Search

Forests form the main body of terrestrial ecosystems and play an important role in mitigating global climate change through carbon dioxide sequestration in forest biomass. Biomass and productivity are essential characteristics of forestecosystem structure and function,and knowledge of both are essential for the study of carbon sink function and carbon sequestration. Cunninghamia lanceolata,Pinus massoniana,and Eucalyptus urophylla × Eucalyptus grandis are the primary plantation trees used in southern China,accounting for 90% of the plantation area in ten southern provinces. However,few studies have analyzed the dynamics of forest biomass and productivity of these forest types. Forty-five 20 m × 50 m research plots were established and analyzed using three dominant plantation species( C lanceolata,P. massoniana,E. urophylla ×E. grandis) in southern China with the goal of improving our understanding the vertical structure of each community,the distribution of biomass to the various organs,and gaining a better understanding of forest biomass and productivity of differently aged stands. Each plantation type was studied using five age classes: young,middle-aged,near-mature,mature,and over-mature forest,with three replicates of each. Regression models relating tree biomass to diameter at breast height( DBH 1.3 m) were developed to estimate tree biomass. Other biomass components were sampled in quadrats within the same forty-five research plots: shrubs( three 4 m2quadrats),herbs( three 1 m2quadrats),and litterfall( three 1 m2quadrats). This method was used for estimating biomass,productivity,and biomass allocation rates to various organs in the three main plantations types; we also analyzed the relationships between stand age and biomass productivity to determine the biomass allocation rates to various organs. Results showed that a significant relationship exists between stand biomass and stand productivity of the three main plantation types as they relate to stand age,with a high degree of fitting in growth models. The total biomass of C. lanceolata,P. massoniana,and E. urophylla × E.grandis plantations increased with stand age and the biomass of mature forest was 192.30,191.53,105.77 Mg /ha,respectively. Living biomass made up 95.76%—98.39%,75.01%—99.14%,85.60%—97.61% of these three plantation types,respectively. Most of the biomass of the three main plantation types was concentrated in the tree layer and biomass increased with stand age for all three types. The biomass of other layers accounted for only a small percentage of total biomass,and generally litterfall herb shrub biomass. The trunk biomass occupied the greatest proportion of the tree layer; for C. lanceolata,P. massoniana,and E.urophylla × E. grandis truck biomass made up 54. 89%—75. 97%,49. 93%—83. 10%,and 51. 07%—98. 48% of total biomass,respectively,and trunk biomass increased with stand age. Root biomass made up the second largest percent of tree biomass and the percentages of both branch and leaf biomass were lower than root biomass and decreased with stand age.Shrub branches made up the majority of shrub biomass; both the above-and belowground biomass allocation of herbs did not exhibit an obvious trend or pattern of change. Compared with other forest types,the total biomass of C. lanceolata plantations and P. massoniana plantations were both greater than most and the total biomass of E. urophylla × E. grandis was lower than most,but the level of productivity of all three plantation types was high,or 12.37,8.98,21.10 Mg hm-2a-1,respectively. All three are fast growing forest tree species with higher photosynthetic efficiency and potential carbon sequestration than other forest plantation species in South China.