Quantifying Washington's Forest Practices Buffers
NRSIG Budget:
Project Budget:
Sponsors:
Timeline: January 2001 through January 2050
Partners: FFF, WA DNR, WFFA

Introduction

We developed a parcel census-based analysis of the economic impacts on private lands in Western Washington of the proposed Forest Practice riparian buffer rule change for Type Np streams. The analysis was based on our 2019 Forestland Database and the 2025 Washington DNR Watercourses spatial dataset. We implemented both current and proposed buffer rules in ArcGIS and summarized the impacts by owner subclass, county, and Watershed Resource Inventory Area (WRIA).

Methods

Our analysis used the 2019 Forestland Database to identify all private forested parcels in western Washington. Each parcel was also attributed with owner subclass (industry, SFLO, or other), county, and WRIA. We used 2025 DNR hydrology layers including watercourses, waterbodies, and wetlands. All Water Type buffers were developed including those for fish and non-fish streams, wetlands, and waterbodies.

A large number of streams in the watercourses dataset have unknown water type and/or seasonality. To account for this, we buffered streams using three sets of assumptions. First, we buffered all unknown streams as Np. This overestimates buffers adjacent to Np streams which is offset by watercourses not present in the DNR dataset. This assumption is also useful for bracketing the results. Second, we assumed 60% of unknown stream length was Np, with the remaining classified as Ns. To determine this value, we calculated the ratio of known Np streams to all Type N streams with a known seasonality. Within this assumption, we further assumed the Np proportion was the lower 60% (nearest to a fish stream) by stream network or by segment. Figure 1 illustrates buffering results under each of these assumptions.

We developed core, inner, and outer buffers around all streams, wetlands, and waterbodies. Np streams within 600 feet of a fish stream received a 75-foot core buffer. Np streams more than 600 feet were buffered with core, inner, and outer buffers to account for alternative harvest options under the proposed rules. The first option requires only a 65-foot core zone (no harvesting). The second option requires a 50-foot core zone and 25-foot outer zone where thinning is allowed. To account for both alternatives, we buffered these Np streams with a 50-foot core zone, 15-foot inner zone, and 10-foot outer zone.

After buffering streams and other waters we unioned the buffers with the Forestland Database to identify management zones (upland and core, inner, outer, and wetland buffer) by parcel. For each polygon segment in the unioned layer we summarized the mean standing board foot volume and species proportion (by basal area) for red alder, other hardwoods, Douglas-fir, western hemlock, western red cedar, and other conifer. We used volume and species proportion rasters developed through a modeling project that related field plot summary attributes to predictor variables derived from digital aerial photogrammetry, spectral imagery, climate, and other environmental datasets (Washington Forest Structure from Digital Aerial Photogrammetry).

Next, we derived harvestable standing volume from estimates of standing volume for each management zone. We made assumptions for the harvestable proportion of volume by management zone, including 1 in the upland, .33 in the inner buffer, .67 in the outer buffer, and 0 in all other zones. These values can be adjusted in an Excel spreadsheet to account for different buffer zone harvest options. To calculate value from harvestable volume, we used the most recent Department of Revenue stumpage value reports with the average $/MBF for species in western Washington.

It is important to note that we only account for the economic impact of the direct loss of harvestable land. Additional factors we did not assess but we presume to have an impact are:

Additional loss of acres due to increased operational challenges imposed by the geometry of additional buffers in harvest units.
Loss of value in carbon markets as regulatory set asides are not eligible to participate.
Additional road density anticipated to work around additional buffers.
Additional Forest Riparian Easement Program (FREP) costs for small forest land owners.
Loss of milling infrastructure due to decreased timber supply.
Downstream industry and economic losses from decreased timber supply.

Results

All Species

Here we report results comparing the current rules to the proposed rule assuming 60% of unknown streams are Np packed nearest to fish streams. We estimate the proposed rule change will result in a decrease of 4.1 billion board feet of harvestable timber across all private forestland in western Washington. This represents a 5.1% reduction in on-base standing inventory. At current prices, this inventory is valued at $1.8 billion. The relative impact on volume and value is larger on private industry (-7%) compared to small forest landowners (-2.2%). We suspect industry results better reflect actual impact due to a higher rate of field-verified streams of unknown water type or seasonality. Regardless, we estimate the value of the proposed regulatory taking at $1.5 billion for industry and $284 million for SFLO.

Across all private owners in western Washington, upland area declined by 204,066 forested acres under the proposed rule change. This includes a forested upland reduction of 168,276 acres from industry and 27,457 acres from SFLO. The reduction in upland harvestable volume is 4.5 billion board feet. A small amount of this volume is offset by increases in harvestable volume in the inner and outer buffer zones.

Overall impact was obtained by first summarizing parcel acres, forested acres, volume, harvestable volume, and value by owner subclass and management zone under the current and proposed rules. A detailed breakdown of these values is provided in the next table.

The impact of the proposed rule on harvestable volume and value are listed by county in the next two tables.

Hardwoods

We also summarized the harvestable volume and value for hardwood species under the current and proposed Np buffer rule. Our total hardwood inventory estimate of 22 billion board feet aligns with our 2013 estimate (19 billion board feet) (Western Washington Hardwood Assessment). Under the proposed rule change, harvestable volume for hardwood species across all private ownership in western Washington declined by 4.6%, from 17.3 billion board feet to 16.5 billion board feet. For industry, the proposed rule reduces harvestable hardwood volume by 488 million board feet (-7.8%) valued at $155 million (-8.3%). SFLO harvestable inventory is reduced by 266 million board feet (-2.7%) valued at $72 million (-2.8%).

The size of the impact varies across western Washington. The next two tables breakdown hardwood harvestable volume and value by county. For both industry and SFLO, we estimate the largest impact in Pacific county, followed by other counties located in southwest Washington.