Silvicultural Options Study: plot locations, tree growth, tree regeneration, and understory species abundance

The Silvicultural Options Study (SOS) is a long-term study replicated on three sites (blocks) containing mature second-growth Douglas-fir on the Capitol State Forest, Washington State Department of Natural Resources, near Olympia, Washington. Each site contains six treatment areas that are being managed and regenerated according to standard silvicultural regimes (i.e., clearcut, two-age, patch cutting, group selection, thinning, and non-treated; the latter two regimes represent a deferred final harvest). The six silvicultural regimes were implemented in 1998, 2002, and 2004 at the Blue Ridge, Copper Ridge, and Rusty Ridge sites, respectively, and they include even- and uneven-aged silvicultural regimes assuming a 50-year rotation. The patch and group treatments have a 10-year harvest interval, while the thinning treatment has a 20-year harvest interval. This data publication contains the tree and understory vegetation measurements being taken from a systematic grid of permanent 0.20-acre circular plots, including: (1) tree stem and crown growth (measured December 1996 - May 2019), (2) tree regeneration size and abundance by species and origin (i.e., natural versus planted) (measured January 1997 - November 2009), and (3) visual estimates of cover by dominant understory species (measured December 1997 - November 2009). Initial measurements were taken at 5-year intervals, but later the measurement interval was changed to 10 years. These data are being used to compare forest productivity and stand structure among silvicultural regimes.
The long-term Silvicultural Options Study was initiated in 1998 to provide examples of a range of harvest, stand tending, and regeneration practices that could be used to achieve a wide range of management objectives, including improved visual aesthetics and wildlife habitat. The study is serving as the basis for comparing yields and associated costs of alternative silvicultural systems for coast Douglas-fir in western Washington, as well as a visual demonstration area for foresters, planners, and the public. In the study, a silvicultural regime is defined as a planned program of silvicultural treatments covering the entire life of the stand, but it may or may not include a pre-determined date or method of harvest and regeneration (i.e., a “deferred harvest”). Six silvicultural regimes were selected to represent a wide range of management alternatives thought to be biologically, operationally, and economically feasible for regenerating and managing Douglas-fir based on existing knowledge and experience.
These data were originally published on 06/08/2022. On 09/15/2023, minor metadata updates were made and diameter at breast height (dbh) values for SOS_tree_growth_data.csv were corrected. In processing, dbh values for all years were rounded to whole numbers. However, only 1996-1997 dbh data were recorded as whole numbers and for all other years dbh was measured to the nearest 0.1 inches. Dbh values are now provided as measured (whole numbers for 1996-1997 and to the nearest 0.1 inches for 1998+).