Deciphering the meaning of "blue" in dendrochronology and wood anatomy

The colour blue has recently become popular in dendrochronology. Two parameters, blue intensity (BI) and blue rings (BRs), are frequently confused, leading to misinterpretations of tree-ring data and potentially overlooking their distinct physiological meanings. This note clarifies the difference between BI, a surrogate for traditional wood density measurements that quantifies the reflectance of blue light from cross-section surfaces, and BRs, an anatomical anomaly characterised by reduced cell wall lignification. We briefly discuss their origins, detection methods, applications, and significance in understanding environmental stress and tree growth patterns.