【作者】 郭垚鑫；

【导师】 杨改河； 王得祥；

【作者基本信息】 西北农林科技大学 ， 作物栽培学与耕作学， 2013， 博士

【摘要】 随着全球生态环境的不断恶化，探索生物与环境相互作用机理及其适应机制一直是当今生态学研究的热点问题，其中森林群落的稳定性及其维持机制就是其中主要的一方面。秦岭作为我国具有国际意义的陆地生态系统关键区域之一，一直是国内外森林生态系统研究的热点区域。然而，红桦作为秦岭主要的植被类型之一，有关其在秦岭的稳定性及其在山地垂直带谱的地位和作用一直存在争议,至今未有明晰的结论。鉴于此，本研究选择秦岭山地红桦群落为研究对象，通过全面的资料收集和野外调查，从种群、群落及其环境因素三个角度详细的研究和分析秦岭山地红桦林群落稳定性和维持机制，从而为红桦在秦岭山地植被带谱中的定位以及保护利用提供科学依据。本研究的主要研究结果如下：(1)秦岭红桦林群落内共含维管植物182种，隶属128属66科，其中乔木层16科18属39种；灌木层21科34属54种；草本层32科76属82种；层间植物5科6属8种。其中，科的地理分布类型中，世界分布科最多，占到42.41%；属的地理分布区类型中，78.13%的属为温带分布属，其中北温带属（包括北温带和南温带间断分布、欧亚和南美洲温带间断分布）为主要分布属。可以充分说明秦岭红桦林具有明显的温带特性。从秦岭山地红桦林群落外貌来看，秦岭红桦林中高位芽植物占61.82%，在高位芽植物种，落叶阔叶植物78种，占95.12%；说明红桦林中落叶阔叶成分占绝对优势，反应出红桦林分布区的温带气候特征。根据红桦林群落的外貌和乔木优势种组成将所调查红桦林群落分为红桦纯林（B. ablosinensis community）、红桦-辽东栎林（B.ablosinensis-Quercus liaotungensis community）、红桦-五裂槭-华山松林（B.ablosinensis-Acer oliverianum-Pinus armandii community）、红桦-太白杨-少脉椴林（B.ablosinensis-Populus purdomii-Tilia latevirens community）、红桦-华西枫杨林（B.ablosinensis-Pterocarya insignis community）、红桦-华山松林（B. ablosinensis-Pinusarmandii community）、红桦-华山松-牛皮桦林（B. ablosinensis-Pinus armandii-Betula utiliscommunity）、红桦-牛皮桦-巴山冷杉林（B. ablosinensis-Betula utilis-Abies fargesiicommunity）、红桦-牛皮桦林（B. ablosinensis-Betula utilis community）9个群落类型。（2）对秦岭天然红桦林群落的更新调查表明：红桦林下乔木更新幼苗以槭树科（Aceraceae）和松科（Pinaceae）为主。其中，红桦幼龄林中优势种红桦更新较好，而熟林和过熟林中幼苗更新极差。群落更新受群落密度的影响较大，乔木的胸高断面积和灌木盖度都与林下更新幼苗和幼树密度存在一定的负相关关系，随胸高断面积和灌木盖度的增加幼苗幼树呈减小趋势；草本植物的盖度对幼苗的更新密度的影响比较复杂，没有明显的趋势。此外，红桦林择伐迹地的研究表明，择伐能明显促进红桦的天然更新，小面积择伐更新50年后，尽管红桦林物种组成上没有变化，但红桦种群的比重及其幼苗、幼树的密度明显增加。（3）秦岭红桦林的林隙形成方式主要以自然立枯和折干为主，林隙密度约为11.42个hm-1；林隙形成木多1-2株形成木形成，3株以上林隙形成木导致的林隙较少；多数林隙由优势种红桦导致或者参与形成；林隙平均面积（林冠隙）约为73.71±21.54m2，多数林隙面积在20-80m2范围；林隙下幼苗组成以红桦的为主，红桦幼苗在60m2以上的林隙中更新较好，说明林隙更新是红桦成功更新的一种重要方式，且林隙面积越大越利于红桦幼苗的建立。（4）空间格局分析是揭示群落和种群生态学过程的有效手段。天然红桦林中，红桦种群整体表现为随机分布，但由于其依赖于扰动进行更新，幼树主要表现为小尺度聚集型分布。红桦不同发育阶段的空间关系表明，红桦大径级个体和幼树呈现明显的负关联，说明大径级红桦对红桦幼树有一定的排斥作用，这种现象可能由于大径级红桦树冠的遮阴作用抑制幼苗的建立。此外，红桦幼树与立木残干在空间分布上呈明显的正关联，进一步证明红桦依赖于树木残干导致的林隙干扰进行斑块更新。（5）红桦的种子为具膜质翅的小型坚果，长宽约为1.5-2mm。红桦种子具有较强的扩散能力，种子雨强度随着离母株的距离先增加后减少，在离母株20-30m处的种子雨强度最大。红桦种子雨强度受风力和风向的影响较大，即使在逆风方向种子也能传播到100m以外。红桦种子成熟进入种子库中，大部分被截留在枯枝落叶层，少部分进入腐殖质层，其中大约50%的种子具有活性。红桦强大的种子雨强度和扩散能力为其保存着数量庞大的种子库，为红桦幼苗的补充和种群的持续提供了基础。（6）秦岭红桦林群落中，红桦-华山松、红桦-华山松-牛皮桦、和红桦-牛皮桦-巴山冷杉三个群落的稳定性最高，其次为红桦-五裂槭-华山松、红桦-辽东栎、红桦-牛皮桦和红桦-华西枫杨。红桦纯林和红桦-太白杨-少脉椴的稳定性最差。从海拔角度看，海拔在2300-2600m范围内红桦群落的稳定性最高，说明这个海拔范围是秦岭红桦群落最稳定的分布区域。对天然红桦群落稳定性影响最大的五个因子是：枯落物厚度、乔木竞争指数、乔木幼苗、幼树及成树的比例。Godron稳定性测定方法与稳定性指数法对群落稳定性的评价结果基本一致。群落物种多样性在群落稳定性方面起到很重要的作用，但二者并不一致，并不能完全代表群落的稳定性，因此不能机械的用多样性判断群落的稳定性,要结合群落的结构、树种特征、立地条件进行具体分析，综合评价群落的稳定状况。从环境条件看，秦岭中高海拔区域气候温凉湿润且气候波动较小、没有极端的恶劣气候，这就为红桦形成稳定群落提供了优越的环境条件，红桦群落的结构特征也证明了其对环境的高度适应性，因此红桦在秦岭不同区域都能在相似的海拔范围内形成稳定的群落类型；从种群角度看，优势种红桦能形成庞大的活性种子库，并能依赖林隙干扰进行幼苗补充保持其种群的延续性；此外，林隙干扰通过调节林分环境维持群落内物种组成和多样性，使红桦群落始终保持相对稳定的结构组成。通过这种机制，自然条件下红桦群落表现为时空异质的斑块聚集体，呈现局部过渡而整体稳定。因此，只要干扰存在，红桦就可以在秦岭长期存在，形成稳定的植被类型。更多还原

【Abstract】 With the worsening of ecological environment over the world, exploring the mechanismof the biological and environmental interactions and adaptation mechanism has been a hotissue in today’s ecological studies. Therein, the stability of forest communities and theirmaintaining mechanism is one important aspect. As a key region of the terrestrial ecosystemin China, the Qinling Mountains has been a hotspot over the global forest research. Betulaalbosinensis is an important vegetation type in Qinling Moutains. The palynological evidenceindicates that the Betula forests have been existing as zonal forests at geological period andmodern times in Qinling Moutain. However, the published reports on B. albosinensis forestsuggest that the natural regeneration of B. albosinensis in mature B. albosinensis forests ispoor, and it is impossible for B. albosinensis to keep their dominance for long time. So, thesereporters conclude that B. albosinensis is one of successional series and would be replaced bythe climax species. Until now, there is no a clear conclusion about the stability of B.albosinensis forests. Therefore, in order to determine the stability of B. albosinensiscommunities and its predominant mechanism in the Qinling Mountains, we studied thepopulation