| With climate change have caused severe impacts on the social economy and ecological environment,the international community has started negotiations on global climate governance.As a major developing country with a strong sense of responsibility,China has actively launched corresponding measures in response to the rising climate issue.China has launched a number of major ecological conservation and restoration projects around the year2000,and in 2020,China set a strategic target of carbon dioxide emissions.Net carbon sequestration of vegetation,which is evaluated with Net Primary Productivity（NPP）,implies potential of vegetation to offset anthropogenic carbon emissions.NPP plays an important role in maintaining the carbon balance and regulating the carbon cycle,and it is often used to assess the carbon budget of ecosystems.Based on the validated TEC model,this study scientifically evaluated the spatial-temporal change of NPP and its major drivers in Heilongjiang Province during the implementation period of ecological protection and restoration from 2000 to 2020by using M-K,T-test,Geodetector and residual analysis method,analyzed the impacts of ecological protection and restoration projects on NPP,and quantified the effects of ecological protection and restoration in Heilongjiang Province.The results of this study further revealed the spatial-temporal change pattern and main driving factors of carbon sequestration capacity of terrestrial vegetation in Heilongjiang Province at the regional scale.These results enriched ecological restoration theory,and provided scientific reference basis for China’s future ecological environment management practices and policy making,as well as the realization of"carbon neutrality"goal.The main results are as follows:（1）The 21-year average value of annual average NPP was 602.7 g C·m-2·a-1 in Heilongjiang Province from 2000 to 2020.The average values of annual NPP significantly increased（p<0.01）.The growth rate of NPP increased significantly after 2010 and reached a new high in 2020.NPP abrupt change distributed in a phased manner and peaked in 2010.The high frequency and peak time of abrupt change were highly consistent with the key nodes of major ecological protection and restoration projects.In general,ZZ pattern（increasing trend before and after abrupt change）was the most obvious NPP abrupt change pattern in Heilongjiang Province.However,forest showed the highest proportion of FZ pattern（decreasing trend before abrupt change,increasing trend after abrupt change）indicating that the ecological restoration results were most significant in forest.After 2010,the proportion of forward abrupt changes（ZZ and FZ patterns）was leveled off,reaching 96.9%per year.At present,forest,farmland and grassland were the top three ecosystems in terms of NPP.As NPP of the farmland rose rapidly,proportion of farmland NPP to regional total NPP increased significantly.（2）From 2000 to 2020,the climate in Heilongjiang Province showed a warming and wetting trend,which improved the thermal and moisture conditions for vegetation significantly.In particular,precipitation was of obvious increase in the most parts of the province,and there was a marked rise in the average temperature in the northern part of the Great Xing’an Range.From 2000 to 2020,the area of forest,human settlement and open water in Heilongjiang province increased,among which the increase of forest area was the largest.The increase of human settlement area indicates that urbanization process in Heilongjiang province has been gradually advancing,and the speed of urbanization has been accelerated since 2010.Precipitation was the main climate factor affecting NPP,and NPP was significantly positively correlated with precipitation（p<0.01）.（3）From 2000 to 2020,the contribution rates of climate and anthropogenic impacts on the total change of NPP in Heilongjiang Province were 35.2%and 64.8%,respectively.Analysis of the driving factors of NPP change in different ecosystems showed that NPP change in the forest was dominated by anthropogenic impact.The anthropogenic impact on NPP of farmland and grassland was slightly greater than climate impact.The climate and anthropogenic impacts on NPP change were significantly increased from 2000 to 2020（p<0.01）.During 2000-2010 and2011-2020,ecological conservation and restoration directly contributed 56.8%and 33.2%to the growth of NPP,respectively.Compared with returning farmland to grassland or returning farmland to wetland,afforestation is a better ecological protection and restoration solution to promote NPP growth.The comprehensive analysis showed that NPP in Heilongjiang province was characterized by positive abrupt changes and continuously accelerated growth under the process of ecological conservation and restoration in China.On the basis of strong carbon storage,Heilongjiang Province still showed continuous enhancement of vegetation carbon sequestration capacity,and farmland carbon sequestration capacity was growing the fastest.In the future,more attention should be paid to potential and methods of agricultural carbon sequestration.The rapid growth of NPP in 2000-2020 was driven by both climate and anthropogenic impacts,and anthropogenic impacts were larger than climate impacts.Ecological conservation and restoration projects have had an important impact on vegetation NPP.It is expected that vegetation in Heilongjiang Province will have a huge potential of carbon sink and play an important role in global and regional carbon balance under the background of major ecological projects in the northeastern forest belt and global climate warming. |
