Evaluation of biological diversity considers elements of the diversity of whole ecosystems, the diversity among species, and genetic diversity within species. The ultimate goal of conserving biological diversity is to ensure the survival of species and the genetic variability within those species. Viable breeding populations of species and their natural genetic variation are part of interdependent physical and biological systems or processes--communities or ecosystems. The successional stage, condition, and distribution of forest communities are important to fundamental ecological processes, as well as to the systems themselves and the future of species diversity associated with forests.
Data for biological diversity indicators are currently available from various sources. Analysis and interpretation in this data describes trends and identifies additional data needs. Definitions used here are based on those used in the US Forest Service, Forest Inventory and Analysis program (FIA). Additional definitions are taken from the USDA Natural Resources and Conservation Service's National Resources Inventory program (NRI), the USDA National Biological Survey program (NBS), the Federal Geospatial Data Committee (FGDC), and a multitude of State- and local-level natural resource inventory and survey efforts.
Care must taken in using vegetation data because of variations in its definition, e.g., forest lands must have a certain percentage of trees per acre. Care must also be used in calculating fragmentation, for example, multi-scale measures of fragmentation may be difficult to interpret or may have little meaning.
Two primary sources of natural resource data have been available on a broad scale: the FIA program and the NRI program. Standard methodologies are used in both programs. In recent years the two agencies have developed standard protocols to ensure that the methods used for future inventories will be consistent with one another. A third source for biological data is the Northern Breeding Bird Survey.
In southern States, the average cycle for FIA data is approximately 7 to 8 years. In western States, the average cycle is well beyond the national goal of every ten years. The NRI is conducted every 5 years on a national level. Data for groups of States and individual States may be compiled using the 1992 RPA database. Updated data and data for areas described by nontraditional boundaries may be compiled for groups of States, individual States, and counties, using FIA's Eastwide and Westwide databases and auxiliary databases maintained by regional FIA projects. On a broad scale, RPA data are reliable; the determination of forest type is reasonably consistent across the country and can be used with confidence.
To date, national inventory data are available for all commercial forest land in the U.S. Inventory of reserved forest land, including wilderness areas, national parks, State parks, and some other publicly owned forest land, is underway. Trend data for smaller areas such as States, or groups of counties within states, are available for some areas from regional FIA projects. In most cases, the data are available by State for ownership, stand size class, and stocking class, etc. Information on forest type is available for 1952, 1962, and 1972.
Additional data are available from a variety of Federal, State, and local agencies, but these sources generally are not national in scope, may have limitations on compatibility both spatially and temporally, represent a wide variety of methodologies, and are often concentrated within specific ownerships. Therefore, the value of these data are limited for purposes of a national assessment.
INDICATOR 1: Extent of area by forest type relative to total forest area.
Ecological processes and viable populations of species that are characteristic of forest ecosystems are usually dependent on a contiguous ecosystem or ecosystems of a certain minimum size. Genetic diversity within a species population depends on the maintenance of sub-populations and the existence of forest ecosystems that cover a large part of their natural range. Forests may constitute all or a part of the habitat necessary for a species= survival.
Data on extent of area by forest type is presented here for 1977, 1987, and 1982. Additional information is available and a more in-depth analyses of status and trends of forest/timberland area by forest type have been reported elsewhere.
Area of Forest Land: With the arrival of European immigrants around 1630, the total area of forest land is estimated to have been 423 million hectares (1,045 million acres). This represented about 46 percent of the total land area. The area of forest land steadily declined as settlement proceeded, to an estimated 307 million hectares in 1907, or 33 percent of the total land area. This decline continued until the mid-1980's when a low of 295 million hectares was recorded. The Eastern U.S., particularly the Northeastern/North Central portions, experienced a majority of the decrease, having declined from approximately 263 million hectares in 1630 to 157 million hectares in 1953. Since the 1950's, the area of forested land in the East continued to decline but at a much lower rate; from 157 million hectares in 1953, to 155.6 million hectares in 1992. In the West, the area of forest land has experienced only slight declines, from 150 million hectares in 1953, to 142.5 million hectares in 1992.
Area of Timberland by Forest Type: Between 1977 and 1992 in the eastern States, the timberland area of white-red-jack pine, oak-hickory, and maple-beech-birch increased. The area of spruce-fir, oak-gum-cypress, and loblolly-short leaf pine remained relatively static from 1977 to 1992. During the same time period in the western States, the timberland area of Douglas-fir, fir-spruce, redwood, other softwoods, and western hardwoods increased. Changes for fir-spruce and other western softwoods may reflect reclassification between inventories by FIA, rather than an actual on-the-ground change in area. Of note is that the area of nonstocked timberland significantly decreased in both regions between 1977 and 1992.
Conversely, between 1977 and 1992, the timberland area of longleaf-slash pine, oak-pine, elm-ash-cottonwood and aspen-birch declined in the eastern States. In the West, the timberland area of ponderosa pine, western white pine, hemlock-Sitka spruce, larch, and lodgepole pine decreased during the same time period.
Table 2-2. Forest cover types (a), 1950-1992 in million hectares. (Source: 1992 RPA Assessment Report GTR-RM-234.)
In the eastern States, forests are maturing as represented by the increase in the area of forest types that are more representative of later stages of succession, and by the decrease in the area of forest types that are more representative of earlier successional stages. Increases in earlier successional forest types, such as cottonwood, birch, and poplar, reflect either new forest land or forest land that was harvested to the point where a completely new stand was established.
