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Estimating Areas and Timber Values of Riparian Management on Forest Lands1

Posted on: Tuesday, 21 March 2006, 06:00 CST

By Ice, George G; Skaugset, Arne; Simmons, Amy

ABSTRACT:

Buffers, filter strips, and other riparian protection zones are widely accepted practices used to minimize water quality impacts from forest management and other land use activities. Riparian management prescriptions are often developed with limited or inconsistent consideration of the impact they will have on land management opportunities or economics. A combination of factors influences the area and value of riparian management zones (RMZs). A simple tool can determine the percentage of a watershed in RMZs where they comprise only a small fraction of the watershed. For a more detailed analysis, the Oak Creek Watershed in Oregon served as an example of a geographic information system (GIS) assessment. The same watershed can have dramatically different areas and values of timber in RMZs depending on the resolution used to determine the stream network, different stream types (perennial fish-bearing, perennial nonfish bearing, and nonperennial; small, medium, and large), and different RMZ widths and management restrictions for each stream type. The areas of watershed put into riparian protection for two drainage densities and three RMZ prescriptions were determined. Finally, the volumes of merchantable timber in the RMZs and their subsequent values were determined.

(KEY TERMS: digital elevation model (DEM); economics; forest; geographic information system (GIS); Riparian Management Zone (RMZ); watershed management.)

INTRODUCTION

Buffers, equipment exclusion zones, filter strips, riparian management zones, riparian management areas, water course and lake protection zones, and shade strips are widely accepted management practices that minimize the impacts of forestry and other land uses on water quality. These areas will be referred to throughout this paper as RMZs. These practices involve management restrictions near streams and lakes to maintain riparian functions, including shading, wood recruitment, nutrient uptake, sediment trapping, and channel stabilization. Management restrictions near streams are based on an understanding of the connection between streams and uplands through the riparian area. In weighing stream protection options, two primary questions about these riparian treatments must be answered. First, how effective in protecting riparian functions are different management restrictions, such as widths, timber harvesting limits, restrictions on yarding and site preparation, etc.? Second, what are the tradeoffs between management restrictions and the economic costs of alternatives? Watershed specialists and policy makers often have little idea what riparian protection prescriptions will cost. Here, tools are provided to determine how drainage network densities, classifications of stream reaches, and RMZ widths and management restrictions tied to those stream reach classifications combine to determine the area and value of timber left in RMZs.

EFFECTIVENESS OF RIPARIAN MANAGEMENT AREAS

It is beyond the scope of this paper to comprehensively assess the relative effectiveness of riparian management prescriptions; however, it is important to demonstrate the overall effectiveness of these practices. If restricted management in riparian areas showed no water quality advantage, it would be hard to justify additional management restrictions and costs. However, research has shown that riparian management prescriptions do effectively minimize water quality impacts and maintain valuable riparian functions.

One of the first studies to look at the effectiveness of RMZs was the Alsea Watershed Study (Moring, 1975). Three small streams in coastal Oregon were monitored for 15 years beginning in 1959. After seven years, one watershed was completely clear-cut without RMZs. Logging and yarding of timber were carried out literally through the stream network. A second watershed was 25 percent patch-cut and RMZs (no harvest buffers) were left around the fish bearing stream segments. A third watershed was left as a control. Water temperatures in the clear-cut watershed rose by 16C and by 1.7C in the patch-cut watershed. The heating of the stream and introduction of fresh slash also caused a drop in dissolved oxygen (DO) concentrations for the surface runoff of the clear-cut watershed. The DO concentrations averaged 2.5 mg/l for one stream reach in July, a concentration considered below the lethal limits for juvenile coho salmon (Moring, 1975). This depression in DO concentration was not observed for the patch-cut watershed with RMZs.

