Long-term effects of stand density and shrub control on ponderosa pine plantation in the Mendocino National Forest

This data publication includes tree growth measurements collected on a ponderosa pine plantation on the eastern side of California’s north Coastal range within the Grindstone Ranger District of Mendocino National Forest, Colusa County, California. Measurements include diameter at breast height (DBH at 4.5 feet) and tree condition measured in 1970, 1975, 1980, 1985, 1990, 1996, 2005, and 2016. Tree height, height to live crown, and crown width were also measured for approximately 20 percent of the trees on each plot each measurement year except for 2005 when only tree height was the additional measurement. The study was established in 1970 by William W. Oliver, a Research Silviculturist at Pacific Southwest Forest and Range Experiment Station (currently, Pacific Southwest Research Station) as one of the west-wide levels-of-growing-stock study (LOGS) sites for even-aged ponderosa pine. The original plots were installed on 11-year-old ponderosa pine plantations regenerated following the Trough Fire in August 1959. Fifteen, 0.5-acre plots were randomly assigned with 4 square spacings (7, 8, 10, and 14 feet) and control. Each density plot with 20-foot buffer was replicated three times. The highest density treatment was later similar to the unthinned control plots and, therefore, all analyses in the subsequent publications treated this density as the control (six total control plots). A diagram of the treatment design for this study is also included in this package. After the 5-year remeasurement it was determined that tree stand density had no influence on tree growth because of the dense shrub understory. Therefore, this study site was taken off the LOGS study list. The field design was altered to investigate the inter-relationships of tree spacing and shrub density on growth of ponderosa pine. Each major plot was subdivided into 3 equal subplots. Shrubs were left undisturbed on one subplot. Shrubs were thinned “from below” leaving the larger shrub crowns separated by a minimum of 1 foot, which yielded that half of shrubs were removed. All shrubs were cut at ground line on the remaining subplot. The non-sprouting forms of Arctostaphalos made retreatment unnecessary, although no further shrub treatment was conducted in the half-shrub removal subplots.
When Cliff Meyer constructed the LOGS study plan in 1976 based on data analyses from the earlier observational plots established by field foresters in the Black Hills of South Dakota and Northern Idaho, young ponderosa pine management was in its infancy. Therefore, original objectives were "to determine (i) optimum stand densities for maximum growth of usable wood per tree and per hectare over a range of site qualities and average diameters and (ii) growth and yield obtainable with repeated thinning." Later, after competing vegetation treatments were installed, the purpose had been changed to investigate the inter-relationships of tree spacing and shrub density on growth and stand development of ponderosa pine plantations. The goals of the post fire measurements in 2016 were to quantify the resilience of a ponderosa pine plantation to a backfiring operation (that occurred in 2012 during the Mill Fire), and to glean information that might help to broaden options available to managers concerned about managing fuels in plantations to improve resilience to future fires.
These data have been summarized in various publications since 1984, which are listed as cross-references below.