Forest lands of the United States are in the process of converting between forest types and are increasing in overall total area and stocking levels. Some forest types are not maintaining themselves at the current levels but this may result from natural successional processes or landowner management decisions. For example, the level of aspen-birch could be maintained, but it would require greatly increased harvesting or other disturbance. Currently, landowners are not interrupting the natural successional processes to ensure the long-term maintenance of forest types such as aspen-birch; however, the overall total of forest land is not impacted from swings in area between forest types.
From an ecosystem diversity viewpoint, one of the greatest concerns is for those forest types that are decreasing in area, such as aspen-birch, and for those forest types that might be increasing in area but are subject to selective harvesting, such as oak-hickory. Selective harvesting and management does tend to remove Anoncommercial@ species and lower value species which can reduce the overall diversity, even while it enhances these forests from a timber production standpoint. Questions concerning wildlife habitat acreage requirements for forest types cannot be addressed with the current data.
INDICATOR 2: Extent of area by forest type and age class or successional stage.
Ecological processes and the species associated with those processes, within any forest ecosystem or forest type, are associated with vegetative structures (age of the vegetation, its diameter, and height) and successional stages (variable species of vegetation).
One of the primary reasons for evaluating age class/successional stage is that ecological processes and the species associated with those processes, within any forest ecosystem or forest type, are associated with vegetative structures (age of the vegetation, its diameter, its height) and successional stages (variable species of vegetation).
Average stand age class is based on the dominant trees in the stand. The actual stand age, however, may vary from the dominant trees. Correlation of average stand age/size class and successional stage are in the early stages of development. Projections of age class trends into the future are difficult to make because of a lack of historical trend data. Techniques used to determine the average stand age differ among the regions, especially between eastern and western regions, and need to be reconciled before nation-wide data can be collected.
In the east, approximately 48 percent of all forest land is classified as having an average stand age of more than 40 years old, 23 percent is between 20 and 40 years in average stand age; and 29 percent has an average stand age of less than 20 years. The age class distribution follows a general decrease through the classes (with the exception of the 80 to 89 year stand age class) as would be expected for most biological populations. The average stand age class of forest land varies by region. The North Central region has the oldest average age classes while the Southeast and South Central have the youngest average age classes. This is probably due to the more intense harvesting levels associated with southern forests. From a diversity standpoint, the increasing average stand size bodes well for those forest types forests that represent later successional stages and for timberland in general. However, early successional forest types such as Aspen-birch will be replaced by other forest types and specific management actions may be needed to ensure enough disturbance to provide potential regeneration of pioneering forest types. This forest type is somewhat unique in that if it ages to the point where it is large enough to be classed as sawtimber, it is probably in the process of converting to another forest type.
In 1992, almost 70 percent of all timberlands were classified as sawtimber sized in the Western U.S. The remaining area was split between seedling-sapling (13 percent) and poletimber (15 percent). In comparison, in 1977, sawtimber sized stands accounted for 66 percent, poletimber 17 percent, and seedling-sapling 12 percent of all timberlands. The totals do not sum to 100 percent due to the area of nonstocked timberland being included into the total area of timberland. The area of nonstocked timberland in the west decreased from 5 percent of the total in 1977 to 2
percent in 1992.
The area of sawtimber is increasing at the expense of poletimber, a natural occurrence if disturbance is limited. The decreased area of nonstocked perhaps reflects what is occurring
across the landscape, as stands mature their stocking tends to increase. Nonstocked areas often have some stocking but it is not sufficient to qualify as stocked timberland. As stocking increases, these nonstocked areas are reclassified into the dominant size class which can range from seedlings to sawtimber.
The nation's forest land is maturing with a resulting increase older forests. Without increased levels of disturbance, this trend will probably continue into the future, allowing succession to progress. From an ecosystem diversity perspective, this maturation will lead to increased diversity of forest structure but a decreased diversity of forest types, because later successional stages continue to increase at the expense of earlier successional stages.
Higher stumpage prices suggest that some of the old-forest timberland will be harvested in the near future. The area of old and potential old forest has increased. The amount of old forest on public lands is increasing and is likely to continue expanding there, because the public continues to demand old forests and the benefits they bring.
The forest land information provided in this Indicator includes those portions of reserved forest land that have been inventoried, as well as estimates of area by stand age class for reserved land that has not yet been inventoried. Stand age data are not available for all sample locations in the 1992 RPA data base. In such cases, the data were either not collected or not retained in permanent data sets.
The FIA programs collect stand age data at sample locations across the nation. The data are not typically included in the RPA publications or standard FIA reports, but are available from the 1992 RPA database, as well as the Eastwide and Westwide databases. Users of this information should be aware that, although techniques used to gather this data may be similar, there are some significant differences in techniques. For example, some FIA programs recognize a "mixed" age class, while some others do not. The techniques used in conducting individual FIA projects have been designed to address the needs of clientele in the respective regions and have been adapted to be sensitive to differences in forest character among the regions. Because of the differences in techniques, the data should not be combined to produce a national summary of land area by stand age class. More information about the techniques used to measure stand age is available from 29 percent has an average stand age of less than 20 years. The age class distribution follows a general decrease through the classes (with the exception of the 80 -89 stand age class) as would be expected when discussing most biological populations.
One possible proxy for the cross-tabulation of forest land area by forest type and stand age class has resulted from research on forest biomass. This is reported in biomass units under Criterion 5, Indicator 26. Estimates of stand age class for all sample locations are in the 1992 RPA database and could be used to compile forest land area information. The results, however, are subject to assumptions used in the study.
