Report No. 8
Design of Forest Riparian Buffer Strips for the Protection of Water Quality:
Analysis of Scientific Literature
(Part 3)

INTRODUCTION

The main purpose of this report is to identify, evaluate, and synthesize research-based information on the relationship of riparian buffer strips to forest practices, water quality, and fish habitat. If you are uncertain of the meaning of these and other technical terms, used in this report please refer to the Glossary at the end of the report.

Three basic opportunities exist for protecting water quality and aquatic habitat from nonpoint source pollution within a watershed. The first is in the upland areas where the source of erosion or water yield modification from forest practices such as road construction and timber harvesting can be reduced by best management practices, or BMPS. The second is to avoid cumulative effects in the watershed by attempting to minimize the combined impacts of forest practices in either time or space through scheduling. The third opportunity, and focal point of this report, is to provide additional protection in the riparian zone. More specifically, this report examines interrelationships between forest practices and stream protection activities with the riparian zone.

Protecting Idaho's water quality and aquatic habitats from pollution caused by forest practices is a major objective of the Idaho Forest Practices Act (FPA). The act regulates timber harvesting, road construction, reforestation, slash disposal, and the application of fertilizers and pesticides. Beginning in 1991, the FPA applies to national forest lands as well as state and private timberlands. The Idaho Department of Lands (IDL) administers and enforces the FPA using BMPs as minimum standards. BMPs are forest practices, or combinations of forest practices, set forth in the Idaho Forest Practices Act rules and regulations established by the State Board of Land Commissioners and published by the IDL (1990) pursuant to Title 38, Chapter 13, of the Idaho Code. Under the FPA, protection of water quality and aquatic habitat from activities in or near the riparian zone is done by establishing stream protection zones (SPZs), which are strips of land beside streams designed to buffer them from the impacts of land management activities. The vegetation, rocks, and debris in the SPZs limit the soil erosion, provide food and cover for fish and wildlife, moderate microclimatic extremes, and provide a barrier to overland movement of sediment.

The Idaho Forest Practices Act provides for the development of site-specific BMPs for land bordering on timber stream segments of concern by a local working committee (LWC). If the LWC fails to develop consensus on BMPs for stream segments of concern, the IDL is empowered to determine and implement appropriate measures. Recently the IDL has had to make several administrative determinations regarding site-specific BMPs because the LWC could not develop a consensus. Similar determinations will likely have to be made in the future. One of the key issues has been the design of SPZ, or riparian buffer strips to meet site-specific needs.

WHAT IS A BUFFER STRIP?

Within a watershed, generally the stream channel and adjacent land areas are divided into three zones: aquatic, riparian, and upland. The aquatic zone includes the stream and the area of the streambed that is normally underwater, i.e., the area below the high water mark. The riparian zone lies between the aquatic and upland zone and is an area of transitional vegetation influenced by its nearness to water. Riparian areas sometimes include other types of wetlands and may have distinctive soil characteristics (Helm 1985). Upland areas adjoin the riparian zone and are usually characterized by vegetation and soils different from those in the riparian zone.

To protect aquatic and riparian resources, buffer strips are established in the riparian

zone directly beside the stream, and may extend to the adjacent upland zone. Buffer strips are defined as strips of vegetation left beside a stream or lake after logging (Helm 1985). Buffer strips are also referred to as filter strips or protection strips. The term buffer strip is also loosely applied to a variety of administratively designated protection zones managed by state and federal agencies, including Idaho's Stream Protection Zone (SPZ), Washington's Riparian Management Zone (RMZ), and the U.S. Forest Service's Streamside Management Zone (SMZ). These administratively defined terms all denote riparian areas where forest practices are limited by administrative or legislative requirements. Nutter and Gaskin (1988) noted the lack of a universal definition for such areas and described a U.S. Forest Service SMZ as "an area with often undefined boundaries, adjacent to a stream or wetland, with recognized sensitive biological and physical attributes that serve to ameliorate impacts of upland influences." In our report, the term buffer strip means a strip of land immediately adjacent to a stream designed to protect aquatic and riparian resources. The terms "filter strip" and "protective strip" are sometimes used in the literature, and mean the same thing as buffer strip.