Many other studies have demonstrated the effectiveness of special management restrictions in the riparian area for minimizing impacts to temperature (Brown, 1969; Vowell, 2001), DO (Moring, 1975; Ice, 1990), sediment (Moring, 1975; Swift, 1986; Rivenbark and Jackson, 2004), and nutrients (Lowrance et al., 1984). Forest managers are now being asked not only to avoid polluting water but also to maintain beneficial riparian functions such as the recruitment of large wood and fine organic debris (ODF and ODEQ, 2002). Riparian prescriptions are designed to maintain these functions as well.

In fact, riparian management is now considered an essential element of an effective forest practices program to control nonpoint source pollution from silviculture. One performance measure for company certification under the American Forest and Paper Association's Sustainable Forestry Initiative is the implementation of riparian protection measures (SFB, 2002). Similarly, the Forest Stewardship Council (FSC, 2005) defines standards for water protection, including riparian protection measures. Riparian management is widely used to reduce the water quality effects of forest management to acceptable levels. The particular dimensions and restrictions for forest riparian buffers require management for specific functions. Belt and O'Laughlin (1994) provided key considerations for riparian functions.

An important economic concept that relates to ecological objectives in managing near streams is the law of diminishing returns. It states that if one factor of production is increased but the other remains constant, the overall returns will relatively decrease after a certain point (Spillman and Lang, 1924). Research indicates that a high proportion of the shade, litter inputs, large wood recruitment, and stream bank stabilization functions are provided by the area and vegetation within one mature tree height distance from the stream (Castelle and Johnson, 2000). Clearly it is difficult for trees to be recruited to streams as large wood inputs if they cannot fall and reach the channel. However, these functions are not linear. The vegetation nearest the stream contributes disproportionately to the stream. Even if a tree can theoretically fall and reach the stream, the probability that it will enter the stream channel diminishes the farther away it is, and if it does reach the stream it may only contribute a small top, not a large key piece (Bilby and Ward, 1989).

One strategy used by states is to apply the law of diminishing returns to various functions so that different types of protection depend on the distance from the stream. For example, operators are required to leave all vegetation within 3 m of the high water level and all trees within 6 m of the high water level (Logan, 2002) near fish bearing streams in Oregon. Harvesting may be allowed in part of the RMZ, but only if residual goals for the number of trees and basal area can be met.

This paper focuses on estimating the areas and timber values of alternative riparian management restrictions. A complete cost benefit analysis would require that both costs (including costs other than the timber value) and benefits be estimated. Much work has been directed at identifying the environmental benefits of riparian zone protection (Moring, 1975; FEMAT, 1993; Castelle and Johnson, 2000), but less has been done to translate these values into units that can be compared to the economic costs. One of the most comprehensive efforts to estimate values of forested RMZs is provided in the Chesapeake Bay Riparian Handbook (Palone and Todd, 1997). One section provides information about the value of forested RMZs for stream stability, nutrient removal, air pollution prevention, stream temperature control, erosion control, flood reduction, and other values. This paper focuses on one component of cost, the areas and values of the timber within alternative RMZs, but much work is still needed to quantify other costs and benefits for decision makers.

A HISTORY OF RIPARIAN PROTECTION PRESCRIPTIONS WITHOUT INFORMATION ON COST

Policy proposals for "enhanced" RMZs have consistently created controversy because of potential costs and losses of management opportunities to landowners and managers. These costs have usually been only crudely estimated by those proposing the added protection and those required to implement the restrictions. This controversy was heightened when the Forest Ecosystem Management Assessment Team (FEMAT, 1993) developed interim riparian reserves (a type of RMZ) for federal forestland in the Pacific Northwest under the President's Forest Plan (PFP). Among other objectives, the PFP was design\ed to provide riparian habitat for threatened and at-risk species including salmon and trout, and the interim rules were designed to be conservative in their protection. These rules called for default riparian reserves at least 91 m wide along both sides of fish bearing streams and smaller reserves (46 and 30 m, respectively) along perennial nonfish bearing and intermittent streams. Wider riparian reserves were required if the site potential tree height exceeded 46 m or where wider reserves would protect an inner gorge, the 100-year floodplain, or the outer edge of riparian vegetation.

