Robert C. Szaro
Abstract
There is surprisingly little integrative information on the status of forest biodiversity. Many exhaustive studies have been done on the attributes of particular forest ecosystems, their associated animal faunas, and their distribution across the landscape. Much of this information is fragmented, disorganized, and hardly comprehensive. Rarely have studies been done examining all vascular plants and vertebrates and their relationships in any given ecosystem, let alone the thousands of other species found.
Along the Pacific coast of North America lie some of the most valuable and complex forests in the world. Many of the tree species are unsurpassed in their size and longevity. In addition, there are hundreds of species of shrubs and other plants. The forests contain highly valuable watersheds, and they provide significant timber, range and recreation resources as well as prime habitat for wildlife and fish. Most Pacific coast forests originated following major land disturbances. Initially, the forests that became the present oldgrowth and younggrowth forests were even-aged or nearly so, with the relatively simple structure and species composition associated with stands of pioneer tree species.
Forests of the inland West blanket the foothills and mountains with a wide array of tree and understory species. Nearly all forests of the inland West are composed of conifers. The trees, associated vegetation, and animal life have adapted to each other and the various environments that occur on a range of mountains, or even a single mountain or plateau. Because the inland West is subject to seasonal drought, forest adaptations include responses to wildfires that occur at different intervals and intensities in the diverse mountain environments.
A new paradigm is needed for managing these forest ecosystems, one that balances all uses looks beyond the immediate benefits. Ecosystem Management is such an emerging ecological philosophy and approach to this challenge. Its goal is to restore and maintain the health, sustainability, and biodiversity of ecosystems while supporting sustainable economies and communities. Implementing biodiversity goals will require resources and knowledge. Current scientific understanding of ecological and social processes are far from perfect and will require additional resources for improving efforts in inventory, monitoring, and basic research.
Keywords: Biodiversity, Western North America, ecosystem management.
Introduction
There is surprisingly little integrative information on the status of biodiversity in forested ecosystems. Particularly as Maini (1992) pointed out that "forests are a rich repository of planet earths' genetic heritage." Forests are usually delineated by the presence of a few dominant species but this barely touches the surface of their species richness and all the thousands of other species likely to be found. Many exhaustive studies have been done on the attributes of particular forest ecosystems, their associated faunas, and their distribution across the landscape but it is extremely difficult to assess the overall status of forest biodiversity as much of this information is fragmented, disorganized, and hardly comprehensive. Rarely have studies examined all vascular plants and vertebrates and their relationships in any given ecosystem, let alone the thousands of other species found. Forest area in North America varies from a high of 45% in Canada to a low of 29% in Mexico (Szaro 1993). Canada, the United States, and Mexico all have some type of forest inventory. However, all have primarily been directed at determining volume of timber, predominant genera, and to varying degrees forest types or ecosystems. There are many problems in comparing data among the three countries including differing definitions for forest land, scales of resolution, and methods of access to available but oftentimes unpublished information. These problems are further exacerbated by the fact that there is no agreed-upon ecosystem classification that could serve for forest biodiversity in the continent as a whole. As a result data on forest biodiversity is artificially fragmented into sections based on political boundaries that obviously would not be a first choice in organizing any information on North American forest biodiversity, but is an unfortunate necessity.
Ecological characteristics of forests should be examined in terms of compositional, functional, and structural features (Crow 1989). Forests are much more than simply a collection of varying tree species. There are thousands of vascular plants, vertebrates, and other plant and animal species in any forest type interacting through many processes and pathways. For individuals and populations, these interactions include such mechanisms as predation, competition, parasitism, and mutualism, while communities change through the process of succession in response to disturbance phenomena and interact through nutrient and water recycling (Reid and Miller 1989).
