【作者】 黄从德；

【导师】 张健； 杨万勤；

【作者基本信息】 四川农业大学 ， 森林培育， 2008， 博士

【摘要】 以大气CO₂浓度增加和温度升高为主要特征的全球气候变化正在改变着陆地生态系统的结构、功能和过程,威胁着人类的生存和安全,同时,《京都议定书》（KyotoProtocol）又使碳减排增汇成为与国家经济、政治、外交和生态安全等密切相关的生态与环境科技问题。因此,全球气候变化适应与减缓就成为各国政府和科学家关注的热点问题。迄今,有关国家水平和区域尺度的植被和土壤碳储量的研究报道已经不计其数,但基于森林清查资料、土壤普查资料、生命带类型法和遥感方法存在的局限性,可能会限制地形地貌复杂、森林植被和土壤类型丰富的地区的森林生态系统碳密度和碳储量的估算精度,这需要结合不同植被与土壤组合条件下的森林植被和土壤实测数据进行估算。四川森林地处长江上游和“世界第三级”的青藏高原东缘,不仅是我国第二大林区（西南林区）的主体,而且是天然林资源保护工程、退耕还林（草）工程和长防林工程重点实施的地区,其多样化的植被与土壤组合类型、明显的气候垂直分异特征、复杂的地形地貌等使其成为研究区域森林生态系统碳储量空间分异特征的理想实验室。但迄今为止,有关四川森林生态系统碳储量及其空间分异特征的研究还未见报道,这不能满足四川和我国森林碳循环研究的需要。因此,本项研究采用森林清查资料与实测数据相结合的研究方法,研究了四川森林生态系统的碳储量,并运用GIS技术绘制了碳密度空间分布图,初步探讨了碳储量和碳密度的空间分异特征,探索了基于碳储量和碳密度空间分异特征的森林分区碳库管理措施。四川森林植被的平均碳含量为51.09%（46.75%～54.89%）,其中,针叶林的林分平均碳含量为52.82%（50.50%～54.89%）,大于50.00%,阔叶林林分平均碳含量为49.37%（46.75%～50.50%）,小于50.00%,大于45.00%。这表明,采用50.00%或45.00%作为转换系数估算四川森林植被碳储量可能低估其碳储量和碳汇功能。通过对生物量-蓄积量进行多目标函数拟合,确定w=avb为四川森林乔木层蓄积量-生物量最优模型。本研究基于实测的林分碳含量与区域生物量-蓄积量模型相结合的方法估算了研究区域森林乔木层碳储量。采用本方法估算的四川森林植被碳储量（2004年）为478.25TgC,比通用转换系数45.00%和50.00%估算的结果分别高11.56%和1.73%。可见,基于实测的森林碳含量与区域生物量-蓄积量模型相结合的方法对于精确估算区域森林碳储量具有重要意义。四川森林的碳汇功能明显。1974年～2004年的30年期间,四川森林乔木层碳储量从305.37 TgC增加到478.25 TgC,增加了172.88 TgC,年均增长率为1.51%。可见,四川森林植被起着一个的碳“汇”的作用。四川森林生态系统有机碳的总储量为2926.81 TgC,不同组分的碳储量表现为土壤层（2394.26 TgC）＞乔木层（478.25 TgC）＞枯落物层（41.14 TgC）＞灌草层（13.16TgC）,分别占总碳储量的81.80%、16.34%、1.41%和0.45%。这表明,森林土壤是森林生态系统中最大的有机碳库。尽管枯落物层的碳储量不高,但其作为植被与土壤之间进行物质循环和能量转换最活跃的生态界面,以及森林土壤有机碳的直接来源,如果忽视这部分碳,不仅会低估森林生态系统的碳储量,而且会限制我们对森林土壤碳汇形成机制的理解。不同森林类型之间的碳储量差异较大。冷、云杉林生态系统具有最大的碳储量,为1384.09 TgC,占碳储量的47.29%,栎类及其硬阔林生态系统的碳储量为327.56TgC,占11.19‰软阔林生态系统的碳储量为309.21 TgC,占10.56%。这三类森林生态系统的碳储量达2020.86 TgC,占四川森林碳储量的69.05%,其余森林生态系统碳储量约为30.95%。这与其面积较大和碳密度相对较高有关。这表明,以天然起源为主的森林仍然是四川森林碳储量的主要贡献者,而以人工起源为主的森林生态系统碳储量相对较低。四川森林生态系统碳储量主要分布在坡度＞25°和高海拔地区（3000-4000 m）。在坡度＞25°以上的地带达到1598.22 TgC,占到了总储量的54.61%,在海拔3000-4000 m之间的地带达到1313.24 TgC,占总碳储量的44.87%。由于坡度＞25°和高海拔地区是典型的生态环境脆弱带,森林植被一旦遭到破坏,其恢复难度较大,因此,保护和稳定四川森林生态系统碳储量首先应减少人类活动对森林的破坏。四川森林生态系统的平均碳密度为232.81 MgC·hm^-2,其中土壤层为190.45MgC·hm^-2,乔木层为38.04 MgC·hm^-2,枯落物层为3.27 MgC·hm^-2,灌草层为1.05MgC·hm^-2,均低于我国的平均水平。不同森林类型的土壤与植被碳密度比值介于3.44～17.41,平均为4.96。这表明四川森林植被的碳密度较低,但碳吸存潜力大。四川森林生态系统的碳密度空间分异明显,总体上表现出明显的经向地带性、纬向地带性和垂直地带性。但受到青藏高原隆升以及人口稠密区（平原、低山、丘陵区）人类活动干扰及其叠加效应的影响,四川森林生态系统的碳密度又表现出明显的特殊性和复杂性。四川森林土壤有机碳密度总体上均随着纬度和海拔高度（0～4000m）的增加而增加,随经度的增加而降低。这与国内外绝大多数的研究结果一致,这与经度、纬度和海拔的增加引起的水热动态变化驱动的土壤有机碳收支有关。四川森林植被的碳密度总体上也随着纬度和海拔高度的增加而增加,随经度的增加而降低。这与国内外有关“森林植被的碳密度随着纬度和海拔高度的增加而降低”的结论不一致,原因是其地带性分布规律还受到垂直地带性、人类活动干扰及其叠加效应的影响。导致“四川森林植被碳密度随着海拔的升高而增加”的原因是随着海拔高度的上升,森林植被受到人类活动的干扰强度降低,森林植被的碳密度较高。这表明,人类活动干扰是影响四川森林植被碳密度和碳储量空间分异特征的特殊性和复杂性最重要的因素。同时也意味着,结合天然林资源保护工程、退耕还林（草）工程进行森林植被保护、退化森林生态系统恢复重建可能显著增加四川森林植被的碳汇功能。从四川森林生态系统碳密度和储量的空间分异特征来看,森林分区经营管理是增强四川森林碳汇功能的有效途径。以人工林和少量次生林为主的丘陵平原区应采取低效林改造、封山育林、速生丰产林营建等相结合的经营技术,以增强该区的森林碳吸存潜力。以天然次生林和少量人工林为主的盆周低山区应采取封山育林与高效人工林营造相结合的经营技术,以稳定和提高该区森林的固碳能力。以冷、云杉为优势树种的亚高山和高山林区应进一步加强天然林保护。更多还原

