Research On The Difference Of Urban And Rural Vegetation Productivity Under The Background Of Urbanization

Vegetation plays an important role in improving urban environment and improving the physical and mental health of residents.In the process of rapid urbanization,the increase of impervious surface area reduces urban vegetation coverage,changes terrestrial carbon storage and flux,and affects ecosystem function.there are various factors affecting urban vegetation growth.Local environmental changes such as the urban heat island effect and human management may create conditions that are more suitable for vegetation growth in cities than in rural areas.For example,cities have more comprehensive vegetation management and landscape planning,including irrigation,green belt construction,and urban landscape vegetation.The city has a certain human-dominated recessive features,which enhance the ability of urban vegetation to resist natural disturbances,and urban vegetation in open green areas dominates urban vegetation,resulting in vegetation growth in urban areas showing different characteristics and growth patterns.Since the end of the 20th century,China has experienced an unprecedented rapid urbanization process.At the same time,a number of vegetation construction and ecological protection projects have been formulated.which Effectively analyzing and quantifying the impact of urbanization on the growth and changes of vegetation are of great significance to promote ecological civilization city construction and urban planning.This study took 34 major cities in China as the research area,analyzed the urbanization of different major cities and the temporal and spatial characteristics of gross primary production（GPP）of vegetation from 2000 to 2018,analyzed the differences of the fluctuation changes for GPP in urban and rural areas,quantified the impact of urbanization on vegetation GPP,and explored the differences in the impact of climate change and human activities on GPP.This study mainly obtained the following conclusions:（1）From 2000 to 2018,the urban area,impervious surface coverage（ISC）,and GPP of the study area all showed an overall upward trend.Temporally,the urban area of the 34 major cities increased by 29,846 km²,the average ISC increased by 13.25%,and the average GPP increased by 211 g C m^-2 between 2000 and 2018.There was a trend of significant increase in ISC in the urban centers for most major cities,while due to the large amount of vegetation loss caused by land use conversion,there was a trend of significant decrease in GPP in the urban expansion areas.（2）This study divided the study area into urban area（Urban area,UA）and rural area（Rural area,RA）by defining the urban-rural boundary.There were differences in the fluctuation of vegetation GPP between UA and RA from 2000 to 2018,and the fluctuation of GPP in UA was generally lower than that in RA,indicating the special of urban areas,and this special environment promoted the growth of vegetation.Based on an continue fluctuation calculation method,this study quantified the fluctuation changes of GPP in UA and RA.The results showed that there were obvious fluctuation differences in GPP between UA and RA.On the whole,the GPP in UA showed a steady upward trend relative to that in RA,which further indicated that the UA had a suitable environment for vegetation growth.（3）There is an indirect effect of promoting vegetation growth during the process of urbanization,and this indirect effect in 2018 is higher than that in 2000.The changes of the urban environment and the human management and protection along with the urbanization process promote the growth of urban vegetation,which can offset the direct effects caused by land use changes.This growth offset increased from 4.96%in 2000 to 12.35%in 2018.In particular,the growth offset for GPP in the areas with high middle and high ISC proportion was high,while the growth offset in the areas with very high ISC or very low ISC was low;the impact of urbanization on vegetation varied in different years,which is mainly due to the process of urbanization.（4）Climate change and human activities promoted the growth of vegetation,and the contribution rate of human activities to vegetation change in UA was higher than that of climate change.In this study,air temperature,precipitation,reference evapotranspiration,and actual evapotranspiration were used as climate factors to characterize climate change,and the differences in the contribution of climate change and human activities to vegetation in UA and RA also were analyzed.The results showed that there was a large difference in the contribution rate of climate change and human activities to vegetation in UA during the process of urbanization.Overall,the contribution rates of climate change and human activities to GPP changes were 49%and 51%in UA,respectively;and the contribution rates of climate change and human activities to GPP changes were 76%and 24%in RA,respectively.With the urbanization,the vegetation change in UA was mainly affected by the joint positive effect of climate change and human activities,and the contribution rate of human activities to vegetation is slightly higher than that of climate change,especially in cities with rapid urbanization.Therefore,during the process of rapid urbanization in China,along with the expansion of the urban impervious surface,along with urban climate change and human activities,the overall primary productivity of urban vegetation has shown positive changes,which further illustrates the effect of ecological civilization city construction.Significantly,these study results have implications for the planning and development of other cities in China.