Although intensive forest management can simplify ecosystems, other forestry practices can maintain ecosystem integrity (U.S. Council of Environmental Quality 1990). Strategies for maintaining complex forest ecosystems include preventing soil erosion, leaving standing dead trees (snags) and fallen trees, leaving living trees as biological legacies. In the Blue Mountains of Oregon, those plant communities most affected by timber management activities, i.e., ponderosa pine (Pinus ponderosa) and mixed conifer, are also the most productive in terms of wildlife (Thomas 1979). Yet, timber management or other natural disturbance processes can maintain the mosaic of successional stages across the landscape. Conserving the biodiversity of temperate forests requires the maintenance of all forest successional stages (Franklin 1988), For example, in the Blue Mountains, as in other forests, the primary forest types have differing mixes of vertebrate species richness from the grass-forb stage to old-growth condition (Szaro 1993).
Alterations in forest structure can effect the conditions necessary for the survival of many species. Clearcuts within a forest create open areas that change temperature and moisture regimes and reduce the amount of cover (U.S. Council of Environmental Quality 1990). Fragmentation also exposes the interiors of the remaining patches to both external physical and biological factors that enhances the conditions for some species but decreases them for others. In a larger spatial context of a landscape, species diversity is usually reduced, not increased, by fragmentation. Species adapted to conditions in the interior of large contiguous forest patches are often lost as patch sizes are reduced and the numbers of openings increased.
Much of the concern for biodiversity stems from the increasing evidence for growing losses of species (McNeely et al. 1990, Wilson 1988, WRI/IUCN/UNEP 1992). Habitat loss, degradation, and fragmentation are the most important influences upon species extinction rates (Reid and Miller 1989). Human impacts on the environment do not threaten all groups of species equally with those at greatest risk having small population sizes, varying greatly in population size, or having slow rates of population growth (Reid and Miller 1989).
Ecoregions of the United States
Bailey (in press) described ecoregions of the United States that were differentiated according to a hierarchical scheme modified from Crowley (1967) based upon using climate and vegetation as indicators of the extent of each unit (Figure 1). There are three levels or categories of this hierarchy with the two broadest, domains and divisions, based on the large ecological climate zones identified by Koppen (1931) and modified by Trewartha (1968). Climate was emphasized at the broadest levels because of its overriding effect on the composition and productivity of ecosystems from region to region.
By interpreting the climatic levels of mountains as altitudinal variations of corresponding climatic zones, it is possible to distinguish the following domains and divisions:
Each division is subdivided on the basis of vegetational macro features into provinces, which express more refined climatic differences than the domains and divisions. Mountains exhibiting altitudinal zonation and the climatic regime of the adjacent lowlands are distinguished according to the character of the zonation. The following describes the major forest types within the Humid Temperate and Dry Domains of North America in order to help describe the depth and breadth of its diversity (condensed from the accounts of Fiske and Debell 1989 and Schmidt and Larson 1989 as given in Burns 1989).
Figure 1. Ecoregions of the Western United States (Adapted from Bailey et al. 1994).
Pacific Coast Forests (Humid Temperate Domain)
Along the Pacific coast of North America lie some of the most valuable and complex forests in the world. Many of the tree species are unsurpassed in their size and longevity. In addition, there are hundreds of species of shrubs and other plants. The forests contain highly valuable watersheds, and they provide significant timber, range and recreation resources as well as prime habitat for wildlife and fish. The various tree species have different traits that enable them to become established, grow, and reproduce under specific forest environments. Most Pacific coast forests originated following major land disturbances. In coastal Alaska, glacial advance and retreat has been and continues to be a significant factor in establishment of forests. In Washington, Oregon, and California, however, most of today's oldgrowth forests were established following fires occurring centuries ago. Many of today's young-growth forests typically were established after fires and timber harvesting since the 1830's. Initially, the forests that became the present oldgrowth and younggrowth forests were even aged or nearly so, with the relatively simple structure and species composition associated with stands of pioneer tree species. Where disturbances, such as periodic fires, have been frequent, the evenaged character and dominance of pioneer tree species have been sustained. In some stands these trees occur in two or three age classes; the origin of each age class followed a fire or other major disturbance, such as a windstorm or tree harvest.
