【作者】 徐飞；

【导师】 王开运；

【作者基本信息】 华东师范大学 ， 生态学， 2010， 硕士

【摘要】 城市是人类活动的重要场所,尽管城市区域仅占了地球表面的一小部分,但是它们在促使碳循环改变的过程中发挥着巨大的、逐渐增强的作用,而且其影响不仅仅局限于城市边界之内。从这个意义上讲,城市生态系统是全球碳循环中重要的碳源／汇。城市森林被称为“城市之肺”,是城市复合系统的重要组成部分,在改善和维持城市生态环境中发挥着核心作用。近年来,随着大气中温室气体浓度升高引起的全球气候变化,城市森林的固碳作用已受到国内外学者越来越多的关注。城市森林群落结构是研究城市森林生态效益及规划管理的基础,城市森林的群落结构差异可以在较大程度上影响其整体生态效益的发挥,而在当前城市土地资源紧缺和新建绿地成本过高的背景下,优化城市森林的群落结构对提高城市生态系统固碳、贮碳能力有重要作用。本文以上海市区城市森林为研究对象,通过卫星遥感影像数字化,结合代表性群落调查和主要植物生理参数测定,研究上海城市森林的总体结构特征和常见森林群落的群落特征。而后,利用CITYgreen模型对城市森林的固碳、贮碳现状及能力进行模拟和估算,以期了解上海城市森林固碳能力的现状。在此基础上,利用方差分析、独立样本t-检验、相关性分析等统计分析方法,探讨城市森林群落结构因子与其固碳能力之间的关系,为更好地理解群落尺度下城市森林固碳能力的影响因素打下理论基础,同时也为探索一条即经济又实际的提高城市森林固碳能力的有效途径和优化城市绿化的营造和管理提供理论依据。主要研究结果和结论如下：1)上海城市森林的总体结构、群落特征和分布格局截止至2007年底,在上海市688 km2的中心城区内,城市绿地面积为13910hm2,绿地覆盖率约为20.4%。城市绿地主要集中在行政办公区、居住区和公共空间。森林群落占上海城市绿地总面积的72%。从城市森林群落面积的角度来看,上海城市森林中占主导地位的是面积在500～3000 m2之间的中型群落,占城市森林总面积的43.7%。上海城市森林中常见的乔木树种约68种,小乔木或灌木树种约105种,其中出现频度高于2%的常见树种共有18种,常见群落有香樟、悬铃木、雪松、水杉、柳树、银杏、广玉兰等17种群落,总体上讲,上海城市森林树种组成的单种优势明显。城市森林的郁闭度主要集中40%-70%之间,平均郁闭度约为53%；树木的平均胸径约为22 cm,约66%的树木为10～30 cm的中径木；树木的总体健康状况良好,95%的树木健康等级处于3级以上。对于不同功能区,公共空间城市森林在树种数、平均郁闭度、群落平均胸径、树高等级以及树木的健康状况等方面都高于其他功能区。将城市森林按建群树种的生活型划分植被类型,上海城市森林主要以常绿阔叶林、落叶阔叶林、常绿针叶林、落叶针叶林4种植被类型为主,混交林只占很小的比例。4种植被类型的森林中,除落叶针叶林以外的3种植被类型在群落的平均郁闭度、群落密度、平均树高、胸径、冠幅及胸径断面积和等群落特征方面都比较接近。2)上海城市森林的碳贮存现状、群落的固碳能力和分布格局上海城市森林总碳贮量为478472 t,平均碳密度为47.80 t·hm-2,年碳吸收总量为6256 t·a-1,平均固碳率为0.625 t·hm-2a·-1。对于不同功能区中的城市森林,对总体碳贮量和年碳吸收量的贡献按从高到底排序依次为：行政办公区>居住区>公共空间>道路区；按城市森林的碳密度排序：公共空间>居住区≈行政办公区≈道路区；按城市森林的固碳率排序：公共空间≈居住区≈行政办公区>道路区。在17种常见森林群落中,碳密度最大和最小的分别是杨树群落和合欢群落,平均碳密度分别为57.10 t·hm-2和27.81 t·hm-2;固碳率最大和最小的分别是女贞群落和槐树群落,平均固碳率分别为1.08 t·hm-2·a-1和0.37 t·hm-2·a-1。根据碳密度和固碳率的大小,可将上海城市森林的常见群落分为4类：(1)碳密度和固碳率都较大的群落,(2)碳密度较大、固碳率较小的群落,(3)碳密度较小、固碳率较大的群落,(4)碳密度和固碳率都较小的群落。对于不同植被类型的森林群落,上海城市森林碳贮量和年碳吸收量的总体分布规律为：常绿阔叶林>落叶阔叶林>落叶针叶林>常绿针叶林,且常绿阔叶林占总碳贮量的47%～63%,对总年碳吸收量的贡献达到50%～63%。从固碳能力的角度来看,按群落的碳密度从大到小排序：常绿针叶林>常绿阔叶林>落叶阔叶林>落叶针叶林;按群落的固碳率从大到小排序：落叶针叶林>常绿阔叶林>落叶阔叶林>常绿针叶林。3)上海城市森林群落结构对固碳能力的影响城市森林的郁闭度、平均胸径、群落密度、层次结构以及种植结构等群落结构因子都对固碳能力造成不同程度的影响。首先,城市森林的郁闭度对其碳密度和固碳率都起到决定性作用,郁闭度与群落的碳密度和固碳率都呈极显著正相关,而且随着郁闭度的提高,群落的碳密度和固碳率的增幅显著；其次,平均胸径在某种意义上代表了群落的年龄结构,在树木生长增加生物量累积并同时加速树木衰亡和叶脱落的双重影响下,平均胸径与群落的碳密度呈正相关,与固碳率呈负相关；再次,对于群落密度,它与城市森林的固碳率呈极显著正相关,与碳密度无显著相关,综合考虑林龄、郁闭度和群落密度的共同作用依然可以发现,低密度高胸径群落比中、高密度群落具有更高的碳密度；最后,从树种组成类型与层次结构角度来看,混交林碳密度高于纯林,复层林碳密度和固碳率都高于单层林,且固碳能力的差异在一定程度上受平均胸径、群落密度等因子影响。更多还原

【Abstract】 Cities are important places of human activity. Although urban areas are account for only a small part of the Earth’s surface, they play a significant role in changing the world’s carbon circulation process, and its role is more and more important nowadays. Furthermore, its impact is not limited to city boundaries. In this sense, urban ecosystem is the important carbon source/sink in the global carbon circulation. Known as the "City’s lung", urban forest is an essential part of urban ecosystem, which plays a central role in maintaining the urban environment and making it better. In recent years, the increasing of concentrations of greenhouse gases in the atmosphere leads to global climate change. Therefore, the carbon sequestration of urban forest has received increased attention of scholars. Study on community structure is the foundation of the study on the ecological benefits and management of urban forest. The differences of urban forest’s structure will affect its overall ecological benefits in a large extent. In the current background of shortage of urban land