Appropriately designed and managed buffer strips can contribute significantly to the maintenance of aquatic and riparian habitat and the control of pollution. Riparian buffer strips fulfill at least three basic roles. First, they help to maintain the hydrologic, hydraulic, and ecological integrity of the stream channel and associated soil and vegetation. For example, riparian vegetation contributes to the maintenance of stream bank stability and channel capacity. Riparian vegetation also contributes the large organic debris that provides hydraulic structure to the channel. Second, buffer strips help protect aquatic and riparian plants and animals from upland sources of pollution by trapping or filtering sediments, nutrients, and chemicals from forestry and agricultural activities. Third, buffer strips protect fish and wildlife by supplying food, cover, and thermal protection, and in some cases providing unique habitat.

Buffer Strip Requirements in Idaho, Washington, California and Oregon

This section highlights and summarizes regulations concerning buffer strip size, and shade, vegetation, and filter strip requirements in four western states. These summaries only highlight some of the regulations on buffer strips. More detail is contained in the respective forest practices acts in the four states.

Idaho: Stream Protection Zones (SPZs). Buffer strips are termed stream protection zones (SPZs) in the Idaho Forest Practices Act (FPA). Their width is measured along the slope distance starting at the ordinary high water mark and determined by the beneficial uses of water in the stream. Streams used for domestic water supply, or important for spawning, rearing or migration of fish, are designated as Class I streams and are protected by a minimum 75-foot wide SPZ on each side of the stream. Headwater streams without a fishery whose principal value lies in their influence on downstream water quality are designated Class II streams and are protected by a minimum 5-foot-wide SPZ on each side of the stream.

SPZs different from those described above may be established for stream segments of concern (see Turner and O'Laughlin 1991). The width and other requirements for such zones are based on site-specific best management practices recommended by a Local Working Committee and adopted by the Idaho Department of Lands.

Additional requirements found in other sections of the Idaho FPA that protect aquatic and riparian zones within the SPZ are as follows (Idaho Department of Lands 1990):

(1) For Class I Streams, provide the large organic debris (LOD), shading, soil stabilization, wildlife cover, and water filtering effects of vegetation. Specifically, operators are to: (a) Leave hardwood trees, shrubs, grasses, and rocks wherever they afford shade over a stream or maintain the integrity of the soil near a stream; (b) Log mature

timber from the Stream Protection Zone in such a way that filtering effects of the SPZ are not destroyed and 75% of the current shade is retained; and (c) Retain standing trees, including conifers, hardwoods and snags within 50 feet of the ordinary high-water mark on each side of all Class I streams in the minimum numbers per 1,000 feet of stream as shown in Table 1.

Source: Idaho Department of Lands (1990)

(2) For Class II streams, provide soil stabilization and water filtering effects by leaving undisturbed soils in widths sufficient to prevent washing of sediment into Class I streams. In no case shall this width be less than 5 feet sloped distance above the ordinary high-water mark on each side of the stream.

(3) Cable yarding within an SPZ shall be done so as to minimize disturbance to the stream bank vegetation and stream channel.

(4) Skidding logs in or through streams is prohibited. Tractor or wheel skidding is prohibited on slopes exceeding 45% gradient immediately adjacent to Class I or II streams.

(5) Temporary structures to carry stream flow are required for stream crossings

and must be removed after use.

(6) Water bars must be provided for skid trails. New or reconstructed skid trails, landings, and fire trails must be located on stable areas outside of the SPZ.

(7) Slash must be removed from the stream and piled at least 5 feet above the high- water line on Class I streams. On Class II streams, slash must be removed if it could block the stream or there is sufficient water to transport the material.

(8) Forest practices are to be carried out to minimize the introduction of sediment, debris, petroleum products or other chemicals into streams. This includes planning for transportation networks to minimize road construction within SPZs and the replanting of vegetation between roads and streams as necessary.

(9) Use of chemicals is restricted in SPZs. A minimum of 100 feet of untreated strip must be left on each side of Class I or flowing Class II streams, and a minimum of 25 feet for ground application with power equipment.