Where frequent major disturbances have not occurred, tree species that are not dependent on major disturbances for establishment, such as western hemlock (Tsuga heterophylla), some true firs (Abies spp.), and tanoak (Lithocarpus densiflorus), have become established under the canopies of pioneer species. These species are adapted for establishment and growth in small openings caused by minor disturbances, such as the death or harvesting of a single large tree and are generally characterized by tolerance of shade. This results in the creation of multiaged stands with greater structural and species diversity. Given enough time, western hemlock will gradually replace Douglas-fir (Pseudotsuga menziesii) or red alder (Alnus rubra) in stands in western Washington or Oregon (Williamson and Twombly 1983), tanoak will replace Douglas-fir in southwestern Oregon and northwestern California (McDonald et al. 1983), and white fir (Abies concolor) and incensecedar (Librocedrus decurrens) will replace ponderosa pine in the mixed conifer forests of the Sierra Nevada (Laacke and Fiske 1983).
In contrast, other species are well adapted to large openings, created
by wildfire, extensive windthrow, flooding, timber cutting, or agricultural
cultivation. Such species are referred to as "pioneers" and include
some of the most soughtafter timber trees: Douglas-fir, ponderosa pine,
redwood (Sequoia sempervirens), and sugar pine (P. lambertiana).
These species can become established and grow rapidly in conditions of
bare soil, full sunlight, and wide temperature fluctuations associated
with large
forest openings.
Millions of hectares have also been logged selectively, many stands several times. Typically, the larger, more valuable trees were harvested, leaving substantial acreage with small trees of poor quality. This situation is particularly prevalent in California. Selective harvesting often caused a shift in dominant species from the more valuable pioneer species, such as Douglasfir, ponderosa pine, and sugar pine to the shadetolerant, commercially less valuable species, such as tanoak, Pacific madrone (Arbutus menziesii), grand fir (Abies grandis), and white fir (Dunning 1923, Isaac 1943, Munger 1950).
Between the extremes are many other species that are well adapted to openings of intermediate sizes or to disturbances of moderate severity. Moreover, many species are able to complete their life cycles in openings of various sizes. Many Pacific coast tree species have adaptations to cope with periodic wildfires. Redwood, tanoak, Pacific madrone, and the live oaks sprout vigorously from root crowns or the base of the trunk, even after being severely burned. Many hardwood seedlings or saplings develop root burls so that they can sprout after fires. Other species develop thick bark to insulate against heat injury, such as ponderosa pine, sugar pine, redwood, and giant sequoia (Sequoiadendron giganteum). Some species, such as lodgepole pine (Pinus contorta), Monterey pine (P. radiata), and knobcone pine (P. attenuata), take advantage of wildfirecreated openings by having cones that stay closed until heated. Douglasfir, hemlock, and white fir can disperse their seed via wind over considerable distances to burnedover areas.
Pacific coast forests occupy about 28.3 million hectares of commercial forest land in south central and southeastern Alaska and in Washington, Oregon, and California west of the crests of the Cascade and Sierra Nevada Mountains (USDA Forest Service 1982). Timber harvesting and occasional wildfires have substantially reduced the acreage of oldgrowth forests; this is a continuing trend. Millions of hectares of oldgrowth forests have been harvested, typically by clearcutting, and replaced by young, more rapidlygrowing plantations, especially in western Washington, western Oregon, and northwestern California The Society of American Foresters has classified 28 forest types in the Pacific coast forests, indicating the great ecological and geographic diversity occurring there (Eyre 1980). The 28 types occur in different environments, usually caused by the different temperature and moisture conditions associated with coastal, inland, or mountainous conditions. For convenience in this discussion, the 28 types have been combined into six major kinds of forests.
Western hemlock-Sitka spruce forests are northern coastal forests dominated by western hemlock and Sitka spruce (Picea sitchensis), occurring in areas with a maritime climate from southcentral Alaska to southern Oregon. Associated coniferous and hardwood species include Douglasfir, western redcedar (Thuja plicata), Alaskacedar (Chamaecyparis nootkatensis), red alder, vine maple (Acer circinatum), and bigleaf maple (A. macrophyllum) (Minore 1980). Hardwooddominated stands are a minor component of these forests.
Douglas-fir forests are widely distributed inland from the hemlockspruce
forests, at low elevations west of the Cascade Range in Washington and
Oregon, and on the west side of the Coast Range in northwestern California.