resources and the high cost of new development of green space, how to improve urban forest’s community structure to increase the urban ecosystem carbon sequestration and carbon storage capacity is very important.In this study, based on RS image digitization, investigation into representative community, measurement on physiological variables of dominant species, the overall structure characteristics of urban forest in shanghai were studied. Also, with CITYgreen model, carbon fixation of urban forest in Shanghai was evaluated. Furthermore the effects of community structure on carbon fixation of urban forest were studied.The results and conclusions are as follow: 1) Overall structure, community characteristics and distribution pattern of the urban forests in ShanghaiBy the end of 2007, in 688 km2 of the central city, the area of urban green space was 13910 hm2, the coverage rate of the green space was about 20.4%. Urban green space primarily concentrated in the executive office area, residential area and public open space. Forest communities are accounts for 72% of the total area of green space in Shanghai. Medium area communities of 500～3000 m2 were mainly area types, accounting for the total urban forest area 43.7%.Shanghai urban forest tree species common in about 68 species of small trees or shrubs of about 105 species, of which frequency of occurrence than 2% of the common species there are 18 species of common communities are camphor, sycamore, cedar, fir, willow, Ginkgo biloba, Magnolia grandiflora and other 17 kinds of communities, generally speaking, the Shanghai urban forest tree species composition of a single kind of obvious advantages. Urban forest canopy mainly 40% to 70%, averaging about 53% canopy density; trees, the average diameter of about 22 cm, about 66% of the trees for the 10～30 cm in the diameter wood; trees overall good health, the health level of 95% of the trees in three or more. For different functional areas, public space, urban forest in the trees, average canopy density, community average DBH, tree grade, and the health of trees such as higher than other functional areas.The urban forest by the construction division of group life form species of vegetation types, mainly in Shanghai urban forest evergreen broad-leaved forest, deciduous broadleaf forest, evergreen coniferous forest, deciduous conifer forest vegetation types 4, mainly mixed only small percentage.4 types of forest vegetation, in addition to deciduous conifer forest vegetation types other than 3, the average canopy density in the community, community density, average tree height, diameter, crown width and diameter at breast height basal area and other community characteristics are rather close to. 2) Carbon storage status, carbon fixation capacity and distribution pattern of urban forest in ShanghaiThe total carbon storage of urban forest in Shanghai was 478472 t, the average carbon density was 47.80 t·hm-2, the total amount of annual carbon sequestration 6256 t·a-1, the average carbon sequestration rate of 0.625 t·hm-2·a-1.As for different functional areas in the urban forest, the overall carbon storage and annual carbon uptake by the contribution of the order of from high to low was: administration area>residential area>public space>road area; by urban forest carbon density order:public space> residential area≈administration area≈road area; by city rate of forest carbon