The area of forest land by age class may be derived from timberland area by broad stand size classes. Data are available for timberland area by seedling-sapling, poletimber, and sawtimber. Timberland does not reflect the overall forest situation in the U.S., however. The majority of reserved and other forest land that is not classified by size would be at least of poletimber and most probably of sawtimber size. Therefore, the trends and analyses that result would be conservative for the larger average stand size classes. The advantage of using average stand size classes for timberland is that analyses can be completed by forest type.
It is therefore not recommended that the forest type and stand age variables be cross-tabulated. As such, information contained in this Indicator show total forest land area by stand age class. Also, combining States= data that were measured by differing techniques should be avoided. In general, analyzing data on either an eastern- or western-States basis would eliminate most of the problems that stem from using data that have been gathered using radically different techniques.
One age group that is of particular interest in the U.S. is old growth forest. Forests which have been reserved from timber harvesting will remain old forest or become old forest in time, unless
a natural disturbance occurs. Old growth forest on unreserved land may be lost to harvesting, land conversion, and natural disturbances, any of which could result in reclassification to either earlier seral stages or to nonforest land.
INDICATOR 3: Extent of areas by forest type in protected area categories as defined by IUCN or other classification systems.
The amount of a forest ecosystem reserved in protected areas is a measure of the social priority for its protection. Data is available in the United States for the classifications used by the International Union for the Conservation of Nature. IUCN categories include: I. Strict Protection; II. Ecosystem Conservation and Tourism; III. Conservation of Natural Features; IV. Conservation Through Active Management; V. Landscape/Seascape Conservation and Recreation; and VI. Sustainable Use of Natural Ecosystems.
There are currently no complete sources of information on America=s forest land by IUCN standards. However, forest lands classified as reserved by the Forest Service include areas whose various designations by statute or administrative regulation would place them within IUCN Categories I, III, IV, or V. FIA programs are in the process of measuring and estimating the area of reserved forest land in the U.S. Data used to quantify this indicator are taken from the 1992 RPA database and only cover portions of reserved forest land that were inventoried at that time. More current and detailed information is available from each of the regional FIA programs. By definition, reserved forest lands are publicly owned. Information on privately owned "protected" forest land derived from a nationwide survey of landowners= intention to harvest (Birch, 1966).
Productive reserved lands are forested land that have statutory or administrative restrictions prohibiting the harvest of trees. Typically, these are in public ownership, though occasionally they may be privately owned. Productive deferred forest lands were unroaded forested lands that were under consideration for becoming reserved lands. Some of those lands were eventually reserved and the rest were >returned= to a timberland classification. Because the final designation of these lands was unknown in 1977, they were classified as deferred.
In 1992, 19.6 million hectares (48.4 million acres), or 6.6 percent of the total area of forest land, was classified as reserved. Compared to 1977, this represented a 130 percent increase in the area of reserved forest land. There were 4.5 million hectares of reserved forest lands in the eastern States in 1992, which was about 5 percent of the total area of forest land. This increase in area of reserved forest land from 1977 to 1992, 3.4 million hectares to 4.5 million hectares, was significant because the total area of publicly owned land remained relatively constant--about 15 percent. The increase reflects the fact that a greater percentage of publicly owned land in the eastern States was classified as productive reserve in 1992 than in 1977. In the East, more than 70 percent of the reserved forest land was located in the northern portions of the region. The North is also where the majority of the publicly owned land is found, which illustrates the correlation between the total area of public land and the total area of reserved forest lands.
In addition to the Federally reserved forest land, some other public land, as well as some privately owned land, should be considered protected under one of the IUCN categories. The ownership of protected private land ranges from non-governmental organizations such as The Nature Conservancy, which will probably be as well reserved as publicly owned land; to small, non-industrial lands whose owners may intend never to harvest, but which may, if sold, become available for harvest. Whatever the distribution of ownerships and ownership intentions, some privately owned lands should be considered as protected. In a 1994 survey of private forest landowners from across the nation, 34 percent of those who responded said they never intend to harvest.
In most forest types, the area of reserved forest land is increasing. Generally, between 1977 and 1992, the percentage of reserved forest land by forest type groups, compared to the percentage of total forest land in each forest type group expanded. The expected future trend is a continued increase in the area of reserved forest lands.
In the eastern States, forest type groups that are most restricted are the southern conifers. Forest type groups whose reserves are limited, and which have therefore become of concern, include longleaf-slash pine, oak-pine, and loblolly-short leaf pine. The area of reserved mid- to late-successional forest types, such as maple-beech-birch, will continue to increase, mostly in the northern U.S. In the absence of disturbance, earlier successional forest type groups, such as aspen-birch, will convert to these later successional forest types.
In the western States, almost all forest type groups, on both timberlands and reserved forest lands, are conifers. However, between 1977 and 1992, the area of reserved hardwoods in the West increased. The area of western white pine, larch, and redwood, both on reserved forest land and in total, is limited. Concerns for maintaining these forest type groups should be addressed.
There are many areas of privately owned forest land that are currently protected. A combination of inoperability and landowner intent may render some areas of forest land >protected= although such lands have not been classified as reserved. While the total area of such land may not be known, the fact remains that a relatively large number of landowners consider all or part of their forest lands protected.
Perhaps the most important forest type groups, from a protection viewpoint, are those that represent unique ecosystems such as western Red cedar and Port Orford cedar, or are at the edge of their natural range. Data is not available for analysis of the protected status of these types.