The environments are characterized by moderate temperatures and soil moisture
conditions.
Associated conifers and hardwoods include western hemlock, western redcedar,
red alder, black cottonwood (Populus trichocarpa), bigleaf maple,
vine maple, tanoak, and Pacific madrone (Williamson 1980).
True fir-hemlock forests occur on the middle and upper slopes
of the Cascade Range in Washington, Oregon, and California; in the
Olympic Mountains of Washington; and on the upper
slopes of the Sierra Nevada and northern Coast Ranges in California. The
climate is cool and wet; snowpacks are present up to 8 months each year.
The common dominant conifer species vary by latitude and elevation, occurring
singly or in different associations: Pacific silver fir (Abies amabilis),
mountain hemlock (Tsuga mertensiana), noble fir (Abies procera),
California red fir (A. magnifica), grand fir, white fir, western redcedar,
Alaskacedar, and western white pine (Pinus monticola) (Franklin
1980a, 1980b, Gordon 1980a & b).
Hardwood forests occur at low to middle elevations from Alaska to southern California. These forests are not extensive in the Pacific Northwest but cover millions of hectares around California's Central Valley and southern Coast Range. The species composition also varies greatly with latitude. Red alder and black cottonwood stands dominate in the cool, moist northern environments. Tanoak and Pacific madrone occur in the somewhat drier and warmer environments of southwestern Oregon and northern California. Farther south, coast live oak (Quercus agrifolia) woodlands are sometimes associated with Californialaurel (Umbellularia californica) near the coast. Inland central and southern California woodland associates include canyon live oak (Quercus chlysolepis), valley oak (Q. lobata), and blue oak (Q. douglasii) (Finch and McCleery 1980).
Redwood forests typically occur on moist river flats and cool slopes near the coast up to about 915 m elevation in northwest and central California, and in the extreme southwestern corner of Oregon (Roy 1980). Common associates of redwood are Douglasfir, PortOrfordcedar (Chamaecyparis lawsoniana), tanoak, Pacific madrone, and Californialaurel.
Mixed conifer forests occur on drier sites inland from the Douglasfir forests and at lower elevations than the true fir-hemlock forests in southwestern Oregon and northern California. The range extends south along the Sierra Nevada Range to the Transverse Ranges of southern California. Stands typically consist of Douglasfir, ponderosa pine, sugar pine, white fir, and incensecedar, but composition varies considerably. Common associates are Oregon white oak (Quercus garryana), California black oak (Q. kelloggili), and canyon live oak (McDonald 1980, Sawyer 1980, Tappeiner 1980).
Western Inland Forests (Dry Domain)
Forests of the inland Western United States blanket the foothills and mountains with a wide array of tree and understory species. Nearly all forests of the inland West are composed of conifers that have regenerated from seed dispersal naturally from immediate or adjacent areas. Lands between the mountain ranges are typically occupied by grasses and shrublands. The mountains themselves strongly influence the environment and the forests they support, causing significant changes over relatively short distances, typically ranging from semiarid, warm foothills in the lowlands to cold tundralike conditions at high elevations. The trees, associated vegetation, and animal life have adapted to each other and the various environments that occur on a range of mountains, or even a single mountain or plateau. Because the inland West is subject to seasonal drought, forest adaptations include responses to wildfires that occur at different intervals and intensities in the diverse mountain environments. The coupling of this with various insects, diseases, weather, and maninduced disturbances results in very complex and dynamic ecosystems.
Obviously, the inland West encompasses a wide variety of ecosystems and resources that do not necessarily behave in similar fashion. For this discussion inland forests are dealt with in three groupings or zones: lower slopes and foothills, montane, and subalpine. In general, the lower slopes and foothills zone is low, the montane is middle, and the subalpine is high elevation in relation to each other. This corresponds in most cases to drywarm at the lower elevation and coldmoist at the higher elevation with a gradient in between.
