【作者】 钟宇；

【导师】 张健； 杨万勤；

【作者基本信息】 四川农业大学 ， 森林培育， 2009， 博士

【摘要】 人工林在为人类提供木材、减缓大气CO₂浓度上升、增加陆地森林覆盖率和减少人类对天然林依赖的同时,也带来了生物多样性下降、土地退化、生产力降低、地下水位下降等人类普遍关注的林业生态问题,其核心是生物多样性问题。如何使人工林在满足人类对木材的需求、增加经济效益的同时,发挥其应有的生态功能,实现可持续发展是人工林生态研究的焦点之一。现在的科学问题是:尽管迄今已有大量的桉树人工林生物多样性研究,但有关桉树人工林经营管理是否导致其生态系统生物多样性的降低还存在很大的争议。这是否与桉树人工林的立地条件有关?目前尚无深入系统的研究。因此,本研究采用野外调查和室内分析相结合的研究方法,深入系统地研究了不同立地类型的巨桉人工林生态系统地上/地下生物多样性特征,探讨了立地对巨桉人工林生态系统生物多样性的影响,以期为巨桉人工林的立地选择和生物多样性保育提供理论依据,研究结果对于指导巨桉人工林的可持续经营与管理具有重要的科学意义。研究结果如下:（1）巨桉人工林林下植物种类丰富,调查林分共有维管束植物71科,158属,193种,双子叶植物占有绝对优势。阶地立地类型林分有维管束植物45科,81属,90种;丘坡中厚土有维管束植物61科,111属,132种;丘坡薄土有维管束植物52科,99属,118种,丘坡中厚土林下植物科属种的组成最为丰富,其次为丘坡薄土,阶地林分最少。造林前土地利用属性影响林下植物种类成分,现有植物也在一定程度上反映了林分的起源,如茶（Camellia sinensis）、柑桔（Citrus reticulata）、杉木（Cunninghamialanceolata）等具有明显栽培性质的种类。阶地类型林分多起源于农耕地,物种构成主要以草本为主;丘坡两种类型的林分起源较为一致,主要是荒山迹地、林地和茶园遗弃地等,物种组成上灌木和草本比例都接近1:1。在科、属、种的相似性上,两种丘坡立地类型的林分相似程度最大,而最不相似的则是丘坡中厚土林分与阶地林分。区系分析表明,各立地类型林分林下植物科、属的分布类型一致。从属的水平上进行地理成分分析,能更好地揭示出植物区系的实质,巨桉人工林林下植物属的地理分布以热带性质为主兼具温带性质,属的间断分布类型比较丰富。各立地类型共有种比例少,物种没有表现出趋同性,并非只有特定的植物才能存留于巨桉人工林。（2）巨桉人工林林下植被可划分为14个群落类型,基本反映了调查区域内巨桉人工林林下植被的主要类型。根据分类结果,巨桉人工林群落层次结构包括三种类型:“巨桉+灌木+草本”型,占所有样方的74.1%;“巨桉+草本”型,占所有样方的22.2%;“巨桉”型,占所有样方的3.7%。阶地类型的林分群落结构特征主要为“巨桉+草本”型,丘坡两种类型的林分群落结构主要为“巨桉+灌木+草本”型。（3）同一立地类型不同样地之间物种组成相似性也较低,反映了林地起源的多样性与复杂性。巨桉人工林的物种主要来源于原立地保留下来的物种及繁殖体,以及从系统外特别是毗邻生态系统通过风、动物、人等途径传播和扩散进来的繁殖材料。由于丘陵地貌特点,林地多呈块状与农业耕作区镶嵌分布,物种多样性特征在很大程度上受制于立地原土地利用状况。三种立地类型物种构成均以偶见种多,非优势种群占据了物种丰富度的主体,物种分布不均匀,暗示了植被分化和演替的趋势。阶地立地类型林下植物出现频率最高的有空心莲子草（Alternanthera philoxeroides）和野塘蒿（Conyza bonariensis）,丘坡中厚土有里白（Hicriopteris glauca）、毛桐（Mallotus barbatus）和宜昌悬钩子（Rubus ichangensis）,丘坡薄土有野牡丹（Melastoma normale）。在现行巨桉人工林栽培制度下,大部分种易丢失,物种组成还会发生变化。（4）总体上,不同立地类型的巨桉人工林林下植物的物种均匀度差异不显著,丘坡薄土与阶地林分之间的物种丰富度差异也不显著,但丘坡中厚土物种丰富度显著高于丘坡薄土和阶地林分。丘坡中厚土林分的多样性指数显著高于阶地林分,但丘坡中厚土林分与丘坡薄土林分之间以及丘坡薄土林分与阶地林分之间的多样性指数差异不显著。阶地立地类型的灌木层物种丰富度和多样性指数显著低于草本层,而丘坡中厚土和丘坡薄土林分的灌木层和草本层物种丰富度和多样性指数差异不显著,三种立地类型林分的灌木层与草本层物种的均匀度均较高,且层次之间差异不显著。不同立地类型之间的草本层物种丰富度、均匀度和多样性指数差异均不显著（P＞0.05）。立地类型之间的灌木层物种均匀度差异不显著,但物种丰富度存在显著差异,以丘坡中厚土最高,其次为丘坡薄土,最少为阶地林分。此外,丘坡中厚土与丘坡薄土灌木层之间的植物多样性指数差异不显著,但二者均显著高于阶地林分。（5）巨桉人工林林下植被的种间关系联结性不强,呈负联接的趋势,表明林下物种种间关系还比较松散,物种趋向于随机性,现阶段植被稳定性还不高,预示着林下物种的组成还会发生变化,种间关系还会受到立地综合因子以及上层乔木巨桉双重影响而发生变化。草本层的稳定性低于灌木层。依据χ²检验和Spearman秩相关分析的结果,灌木层植物可划分为4个生态种组,草本层植物可划分为3个生态种组。（6）巨桉人工林生态位较宽的物种灌木层有野牡丹、宜昌悬钩子、盐肤木（Rhuschinensis）等,草本层有里白、芒（Miscanthus sinensis）、艾蒿（Artemisia argyi）等。这些种群具有相对较宽的资源利用谱,具有较强的生态适应性,因而生存机会多,分布范围也较广,成为巨桉人工林林下植被的主要种群。但与此同时,它们是以牺牲对有限资源的有效利用为代价的,这也预示着其它生态位较窄的物种容易丧失。可通过抑制生态位宽度较大物种的生长或改变环境资源状态,调整不同物种的现实生态位的方法实现资源的释放,从而增加生态位宽度较窄物种的生态位宽度,使其能够在巨桉人工林中存留下来。（7）丘坡中厚土和薄土两种立地类型巨桉人工林大型土壤动物和中小型干生土壤动物密度高于阶地类型林分,而中小型湿生土壤动物密度则是阶地类型大于丘坡类型。三种立地类型林分土壤动物同功能种团均以腐食性占绝对优势,植食性比例非常低,表明栽植巨桉以后立地仍处于一种良好的结构状态。以密度-类群指数衡量的土壤动物群落多样性特征与各立地类型林分实际情况相符,表现为丘坡中厚土型林分＞丘坡薄土型林分＞阶地型林分。（8）应用PCR-DGGE技术研究不同立地类型巨桉人工林土壤细菌群落的种群结构,结果表明不同立地类型的土壤细菌多样性存在差异,以阶地类型林分的土壤细菌多样性最高,其次为丘坡中厚土林分的,最少为丘坡薄土林分。这与不同立地类型土壤动物的多样性特征不一致。调查林分没有出现微生物结构趋同的情况,并非只有特定种类的微生物才能适生于巨桉人工林土壤中。综上所述,与土层厚度、土地利用历史等密切相关的立地条件调控着巨桉人工林生态系统地上/地下生物多样性特征。这意味着,为保育巨桉人工林发展区域的生物多样性,在发展短轮伐期巨桉工业原料林时,必需在巨桉人工林区域内保留一定面积和镶嵌结构合理的乡土植被,使短轮伐期巨桉工业原料林与乡土植被之间形成景观结构合理的镶嵌体,增加物种进入巨桉人工林生态系统的机会,防止巨桉工业原料林阻碍乡土植被之间的基因流通道。但有关乡土植被与巨桉工业原料林之间的镶嵌发展模式（如乡土植被保留的面积大小、乡土植被之间的廊道、巨桉工业原料林的面积与规模等）以及工业原料林经营管理方式与立地质量的耦合作用对乡土植被生物多样性的影响等研究尚未见报道,亟待深入研究。更多还原

