Criterion 4 CONSERVATION AND MAINTENANCE OF SOIL AND WATER RESOURCES

I. Introduction

Soil and water are basic to all of the other resources in the forest. Without their conservation and maintenance, no other resources will survive. Forests are also an important part of the earth's hydrological cycles, especially in the regulation of surface and ground water flow. Documenting the results of research currently underway will provide a stronger foundation for understanding both human and natural-caused changes in the physical, chemical and biological properties and processes of both land and water resources.

Assessment and ongoing monitoring of the physical and biological characteristics of forests have been and continue to be regular practice on public and industrial ownerships, and on some non-industrial lands. These programs provide an extensive data base of soil, water, and related resources over time.

Some areas of Federal lands are set aside at the Federal, State and occassionally, local level for protection of their basic values such as wilderness, wild and scenic rivers, and outstanding native resource waters. In addition to set-asides, regulation of land uses and practices to protect soil and water is provided at different levels of government through a variety of approaches.

ii. Indicator Reports

INDICATOR 18: Area and percent of forest with significant soil erosion.

The loss of soil must inevitably influence the vitality and species composition of forest ecosystems. Extensive areas of soil erosion can have a major effect on aquatic ecosystems associated with forests, recreational opportunities, potable water supplies and the life span of river infrastructure such as dams.

Erosion concerns tend to be at the local scale and centered on management practices. Much of the forest land in the Eastern United States is on former agricultural lands which were abandoned at least in part because of erosion. However, even on short rotation, intensively managed forest lands, these former agricultural soils are being regenerated. Erosion on forest land is most likely at the time of harvest or management activity. Harvest methods, road building, and other soil disturbance can affect the severity of erosion. Prescribed burns that get too hot and expose the root layer can also affect erosion. Other factors are topography and the severity of rainstorms and their timing. With best management practices, mitigation measures, and care in building roads and skid trails, erosion should not be a major problem.

Data Summary

Current knowledge is lacking for estimating the erosion rates from forested areas, because the rill erodabilities of forest lands in either undisturbed or disturbed conditions are lacking. Also unknown are the impacts of upland forest conditions on downstream aquatic ecosystems because there has been only limited development of models for sediment transport through steep forest stream networks.

The Natural Resources Inventory (NRI) is conducted by the USDA, Natural Resources Conservation Service at 5-year intervals. This inventory provides a "snapshot" of land cover and use, soil erosion, prime farmland, wetlands, and characteristics of other natural resources. NRI data is collected for non-Federal lands of the United States: the 48 contiguous states, Hawaii, Puerto Rico, and the U.S. Virgin Islands, but not Alaska. The focus of data collection is on soil, water, and related resources on farms, non-Federal forests, and grazing lands.

The plot layout in the NRI consists of a grid of 800,000 points within permanent sample units (PSUs) on non-federal and federal lands. A stratified random sample is taken every 5 years, but Federal lands are not sampled.

Data is collected which can be used in modeling soil loss on forested lands. Data are for cover factor, the erosion control practice, the slope percent, and the slope length. The 1982 NRI data includes sheet, rill, and gully erosion types. The 1987 and 1992 NRI data sets cannot be used to estimate soil loss because Universal Soil Loss Equation (USLE) data were not collected separately for forested lands.

A new erosion prediction technology is being cooperatively developed by a number of Federal agency and university cooperators. This technology describes the erosion processes, rather than empirical relationships, and predicts not only erosion, but sediment yield, making in an appropriate tool for predicting water quality as well as soil quality. This approach has been shown to be as good as, or better than the USLE in predicting soil erosion on USLE plots. The model makes use of a daily climate descriptor, soil properties, management (which describes rates of vegetation regrowth and degree of disturbance), and topography. In forest conditions, rainfall simulation and natural runoff data collection have been collected to run the model for forest roads and harvest areas. Generally, a reasonable data set now exists for predicting road erosion and sediment yield across a riparian buffer area. Simplified relationships are being developed to allow rapid estimation of sediment yield from roads to upland channels.

Trends in soil loss can be derived from the 1982, 1987 and 1992 NRI data, if the 1982 data is used as a base-line and the model is extended for all forested lands in 1987 and 1992. Because of data limitations, assumptions will have to be made for the model and documented well.