sequestration order:public space≈residential area≈administration area>road area.17 species common in forest communities, the carbon density, respectively the largest and the smallest communities and the acacia community of poplar, the average carbon density was 57.10 t·hm-2 and 27.81 t·hm-2; carbon sequestration rates of the largest and the smallest difference community and the community for privet locust, the average carbon sequestration rate was 1.08 t·hm·a-1 and 0.37 t·hm-2·a-1. According to the carbon sequestration rate density and size, can be a common community in Shanghai urban forest is divided into four categories:(1) carbon sequestration rate density and the larger community, (2) higher density of carbon, carbon sequestration rate in small communities, (3) lower carbon density, carbon sequestration rates of the larger community, (4) carbon sequestration rate density and smaller communities.For different types of forest vegetation communities, Shanghai urban forest carbon storage and carbon absorption in the overall distribution are:evergreen broad-leaved forest> deciduous forest> deciduous coniferous forest> evergreen coniferous forest, and evergreen broad-leaved forest of the total carbon storage of 47% to 63% of the total annual carbon uptake contributed 50% to 63%. From the perspective of carbon sequestration, carbon density by beginning with the largest community order:evergreen coniferous forest> evergreen broadleaf forest> deciduous forest> deciduous coniferous forest; by community in carbon sequestration rates from large to the small order:deciduous conifers> evergreen broadleaf forest> deciduous forest> evergreen coniferous forest.3) Effects of community structure on carbon fixation of urban forest in ShanghaiUrban forest canopy, the average diameter at breast height, density, community, hierarchy, community structure and community type of carbon sequestration capacity factors are all caused by different degrees. First, the urban forest canopy density and its carbon sequestration rates have played a decisive role, canopy density and community density and carbon sequestration rates of carbon were tested significantly positive correlation, and with the canopy density increased, Community sequestration of carbon density and a significant increase in the rate; Second, the average diameter in a sense represents the community’s age structure, increase in tree growth and biomass accumulation also accelerated the decline and leaves off the trees under the double impact, the average diameter at breast height and community carbon density was positively correlated with carbon fixation rates were negatively correlated; again, for the community density, its urban forest carbon sequestration rate showed a significant positive correlation with the carbon density of not significant, considering the stand age, canopy degree of interaction and community density can still be found, low-density communities with high diameter ratio, the high-density communities with a higher carbon density; finally, from the type of tree species composition and structure of point of view, mixed forest carbon density than pure, multi-storied plantation carbon density and carbon sequestration rates are higher than the single forest, and carbon sequestration capacity of the differences to some extent by the average diameter at breast height, density and other factors affect the community.更多还原