Riparian management on private lands in the Pacific Northwest is also designed to protect fish habitat and water quality and is regulated under several state's forest practices acts. The forest practice rules must balance economic and environmental objectives.

Two evaluations of the costs of riparian management options are those by Lippke and Bare (1999) and Olsen et al. (1987). Lippke and Bare used a range of simulations to estimate the consequences of alternative riparian regulations in western Washington. In their example they considered a base condition in which about 2 to 3 percent of forestland was in riparian habitat and two additional proposals. One proposal had no management in the RMZs, and the other had management to accelerate late successional forest characteristics. Their analysis included consideration of how the two new riparian management alternatives would affect the area impacted, short term and long term harvest levels, short term and long term job levels, net present value (NPV), state and local tax receipts, and late succession species-dependent habitat in the RMZs. While both new riparian proposals increased the area in RMZs to 14 percent, the nomanagement option cost landowners an aggregate US$5.2 billion in NPV, while the option that allowed management for old growth characteristics cost US$3.2 billion and resulted in more rapid achievement of desired riparian habitat characteristics.

Olsen et al. (1987) conducted a case study of how new, more restrictive rules for RMZs would affect costs to a landowner. They performed an assessment on a 540 ha drainage in coastal Oregon that considered both logging costs and the cost of timber left in the RMZs for three alternatives. Costs increased with the new rules, especially with additional requirements for conifer retention in buffers. The authors provided a useful discussion about the sensitivity of costs to stumpage values and some other research considerations such as administrative costs and engineering capabilities. They also found that some restrictions, such as requirements to not cross streams with new roads, can create additional costs (for construction of 0.18 km of new roads) and potential hazards (forcing construction into headwall areas susceptible to landslides).

KEY FACTORS INFLUENCING AREAS IN SPECIAL RIPARIAN PROTECTION AND COSTS OF PROTECTION

Several factors must be considered in determining the amount of land that will be excluded or restricted from management by riparian protection measures. These include stream density, the stream classification system, and the width of RMZs prescribed for each class of stream. Another factor that can influence area under special riparian protection is the drainage pattern. Economic implications are determined by the area under special riparian management, the management options that are available (often based on stream type or class), and the distribution of vegetation in the riparian area.

Stream Density

Stream density is the length of stream in a unit of area. Forest watersheds display a wide range of stream densities. Stream density varies with geology and climate and with the approach used to identify stream channels. Tague and Grant (2004) reported very low stream densities in the High Cascades geology, which is characterized by recent volcanism, high elevation (snow), and relatively low relief. The porous igneous rock and snow packs result in high infiltration and few channels. Channels in this geology often arise from springs. This contrasts with the Western Cascades geology, which is deeply weathered and layered volcanics. Relief is greater, soils are more developed, and the elevation is lower than in the High Cascades. Tague and Grant (2004) reported that the Western Cascades have a more developed runoff channel network than the High Cascades. FEMAT (1993) provided examples of stream densities ranging from 1.15 to 7.96 km/km^sup 2^. Stream densities are often developed from aerial photography and from maps [blue line streams on U.S. Geological Survey (USGS) maps]. With on the ground, detailed surveys of stream channels, Alverts (1994) found increases in the stream network. He concluded that stream densities in the FEMAT report were probably underestimated because of missing first- order and second-order streams.

Classification and Width Prescriptions

The nature of the streams to be protected and the level of management restrictions can also vary widely (Bren, 2003). Just what is defined as a stream can greatly influence the density and various classes. In some cases, active perennial flow may be used to classify streams, while in other cases the presence of a defined channel is sufficient. An example of a stream classification system is the Idaho Forest Practices Act's classification using two stream types: Class I streams are fish bearing and receive the most protection; Class II are nonfish bearing and have less protection. The Oregon forest practice rules recognize a matrix of nine stream types based on stream beneficial uses - fish bearing (F), domestic water supply sources (D), or nonfish bearing/nonwater supply streams (N) - and stream size - average flows greater than 0.28 m^sup 3^/s (large), between 0.06 and 0.28 m^sup 3^/s (medium), and less than 0.06 m^sup 3^/s (small). Management requirements in terms of average width of the streamside management area and residual trees and other requirements are tied to the stream type and size (Logan, 2002).

