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    Author(s): Douglas D. Piirto; Mitchell Haydon; Steve Auten; Benjamin Han; Samantha Gill; Wally Mark; Dale Holderman
    Date: 2017
    Source: Gen. Tech. Rep. PSW-GTR-258. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 55-71
    Publication Series: General Technical Report (GTR)
    Station: Pacific Southwest Research Station
    PDF: Download Publication  (597.0 KB)


    The 1,295 ha (3,200 ac) Swanton Pacific Ranch (Swanton) and the associated Valencia Tract in Santa Cruz County have been managed by California Polytechnic State University, San Luis Obispo (Cal Poly) since 1987. Swanton’s Valencia Tract is a 239 ha (591 ac) property located north of Watsonville, California. Cal Poly forest managers have conducted two harvest entries since acquiring ownership of the Valencia tract utilizing a modified BDq individual tree selection approach. A 10-year continuous forest re-inventory (CFI) was completed for the Valencia coast redwood tract to update and enhance the growth and yield analysis needed for the Non-Industrial Timber Management Plan (NTMP) sustainability analysis.

    The California Growth and Yield Modeling Cooperative -Forest and Stand Evaluation Environment (FORSEE) program and 10-year CFI data were utilized to perform a sustainability analysis comparing trees per acre, basal area per acre, quadratic mean diameter, and gross volume per acre. Several tree volume estimation methods were evaluated for differences in yield reporting.

    It was determined that: 1) by 2012 actual stand volume growth had completely recovered from harvest and exceeded the pre-harvest 2001 gross volume by 9.7 percent (i.e., average stand growth of 1,266 board feet per acre per year, or 3.0 percent growth rate per year); 2) the Spaulding equation appears to be a solid medial choice for Valencia Tract sustainable yield analysis; 3) sustainable uneven-age stand management resulted from setting residual stand basal area (b), maximum diameter (d) and trees per acre by diameter prescription targets (q) while leaving a few trees greater than the established maximum diameter (i.e., a modified BDq approach); 4) the project model underestimated basal area per acre growth, overestimated change in quadratic mean diameter (QMD), overestimated diameter growth of smaller trees (< 30.5 cm (12 inches) diameter at breast height (DBH; 1.37 m)); underestimated diameter growth of larger trees (> 33 cm (13 inches) DBH), underestimated height growth of larger trees (> 53.3 cm (21 inches (DBH), underestimated volume (16.3 percent lower than actual CFI volume figures). It is postulated that this difference in FORSEE model projection is either a result of the way the CFI data was processed in FORSEE, regional differences, or inherent projection inaccuracies not fully understood by FORSEE users.

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    Piirto, Douglas D.; Haydon, Mitchell; Auten, Steve; Han, Benjamin; Gill, Samantha; Mark, Wally; Holderman, Dale. 2017. Sustainability analysis using FORSEE and continuous forest inventory information to compare volume estimation methods for the Valencia coast redwood tract in Santa Cruz County, California. In: Standiford, Richard B.; Valachovic, Yana, tech cords. Coast redwood science symposium—2016: Past successes and future direction. Proceedings of a workshop. Gen. Tech. Rep. PSW-GTR-258. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 55-71.


    coast redwood, continuous forest inventory, FORSEE, growth and yield model, Sequoia sempervirens, sustainability analysis, uneven-age forest management, volume equation comparison

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