Response of resin canal area of Pinus tabuliformis with different ages to climate change in Taiyue Mountains, China.

To investigate the responses of resin canal area of Pinus tabuliformis with different ages to climate change, we analyzed the relationship between the resin canal area and climate factors from 1972 to 2017 in P. tabuliformis plantation at young age, middle age, near-mature, mature, and over-mature periods in Taiyue Mountains, Shanxi Province. The results showed that 55.7% to 75.2% of resin canal occurred in earlywood. The mature and over-mature periods had the largest resin channel area, sequentially followed by near mature, middle age, and young age periods. Annual mean latewood resin canal area increased significantly in near-mature period and mature period, but not in other periods. There was a significant negative correlation between earlywood resin canal area and minimum temperature during the growing season (May to July) for trees at middle age period. Earlywood resin canal area of mature trees showed significant negative correlation with minimum temperature during the growing season, but significant positive correlation with drought (PDSI) in the non-growing season (previous September to current April). The total area of earlywood resin canal at the young, near-mature, and mature periods was less influenced by climate than other periods. The minimum growing season temperature was a limiting factor to earlywood resin canal growth, while the non-growing season drought gradually became a limiting factor for earlywood resin canal with increasing tree age. The total area of earlywood resin canal decreased with increasing non-growing season drought and increasing growing season minimum temperature. In the context of global warming, the earlywood resin canal area may gradually decrease at all five periods, and the most reduction in the over-mature stage.

Differences in ecological resilience of radial growth between Larix principis-rupprechtii and Picea meyeri after drought.

To understand the responses of radial growth to climatic factors and the differences in ecological resilience to drought between a heliophilous species Larix principis-rupprechtii and a shade species Picea meyeri in mixed forests, we developed the tree-ring width chronologies of L. principis-rupprechtii and P. meyeri in three mixed forests based on the samples collected from Toudaogou of Saihanba in Hebei, Ningwu County and Kelan County in Shanxi Province. We analyzed the correlation between climatic factors and various chronologies and examined the differences in resistance (Rc), recovery (Rt), and resilience (Rs) of L. principis-rupprechtii and P. meyeri in response to drought stress. The results showed that the radial growth of L. principis-rupprechtii and P. meyeri was negatively correlated with the mean and maximum air temperature from May to July in three mixed forests, and was positively correlated with the Palmer drought index (PDSI) from May to September. Radial growth decline in trees due to drought stress was significantly different between the two species among the three sites, indicating different physiological and ecological regulation strategies. The resistance of P. meyeri was stronger than that of L. principis-rupprechtii at the three study sites, with stronger resilience and resilient elasticity of L. principis-rupprechtii than P. meyeri. As a result, P. meyeri exhibited greater drought resistance than L. principis-rupprechtii. Under global warming condition, L. principis-rupprechtii might be at greater risk of growth decline than P. meyeri in this region.