There is an enormous range of recommended RMZ widths to protect water quality. No-spray buffers to minimize introduction of chemicals to streams are an example. A review by Comerford et al. (1992) found that buffers of 15 m or larger "were effective in minimizing pesticide residue contamination of stream," (p. 27) although the authors noted that efficacy was variable due to the many factors affecting pesticide transport. The forest practice rules in Oregon require 3 m buffers for ground applications, 18 m buffers for aerial herbicide applications around fish bearing or domestic water supply streams or any stream with exposed water, and 91 m buffers for insecticides that are nonbiological. Neary and Michael (1996) reported a study where a 140 m buffer did not completely avoid entry of an herbicide to a stream.

An assessment of the potential area in RMZs for the Blair Creek Watershed in Idaho provides a vivid demonstration of the imPortance of smaller headwater streams (Dennis Murphy, Blair Creek GIS Analysis, Potlatch Corporation, Lewiston, Idaho, 1994, personal communication). The RMZ widths assigned to first-order streams and Class II streams were 30 and 46 m, respectively, compared to 91 m for Class I (fish bearing) streams, but these fishless headwater reaches can represent anywhere from 60 to 90 percent of the stream network, depending on the definition used. In Blair Creek the combined area around these fishless reaches represented about 70 percent of the predicted RMZs.

Channel Pattern

A theoretical maximum area for riparian management protection is simply the width of the riparian reserve or management zone around the length of stream. This assumes that all stream reaches are isolated and the RMZs around them do not overlap. To have this type of independence of stream reaches, they need to flow parallel to each other. Even with uniform separation, beyond a certain limit they will overlap, depending on the width of zone around each stream. For example, if RMZs were all independent in a stream network with a density of 0.6 km/km^sup 2^ and 91 m buffers on each side, 11 percent of the watershed would have riparian protection. By the time the stream density increased to 5.6 km/km^sup 2^, the entire watershed would be covered in riparian protection.

In reality, stream networks tend to display density and distribution patterns that can vary widely with precipitation and geology (FEMAT, 1993). Small headwater streams often feed into and form larger stream segments. The three most common stream network patterns are probably dendritic (a leaf vein-like pattern), trellis (parallel channels with right-angled connecting streams such as those found in limestone regions and in areas with geologic fault lines), and centripetal (converging inward toward a lake). The maximum area in riparian zones that would result from a parallel stream pattern is seldom experienced, especially as stream densities increase.

Management Options in Restricted Riparian Areas

State and federal policies show a wide range of allowances and options for management in riparian areas. At one extreme is complete exclusion of timber harvesting and other management practices. At the opposite is an equipment exclusion zone, where management and even timber harvesting may be allowed but disturbance from equipment is limited. While the area under special management requirements would be the same under these two options, the economic implications are quite different. It is common in southern states, for example, for riparian RMZs to limit equipment and site preparation activities near streams, allowing harvesting of high value pines while retaining hardwoods in the riparian area. Barringer (1987) discussed the economic implications of differing state regulations to one timber sale. Under one set of forest practice rules, 24 percent of the timber value w\ould be left in the RMZ. This set of practices allowed harvesting of some high value conifers in the RMZ. However, with newer rules that excluded harvesting from a portion of the riparian area, the value of timber left in the RMZ would have almost tripled. In this case, the same stream length with different sets of regulations resulted in different costs. Lippke and Bare (1999), as discussed above, provided another example of how alternative management options in the riparian area can dramatically affect the NPV.

Vegetation Pattern in the Riparian Area

Different regions and forest types have different distributions and gradients for vegetation in the riparian area. These patterns can greatly influence the value of the timber that will be forgone in a RMZ. In some low precipitation regions, commercial timber may only grow near streams where there is adequate soil water. Commercial timber may also be largely isolated along stream bottoms in other regions, such as in some glaciated valleys where soil depths are only suitable for timber in the flat bottoms. In other areas, such as low gradient, wet sites, hardwoods and shrubs may dominate the riparian area (Andrus and Froehlich, 1987), and more valuable conifers are found away from streams where drainage is adequate.

