Bark Thickness and Bark Volume in Southwestern Oregon Douglas-Fir

A segmented polynomial taper equation for southwestern Oregon Douglas-fir (Pseudotsuga menziesii) predicts double bark thickness (dbt) at any point above breast height. Below breast height predictions a sume conformity oa neiloid frustrum. The equations facilitate estimation of inside bark diameter (dib) given outside bark (dob) measurements. Bark volume and bark biomass can also be estimated when supplemented with existing dib taper equations developed for southwestern Oregon. West J. Appl. For. 5(1):5-8. Foresters often eed to estimate bark thickness on standing trees, either to subtract from outside bark measurement in estimating bolewood diameter, or to apply directly in computations of bark volume and biomass. The first application has more commonly dictated the form of bark thickness equations, although interest has arisen in bark as a raw material as well. Several million tons of Douglasfir (Pseudotsuga menziesii) bark are produced annually by the forest products industry in Oregon alone, and since 50-55% of the inner bark is carbohydrate, this represents a resource of considerable potential for pulping (Fernandez and Laver 1986). Numerous other uses of bark likewise have been recognized (Hall 1971), including energy production (Schneider 1977). The most common type of bark thickness equation facilitates estimation of current breast height diameter 1 Funding and logistical support were provided by the Southwest Oregon Forestry Intensified Research Cooperative. The authors gratefully acknowledge field work performed by Steve Stearns-Smith, Dave Larsen, Merlise Clyde, Brian Ferguson, Paul Gremand, Harvey Huber, Rick Knight, Kevin MacNamara, Alan Matricardi, Rick Perkins, John Scrivani, Red Wheelis, and all other members of the Growth and Yield Project field crews. inside bark (DIB) from breast height diameter outside bark (DOB) (Myers 1964, Monserud 1979). Similarly, breast height bark or DIB/DOB equations are necessary to estimate past DOBs from measured radial wood increment (Powers 1969, Myers and Alexander 1972), and to estimate future DOBs from predicted radial wood increment (Cole and Stage 1972). Other bark thickness equations were constructed to serve the dual purpose Of estimating both past and future DOB (Dolph 1984). Meyer (1946) constructed bark thickness equations for estimating bark volume of felled trees, assuming that the ratio of inside to outside bark diameter was constant along the stem. Work with high-performance optical dendrometers later prompted additional work on describing bark thickness above breast height. Upper stem diameters outside bark on standing trees could be converted into underbark wood volume provided that reliable bark thickness estimates were available. As a result, numerous equations were developed to estimate bark thickness at any height for southern pines (Mesavage 1969, Cao and Pepper 1986), northern Rocky Mountain conifers (Brickell 1970), ponderosa pine (Pinus ponderosa) (Cochran 1976), Douglas-fir (Khan et al. 1977), and radiata pine (P. radiata) (Johnson and Wood 1987, Gordon 1983). Although it seems a logical step from these bark thickness equations to bark volume estimates, especially when compatibility is desired, existing bark volume equations have predicted total bark volume directly from: (1) total stem volume outside bark and inside/ outside bark diameter ratio at a fixed height (Meyer 1946); (2) breast height bark thickness, DOB, and total height (Kozak and Yang 1981); or (3) DOB and total height only (Faurot 1977). One exception was Gordon's (1983) simultaneous application of a double bark thickness equation and inside bark taper function. Total bark b•omass also has been estimated directly from DOB, and sometimes from both DOB and total height (Gholz et al. 1979). Alternatively, bark biomass can be estimated from bark volume and average specific gravity (Meyer 1946). The objective of this study was to develop equations for predicting double bark thickness at any height in southwestern Oregon Douglas-fir. Several applications are demonstrated, including computation of bark volume by simultaneous application of inside bark taper equations developed for the same population (Walters and Hann 1986).