| The climate is the main abiotic factor affecting tree growth.However,the radial growth patterns of trees at different elevations and their responses to climate factors are significantly different in mountain ecosystems.Changbai Mountain region has typical mountain climate characteristics,and there are many studies on the correlation between tree rings and climate.However,it is not clear how radial growth rate and growing season length affect the radial growth of Betula ermanii at different elevations.In order to investigate the radial growth patterns of Betula ermanii at different elevations and their responses to climate factors.In this study,a two-year radial growth monitoring experiment was conducted on 90 years old Betula ermanii at two elevation gradients(1700m and 2000m)on the western slope of Changbai Mountain,and the core samples of Betula ermanii were collected at corresponding tree ages.By comparing the radial growth rate and radial growth amount of Betula ermanii at different periods and different elevations and their responses to climate factors,the changes in the radial growth pattern of Betula ermanii at different elevations with climate change were analyzed.The daily radial growth data of Betula ermanii were processed by the maximum value method,Gompertz function,and linear regression,and the differences in radial growth,growth rate,and growing season length at different elevations were compared.The responses of radial growth to climate factors at different elevations were compared by Pearson correlation analysis.Finally,sensitivity analysis was used to determine the contribution rates of radial growth rate and growing season length to radial growth of Betula ermanii at different elevations.The main conclusions of this study are as follows:(1)According to the characteristics of climate change in Changbai Mountain,the first 30 years of the past 60 years are divided into the base period,and the last 30 years are divided into the warming period.There was no significant difference in the growth rate of Betula ermanii at different elevations.The growth rate and amount of the same elevation in the warming period were higher than that in the base period,but the difference in the growth rate was not significant,while the difference in the growth amount was significant.There was no significant difference in the radial growth of Betula ermanii at different elevations in the basal period,but the low elevation was significantly higher than the high elevation in the warming period.(2)The radial growth of Betula ermanii at high and low elevations was positively correlated with temperature in July and during the growing season,but the sensitivity of radial growth of Betula ermanii at high elevation to climate was higher than that at low elevation.The correlation between precipitation and radial growth of Betula ermanii was not significant.For nearly 60 years,the response of radial growth of Betula ermanii at different elevations to climate factors varied with the change of climate,The growth of Betula ermanii showed the same trend in response to temperature factors,but in response to precipitation in the growing season,both elevations showed a significant negative correlation to a weak positive correlation.(3)The radial growth dynamics of Betula ermanii at low elevation were more sensitive to climate factors than those at high elevation,which showed that the daily radial growth of Betula ermanii at high and low elevation was significantly positively correlated with mean air temperature,maximum air temperature,and minimum air temperature,but the daily radial growth of Betula ermanii at low elevation was more sensitive to soil temperature than that at high elevation.At the beginning of the growing season(15 days after the beginning of the growing season),there was no significant correlation between daily radial growth of Betula ermanii at low elevation and climate factors,while there was only a significant positive correlation between daily radial growth of Betula ermanii at high elevation and maximum air temperature.During the flourishing growth season(7 days before and after the maximum growth rate),the daily radial growth of Betula ermanii at low altitude was significantly positively correlated with mean air temperature,maximum air temperature,mean soil temperature,maximum soil temperature and minimum soil temperature,while that at high elevation was significantly positively correlated with mean air temperature and maximum air temperature.(4)The radial growth and growing season length of Betula ermanii at low elevation were significantly higher than those at high elevation,but there was no significant difference at the beginning of the growing season,the end of the growing season,growth rate,maximum growth rate and time of maximum growth rate.The contribution rate of radial growth rate and growth season duration to radial growth of Betula ermanii at low elevation was not significantly different.The contribution rate of radial growth rate to radial growth of Betula ermanii at high elevation was much greater than the duration of the growing season.But the combined effects of elevation suggest that the contribution of radial growth rate to radial growth was slightly greater than the duration of the growing season.The above results showed that climate warming significantly promoted the radial growth of Betula ermanii at different elevations in Changbai Mountain.The radial growth of Betula ermanii at low elevation was significantly higher than that at high elevation,and the sensitivity to climate factors at interannual scale was lower than that at high elevation.The contribution difference of growth rate and growing season length to the radial growth of Betula ermanii at low elevation was not significant,but the radial growth of Betula ermanii at high elevation and the whole elevation gradient was mainly determined by growth rate. |