Analysis indicates that forest erosion is predominantly due to forest roads and wild fires. Current work at the Rocky Mountain Research Station will allow estimating road surface erosion and sediment yields from roads entering waterways by developing a database of typical road topographies, soils, and distances to watercourses for a given climate. Much of this information is readily available, but the technology has not yet been tested. There are still some major unknown factors in estimating erosion rates triggered by wildfires. The most important gaps in current knowledge are the nature and spatial distribution of impacts on rill erosion, the dominant form of upland surface erosion.

Interpretation

Soil loss can be modeled for 1997 using the 1982 using the 1982 NRI data using a data element called "treatment needs" which includes all erosion types (sheet, rill, gully and ephemeral) and data elements called "critical eroding areas" and "degree of erosion" or erosion classes on all lands. This was done for the Nation as a whole in 1982. A similar analysis was completed for the 1992 NRI data in 1994 and revised in 1995. Tables 5-1 and 5-2 provide interpretations of the 1982 and 1992 NRI data for non-Federal forested lands. Additional data is available for:

Estimates of average annual wind erosion by 1982 land cover/use;

Percentage of each major land use/cover category for which erosion exceeds the soil loss tolerance (T);

Estimated average annual rates of sheet and rill erosion, by State; and

Estimated average annual rates of wind erosion, by State.

Some assumptions can be made to predict soil loss for Federal forest lands using 1982 USLE data. The results could then be added to non-Federal forest land soil loss estimates to obtain a National figure. On Federal lands, the categories would have to be adjusted to address land uses including undisturbed forests, areas harvested, and areas disturbed by prescription burning, wildfires, and roads.

INDICATOR 19: Area and percent of forest land managed primarily for protective functions. e.g. watersheds, flood protection, avalanche protection, riparian zones.

This indicator provides a measure of forest land allocated primarily for the protection of valuable environmental amenities associated with clean air, water, soil, flood and avalanche protection, etc. (public health and safety functions). Good results will confirm the degree to which society values ecosystems and protects them.

Some areas of federal lands are set aside for protective functions as identified in their respective planning processes. Special resource areas are protected on the basis of amenity values such as wilderness or wild and scenic rivers, as well as safety or functional resource values. Most States also have areas set aside for similar protective functions. Data showing such areas and objectives for their protection are available on a State-by-State basis. Additional analysis will be required to provide national figures, because of inconsistencies in definitions and use or management restrictions.

In addition to set-asides, regulations on Federal lands and in best management practices in those States that have them allow for protection of streams through buffer zones where trees are not harvested. Analysis of management at the watershed level is becoming increasingly important to assess the implications for sustainability.

Some jurisdictions manage watersheds specifically for quantity and quality of water, but data on the total area is not currently available. Flooding and other disasters in recent years may also cause jurisdictions to consider precluding selected types of development in areas vulnerable to severe impacts resulting from these events.

When lands are managed for multiple uses, it is difficult to attribute the area just to the protection functions. Developing this information on a national basis will be complex and time consuming, but could better reveal the extent of protection for various ecosystem functions.

INDICATOR 20: Percent of stream kilometers in forested catchments in which stream flow and timing has significantly deviated from the historic range of variation.

Changes in historic stream flow and the timing of flow, resulting in flooding and/or dewatered streams, can reflect on the health of aquatic ecosystems and the management and conservation of associated forest areas and downstream agriculture areas. This may indicate the extent to which water supply conditions are affected by forest management.

Data are gathered at the locations of stream gauges, but the relationship between an individual gauge and a specific length of stream in forested catchments needs to be defined. The United States Geological Survey (USGS) maintains a large network of stream gauging stations across the US, so data is potentially available. Streamflow records go back to the late 1800's. However, data sets, analyses and reports for forested catchments have not been assembled. USGS data are reliable. Results could also be reported by major aquatic ecoregions, and displayed in map form nationally at some future date.

Assessments of data measuring "natural" streamflow in the conterminous U.S. link increasing streamflow to changes in global climatic conditions. These data indicate that unimpaired streamflow has increased in nearly all regions of the conterminous United States since the early 1940's. They also show that, with one exception (New England), all of the observed positive trends occurred in autumn and winter.

Analysis of current trends may indicate significant impairment of the nations waters in some forested areas or regions. Data is available to provide a general summary for the type of change in historic stream flow and/or timing of flow, but has not been gathered and analyzed for this report. Impacts or changes to water quality, quantity and timing vary by region of the United States and trends for forested lands could be shown. Land use history and ownership may provide additional insight.

