Growth response data from overstory trees and planted Douglas-fir, western hemlock, and western redcedar after residual density treatments in Capitol State Forest, Washington

We conducted a study in conjunction with the Washington State Department of Natural Resources examining the response of overstory trees and under-planted conifer seedlings to a range of residual overstory densities. Conifer seedlings included Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), western hemlock (Tsuga heterophylla (Raf.) Sarg.), and western redcedar (Thuja plicata Donn ex D. Don). The study is comprised of three sites within the Capitol State Forest west of Olympia, Washington, each consisting of treatment plots of 1.4-1.5 hectares. Initially 40 to 70 years old, these stands were harvested in the summer of 2000 leaving six retention levels (treatments) of 0, 8, 16, 24, 32 and 40 percent of full basal area stocking. In each plot, 609 trees were planted in 2001 for a total of 10,962 understory trees. The number of overstory trees varies by site and year but were approximately 208, 139, and 136 at sites 1, 2, and 3, respectively. This publication contains data from seedling and overstory tree measurements taken in 2000, 2001, 2002, 2003, 2004, 2005, and 2009. Some years are subsets and do not include all trees. Measurements include height and diameter, along with other attributes such as height to live crown and any damages present. Also included are temperature data from years 2001-2006 and soil moisture data from 2001 and 2002.
Land managers looking for alternative silvicultural systems to enhance non-timber values and reduce the visual impact of clearcutting will be interested in how levels of overstory retention may affect the growth of understory trees. Other questions might include how Douglas-fir, western redcedar and western hemlock will regenerate and develop under these alternative systems. This study was also an attempt to help understand some of the physiological and genetic aspects involved in the response to different growing environments.
The materials and methods of the study are described in more detail in Brodie and DeBell (2013).