西南桦纯林与西南桦×红椎混交林碳贮量比较

用乡土树种培育优质大径材已成为南亚热带满足林产品需求和生态保护的重要途径,如何通过优化森林经营模式提高人工林生态系统碳储量已成为关注的重点.对广西凭祥伏波林场13年生西南桦纯林、12年生西南桦×红椎混交林生态系统的碳素密度、碳贮量及其分布特征进行了比较研究.结果表明:(1)西南桦与红椎不同器官碳素密度变化范围分别为481.11-600.79 g/kg和451.24-543.42 g/kg,与中国南亚热带地区其他树种的碳素密度接近.相同树种不同器官之间以及不同树种相同器官之间的碳素密度差异显著(P＜0.05).西南桦纯林与西南桦×红椎混交林灌木层的平均碳素密度分别为437.15 g/kg和436.98g/kg,混交林草本层平均碳素密度比纯林高,差异性显著(P＜0.05).西南桦纯林土壤各层碳素密度均高于西南桦×红椎混交林,但差异不显著(P＞0.05).(2)西南桦×红椎混交林乔木层碳贮量(29.144 t/hm2)略高于西南桦纯林(28.541 t/hm2),混交林生态系统碳储量(276.486 t/hm2)比纯林生态系统碳储量(305.514 t/hm2)低.西南桦纯林、西南桦×红椎混交林植被层碳贮量分别占其生态系统碳贮量的9.64％和10.58％,凋落物层分别占生态系统碳储量的0.19％和0.56％.(3)西南桦纯林和西南桦×红椎混交林土壤碳贮存主要集中在0-20cm土层,且随土层深度增加而减少.西南桦纯林土壤层(0-60cm)碳贮量(275.488 t/hm2)明显高于西南桦×红椎混交林土壤层(0-60cm)碳贮量(245.688 t/hm2),分别占其生态系统碳贮量的90.17％和88.86％.(4)西南桦×红椎混交林乔木层碳素年净固定量(2.428 t·hm-2·a-1)高于西南桦纯林乔木层碳素年净固定量(2.196 t·hm-2·a-1),表明混交林比纯林的碳固定速度快.

Carbon storage capacity of a Betula alnoides stand and a mixed Betula alnoides ×Castanopsis hystrix stand in Southern Subtropical China: a comparison study

We made a comparative study of the carbon content, carbon storage, and carbon accumulation of a 13-year-old stand of Betula alnoides and a 12-year-old stand of mixed Betula alnoides × Castanopsis hystrix located at the Fubo experimental farm of the Experimental Centre of Tropical Forestry in Pingxiang, Guangxi, China. The purpose was to evaluate the potential carbon storage and content of large-sized trees in plantations, and to provide more perspective about commercial forest plantations that are being adaptively managed for timber production objectives in conjunction with carbon storage and biodiversity conservation objectives. The variation in mean carbon content of all components ranged from 481.11 to 600.79 g/kg for Betula alnoides, and from 451.24 to 543.42 g/kg for Castanopsis hystrix. These results are similar to the carbon content found in other tree species in China's southern subtropical area. The carbon content of the understorey vegetation was ranked as trees > shrubs. The average carbon content of the shrub layer was 437.15 g/kg in the Betula alnoides stand and 436.98 g/kg in the mixed Betula alnoides × Castanopsis hystrix stand. The average carbon content of the herbaceous layer in the mixed Betula alnoides × Castanopsis hystrix stand was higher than that in Betula alnoides stand; the difference was significant (P<0.05). The carbon content of the soil decreased as the depth of soil increased. The average carbon content of the soil in the Betula alnoides stand was more than that in the mixed Betula alnoides × Castanopsis hystrix stand; the difference was not significant (P > 0.05). The carbon storage of the tree layer in the mixed Betula alnoides × Castanopsis hystrix stand (29.144 t/hm²) was a little higher than that in the Betula alnoides stand (28.541 t/hm²). The total carbon storage in the mixed Betula alnoides × Castanopsis hystrix stand (276.486 t/hm²) was less than in the Betula alnoides stand (305.514 t/hm²). The carbon storage in the vegetation of the Betula alnoides stand was 29.444 t/hm², and in the mixed Betula alnoides × Castanopsis hystrix stand it was 29.265 t/hm², comprising 9.64% and 10.58% of total carbon storage respectively. The litterfall plays a very important role in the carbon cycle, although in this study litterfall stored relatively little carbon, accounting for only 0.19% in the single-species stand and 0.56% in the mixed stand. In the case of the soil, the carbon was stored mainly in the 0 to 20 cm layer, which accounted for 38.05 to 45.76% of the carbon stored in all the soil. Carbon storage declined as the depth of soil increased. The carbon storage in the 0 to 60 cm soil layer of the Betula alnoides stand (275.488 t/hm²) was greater than that in the mixed Betula alnoides × Castanopsis hystrix stand (245.688 t/hm²), accounting for 90.17 and 88.86% of the carbon stored in the respective stands. The annual carbon accumulation rates in the tree layer of the Betula alnoides stand and the mixed Betula alnoides × Castanopsis hystrix stand were 2.196 t·hm²·a^-1 and 2.428 t·hm²·a^-1 respectively, which indicates that the rate of carbon accumulation was greater in the mixed stand than in single-species stand.