Response Of Aboveground Biomass Of Cupressus Funebris To Land Use Dynamics In Hilly Region Of Central Sichuan

With the increasingly serious problem of global warming,carbon emission reduction has become an important topic in international climate negotiations.As a terrestrial carbon sink,forest plays an important role in regulating the carbon cycle.Rapid and accurate estimation of forest biomass and carbon storage is of great value for understanding the carbon sink capacity.Since the 20th century,the impact of land use on climate change has attracted the attention of scholars from all over the world.Drastic land use change has an important impact on forest biomass and carbon stock.Revealing the impact of land use change on forest biomass and carbon stock is of great significance for improving the function of carbon sink and realizing the goal of carbon sink.In this paper,the biomass model method was used to estimate the biomass of C.funebris at plot scale and regional scale,and its dynamic changes were analyzed.Land use change amplitude,dynamic attitude,transfer matrix and comprehensive degree of land use were used to analyze land use change.The effects of land use change on biomass of C.funebris were studied by using spatial econometric model.The main results were as follows:（1）The biomass model of individual wood was established according to the measured data of 55 different places of C.funebris.By comparing the fitting effects of different models,the highest goodness of fit of each part was obtained as a power function.The models of above-ground biomass（y₀）,trunk biomass（₁y）,branch biomass（y₂）and leaf biomass（y₃）were respectively:y₀（28）0.728D^1.558,y₁（28）0.334D^1.735,y₂（28）0.121D^1.578andy₃（28）0.203D^1.322.The nonlinear error variable model method was used to study the compatible biomass model of C.funebris per plant in the study area.The relevant parameters₀c,₀b,₁a,a₂,₃a,a₄ were 0.3068,2.037,0.752,0.783,0.215 and 0.197,respectively.Based on the biomass model of individual trees,the volume compatibility model was established,and the biomass changes of C.funebris were analyzed from the sample plot scale and regional scale.The volume compatibility model was expressed as:B（28）1.013V^0.928.（2）At the plot scale,the biomass of C.funebris showed an overall increasing trend from 2007 to 2017,and the biomass differences among plots increased.At the regional scale,the area of C.funebris forest increased by 0.08×10⁴hm²,the stock of living wood increased by 0.78×10⁶m³,and the aboveground biomass of C.funebris increased by0.65×10⁶t from 2007 to 2017.（3）At the plot scale,the cultivated land area changed obviously from 2007 to 2017,and the number and area of patches both showed a decreasing trend.Other forest land area,C.funebris forest area,water area and construction land area showed an increasing trend.In 2017,the number of land classes increased significantly,the fragmentation of landscape intensified,and the transformation of cultivated land classes to other land classes was significant.At the regional scale,from 2007 to 2017,the proportion of arable land decreased from 87.36%to 84.80%,the proportion of other forest land increased from6.54%to 6.77%,the proportion of C.funebris forest land increased from 2.93%to 2.98%,and the proportion of water area increased from 1.73%to 1.85%.The proportion of building area and unused land area changed from 1.42%and 0.02%to 3.59%and 0.02%respectively.（4）At the plot scale,the cultivated land landscape pattern analysis showed that the biomass of C.funebris was significantly correlated with the changes of maximum patch index,landscape shape index and patch aggregation degree（P<0.01）.It was significantly correlated with the changes of patch number and the proportion of patch in landscape area（P<0.05）.There was no significant correlation with patch density.The biomass of C.funebris was positively correlated with the changes of patch number and landscape shape index,but negatively correlated with the changes of maximum patch index,the proportion of patch in landscape area and the degree of patch aggregation.At the regional scale,grid units were constructed using the vector data of the study area,and the biomass of C.funebris was analyzed by the global Moreland index.It was found that the spatial distribution of C.funebris biomass had a certain spatial correlation.Through the study of local Moreland index,it was found that the biomass of C.funebris had obvious aggregation effect in spatial distribution.Based on the autocorrelation results,a spatial econometric model was established,and the spatial error model was determined to be the most suitable model for the biomass and land use change of C.funebris by comparing the fitting degree of the models.According to the results of the model,the dynamic attitude of cultivated land and C.funebris forest was positively correlated with the change of C.funebris biomass,the dynamic attitude of water area and construction land was negatively correlated with the change of C.funebris biomass,and the comprehensive index of land use was negatively correlated with the change of C.funebris biomass.