中国南方3种主要人工林生物量和生产力的动态变化

基于中国南方杉木、马尾松、桉树3种主要人工林的幼龄林、中龄林、近熟林、成熟林、过熟林5个不同年龄各3块1000 m2样地(共计45块)的建立和调查,采用样木回归分析法(乔木层)和样方收获法(灌木层、草本层、地上凋落物)获取不同林型不同林龄径级样木和其它基本数据,探讨了3种人工林各组分各层次林分生物量和生产力的分配特征及随林龄的变化规律,结果表明,林分生物量和生产力与林龄密切相关,增长模型的拟合度均较高,相关显著;杉木、马尾松、桉树人工林的生物量随林龄的增长呈增加趋势,成熟林的生物量分别为192.30、191.53、105.77 Mg/hm2,其中活体植物分别占95.76%—98.39%、75.01%—99.14%、85.60%—97.61%;生物量的层次分配乔木层占绝对优势,并随年龄而增加,其它层次所占比例较小,总体趋势为凋落物草本层灌木层;乔木层的器官分配以干所占比例最高,杉木、马尾松、桉树分别占54.89%—75.97%、49.93%—83.10%、51.07%—98.48%,随年龄的增加而增加,根的比例次之,枝叶所占比例较小,随林龄而下降;灌木层器官分配以枝的相对生物量较大,草本层的地上和地下分配规律不明显;与其它森林类型相比,杉木和马尾松的生物量处于中上游水平,桉树的生物量较低,但3种人工林的生产力均很高,分别为12.37、8.98、21.10 Mg hm-2a-1,均是光合效率高、固碳潜力大的中国南方速生丰产优良造林树种。

Dynamics of biomass and productivity of three major plantation types in southern China

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 forest ecosystem 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 m² quadrats), herbs (three 1 m² quadrats), and litterfall (three 1 m² quadrats). 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^-2 a^-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.