Text Size:   A+ A- A   •   Text Only
Find     
Site Image
Background on Strategy D
Protect, maintain, and enhance soil and water resources of Oregon's forests

Why is protecting, maintaining, and enhancing soil and water resources important?
Soil and water are basic elements of forest productivity. Forest soils are also an important part of the regulation of surface and groundwater flow. The interaction of soil and water plays an important role in the health of the streams and rivers flowing through Oregon's forests. Clean water is critical to our quality of life. More than half of Oregon's population depends on water supplies that originate on or are protected in part by forestlands. Oregonians also depend on high-quality water for fisheries, industry, recreation, and agriculture.
 
What do we know about Oregon's forest soil and water resources?
Water quality from forest streams is good
We have a relatively poor understanding of how current water quality conditions on forestlands compare to those of presettlement times. In particular, we lack data on the presettlement range of variability, both spatial and temporal, of natural disturbances such as fire, insect and disease infestations, windstorms, and floods. However, the recent Oregon State of the Environment Report found that water quality and the condition of riparian (streamside) vegetation on forestlands has improved with increasing regulation of forest practices. The report concluded that water quality on forestland remains good and is generally better than that found on land devoted to other uses.
 
Rates of natural soil erosion are highly variable
Forest soils and water have been well studied, but there are little comprehensive data with which to assess the condition and trends of soil and water resources across large areas of forestland and over time. Soils in unmanaged forests erode and deposit sediments into streams at varying rates depending on soil type, topography, vegetation cover, and the amount of rainfall received. Sediment enters water from soil-surface erosion, channel erosion, and mass soil movements such as landslides and debris flows. These inputs are both chronic (relatively steady and continuous over time) or episodic (characterized by occasional sudden pulses). These erosion and sedimentation processes are functions of the disturbance regime-the spatial and temporal pattern of occurrence of wildfires, floods, and windstorms-that characterizes the forest.
 
Landslides are a major source of natural soil erosion in Pacific Northwest forests west of the Cascade Mountains. Undisturbed forest soils in western Oregon have a high capacity to absorb rain-up to three feet per hour. Surface erosion is usually not a major source of sediment in these forests. In eastern Oregon, natural surface erosion is the most significant source of sediment in streams. Erosion can be particularly severe after wildfire or heavy rain.
 
Many of Oregon's forest soils are highly productive
Some of the most productive tree-growing soils in the world are located in parts of western Oregon. Levels of organic soil matter are relatively high in most western Oregon forests. The cycling and maintenance of organic matter in the forest influences the productivity and water-retention capabilities of the soil. Since the 1960s, fertilization and stand manipulation studies have produced localized data on major soil nutrients and organic matter. Overall organic carbon levels are higher in western Oregon than in eastern Oregon. Most Pacific Northwest forests are nitrogen-limited, so fertilizing with nitrogen, or nitrogen and phosphorous, enhances productivity, decomposition, and nutrient recycling.
 
What human activities on Oregon's forestlands affect soil and water resources?
A variety of activities occurring on forestlands, including forest management (timber harvesting and road construction and use), fire suppression, recreation, and livestock grazing, can affect soil and water resources. We do not have enough long-term data to tell us whether soil and water resources have been significantly changed in areas actively managed for timber production or areas in which wildfire has been suppressed. Long-term monitoring of the physical and biological characteristics of forests could provide a stronger foundation for understanding both human and natural-caused changes in forest soils and water. In general, we know more about the effects of forest practices on water quality than on soils and forest productivity.
 
For example, we know that natural disturbances that trigger large erosion events can produce important changes in aquatic conditions. These episodic changes are critical in maintaining aquatic habitat over time. Similarly, we know that maintaining organic matter in forest soils is critical to their productivity and water-holding capability. This knowledge and other findings have prompted periodic upgrades of state forest practice rules. Following are observations on how forest management, road construction, and fire suppression affect soil and water resources in the forest.
 
Forest management and road systems
Many studies have shown that timber management at individual sites can increase erosion in the short term. We know less about how timber management affects soil and water over time and at a landscape scale. Roads used for log hauling and recreational use have been found to be the primary source of stream sediment from forest management activities in the western United States. Roads characterized by high surface erosion or failure of the road fill, and located near streams, are those most likely to cause erosion problems. Research has also found that best management practices can be effective in reducing potential impacts of forest management and road systems.
 
Forest management and landslides
The effect of forest management on the occurrence of landslides is another major concern. After two large storm and flood events of 1996, a major ground-based study was undertaken in western Oregon to evaluate the relationship between forest practices and shallow, rapidly moving landslides. The study was the largest to date in the Pacific Northwest to collect detailed data about landslides on the ground and compare them with data from aerial photos. It is also the first study whose findings reflect current management practices on different forestland ownerships in Oregon, and the only one so far to collect detailed information on forest stands of intermediate age, 20 to 100 years old.
 