Timber stand inventories developed for upland sites are often assumed to apply to RMZs, but these are not always appropriate. Means et al. (1996) studied Douglas-fir (Pseudotsuga menziesii) stands in riparian and upland sites in the Western Cascades of Oregon and found high productivity in some riparian areas. Timber inventory information available for GIS applications may not be suitable to predict riparian vegetation. Although more research on the distribution of riparian vegetation is needed, the U.S. Department of Agriculture (USDA) Forest Service has been conducting riparian plant community classifications since the early 1980s. These classifications have been published for most national forests as general technical reports and can be a useful source of information (for example, see Winward, 2000).

CALCULATING RIPARIAN AREAS AND COSTS

The most accurate way to evaluate the area in RMZs and the cost of those zones is to incorporate the factors discussed above into a GIS analysis, assuming good data for the stream network (see Oak Creek example described below). However, it is useful to have a simpler method for quick calculations, especially when policy makers are weighing the benefits and costs of broadly applied riparian protection measures.

The theoretical maximum area assumes parallel stream segments with optimal spacing to avoid overlap of RMZs. The percentage of a watershed in RMZs can be calculated using the stream density and width of protection around the stream. Table 1 shows the fractions of a watershed in RMZs for different stream densities and widths (applied to each side of the stream).

Table 1 can be used directly if only one class of stream is being treated. For multiple stream classes or types, these values must be calculated for each type and summed. As an example, consider a watershed with a stream density of 5 km/km^sup 2^ where 75 percent of the watershed network is in Class II streams requiring 8.2 m RMZs and 25 percent is in Class I streams requiring 30 m RMZs. In this case, 6.1 percent of the watershed would be in Class II riparian protection and 7.5 percent in Class I riparian protection, or about 13.6 percent of the watershed.

Table 1 was developed based on the theoretical maximum. As previously explained, this maximum is not usually experienced because of channel junctions and overlapping RMZs. Bren (1995) used a GIS analysis of a watershed in Australia with a dendritic stream network and a drainage density of 3 km/km^sup 2^ to determine the area in RMZs as a function of RMZ width. The relationship the author developed was compared to the theoretical maximum area in RMZ. In this case the potential and actual percent of the watershed in RMZ remain reasonably close as long as less than one-third of the watershed is in RMZs. As more of the watershed is placed in RMZs, the actual and theoretical percent of the watershed in RMZs diverge. More work is needed to determine how the actual percent of the watershed in RMZs diverges from the theoretical maximum for other stream patterns and drainage densities.

Bren (1995) and others have also noted that as RMZs become an increasingly large proportion of the watershed, they create "islands" of small, isolated, or oddly shaped units that are not classified as RMZs but are no longer operationally or economically viable. This is one of the added costs that RMZs can create. These include unmanageable areas due to size or access, more costly yarding on managed areas because of limits to yarding through RMZs, and increased road costs to avoid RMZs. While the actual amount of land in RMZs begins to diverge from the theoretical with an increasing proportion of the watershed in RMZs, the amount of land in unmanageable islands increases until it begins to finally shrink as the entire watershed is covered in RMZs.

TABLE 1. Maximum Percentage of Watershed in Riparian Management Zones (RMZs) Assuming No Overlap of RMZs for Varying Stream Densities and RMZ Widths (both sides of stream).

