黄土丘陵区油松人工林生态系统碳密度及其分配

以子午岭林区油松(Pinus tabulaeformis)人工林为研究对象,通过野外调查与室内分析,探讨了幼龄9a、中龄23a、近熟33a和成熟47a等不同林龄林分的生物量、含碳率、碳密度及其时空分布特征。结果表明:(1)油松林各群落平均生物量大小排序为:乔木层(76.12 t/hm2)枯落物层(14.56 t/hm2)林下植被层(3.66 t/hm2)。乔木层生物量随林龄增大而持续增加,各器官中树干所占比例最大(38%—46%),其次为叶和根,枝和皮所占比例最小;林下植被层生物量随林龄增大呈先降低后增加趋势;枯落物层生物量随林龄增大则明显增加。(2)油松乔木、林下灌木、草本、枯落物平均含碳率依次为50.2%、44.5%、43.8%和40.6%。林龄对乔木各器官含碳率无显著影响,不同器官之间含碳率存在显著性差异,具体表现为叶(53.3%)枝(51.4%)皮(50.6%)干(49.8%)根(47.3%);灌木各器官含碳率表现为枝(46.0%)叶(44.8%)根(42.5%),草本则是地上(45.2%)地下(40.2%)。土壤(0—100 cm)含碳率在0.3%—2.7%之间,且具有明显的垂直分布特征:表层含碳率高,并随土壤深度的增加逐渐降低。(3)9、23、33和47年生油松林生态系统碳密度分别为70.49、100.48、167.71和144.26 t/hm2,其空间分布序列表现为土壤层植被层枯落物层,且植被层和土壤层是油松人工林的主要碳库。林龄是影响油松林木及群落碳密度积累的主导因子之一。随林龄增加,土壤碳密度所占生态系统碳密度份额逐渐降低,乔木层和枯落物层则逐渐增加。

Carbon density and distribution of Pinus tabulaeformis plantation ecosystem in Hilly Loess Plateau

Currently, most studies related to carbon storage focus on the arbor layer; however, few in-depth studies have analyzed the variations in carbon storage allocation of different layers of plant communities with different stand ages. To estimate carbon density of Pinus tabulaeformis plantation ecosystems for different stand ages more accurately, we tracked 9-, 23-, 33-and 47-year-old P. tabulaeformis plantations in the Hilly Loess Plateau region of China and studied the carbon content in plant organs, litter and soil, as well as the carbon storage and its allocation in different layers. By analyzing carbon sequestration characteristics of P. tabulaeformis plantations at different age stages, this paper provides a theoretical basis of evaluating the function of carbon sinks in P. tabulaeformis plantations during forest management. In addition, the carbon density of the forest ecosystems was measured and evaluated based on "The Research Norms of Chinese Forest Ecosystem Carbon Sequestration, Rate and Potential", which provides a basis for comparative study of cross-regional forest types. The main results were as follows. (1) Average biomass in the different components of the studied forest ecosystems were in the order of: arbor layer (76.12 t/hm²) > litter layer (14.56 t/hm²) > undergrowth vegetation layer (combined herb and shrub layer vegetation; 3.66 t/hm²). The biomass of the arbor layer of P. tabulaeformis increased with stand age. The Pinus arbor organ biomass was as follows: stem accounted for the largest share, followed by leaves and roots, the contribution of branches and bark were minimal. Undergrowth biomass first increased then decreased with increasing tree age, while litterfall biomass increased with tree age. The biomasses of shrub organs were markedly different, which showed that biomass of branches > roots > leaves. In the herb layer, the above-ground portion of biomass was significantly greater than the underground portion. (2) The average carbon content was 50.2% for P. tabulaeformis and for different organs the order was leaves (53.3%) > branches (51.4%) > bark (50.6%) > stems (49.8%) > roots (47.3%). The amount of carbon stored in the shrub, herb and litter layers was 44.5%, 43.8% and 40.6%, respectively. Shrub carbon content of various organs was in the order of branches (46.0%) > leaves (44.8%) > roots (42.5%). The carbon content of herbs was greater in the above-ground portion (45.2%) than in the underground portion (40.2%). Forest age had no significant effect on the carbon content of arbor organs. The carbon content of different shrub organs was significantly different for each herb species. The carbon content of soil (0-100 cm) was between 0.3 and 2.7% and had an obvious vertical distribution characteristic: the surface soil layer had a higher carbon content and carbon content gradually decreased as soil depth increased. (3) Forest age was a dominant factor affecting the carbon density of the P. tabulaeformis forest community. The carbon density of 9-, 23-, 33-and 47-year-old P. tabulaeformis forests was 70.49, 100.94, 167.09 and 144.93 t/hm², respectively. Carbon density in different components of the studied forest ecosystems was in the order of: soil layer > vegetation layer > litter layer. The proportion of vegetation carbon density increased with increasing tree age continually, whereas that of soil carbon density had the opposite pattern. 9-, 23-, 33-and 47-year-old P. tabulaeformis forest arbor layer carbon densities increased with stand age (0.90, 26.56, 59.73 and 60.20 t/hm², respectively), as did carbon density in the litter layer. The vegetation layer and soil layer carbon density first increased and then decreased with increasing stand age.