The actual area of privately owned forest land that can be considered >protected= under IUCN categories has not been determined. Analyses of reserved forest land by forest type in sub-regions are difficult to conduct, but with increased coverage by FIA programs, this should be possible within 10 to 15 years.
Additional information on forest land in protected areas is included under Cultural, Social, and Spiritual Needs and Values in Criterion 6, Indicator 42.
INDICATOR 4: Extent of areas by forest type in protected areas by age class or successional stage.
The distribution of reserved forest land by forest type is based on the best available technique for a given area. Very often, aerial photography has been used to quantify the area and composition associated with the FIA sample location. Estimates of stand age or succession stage require ground visits to the sample locations to measure the age of existing vegetation. The process of taking ground measurements on reserved forest land lags behind the use of other techniques and is not far enough along to provide estimates of stand age or successional stage at the national level. Some information on stand age for reserved forest land might be obtained from regional FIA programs.
Due to the lack of available data on regulated areas, trends in the extent of these areas cannot be discerned. However, based on the maturation of the nation's forest in general, one could assume that the same trend is occurring on reserved lands but to a greater degree since they are less susceptible to disturbances that set back natural successional processes. Therefore, because they are based on trends for lands that are available for harvest or other human-caused disturbances, estimates concerning the extent of reserved forest land by age class are probably conservative.
As discussed for Indicator 2, the maturation of America=s forest land is evident in increased average stand sizes and later successional forest types. The amounts of forest land in early successional stages is decreasing, as the amount of forest land in mid- to late-successional stages is increasing. The area of reserved forest land is increasing in all regions.
There have been regional/local studies conducted of forest lands and disturbances that will substantiate these estimated trends. One study in the Lake States found that about 25 percent of disturbed areas in timberlands composed of stands older than 80 years were the result of natural events, such as fire or windthrow, and that the other 75 percent of the disturbances resulted from human-caused events, such as timber harvest. Losses to the base level of old forest in the Lake States--from disturbances between inventories--were more than offset by increases in the average stand age, and from land that had trees present in the previous inventory but not to the stocking level necessary to qualify those lands as forested. That is to say, that within the latter, stocking had increased to the extent necessary to qualify the areas as forest land in the most recent inventories. However, it is questionable whether these results can be applied to reserved forest lands. One might assume that a majority of the existing reserved forest lands in the Lake States will not be disturbed in the short term, based on the history of other forest lands in that region. All lands are potentially susceptible to disturbance, and eventually will be disturbed, though on reserved lands it may be hundreds of years between disturbance events. Therefore, we might conclude that aging and the subsequent progression through successional stages on reserved forest lands will be at least at the level expected on timberlands.
More than half of all reserved forest lands are estimated to contain stands in size classes whose dominant conifers have an average diameter (dbh, or 1.37 meters) of at least 23 centimeters, and whose hardwoods have an average diameter of at least 28 centimeters. It is also assumed that increases have occurred in the acreage of older and later successional stage forest types on reserved land and reserved forest lands in younger, earlier successional stages have decreased. While natural disturbances will result in some losses in the older age classes, such losses will likely be more than offset by gains from both the aging/maturing of the existing reserved forest lands and from additions to the current reserved forest land base.
INDICATOR 5: Fragmentation of forest types.
Fragmentation of a forest type into small pieces disrupts ecological processes and reduces the availability of a habitat. Fragmented areas may be too small to maintain viable breeding populations of some species. The distances between and among forest fragments can interfere with pollination, seed dispersal, and wildlife movement, and breeding. Ultimately, excessive fragmentation can contribute to the loss of plant and animal species that are unable to recolonize after an area is disturbed. In areas converted to agricultural purposes, remnant forest fragments will provide refuges for many, although not all, components of the original, diverse forest communities.
An increase in the level of fragmentation of forest land, while detrimental to some wildlife species, will improve the habitat for other species, especially those that prefer forest edges. The approach for this indicator is not to determine the positives or negatives of fragmentation but to attempt to quantify what has occurred and the current conditions, in order to improve the knowledge base for management decisions.
Increased interactions of people and the environment increase the likelihood of fragmentation. With ever-increasing human populations and use, forests and forest conditions are becoming more fragmented. As a result, concerns have surfaced with regard to patch size, edge, distances between habitat areas, interconnectedness, etc.
There are no national data sets available concerning fragmentation of forest land, although some regional studies have been produced. For example, in the Cascade Range of Oregon between 1972 and 1987 the degree of forest fragmentation increased significantly; the average patch area declined by 17 percent; and that the average patch perimeter length declined by 11 percent.
Two primary threats to neotropical migratory birds in the Midwest are habitat fragmentation and habitat loss, which are usually closely associated. Forest types associated with the midwest are central hardwoods and oak-hickory. In 1995, a map of the forest cover in Missouri, Illinois, Indiana, and Ohio, was overlaid with 1,000-hectare hexagons. It was estimated that only 6 percent of the landscape contained hexagons with more than 80 percent forest cover, while 63 percent of the landscape contained hexagons with less than 20 percent forest cover.
Fragmentation refers both to the forest patch size after land conversion, and to the size of forest patch of a certain condition, e.g., old growth, shrub, etc. Many Eastern forest types, such as oak-hickory, are disturbance-adapted ecosystems and developed with a degree of fragmentation as a part of their evolution. In association with these disturbance-oriented ecosystems, many wildlife species also developed with disturbance-oriented habitat requirements.