The National Inventory of Dams is maintained by the U.S. Army Corps of Engineers. This data set contains 1995 and 1996 data with plans for annual updates. The database contains information on 75,187 dams including dam name, location, size, capacity, etc. This information is used to asses safety hazards posed by dams in the U.S. and to analyze needs and target resources for navigation, flood control, water supply, hydroelectric power, environmental restoration, wildlife protection, and recreational projects. The Nature Conservancy is developing an Index of Hydrologic Modification that may provide more predictions of aquatic resource modification.

INDICATOR 21: Area and percent of forest land with significantly diminished soil organic matter and/or changes in other soil chemical properties.

Forest ecosystems recycle most of their nitrogen, phosphorus and other nutrients through the soil. Soil organic matter also is a major component of the global cycling of carbon. Being at the soil surface, organic matter status strongly reflects ecosystem disturbance. Soil organic matter is important for water retention, carbon storage, and soil organisms and is an indication of soil nutrient status. Changes in soil organic matter can affect the vitality of forest ecosystems through diminished regeneration capacity of trees, lower growth rates, and changes in species composition.

There are standard definitions of soil organic matter as well as standard procedures for measuring it, but sufficient data are not available to make reliable estimates in most regions. Some estimates have been made from existing soils databases, but the reliability of these estimates is unknown. There is limited probabilistic data in forested areas.

Studies have been conducted or are underway throughout the United States where changes in soil organic matter are monitored for different intensities of forest management. For example, the Long Term Soil Productivity research initiative (LTSP) by the Forest Service was initiated in 1989 evaluate timber management impacts on long-term soil productivity. By modeling losses of soil organic matter in the LTSP studies, with statistics on forest management practices by regional ecological units, a relative estimate can be shown for all forest lands with significantly diminished soil organic matter. This might be done also for other soil nutrients removed by harvesting or lost by leaching or in smoke after prescribed fire. These measurements can be related to results of fertilizer studies where growth response to additions of nutrients is measured. At least 10 years of study is needed to be able to estimate trends in the United States after installation of LTSP studies, which is 2 to 10 years past the present. Responses from treatments may be slow to develop. More robust data may have policy implications as it becomes available later.

During the last half century soil organic matter levels have increased in many forested areas of the eastern U.S. as forests recover from past exploitative use (e.g. clearing, cutting for charcoal, widespread grazing) and increase their biomass, both above ground and below. In some areas of the west, there probably was a slight overall decline in this indicator.

INDICATOR 22: Area and percent of forest land with significant compaction or changes in soil physical properties resulting from human activities.

Nutrient and water availability to forest vegetation is dependent on the physical ability of roots to grow and access nutrients, water, and oxygen from the soil. This in turn is dependent on soil texture and structure. Subsurface hydrology can also be affected by soil compaction resulting from extensive human activities. Compaction of the surface soil reduces water infiltration, resulting in more runoff. This can increase erosion, reduce biomass production and impair watershed function.

Data Summary

Like soil organic matter, soil compaction can be assessed by the Long Term Soil Productivity research initiative. Changes in soil bulk density and soil strength are measured at the initiation of a LTSP study and at least every 5 years thereafter. Because of the large number and diversity of soils in the LTSP studies, researchers expect eventually to have a good approximation of the forest soils in the country.

Repeated measurement in the LTSP studies will also provide researchers with information about the effects of compaction on plant growth, both for trees and for associated vegetation. Recovery rates of soil after compaction are also being studied. The effects of understory vegetation (especially grasses), climate, clay type, and other factors on the recovery rates will also be determined.

By modeling significant compaction or change in soil physical properties with statistics on forest management practices for the United States by regional ecological units, a relative estimate can be given for all forest lands with significant changes in soil physical properties and reduced productivity.

The LTSP studies will need to be continued for at least 10 years to develop an adequate data set. Also, research can not be extrapolated to estimate the effects of compaction on ecological regions that are not included in the study, currently the New England states and Oregon and Washington.

Grazing of forest land has decreased in some areas, so the extent and severity of compaction probably have decreased. However, areas of forest land intensively used for recreation have increased in many areas, increasing the potential for compaction in heavy use zones. Much logging equipment is larger than in former years, but operators are more sensitive to damage. Overall, the trend in forests with respect to physical damage to soils is difficult to assess.