【Abstract】 Plantation often plays important roles in providing wood for human being, slowing the increased tendency of CO₂ concentration, increasing forest coverage and alleviating the relied degree to natural forest. However, many problems as biodiversity decline, land degradation, production reduction and groundwater table drop were also co-occurred in plantation. Including others, biodiversity has been documented as the core of the problems. How to exert the ecological function, meanwhile satisfy the wood need and increase economy, and consequently to sustainable development is always the focus in plantation ecology. Despite of many previous studies have taken biodiversity in eucalypt plantation into consideration, there were inconsistent conclusions in whether the biodiversity reduction caused by unreasonable plantation management. The reduced biodiversity might be related with the site condition, but little information has been available on. Therefore, to understand the effects of site type on biodiversity in eucalypt plantations, the characters of above/below ground biodiversity were studied in different Eucalyptus grandis plantations with different site types by field investigation and laboratory analysis. The results could provide important data for site selection and biodiversity conservation in sustainable management of eucalypt plantation. The results as follows:（1） Rich plant species were observed under the eucalypt plantation. There are 71 families, 158 genus and 193 species of vascular plant in the investigated plantations, dicotyledon plants dominated the plantations, 45 families, 81 genus and 90 species for terrace site, 61 families, 111 genus and 132 species for hilly site with middle-thick soil, 52 families, 99 genus and 118 species for hilly site with thin soil. Land use character influenced the species composition of plant understorey. The standing plant species reflected the origin of forest, as Camellia sinensis, Citrus reticulata, Cunninghamia lanceolata, et al. Terrace site was dominated by herbs, originated from farmland; hilly site was dominated from shrub and herb with ratio of 1:1, originated from barren, forest and tea garden. As the result of it, the closely forest similarity was observed between two hilly site, the weak one between terrace site and hilly site with middle-thick soil. The analysis of plant flora indicated that the distribution characters of genus and species were similar among the different forest lands. The results hinted that geographic analysis of genus could better reveal the nature of plant flora. The geographic distribution of plant genus under eucalypt plantations dominated by tropic and warm zone characters. Rich disconnected distribution types of genus were observed.（2） Understorey vegetation in eucalypt plantations could be divided into 14 community types, which mainly reflected the main types in the investigated region. According to classified results, community structure of eucalypt plantations included three types: "eucalypt + shrub + herb" accounted for 74.1% of total sampling sites, "eucalypt + herb" accounted for 22.2% of total sampling sites, "eucalypt + shrub" accounted for 3.7% of total sampling sites. "Eucalypt + herb" dominated the terrace site, and "eucalypt + shrub + herb" dominated two hilly site.