The question is: What degree of fragmentation can be tolerated above historical levels? Current forest management practices, landownership patterns, and transportation corridors are all contributing to an ever-increasing fragmentation of the forest environment in almost all forest types in the eastern States. Some forest types, such as aspen-birch, are probably more likely to be fragmented due to the harvesting techniques employed. For example, while aspen-birch is typically clear-cut (even-aged management), most maple-beech-birch forests are selectively harvested (uneven-aged management). Generally, clearcuts lead to increased fragmentation, whereas selective harvest does not often result in increased forest fragmentation.
On a regional and local scale, data show that fragmentation of forest land has occurred. Today, a methodology for determining national-level fragmentation of forest land by forest type is not available. Because true estimates of the historical base for factors such as tract size cannot be made, change over time is limited to a starting point of the 1970's.
There are several dimensions to the ecological impacts of the >fragmentation effect= and several indicators are necessary to characterize it. Typically, fragmentation involves a loss of area, a decrease in the average size of habitat patches, an increase in the average distance between and among patches, and an increase in the amount of >edge= habitats. Some work has been done to quantify forest fragmentation in the Pacific Northwest. The focus of work in the East is on fragmentation=s effects on the regions' ecology, and on birds in particular. A number of forest wildlife species require a minimum size of homogeneous forest land to survive.
Different species will perceive fragmentation at different scales. This is particularly important for ecological analyses. Case studies have shown an increase in fragmentation according to indicators such as size of patches.
Fragmentation can be quantified, but not with a single indicator. The ideal data for quantifying are map-based. Some surrogate measures for fragmentation could be derived from point-based inventories. In the United States, vegetation maps derived from AVHRR satellite data could be used to evaluate fragmentation at a very coarse scale. Similar analyses have been done by the Food and Agriculture Organization of the United Nations (1993) for West Africa and the Amazon Basins. Fragmentation is best understood by examining trends over time, and therefore requires before-and-after information. The earliest feasible date for establishing a base line of information for the United States is 1970.
Species diversity describes the variety of different organisms found in a particular location. It can vary from place to place, and from season to season within the same place. The traditional starting point for species relations and diversity assessment is at the community level. For such analysis, community means all the organisms in a chosen area that belong to the taxonomic group the ecologist is studying. The chosen area is usually one that the ecologist regards as a convenient entity and is willing to consider as homogeneous in some intuitive sense. It is impractical to consider every living thing in such an area--the mammals, birds, reptiles, amphibians, arthropods, and soil microfauna, together with the trees, shrubs, herbs, ferns, mosses, fungi, and bacteria. A taxonomic group that the ecologist regards as the relevant entity is usually chosen. This may be a family, order, class, or other taxon with which taxonomists are familiar, so that individuals can be fairly easily identified to species. The members of such a taxon that occur together at one place are designated a taxocene.
INDICATOR 6: The number of forest dependent species.
The most fundamental element of diversity is species number. >Species richness= is used to represent the concept of number of species per fixed number of individuals. Species density refers to the number of species occurring per unit area. The relative abundance of individual species is called >evenness.= Species diversity is generally accepted as embodying the concepts of both species richness and evenness. That is, species diversity is a function of the number of species present and the evenness with which the individuals are distributed within these species.
The availability and extent of up-to-date data on species richness and evenness depends primarily on the taxonomic group. Botanists have combed the world and described nearly all vascular plants in the temperate regions. Today, it is rare to find a new vascular plant, at least in the United States. The World Resource Institute estimates the total number of vascular plant species in the U.S. at around 20,000. Even many groups of nonvascular plants are well understood, e.g., Bryophyta, the mosses and liverworts.
Many data sources provide information on plant species numbers, distribution and abundance. All major State universities and many private universities, maintain herbariums of the plants in their region, and many of the major museums nationwide maintain such collections. Most, if not all, of the major State universities have published manuals on plant species identification for their State, with appropriate distribution and abundance information. The exceptions are the algae and, especially, the fungi. Algae exist in every drop of soil and every drop of water on the planet. In fact, some believe algae account for nearly 90 percent of the planet=s oxygen production, although this has not been proven. Fungi are important for a variety of reasons. They are the primary decomposers on the forest floor; they are pathogens for many diseases; many animals, primarily rodents, depend on them as a food source, and many higher plants require mycorrhizal fungi to function properly. The number of fungal species in the U.S. has recently been estimated at 56,800.
Two national databases deal with tree species, estimating 865 native tree species in the U.S. Forest Service FIA units conduct periodic, nation-wide, statistically based inventories of forest resources, primarily the woody vegetation, although some understory herbaceous vegetation is also inventoried. The agency=s Forest Health Monitoring units conduct nationwide, statistically based inventories to assess the health of U.S. forests. These and other data are readily accessible over the internet.
There are 419 native species of mammals that regularly occur in the U.S. As with plants, most major State universities maintain collections of mammalian species within their respective States/region and publish manuals with appropriate distribution and abundance information. All State wildlife agencies conduct periodic surveys/inventories to keep abreast of wildlife resources. Today, most of these programs are based on sound statistical designs.