Lower Slope and Foothill Forests zone includes all or portions of the cover types - Northwest ponderosa pine and associated species, ponderosa pine, Rocky Mountain Douglasfir, Southwest ponderosa pine, Interior ponderosa pine in the Black Hills, and pinyon (Pinus edulis) - juniper (Juniperus spp.) (Burns 1983). These are the warmest and driest of the western forests. High temperatures and low moisture limit the number of species that grow together in this zone. One or two major species on any given site is the general rule. Ponderosa pine, Douglasfir, limber pine (Pinus flexilis), and various species of juniper or pinyon pine dominate the potential natural vegetation. Even in the absence of wildfire or other disturbance, these trees tend to replace themselves as the mature stands gradually die out.
Historically, wildfires burned through these stands very frequently, generally in the range of 5 to 30 years. This frequency prevented buildups of fuel and consequently most fires were of low intensity. Ponderosa pine and, to a lesser extent, Douglasfir develop thick, fireresistant bark as the trees mature. As a result large trees commonly survive fires, but their younger counterparts, particularly those with low crowns, usually succumb to fire. Open, parklike stands are perpetuated by frequent low-intensity fires. Early photographic records document the prevalence of these conditions when the West was being settled (Arno and Gruell 1987).
In the last 50 years, effective fire control has resulted in the establishment of dense multilayered stands of younger trees - often Douglasfir - below the canopy of the larger and older trees. Because of greater shade tolerance than ponderosa pine, it tends to replace ponderosa pine on shaded, lessdisturbed sites in this zone. Also, stands of ponderosa pine, pinyon pine, and junipers have become denser and, in some parts of the West, have extended their range into areas that formerly supported only grasses. Douglasfir is a particularly unique species because of its broad ecological amplitude-it can be found at low, mid, and high elevations from the southern to northern borders of the United States. As a result, on most sites in this zone it behaves as a late successional (relatively shade tolerant) species and in zones above this behaves as an early successional (relatively shade intolerant) species.
Because the lower slope areas adjoin grasslands, grazing of these stands by domestic livestock has been a major use from the time of earliest European settlement. Grazing, while it can be harmful to seedling trees, has also reduced the competition for moisture by the grasses. As a result trees have become established on some heavily grazed sites that formerly were considered grasslands.
Timber has been extensively harvested from this zone since the times of early settlement. The building of railroads, towns, and cities during this era of expansion in the United States depended heavily on these oldgrowth, easily accessed stands of timber. Towns and cities generally were established in the warmer valley areas and the adjoining forests became convenient and valuable sources of timber and fuel. This also affected the stands that exist today because most of the larger, older trees were removed, and dense stands of smaller, lesser value trees remained in place. In addition, some of these residual stands were comprised of shadetolerant species that are far more subject to insect and disease problems.
Montane Forests are widespread throughout the West, occupying that broad band between the mountain foothills and the subalpine zones. Much of the montane zone occurs on steep mountain topography. Exceptions to this are the extensive lodgepole pine forests of the Rockies and the spruce forests of interior Alaska, both of which occur mostly on relatively gentle terrain. The large number of species in the Montane zoneranging from 2 or 3 on some sites up to 10 on others. These forests occur in a moderate temperature and moisture belt, usually dictated by elevation. As a result they are diverse in both flora and fauna. The area is often referred to as mixed conifer forests. Interior Douglasfir is the most commonly found species throughout much of this zone, both geographically and elevationally, but it nearly always grows in association with other conifers. This zone includes all or portions of the following types: northwest ponderosa pine and associated species; grand fir; Douglasfir and associated species; ponderosa pine; Rocky Mountain Douglasfir; western larch (Larix occidentalis); lodgepole pine; mixed conifers; western white pine (Pinus monticola); western redcedar (Thuja plicata); Southwestern mixed conifers; Rocky Mountain aspen (Populus tremuloides); and interior ponderosa pine in the Black Hills (Burns 1983). Interior Alaska white spruce (Picea glauca) is not a montane type but tends to respond in a similar way.
