Abstract:

Objective: The relationship between radial growth of Pinus yunnanensis and climatic factors and growth dynamics under the extreme drought events at different altitudes were studied to explore the ecological resilience and growth degradation history of P. yunnanensis, which could provide a basis for predicting the future effects of extreme disturbance on the growth dynamics of P. yunnanensis and provide theoretical support to forest protection in this area. Method: Increment cores of P. yunnanensis at different altitudes in Yongren County, Jinsha River basin were collected by increment borer and established chronologies. Percentage changes of radial growth were used to evaluate the growth degradation. Resistance and resilience were used to assess the ecological resilience of P. yunnanensis. Response analysis and redundancy analysis were used to study the relationship between growth and climate factors of P. yunnanensis at different altitudes. Result: The main limiting factors for the radial growth of P. yunnanensis at low (1 845 m) and medium (2 340 m) altitudes are the monthly mean air temperature, precipitation and drought intensity of initial growing season from March to May, and the monthly precipitation and drought intensity of growing season from June to August. Monthly air temperature of July during growing season and drought intensity of the initial growing season are the main limiting factors for the radial growth of P. yunnanensis at high altitude (2 740 m); In the past 150 years, growth of P. yunnanensis degraded during the period of 1884-1886, 1897-1900, 1903-1906, 1947-1949, and 2009-2011. The radial growth degradation of P. yunnanensis was most obvious in low-altitude area, followed by high-altitude area, and the degradation in the middle-altitude area was weaker. The ecological resilience of P. yunnanensis to the same extreme drought events varies among different altitudes. The drought resistance of P. yunnanensis is in an order of medium altitude > high-altitude > low-altitude. The resilience to extreme drought is just in an opposite order. With the increase of age, the drought resistance has enhanced at low-altitudes, while the resilience has weakened. The resistance of P. yunnanensis at the middle-altitudes is stable, the resistance and resilience at the high-altitudes are stable. Conclusion: Trees growing in the marginal distribution of P. yunnanensis are more prone to growth degradation, trees under favorable hydrothermal conditions are more resistant to the interference of extreme events, and trees near the limit environments of P. yunnanensis are more resilient to disturbances.

Key words: Pinus yunnanensis, annual rings, altitudes, ecological resilience, growth degradation