There are an estimated 844 forest-dependent bird species in North America. Birds have been monitored for many decades, and much has been written about recent declines. There are many important and readily accessible national databases on bird resources. The breeding bird survey (BBS), administered by the U.S. Geological Survey, has been ongoing since 1966. Hawk migration counts, sponsored by the Hawk Migration Association of North America, have some sites that have been observed for more than 50 years. Breeding Bird Censuses (BBC) determine population densities of breeding birds in specific habitats. Researchers can access a computerized database of more than 4,000 BBC's, dating back to 1937. Breeding Bird Atlases (BBA), overseen by the North American Ornithological Atlas Committee, are 5-year projects going on in each State. To date, more than 28 States have completed atlas projects to determine the distribution and reproductive status of breeding birds. Most atlases are fully computerized. The Audubon Christmas Bird Count Database (CBC) is collected to monitor population dynamics of North American birds in winter. Ongoing since 1900, a computerized database from 1960 forward is maintained by the FWS. Additional bird demographic information are available from mistnetting, nest monitoring, and bird banding programs conducted by State agencies, universities, and the FWS.
The native herpetofauna of the U.S. includes 281 species of reptiles (about 19 percent turtles, 35 percent lizards, 45 percent snakes, and less than 1 percent crocodilians) and 240 species of amphibians (about 62 percent salamanders and 38 percent frogs). The distribution of reptiles and amphibians as a whole is not well understood. No national program of monitoring populations of reptiles and amphibians, comparable to the Breeding Bird Survey, is operational. However, the USGS has recently started an amphibian monitoring program based on call counts. Some recent regional studies have documented declines of amphibians. Amphibian species tend to exhibit either endemic (small ranges and/or specific habitats) or widespread distributional patterns. Table 2-5 shows that the number of amphibian species suffering losses or suspected of having severe threats to their continued existence increased significantly in the last 15 years.
Synergistic interactions between the effects of low pH and increased ultraviolet-B radiation (UV-B) have been suggested as possible causes of the decline and disappearance of amphibians.
The American Fisheries Society in 1979 developed a list of 198 freshwater fishes in danger of disappearing in the U.S. A decade later the list was expanded to 254 species. Ten species became extinct and 75 taxa were added in a single decade, an increase of 38 percent. About 800 species of native freshwater fishes exist in the continental U.S. There is currently no national fish monitoring program. However, many regional studies have established that fish species are not equally distributed across the nation, but tend to concentrate in larger, more diverse environments such as the Mississippi river drainage (375 species). Isolated drainages, such as the Colorado River, have low fish diversity (36 species). Arid states west of the 100th Meridian average about 44 native fish species per state, while states east of that boundary average around 138 species per state. Habitat degradation and destruction were the primary causes.
Invertebrates, members of the phylum Chordata (arthropods, flatworms, mollusks, roundworms, etc.), are a poorly understood group and were not analyzed for this report.
Insects are a vast group, with most species yet to be identified. A national insect database is available. The Hopkins U.S. System Index (HUSSI) provides access to the Hopkins U.S. System, a collection of written records containing information on thousands of insect and damage specimens from forests in the United States. These insect or damage specimens were collected by entomologists in the U.S. Department of Agriculture (USDA) and collaborators over a period of more than 80 years, including data on location, date, taxon, insect- and plant-host association, and other information in tabular or narrative form. The Forest Insect and Disease Research branch of the Forest Service began building a computerized database of the Hopkins System in 1987 which now contains about 61,000 records. Records held by the Agricultural Research Service, Systematic Entomology Laboratory, have not yet been entered in the database. Of the records in the database, 5,847 unique species are identified.
A national survey program, the Fourth of July Butterfly Count, was started by the Xerces Society in 1975, and sponsored by it annually until 1993, when the North American Butterfly Association (NABA) assumed administration. The results of the FJC, including butterfly data, count-site descriptions, and weather information on count day, are published annually. While the FJC is not a formal scientific survey, the data are nonetheless useful for studying gross population trends and butterfly diversity. For example, monarch (Danaus plexippus) and painted lady (Vanessa carduui) populations have shown dramatic fluctuations in the same years, but they usually vary in opposite directions, suggesting that the same widespread climatic events affect both species in different ways. Four regional Lepidoptera studies from 1993 covering the 17 western states identified 915 species of butterflies and moths. In general there were fewer species of butterflies and moths in more northern states and in states with less topographic diversity, that is, less variety in terrain.
Viable populations of forest dependent species require appropriate habitat, including available food, cover, and water if they are to survive. It is estimated that at least 90 percent of the total bird, amphibian, and fish species of the country, and at least 80 percent of mammal and reptile species can be found on forested land. Over time, forest cover in any area changes, either naturally or as a result of human activities. Maintaining the nation=s forest dependent species requires maintaining healthy ecosystems from a landscape perspective.
Butterflies and moths, among the best-sampled insects, are useful indicators of ecological conditions and environmental change. Changes in buterfly populations have not been detected.
However, there have been definite, documented declines in many forest dependent bird species, especially neotropical migrants, although populations of some forest-dwelling birds have shown increases.
Amphibian populations have also been documented as in decline. Available data seem to indicate extensive declines in the northwestern U.S. and limited declines in the southeastern U.S. Forest pests, such as the southern pine beetle (Dendroctonus frontalis), and pathogens such as Phytophthora cinnamomi are causing some serious problems. Native fish communities have undergone significant and adverse changes (reduced distributions, lowered diversity) due to deteriorating quality of aquatic habitats from over-harvesting, dam construction, and sedimentation resulting in physical, chemical, and biological effects to surface waters and underground aquifers. About one-fourth of the native freshwater fishes are considered to be imperiled.
Forest land has declined in many areas of the country, eliminating habitat and putting increasing pressure on many species due to increased competition for shrinking resources. Migratory game birds dependent on forested wetlands and marsh have shown declines, which has been attributed to reduced quantity and quality of wetland areas.