and community characteristics as well as the stability of the B. albosinensiscommunities from the viewpoints of population, community and environmental factors. Theinformation obtained is also useful from ecological and silvicultural perspectives. The mainresults were as follows:1. There exist182tracheophyte plant species, belong to128genera and66families in B.albosinensis forest of Qinling Mountains. Of all the plant species, tree layer shares39speices,18genera of16families; shrub layer shares54species,34genera of21families; herb layershares82species,76genera of32families. Besides, there are8vine species, belong to6genera and5families. World-widely distributed families dominate the flora of the B.albosinensis forest, while the distribution types of plant genera is dominated by temperategenera. This well suggests that there are clear temperate characteristics in B. albosinensisforest. From structural characteristics of B. albosinensis communities, it can be found thatphanerophytes occupied a dominant position among all life form spectra, and deciduousbroad-leaved species accounts for most. It indicates a temperate climate characteristic in B. albosinensis forest region. According to the appearance and dominant species composition,the B. albosinensis communities are divided into nine community types: B. ablosinensiscommunity、 B. ablosinensis-Quercus liaotungensis community、 B. ablosinensis-Aceroliverianum-Pinus armandii community、B. ablosinensis-Populus purdomii-Tilia latevirenscommunity、B. ablosinensis-Pterocarya insignis community、B. ablosinensis-Pinus armandiicommunity、B. ablosinensis-Pinus armandii-Betula utilis community、B. ablosinensis-Betulautilis-Abies fargesii community、B. ablosinensis-Betula utilis community.2. The study on the regeneration of B. albosinensis communities indicated: the seedlingand sapling pool of B. albosinensis communities is dominated by Aceraceae species andPinaceae species. The seedlings of B. albosinensis recruitment are abundant in young B.albosinensis communities and scarce in mature communities. Dense tree layer and shrub layerrestrict the regeneration of tree species. The density of seedlings and saplings has a significantnegative correlation both with tree basal area and shrub coverage. Differently, there was nosignificant relationship between seedling and sapling pool and herb coverage. In addition, alarge number of recruitments were found in stands with subsequent regenerationapproximately50years after strip clearcutting. After stripclearcutting, the sudden exposure ofpreviously forested lands andmore sunlight reaching the forest floor seemed responsible forthe successful regeneration of sunlight-loving B. albosinensis.3. The gap characteristics and disturbance regime in the B. albosinensis forest in theQinling Mountains were studied, including the type, quanity and causal factors of gaps andthe type, number, species composition and size structure of gap maker. The results indicatedthat the average gap area was73.71±21.54m2, and65.5%of the gaps were between20m2and80m2. Most gaps (78.1%) were caused by one or two standing death, and few werecaused by three or more gap makers. B. albosinensis were the major gap makers, and it wasmost possible to create gap by standing death. There was no apparent change between gap andnon-gap in species compostion, but in species abundance. In the gaps, the seedlings andsaplings of B. albosinensis were the main gap filler, and the large gap was more suitable for B.albosinensis regeneration. The results suggested that B. albosinensis depends on canopy gapsfor pulsed recruitment, which may make them capable of maintaining population stability.4. In order to understand the recruitment mechanism and recovery process of Betulaalbosinensis forest, using data collected from1hm2plots, univariate and bivariate O-ringfunctions were employed to determine spatial distribution of standing trees and snags indifferent age classes and correlate standing trees and snags. The results indicated that all B.albosinensis individuals showed a random distribution in