| The dynamic equilibrium state of carbon cycle have been destroyed by the change of global climate and the intensification of human activities,which brings a series of ecological and environmental problems that made an important effect on the survival and development of mankind.Terrestrial ecosystem carbon pool is one of the most profound and rapid change carbon pools in the earth system.Vegetation plays an irreplaceable role in maintaining global carbon balance and ecological diversity.Vegetation net primary productivity?Net Primary Productivity,referred to as NPP?as an important index and the key parameters to measure the state of carbon cycle of terrestrial ecosystem,which become one of the core contents of geography,ecology and other subjects in recent years.Wan Jiang City belt is located in the eastern section of the Asian continent,along the the Yangtze River.Subtropical humid Moist monsoon climate,moderate temperature,abundant rainfall,rich of vegetation resources.In recent years,the rapid development of economic had brought about the accelerated process of urbanization,and it has a profound influence on the vegetation,so that the vegetation NPP also occurs corresponding temporal and spatial variation.This research is based on the MODIS normalized difference vegetation index?NDVI?data,meteorological data,with the help of improved CASA model,the vegetation NPP was intimated in Wan Jiang City belt during 2000—2013.besides,with the help of linear regression analysis,correlation analysis and other methods,temporal evolution of vegetation and its response to NPP climate characteristics was explored.At the same time,based on the land use data of study area in 2000,2005,2010 and DEM data,The effect of the land use / cover change,slope,slope on NPP was analyzed.The main conclusions are as follows:?1?The annual vegetation net primary productivity of Wan Jiang City Belt showed an increasing trend during 2000 to 2013,the total annual NPP increased from35.99 TgC to 45.34 TgC.With an area of increased NPP region accounted for 79.44%of the entire study area in Wan Jiang City Belt,along the Yangtze River the NPP increased most significantly.Significant difference of the averages of NPP was found in different land use types,forest land>grassland > cultivated land > construction land > water > unused land.?2?In the past 14 years,There is a significant spatial variation of average annual NPP in the study area,mean annual NPP decreased from south to north-west and the reduce trend of the northwest is the most obvious.Increases and decreases in the inter annual variation of NPP region was concentrated in the-10 range of10 gC.m-2.a-1.?3?Cultivated land and forest land is the main land use type of Wan Jiang City Belt from 2000 to 2010 years,the land use pattern of the study area is change significantly,main show that the area of farmland,grassland and unused land were reduced,construction land and water area were increased,forestland area increased after reduction first.In the recent 11 years,the area of farm land has decrease of3.58%,the construction land is increasing,with a proportion of 2.92%;other land types relatively little change.Mainly cultivated land and construction land type conversion of land use,land and water area,cultivated land and woodland,grassland and water in between,for the construction of land,woodland,grassland and waters into cultivated land,unused land,as the main features.?4?The land using types of vegetation NPP showed significant spatial difference during 2000 to 2013,the NPP of forest was increased,grassland times,unused land NPP increased minimum.In general,during the study period The vegetation NPP in the north of the Yangtze River region showed a trend of increase gradually,While along and south of the Yangtze river region share the different changing trend which reduce the NPP of vegetation in the hilly and mountainous regions of Southern faster.?5?Temperature and precipitation are the main impact factors of vegetation NPP to the south and north of Yangtze River,On the whole,There was a significant positive correlation between NPP and annual temperature,however no significant correlation between NPP and average annual precipitation,so temperature is the main climate factor which affecting the spatio-temporal distribution and evolution of vegetation NPP in the study area.?6?The vegetation NPP with the increase of altitude,showing the first increase and then decreased space.Distribution characteristics,the regional vegetation NPP altitude less than 50 meters,the minimum altitude of 1500 meters above the vegetation NPP maximum.There was a positive correlation between vegetation NPP and slope gradient,and there was no significant correlation between slope direction and slope aspect.?7?The main reason which caused the change of vegetation NPP in Wan Jiang City belt is The construction of farmland to construction land.And with the intensification on urbanization of the region the NPP loss of vegetation caused by the conversion of cultivated land to construction land is increasing continuously.Conversion of cultivated land into waters,forestland converted to farmland,woodland conversion of land for construction purposes,the grass turn farming zone of vegetation NPP loss is relatively large. |
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