Because it is based on an inventory following individual storm events, the study has several limitations. Nonetheless, its findings suggest that, while timber harvesting does have an influence on shallow, rapid landslides, these landslides are endemic in unmanaged forests. They also suggest that effects from timber harvesting may only impact the timing of landslide-occurrence, rather than the absolute number of landslides that occur over space and time.
 
The study's key conclusions:
  • There is significant landslide risk on very steep slopes regardless of forest age, especially in certain geological formations in which major storms and landslide processes are the dominant means by which the landscape is shaped.
  • Higher landslide densities and erosion volumes were found in stands that had been harvested in the previous nine years than in forests older than 100 years, in three out of four study areas monitored by the Department of Forestry for storm effects. However, areas with forest between the ages of 30 and 100 typically had lower landslide densities and erosion volumes than were found in the mature forest stands.
  • Landslides from recently harvested and older forests had similar dimensions, including depth, initial volume, and debris flow volume.
Timber harvesting can affect the occurrence of shallow, rapidly moving landslides on steep slopes with a high inherent risk of landslides.

 
Forest management and soil disturbance
Little quantitative work is available to analyze soil disturbance at a watershed or landscape scale. We know that at the site level, soil disturbance, especially compaction, can reduce forest growth and increase soil erosion. Logging practices can cause compaction as heavy equipment and logs are moved across the forest floor. Oregon's forest practice rules require operators to reduce soil disturbance during and after logging operations. Using cable yarding on steeper slopes, for example, can significantly reduce the impact of timber harvest. Reforestation is also required after timber harvest to ensure that trees promptly reoccupy the land and help protect the soil.
 
Forest management and streams
We have a reasonably good understanding of the effect of forest management on peak flows (streamflows during relatively heavy rainfall events). Forest management can increase small and moderate peak flows (less than or equal to two-year floods) in smaller watersheds; however, the majority of research indicates that large peaks (greater than two-year floods) are not affected by forest management in either small or large watersheds.
 
Increases in stream temperatures from forest management were a concern in the days when logging was allowed down to the edges of streams. For more than three decades, though, forest operators have been required to leave buffer strips of trees and other vegetation along most streams. Maintaining riparian vegetation minimizes or eliminates increases in stream temperature in the years immediately after forest harvesting. At a landscape scale across Oregon, younger, denser forests cover much forestland. In riparian areas, those areas directly adjacent to streams, younger, denser forests provide high levels of shade that can result in relatively cool stream temperatures. The current distribution of forest ages across the landscape is different from historical conditions, where mature and old-growth forests were more common but generally did not produce the high shade levels associated with younger, denser forests. It is unknown how this difference might be affecting stream temperature dynamics at different spatial and temporal scales.
 
Maintaining vegetation cover in riparian areas also helps protect aquatic habitat by preventing adverse levels of sediment from entering the stream. In addition, we know that large pieces of wood in forest streams are essential for high-quality aquatic habitat. Trees and rootwads near the stream are more likely to fall in and produce high-quality aquatic habitat than are trees farther away. Between 70 and 99 percent of large wood in forest streams comes from within 50 to 100 feet, and most of the "key pieces"-the largest ones-come from closer than 50 feet. Significant contributions of large wood can also be delivered to streams by shallow, rapid landslides originating in upland or headwall areas.
 
Fire suppression
Efforts to protect and manage water and soil resources from fire must take into account the dynamic nature of forests. Over the long term, wildfires are inevitable. They cause significant changes in sediment deposition and streamflow, altering the condition of forest soils and water at the watershed or even the landscape scale. These periodic, long-term natural disturbances are critical in maintaining the forest's aquatic habitat features over time. Fire suppression may reduce the risk of harm to water quality in the short term, but fire suppression without active management, as noted in Strategy F, will ultimately result in unnaturally intense fires that cause greater damage to soil and water.
 
Data needs
At the October 2001 symposium, "A Landmark Assessment of Oregon's Forest Sustainability," called by the Board of Forestry to review the current state of scientific data about forests and forest management, several scientists observed that the existing literature on the impacts of forest practices on soil and water is outdated. Most of the watershed data available today comes from research carried out in the '50s and '60s, before Oregon enacted any comprehensive forest practice law. The timber harvested during that time consisted mostly of big, old trees. The machines were large to match the timber, the road system had to be built to handle heavy logs and machines, and, relative to current practices, best management practices were poor. Now we are entering the fourth decade of forest practice regulations. Trees are smaller and more uniform, and the equipment is much smaller and uses, for the most part, an existing road system. The scientists strongly recommended that new research focused on harvest impacts under current practices should be a high priority for the Board of Forestry and the state (Figure 10).
 