For the most part, big-game populations seem more secure, more widely distributed, and abundant than in decades past. In fact, deprivation by elk and deer is getting to be a big issue in the West. Small game animals, such as pheasant, quail, and rabbits, have shown a decline in numbers. Other small game animals, such as grouse and squirrels, have remained stable.
According to existing data, most native tree species are neither endangered nor threatened, with a few prominent exceptions. For example, chestnut, elm, and frasier fir have been seriously affected by forest pests, causing significant impacts on eastern forests.
Decadal trends can be assessed in tree species composition and abundance, as well as growth and mortality, because many FIA plots are visited on a 10-year cycle. Trends in forest pathogens and pests can also be determined. Data on trends in mammal species are available primarily for game species and furbearers. Population trends for bird species are more abundant than for any other taxon.
INDICATOR 7: The status (rare, threatened, endangered, or extinct) of forest-dependent species at risk of not maintaining viable breeding populations, as determined by legislation or scientific assessment.
Ecological processes and the species associated with those processes within any forest type may vary according to the extent, condition, or fragmentation of that forest type.
Several sources of information on the status of threatened and endangered species are available. The most comprehensive national sources are databases of The Nature Conservancy ,the USDA Fish and Wildlife Service, U.S. Environmental Protection Agency, and a private firm called BioData.
The Biological and Conservation Database of the Nature Conservancy is a dynamic atlas that includes ecological and location information about elements of natural diversity. These elements include those plants and animals or natural communities that are so rare and so significant as to merit special consideration as land-use decisions are made. Information for the data base comes primarily from two sources: a network of academicians and private and agency biologists who share information collected through their own work and research, and inventories funded through contracts or grants and resulting from the cooperative efforts of the Nature Conservancy and a variety of agencies.
The U.S. Fish and Wildlife Service maintains the Federal List of Threatened, Endangered and Candidate Species Database. Statistically based biological surveys are used, as well as special project inventories, to build and regularly update records in the database. Similar to The Nature Conservancy, expert knowledge comes from a network of academic, agency, and private biologists, which is incorporated into the database. Species recovery plans are tied to the database.
The EPA Office of Pesticide Programs maintains an Endangered Species by County Database, which is essentially the same information gathered by the FWS. Finally, there is the Threatened and Endangered Species Database of BioData, Inc., a small private research company in Denver, CO. BioData does not conduct field inventories, or other such work; rather they build on all public, and some private, sources of information on threatened and endangered species. BioData may well have the best database on threatened and endangered species, and for a fee anyone can query and use the database.
Native plant and animal diversity has declined over the past three decades, and is likely to continue to decline because of continuing human population growth and associated development. As of August 1995, there were 924 species officially designated as threatened or endangered, shown in Table 2-6. Of these 924 species, 383 are considered forest dependent. The list by broad forest type, is shown in Table 2-7.
There are more than 3,500 candidate species awaiting listing; 59 percent are plants, 27 percent are invertebrates, and 14 percent are vertebrates. The rate at which new species are being listed now exceeds 50 per year. Regions supporting many endangered species are the humid Southeast and the arid Southwest. The Pacific Northwest seems to be emerging as a new hot spot of endangered species. A recent analysis of endangered species patterns shows the greatest number of endangered species occur in Hawaii, southern California, the southeastern coastal states, and southern Appalachia.
Endangered species distributions are mapped at the county level of resolution. This helps in the identification of hot spots of threatened biodiversity. The databases contain what is known about habitat requirements for the listed species. Recovery plans are given in the databases, so we know what steps are currently being taken to protect and enhance the species.
It is clearly inappropriate to assume that because a particular species occurs in a county, that a viable population exists in that county. Historic trends in species listings do not solely reflect trends in endangerment. The rate of listing is most sensitive to changes in the law, budget constraints, bureaucratic processes, and policy changes that effect how many listings can occur in any time period, rather than the status of the particular species itself. As a consequence, the official list underestimates the number of species at risk of extinction.
Genetic diversity is the variability of genes among individuals in a species or population. A species= evolutionary ability depends on sufficient genetic diversity to maintain immediate fitness and adaptability, which, in turn, are a function of population size, subpopulation structure, interpopulation genetic variation, mating structure, generation time, and gene flow.
Concern about genetic diversity is most serious for populations that are either naturally small and isolated, or populations that have become small because of changes in their environment or impacts from human activity such as hunting. Consequently, population size and the distribution of interacting populations are critical attributes in evaluating genetic diversity.
INDICATOR 8: Number of forest dependent species that occupy a small portion of their former range.
Information on geographic distributions of forest associated species was obtained from Natural Heritage central databases. Taxa surveyed included mammals, reptiles, amphibians, birds, and fish. Plant and invertebrate data were not available at this time from this database. There are several databases available to use in examining this question. This one was chosen because species are listed on the basis of concern by local biologists. This should present a truer picture of potential genetic erosion than a list composed only of officially listed threatened and endangered species.
Of all taxa examined, mammals have the apparent greatest proportion of species with reduced ranges (26 percent), while amphibians have the least (9 percent). Fifteen percent of fish species occupy smaller geographic distributions, 13 percent of the bird species and 11 percent of amphibians occupy smaller land areas than previously occupied.
Some degree of genetic erosion occurs in species which occupy small portions of their former range. These species warrant closer examination and, perhaps, management. We cannot determine the extent of genetic erosion, what proportion of the former gene pool of the species remains, or how important it may be to adaptation, survival, or potential human use. This information does not show if important phenotypic polymorphisms are being lost, although given adequate time some inferences about polymorphisms could be teased out of the available literature for a given species.
