Purpose This dataset was used to examine the relationships between heartwood area (HWA) and tree and plot characteristics across four Douglas-fir sites to inform forest management and wood quality assessment. Nature & Scope The dataset includes field measurements from multiple sites, plots, and trees, covering: Identifiers: Site, Plot, Tree, Disc Tree Metrics: Tree Height, Height to Live Crown (hlc), Distance from Apex (DFA), Distance to Crown Base (DCR) Wood Properties: Heartwood Area (HWA), Sapwood Area (SWA) Competition & Health Indicators: Basal Area of Larger Trees (BAL), Belowground Root Infection (BGRI, 0 = healthy, 1 = diseased) This structured dataset enables analysis of heartwood formation, competition effects, and tree health in Douglas-fir.