Forests Response To Drought Over The Yunnan-Guizhou Plateau

Forests,the main body of terrestrial ecosystem,is one of mankind's most important resources.However,the environmental changes caused by drought,such as forest decline,tree mortality and changes in community composition,have a profound impact on the sustainable development of human society.Determining how climate change is affecting forests and the relationship between climate and forests is therefore critically important to understand the impacts of climate change on forests,inform their management,and ensure the protection of forests.The forests on Yunnan-Guizhou Plateau(YGP),the largest natural and economic forest region in China,undertakes multiple ecological functions,such as water regulation and conservation,biodiversity maintenance,as well as social and economic functions such as forestry,poverty alleviation and prosperity.It is extremely important for maintain the security of our national ecological and the stability and prosperity of regional society.On the other hand,with one of the largest exposed carbonate rock areas in the world,YGP forests were considered climate-sensitive and climate-change vulnerable karst ecosystem and may be particularly sensitive to increasing temperatures and drought.However,little is known about how forests respond to climate change over Yunnan-Guizhou region.Tree ring data has been extensively used as an ideal proxy for study interactions between forest ecosystems and climate.By using tree rings,we can obtain information about past forest changes,thereby providing clues for predicting future forest changes.Here we use a large–scale tree–ring data networks along broad climate gradients offer a great opportunity to explore the effect of past and future droughts on forest growth in the region.We explored the ecological significance by tested the drought sensitivity and how the resilience of forests to drought along different regions,elevation,species,as well as different geomorphic environments,respectively.The main contexts and conclusions of this study are summarized as follows:(1)We studied the relationship between the radial growth of 28 chronologies and climate elements in Yunnan-Guizhou region.We show the dominant role that moisture conditions during the dry season(October to May)play in regulating tree growth in large portions of subtropical forests in this region.We found that contrary to expectations,drought,rather than winter or spring temperatures,exerted the strongest limitation on forest growth.This was consistent across species and environments and related to large-scale climate variability.(2)By testing the drought sensitivity and how the resilience of forests to drought along different regions,elevation,species,as well as different geomorphic environments,respectively.We found stronger drought sensitivity under more arid conditions,that is,the drier the environment,the stronger the tree growth was affected by drought.This large-scale tree growth-climate mechanism is consistent across different longitudinal and elevational.We also found forests in karst areas are more vulnerable to drought,indicated different drought-response mechanisms.On the other hand,we found no evidence that supported a strong role of tree species differences in arid environment,while a stronger species independent effects in a more humid environment,which further indicated that climate was generally more important than species in dry environment while reverse effects in humid environments.Our results indicate further increases in drought frequency and dry season drought intensity in the region associated with climate change may pose a larger-than-expected threat to the growth,and ultimately persistence,of many subtropical coniferous forests,especially forests in Western YGP and Karats environment.In addition,as forest response to drought is associated with moisture availability,future changes in precipitation may causing widespread changes in forest productivity.(3)We explored the relationship of tree mortality and climate change and the underlying mechanism of drought-induced mortality in two endangered species,we show that the recent increase in water stress is likely the main trigger for the unprecedented decline in radial growth and spike in mortality of both F.hodginsii and Pinus kwangtungensis,which may have resulted from diminished carbon fixation and water availability.However,climate change has different effects on different types of forests.For forests in no-karst environment,drought has more serious impacts on old trees of those less drought-tolerant species that are difficult to cope with a dryer climate.As a comparison,drought has a more serious impact on young trees,which have not yet adapted to karst environment.The results indicated that forest in karst environment with species richness and humid subtropical environment had a stronger resilience to drought,while the karst forests are more vulnerable to drought.(4)In addition,we studied the relationship between radial tree growth,climate,as well as atmospheric circulation at a regional scale,our study indicates that the radial growth of YGP forests is generally stimulated by climate anomalies(lower water deficit during dry season)negatively associated with NINO3.4 index.Moreover,the results also demonstrate that the negative radial growth response to El Nino is significantly strengthened from east to west in the YGP,which could be attributed to tree growth impaired more from the El Nino-related water deficit in western habitats which are traditionally warmer and drier than the east.The study reveals a large-scale climate-tree growth mechanism that El Nino affects the growth of trees by affecting the changes in regional precipitation.