Fire has done much to shape the character of the stands and the trees that occupy this zone. Fires are frequent but less so than in the drierwarmer foothills zone where ponderosa pine and Douglasfir predominate. Stands here tend to be more productive and contain more natural fuels. When fires do occur, they typically destroy almost all trees in a stand (Burns 1983). To adapt to this situation, two groups of species developed over time. There is a group of plant and animal species (early successional) that benefits from frequent fire. Fireadapted trees tend to invade openings rapidly, grow rapidly in height, and demand full exposure to sunlight. Western larch, lodgepole pine, aspen, and western white pine fit this category - they depend on fires or other disturbances to regenerate. In this zone ponderosa pine and, to a lesser extent, Douglasfir are also favored by fire and major disturbances. Deer (Odocoileus spp.) and elk (Cervus spp.) are two wildlife species that benefit by the forage conditions stimulated by fire (Burns 1983; Thomas 1979).
A second group of species (late successional) are favored by long intervals between fires or major disturbances. These species are adapted to growing in the shade of other trees and are very fire susceptible because of highly flammable crowns and thin bark, which provides little insulation for the heatsensitive cambial layer inside the bark. They typically invade the early successional stands of trees that were established soon after a fire and eventually replace them. Tree species that are favored by lack of fire or other disturbances include white fir, grand fir, western redcedar, and white spruce. Wildlife species found in late succession stands often include cavity nesting birds such as woodpeckers and species favored by multiple canopy levels (Thomas 1979).
Like in the foothills zone, both longterm fire protection and harvesting
have had major effects on montane forests. Prior to settlement in the late
1800's and early 1900's, fire frequencies were likely in the range of 20
to 40 years (Arno and Gruell 1987). This restricted succession and resulted
in stands composed largely of early successional species. For much of this
century effective fire protection has allowed many stands to move further
toward stands comprised primarily of late successional and climax species.
Over much of the West for most of this century, various forms of cutting
that favored late successional species and discriminated against early
successional species were the favored methods of harvesting. These two
practices - fire protection and selection cutting - accelerated the succession
toward stands comprised largely of shadetolerant species such as white
fir, grand fir, and Douglasfir. In the
northern Rockies, there has been more use of clearcutting for the past
three or four decades and the succession toward shadetolerant
species may be less pronounced than in the southern Rockies.
Insects and diseases are a significant management problem in this zone but they vary substantially depending on local situations. Dwarf mistletoe is a serious problem in Douglasfir, western larch, lodgepole pine, and in some areas of ponderosa pine (Drummond 1982). In areas where grand fir, white fir, blue spruce, or Douglasfir are late successional species, western spruce budworm is a current and increasing problem. Also, Douglasfir tussock moth is a periodic defoliator of Douglasfir, white fir, and grand fir. Douglasfir bark beetle (Dendroctonus pseudotsugae) can be a serious mortality factor of oldgrowth Douglasfir in some locations. Mountain pine beetle causes recurring losses in lodgepole pine forests and is a significant management problem over a wide range of ecological habitats, in many cases essentially dictating management direction (Schmidt and Larson 1989). Root rots (Armillaria mellea and Phellinus weiril) are serious problems in localized areas killing most species of trees near infection centers. Various stem rots and decays also cause defects in all species. Indian paint fungus (Echinodontium tinctorum) is a major cause of defect in grand fir and white fir. The susceptibility and vulnerability of these forests to nearly all insect and disease problems are related to tree, stand, and site conditions such as age, stand density and structure, elevation, aspect, and the like.
Subalpine Forests abut the alpine zone and occupy the coldest and generally wettest zone of the inland mountain West. Characterized by short growing seasons and deep snow, these areas are usually dominated by the spirelike forms of Engelmann spruce (Picea engelmannii) and subalpine fir (Abies lasiocarpa) (Alexander 1986). Relatively few tree species are capable of growing on these subalpine sites and although these highelevation areas are less productive than the montane zone below them, they are still very important for timber, esthetics and recreation, summer forage for wildlife and domestic stock, and particularly for water.