【Abstract】 Global climate change has been concerned about worldwide because climate change characterized by global warming and atmospheric CO₂ enrichment is changing the structure and function of terrestrial ecosystem as well as threatening the survival and safety of human beings. Furthermore, estimate of carbon stock in national or regional vegetation and soil, as a crucial important scientific basis in the implementation of international environmental conventions, has been an important field in climate change science, as a consequence of which numerous reports on national and regional carbon stock in vegetation and soil have been published in the past three decades. However, the shortcomings of forest resource inventory, soil survey, Holdridge life zone, and satellite data in estimating carbon stock in vegetation and soil still limited the measurement precision of carbon density and stock in regional forest ecosystem with complex landforms and diverse forests and soils, implying that more detailed measurements on carbon density and stock in vegetation and soil of the forest ecosystem are necessary for the region with complex landforms and diverse forests in order to obtain more precise estimates of regional forest carbon stock. Sichuan province, located at the upper reaches of the Yangtze River and in the eastern Qinghai-Tibet Plateau honored by the third pole in the world, is the principal part of the second largest forest region in China as well as the key region of projects on natural forest resource protection, conversion of cropland to forest and grassland and protection forest in the upper and middle reaches of the Yangtze River. Besides the irreplaceable and important roles in conserving water and soil, nursing biodiversity and global carbon cycle, Sichuan forest is also an ideal natural lab for studying the spatial differentiation on regional forest ecosystem carbon stock due to the diverse vegetation and soil combinations, clear vertical climate differentiation and complex landforms. As yet, far less information is available on the characteristics of carbon stock in the forest ecosystem and its spatial differentitation at the regional level in Sichuan, which is difficult to make needs of forest carbon cycle in Sichuan province and China. Carbon density and stock in the forest ecosystem and its spatial differentiation in Sichuan were studied to provide an important scientific basis on carbon sequestration potential in Sichuan forest, employing the methods of measurements on carbon contents in trees and soils, and biomass with forest resource inventory and GIS technology, Consequeathy, the techniques of the regionalized forest carbon management were put forward based on the spatial differentiation of carbon density and stock in the forest ecosystem in Sichuan.Average carbon content in trees of Sichuan forest was 51.09%, varying from 46.75% to 54.89%. Among this, average carbon content was 52.82% （ranging from 50.50% to 54.89%） and 49.37% （ranging from 46.75% to 50.50%） in coniferious and broadleaved forests, which was higher than 50.00% and 45.00%, respectively. It is suggested that carbon stock and the potential of carbon sequestration in Sichuan forest be underestimated by the transform coefficients of 0.50 or 0.45.The equation w=avb, fitted by multiple objectives of biomass and tree volume, was confirmed as the optimum model to express the relationships between tree volume and biomass in Sichuan forest. Here the carbon stock in trees of Sichuan forest was estimated based on the method of carbon content in the forest stand in combination with regional biomass-volume model, and in turn carbon stock in the vegetation was 478.25 TgC in Sichuan forest in 2004, which was 11.56% and 