest to the Southeast. Currently, 4-5 billion cubic feet of timber are lost to insects and disease each year in the United States. The mortality of a tree or group of trees occasionally is part of a healthy forest ecosystem and might not appear in routine forest inventories. When mortality becomes substantial, however, the impact affects large areas and multiple ownerships.
Three factors have increased attention to forest losses resulting from insects
and disease: (1) fragmentation of forest ownership and substantial increases in the number of owners of nonfederal forestland, making even minor insect or disease epidemics a substantial problem for individual forest owners; (2) inadequate management by forest landowners and unthrifty forests, resulting in substantial areas of susceptible forest; and (3) introduction of alien insects and diseases with no natural controls that attack native species. Many nonfederal-forest landowners, particularly nonindustrial forest landowners, do not have the technical knowledge or assistance to design prescription to protect against native insects and diseases.
In the West, native forest insects and diseases are increasingly attacking old forests at epidemic levels, which, in many cases could be protected against through appropriate management. Because many organisms are species-specific or group-specific and attack trees of low vigor, selection of appropriate species or management of a stand to provide adequate vigor might prevent epidemics. Thinning is often effective at reducing competition among trees and results in increased vigor of the residual trees (Waring and Pitman 1980). High-vigor trees are often successful at repelling attacks by insects, such as pine beetles. High-vigor trees that have adequate nitrogen also have been shown to be more resistant to pathogens, such as laminated root rot (Matson and Boone 1984). In such cases, active management can increase protection against insects and disease. For example, in the South, early cultural practices intensified fusiform rust incidence through the planting of infected seedlings, intensive site preparation, fire control, selection for fast-growing genotypes without consideration of disease resistance, and expansion of the range and extent of susceptible species. Today this particular problem has been mitigated partially through the development of rust-resistant tree genotypes and improved stand management (Schmidt 1978).
During the twentieth century, numerous insects and diseases have been introduced in the United States. Many did not find appropriate ecological niches and disappeared. Others found ideal conditions to flourish, at the expense of native species. Among the worst have been the European gypsy moth, Dutch elm disease (American elm), white pine blister rust (white pines), pine shoot beetle (conifers, especially pines), phytophthora root rot (Port Orford cedar), and chestnut blight (American chestnut).
Biotic diversity and wildlife habitat are seriously impaired by these organisms. Some, such as chestnut blight, have resulted in near extirpation of native species by killing the host. Other organisms will affect future losses: white pine blister rust damages mature and kills young whitebark pine, the seeds of which are a critical source of food for grizzly bears in the Rocky Mountains.
Plants that are nonindigenous to a geographic locality are called "alien," as well as "exotic," which does not convey the ecological risk posed by the more
aggressive term "aliens." Some invade only disturbed areas; others invade healthy and normally functioning ecosystems. An example of the former is cheatgrass, which typically invades overgrazed rangelands. The knapweeds are examples of the latter, which are capable of moving into high quality rangelands and deteriorating the range condition.
Aggressive nonindigenous plants are well-adapted to a variety of sites and are resilient to disturbance. Invasions of nonindigenous species are among the most pervasive influences on the biodiversity of ecosystems (Coblentz 1990). Among some of the alien plants affecting nonfederal forestland are scotch broom, gorse, kudzu, haole koa, melaleuca, Australian pine (Casuarina), poka vine, cogon grass, pampas grass, and ivy. Most are well-adapted to fire, and wildfire often results in their continued spread. These problems are likely to increase. Management controls are often ineffective because nonindigenous plants are so well-adapted to disturbance, often more so than indigenous plants. As effective strategies to control some aliens are implemented, others will continue to be introduced.
Ecologically healthy watersheds located within nonfederal forests are maintained by natural disturbance processes (Naiman et al. 1992). A dynamic, rather than a steady-state, equilibrium is characteristic of resilient and productive watersheds. Changes in riparian forests, wildlife habitat, water quantity and quality, and sediment are all part of healthy watersheds from the headwaters to the estuaries. As the watershed increases in scale, more landowners are likely to be involved in the improvement, maintenance, or degradation of watershed quality. State regulations and voluntary Best Management Practices (BMPs) are almost always associated with watershed quality, and federal cost-share programs. Watershed integrity has been of concern to programs administered through the USDA and have often focused on watershed restoration (Agricultural Conservation Programs [ACP] and Conservation Reserve Program [CRP]), as well as the programs of the U.S. Environmental Protection Agency, the U.S. Army Corps of Engineers, the U.S. Fish and Wildlife Service, the National Marine Fisheries Services, and the Bureau of Reclamation. Watershed integrity includes more than just chemical measurements of water quality (Box 5-4).
The cyclic nature of natural disturbances of the past have set into motion complex sediment routing patterns from smaller to larger-order streams (Benda 1990). One of the primary lessons from this behavior is that watershed maintenance and restoration must include a long time frame, whether the focus is for natural forests, transitions from natural forests to plantations, subsequent rotations of trees, conversions of old fields to new forests, or conversions of forests to agricultural or urban uses. Each of those uses will affect watershed integrity in positive or negative ways, and some effects might have considerable time lags, particularly in large-order watersheds (Swanson et al. 1992). The value of watershed
integrity to the public is often expressed for large-scale watersheds across many ownerships (Box 5-4) but the value is derived from the processes occurring at smaller scales.
Summary of Findings and Recommendations
Fundamental sustainability of the ecosystems that are a part of nonfederal forestlands is critical to the production of goods and services that Americans are likely to expect from these forests in the future. The problems caused by forest fragmentation, land conversion, intensive land management, fire, pollution, climatic change, insects, disease, and alien plants are landscape-level and cross the boundaries of many ownerships. From a social and an environmental perspective, it is important that the adverse affects of catastrophic levels of fires, winds, mammals, and insects and diseases be addressed. An enhanced, coordinated approach involving the federal government and nongovernmental landowners is needed for the management or mitigation of these impacts on forest health and sustainability.
Ensure the long-term integrity of forest ecosystems that comprise the nation's nonfederal forests, actively addressing conditions that diminish their ability to contribute to the well-being of the nation's citizens.
This recommendation points to the following specific recommendations:
- The federal government should strengthen programs that monitor nonfederal forest health, with special focus on early detection of conditions that could lead to catastrophic consequences.
- Federal assistance to states should be strengthened for wildfire suppression and fuel management technologies, while recognizing fire as critical to functioning, healthy ecological processes.