Tree monitoring data used to study the adaptability of knobcone x Monterey pine hybrids to lower-elevation, lower-quality forest sites in northwestern California

This data publication contains the data collected for a study that began in 1964, titled "Adaptability of knobcone x Monterey pine hybrids to lower-elevation, lower-quality forest sites in northwestern California". This experimental study of four tree planting test sites (East Fork Burn, Platina, Spring Gulch, and Tom Lang Gulch) was established in Siskiyou and Shasta Counties, California, on U.S. Bureau of Land Management lands. The quantitative data included in this package consist of tree survival, status, and size measured at all four sites in 1964, 1965, and 1966. These same data were also collected in 1973 for Spring Gulch and Tom Lang Gulch. Georegistered historical stem maps with digitized tree locations are also provided for Spring Gulch (1966) and Tom Lang Gulch (1965).This silvicultural field trial was established in 1964 to evaluate the potential of the knobcone-Monterey hybrid pine (KMX pine, Pinus x attenuradiata) for reforesting marginal timber sites in Northern California. The field trial focused on comparing the performance of trees derived from knobcone pine (Pinus attenuata) seed sources in the Siskiyou Mountains of Oregon to knobcone pine seed sourced from Placer County, California. Hybrids were hypothesized to combine rapid juvenile growth rates with drought tolerance suitable for hot, low-elevation sites, while providing sufficient frost tolerance to withstand interior California coast range winters. While 3 of 4 study sites remain intact as of 2022, the study was only followed and measured from 1964-1973. Quantitative data from 3 of 4 test sites, spanning the 1964-1966 period, have already been published. Also included in this package are the georegistered maps used to digitize tree locations to create a spatially explicit dataset used in growth-provenance diversity analyses, based on 1966-1973 tree data for the Tom Lang Gulch and Spring Gulch test sites.Some of these data were originally published by Griffin and Conkle (1967). Additional quantitative data (the smaller Platina test site [1965, 1965, 1966] and later data for Spring Gulch [1973] and Tom Lang Gulch [1973]) were subsequently incorporated into the re-analyses of Looney et al. (2023).