Natural fires in this zone are less frequent than in either the montane or foothills zones, and their intervals are less well documented. When fires do occur, they are generally conflagrations in which all trees in the stand are killed. In the lower part of this zone, lodgepole pine and aspen often invade burned stands in a fashion similar to the montane zone. At the higher elevations, it is too cold for lodgepole pine or aspen and burned areas tend to be reinvaded very slowly by subalpine fir and Engelmann spruce or by mountain hemlock (Tsuga merten siana) in the Northwest (Burns 1983). Very severe sites within the zone are often marked with scattered occurrence of species such as bristlecone pine, whitebark pine (Pinus albicaulis), subalpine larch (Larix lyallii), and tundralike plants in the understory. All of the latter species contribute substantially to the uniqueness and esthetic values of this zone. Whitebark pine is particularly important because it produces cones and seeds that are key items in the diet of the grizzly bear (Ursus arctos horribilis), particularly important in the Yellowstone ecosystem.
In the early days, the alpine zone above timberline was important summer grazing for both sheep and cattle. Since then, grazing has gradually decreased in importance, but it remains a significant resource at certain locations throughout the upper subalpine and alpine zone.
Timber harvesting has long been important locally beginning in areas with long mining histories but more generally from the 1950's to the present. Extensive outbreaks of spruce bark beetles (Dendroctonus rufipennis) in the 1950's were the impetus for much of the cutting in the next two decades. Timber harvest is still a major activity in portions of the subalpine zone. The primary commercial species in this zone are Engelmann spruce and lodgepole pine. Other species, such as subalpine fir and mountain hemlock, are harvested but often have less value or are infected with trunk rot.
Throughout the subalpine zone, recreation use has increased substantially, especially since the 1960's. Substantial portions of this zone occur in wilderness, parks, and other areas dedicated primarily to recreation. Wilderness, backcountry hiking, crosscountry skiing, downhill skiing, and snowmobiling have become very important in parts of the zone. Management of forests to protect the esthetics or for snow retention in highuse recreational areas is becoming increasingly important. Because of the slowmelting deep snows accumulated in the winter months, this zone is the primary contributor to streamflow during the dry summer period. Fisheries, irrigation, and municipal water uses depend heavily on water flowing from this zone (Burns 1983; Alexander 1986).
There are fewer insect and disease problems so common in the lower elevation
areas. For example, budworm may feed occasionally on the true firs and
spruce in this zone but the climate is apparently severe and erratic enough
to limit sustained budworm populations. Much the same situation exists
for mountain pine beetle in this zone. Epidemic populations of beetles
that have built up in lower elevation forests sometimes move upward into
this zone, causing significant mortality of lodgepole pine and occasionally
whitebark pine. However, high populations of the beetle are seldom sustained
in this zone. The most significant insect problem is the spruce bark beetle.
Extensive stands of mature spruce can be decimated by the spruce bark beetle.
Infestations of the beetle are usually triggered by blowdowns, providing
ample food for population buildup and spread to
standing trees.
Future Management Options and Sustainability
The demands and expectations placed on biological resources are high and widely varied, calling for new approaches that go beyond merely reacting to resource crises and concerns (Szaro and Salwasser 1991, Szaro 1992). New approaches must incorporate fundamental shifts in the scale and scope of conservation practice (Miller 1995). These include the shift of focus from the more traditional single-species and stand level management approach to management of communities and ecosystems (Reynolds et al. 1992).
The protection and maintenance of biodiversity is a longterm issue, which will create problems in political systems that deal primarily with the shortterm goals and objectives (Szaro 1995, Szaro and Johnston 1995). The most obvious conflicts will be political and financial. There are inherent biases in a market economy that tend to result in environmental degradation. The environmental costs are generally passed to the public at large. Attempts to internalize such costs are resisted strongly by private industry. For example, installation of scrubbers in smokestacks and catalytic converters on cars in the United States were not welcomed by industry. Similar results are likely in actions to protect biodiversity. Today the timber industry is against setting aside old growth forests on the basis of the impacts on local jobs and economies. The actual monetary costs may not be as large as the political costs. For every action taken, there will be winners and losers. The loss of diversity will have longterm effects as we lose what are essentially building blocks for human survival. Using a financial analogy, we should manage our biological resources so that we can live off the interest. Living off the principal eventually leads to bankruptcy.
