| There have been very few tree-ring studies in southeast China due to the scarcity of old trees and the complexity of relationships between tree growth and climate in subtropical regions of China.Tree rings were used in this thesis to explore the potential spatiotemporal features of temperature and precipitation variations over the past centuries with special attention paid on its linkages with the El Nino-Southern Oscillation variability(ENSO).This enables scientists and policy-makers place recent drought variations into a longer context of climate change to evaluate its severity.For this purpose,the author first collected tree-ring cores of living Pine massoniana in Zhangping,Fujian province.A series of treatment on cores were taking after bringing the cores to the laboratory:fastening,drying and polishing.Each core was cross-dated,assigning each ring to calendar years by checking the total matches of the growth patterns of the tree-ring widths.The cross-dated series were measured to an accuracy of 0.001mm using a LINTAB 6.0 measuring station.The quality of cross-dating was checked using the program COFECHA(Holmes,1983).Then the author clarified the process of the removal of age-related growth trends.The measured tree-ring series were fitted by a smoothed cubic spline curve with two-thirds of the mean lengths of each series.The detrended tree-ring indices were then averaged to produce the standard chronology following the biweight robust mean method by the ARSTAN program.It is suggested to test the homogeneity of tree rings and find tree rings with divergent growth trends or climate associations prior to the establishment of a tree-ring chronology.The 218-yr tree-ring chronology for Masson pine in the humid subtropical region of China was established and growth-climate response analyses were made.Through the correlation analysis of climatic elements of P.massoniana,it was found that there was a positive correlation between winter and spring(January-March)temperature and radial growth of Masson pine,a positive correlation between summer precipitation(July-September)with the radial growth of Masson pine.The standard chronology is employed to study the key linkages between tree growth of southeast China and the El Nino-Southern Oscillation via its correlations with sea surface temperature of Pacific and Indian oceans(SST)and the geopotential height(GPH).Although the correlations between our tree rings with sea surface temperatures(SSTs)are moderately high,the correlation pattern is very close to the correlation pattern with the El Nino-Southern Oscillation variability(ENSO).Besides,the comparisons between the El Nino(La Nina)events and winter-spring(January-March)temperatures in Yong'an station since 1954 indicated most of the years with El Nino(La Nina)events correspond to years with warm(cold)winters in the study region.These suggest that the ENSO could be the major large-scale regulator on the growth of our tree rings.The strength of the correlations between our tree rings and the ENSO matches closely with the ENSO variability during 1950-2015.The modulations of the ENSO on regional tree growth are most conspicuous since the 1950s,which corresponds to its enhanced interannual variability.In addition,positive correlations between the growth of P.massoniana with the Pacific Decadal Oscillation from January to March,suggesting a similar positive correlation between PDO with ENSO.The author further study the historical climate signals and its large-scale features,via comparing the extreme years and periods in tree-ring chronology with nearby tree-ring chronologies in subtropical and tropical parts of the East Asia.The extreme growth anomalies match quite well with the extreme years of the moisture-sensitive chronologies.The dry epoch from 1935-1958 is the most severe long-lasting drought in our tree rings,which is a widely distributed pattern in southeastern Chin and is likely modulated by the La Nina-like modes in that period. |
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