(10) There is no prohibition against slash burning within SPZs.

Washington: Riparian Management Zones (RMZs). Under Washington's Forest Practices Rules and Regulations (Washington State Forest Practices Board 1988), buffer strips are provided to protect various uses such as water supply and fisheries. These variable width buffers, termed Riparian Management Zones (RMZs), are designed differently according to ecological needs for eastern and western Washington. Washington streams are divided into 5 classes according to use. In western Washington, RMZ widths are determined by stream class and stream width. RMZs are required to have a minimum width of 25 feet and a maximum width of 100 feet, measured horizontally from the high-water mark by map projection. In eastern Washington, RMZ width is measured from the ordinary high- water mark to the point where vegetation changes from wetland to an upland plant community. RMZ width is also determined by the type of timber harvest in the adjacent upland area. For partial cutting, the required range is from 30 to 50 feet on each side of the stream; for other types of harvest,

the range is from 30 to 300 feet on each side of the stream.

Additional selected requirements for Washington's RMZs are as follows:

(1) Leave tree requirements are dependent on stream type, stream-bed material and width, the percent of harvest unit within RMZ, and the size of clearcut.

(2) Shade requirements are determined by temperature sensitivity based upon field data from a "...verified water temperature model or method acceptable to the department." Unless a waiver is obtained, operators must leave all unmerchantable vegetation that provides shade and leave sufficient merchantable timber, if it is necessary to provide 50% of summer shade on the water surface. Where the 7-day average water temperatures exceeds 60F, 75% cover may be required.

(3) Slash disposal within RMZs must be by hand methods, e.g., lop and scatter, unless otherwise approved by the Department of Natural Resources.

California: Watercourse and Lake Protection Zones (WLPZs). Under California's Forest Practice Rules (California Department of Forestry and Fire Protection 1991), buffer strips are termed Watercourse and Lake Protection Zones (WLPZs) and are used to protect beneficial uses. California recognizes four classes of watercourse or stream, defined on the basis of beneficial use for water supply and fisheries. Widths of the WLPZs are determined by watercourse class and land-slope adjacent to the stream. WLPZs for Class I watercourses range from 50 to 200 feet, depending on four slope classes. For Class II watercourses, WLPZ widths range from 50 to 150 feet. For Class III and IV watercourses, WLPZ widths are determined by field inspection. Alternative prescriptions for WLPZs are allowed on a site-specific basis if they provide at least as much protection as the standard WLPZ requirements. California further requires that a written timber harvest plan be filed by a registered professional forester, which specifically states how watercourses and lakes will be protected.

Additional selected requirements for California's WLPZs are as follows:

(1) Residual vegetation requirements depend on watercourse class and slope. For service as filter strips and to provide shade on Class I watercourses, 50% of the overstory and 50% of the understory must be left standing and be well distributed. For Class II watercourses, 50% of the overstory and/or 50% of the understory must be left in a similar manner. Future harvesting is restricted until the canopy is re-established. For Class III and IV watercourses, the residual vegetation must be sufficient to prevent degradation of downstream beneficial uses as determined on a site- specific basis.

(2) Materials such as soil, silt, bark, slash, or petroleum must not enter the watercourse or lake. If there is reasonable expectation that timber operations will cause this type of contamination, then the activities must be deferred until a time when equipment, another procedure, or corrective work are approved. Materials accidentally entering Class I,II, and III watercourses shall be immediately removed.

(3) Broadcast burning of slash is prohibited in WLPZs for Class I and II watercourses.

Oregon: Riparian Management Areas (RMAs). Under the Oregon Forest Practice Rules (Oregon Department of Forestry 1991), buffer strips are termed Riparian Management Areas (RMAs). Oregon is divided into three administrative regions: northwest, southwest and eastern. Stream protection regulations for the regions are similar and based on three classes of stream defined primarily on the basis of use as either water supply, fisheries, or recreation. For Class I streams, the width of RMAs is variable and set at three times the average width of the stream at high flow, but not less than 25 feet or greater than 100 feet. RMAs for estuaries are 100 feet and for lakes vary in width by region.

