C I N T R A F O R
Special Paper Abstract
Yield and Inventory Tables for Western Washington: A Technical Supplement to Future Prospects for Western Washington's Timber Supply.
David Anderson, Ralph Alig, Darius Adams. 1994. (149pp) SP12A $20.00
The College of Forest Resources at the University of Washington was commissioned in the spring of 1990 by the Washington State Legislature to undertake a study of the possible future timber supply situation in the State. During the first phase of the study those lands west of the Cascade crest were analyzed, results of which are presented in Future Prospects for Western Washington’s Timber Supply (Adams et al. 1992). This document serves as a technical supplement to the main report.
Two broad objectives for the western portion of the Washington Timber Supply Study (WWTTSS) were: (1) to identify the potential range of future timber harvest in western Washington, highlighting those aspects of owner behavior, policy and the resource base most important in controlling the variation of harvest over time; and (2) to translate harvest and inventory projections into prospective impacts on two key economic and environmental quality measures: employment in the Washington forestry sector and suitability of habitat for an array of wildlife species (Adams et al 1992). To meet these objectives diverse categories of information are required. Of these categories two of the most important are: (1) accurate estimates of current (as of 1990) standing timber volumes and; (2) reliable predictions of future behavior of that volume under a range of silvicultural management regimes. This report presents the methodology used in yield table modeling, input parameters into the timber yield models used and the resultant yield curves that were used in the timber supply modeling. These yield curves are compared against the timber inventory data used in the study. Additionally those estimates of standing timber volume that were used as the basis for timber supply modeling are presented by ownership group and by geographic region.
Standing timber inventory data were derived from the Forest Inventory and Analysis (FIA) unit of the USDA Forest Service decadal remeasurement of privately owned forest lands (Maclean et al l992). FIA survey data is normally classified into ten year age classes; For this study FIA provided the WWTSS with data classified into five year age classes. Stratifying the inventory data by five year age classes doubles the number of data cells that would have to be filled to obtain a complete age class profile of standing timber inventory. This increased number of data cells allows for a greater sensitivity in specification of management regimes, minimum harvest age and landscape level age class distribution. Recognizing the additional data requirements and to reduce the variance in volume estimates, the Washington Legislature provided funds to the FIA to double their normal sampling intensity in Western Washington. Yield tables by five year age class intervals were developed for five species groups: Douglas-fir, Western hemlock, Other softwoods, Red alder and Other hardwoods; three site groups: high, medium and low; and nine management intensities ranging from extensive natural management up to intensive management utilizing genetically improved stock and repeated thinnings and fertilizations(Adams, et al 1992) using computer-based growth simulation models. Development of these tables benefited greatly from extensive consultation with the sub-committee on Growth and Yield of the Technical Advisory Committee of the WWTSS on which yield models to use, the array of management practices to consider and specification of management regimes. Supplemental information provided by the Washington Forest Protection Association provided the detailed information on regeneration stocking; thinning timing and intensity; and fertilization timing to translate management regimes into on the ground management intensities (MI).
This report comprises six sections. Section I describes the methodology used to generate the yield tables. Section II presents the yield tables in both tabular and graphical format. The detailed information used to simulate each management intensity yield table are provided by the tables in Section III. Graphs in Section IV show the yield trajectories overlaid on the FIA inventory data. Tables in the last two sections describe the acreage and total cubic foot volume of the inventory data broken out by species and site class and aggregated by geographic area (timbersheds) in section V and ownership class in section VI.