1.73% higher than those estimated by the common transfer coefficient of 45.00% or 50.00%, indicating that the method of estimating the carbon stock in regional forest by measuring tree carbon content in combination with regional biomass-volume model is important to improvt the precision of estimating regional forest carbon stock.Carbon stock in trees of Sichuan forest increased 172.88 TgC from 305.37 TgC in 1974 to 478.25 TgC in 2004 by 1.51% of annual increment rate over the past 30 years, implying that Sichuan forest played the role of carbon sink in global carbon cycle.The total organic carbon stock in the forest ecosystem was 2926.81 TgC in Sichuan, and the carbon stock was 2394.26 TgC in soil layer, 478.25 TgC in tree layer, 41.14 TgC in litter layer and 13.16 TgC in shrub and grass layer, accounting for 81.80%, 16.34%, 1.41% and 0.45% of the total, respectively, indicating that forest soil was the greatest organic carbon stock. Although carbon stock in litter layer was lower than that in tree and soil layers, organic carbon in this layer was very important since litter layer is one of the most important ecological interfaces in terms of mass cyle and energy transfer between vegetation and soil as well as the source of soil organic carbon pool. Consequently, the formation mechanism on forest soil carbon sink is difficult to be revealed completely as well as carbon stock in the forest ecosystem would be underestimated if organic carbon in litter layer was neglected.Carbon stock varied greatly with the forest stands. Coniferous forest dominated by fir （Abies） and spruce （Picea） trees had the greatest carbon pool with 1384.09 TgC. which accounted for 47.29% of the total carbon stock. Carbon stock was 327.56 TgC and 309.21 TgC in the forest ecosystem dominated oak （Quercus） and other hardwood trees and in the softwood forest ecosystem, accounting for 11.19% and 10.56%of the total carbon stock in Sichuan forest, respectively. In total, carbon stock in the former three ecosystems was 2020.86 TgC, which accounted for 69.05% the total carbon stock, resulting from the relative higher forest area and carbon density. The carbon stock in the rest forest ecosystems only accounted for 30.95%. The results indicated that the forest originating from natural forest was main contributor to carbon pool in Sichuan forest, while the artificial forest had the relative lower carbon stock.Carbon stock in Sichuan forest ecosystem distributed mainly in the region with sharp slope （>25°） and high elevation（3000～4000m）, resulting from relative low human activities in these zones. Carbon stock in the forest ecosystem at the zone with >25°slope was 1598.22 TgC, accounting for 54.61% of the total in Sichuan forest. Similarly, carbon stock in the forest ecosystem at the zone with 3000-4000 m elevation was 1313.24 TgC, which accounted for 44.87% of the total carbon in Sichuan forest ecosystem. In order to protect and increase the carbon stock in Sichuan forest, the first measure is to reduce the human disturbance to forest resulting from that the forest is easy to be damaged and the degraded forest ecosystem is difficult to be restored since the region with sharp slope and high elevation is the typical fragile ecological and environment belt.Average carbon density in the forest