Objective This study aimed to reveal the geographical variations in cork bark thickness of Quercus variabilis and its environmental influencing factors, which could provide scientific reference not only for estimating the cork yield in China, but also for screening and breeding excellent germplasm resources.

Method The study analyzed the thickness of cork bark and its influencing factors across 12 cork oak populations across full range, using methods such as cluster analysis and mixed effect modeling.

Result The cork bark thickness showed highly significant positive correlation with the stem diameter, the stem age and the thickness of xylem and phloem. The cork bark rate, cork bark relative thickness, ratio of outer bark to inner bark and the relative roughness presented significant geographical trends. Through the cluster analysis of the bark rate and the ratio of outer bark to inner bark, six populations, such as Shangluo in Shaanxi, Tianshui in Gansu of northwestern China and Neixiang in Henan, Lincheng in Hebei, Pinggu in Beijing of northern China, Jinzhai in Anhui of eastern China were found to be in one cluster with higher bark rate and outer bark ratio. The bark rate was influenced by trunk diameter, annual total precipitation and slope, while the ratio of outer to inner bark was affected by annual mean temperature and slope. The relative thickness was influenced by mean annual temperature, annual total precipitation and slope, but the relative roughness was affected by trunk diameter, slope and soil N content. On the regional scale, annual mean temperature and annual total precipitation had a significant negative effect on the bark thickness.

Conclusion This study preliminarily quantifies the influencing factors of cork bark thickness, which can provide scientific reference for future cork yield prediction and breeding of improved varieties.