EXAMPLE OF A GIS-BASED APPLICATION

Oak Creek, a small watershed in the foothills of the Coast Range in the Pacific Northwest, serves as an example of a GIS-based approach to estimating the extent of alternative RMZ protection schemes and the economic consequences of those alternatives. The Oak Creek Watershed is in the Oregon State University College of Forestry McDonald-Dunn Research Forest near Corvallis, Oregon (Toman, 2004). This 800 ha watershed supports a forest composed primarily of Douglas-fir and Oregon white oak (Quercus garryana). Hardwoods dominate the riparian areas and consist of red alder (Alnus rubra), big-leaf maple (Acer macrophyllum), black cottonwood (Populus trichocarpa), and shrubs. The drainage pattern is dendritic, and the underlying geology of the area is basalt from the Siletz Volcanics Formation (Knezevich, 1975).

Methods for Calculating Area in RMZs

A delineation of the stream network was completed using commercially available hydrological modeling software for GIS. A discussion of GIS methods for hydrologic analysis is provided in a collection of papers edited by Wilson and Gallant (2000). Two resolutions (6 m and 10 m) of base maps were used in this example. The 10 m digital elevation model (DEM) and stream network were taken from the Oregon State University College of Forestry GIS database (Elevation Grid and Streams, respectively, from OSU, 1997) developed from USGS 10 m maps (Figure 1a). Classification of fish bearing streams was provided by the Oregon Department of Forestry (ODF, 2005). Drainage density based on the 10 m DEM is 5.6 km/km^sup 2^.

The 6 m DEM was created from light detection and ranging (Lidar) returns (Lidar Ground, from OSU, 1997) (reflections from airborne laser pulses). A 6 m grid was created from the elevation returns and then converted to a raster format. The 6 m stream layer was created from the 6 m map by identifying flow direction, accumulating the flow based on the cumulative drainage area, and delineating the stream network. A minimum number of 50 cells, about 0.2 ha, was chosen to represent the initiation of the stream network (Figure 1b). The basin area draining to a channel initiation point is under intensive study in the Northwest and may vary with factors such as geology, slope, and climate (Istanbulluoglu et al., 2002). The 0.2 ha initiation point used here is meant to provide an extremely dense drainage network and is not necessarily presented as a realistic representation for this site. Jaeger (2004) studied five watersheds in Washington and found channel initiation points for basins ranging from 0.06 to 6 ha, with watershed means of between 0.3 and 1.5 ha, so this appears to be a reasonable assumption. Drainage density based on the 6 m DEM is about 8.1 km/km^sup 2^.

On both maps, buffers of varying sizes were created using tools provided in GIS software, and the resulting areas were recorded (Table 2). Total stream length and total stream length in each stream classification were also recorded for each map. The fraction of the watershed in RMZs was calculated for each map based on RMZ widths. Stream density was greater for the higher-resolution 6 m map than for the 10 m map - 8.1 versus 5.6 km/km^sup 2^, respectively. These values fall into the upper end of stream densities reported for this region, which vary from less than 2.4 km/km^sup 2^ to nearly 8.1 km/km^sup 2^ (FEMAT, 1993), although subsequent field investigations generally showed higher values than these regional drainage density values.

Figure 1. Drainage Density Showing Reaches With and Without Fish and the Size Classification of the Fish Bearing Reaches for (a) 10 m Resolution and (b) 6 m Resolution (based on Oregon Forest Practices Act Rules).

TABLE 2. Calculation of Percentage of Area in Riparian Management Zones (RMZs) for Different Width Requirements for Oak Creek, Oregon.

These data can also be used to compare the percentage of the watershed in riparian management area that applicable state and federal regulations would require. The lengths of medium and small fish-bearing streams in this drainage are 1,505 and 814 m, respectively, for the 10 m DEM. These values are slightly different for the 6 m DEM (1,633 and 873 m) because it provides a more detailed representation of the channel.

Results for Area in RMZs

The percentages of watershed in riparian management protection under three regulations are considered herein: those for western Oregon private lands; those for western Washington private lands; and the FEMAT guidelines under the President's Forest Plan for federal lands. In western Oregon, medium and small fish bearing streams have 21 \and 15 m buffers, respectively. For the Coast Range geographic region of western Oregon, nonfish bearing streams do not have tree retention requirements but still must be protected from sediment, chemical introductions, and disturbance. This would translate to riparian protection around medium fish bearing, small fish bearing, and nonfish bearing streams representing about 1.1 to 1.5 percent of the watershed, depending on which map scale is used.