In order to respond to this challenge, it is necessary to look at the dominant social trends affecting future protection, management, and use of natural resources, and evaluate how the trends might affect the content and conduct of natural resource and research programs. After evaluating numerous significant trends, three emerged as being the most important in determining future direction. They are not surprising. First is the expanding world population and associated demographic changes. Second is the increasing competition for the many uses of natural resources - more people are demanding ever increasing amounts of products and services from a finite resource base. And, third is the increasing public awareness and concern for natural resources and for national and global environmental issues. In addition to the traditional forest products - timber, big game animals, fish and water - society is now interested in how forests and climate affect each other; loss of biodiversity especially reflected in threatened and endangered species; growing demand for wood production integrated with the protection of other resources values such as clean water; and maintaining of forest health.
Within the United States, we are moving forward with an ecosystem management approach, one that is scientifically sound, ecologically based and totally integrated (Szaro et al. 1995, Szaro and Sexton 1995). Common sense dictates that this approach, one that considers the sum of the parts rather than each resource in isolation, is the proper and practical way to head. It uses as its foundation principles derived from conservation biology theory for conserving biodiversity and maintaining ecological systems (Soulé and Wilcox 1980, Soulé 1986, 1987, Salwasser et al. 1995). These principles include:
Ecosystem management responds to a significant shift in social values, scientific understanding and land management interests from that of the past. Ecosystem management is an identifying name tag for a new and evolving approach to land management. For practical purposes it is generally synonymous with sustainable development, sustainable management, sustainable forestry and a number of other terms being used to identify an ecological approach to land and resource management. Ecosystem management is a goal-driven approach to restoring and sustaining healthy ecosystems and their functions and values. It is based on a collaboratively developed vision of desired future ecosystem conditions that integrates ecological, economic, and social factors affecting a management unit defined by ecological, not political boundaries. Its goal is to restore and maintain the health, sustainability, and biodiversity of ecosystems while supporting communities and their economic base.
There are four basic operating tenets that provide an "umbrella" for an ecosystem management approach. Under this umbrella are a number of components all driven or related in some degree to participation, collaboration, using the best science and following an ecological approach. These tenets are:
The tough choices posed in the spotted owl (Strix occidentalis) case in the Pacific Northwest of the United States typify many future issues as the conservation of forest biodiversity becomes a higher social priority. Regardless of the eventual outcome of this issue, there is an important lesson to be learned: Conserving biodiversity will not be cheap or noncontroversial. Federal land management agencies in the United States have increasingly come under fire over management decisions that appear to decrease biodiversity. The USDA Forest Service faces numerous appeals and lawsuits on forest plans for insufficient and sometimes conflicting consideration of forest biodiversity in management decisions. The dispute over the spotted owl and old growth forests is the most visible example of how tough it is to blend the conservation of biodiversity with other uses and values of public resources. It illustrates the reality of "no free lunch" in resource allocations. Even though parks, reserves, set-asides, and easements are critical components in the mix for the conservation of biodiversity they will become more difficult to come by and ultimately will require an expansion beyond the "reserve mentality" (Brussard et al. 1992). Multiple-use of public lands is deeply ingrained. Somehow we have to come up with management prescriptions for our public lands that will allow both consumptive and nonconsumptive uses but will do so in such a way that no net loss of native species will occur. This will require encouraging resource conservation and recycling programs that reduce the need for raw materials from public lands (Brussard et al. 1992).
Ecosystemlevel management is going to require new approaches in planning, monitoring, coordination, and administration. A new paradigm is needed, one that balances all uses in the management process and looks beyond the immediate benefits. Future conservation at larger scales will always be confounded by the potentially large number of political authorities that conduct land management practices on watershed, basin, or even landscape scales. Biodiversity cannot be managed in isolation from political and social realities. Population growth and its resulting impact on resource demands is the most important factor in the fate of forest biodiversity. Thus, maintaining the integrity of the remaining natural ecosystems is closely linked with resource and social issues. There will be tradeoffs, commodity production may decline in the shortterm, but in the longterm these tradeoffs will result in gains in sustained productivity while maintaining biodiversity with its complete range of ecological processes.
Acknowledgements
I would like to express my sincere thanks to Bob Bailey for providing me with the latest version of his manuscript and the ecoregion map figure used in this manuscript.
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OE Nov 21, 1996