Prediction Of Carbon(C) Sequestration Capacity Of Secondary Forest And Its Contribution To C Neutrality In Subtropical China

The area of natural secondary forest in China is 74.5604 million hectares,accounting for 41.45%of arbor forest.It plays a very important role in carbon cycle and mitigating climate change.The subtropical region has superior hydrothermal conditions,diverse types of secondary forests,complex stand structure and fast forest growth.Evaluating the carbon storage and NPP of subtropical secondary forests,simulating and predicting the response of forests to future climate change can provide a scientific basis for improving the carbon sequestration and sink enhancement capacity of subtropical secondary forests,realizing carbon neutralization and mitigating climate change.On the regional scale,forest survey data,models and remote sensing are usually used to study forest carbon storage and NPP,but the response of carbon storage and NPP of different secondary forests in the subtropical zone to stand growth and development(forest age)and future climate change is not clear.Therefore,based on the objectives of peak CO2 emissions and carbon neutralization,this study simulates and predicts the variation law of carbon storage and NPP of subtropical secondary forests with forest age,analyzes the response differences of different secondary forests to climate change,and defines the carbon sequestration capacity of different forests in 2030 and 2060 under different climatic conditions,The contribution of different forest types to carbon sequestration was evaluated,and the spatial distribution of carbon storage and NPP in secondary forests was studied.Main research results:1)The TRIPLEX 1.6 model was parameterized with the data of 1/3 of 875 survey plots,and the simulated and measured values were compared to verify the simulation effect of the model.According to the R2 of DBH(R2=0.966,p<0.001),stand density(R2=0.996,p<0.001),carbon storage(R2=0.874,p<0.001)and NPP(R2=0.942,p<0.001),the predicted value is significantly correlated with the observed value.It is proved that TRIPLEX 1.6 model is effective and reliable for the simulation of subtropical secondary forest.2)The carbon storage of the four subtropical secondary forests increased with the forest age,and the mature forest and over mature forest had higher carbon storage capacity.The NPP of coniferous and broad-leaved mixed forest increased first and then remained stable over time;The NPP of deciduous broad-leaved forest,deciduous and evergreen broad-leaved mixed forest and evergreen broad-leaved forest increased first and then decreased.In 2060,the carbon storage of evergreen broad-leaved forest was the largest among the four secondary forests,which was 135.76 t C ha-1;The NPP of evergreen deciduous broad-leaved mixed forest is the largest,which is 3.81 t ha-1 yr-1,with the highest carbon fixation rate.3)Under the two future climate scenarios(rcp4.5 and rcp8.5),the growth rate of carbon storage of subtropical secondary forest in 2030 is 1.94%～21.98%,and the growth rate of carbon storage in 2060 is 3.23%～14.87%,indicating that the impact of future climate change on carbon storage of subtropical secondary forest is limited in the medium and short-term time scale.Among them,the NPP of coniferous broad-leaved mixed forest and evergreen broad-leaved forest is more stable and less affected by climate change;The carbon storage of coniferous and broad-leaved mixed forest is also significantly lower than that of deciduous broad-leaved forest,evergreen deciduous broad-leaved mixed forest and evergreen broad-leaved forest.4)In 2030,the average NPP of secondary forest will be 3.54 t ha-1 yr-1 and the average carbon storage will be 65.74 t C ha-1;In 2060,the average NPP of secondary forest is 3.54 t ha-1 yr-1,and the average carbon storage is 113.71 t C ha-1.According to the forest area of different secondary forests in Hunan Province in 2014,evergreen broad-leaved forest contributed the most to carbon sequestration among the four secondary forests.The spatial distribution of carbon storage and NPP showed a gradual increase trend from the northern Dongting Lake plain to the southeast mountainous high-altitude area,and the central Hunan hilly area to the western mountainous high-altitude area.The carbon storage of secondary forests in Xuefeng mountain in the south of Western Hunan,Wuling Mountain in the northwest of Hunan and Nanling Mountain in the southeast of Hunan is the highest.The change of secondary forests in these areas plays a very important role in increasing the capacity of regional carbon sequestration and sink.This study analyzed the change trend of carbon storage and NPP of different secondary forests with forest age,and compared the response differences of carbon storage and NPP of each secondary forest to climate change.Based on the carbon neutralization target in 2060,the carbon sequestration capacity and regional spatial distribution pattern of subtropical secondary forest are quantified,which provides a scientific basis for the restoration of subtropical secondary forest,the improvement of quality and carbon sink capacity,and forest management.