Climate-growth relationship for different directions of Pinus pumila radial growth at the treeline of northern Daxing'an Mountains, China

Pinus pumila radial growth in differing radii directions' response to climatic factors is inconsistent. The effects of freeze-thaw events on growth differ between spring and autumn. Pinus pumila is a crucial shrub species of sub-alpine treelines in northeast Daxing'an Mountains, China, but the growth-climate relationship for this eccentric shrub is not well understood. A total of 15 disks near the trunk base of individual Pinus pumila were collected at the treeline of Xiaobai Mountain, China. We investigated the growth-climate relationships in four reaction directions (A and B: left and right perpendicular radii; C: opposite radius to compression wood; D: compression wood radius). Results indicated that the shrub-ring width at the D direction was the widest (0.70 +/- 0.14 mm/a) of the four directions, while the opposite direction (C) is narrowest (0.43 +/- 0.07 mm/a). Water availability in June was the major limiting factor for P. pumila growth in the A and B directions. However, the radial growth in the C direction was mainly affected by mean and maximum temperatures in June, and growth in the D direction positively correlated with mean temperature in the current February and the previous October and minimum temperature in the previous November. In addition, the radial growth at all four directions negatively correlated with the sunshine hours in June of the current year, which could be related to the increase of soil drought and respiration caused by higher temperatures. Radial growth at the A, B, and C directions negatively correlated with the freeze-thaw magnitude and frequency in May, which may cause the frost damage in shrub leaves and roots. Our findings suggested that the eccentric shrub growth at the perpendicular radii may not contain the best climate signals, while the growth at the compression wood direction seems to be of normal use in dendroclimatology.