（3） Low similarity of species composition was observed among different sampling plots in the same site type, indicating the diversity and complexity of forest origination. The plant species in the eucalypt plantation was mainly originated from the primary species and propagules in the site, and other spread propagules by wind, animal and human being from abutted ecosystems. The forest land distributed with block and enchased with farmland due to the special character of hilly. Biodiversity was limited by the land use characters of primary land. Predominated species contributed little in plantation species richness. Asymmetric species distribution implied the tendency of vegetation differentiation and succession. Alternanthera philoxeroides and Conyza bonariensis showed the frequently visibility in terrace site. Hicriopteris glauca, Mallotus barbatus and Rubus ichangensis were found in the hilly site with middle-thick soil, while Melastoma normale was found in the hilly site with thin soil. The results suggested that the majority of standing species was reliable to loss, and the composition of plant species would change by the standing planting modification in eucalypt plantations.（4） Species evenness was varied insignificantly among eucalypt plantations with different site types. Species richness was not varied between the eucalypt plantations with terrace site and hilly site with thin soil, but species richness in hilly site with middle-thick soil was significantly higher than that in terrace site and hilly site with thin soil. Biodiversity index in the hilly site with middle-thick soil was significantly higher than that in terrace site, whereas the biodiversity index was significantly different between the hilly sites with middle-thick and thin soil, and between the hilly site with thin soil and terrace site. The richness and biodiversity index of shrub were lower than that of herb in terrace site, but which in hilly site with both middle-thick and thin soil showed little differences between shrub and herb. Evenness of both shrub and herb was high in all of the three plantations, but little varieties among layers. The varieties of richness, evenness and biodiversity index of herb layer were not statistical varied among the plantations with different site types. Species evenness of shrub was not different among the plantations with different site types, but species richness was varied, and showed the order: hilly site with middle-thick soil > hilly site with thin soil > terrace site. In addition, although biodiversity index of shrub layer was not varied between the hilly sites with middle-thick soil and thin soil, their values were relative higher than that in terrace site.