History Of Conifer Forest Health Since 1900 AD In Central Shanxi Prefecture

Forest is an important part of terrestrial ecosystem,which can provide important natural resource for human survival.The ecological value of forest is more and more important.Since twentieth Century,due to the global climate change and human disturbance caused by the occurrence of ecological interference events,the structure and function of the forest has also undergone varying degrees of degradation.Healthy forests play an important role in maintaining their regional ecosystem services,and understanding the history of tree growth has a positive role in assessing the health of forests in the context of climate change.In the present study,we report on the health conditions of eight young conifer forests by applying dendrochronological techniques to measure unexpected growth decline in Xinzhou and Changzhi and Jinzhong District in Shanxi Plateau.We established the method of regional forest health identification period using the method of dendroecology,analyzed the variation characteristics of individual trees and the spatio-temporal pattern of health the area of forest.In this paper,the relationship between tree radial growth and meteorological data was analyzed,and the causes of forest unhealthy events were discussed.A total of 134 samples in the form of increment cores were obtained from the study sites.The widths of tree-rings from all the samples were measured and cross-dated,then each individual tree series was standardized to identify health conditions using spatial characteristics of temporal growth.We defined unhealthy tree growth intervals as being a decrease in the growth of the individual(tree–ring index < 0.9)for at least five years when the mean tree–ring index was less than 0.7 and at least one year of tree–ring index values reached a minimum of 0.5.We calculated the percentage of trees that were unhealthy in each year,and defined an unhealthy event for the site if greater than 30% of the trees were in decline.We found three major unexpected decline growth events in the majority of individual trees in the four forests,these being 1910~1940,1970~1987,and 1990~2012.However,the growth declines in each forest showed deviations in intensity and duration.In 1920 s to 1930 s and 1970 to 1980 s,the health events were longest and most significant.The health event was strong performance in 1970 s in Xinzhou area,but only a few trees showed healthy growth in the Fanshi area.The health event was lag for 1980 s in Changzhi area.The health event occurred in the early twenty-first Century in Changzhi area.Three regions of the forest experienced several serious adverse events after the impact of the trees can survive the adverse environmental conditions are still alive,indicating that these forests have strong resistance or ecological flexibility.To better understand the causes of the unhealthy events,a correlation analysis was performed for the three tree ring width chronologies and the meteorological records.In Xinzhou District,the correlation coefficients showed that forest growth was negatively associated with May~June temperatures.However,precipitation revealed positive correlation in July and the Palmer Drought Severity Index showed positive correlation over the growing season of May~September.In Changzhi District,the correlation coefficients showed that forest growth was negatively associated with May~July temperatures.However,precipitation revealed positive correlation in April~June and the Palmer Drought Severity Index showed positive correlation over the growing season of April~July.In Jinzhong District,the correlation coefficients showed that forest growth was negatively associated with May~June temperatures.However,precipitation revealed positive correlation in May~July and the Palmer Drought Severity Index showed positive correlation over the growing season of April~July.To validate these results,we compared our study with historical records and local paleoclimate studies.The drought events recorded in the historical documents and other paleoclimate reconstructions reasonably matched our results.These results suggest that extreme drought events caused by persistent high temperature or reduction of precipitation in the growing season are the main driving factors for radial growth decreases in trees,which was the main reason for the spatial coherence of unhealthy events.The differentiation of local stand characteristics or tree species might play a role in the inconsistency of the time characteristics.Therefore,the present study provides useful information for forest health,which has positive and realistic significance for assessing the impact of extreme climatic conditions on the healthy growth of forests and for developing reasonable forest protection measures.