Spatio-temporal Change Of Net Primary Productivity In Guizhou And Its Correlationship With Meteorologic Factors

Net primary productivity(NPP)is a key component of the terrestrial carbon cycle,and it is defined as the accumulative organic matters by green plants per unit of time and space.NPP,the direct reflection of plant community productivity for a certain natural environment,is the basis of matter and energy cycle of terrestrial ecosystem.As highlighted during the international negotiation process for the United Nations Framework Convention on Climate Change(LTNFCCC),a better grasp upon the controls and distribution of NPP is pivotal for sustainable human use of the biosphere.In this study,time series dataset of Guizhou terrestrial NPP from GLO-PEM model and corresponding information on climate are used to explore the spatio-temporal variations from 1981-2000,and the relationship between NPP and global climatic change is comprehensively studied.From these researches,some basic conclusion are drawn as follows:(1)NPP temporal variationsThe mean NPP of terrestrial vegetation in Guizhou is 200.11TgC/yr from 1981 to 2000.The total NPP ranges from 179.13 to 239.08 TgC/yr,and the average value is 200.11TgC/yr.The seasonal variation of NPP in Guizhou is significant.The most total of the NPP is occurred in summer,it ranges from 76.40-104.40TgC/yr,and its average value is 91.18 TgC/yr;and the next is autumn,its average value is 51.70 TgC/yr;the average values of the spring and the winter are 40.00Tg C/yr and 15.00 Tg C/yr.As can be seen from the coefficient of variation,the biggest changes of coefficients variation were winter and spring,and their coefficients of variation were 17.17%and 15.09%,followed by autumn,its coefficient of variation is 9.38%,while the coefficients variation of the summer minimum is 7.42%.In the past 20 years,NPP has an increasing trend in the spring and the autumn while the summer and the wintetr have a decreasing trend.The annual NPP growth rate is 0.2999TgC/yr(R~2=0.0187).The maximum NPP value is in 1998, and the minimum is in 1991.5-annual,and decadal growth are also very obvious.(2)NPP spatial variationsThere are clearly strong regional variations in Guizhou terrestrial vegetation NPP.It decreased from Southeast Guizhou toward the northwest.Regions of higher productivity are found in the south,whereas the city of Zunyi and the district of Bijie have very small NPP values.There are great regionaldifferences in the NPP growth rate,though the total NPP of the whole province an increasing trend in the recent 20 years.Most of the province has an increasing trend in vegetation NPP.The relative mean NPP growth rate of the whole province to 1981 is 0.80%.The highest growth rate is mainly in the middle of Guizhou,including Qianxi,Xiuwen,Fenggang,Meitan and Yuqing et.al.,with the values above 6%,whereas the west and the south of the Guizhou province have a decreasing trend,including Haozhang,Shuicheng,Panxian,Dushan and Libo et.al., with the values below-5%.The seasonal variation of NPP in Guizhou is obvious,the difference of the NPP values is also significant.In general,the variations of the southern and the eastern part compared with those of the northern and western part were more significant.(3)Temporal and spatial pattern of climatic factorsMost regions of the province have a temperate climate.Plateau-climate or warmth climate exists only in few areas including high altitude plateau or low-lying valley.Most parts of the province including the mid,the northern and the southwestern part are with an average annual temperature between 14 and 16℃,while other parts such as low-lying valley of the edge of the southern part and Chishui valley of the northern part are with an average annual temperature ranging from 18 to 19℃,and that of the low-lying valley of the eastern part and the northwestern part are with an average annual temperature between 16 and 18℃and between 10 and 14℃, respectively.It is abundant in rainfall here,however,it is not uniform in the space-time.Most areas of the province have an average annual precipitation between 1100 and 1300 mm with extreme values of 1400 mm and 850 mm.(4)Correlation between NPP and climatic factorsThrough the analysis on the correlation between NPP and climatic factors(temperature and precipitation),it can be seen that their relationship is relative strong within inter-annual changes, and weak within annual changes.It seems that the influences of climatic changes on NPP in Guizhou is so complicated that it is very hard to design a general function model to simulate them quantificationally in spatial and temporal patterns,and only could depict their relation in a qualitative method.