Spatial Pattern In Aboveground Biomass Of The Mid-subtropical Evergreen Broad-leaved Forest In The Gutianshan Reserve And Its Causative Factors

Chinese subtropical evergreen broad-leaved forests have unique features of climate,species composition and structure,thus is good ecosystems for studying the determinants of biomass variation.Forest above-ground biomass(AGB)is an important part of the forest ecosystem biomass,it is the most dynamic carbon pool in the forest ecosystem.It accounts for a large proportion of the forest living vegetation biomass.Therefore,the exploration of AGB impact factors is an attractive topic in the study of forest carbon storage.The predecessors’ research on AGB mostly focused on the tropical and temperate regions,and the study of subtropical AGB has relatively smaller scale and sample size.This study systematically sampled the entire territory of the Gutianshan Nature Reserve and set up 380 forest plots to estimate the AGB,and analyzes the distribution of AGB of subtropical evergreen broad-leaved forest in Gutianshan.The physical and chemical properties of each plot were determined by extracting the topographic factors of each plot,and the biological factors were estimated via individual survey data of the plots.Multivariate statistical methods were employed to determine the impact of subtropical evergreen broad-leaved forests on subtropical regions.Analysis of major environmental and biological factors influence the AGB changeing in subtropical evergreen broad-leaved forests in subtropical regions.The main conclusions are as follows:(1)The AGB of natural forest secondary forests in Gutianshan Nature Reserve is approximately normal,with a large spatial variation,with an average of 172.5 Mg ha-1 and a standard deviation of 68.4 Mg ha-1.The minimum AGB of the natural forest is 36.1 Mg ha-1,which was naturally restored after the recent harvest.The maximum AGB was 457.1 Mg ha-1 which is the old primeval forest.In comparison with the results of previous studies on the AGB of subtropical evergreen broad-leaved forests in China,the above-mentioned changes in AGB are similar to changes in forest biomass throughout the subtropical region.(2)Results of the main environmental factors on AGB:In the analysis of the relationship between AGB and fifteen environmental variables,there was a significantly positive correlation between elevation,SOC,AP,AS,AMg and AGB;pH,soil bulk density and TP were negative correlated with AGB significantly(p<0.05).Multiple regression analysis of AGB on environmental factors showed:among topographic variables,elevation,slope and aspect have a positive effect on AGB.In soil variables,soil bulk density,soil moisture and TP have negative effects on AGB.AP has a positive effect on AGB.Among them,elevation has the greatest impact on forest AGB,followed by soil bulk density and soil moisture.Multiple regression analysis of AGB on environmental factors and biological factors showed that after controlling for biological factors,elevation still had a positive effect on AGB,but the effect was reduced;TP,soil bulk density and soil moisture still maintain negative effects on AGB,but the effects of slope,aspect,and AP are no longer significant.(3)Results of the main biological factors on AGB:Among the six biological factors,the 90%quantile of DBH(Q90,R2 = 0.32,p<0.001)has a positive effect on AGB,with the greatest impact,follow by the coefficient of variation of DBH(CV,R2＝0.19,p<0.001).AGB increases with the CV of DBH.Multiple regression analysis of AGB on biological factors shows:Q90 has the greatest effect on AGB(positive effect).The CV is still in the second place,and the effect is unchanged.After controlling for other biological factors,the evenness has no effect on AGB,but abundance and species richness show significant positive effects,and the impact on AGB is relatively small.When the environmental factors are controlled,all biological factors,except Shannon-Wiener index,have a significant effect on the AGB.Q90,CV,abundance and species richness still show significant positive effects.Their order of influence remains unchanged,and Q90 still maintains the greatest impact on AGB.(4)The multivariate regression analysis of AGB on all environmental and biological factors in forest shows:the impact of biological factors on AGB is significantly higher than environmental factors,especially the effect of the 90%quantile of DBH is four times than the total effect of the total environmental factor of total phosphorus Multi;other biological factors such as the DBH variation coefficient and abundance effect are also significantly greater than the effect of environmental factors.Variance decomposition analysis shows that environmental factors and biological factors explain 69%of the above-ground biomass variation.Environmental factors account for 25%of above-ground biomass,and biological factors account for 61%of above-ground biomass.Environmental factors independently account for 8%of AGB,while biological factors independently explain 44%,and biological factors and the environment jointly explain 17%.The above-mentioned estimates of AGB of the entire subtropical evergreen broad-leaved forests may be the important reference for the estimation of biomass and productivity of subtropical evergreen broad-leaved forests.This study provides a reference for forest management for the purpose of carbon fixation and biodiversity conservation in the subtropical regions of China,and practical suggestions for the ecological restoration and biodiversity conservation of evergreen broad-leaved forests in China.It also provides a basic support for future interpretation of ecosystem productivity and biodiversity information from remote sensing information to enable remote sensing monitoring of forest biodiversity and productivity.