Biomass And Carbon Storage Characteristics Of Overmature Pinus Massoniana Pure Forest And Its Mixed Forest In South Subtropical Zone

Although many studies have been conducted on the biomass and carbon stocks of planted forests and many new discoveries have been made,there are still few studies on old-growth forests,especially the comparative studies on old-growth pure plantations and their mixed forests,which need to be further discussed.This study selected 60-years old Pi'nus massoniana pure plantations and un-even aged P.mossoniana and Castanopsis hystrix mixed plantations as the objects and used the field investigation,biochemical analysis and comprehensive comparison methods to discuss characteristics of the ecosystem biomass and carbon stocks of these plantations,and to verify the scientific hypothesis that mixed forests can improve forest ecosystem biomass and carbon reserves and that old-growth forests have high carbon sequestration capacity.The main results are as follows.(1)The biomass of the old-growth pure plantation and its mixed plantation were 584.17 t/hm2 and 655.34 t/hm2,respectively.The biomass of tree layer,shrub layer,herbaceous layer and litter layer of these two plantations were 569.09 t/hm2,4.26 t/hm2,3.02 t/hm2,7.80 t/hm2 and 645.56 t/hm2,1.88 t/hm2,0.98 t/hm2,and 6.92 t/hm2,respectively.The total community biomass and tree layer biomass of the mixed plantation were higher than that of the pure plantation,but the difference was not significant(p>0.05),while the biomass of shrub layer,herb layer and litter layer were all lower than that of the pure plantation,and the biomass of shrub layer and herb layer of the pure plantation was extremely significantly higher than that of the mixed plantation(p<0.01).(2)The carbon stocks of the pure and mixed plantations were 483.08 t/hm2 and 524,80 t/hm2,respectively.The carbon stocks of the tree layer,shrub layer,herb layer,litter layer and soil layer are 300.62 t/hm2,2.26 t/hm2,1.47 t/hm2,4.58 t/hm2,174.15 t/hm2 and 338.11 t/hm2,1.05 t/hm2,0.51 t/hm2,4.21 t/hm2,and 180.92 t/hm2,respectively.In the plantation,the carbon stocks of ecosystem,tree layer and soil layer were all higher than those of in the pure plantation,but the difference was not significant(p>0.05).While the carbon stocks of shrub layer,herb layer and litter layer were all lower than that of in the pure forest,and the carbon stocks of the shrub layer and herb layer in the pure plantation were extremely significantly higher than that in the mixed plantation(p<0.01).(3)The biomass distribution pattern of the pure and mixed plantations were similar with the trend of tree layer>litter layer>shrub layer>herb layer.The biomass of tree layer accounted for 97.42%-98.51%of the total biomass,the litter layer 1.06%-1.34%/the shrub layer 0.29%-0.73%;and the herb layer 0.15%-0.52%.The biomass of reserved and regenerated trees in pure and mixed stands accounted for 91.55%,8.45%,99.62%and 0.38%of the total biomass in tree layer,respectively.The order of organ biomass allocation of masson pine tree was trunk(50.55%-51.35%)>root(19.83%-20.02%)>branch(14.91%-15.56%)>bark(8.37%-8.69%>leaf(5.21%-5.51%.The trend of organ biomass allocation of Chystrix was similar to masson pine with trunk(59.30%)>root(16.84%)>branch(13.04%)>bark(7.26%)>leaf(3.55%).The regenerated trees was different from the reserved trees with trunk(42.81%-55.02%)>root(18.22%-22.22%)>leaf(7.49%-19.34%)>branch(13.93%-15.64%)>bark(0.00-5.34%).(4)The carbon pool distribution pattern of the pure and mixed plantations wass similar with the trend of tree layer>soil layer>litter layer>shrub layer>herb layer,which was 61.95%>36.32%>0.96%>0.47%>0.31%in pure plantation,and 64.75%>34.16%>0.79%>00.20%>10.10%in the mixed plantation,respectively.The biomass and soil carbon stocks account for 64.08%and 36.05%of the ecosystem carbon stocks in pure,and 65.53%and 34.47%in the mixed plantations,respectively.The tree layer and soil layer were the main carbon pool of the forest ecosystem,accounting for 98.28%to 98.90%with the carbon stocks in the tree layer are the highest,and accounting for 62%-64%.In the tree layer carbon pool,the reserved trees contributed 91.34%and the regenerated trees contributed 8.66%of carbon,respectively.In mixed forests,reserved trees contributed 99.61%of carbon(including masson pine:85.10%,C.hystrix:14.51%),and regenerated tree only contributed 0.39%of carbon.(5)The results of this study support the scientific hypothesis that mixed forests can improve the ecosystem biomass and carbon stocks and that old-growth forest have high carbon sequestration capacity.