Relatively little comprehensive monitoring is being done on the condition of soil and water resources. Protocols have been developed to measure some aspects of soil and water conditions, but there is no system that can generate comprehensive information on multiple questions on a broad landscape scale. Collaboration among forestry scientists, government agencies, and private organizations will be a critical in developing a cost-effective monitoring and research system .
 
What is being done to protect soil and water quality?
State and federal protection measures
The Oregon Forest Practices Act was enacted in 1971 to regulate forest practices for the protection of all resources, including soil and water, on non-federal forestlands outside of cities with their own forestry ordinances. State policy designates the Forest Practices Act as the mechanism for water quality protection and gives the Board of Forestry authority, in coordination with the Environmental Quality Commission, to establish best management practices to ensure that water quality is protected.
 
The forest practice law addresses the protection of soil resources through a number of regulations. These require, among many other things, timely reforestation to stabilize soils after a forest harvesting operation. They also require operators to minimize the amount of soil and logging debris entering waterways, and to take particular care in harvesting and road building to minimize disturbance to the ground, especially on steep slopes.
 
Operators must maintain buffer strips of trees and other vegetation within a certain distance of most streams to promote mature-forest conditions in the riparian zone, to help keep the water cool, and to help keep sediment from entering the stream. The forest practice rules also restrict the application of chemical herbicides and fertilizers near forest streams.
On federal forestlands, the regional Northwest Forest Plan and the plans of individual national forests and Bureau of Land Management forests are the primary mechanisms for ensuring soil and water quality protection consistent with the federal Clean Water Act.
 
Measures under the Oregon Plan for Salmon and Watersheds and other voluntary efforts
Many forest roads built before forest practice regulation pose a risk to water quality from sediment and soil erosion. Industrial forest landowners and state forest managers are implementing a voluntary program called the "Road Hazard Identification and Risk Reduction Project" to identify and address sediment risks from roads. The program identifies the most troublesome roads so that landowners can take action to reduce the amount of sediment they produce. Road repairs conducted as part of this project improve fish passage, reduce the potential for washouts and landslides, and reduce the delivery of surface erosion to streams.
Individual forest landowners are taking other initiatives beyond what the law requires, such as voluntarily retaining additional trees along streams (Figures 11 and 12). Finally, incentive programs such as the Conservation Reserve Enhancement Program support efforts to establish riparian forests on agricultural lands.
 
What are the major issues surrounding soil and water quality?
Because of a belief that forest management inevitably harms watershed health, management is often restricted in watersheds that provide drinking water. Such restrictions can lead to unintended and adverse consequences. The ability to actively manage forested watersheds, including those that supply drinking water, is often critical in maintaining both healthy forests and high-quality watersheds. To sustain the health of our forests and watersheds in the future, we must increase the ability of public forest managers, private landowners, and communities to address forest-related water issues and to manage, protect, and enhance forests for water supply, water quality, and watershed health.
 
Oregon has as yet no comprehensive riparian or stream corridor management policy or program. The various state programs that influence the management and use of riparian areas were created to achieve a variety of objectives, and their efforts today are not always well coordinated. In order to achieve water quality and aquatic habitat objectives across Oregon, riparian areas will need to be protected and enhanced not only on forestlands but on other lands as well.
 
Because riparian protection standards on forestlands are generally more protective than those covering other land uses, the policy of ORS 527.714 becomes important in considering future changes to riparian protection policy on forestlands. ORS 527.714 requires that any benefits achieved by adopting more protective riparian standards through regulation be in proportion to the degree that the existing practices of forest landowners, as a whole, are contributing to the overall resource concern that the standards are intended to address.
 
What are the key interactions of this strategy with other strategies?
Protecting, maintaining, and enhancing soil and water resources affects, and is affected by, other strategies and policies for managing Oregon's forests. Here are some examples of these interactions:
  • Forest soils, riparian areas, and aquatic areas provide habitat for diverse plant and animal species. Productive soils and functioning waterways are a basic foundation for providing native plant and animal habitats.
  • Loss of forestland to other land uses directly reduces the amount of forested watersheds and potentially increases the intensity of management on remaining forests.
  • Resource loss from fire, insects, and disease can cause a temporary change in sediment and stream-flow dynamics at a watershed scale.
  • Changes in forest health that influence the types of tree and plant species in and around riparian areas, such as invasions of non-native plant species, can lead to changes in the riparian functions that influence water quality and aquatic habitat.
  • Forest soils can store significant amounts of carbon, and forest practices may potentially affect this storage capability.
What are potential indicators to measure progress toward accomplishing this strategy?
1. Area and percent of forestland with significant soil erosion
 
2. Percent of water bodies in forest areas and other land uses with significant variance of biological diversity from the historic range
 
3. Percent of forest waterways with significant deviations from normal in pH, levels of dissolved oxygen, levels of chemicals, sedimentation, or temperature