Does resin tapping affect the tree-ring growth and climate sensitivity of the Chinese pine (Pinus tabuliformis) in the Loess Plateau, China?

Resin tapping could affect water and nutrient transport processes in Chinese pine trees, rendering them more vulnerable to extreme climatic events, such as drought, and affecting the ecological function of forests in semiarid regions. This study evaluated how resin tapping affects the tree-ring growth and climate sensitivity of Chinese pine in the Loess Plateau. We compared tree-ring growth patterns between the tapped and untapped faces of tapped trees, and investigated tree-ring growth and its response to climate between tapped and untapped trees in a forest stand during the 1967-2017 period. Tapped trees showed asymmetrical growth patterns after resin tapping, with narrower rings near the tapped face and wider ones near the untapped face. Furthermore, tapped trees had inter-annual variations consistent with those of untapped trees except for the years 2000 and 2001, with significantly lower values following resin tapping, and tree-ring growth then returning to normal. The climate response analysis indicated that the tree-ring growth of both tapped and untapped trees was negatively affected by monthly mean temperatures during the early growing season (May to July) in the post-resin-tapping period. Furthermore, tree-ring growth in tapped trees also revealed significant correlation with water vapour deficit and the Palmer drought index, which indicates that tapped trees are more vulnerable to drought. Further studies based on stable isotopes (i.e. delta C-13, delta O-18, and delta N-15) could improve our understanding of the physiological mechanisms that regulate the effects of resin tapping on tree-ring growth.