space. B. albosinensis saplings weresignificantly clustered as a whole at the range from0to10m, but the pattern intensities decreased with increasing age so that large trees showed a stochastic spatial distribution atmost scales. In addition, patterns in the distribution of B. albosinensis saplings appear topersist and were consistent with highly aggregated patterns of snags caused by naturaldisturbances across the stand. Findings suggest cohorts of the B. albo-sinensis populationQinling Mountains are spatially clumped and the aggregation of different cohorts representspulsed recruitment after canopy disturbance.5. We studied the seed dispersal property, the seed bank and the germinationcharacteristics of B. albosinensis seeds. We found the seed density in seed rain is3951±2119ind/m2in the range of100m from mother tree. The seed rain intensity is maximum in thedistance10-30m from the mother tree and it is significantly difference in the differentdirection due to wind. In the seed bank ranged from0to50m from B. albosinensis cohort, thevisible seed density in the up litter layer was4029±2424ind/m2, and the density in the lowerhumus layer762±456ind/m2. The visible seed density estimated from the seeds collected inthe litter layer was significant higher than that estimated from the seeds on the soil surface.Besides, the recorded germination rates found that more than half of seeds in the seed bankwere active. The high output and dispersal capacity of B. ablosinensis them have anoverwhelming advantage in density and space occupation in the seed bank of their range.6. We studied the community sability of B. albosinensis communities in the QinlingMountains with Godron stability index method and principal component analysis method. Theresults indicated that B. ablosinensis-Pinus armandii community，B. ablosinensis-Pinusarmandii-Betula utilis community and B. ablosinensis-Betula utilis-Abies fargesii communityare the most stable community types in the B. albosinensis forest of Qinling Mountains, ofwhich the B. albosinensis communities at2200-2600m range of altitude were most stable,suggesting an optimum environment for B. albosinensis. Additionally, the results showed thatthe thickness of fallen leaves, trees competition index, the quantity proportion of seedlings,saplings and adults were the main factors influencing the community stability. The evaluationresult on the community stability from Godron stability index is consistent to the resultexamined by principal component analysis method. The species diversity index is a importantfactor in accessing the stabiligy of a community, However, we could not ascertain the stabilityof community only according the diversity index due to the interaction of other factors.The results above indicate that B. albosinensis forest in the Qinling Mountains is a stablevegetation type. On the one hand, high seed output and dispersibility make B. ablosinensispopulation have a large seed bank in density and space occupation.On the other hand, the B.ablosinensis population prone to cause canopy gaps under the natural disturbances (e.g.,windstorms, floods, heavy snows), which would provide a ideal environment for their regeneration. The rapid growth after germination of B. ablosinensis seeds can colonize rapidlythe new patchs created by canopy gaps, and than make them persist and dominate. At thesame time, the frequent canopy gaps also can reduce the dominance of the bettershade-tolerant species and maintain the typical species compostion. With the help of canopydisturbance, B. albosinensis achieve a stable mosaic structure of different-spatiotemporalcohorts. Besides, environment condition is also important for the persistence of B.ablosinensis forest. The altitude range between2000m and2800m in the Qinling Mountainshas a stable and cool-warm moist climate, which is most adaptive for the growth of B.albosinensis. Therefore, B. ablosinensis that distributes in the cool-warm moist zone betweenthe temperate deciduous broadleaf forest and the cold-temperate conifer forest in QinlingMountains attain stability.更多还原