Major challenges remain in the analysis of soil properties. Soil scientists agree on what compaction is, but there is wide disagreement on what measurement(s) truly reflect compaction (for example, bulk density, penetrometer readings, visual estimate of structure). Few quantitative, probabilistic data are available. Also, there is disagreement on how to assess the extent and effects of compaction and estimates of the severity of compaction on forest land are subject to dispute.

INDICATOR 23: Percent of water bodies in forest areas (e.g. stream kilometers, lake hectares) with significant variance of biological diversity from the historic range of variability.

Biological diversity is a critical indicator of the health of aquatic ecosystems. Organisms that live at the bottom of water bodies (benthos populations) are sensitive to a variety of possible changes, including silt, oxygen levels, and temperature. Such changes may be the result of changes in upland forest areas illustrating the extent to which aquatic biodiversity has been affected by forest management.

Although aquatic biological data have been gathered for many years, only recently has there been an effort made to develop and implement consistent methods on a National scale in Federal programs. There is not yet sufficient data to quantify changes in aquatic biodiversity in forest areas at the National level.

The new National Water-Quality Assessment (NAWQA) Program of the U.S. Geological Survey (USGS) has recently developed a set of biological sampling protocols to provide national consistency in collecting samples of biological communities and characterizing physical habitat conditions. It will be almost a decade before the NAWQA Program is able to describe what happened during the last few years of the 20th Century, and historical data is lacking as well. However, the resources available to NAWQA for forest environments may not be intensive enough to provide adequate data for this indicator. Regardless of the level of detail obtained in the data, the number of indicator sampling sites in forested areas that will be necessary to quantify this indicator still needs to be determined. Also, the majority of sampling sites are located in streams and well sites, so other water bodies (lakes, ponds, reservoirs, etc.) may not be adequately sampled.

The surface waters component of the EPA Environmental Monitoring and Assessment Program (EMAP) is designed to estimate the current status, extent, changes, and trends in the indicators of the biological condition of our Nation=s waters. This program monitors indicators of pollutant exposure and habitat condition; seeks associations between human-induced stresses and ecological conditions; and provides periodic statistical summaries and interpretive reports on status and trends at the regional and national scale. However, the same problems described for NAWQA may also apply to EMAP.

The Second RCA Appraisal describes the use, conditions and trends of the soil and water resources on non-Federal lands of the United States, documenting resource conditions based on the 1982 Natural Resource Inventory. For the Appraisal, data were analyzed at the major land resource area level and aggregated to land resource regions, or multi-state farming regions.

EPA maintains a national database called the STOrage and RETrieval (STORET) system which contains over 200 million observations of water quality monitoring data from multiple data sources, both public and private. STORET is designed to collect and disseminate basic information on chemical, physical, and biological quality of the nations waters. It is a repository of water quality data, including information from ambient, intensive survey, and effluent water quality monitoring of the waterways within and contiguous to the United States.

Since the data were collected over several years and by various organizations, the collection and analysis methods and equipment vary. This makes it difficult to ensure the comparability of the data from one organization to another. Users have not entered into the present system the needed information to document the quality of the data even though the data have met all of the quality control requirements generally considered acceptable for the collection and analysis of water data.

EPA is currently modernizing the system to make it easier to access data, store information about data quality and equipment used to acquire the data, and expand the fields to store biological and habitat information. Once the new system is implemented in late 1998 or early 1999, data from various studies and organizations will be more readily comparable. Links to other systems such as modernized USGS data systems will also be increased so STORET users have access to additional data as well.

Data from biological field surveys within and adjacent to forested lands would be most useful in addressing this indicator. A correlation of station geographic location and description with the proximity forest lands would indicate available information. In some instances, biological field surveys may not exist for non-Federal or Federal forest lands, and information will have to be modeled from existing field survey data.

Interpretation

The biological components of water resources in all ecosystems of the U.S. are declining. A large variety of indicators demonstrate this point. For example, more than 70 percent of the original floodplain forests in the country have been converted to urban and agricultural use, and 34 percent of fish, 75 percent of unionid mussels, and 65 percent of crayfish have been classified as rare to extinct. However, at this time, we cannot quantify National trends in aquatic biodiversity specifically in forest environments.

The Second RCA Appraisal provides some data showing probable sources of water quality problems affecting aquatic habitat, by stream mileage affected, as presented in Table 5-3. It estimates the extent of damage from all sources to aquatic habitat in rivers and streams, indicating that more miles of streams are damaged by non-point than point sources.

