Radial growth in Qinghai spruce is most sensitive to severe drought in the Qilian Mountains of Northwest China

Global warming and frequent extreme drought events lead to tree death and extensive forest decline,but the underlying mechanism is not clear.In drought years,cambial development is more sensitive to climate change,but in different phenological stages,the response rela-tionship is nonlinear.Therefore,the dynamic relationship between tree radial growth and climatic/environmental fac-tors needs to be studied.We thus continuously monitored radial growth of Qinghai spruce(Picea crassifolia Kom.)and environmental factors from January 2021 to November 2022 using point dendrometers and portable meteorological weather stations in the central area of the Qilian Mountains.The relationship and stability between the radial growth of Qinghai spruce and environmental factors were compared for different levels of drought in 2021 and 2022.The year 2022 had higher temperatures and less precipitation and was drier than 2021.Compared with 2021,the growing period in 2022 for Qinghai spruce was 10 days shorter,maximum growth rate(Grmax)was 4.5μm·d^(-1) slower,and the initiation of growth was 6 days later.Growth of Qinghai spruce was always restricted by drought,and the stem radial increment(SRI)was more sensitive to precipitation and air relative humidity.Seasonal changes in cumulative radial growth were divided into four phenological stages according to the time of growth onset,cessation,and maximum growth rate(Grmax)of Qinghai spruce.Stability responses of SRI to climate change were stronger in Stage 3 and Stage 4 of 2021 and stronger in Stage 1(initiation growth stage)and Stage 3 of 2022.The results provide important information on the growth of the trees in response to drought and for specific managing forests as the climate warms.

Climate response and radial growth of Pinus tabulaeformis at different altitudes in Qilian Mountains

In order to test whether the relationship between climate and the radial growth of trees is affected by altitude,altitude variability and time stability of climate-influenced radial growth of a dominant conifer,Chinese pine(Pinus tabulaeformis),in the eastern Qilian Mountains were studied against the background of climate change using dendrochronology.Results show that 1)droughts at the end of the growing season of last year and during the early and middle growing season of the current year were the main limiting factors for the radial growth of Chinese pine at two altitude gradients;this was determined by analyzing the relationship between tree-ring width chronologies and climate factors.2)The sensitivity of the radial growth of trees to climate change gradually decreased and was affected more by drought stress at a lower altitude.3)An unstable divergence response was observed in the radial growth at the two altitudes,in response to controlling climatic factors;this observation was based on the moving correlation analysis of growth/climate relationships,and the aggravation of drought stress caused by increasing temperature was the main reason.4)The growth rate of Chinese pine at the two altitudes increased at first and then decreased,as measured by basal area increment(BAI)modeling.Future temperature rises may have significant effects on mountain forest ecosystems in arid and semi-arid regions.Effective management and protection measures should be taken,according to the response patterns of trees to climate change at different altitude gradients.