Study On The Carbon Sequestration Effect Of Forests In Guangxi Under The Background Of Ecological Restoratio

With the implementation of comprehensive management of large-scale stone desertification in karst areas and national ecological restoration projects,karst areas in southwest China have become one of the world’s fastest growing areas in terms of vegetation cover and above-ground biomass,and are expected to become a potential area for China to lead in achieving the great goal of carbon neutrality.However,there is considerable uncertainty in current studies’biomass estimations,particularly in the geologically complicated environment of the southwest,where there is an obvious issue of underestimating the substantial carbon sinks of afforestation.As a result,studies on the accurate estimation of above-ground biomass in southwest forests,as well as the assessment of carbon sequestration effects under ecological restoration,have become an urgent need that can provide scientific guidance for future ecological management,carbon neutrality,and forest management,have become an urgent need.Based on field measurements,forestry inventories and multi-source remote sensing data,this study uses three basic methods(multiple linear regression,random forest and support vector machine)to construct above-ground biomass estimation models for different forest types(planted eucalyptus forests,planted coniferous forests,natural coniferous forests and natural broad-leaved forests)by integrating forest age and remote sensing information,and further obtained the optimal estimation model through integrated learning.The above-ground biomass of the forests in the study area is estimated using the optimal model,and key information on carbon stock,carbon density,and carbon sequestration rate in the study area at different times is extracted to quantify the carbon sequestration effect and potential of forest vegetation restoration in Guangxi.The following are key findings:(1)The inclusion of stand age information and integrated learning may considerably enhance the accuracy and minimize the uncertainty of forest above-ground biomass estimate.Of all input parameters,forest age contributed the most to predicted biomass.For diverse stand types,the incorporation of stand age leads in a maximum improvement of 0.27 in R~2and a maximum decrease of 47.47%in RMSE for above-ground biomass estimate accuracy.Model integration results in a 0.02-0.03improvement in estimated R~2and a 5.20%-14.89%decrease in RMSE.(2)The carbon sequestration capability of Guangxi’s forests has continuously grown between 2005 and 2015.The average carbon density and carbon storage rise by 0.77t/ha and 11.17Tg per year on average.And this increase is more obvious after 2010 due to the expansion of the integrated rock desertification management area and further promotion of ecological engineering in the later years.Carbon density is high in the west and low in the southeast,and the number of similar components with high carbon density values is growing,particularly in Baise City,where the advantages of stone desertification management are spectacular.(3)The carbon sequestration capacity of forests in karst areas is lower than that of forests in non-karst areas due to geological constraints,but the implementation of ecological projects has increased the carbon sequestration capacity of forests in karst areas more rapidly,and the gap between regional average carbon densities has gradually decreased.The average rate of carbon sequestration in broadleaf forests of the same age group was higher in karst areas than in non-karst areas.The rate of carbon sequestration was higher in limestone areas than in dolomite areas for all forest types except planted eucalyptus forests;among the different project areas,the ecological management of the crested depressions was the most effective,and the rate of carbon sequestration was higher in the project areas for all forest types except planted coniferous middle and young forest stages.(4)The carbon sequestration capacity of the forests in the research region is often highest in middle-aged forests,and the rate of carbon sequestration rises independently with forest age,then progressively falls after reaching the peak state.The rate of carbon sequestration varies significantly across forest types,with the rate of carbon sequestration in planted eucalyptus forests gradually decreasing with increasing age and tending to zero,with the rapid period of carbon sequestration occurring in young forests;the rate of carbon sequestration in planted coniferous forests tends to decrease first and then increase in stages.The rate of carbon sequestration in natural coniferous forests increases unilaterally with increasing age and then decreases,with the peak occurring around 20 years of age;and Natural broadleaf forests grow gradually until they reach maturity,with peak depressions showing the most growth.(5)The average rate of carbon sequestration in Guangxi’s forests is negatively correlated with changes in the composite index of stone desertification,changes in the nighttime light index,and changes in population density,and the average rate of carbon sequestration in areas with improved stone desertification is higher than that in degraded areas.The effective management of rock desertification has significantly contributed to the recovery of regional forests and thus to the enhancement of carbon sequestration capacity.