Biomass and Its Allocation of the Main Vegetation Types in Liupan Mountains

In 2009,the biomass and its allocation among vegetation layers and organs were invested for the main forest types in the small watershed of Xiangshuihe,which locates at the southern part of Liupan Mountains.The results showed that there was an obvious difference in the total living biomass among different forest types,which followed the order of Pinus armandii forest(102.70 t·hm-2) Birch forest(84.42 t·hm-2)Populus davidiana forest(79.97 t·hm-2)Larix principis-rupprechtii plantation(58.37 t·hm-2)open forest(44.91 t·hm-2).The area-weighted average of biomass of all forests investigated was 78.37 t·hm-2,which was much higher than that of shrubs(20.77 t·hm-2),grassland(1.07 t·hm-2) and meadow(2.29 t·hm-2).The order of litter biomass of each forest type was Larix principis-rupprechtii plantation(18.21 t·hm-2)Pinus armandii forest(11.99 t·hm-2)Birch forest(10.90 t·hm-2)Populus davidiana(7.67 t·hm-2)open forest(7.06 t·hm-2),all of them was also much higher than that of shrubs(3.13 t·hm-2),meadow(0.82 t·hm-2) and grassland(0.49 t·hm-2).Most of the biomass in forest ecosystems concentrated in the tree layer with a ratio of 91.04%,while the ratio amounted to only 8.09% for the shrub layer and even 0.87% for the herb layer.The organ allocation of biomass in forest ecosystems was trunk(54.06%)branch(21.04%)root(16.92%)bark(5.34%)leaf(2.65%) for the tree layer,while it was stem and branch(62.68%)root(30.55%)leaf(6.77%) for the shrubs layer,and over-ground shoot(58.32%)root(41.18%) for the herb layer.The averaged ratio of above-to underground biomass for the tree layer of all forest types investigated was 4.49,while it was around 4.0 for the broadleaf forest types,6.41 for the Larix principis-rupprechtii plantation and 5.80 for the Pinus armandii forest;all of those were higher than that of shrubs(2.82),grassland(1.89) and meadow(1.20).The forest biomass increased nearly linearly with increasing forest age and canopy density within the range of the investigation.The forest biomass also increased rapidly with increasing stand density before the density reaches a threshold of 900 trees·hm-2;thereafter the biomass increased more slowly and towards its maximum.The forest biomass in Liupan Mountains is higher compared with that in the similar regions,showing a good result of the forest protection in last decades.