Forest Carbon Sink Evaluation Based On New Indicators

In recent years,with the increasing concentration of greenhouse gases,the global climate change problem has become more and more serious,disrupting the balance of the earth's ecosystem.The carbon sequestration function of forest ecosystem can effectively alleviate global climate change and is an important guarantee for the ecological balance of the earth.However,when evaluating the forest carbon sequestration benefits,the carbon reserve as the evaluation index cannot reflect the additional benefits brought by the carbon sequestration time,and the forest management decision cannot be combined with the life cycle of wood forest products.Therefore,this study proposed a more comprehensive science of carbon sequestration benefits indicators—ton-year,defines ton-year in considering the number of forest carbon sequestration and carbon sequestration time of forest carbon sequestration benefits measure,its mathematical meaning for several years of carbon sequestration forest carbon amount multiplied by the parts are fixed number of years of accumulation,such as If the stand holds 1 ton of carbon for 1 year,it is 1 ton-year.If one ton of carbon is fixed for 10 years or 10 tons of carbon is fixed for 1 year,both are 10 ton-year.Comparing the carbon storage,the extra benefits brought by the carbon sequestration time are comprehensively considered in ton-year.By organically combining the measurement of forest carbon sequestration benefits with the life cycle length of forest products,the carbon sequestration benefits can be considered as well as the economic benefits,so as to provide more scientific and effective guidance for the management and production practice of plantations.This study took Guangxi zhuang autonomous region as the research sites and chose Cunninghamia lanceolata and Eucalyptus robusta Smith as the research object.The calculation is based on the survey data of category I in the three periods of 2005-2015 and some data of field survey and measurement in Guangxi autonomous region.Based on the standard land division of each forest farm,295 Cunninghamia lanceolata sample plots and 481 Eucalyptus robusta Smith sample plots were used as modeling and test data.The specific research conclusions are as follows:(1)On the basis of the data,compare four kinds of commonly used the theory of growth equation,respectively by the nonlinear least squares method for fitting,screening for optimal growth of Cunninghamia lanceolata and Eucalyptus robusta Smith,equation respectively Gompertz and Richards model,through the independence test,conform to the requirements of the prediction precision,each equation as the basis of predicting stand growth.(2)Based on the hypothesis of bare land afforestation,the growth curves of each tree stand were simulated,the carbon sequestration amount of each stand period was calculated by biomass factor conversion method,and then the carbon sequestration benefit value described by the new index "ton-year" was calculated..The study found that in the prediction period of each tree species,if the subsequent wood forest products were not considered,the annual growth rate of forest tons would continue to increase when the stand growth rate gradually leveled off to no longer increase,and no peak occurred.At this time,the harvest time should be delayed as much as possible for greater carbon sequestration benefits.(3)After the addition of forest product carbon pool for analysis,with the improvement of forest product life cycle level,stands showed an increasing trend of annual average ton per year,and began to show a peak in the forecast period,The mature age of stands also decreased with the increase of life cycle level.Taking Cunninghamia lanceolata as an example,when the life cycle of forest products was extended from 40 years to 60 years,the maximum annual mean tonnage per hectare of Chinese fir plantation increased from 67.82t·a to 85.81t·a,and the maturity age of stand carbon sink decreased from 48 years to 34 years.When the life cycle of forest products is extended to 300 years,the maximum annual growth rate of Chinese fir plantation is 335.23 t·a and the maturity age of stand carbon sink is 27 years,which is close to the maturity age of quantity.The causes of this phenomenon is to consider as a carbon sink forest products,with the constant improvement of the level of forest product life cycle,which provide the carbon sequestration benefits are also increasing,when the forest products take up of the total carbon sequestration forest carbon sequestration benefits ratio rose to a certain extent,shorten the rotation period to get more wood products continue to carbon is the best solution.(4)Compared with Cunninghamia lanceolata and Eucalyptus robusta Smith,the annual ton-year index of stand tonnage increased with the growth of forest age,but the change of Eucalyptus robusta Smith was sensitive.For example,without considering the follow-up forest products,when the forest age increased to 20 years,the average annual ton per hectare of Eucalyptus robusta Smith plantation was 98.31t·a,while that of Cunninghamia lanceolata was only 11.32 t·a.Eucalyptus robusta Smith is also sensitive to the life cycle of forest products.For example,when the life cycle of forest products was extended to 40 years,the mature age of carbon sequestration of Eucalyptus robusta Smith decreased to 5 years,which was the same as the mature age of Eucalyptus robusta Smith(5a),while the mature age of Cunninghamia lanceolata carbon sequestration was 48 years,which was still somewhat different from the mature age of Cunninghamia lanceolata(26a).However,the annual ton-year value of Eucalyptus robusta Smith was larger at different life cycle levels of forest products.The results showed that in terms of carbon sequestration efficiency,Eucalyptus robusta Smith> Cunninghamia lanceolata.The tree species with high growth rate and short growth cycle have some advantages,but they are also affected by other factors such as biomass conversion coefficient and wood density.