If Oak Creek were managed under the regulations in western Washington, a 46 m riparian zone would be required along fish bearing streams and a 15 m zone along nonfish bearing, perennial streams for half their distances. This example assumes that all the nonfish bearing streams would be classified as perennial, but the definition of perennial is still under debate in Washington. This would require about 2.6 to 2.8 percent of the watershed to be in RMZs around fish bearing streams, depending on map scale. The main difference between Oregon and Washington regulations is management along the nonfish bearing streams, where an additional 7.9 to 10.6 percent of the watershed would be in RMZs. Total watershed in riparian protection then would be 10.5 percent for 10 m DEM maps and 13.4 percent for 6 m DEM maps.

The interim riparian guidelines developed by FEMAT (1993) for federal watersheds in this region would require 91m RMZs on fish bearing streams, 46 m RMZs on perennial nonfish bearings streams, and 30 m RMZs on intermittent streams. This assessment assumes that two-thirds of nonfish bearing reaches are intermittent streams and would receive the least protection. With these levels of protection, RMZs around fish bearing reaches would represent between 5.1 and 5.5 percent of the watershed (10 m and 6 m DEM maps, respectively). The RMZs around perennial nonfish bearing streams would cover between 15 and 16.5 percent of the watershed, and intermittent reaches would have RMZs covering another 20.6 to 24.9 percent. Cumulatively, this would represent somewhere between 41 and 47 percent of the watershed.

Methods and Results for Timber Value Calculation

Finally, tree retention levels are translated into an economic impact. An estimated 1.1 million cubic meters of timber are on the 4,650 ha of McDonald-Dunn Forest, representing an average volume of 237 m^sup 3^/ha. Because riparian areas nearest streams have a higher component of lower value hardwoods and shrubs, this example assumes that the first 15 m near a stream has about half as much value as upland forests. Assuming a standing ("stumpage") value of US$62 per m^sup 3^, the value of timber within the riparian management areas can be calculated.

Oregon regulations would require that between 1 and 1.5 percent of the watershed be in riparian management areas. Most (but not all) of this is within 50 feet of the stream, where it is assumed to have less stocking and value than on upland sites. This represents about 1,150 to 1,730 m^sup 3^ of timber, with a potential standing timber or stumpage value of US$70,000 to US$110,000. With sufficient stocking of trees in the RMZ, there is some potential for harvesting in this area, which will be discussed later.

Under the Washington regulations, most of the area in protection would be within 15 m of the stream network, but fish bearing reaches would have more extensive protection. Between 11,100 and 13,500 m^sup 3^ of timber would be in these riparian protection areas, representing between US$690,000 and US$840,000 in stumpage value.

Under standards similar to FEMAT's, large areas would have restricted management due to much wider riparian reserves and reserves that apply to more of the stream network. The estimated volume in these reserves is between 52,900 and 62,500 m3. This represents between US$3,300,000 and US$3,900,000 in timber in the reserves. A summary of the area in RMZs and value of the timber is provided in Table 3.

It is important to note that some management is allowed in these RMZs under all three sets of rules, depending on site specific factors and harvesting conditions. For example, in Oregon some timber harvesting is allowed if required tree retention levels (based on minimum tree numbers, diameters and species of trees, and basal area) can be maintained, but in many cases landowners choose not to harvest to the legal limits due to regulatory complexity and planning requirements. Under FEMAT requirements, the areas in riparian reserves can be modified after a detailed watershed analysis (WA) is conducted, and timber harvesting can be conducted in these reserves where it accelerates the development of old- growth forest characteristics. However, it is uncommon for WA to reduce the riparian reserves, and once old-growth forest characteristics are achieved, any further timber harvesting will be limited.

