Data for: Effectiveness of forest density reduction treatments for increasing drought resistance of ponderosa pine growth

As the climate changes, it is increasingly important to understand how forests will respond to drought and how forest management can influence those outcomes. In many forests that have become unnaturally dense, "restoration treatments," which decrease stand density using fire and/or mechanical thinning, are generally associated with reduced mortality during drought. However, the effects of such treatments on tree growth during drought are less clear. Previous studies have yielded apparently contradictory results, which may stem from differences in underlying aridity or drought intensity across studies. To address this uncertainty, we studied growth of ponderosa pine (Pinus ponderosa) in paired treated and untreated areas before and during the extreme California drought of 2012–2016. Our study spanned gradients in climate and tree size and found that density reduction treatments could completely ameliorate drought-driven declines in growth under some contexts, specifically in more mesic areas and in medium-sized trees (e.g., normal annual precipitation > c. 1100 mm and tree diameter at breast height < c. 65 cm). Treatments were much less effective in ameliorating drought-associated growth declines in the most water-limited sites and largest trees, consistent with underlying ecophysiology. In medium-sized trees and wetter sites, growth of trees in untreated stands decreased by more than 15% during drought, while treatment-associated increases in growth of 25% or more persisted during the drought. Trees that ultimately died due to drought showed greater growth reductions during drought relative to trees that survived. Our results suggest that density reduction treatments can increase tree resistance to water stress, and they highlight an important pathway for treatments to influence carbon sequestration and other ecosystem services beyond mitigating tree mortality.All data files are .csv format and can be opened by standard spreadsheet software or read by common scripting languages (e.g., the read.csv function in R).Funding provided by: U.S. Forest ServiceCrossref Funder Registry ID: http://dx.doi.org/10.13039/100006959Award Number: Forest Health Protection ProgramFunding provided by: U.S. Forest ServiceCrossref Funder Registry ID: http://dx.doi.org/10.13039/100006959Award Number: Pacific Southwest RegionPlease see the accompanying manuscript for detailed data collection and processing methods. Briefly, we collected tree cores from live and dead ponderosa pine trees in a series of paired "treated" and "untreated" forest stands along a precipitation gradient. Treatments included prescribed fire and/or mechanical thinning intended to reduce stand density and increase resilience to droughts and fires. We measured ring widths and assigned each ring to a year following standard dendroecological methods. We detrended the ring width series by dividing ring widths by a modified negative exponential function fitted to the raw ring widths. We summarized both raw and detrended ring widths across three periods – "baseline" (1970-1999), "pre-drought" (2000-2010), and "drought" (2013-2014) – by computing the mean. We also measured the diameter at breast height of all cored trees and recorded any evidence of insect pest presence. Finally, we tallied the number of trees (DBH > 7.6 cm) and saplings occurring with 12.6 m radius plots where cored trees were located