Genetic diversity is not threatened in woodland breeding birds with positive or neutral population trends. Genetic diversity may be eroding in populations of species with declining trends, depending on the severity of the decline and size of remaining effective breeding population levels. Genetic diversity is likely eroding in declining populations of anadromous fish, declines are severe in some cases and effective population sizes are known to be low.
Population levels in unmanaged species may reflect trends in genetic diversity (Frankham 1996). However this may not be the case for managed species. Existing data is not sufficient to determine the role of genetic diversity in population levels or trends in unmanaged species. Management activities such as transplanting programs and harvest have definite genetic effects, (such as founder effects, artificial selection, and increased inbreeding) which may not be evident when looking only at demographic parameters. Consequently, population levels or trends in these species may indicate only population abundance, not trends in genetic diversity.
Although there are large apparent differences between taxa in the proportion of species with reduced ranges, we cannot really say one taxa is faring worse than another. Mammals, by their nature, attract more attention and are easier to observe than other taxa such as amphibians. Consequently there is more data for mammals and it is more reliable than information for other taxa.
INDICATOR 9: Population levels of representative species from diverse habitats monitored across their range.
Representative species are defined here to include forest dependent species whose population levels are indicative of overall levels of genetic diversity for a larger group of forest species.
Data consists of population estimates for selected large game animals, harvest estimates for selected small game animals, population trends for woodland breeding birds, and population trends for evolutionarily significant units in one anadromous salmonid species, steelhead.
Population and harvest level estimates are compilations from state wildlife agencies and are displayed by broad assessment region and for four time periods to indicate trends. A states data was included only if estimates were available for the years 1975, 1980, 1985, and 1990, and therefore some estimates are based on only a few states information. The choice of species to monitor, data collection methods, and data analysis/interpretation are influenced by management emphasis at the state level and species geographic distribution. Consequently these data are inconsistent and often unreliable. However, if states are consistent year to year in collection methods, then trends should be more consistent and reliable than the estimates themselves.
Existing data indicates that population levels are high enough that genetic diversity does not appear to be a major concern for most species of large carnivores, herbivores, and large game birds. Populations for these species generally increased or at least remained steady. Populations of small game mammals and birds are not as secure. Some, such as Eastern Cottontail Rabbits declined precipitously; however, genetic diversity is probably not threatened in these species because geographic distribution remains widespread and census numbers, and consequently effective breeding population sizes, remain relatively high.
There is no way to determine cause and effect relationships from this information. There may be a multitude of factors other than forest practices which cause population increases or declines.
We do not know that observed trends in one or a very few representative species accurately reflect trends or levels of larger groups, but examining trends in several species should be more indicative of trends for a group. Also, more work is needed to define groups on the basis of common genetic diversity attributes. Current groupings are based on common life histories, which may or may not reflect genetic diversity characteristics.
The conservation of biological diversity in U.S. forests has been measured by nine indicators of ecosystem, species and genetic diversity. In general, the data available for measuring this criterion are extensive and comprehensive. The following highlights reflect the significant trends and indications of this criterion in relation to the sustainability of U.S. forests.
Minimum size habitat requirements of a for specific forest types cannot be addressed with the current data. The size of tract and the successional stage of development within the forest type, cannot be currently determined.
A correlation of age class with diameter/height classes cannot be accurately made at this time.
The current data sets do not provide answers to questions related to unique ecosystems or ecosystems at the edge of their natural habitat. The area of privately-owned forest land that is protected as per the IUCN categories cannot currently be determined. Analyses of reserved forest land by forest type in sub-regions are currently difficult, but with increased coverage by FIA programs in the near future will be possible.
We cannot quantify the amounts of reserved forest land by age class or successional stage.
We cannot determine a national level of fragmentation of forest land, in general nor by forest type. Since true estimates of the historical base for factors such as tract size cannot be derived, change over time is limited to a starting point of the 1970's. The unknown question is what degree of fragmentation can be tolerated above historical levels.
Few population estimates exist for fish species. Trend information on distribution and abundance are lacking, except for a few specific regional studies on commercially or recreationally important salmonid species. Data on trends in amphibian populations are largely anecdotal.
Historic trends in species listings do not solely reflect trends in endangerment. The official list underestimates the number of species at risk of extinction because the rate of listing is sensitive to changes in the law, budget constraints, bureaucratic processes, and policy changes that effect how many listings can occur in any time period.
We cannot determine the extent of genetic erosion, what proportion of the total gene pool of the species it represents, or how important it may be to adaptation and survival. This information does not show if important phenotypic polymorphisms are being lost. Also, cause and effect relationships cannot be inferred from this information.
Population levels or trends may not reflect levels or trends in genetic diversity for managed species. Management activities such as transplanting programs and harvest have definite genetic effects, (such as founder effects, artificial selection, and increased inbreeding) which may not be evident when looking only at demographic parameters. Consequently, population levels or trends in these species may indicate only population abundance, not trends in genetic diversity.
There is no way to determine cause and effect relationships from the indicators of genetic diversity. We do not know that observed trends in one or a very few representative species accurately reflect trends or levels of larger groups, examining trends in several species is more indicative of trends for a group. Also, more work is needed to define groups on the basis of common genetic diversity attributes. Current groupings are based on common life histories, which may or may not reflect genetic diversity characteristics.
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