Response And Adaptation Of Qinghai Spruce Forest To Climate Change In The Qilian Mountains

The global climate system is undergoing changes characterized by climate warming,alteration of precipitation pattern and frequent extreme climate events.The response and adaptation of forest ecosystems to those changes are complicate and differ among regions,which has caused global concern.The Qilian Mountains,located in the temperate arid and semi-arid region,is an important part of the ecological security barrier in Northwest China and even the whole country.The forest structure in the region is relatively simple,fragile and extremely sensitive to climate change.It plays an important role in keeping global carbon and oxygen balance,slowing global warming and maintaining biodiversity.In recent decades,the climate in the Qilian Mountains has changed significantly,which will inevitably exert impacts on the stability of the forest ecosystem in the Qilian Mountains.However,there was still a lack of comprehensive and in-depth research on the forest ecosystem in this area.In this study,Qinghai spruce(Picea crassifolia Kom.),the main constructive species in the Qilian Mountains,was taken as the research object.Specifically,the P.crassifolia in typical timberline and different altitude gradients across five longitudes from east to west in Qilian Mountains were sampled.Based on detailed forest quadrat survey and tree ring sampling,a variety of research methods were used to comprehensively analyze the response and adaptation of P.crassifolia forest to climate change in the Qilian Mountains,and to clarify the impact of climate change on forest ecosystems in arid and semi-arid areas in recent decades.This study was expected to be helpful to understand the stability of forest ecosystem and provide a reliable basis for accurately predicting the forest dynamics in arid and semi-arid areas under the background of global climate change,provide scientific basis for regional vegetation restoration,and provide theoretical guidance for the ecological protection and construction of National Park in the Qilian Mountains.The main conclusions are as follows:(1)The relationship between radial growth of P.crassifolia at the alpine timberline with climate change differed among regions of the Qilian Mountains.The radial growth of P.crassifolia at the alpine timberline in the eastern Qilian Mountains showed a significant upward trend,which was positively correlated with temperature,while weakly with moisture or not.The radial growth of P.crassifolia at the alpine timberline in the western Qilian Mountains showed a fluctuating and overall gentle growth trend,which was positively correlated with moisture and negatively with temperature.Such pattern may mostly attributed to the tremendous east-westward hydroclimate gradient of the Qilian Mountains.The results indicate that the radial growth of P.crassifolia at the alpine timberline in the eastern Qilian Mountains will be facilitated by rising temperature in the future,whereas those at the alpine timberline in the western Qilian Mountains was complex to make further predictions,and it mainly depends on the degree of drought triggered by temperature and precipitation.In addition,according to the significant correlation between the regional chronology and summer temperature in the eastern Qilian Mountains,the summer temperature changes of the eastern Qilian Mountains over the past 166 years(1853-2018)were reconstructed.The results showed that the high-frequency and low-frequency changes between the reconstructed values and the measured values were in good agreement,and the reconstruction results can represent the climate change in the eastern Qilian Mountains and its surrounding areas.(2)The diameter class structure of P.crassifolia in the Qilian Mountains was relatively complete,basically showing an inverted “J” type,indicating an increasing population structure,and the stand factors of P.crassifolia at the alpine timberline in the Qilian Mountains have significant vertical gradient differences and east-west differences.The community regeneration density of P.crassifolia at the alpine timberline in the Qilian Mountains has increased since the establishment of the group,and the difference between the eastern and western regions was little.The temperature from April to October was the main climatic factor affecting the regeneration of P.crassifolia at the alpine timberline in the Qilian Mountains.Since the 20 th century,the treeline position of P.crassifolia showed an upward trend in the Qilian Mountains,with an average increase of 28.1 m.However,there was a large difference in the rising distance of the treeline position between different sampling sites,and there was no obvious temporal and spatial variation.The rise of treeline position in the Qilian Mountains was mainly affected by temperature and forest density.The higher the temperature,the greater the forest density,and the more obvious the treeline position rise.(3)The correlation between radial growth of P.crassifolia at different altitude and climatic factors has significant spatial variation in the Qilian Mountains.The radial growth at high altitudes in the eastern Qilian Mountains was mainly affected by temperature,and the rest were limited by moisture.The sliding correlation between the radial growth and main climatic factors showed that the response of the radial growth to temperature began to show obvious differentiation in the 1980 s,and the response differentiation intensity increased with the increase of altitude,while the response differentiation of tree radial growth to precipitation and SPEI-12 was not obvious.The response differentiation intensity of P.crassifolia to climate change at different altitudes was mainly affected by temperature.(4)The adaptability of P.crassifolia to drought has both temporal and spatial variations in the Qilian Mountains.In terms of time,the resistance of P.crassifolia showed a downward trend,while the recovery showed an overall upward trend.Spatially,from east to west(from south to north),from high altitude to low altitude,the resistance of P.crassifolia gradually decreases,while the recovery gradually increases,which was mainly related to the sensitivity of P.crassifolia to drought.Under the influence of drought,P.crassifolia in the middle and low altitudes in the Qilian Mountains and the high altitudes in the west of Qilian Mountains experienced growth decline in the 1980s-1990 s,and the regression analysis of growth decline with longitude,latitude and altitude could reach significant correlation.The occurrence of growth decline was mainly related to the adaptability of P.crassifolia to drought.The stronger the resistance of P.crassifolia to drought,the smaller the possibility of growth decline.