Effects of competition on drought adaptability and growth decline of Pinus koraiensis trees

  Objective  This paper aims to reveal the potential effects of competition on drought adaptability and growth decline of Pinus koraiensis, provide scientific basis for forest management.

  Method  Based on the samples taken from natural forest in the south of Xiaoxing’anling Mountains, northeastern China, the dendrochronology method was used to analyze and compare the radial growth rate of P. koraiensis with different competition intensities and tree growth adaptabilities to extreme drought based on index of resistance (R_t), resilience (R_c), and restore elasticity (R_s).

  Result  The tree ring width index and radial growth rate of P. koraiensis in the south of Xiaoxing’an Mountains reflected the growth decline appeared in the periods of 1980−1990, 1990−2000 and 2002−2017. Under varying competition intensities, the period and intensity of growth decline of P. koraiensis were different. The period of growth decline of P. koraiensis at middle and low competitive intensities was relatively consistent. During the rapid warming period from 1990 to 2000, the growth decline was not seen for P. koraiensis at high competitive intensity, while the growth decline for P. koraiensis at low competitive intensity was the most serious with the lowest value of −40.28%. The standard chronology of P. koraiensis with different competitive intensity was positively correlated with Palmer drought index (PDSI) from June of previous year to August of that year, and the high competitive index group reached a significant level from September of previous year to February of that year (P < 0.05). The resistance and resilience of P. koraiensis at high competition intensity to drought were weak, especially in severe drought period, competition intensified the sensitivity of trees to drought, and the higher the competition index (the greater the competition pressure was) was, the weaker the resistance and resilience of P. koraiensis to drought were. During the rapid warming period before 2000, the resilience of P. koraiensis to extreme drought under different competition intensities showed a downward trend, and the resilience of P. koraiensis to drought rebounded during the warming hiatus period around 2000.

  Conclusion  With the increasing frequency of extreme drought events in the future, P. koraiensis may face a more severe recession. Competition affects the adaptability of trees to drought. Trees under high competition intensity are more sensitive to drought and have weaker adaptability, but don’t show more serious growth decline. Further research needs to be combined with in-depth analysis at different time and space scales to deal with the adverse effects of climate warming. It is of great significance to strengthen the research on the response of trees to drought for forest management and resource protection.