Sediment contributes to other pollutant problems because pesticides, nutrients, and other contaminants are absorbed to the soil particles. Erosion from all sources is the origin of 80 percent of the total phosphorous and 73 percent of the total Kjeldahl nitrogen in the Nations waterways. The Second RCA Appraisal provides an estimate of erosion and associated pollutant discharge into waterways of the United States, presented in Table 5-4.

Environmental Indicators of Water Quality in the United States is a 1996 report prepared by EPA=s Office of Water. This report indicates that methods for biological monitoring of lakes are under development. Consequently, there are not enough data to confidently report the number of lakes that support healthy aquatic life. However, 9 percent of the nations rivers and streams and 50 percent of all estuaries have been monitored. Of those aquatic systems that are regularly monitored, 50 percent of each category were found to support healthy aquatic life.

Location and description data in the STORET database will be useful in identifying stations that are within and adjacent to all forested lands. Coefficients can be provided which indicate a significant change in the aquatic ecosystem from siltation, oxygenation, and/or temperature fluctuation causing an adverse affect on benthos fauna. The extent of water bodies (streams and lakes) where benthos fauna may be adversely affected might be estimated from extensive road construction (siltation, change in pH from acid rock) and other forestry practices that have the potential of causing a significant change.

INDICATOR 24: Percent of water bodies in forest areas (e.g. stream kilometers, lake hectares) with significant variation from the historic range of variability in pH, dissolved oxygen, levels of chemicals (electrical conductivity), sedimentation or temperature change.

Monitoring of water quality over large areas of forest land serves as an initial indication that activities within or outside that area may be affecting ecosystem health. This may indicate the extent to which water quality conditions are affected by forest management.

Nationally consistent water quality data sets, analyses, and reports for forested catchments have not been assembled. However, this could be accomplished in future years in a manner similar to that currently used for National reporting by the USGS and EPA. For example, The National Water Summary for 1990 to 1991 uses a Nationally consistent data base and methods of statistical analysis to document stream water quality in the US, Puerto Rico, and the Western Pacific Islands.

Few water-quality data collection programs are National in scope. The USGS Hydrologic Bench-Mark Network began in 1964 and monitors 55 of the Nation's streams that are minimally affected by human influence. The USGS National Stream Quality Accounting Network (NASQAN) began in 1973 and monitors the quantity and quality of water that flows from major drainage basins. The EPA, beginning in 1974, has prepared a series of biennial National Water Quality Inventory reports to Congress which are based on individual reports prepared by the States as required by section 305(b) of the Clean Water Act. Also, about a thousand State and local agencies participate in the Federal-State Cooperative program, however differences in sampling methods and criteria, sample handling methods, and analytical techniques result in inconsistent and incomparable data for national or regional analyses.

Two Federal water-quality monitoring programs currently underway will enhance our databases for future analyses -- the USGS National Water Quality Assessment Program and the US EPA Environmental Monitoring and Assessment Program, both described above for Indicator 23. Early in the 21st Century, these programs will have gathered enough data needed to document statistically significant trends at the national level. Since the sources or consequences of stream contamination are strongly associated with specific regions of the country, results should be reported by major aquatic ecoregions.

The National Water Summary shows that concentrations of several of the traditional water-quality indicators (fecal coliform bacteria and total phosphorus for example) decreased during the 1980's and provide evidence of progress in pollution control during the decade. Trends in the concentrations of other traditional indicators (dissolved oxygen and nitrates) changed little.

The extent of water bodies with a significant change in water quality can be assessed using STORET data and modeling techniques including panametric data of water bodies within and adjacent to forested lands. Geographic locations and descriptions of stations would have to be correlated within a certain proximity to forest lands. In some instances, water quality data may not exist for Federal lands, and predictions would have to be made. By looking at annual sampling sites beyond and within forested areas, trends in significant change may be observed and displayed geographically.

Location and description data will be useful in identifying stations that are within and adjacent to forested lands. Coefficients can be provided which indicate a significant change in the aquatic ecosystem from siltation, oxygenation, and/or temperature fluctuation causing an adverse affect on benthos fauna. The extent of water bodies (streams and lakes) where benthos fauna may be adversely affected might be estimated from extensive road construction (siltation, change in pH from acid rock, etc.) and other forestry practices that have the potential of causing a significant change.

INDICATOR 25: Area and percent of forest land experiencing an accumulation of persistent toxic substances.

