Tree size and soil characteristics in the 1925 Wind River spacing trial for Douglas-fir

A spacing trial for Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco) was established in 1925 near Wind River in southwestern Washington. This was the earliest field trial to compare the long-term effects of initial spacing on tree growth and yield of planted seedlings for this species. Initial square spacings were 4, 5 ,6, 8, 10 and 12 feet. The area had been logged and burned prior to planting with a low elevation, non-local seed source. Mortality was replaced for 5 years with the same or similar seed source. The blocks of each spacing were 2.8 acres for the 4-, 5-, 6-, 8-, and 10- feet (ft) spacings and 0.34 acres for the 12-ft spacing which was expanded 2 growing seasons later to 0.52 acres. This data publication includes diameter at breast height (4.5 ft) measurements on all trees in the measurement plots at approximately 5-year increments between 1951 and 1991, with tree condition noted. Heights were subsampled across the diameter range with a minimum of 10 height trees at the beginning of the sampling in each subplot. At age 48 the measurement plots were gridded into 16 squares and the largest tree in each square was measured for height as well as the previously designated height trees. Also included in this data publication are height-to-live-crown measurements taken on a subset of trees in each plot, in 1991 (total of 430 trees measured). Volume calculations as well as predicted heights (for trees where height was not measured) are also included. Soil characteristics were determined from observations and samples taken in pits, transects, and seismic sampling points; these were done between 1968 and 1994. Soil physical properties were determined for each sample and based on these sample, three soil phases were mapped in the study area and their textural characteristics, available water, nitrogen, cation exchange capacity, carbon to nitrogen ration, bulk density and resistance provided for each soil layer by depth. Tree growth rates were related to soil characteristics as well as spacing.<br>These data were collected to document the effect of plantation spacing on tree growth and stand yield and also the effects of soil characteristics on tree growth.<br>For additional background information on the original study associated with tree growth and soil relations, see Miller et al. (2004).