Biomass and carbon fixation ability of typical larch- poplar and betula mixed forest in Mulanweichang

A mixed Dahurian larch and polar birch forest,artificial Larix principis-rupprechtii forest,natural Betula platyphylla secondary forest,and natural Populus davidiana secondary forest,which are all part of the Bei-gou Forest Farm in Mulan Forestry Bureau were studied here. The layered cut method was used to measure aboveground biomass in all four forests. The layered mining method was used to measure underground biomass. The trunks were divided into segments 0. 5m in diameter and 5 cm thick. The north-south diameter of each disk was recorded. Tree roots were divided into 0. 5 cm layers,and the crown projection area was dug up. Fresh weights of the trunks( with bark),branches,leaves,and roots of model trees were recorded in the open air. Samples of each organ were dried to( 105℃) constant weight and weighed. To determine biomass,leaf and branch samples were collected from different parts of the crown cover. They were weighed and dried,and their moisture content was calculated. For trunks,disk sections were obtained and weighed before and after drying. Moisture content was calculated. The leaf,branch,and root biomass of each model tree was calculated. Incrementswere measured in analytic trees. Then models of biomass and increments were established. Carbon reserve and carbon sequestration were estimated. Significant power functions and logistic equations were chosen as biomass prediction models.DBH( diameter at breast height) served as an independent variable and the napierian logarithm of biomass and total biomass of organs as the dependent variable. Optimization was performed according to regression curve and residual sum of squares( SSE),discriminant coefficient( R2),total relative error( RS),average relative error( E1),absolute value of average relative error( E2),AIC( Akaike Information Criterion),and BIC( Bayesian Information Criterion). DBH increments were measured with analytic trees,wooden cores,and DBH increments of the past five years as a baseline. A power function regression model was established. Then the DBH increments of trees over the past five years were estimated.Then the fixed carbon content of each forest was calculated for that period using the carbon content of different tree species and organs. Results showed the Dahurian larch and polar birch mixed forest stored more carbon than other forests. The Dahurian larch,Betula platyphylla,and Populus davidiana in the mixed forest were all superior to their respective artificial and natural forests. The mean DBH( diameter at breast height) was higher by about 6. 7%,12. 8%,and 4. 1%. The mean was higher by about 12. 1%,1. 4%,and 11. 1%. The fixed carbon content growth rates of Dahurian larch,Betula platyphylla,and Populus davidiana in the mixed forest were 29. 74%,28. 36%,and 34. 52%,respectively. The rate of carbon fixation was 27. 09% in the artificial Larix principis-rupprechtii forest; 26. 34% in the natural Betula platyphylla secondary forest; and 26. 24% in the natural Populus davidiana secondary forest. The rates of carbon fixation of Dahurian larch,Betula platyphylla,and Populus davidiana in the Dahurian larch and polar-birch mixed forest were 2. 65%,2.02%,and 8. 28% higher,respectively,than in the corresponding monoculture forests.