Relationship Between Climate Change And Tree Growth At Huoditang Forest Region In The Qinling Mountains

As one of the main terrestrial ecosystems, forest ecosystem plays a vital role in adjustingglobal carbon balance. The Qinling Mountains, as the geographical boundary of the southernand northern part of China, are mainly constituted by forest ecosystems and are sensitive tothe climate change. We select the Huoditang forest region located on the south-facing slope ofthe Qinling Mountains as research area. We selected Pinus tabulaeformis, Abies fargesii andPicea wilsonii forests as research objects. Based on the principles of dendrochronology, treering width chronologies were constructed and the relationship between the climate change andradial growth of the three tree species were analyzed. At the same time, plots were establishedin the secondary natural forests of P. tabulaeformis and P. armandi along the altitudinalgradient. By using tree-ring method and regression equations between the diameter at breastheight and the height, the annual biomass and Net primary productivity （NPP） of tree layer ofP. tabulaeformis and P. armandi forests were calculated. Then correlation between climatechange and the NPP of the tree layer were analyzed to explore the relationship between theclimate change and NPP, and to reveal the relationship between tree growth and climatechange so that to provide references for forest management under climate change. The mainresults are as follows:（1） A relatively consistent dynamic trend was found in the biomass and NPP of the P.tabulaeformis and P. armandi forests. The biomass of the tree layer increased dramatically inthe past39years from15.32t hm^-2and7.53t hm^-2to175.97t hm^-2and130.98t hm^-2,respectively, the volume increased from19.46m³Â·hm^-2and4.79m³Â·hm^-2to210.18m³Â·hm^-2and179.92m³Â·hm^-2and the mean annual NPP were4.18t hm^-2 a^-1and3.20t hm^-2 a^-1respectively. Higher biomass and NPP of the tree layers were found in P. tabulaeformis standscompared to those of P. armandi stands.（2） From1973to2011, the biomass and volume of the tree layer in P. tabulaeformis andP. armandi forests at all the three altitudes grew dramatically. At the altitudinal gradient from1550m to1650m the biomass and volume of P. tabulaeformis forest remained the highest,while those of P. armandi forest appeared the highest from1850m to2000m compared withthe other two altitudinal gradients; at the optimal altitudinal gradient, the biomass and volumeof the tree layer in P. tabulaeformis forest increased from44.40t hm^-2and54.98m³hm^-2in1977to214.67t hm^-2and237.50m³hm^-2in2011and those in P. armandi forests increased from16.74t hm^-2and25.20m³hm^-2in1977to182.75t hm^-2and225.14t hm^-2respectively;A consistent dynamic of the NPP of the forests at different altitudes were observed. Theconsistent dynamics observed among the productivity of the same tree species along differentaltitudinal gradients may partly owe to annual variations of climatic factors.（3） No significant correlation was observed between the NPP and monthly and seasonalprecipitation; in contrast the NPP was closely correlated with the monthly and seasonaltemperature. Among the monthly temperature factors, the temperature in July of the previousyear correlated positively with NPP for P. tabulaeformis and P. armandi forests. Also thetemperature in the current July correlated with NPP in the same year in P. tabulaeformisforests. Among the seasonal temperature factors, a significant coefficient was observedbetween the NPP of P. tabulaeformis forests and the mean temperature from January to July. Asignificant coefficient was observed between the NPP of P. armandi forests and the meantemperature from May to July; higher coefficients were found between the NPP of andclimatic factors in P. tabulaeformis forests than that in P. armandi ones. The difference in thebiomass and productivity between two kinds of forest types are due to their differentbiological characteristics.（4） All the tree species studied had apparent ring boundaries, few absent rings and wereavailable for cross-dating. All the chronologies showed a high mean sensitivity andinter-series correlation; the quality of residual chronology was superior to stand chronologyfor all the three tree species. The best chronology quality of P. tabulaeformis was observed,which was followed by A. fargesii and P. wilsonii. Different tree species showed differentrelationship with the climate change. The radical growth of P. tabulaformis was mainlyimpacted by the average temperature and total precipitation of the current May and June. Thedecrease in the soil moisture due to high temperature in the early growth season may be themain limiting climatic factors to the radical growth of P. tabulaeformis. The radical growth ofA. fargesii was not only significantly correlated with temperature of the current May to June,but also greatly affected by the monthly temperature and precipitation of August in theprevious year; P. wilsonii was least sensitive to the climate change among the three species.Among the climatic factors, the monthly temperature and precipitation of August most greatlyaffected the radical growth of P. wilsonii, which indicated the lag effect of climate change onthe tree growth. The temperature and precipitation of the end of growth season in the previousyear could greatly affect the radical growth in the next spring and growth season by affectingnutrient storage in the tree.