| The upper reaches of the Minjiang River Basin is located in the northwest of Sichuan Province,China.It is the transition zone between the Western Sichuan Plateau on the east edge of the Qinghai Tibet Plateau and the Sichuan Basin on the second step of the topography.The topography is complex and geological disasters occur frequently.The upper reaches of Minjiang River is one of the most important water sources in Chengdu Plain,and it is also an important ecological barrier in Sichuan Province and even in Southwest China.In recent years,the vegetation growth in the upper reaches of Minjiang River is slow and the ecological environment is relatively fragile,while natural disasters and climate change aggravate the instability of the watershed ecosystem and affect the normal realization of the watershed ecological function.Therefore,in the face of the severe ecological situation in the upper reaches of Minjiang River,there is an urgent need for effective methods to monitor the ecological environment changes in various regions of the basin.The net primary productivity?NPP?of vegetation is an important index to evaluate the structure and function of terrestrial ecosystem.The study of NPP can provide scientific basis for the management of ecological resources,reconstruction and maintenance of ecological environment,and is of great significance to the sustainable development of river basin.Based on remote sensing data,meteorological data and vegetation data,this paper uses CASA model,linear regression method,coefficient of variation method,vegetation damage and recovery evaluation method,correlation analysis method and GIS?Geographic Information System?technology to respectively carry out the simulation estimation,spatiotemporal dynamic analysis and response to climate change of vegetation NPP in the study area.At the same time,the damage and restoration of NPP were evaluated in Wenchuan County,the earthquake center of the study area.The main work of this paper is as follows:?1?The vegetation NPP in the upper reaches of Minjiang River from 2001 to 2015 was estimated by CASA model,and the accuracy of the model was tested.According to the estimated results,the annual average NPP of the upper reaches of Minjiang River in the past 15 years is 422.56 gC·m-2·a-1,of which,nearly half of the vegetation NPP is distributed in the range of 400-600 gC·m-2·a-1.There are some differences in NPP of vegetation in different areas,among them,Mao county has the highest annual NPP,while Wenchuan has the lowest annual NPP.The area of Songpan county is almost twice that of other counties,so the annual contribution of Songpan county to the NPP of vegetation in the upper reaches of Minjiang River is the largest.Among the nine vegetation types,the average annual NPP of typical evergreen broad-leaved forest is the highest;the distribution of shrub forest is the widest in the study area,and the total annual NPP is the largest.?2?The annual average NPP of vegetation in the upper reaches of Minjiang River from 2001 to 2015 was calculated and analyzed.From the change trend,the average growth rate of NPP of vegetation in the past 15 years was 2.03 gC·m-2/10a,and the overall growth trend was relatively slow.NPP of vegetation also has a certain relationship with weather change.Due to the increase of temperature and precipitation,the total NPP of vegetation in summer is the highest;on the contrary,the total NPP of vegetation in winter is the lowest in four seasons.?3?The coefficient of variation of NPP in the upper reaches of Minjiang River in the past 15 years was calculated by the method of coefficient of variation.According to the distribution results,the areas of severe variation are mainly in Wenchuan County.The spatial variation trend of NPP in the upper reaches of Minjiang River in the past 15 years was calculated by linear regression method.From the distribution map,the area with NPP increasing trend is about 1.25 times of the area with NPP decreasing trend.At the same time,the regional distribution of NPP increased to the north and decreased to the south.?4?In 2008,the Wenchuan earthquake damaged the local ecological environment.Using the algorithm of damage rate and recovery rate to calculate the NPP damage and recovery progress of vegetation in Wenchuan County,the earthquake center in the upper reaches of Minjiang River.According to the damage situation,some areas with high altitude in Wenchuan County are not affected by the earthquake damage,while the seriously damaged areas are mainly concentrated in the epicenter area.In 2010-2012,the recovery of vegetation NPP in Wenchuan County was relatively slow;in 2013-2015,the recovery of vegetation NPP in Wenchuan County was more than two-thirds of that in Wenchuan County,and the overall recovery progress was relatively ideal.?5?Correlation analysis was used to analyze the correlation between NPP and climate factors.On the multi-year scale,the relationship between NPP and precipitation in the upper reaches of Minjiang River is closer than that of temperature.Among them,the NPP of Songpan,Wenchuan and Li counties has a higher correlation with precipitation,and the NPP of Mao county and Li county has a closer relationship with temperature than other regions.On the annual scale,the correlation between vegetation NPP and precipitation is higher than that between vegetation NPP and temperature,and both are negative correlation. |
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