Axial resin duct quantification in tree rings: A functional defense trait

Resin ducts in the secondary xylem of tree rings are a measure of a tree's defense capacity from insects and pathogens. Because resin ducts are permanently embedded within the xylem, retrospective analysis can be performed to quantify changes in defense over time and determine factors that contribute to this change, such as climate and disturbance. Here, we provide methods on how to measure axial resin ducts in secondary xylem. These methods provide the necessary protocols for consistent quantification of xylem resin ducts and terminology, which will also allow easier cross-comparison among studies in the future. We describe: • Steps to prepare tree cores for resin duct measurements. • Procedure to obtain image and measure individual resin ducts. • Software code to compile duct measurements into a complete chronology with both standardized and unstandardized resin duct metrics for further analyses.