| Cunninghamia lanceolata is an important commercial tree species in southern China,which has the advantages of higher growth rate,wood quality and economic value.C.lanceolata plantation plays an important role in assuring wood production safety,maintaining terrestrial ecosystem carbon balance and sequentially achieving the goal of carbon neutral.Stand age,climate and competition play an important role in governing the tree growth of C.lanceolate.Investigating the variation of radial growth with stand age for C.lanceolata plantation along with the response of radial growth to climatic conditions and competition under scenarios of global climate change are of great significances in enhancing the ecosystem stability of C.lanceolata plantation and its sustainable management.This experiment was carried out at the Huitong National Field Station for Scientific Observation and Research of Chinese Fir Plantation Ecosystem in Hunan Province.The monthly radial growth of 240 C.lanceolata trees with 6 stand ages in 24 experimental plots were monitored continuously for 3 years(2018-2021)using the strip tree meter.Combining the radial growth measurements,tree characteristics,meteorological data and the estimated single tree competition index,we analyzed the variation of radial growth with stand age,and quantified the influences of climate and competition on the radial growth of C.lanceolata.The main results are as follows:(1)The annual radial growth curve of Chinese fir showed that the radial growth of Chinese fir could be divided into four stages.1)The initial growth stage:radial growth of Chinese fir began to recover after winter dormancy;2)Growth peak stage:the cell activity of Chinese fir was the most active during this period,and the highest radial growth appeared in May and September.The maximum radial growth of Chinese fir occurred in May,and the radial growth during this period accounted for about 80%of the annual radial growth;3)End of growth:radial growth almost came to an end,and radial growth started to decline sharply;4)Dormant period:radial growth of Chinese fir almost stopped during this period.The radial growth of C.lanceolata would begin to recover until the late February of the next year.With the increase of stand age,the initiation time of radial growth for C.lanceolata gradually delayed.At the same time,the annual radial growth varied with stand age.The annual radial growth reached the maximum value for C.lanceolata plantation at the age of 10-15 years,and then gradually decreased.When the stand age was older than 20 years,the annual radial growth began to decline slowly and gradually stabilized at 2 to 3 mm.(2)Temperature and precipitation are the two main limiting factors influencing radial growth of C.lanceolata.The radial growth of C.lanceolata was positively correlated with the temperature during April,May and October(p<0.05),while the radial growth of C.lanceolata was negatively correlated with the temperature in July and August(p<0.05).There was a significant negative correlation between precipitation and radial growth of C.lanceolata in August(p<0.05),while there was a significant positive correlation between radial growth of C.lanceolata and precipitation in June or October(p<0.05).(3)Variance analysis of competition coefficients among C.lanceolata forests with different stand ages showed that the competition coefficients of middle-aged and mature forests were significantly different from those at other stand ages.Competition in middle-aged forests was fierce,while competition in mature forests was minor.Radial growth of C.lanceolata agreed well with competition coefficient using general linear regression model in young and middle-aged C.lanceolate plantation,with the fitting degree higher in middle-aged plantation and fitting degree lower in mature forests.For all the studied 6 different stand ages,the radial growth of C.lanceolata was negatively correlated with competition coefficient(p<0.05).(4)The radial growth of C.lanceolata was jointly regulated by both competition and climatic conditions,with the influences of competition larger than those of climatic condition.As the Chinese fir plantation matured,the influence of competition on C.lanceolata radial growth gradually decreased,while the contribution of climate to radial growth increased instead.At the same time,competition and stand age also affected the sensitivity of radial growth to climate.Through the study on the radial growth of Chinese fir with the change of stand age and its response to climate and competition,the following theoretical framework is obtained.With the increase of Chinese fir age,the annual radial growth of Chinese fir gradually decreases,until it is nearly mature,the annual radial growth of Chinese fir gradually keeps stable.The radial growth of Cunninghamia lanceolata was significantly influenced by climate and competition,and the relative influence of competition gradually decreased with the increase of the age of cunninghamia lanceolata. |
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