（5） Weak relationships even negative associations were observed among the plant species under eucalypt plantation, suggesting the randomicity of species. This implied that low vegetation stability of standing plantation could induce the changes of species composition. The interspecific relationships among species might be influenced by both canopy eucalypt and the land characteristics. Compared to shrub layer, herb layer hadlower stability. According to the result of x² test and Spearman rank correlations, shrubplants could be divided into 4 ecological groups and herb plants could be divided into 3 ecological groups.（6） Rhus chinensis, Hicriopteris glauca and Rubus ichangensis of shrub, and Melastoma normale Miscanthus sinensis and Artemisia argyi of herb had wider niche under eucalypt plantation than others. These populations had more survive opportunities, wider distribution scale with better ecological adaptation. Meanwhile, the species with narrower niche were liable to disappear since the species with wider niche could better occupy and use the limited resources. Inhibited the growth of species with wider niche or changed the status of environment resources could manual modified the present niche, wide the niche of the species with narrower niche, resulting more species existed in eucalypt plantation. （7） The macro fauna and mesofauna densities of dry types were higher in the eucalypt plantations with hilly site than that in plantation with terrace site, but mesofauna densities of wet types were lower in hilly plantation. Saprophagous animals dominated the soil animal group in all of the three plantations with different sites, while the ratio of phytophagous animals was relative lower, suggesting land structure still kept the good status after planting eucalypt. The index of density-population could indicate the diversity character of soil animal community in the plantations with different site types, showed the order as: hilly site with middle-thick soil > hilly site with thin soil > terrace site.（8） The significant varieties of bacterial communities were found among the plantations with different site types by PCR-DGGE, showed the order as: terrace site > hilly site with thin soil > hilly land with middle-thick soil. This was inconsistent with the soil animal biodiversity in the plantations with different land types. The investigated plantations had different microbial structure, which was contrary to the opinion that only special microbial communities could adaptive to the soil in the eucalypt plantation.In conclusion, the related land condition as soil depth and land use controlled the characters of above/below ground biodiversity in eucalypt plantation. The results suggested that preserving native vegetation with a number of areas and mosaic structure could play essential roles in increasing opportunities that species input, preventing the baffle of gene flow corridors among native vegetations in eucalypt plantation regions. The mosaic structure formed by native vegetation and eucalypt plantation would conserve the biodiversity in the regions of eucalypt plantations. However, little attention has been paid to the effects of mosaic development modifications （such as, the size of preserving patch, corridors between native vegetations, the size and scale of eucalypt plantation）, plantation management, land quality and their synthesis on the biodiversity of native vegetation. Further study is urgently.更多还原