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Best Management Practices

Our national economy benefits from vast forest lands and the products they produce. In many states, forest based industries are among the largest manufacturing-based employers. Wood-based industries produce over $100 billion worth of products each year.

One important product of these forests may be difficult to put a dollar value on. Production of high quality water is a major benefit of forest land that often is taken for granted. Recently, concern has focused on the impact of forest management practices on water quality. Several Best Management Practices (BMPs) have been developed to help protect the environment during timber operations, particularly aimed at reducing water pollution.

Nonpoint Source Pollution

Nonpoint source (NPS) pollution is water pollution that is created from an activity that has no particular permanent location. Typically, NPS pollution arises from man's activities and is carried over and through the soil by rainfall runoff. Agriculture, urban/suburban development, mining, construction, and silviculture are categories of NPS pollution.

Silviculture is the art and science of growing and tending forest trees. More generally, silviculture includes all activities from planting tree seedlings to transporting the harvested timber from the forest.

Types of silvicultural nonpoint source pollution include sediment, nutrients, organics, thermal pollution, and chemicals.

Sedimentation is the most significant type of silvicultural NPS pollution. In an undisturbed forest, the tree and understory canopy, forest litter, organic matter, and root systems protect the soil from the erosive action of falling raindrops. Silvicultural activities such as timber harvesting, skidding, road building, and mechanical site preparation disrupt this natural erosion protection. As a result, they have the potential to accelerate erosion and increase sedimentation of adjacent streams. Sediment may be harmful to fish and other aquatic organisms that depend on surface water for food or habitat. It also decreases the water's value for recreational and commercial activities, fills in reservoirs, and increases drinking water treatment costs.

Nutrients such as nitrogen and phosphorus exist naturally in forest soil and some finds its way into adjacent streams and groundwater. Silvicultural operations, especially timber harvesting, alter the normal nutrient cycle of the forest. This may lead to changes in the nutrient content of discharge water. Excessive nutrient levels in water can stimulate abnormal plant growth, alter levels of dissolved oxygen, and disturb aquatic ecosystems.

Organic material is a third form of NPS pollution. In forests, this type of pollution may result from logging debris, such as tree tops, logs, and branches, that have fallen or washed into stream channels. Decomposition of this material reduces oxygen levels in the water and may lead to undesirable changes in the taste, color, and odor of the water. Although some organic material will naturally be deposited in streams, harvesting operations may increase levels if precautions are not taken.

Thermal pollution is a term that describes the adverse changes in water temperature caused by forest practices which eliminate shading vegetation. Removal of shading forest cover exposes the stream to direct solar radiation. As a result, water temperatures fluctuate more widely and peak temperatures are higher. This affects water quality by impacting the level of dissolved oxygen, rates of chemical processes, and biological oxygen demand.

Chemicals, including herbicides and other pesticides entering water bodies can be harmful to aquatic life. Also, petrochemicals from machinery are hazardous to water quality if not disposed of properly. These chemicals may enter the water in runoff, through leaching, by aerial drift during application, or directly through accidents or carelessness. Trash, garbage, and equipment parts left on the site are also water quality hazards; not to mention unsightly.

Best Management Practices

The  Best Management Practices  (BMP's) are designed to help landowners, foresters, loggers, and others protect water quality during silvicultural operations. BMPs can prevent, or at least greatly reduce, NPS pollution from forest management activities. Use of BMPs is voluntary; however, implementing these practices by all involved in forest management will help protect water quality without strict government regulations.

BMP's can be organized into 8 activity areas:

Planning

Careful planning of forestry operations can help reduce the potential for nonpoint source pollution. Unit boundaries, road systems, and log sets should be designed so that streams and other water bodies are avoided. Timing activities to avoid seasons when the soil in low areas is wet will help avoid problems.

In planning activities, topographic maps, aerial photographs, and soil surveys in combination with field reconnaissance and landowner knowledge should be used to determine site conditions and pin-point problem areas. Natural drainage channels and topography should be major considerations in determining cutting unit boundaries. The goal is to minimize the number of stream crossings and the length of roads and skid trails needed, thus reducing overall soil disturbance.

Road Construction and Maintenance

Several studies have shown that poorly designed road systems are the major cause of silvicultural NPS pollution. A well-located, constructed, and maintained system of forest roads minimizes pollution impacts on forest streams.

The road design should be the minimum needed to accommodate expected traffic. Narrower roads require less soil movement during construction and provide less surface area for potential erosion.

A good drainage system is an essential ingredient for preventing roads from eroding and causing NPS pollution. Roads should be crowned and sloped so that water drains from the road surface to the roadside. Water draining down the middle of roads on long slopes will soon cause gullies that make the road both unusable and a potential water quality problem. Ditches, culverts, cross drains, and wing ditches should be installed where needed to direct water off the road and onto the undisturbed forest floor.

