Aims This study aims to determine the radial growth characteristics of natural secondary forests along an elevation gradient and their responses to climate change, and to identify the main factors affecting the radial growth of trees on mountain sites. The outcome of the study would be of great significance for understanding the impact of climate change on growth adaptation, succession and sustainable management in temperate forest ecosystems.
Methods Field plots were set up at 1 350, 1 550, 1 750, and 1 950 m above sea level in the study area to collect samples of wood cores and discs. Tree-ring climatology method was adopted to establish the standard chronology of Betula platyphylla in natural secondary forest, and the annual ring width index and climate factors were subjected to correlation analysis and multiple stepwise regression analysis.
Important findings From 1960 to 2018, climate in the study area showed a warming and drying trend, with 1960-1989 as a stable period and 1989-2018 as a period with rapid changes. A change occurred in the radial growth of B. platyphylla in 1989, with the annual ring width index displaying an “up-down” growth trend. During the stable period of climate change, the radial growth of B. platyphylla at the low-elevation sites (B1350, B1550) was positively correlated with temperature variables (i.e. average air temperature, maximum air temperature, minimum air temperature); whereas at the high-elevation sites (B1750, B1950), the growth was significantly and positively correlated with the precipitation of the previous year and during the growing season of current year. During the period of rapid climate change, the radial growth was negatively correlated with temperature and potential evapotranspiration (ET0) during the growing season at the low-elevation sites (B1350, B1550), and negatively with ET0 during the growing season and end of the growing season at the high-elevation sites (B1750, B1950). During the stable period of climate change, temperature explained 76%, 54%, and 51% of the variations in radial growth, and moisture explained 24%, 46%, and 49%, at the B1350, B1550, and B1750 sites, respectively. During the period of rapid climate change, temperature explained 58%, 41%, and 38% of the variations in radial growth, and moisture explained 42%, 59%, and 62%, at the B1350, B1550, and B1750 sites, respectively. The radial growth of trees at the high-elevation site B1950 was always controlled by the moisture during the study period.