Additional requirements for Oregon's RMAs are as follows:

(1) Leave tree requirements vary with stream width and are specified as conifers per 1,000 feet of stream and basal area per 1,000 feet of stream for Class I streams. These trees must be in the 50% of the RMA nearest the stream or within 25 feet, whichever is greater. These requirements do not apply to the eastern region.

(2) For Class I and Class II (special protection waters), 50% of the tree canopy and all snags that are not hazardous must be left. Also downed timber present prior to harvest and unmerchantable logs must be left.

(3) Other requirements for Class II streams consist of "minimizing channel disturbance from yarding and avoiding tractor skidding in or through any stream" in the southwest and northwest regions. In eastern Oregon, operators are required to "leave stabilization strips of undergrowth vegetation along Class II streams sufficient to prevent washing of sediment into Class I streams below."

(4) For Class I and Class II (special protection waters), 75% of the shade present prior to harvest must be left.

(5) Slash burning is prohibited in riparian areas designated Class I water.

Comparison of Buffer Strip Requirements in Four States

The type of beneficial use derived from a stream is used by all four states as a primary determinant of the need for, and width of, a buffer strip. Washington, Oregon, and California use additional site-specific factors, such as stream width and the slope or type of harvest on adjoining land, to refine buffer strip width prescriptions. Research indicates that consideration of these and other factors enhances the effectiveness of buffer strips (Potts and Bai 1989, Steinblums et al. 1984, Brazier and Brown 1973, Haupt 1959a). In Idaho, buffer strip width is determined primarily by stream class on the basis of beneficial uses without consideration of site-specific factors, except in the special cases of stream segments of concern. The fixed minimum width, use-dependent approach used in Idaho has the virtue of simplicity in application, but has greater potential for providing either not enough or too much protection. The use of stream classification with additional site-specific factors in the other three states adds operational complexity but is more flexible with greater potential sensitivity to local stream protection needs.

Requirements in the four states for buffer zone width, shade or canopy, and leave trees are summarized in Table 2. Leave tree and shade requirements appear in the buffer strip designs for all four states. Because of the different prescriptions for the number, species, and sizes of trees to be left, it is difficult to compare the prescriptions. For example, California requires, in addition to marked leave trees, that 50% of the overstory and 50% of the understory be left on Class I streams; whereas in Oregon the number of leave trees is determined by the stream width and specified in terms of the number of trees per 1,000 feet of stream. The purposes of retaining leave trees and other residual vegetation such as snags and understory are to provide LOD, maintain bank stability, provide fish and wildlife habitat, and control of excessive stream temperature. The measure of the effectiveness of leave trees is not stated directly in terms of sedimentation prevented, fish cover provided, or reduced stream temperature. The exception is Washington, which requires an increase in residual canopy from 50% to 75% when water temperature is 60F or more. In Washington, Oregon, and Idaho, the measure of effectiveness is stated as shade retained after harvest, expressed as a percent of that existing before harvest. California requires 50% of the overstory and understory be retained; residual shade is not specified. Methods for estimating or measuring the percent canopy or percent shade retained are not specified.

* Human water supply or fisheries use.
** Streams capable of sediment transport (California) or other influence (Idaho and Washington) or significant impact (Oregon) on downstream waters.
^aIn Idaho, the shade requirement is specifically designed to maintain stream temperatures.
^bIn Idaho, the leave tree requirement is specifically designed to provide for the recruitment of large organic debris (LOD).
^cMay range as high as 300 feet for some types of timber harvest.
^dTo be determined by field inspection.
^eResidual vegetation must be sufficient to prevent degradation of downstream beneficial uses.
^fIn eastern Oregon, operators are required to "leave stabilization strips of undergrowth...sufficient to prevent washing of sediment into Class I streams below."

Restrictions on felling, bucking, yarding, and equipment operation within the buffer zones are similar but not identical. One important difference is the prohibition against slash burning within buffer strips along some stream classes that appears in the regulations of Oregon, California, and Washington, but not in Idaho (Skille 1990).