The primary source of persistent toxic substances would be industrial waste and pollution. Although some forest land may be affected by adjacent industrial activity, the total area is unknown and is probably small. Some forest land may be affected by mining operations for arsenic, cadmium, copper, lead, mercury, and zinc. In general, however, these operations are of concern for water quality rather than forest area.

Concerns over accumulation of toxic substances tend to be at the local scale. Dumping of toxic wastes and waste accumulation produced by wood preservatives has occurred on some forest lands. Toxic substances may also accumulate as a result of various management practices, such as application of fertilizers or herbicides. EPA maintains a database which provides the location of Superfund sites in forests but there is no data available for sites of smaller magnitude or lower toxicities that do not qualify for Superfund cleanup.

EPA's Permit Compliance System (PCS) was developed to meet the informational needs of the National Pollutant Discharge Elimination System (NPDES) under the Clean Water Act. This system tracks permit compliance and enforcement status for the NPDES program. It was designed to support the operational and reporting needs of regional and State personnel as well as EPA's Office of Enforcement and Compliance Assurance. The PCS has information on pollutants regulated by permits for major and minor facilities. It contains the amount and location of pollutants being discharged to water sources from major facilities such as wastewater treatment plants and factories. A user can also determine when facilities have violated their permits indicating unsafe levels of pollutants are being discharged into water sources.

In EPA's National Watershed Assessment Project (NWAP), data layers have been developed from national data sets to address watershed condition and vulnerability. Among other elements, this data base describes toxic pollutant loadings discharged annually in a watershed above the discharge limits allowed by the National Pollution Discharge Elimination System permits. This provides a measure of pollutant stress in a particular watershed. Location data is included so a relationship of point sources to forested lands can be determined.

Table 5-5 shows results of surveys completed by thirty-six States and Tribes in which toxicants are reported in 160,335 miles of rivers and streams. The survey covered only 5 percent of the Nation=s 3.5 million river miles for toxic contamination, but elevated concentrations of toxicants were detected in 25 percent of the surveyed rivers and streams. Thirty-four States and Tribes reported that they sampled toxicants in more than 7.5 million acres of lakes, reservoirs, and ponds. These surveys represent 18 percent of the Nation=s 40.8 million lake acres. The States and Tribes found elevated concentrations of toxicants in 29 percent of the sampled lake acres. Seventeen States sampled for toxicants in 23 percent of the Nation=s estuaries detecting elevated toxic concentrations in 26 percent of the 7,865 square miles of estuarine waters that were sampled.

iii. Summary for the Criterion

Highlights

Erosion concerns tend to be at the local scale and centered on the quality of management practices.

Assessments of data measuring "natural" streamflow in the conterminous U.S. establish the link between increasing streamflow and changes in global climatic conditions.

During the last half century, soil organic matter levels have increased in many forested areas of the eastern U.S. as forests recover from past exploitative use (e.g. clearing, cutting for charcoal, widespread grazing) and increase their biomass, both above ground and below. In the West, however, there probably was a slight overall decline in this indicator.

The overall trend in forests with respect to physical damage to soils is difficult to assess although grazing has decreased in some areas which would decrease the extent and severity of compaction, while recreation use has increased which would increase the potential for compaction in heavy use zones.

In the United States, the biological components of water resources are declining. For examples, more than 70 percent of the original floodplain forests in the country have been converted to urban and agricultural use, and 34 percent of fish, 75 percent of unionid mussels, and 65 percent of crayfish have been classified as rare to extinct.

Preliminary assumptions from regional and localized data sources suggest that concentrations of several of the traditional water-quality indicators (fecal coliform bacteria and total phosphorus, for example) decreased during the 1980's. Accordingly, they provide evidence of progress in pollution control during the decade. Trends in the concentrations of other traditional indicators (dissolved oxygen and nitrates) changed little.

Gaps

Trends that are limited to forested catchments cannot be determined at this time.

Sufficient data are not available in most regions to make reliable estimates of the area and percent of forest land with significantly diminished soil organic matter and/or changes in other soil chemical properties.

Data are lacking to quantify changes in aquatic biodiversity in forest areas at the national level.

Little quantitative, probabilistic data are available. There is disagreement on how to assess the extent and effects of compaction. Estimates of the severity of compaction on forest land are subject to dispute

The primary source of persistent toxic substances would be industrial waste and pollution. Although some forest land may be affected by adjacent industrial activity, the total area is unknown and is probably small.

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