Seasonal Stem Radial Variation And Its Influencing Factors Of Six Tree Species In Northeast China

Radial growth of tree stem is an important observable indicator of carbon sequestration in forest vegetation.Since the growth characteristics and response to environmental factors vary greatly depending on the tree age,diameter class,species,latitude,longitude and elevation of trees.It is particularly important to explore the spatio-temporal dynamic pattern of growth of different tree species and their responses to environmental factors under the background of global changes.The high-precision dendrometer was employed to continuously monitor the stem radial changes of six dominant tree species in temperate forests in northeast China during2021 ～ 2022,including Pinus koraiensis Sieb.,Betula platyphylla Suk.,Populous davidiana Dode.,Quercus mongolica Fisch.,Fraxinus mandshurica Rupr.,and Juglans mandshurica Maxim.The aim was to investigate the intra-and interspecific differences in stem radial variation,and to reveal their response mechanisms to environmental factors.The results show that:There were significant interspecies and interannual differences in the dates of stem radial changes(SRC)of the dominant tree.The starting growth dates of the six tree species were Day138-173 in 2021,and Day 123-156 in 2022.And the stopping growth period were Day193-257 and Day 196-246,with the length of the growth period ranging from 52 ～ 98 days and 69～ 112 days.There was significant interspecific variation in the date of radial growth peak,with Pinus koraiensis Sieb.reaching peak growth earliest(days 145-155)and Quercus mongolica Fisch.reaching peak growth latest(days 180-193).Annual stem diameter growth at breast height of superior tree ranged from 0.64 ～ 3.75 mm(in 2021)and 1.45 ～ 5.61 mm(in 2022),respectively,and with significant interspecific differences.The stem radial growth was limited by water condition.The SRC of the six main tree species was significantly positively correlated with precipitation and relative humidity,and significantly negatively correlated with vapor pressure deficit(VPD)during 2021-2022.The correlation between tree water deficit-induced reversible stem shrinkage(TWD)and environmental factors is opposite with SRC.However,the strength of this correlation varies among different tree species,different diameter classes and different locations.The correlation between the SRC/TWD and environment factors at the suppressed trees or at the height of 6 m was weaker than that at the DBH of the superior trees,and the correlation between Juglans mandshurica Maxim.and environment factors is stronger than other tree species.The precipitation had a significant promotion effect on the radial growth of stem,the cumulative trunk growth was positively correlated with cumulative precipitation,but the significance varied by species.Six tree species showed different patterns of stem radial change in response to seasonal drought.Among them,the SRC of Pinus koraiensis Sieb.and Quercus mongolica Fisch.showed a obviously shrinkage trend,while Fraxinus mandshurica Rupr.and Populous davidiana Dode.showed no clearly change,however,Juglans mandshurica Maxim.and Betula platyphylla Suk.showed a continuous regular growth.The growth duration and growth rate of all tree species except Betula platyphylla Suk.and Pinus koraiensis Sieb.were significantly reduced when soil moisture content was lower.This study provides a data base and scientific basis for the formation of productivity and carbon sink,and its sustainability for temperate forest in Northeast China under the context of climate change.