ecosystem was 232.81 MgC·hm^-2 in Sichuan, and the corresponding carbon density was 190.45 MgC·hm^-2 in soil layer, 38.04 MgC·hm^-2 in tree layer, 3.27 MgC·hm^-2 in litter layer and 1.05 MgC·hm^-2 in shrub and grass layer, respectively, all of which were lower than those of average carbon density in China. Average ratio of soil to vegetation carbon density was 4.96, ranging from 3.44 to 17.41 in Sichuan forest ecosystem, indicating that Sichuan forest had lower vegetation carbon density and higher potential of carbon sequestration.Carbon density in the forest ecosystem had clear spatial differentiation with the zonalities of longitude, latitude and altitude in Sichuan, and also showed obvious speciality and complexity because of the uplift of Qinghai-Tibetan plateau and the disturbance of human beings in densely populated area （such as the plain and low-mountain and hilly area）. Soil organic carbon density in Sichuan forest ecosystem increased with longitude and altitude （0-4000m a.s.l.）, and decreased with the latitude, which was in agreement with the results worldwide resulting from the budget of soil organic carbon driven by hydrothermal dynamics caused by the increases of longitude, latitude and altitude. Meanwhile, carbon density in trees of Sichuan forest ecosystem also increased with longitude and altitude, and decreased with the latitude, which was not in agreement with the result of "carbon density in trees decreased with the increases of longitude and altitude" worldwide, resulting from that carbon density in tree layer increased with the longitude and the elevation resulted from the vertical zonality, the disturbance of humana activities and their interactions, while the reason that carbon density in tree layer increased with the altitude was the decline of human disturbance intensity with the elevated altitude. The results indicated that the speciality and complexity of spatial differentiation on carbon density and stock in Sichuan forest ecosystem caused mainly by the disturbances of human beings, which also meant that the measures of forest conservation and degraded forest ecosystem restoration in combination with the projects of natural forest resource protection and conversion from farmland to forest （grass） could significantly increase the potential of forest carbon sequestration in Sichuan.An effective approach to increase the capacity of carbon sequestration in Sichuan forest was to implement regionalized forest management concluded from spatial differentiation of carbon density and stock in the forest ecosystem in Sichuan province. The hilly and plain area dominanted by artificial forest and a few secondary forests should adopt the method of low-benefit forest improvement in combination with the forest conservation and fast-growing plantation construction in order to enhance the potential of carbon sequestration. The low mountain area dominanted by natural secondary forest and a few plantations around the basin should adopt the forest management in combination with forest conservation and high-efficiency plantation construction in order to stabilize and enhance the capacity of carbon sequestration. The subalpine and alpine region dominanted by fir and birch forests should further strengthen the natural forest consersvtion.更多还原