TABLE 3. Comparison of Area in Riparian Management Zones (RMZs) for Oak Creek using Two Resolutions of the Stream Network (based on 10 m and 6 m DEMs) and the Rules or Guidelines for the Oregon Forest Practices Act, Washington Forest Practices Act, and Forest Ecosystem Management Assessment Team (FEMAT).

For a specific watershed, a more detailed economic assessment could utilize inventory data collected for alternative riparian forest conditions. For example, DEM data combined with channel types could be used to predict riparian forest conditions. In Oak Creek, the perennial fish bearing reaches tend to have less confined channels and more low value hardwoods. Steeper reaches in the watershed tend be more confined and well drained, with vegetation similar to that found in adjacent uplands. These patterns can be used to fine tune assessments of timber value in riparian areas.

CONCLUSIONS

It is possible to make preliminary estimates of the area that will be in restricted management, based on stream density and the width of protection around the riparian area. As the stream density, percent of stream network designated for protection, and width of riparian management zone around streams increase, more of the watershed will be in restricted management. As this fraction increases, there will be a divergence from the theoretical maximum area in protection, and it may be important to conduct GIS or other mapping exercises to more accurately estimate the area in restrictions. Economic values associated with tree retention in RMZs are dependent on the vegetation patterns in the near stream area. In some regions most of the commercial vegetation is near streams, while in other areas less valuable species or fewer trees are adjacent to streams. Because small headwater streams without fish often dominate the length of streams in a watershed, decisions about how to manage these reaches can have a disproportionate effect on the economic viability of commercial activities. There tends to be an effect of diminishing returns, with the greatest benefits to streams gained by the protection nearest streams. Both the benefits and costs of riparian area protection need to be assessed and considered to achieve environmental goals in an economically sustainable manner.

Ice, George G., Arne Skaugset, and Amy Simmons, 2006. Estimating Areas and Timber Values of Riparian Management on Forest Lands. Journal of the American Water Resources Association (JAWRA) 42(1):115-124.

1 Paper No. 04192 of the Journal of the American Water Resources Association (JAWRA) (Copyright 2006). Discussions are open until August 1, 2006.

LITERATURE CITED

Alverts, R., 1994. Landscape-Level Watershed Analysis. An Experience Report from BLM Districts in western Oregon. Oregon State Office, USDI Bureau of Land Management (BLM), Portland, Oregon.

Andrus, C. and H.A. Froehlich, 1987. Riparian Forest Development After Logging or Fire in the Oregon Coast Range: Wildlife Habitat and Timber Values. In: Streamside Management: Riparian Wildlife Interactions, K.J. Raedeke (Editor). Contribution 59, Institute of Forest Resources, Seattle, Washington, pp. 139-152.

Barringer, J., 1987. Cost and Constraints of Riparian Zone Management of the Wiley Creek Cleanup Sale. In: Managing Oregon's Riparian Zone for Timber, Fish and Wildlife. Technical Bulletin No. 514, National Council for Air and Stream Improvement, Inc., Research Triangle Park, North Carolina, pp. 64-67.

Belt, G. and J. O'Laughlin, 1994. Buffer Strip Design for Protecting Water Quality and Fish Habitat. Western Journal of Applied Forestry 9(2):41-45.

Bilby, R.E. and J.W. Ward, 1989. Changes in Characteristics and Function of Woody Debris With Increasing Size of Streams in Western Washington. Transactions of the American Fisheries Society 118:368- 378.

Bren, L. J., 1995. Aspects of the Geometry of Riparian Buffer Strips and its Significance to Forest Operations. Forest Ecology and Management 75:1-10.

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George G. Ice, Arne Skaugset, and Amy Simmons2

2 Respectively, Principal Scientist, National Council for Air and Stream Improvement, Inc. (NCASI), P.O. Box 458, Corvallis, Oregon 97339; and Associate Professor and Research Assistant, Forest Engineering Department, Oregon State University, Peavy Hall 213, Corvallis, Oregon 97331 (E-Mail/Ice: GIce@wcrc-ncasi.org).

Copyright American Water Resources Association Feb 2006

Source: Journal of the American Water Resources Association

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