不同林龄尾巨桉人工林的生物量及其分配特征

根据1,2,3,5,8a共5个不同年龄的15块1000 m2尾巨桉样地(3次重复)调查资料,利用18株不同年龄和径阶的样木数据,建立以胸径(D)为单变量的生物量回归方程。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)获取不同林龄尾巨桉人工林的生物量,分析了其组成、分配及不同林龄生物量的变化趋势。结果表明:林分总生物量随林龄而增加,1,2,3,5年生和8年生尾巨桉人工林生物量分别为12.49,47.75,64.51,105.77和137.51 t/hm2,其中活体植物占85.60%—97.61%,地上凋落物占2.39%—14.40%;层次分配方面乔木层占绝对优势,占54.80%—91.56%,且随林龄的增加而增大,其次为凋落物,灌木层和草本层生物量较小,分别占1.02%—6.47%和0.28%—24.33%,均随林龄的增加呈递减趋势;乔木层以干所占比例最高,占51.07%—98.48%,且随林龄而增加,枝、叶、根分别占5.76%—11.80%,2.17%—21.01%和6.72%—14.87%,均随林龄而下降;灌木层以枝所占比例最高,为37.89%—56.79%,叶和根分别占16.35%—34.24%和19.52%—39.52%,随林龄的变化均不大;草本层分配1—5年生以地上所占比例较大,8年生地下所占比例高达63.87%;尾巨桉人工林乔木层各器官、地上凋落物及总生物量具有良好的优化增长模型,其总生物量的增长模型为Y=-1.693×104+3.337×104X-1.761X2;8年生尾巨桉人工林总生物量与30年生的木莲人工林持平,低于热带雨林,但其年均净生产量高达17.19 t/hm2,是一个光合效率高、固碳潜力大的速生丰产优良造林树种。

Biomass and its allocation characteristics of Eucalyptus urophylla × E. grandis plantations at different stand ages

To explore biomass dynamics and its allocation in Eucalyptus urophylla×E. grandis plantations at different stand ages (1, 2, 3, 5, 8a), fifteen plots with an area of 20 m×50 m each, were constructed in Guangxi, southwest China. The biomass of single variable regression equation for DBH (diameter at breast height) was established based the data of 18 sample trees of E. urophylla×E. grandis with different ages and DBH. Regression analysis of sample trees in arbor layer and harvest method in quadrats for shrubs, herbs and litterfall layers, were applied to calculate the biomass of Eucalyptus urophylla × E. grandis plantations at different ages, and to analyze its composition, distribution patterns, and variation trend. The results showed that the total biomass of the plantations increased with stand age, being 12.94 t/hm² in 1a stand, 47.75 t/hm² in 2a stand, 64.51 t/hm² in 3a stand, 105.77 t/hm² in 5a stand, 137.51 t/hm² in 8a stand, with the living biomass and litter accounted for 85.60% to 97.61%, and 2.39% to 14.40%, respectively, for the five stages. Arbor layer dominated the E. urophylla × E. grandis plantation responsible for from 54.80% to 91.56% of the total biomass and the dominance increased with stand age. The litter layer was ranked the second in plantation biomass. The biomass of shrub and herb layers was very low, responsible for 1.02% to 6.47% and 0.28% to 24.33%, respectively, and the ratios decreased with stand age. In the arbor layer, trunk accounted for 51.07% to 98.48% of the biomass, and the ratios increased along with stand age, while branches, leaves, and roots were responsible for 5.76% to 11.80%, 2.17% to 21.01%, 6.72% to 14.87%, respectively, and the ratios of all the compartments decreased with stand age. In the shrub layer, branch accounted for the highest proportion (37.89% to 56.79%) of the total biomass while leaves and roots accounted for 16.35% to 34.24% and 19.52% to 39.52%, respectively, with little variations among stand ages. In the grass layer, the aboveground biomass was larger than the underground biomass from 1a stand to 5a stand, while the underground biomass accounted for 63.87% of the total biomass for the 8a stage. The total biomass and biomass of different compartments for E. urophylla × E. grandis plantations had good growth models with the total biomass increase represented by Y=-1.693×10⁴+3.337×10⁴X-1.761X². Compared with other forests, the total biomass of 8a E. urophylla × E. grandis plantation was equal to the 32 a Phoebe bourmei plantation, while lower than the tropical rain forests. However, the net annual biomass increment of E. urophylla × E. grandis plantation was 17.19 t hm^-2 a^-1, which indicated that E. urophylla × E. grandis was a fast-growing forest tree species with high photosynthesis efficiency and carbon sequestration capacity.