More tree growth reduction due to consecutive drought and its legacy effect for a semiarid larch plantation in Northwest China

Extreme climate has increasingly led to negative impacts on forest ecosystems globally,especially in semiarid areas where forest ecosystems are more vulnerable.However,it is poorly understood how tree growth is affected by different drought events.In 2006–2009,the larch plantations in the semiarid areas of Northwest China were negatively affected by four consecutive dry years,which was a very rare phenomenon that may occur frequently under future climate warming.In this study,we analyzed the effect of these consecutive dry years on tree growth based on the data of the tree rings in the dominant layer of the forest canopy on a larch plantation.We found that the tree-ring width index(RWI)in dry years was lower than that in normal years,and it experienced a rapidly decreasing trend from 2006 to 2009(slope=-0.139 year^(-1),r=-0.94)due to water supply deficits in those dry years.Drought induced legacy effects of tree growth reduction,and consecutive dry years corresponded with greater growth reductions and legacy effects.Growth reductions and legacy effects were significantly stronger in the third and fourth consecutive dry years than that of single dry year(p<0.05),which might have been due to the cumulative stress caused by consecutive dry years.Our results showed that larch trees experienced greater tree growth reduction due to consecutive dry years and their legacy effect,and the trees had lower recovery rates after consecutive dry years.Our results highlight that consecutive dry years pose a new threat to plantations under climate warming,and thus,the effect of climate extremes on tree growth should be considered in growth models in semiarid areas.

Vegetation dynamics and its response to driving factors in typical karst regions,Guizhou Province,China

Analyzing the vegetation dynamics and its response to driving factors provides a vital reference for understanding regional ecological processes and ecosystem services.However,this issue has been poorly understood in karst areas.Taking Guizhou Province as a case study,based on the Normalized-Difference Vegetation Index of the Global Inventory Modeling and Mapping Studies and on meteorological data sets during 1982-2015,we evaluated vegetation dynamics and its response to climatic factors and human activities.We used several methods:the Mann-Kendall test,rescaled range analysis,partial correlation analysis,and residual analysis.The results are as follows:1)the mean annual Normalized-Difference Vegetation Index was 0.46 and exhibited a significant increasing trend with a variation rate of 0.01/10a during 1982-2015 in Guizhou Province.The vegetation cover showed was spatially heterogeneous:High vegetation cover was distributed mainly in the center and western margin of the study area,while the other parts of the study area mainly distributed with low vegetation cover,although the vegetation cover was higher in the nonkarst areas than in the karst areas;2)in general,the climate was getting warmer and drier in Guizhou Province during 1982-2015.Vegetation cover was positively correlated with temperature and negatively correlated with precipitation.Compared to precipitation,temperature was the dominant climatic factor impacting vegetation dynamics;3)'large-scale ecological restoration projects have obviously increased vegetation cover in Guizhou Province in recent years.The contribution of human activities to vegetation changes was 76%,while the contribution of climatic factors was 24%.In summary,compared to natural forces such as climatic factors and geographic parameters,human activities were the main factor driving the vegetation dynamics in Guizhou Province.