Stream crossings, where necessary, should be at right angles and should include erosion protection measures. Crossings should be designed to protect the approach to the stream, the stream banks and stream bottom. There are several options for stream crossings including using gravel, a cement slab, or  GEOWEBTM  to harden the bottom, installing culverts, or bridges. The choice should depend on the expected use of the crossing and its susceptibility to erosion. Temporary structures should be removed promptly after use.

A well-designed road system will be much less expensive to maintain than a poorly designed, erosion prone, system. Routine maintenance should be conducted to keep drainage systems free of blockage and to rework problem areas before they become unmanageable. Seeding of temporary roads should be considered to help protect against surface erosion.

Harvesting

Harvesting trees is an integral part of forest management. The degree to which the forest environment is affected depends largely on the care taken by the logging contractor. The timberland owner also shares a part of the responsibility in planning a harvest that protects the environmental quality of the site. Tree felling, skidding, loading, and hauling will always disturb the forest floor and expose bare soil to some extent. However, use of BMPs can minimize this impact.

Directional tree felling should be used near streams to minimize debris entering the stream. To reduce soil disturbance during skidding, trees should be felled parallel to the skidding direction with butts toward the landing.

Skid trails should be laid out to take advantage of topography and minimize disruption of natural drainage patterns. Skid trails on long slopes should have occasional breaks so water does not run straight down the skid trail over long distances. Where stream crossings cannot be avoided, the most direct route should be used, taking advantage of natural fords with firm bottoms, stable banks, and gentle slopes along approaches. Upon completion of use, skid trails should have water bars installed. Seeding should be considered when necessary to prevent erosion.

Log sets or landings are areas where harvested trees are collected, temporarily stored, and loaded onto trucks. They can be a source of soil erosion if not well planned. Landings are subject to concentrated traffic of heavy equipment. They are also sites for equipment maintenance. For these reasons, they should be located on firm ground away from streams. Provisions should be made to provide drainage if water will tend to collect on the site.

Disposal of logging slash and debris should be done to protect water quality. Debris accidentally deposited in streams should be removed. Erosion prone areas should be mulched or seeded to reestablish vegetative cover.

Mechanical Site Preparation and Planting

Like harvesting, the major problem associated with site preparation and planting involves the potential for soil erosion. Site Preparation with heavy equipment exposes bare soil and creates opportunities for erosion. The primary factors in determining erosion potential are the percent of the area with exposed soil, the degree of slope, and the type of soil.

Mechanical site preparation should minimize disturbance of areas adjacent to streams or other water bodies. Heavy mechanical site preparation should be avoided on slopes of more than 30 percent, or on highly erosive soils. Operators of equipment should be trained to minimize soil disturbance and compaction.

Prescribed Fire

A major concern of the forest manager is how fires affect surface runoff and soil erosion. However, if the burn is under a timber stand and much of the forest litter remains, soil movement will be minor on slopes of up to 25 percent. Site preparation burns are the hottest type burn and can remove the natural erosion protection of the surface organic material.

A significant amount of soil movement can be caused by the construction of the firebreaks rather than the burn itself. To minimize erosion, firebreaks on slopes should have water bars and wing ditches.

Silvicultural Chemicals

The use of silvicultural chemicals can be a potential problem, though less than 1 percent of all pesticides are used in forest management. BMPs for silvicultural chemicals include recommendations for preventing direct or indirect application of forest chemicals to water sources. Precautions should be taken during mixing, application, container handling, and cleanup to prevent the accidental introduction of chemical contaminants into the groundwater or nearby streams.

Streamside Management Zones

One of the most environmentally sensitive areas in the forest is the zone along a stream channel, often called the  streamside management zone.  Disturbances within the area 50 to 100 feet or more along each side of the stream have the potential to affect water quality. BMPs for streamside management zones are designed to protect these areas. Generally, these zones should be left relatively undisturbed. Ground cover should be retained as a filter to capture any sediment or other pollutants running towards the channel. Although selective tree cutting is allowable, most trees should be left standing and the ground cover preserved within the streamside management zone to protect the water from solar heating. Both perennial and intermittent streams need well delineated streamside management zones. Management priority should be to protect water quality. If degradation occurs, remedial action should be immediate.

Conclusions

The timberland owner is responsible for the implementation of practices to control nonpoint source pollution on his/her land. At present, Best Management Practices are voluntary. However, if voluntary BMPs fail to eliminate NPS pollution problems, the next step could well be regulations and permitting. By implementing BMPs, the forestry community has an opportunity to demonstrate respect for those natural resources including water quality upon which it depends.