| Tree-ring analysis provides an excellent source of proxy information for climate change and it is often used in long-term paleoclimatic reconstructions due to its accurate dating,annual resolution,wide distribution,ease of access,long time series,and abundance of information.Changbai Mountain,located in the mid-latitude region of Northeast China,is severely affected by temperature continental monsoon and global climate change.The broad-leaved Korean pine forest in this area is a regional climax community in the mountainous areas of Eastern China.It is rich in biodiversity and biomass.The original broad-leaved Korean pine forest is now close to the climax stage of forest potential development.At present,global warming has seriously affected the forest ecosystem in Changbai Mountain.Therefore,in the context of global warming,it is of great significance to explore the relationship between tree radial growth and climate factors in this area,in order to understand the response of northern forests under the background of global climate change,especially the dynamic changes of broad-leaved Korean pine forests in Changbai Mountain.Based on the study of broad-leaved Korean pine forest in Changbai Mountain,core samples of tree rings were collected from seven tree species in the forest.Firstly,the tree ring width chronology of different tree species in broad-leaved Korean pine forest was established to clarify the effects of climate change on the radial growth of trees of different tree species.Secondly,the standard chronology of Pinus koraiensis and Fraxinus mandshurica at different elevation gradients was established to explore the response of the standard chronology of Pinus koraiensis and Fraxinus mandshurica to climate factors at different elevation gradients.In order to clarify the key climate factors affecting the radial growth of Pinus koraiensis and Fraxinus mandshurica trees at different elevations,and to the specific reasons for the difference of response of different tree species radial growth to climate factors at different altitudes.In addition,the core of tree rings in the transition zone between broad-leaved Korean pine forest and dark coniferous forest on the northern slope was collected,and the standard chronology of Pinus syluestriformis and Picea jezoensis was established in order to reveal the response of radial growth of two main tree species to climate change in the transition zone under the background of global climate change,and to provide basic data for paleoclimate reconstruction in the future.Finally,the mean temperature changes over the past 200 years in Changbai Mountain were reconstructed using tree-ring width,in order to provide new references for the study of climate change in the Changbai Mountain and even in Northeast China for hundreds of years.In conclusion,the above research is of great significance to understand the response of the northern forest ecosystem under the background of global climate change,especially the dynamic change of the forest in Changbai Mountain.It also provides a reference basis for the rational management and protection of the broad-leaved Korean pine forests in this area in the future.(1)The annual mean temperature in Changbai Mountain was 2.93?,and its climatic tendency was 0.39? 10a-1.Mean annual precipitation fluctuation in the study area is small,showing an increasing trend year by year.Mean annual precipitation was 682.34 mm,and its climatic tendency was 6.49 mm·10a-1.Except that the annual precipitation in autumn showed a slight downward trend,the precipitation in other seasons showed an increasing trend,but the increasing trend was not obvious.In summary,there is an obvious increasing trend of temperature and no obvious increasing trend of precipitation in this area.(2)Under the same stand conditions,the responses of tree radial growth to climate change were different among different tree species.The radial growth of Pinus koraiensis was mainly controlled by precipitation,showing a significant negative correlation with temperature and a significant positive correlation with precipitation.The radial growth of Fraxinus mandshurica and Ulmus davidiana were more affected by temperature than precipitation,and the increase of temperature was beneficial to the increase of their radial growth.The radial growth of Quercus mongolica and Phellodendron Amur were not very sensitive to climate change,which is affected by temperature and precipitation.(3)The responses of the two species to climate factors were different,the growth of Pinus syluestriformis was more sensitive to climate change than Picea jezoensis,which was suitable for dendroclimatological analysis.Response function coefficients indicated that Pinus syluestriformis was limited by temperature,and the increase of temperature was beneficial to the increase of radial growth Picea jezoensis is affected by temperature and precipitation.Warming caused drought stress,which was the main factor that limits the growth of Picea jezoensis,and it might have adverse effects on the Picea jezoensis if global temperature continues to increase.The coupling effects of large-scale atmospheric-oceanic variability may affect tree growth in Changbai Mountain.(4)Tree ring chronologies from low altitudes were more superior than others,revealing that trees at low altitudes are more sensitive than at high altitudes.The growth of Pinus koraiensis at low altitude is mainly controlled by precipitation,which is adversely affected by the increase of temperature.With the increase of altitude,Pinus koraiensis at high altitude is limited by both temperature and precipitation.The increase of temperature and precipitation can increase the radial growth of Pinus koraiensis at high altitude.However,the radial growth of Fraxinus mandshurica trees at different altitudes is affected by temperature,and the increase of temperature can increase radial growth.RDA between the three chronologies and climate factors showed the same as between the results of the correlation analysis,which further proved that the RDA is also effective in quantifying the relationship between tree-ring indices and climatic factors(5)We developed a new tree-ring width chronology from Pinus syluestriformis spanning the period 1762-2017.Climate-growth correlation analysis revealed that summer mean temperature was the main climatic factor controlling tree-ring growth.July-August mean temperatures from 1767-2009 were reconstructed using the standard chronology.Reconstruction results explained 32.4%of climatic variance over the calibration period 1960-2009,and they indicated that the Changbai Mountain have experienced four major warm periods,three major cold periods,and several cold years that coincided with a sequence of major tropical volcanic eruptions.Temperature reconstructions have successfully captured the most recent climatic warming events and are consistent with other reconstructions from nearby regions on decadal timescales.Spatial climate correlation analyses with a gridded temperature dataset revealed that our temperature reconstructions contain strong regional temperature signals for the eastern Eurasian continent.Power spectrum revealed the existence of significant frequency cycles,which may be linked to large-scale atmospheric-oceanic-land variability,such as the El Nino-Southern Oscillation,solar activity,and the Pacific Decadal Oscillation.(6)Based on dendrochronological methods,we established tree-ring widths chronologies of Fraxinus mandshurica.In order to identity the key climatic factors that affected the radial growth of the F.mandshurica in Changbai Mountain,Northeastern China.Correlation functions between tree-ring index and climatic variables indicate that temperature(especially the autumn temperature)is essential for radial growth of Fraxinus mandshurica in Changbai Mountain.The precipitation on the growth effect is relatively weak.According to the stronger relationship(r=0.665,p<0.0001)between August-November mean temperature in the previous year and tree-ring widths chronology,we reconstruct the August-November mean temperature in Changbai Mountain using a simple liner regression model.The reconstruction equation explained 44.3%of the variance of the mean temperature.The equation is checked by leave-one-out method.The regression equation is deemed stable and reliable.Five cold periods and five warm periods occurred in this region for the past 249 years.We found that the cold and warm periods of the reconstructed sequences were in accordance with other sequences from nearby regions on decadal timescales,which further demonstrated the reliability of the reconstructed results.Spatial correlation analyses with a gridded temperature dataset showed that our temperature reconstruction sequences had a good representation for the variation of August-November mean temperature in Changbai Mountain.In addition,the spatial analysis with SST data also showed that the temperature reconstruction sequences of this study had a significant positive correlation with SST in the Pacific,Indian Ocean,North Atlantic ocean.Power spectrum reveals the existence of significant frequency cycles of variability at 2.0,2.6,3.1,3.5,4.5,6.4,16.6,22.9 and 26.2 years(p<0.05).At the same time,August-November mean temperature had a better correspondence with ENSO and PDO in the comparison of interannual and decadal scales.To sum up,ENSO and PDO may influence August-November mean temperature through their teleconnection in Changbai Mountain. |
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