【作者】 段仁燕；

【导师】 王孝安；

【作者基本信息】 陕西师范大学 ， 植物学， 2009， 博士

【摘要】 太白红杉(Larix chinensis)是我国特有的国家二级保护物种,分布区极其有限,是秦岭地区最上线的唯一乔木树种,是该地生态系统的重要组成部分,在涵养水源、稳固山石和保持水土等方面发挥着重要作用。但是,这些植被带也是生态敏感带,易受外界干扰的影响。不同海拔梯度下,太白红杉的种群特征和群落动态存在着明显的差异。本文在太白山国家级自然保护区太白红杉集中分布的区域分低海拔(2 900～3 000 m)、中海拔(3 100～3200 m)和高海拔(3 300～3 400 m)三个海拔梯度研究了太白红杉的种群特征及群落动态变化规律。通过对不同海拔梯度下太白红杉种群特征及群落动态的研究,分析了太白红杉种群大小和年龄结构的变化规律、生存状况、幼苗的更新动态、叶绿素荧光特性以及斑块动态变化,初步探讨了亚高山针叶林带物种多样性维持机理,并提出太白红杉的保护措施。主要结果归纳如下:1.通过对不同海拔梯度下太白红杉种群大小和年龄结构的调查和分析,结果表明:①不同海拔梯度下,太白红杉种群的更新密度、立木密度、死树密度、平均胸径、平均高度和平均郁闭度均存在着显著的差异(p＜0.05)。②在不同海拔梯度范围内建立的年龄-胸径(适用于成树)、年龄-高度(适用于幼苗和幼树)回归方程有较高的回归优度。这些方程可较好地拟合年龄-胸径以及年龄-树高之间的相互关系。③在低海拔和中海拔,太白红杉的年龄结构与胸径的散布模式相似,均为钟型;但在高海拔,年龄结构与胸径的散布有一定的差别。④不同海拔梯度下,太白红杉的年龄结构差异显著(p＜0.05)。在低海拔和中海拔,年龄结构均为钟型;而在高海拔,太白红杉种群的年龄结构为波形。2.通过编制林线附近太白红杉种群特定时间生命表,绘制了存活曲线、死亡率曲线和消失率曲线,分析太白红杉的分布格局及生存状况。结果表明:①在林线附近,太白红杉种群存活曲线介于DeeveyⅡ型和DeeveyⅢ型之间。②太白红杉种群整个生长期中出现了两个死亡高峰期,一个出现在中龄时期,另一个出现在老龄时期。太白红杉幼苗较高的存活率可能与其以萌生为主的更新方式有关。③太白红杉种群各龄级的空间格局基本上为聚集型;但随着植株年龄增加,种群分布由聚集型向随机型过渡,聚集强度降低。3.通过对不同海拔梯度下不同大小林窗内太白红杉的更新状况调查,探讨了太白红杉的更新动态。结果表明:①在太白红杉分布的低海拔和中海拔,林窗大小以中小林窗为主,大林窗较少;而在高海拔,以大型林窗为主。太白红杉在中海拔更新相对较好。②与巴山冷杉相比,太白红杉的更新较差;林窗内和林冠下,巴山冷杉有大量的更新库(幼苗和幼树库),更新密度较高。③林窗的形成有利于太白红杉的更新,林窗大小和太白红杉更新关系密切。在太白红杉分布的低海拔和中海拔,中等大小林窗(100～150 m~2)有利于太白红杉的更新;小林窗(＜50 m~2)有利于巴山冷杉的更新。而在太白红杉分布的高海拔,太白红杉的更新更倾向于小林窗(＜50 m~2)。研究表明,不同大小林窗为不同树种的更新提供了条件,也决定了未来上层优势树种组成的差异。4.以移栽的太白红杉幼苗为材料,研究其叶片叶绿素荧光参数的变化规律。结果表明:①自然光下,从早上6:00～下午14:00,太白红杉幼苗叶片的PSⅡ光化学效率(F_v/F_m)、PSⅡ光量子效率(Yield)和光化学猝灭系数(qP)均呈下降趋势;其中在下午14:00最低(接近于0);而非光化学猝灭系数(qN)呈上升趋势,其中在下午14:00最高(接近于1)。②高温(＞25℃)或低温(＜0℃)胁迫下,太白红杉幼苗的F_v/F_m均随胁迫时间的延长急剧下降,而在5～20℃,F_v/F_m的变化范围相对较小。结果表明,适宜太白红杉幼苗生长的温度在5～20℃,过高的温度或者过低的温度,均影响到太白红杉幼苗正常生长。5.根据森林循环理论,森林群落的动态是处于不同发育阶段的镶嵌系统。通过对不同海拔梯度下太白山亚高山针叶林带太白红杉林结构的研究,确定4种斑块阶段(林窗阶段、建立阶段、成熟阶段和衰退阶段),研究森林斑块动态变化和生物多样性变化规律,并测定和分析了不同斑块类型内光照和温度的日变化规律。结果表明:①不同海拔梯度下,优势斑块的比例不同,表明群落处于不同的发育阶段。在低海拔,衰退阶段斑块的比例最高;在中海拔,林窗阶段和建立阶段斑块的比例最高;在高海拔,林窗阶段斑块的比例最高。②在中海拔,斑块大多呈随机分布。在低海拔和高海拔,在中小尺度上,斑块呈随机分布;在大尺度上,斑块为聚集分布。③在太白红杉分布的不同范围内(低海拔、中海拔和高海拔),林窗阶段光照强度和土壤表面温度均要比其他3个阶段变化明显。而在成熟阶段包含了一个相对温和的环境。④在森林循环的不同阶段,不同大小个体的密度变化存在一定的差异。表明不同大小个体的补充速率存在着差异。群落内可被不同大小个体利用的环境因子,也存在着明显的差异。⑤在斑块的不同发育阶段(G-B-M-D),物种丰富度、多样性和密度变化均呈波形。总之,在太白红杉分布的不同海拔范围内,太白红杉群落处于不同的发育阶段。在低海拔,太白红杉更新相对较差,群落处于衰退阶段;中海拔更新相对较好,中等径级个体占优势,群落相对稳定;在高海拔,存在较大尺度的干扰,群落处于动态变化之中。因此,可采取相应的保护措施来保护太白红杉:①在低海拔,太白红杉更新与中等大小林窗的出现有一定的相关性。应对中小径级的太白红杉采取抚育措施和合理择伐小林窗内的灌木及林窗边缘较大径级的巴山冷杉,人工制造中等大小林窗(100～150 m~2)来加强对太白红杉的保护。②在中海拔,限制太白红杉更新的主要因子可能是林窗内能否有太白红杉种子萌发和生长的条件。可适当择伐高大植株中较长的枝,为其他较小植株的生长提供必要的光照和空间。另外,还应适度清理林窗内灌木层和扰动草本地被物层,使太白红杉种子能顺利落入土壤。③在高海拔,限制太白红杉更新的主要因子可能是气候因子(如大风和暴风雪)和能否有较小林窗(＜50 m~2)的出现。应对林窗内的灌木进行人工去除,制造较小的林窗,为太白红杉种子萌发和幼苗更新提供合适的空间和适宜的光照。④太白红杉幼苗生长适宜温度可能在5～20℃,过高的温度或者过低的温度,均能影响到太白红杉幼苗正常的生长。因此,应对太白红杉幼苗进行人工保护(如添加覆盖物等),防止极端温度对幼苗造成伤害。更多还原

【Abstract】 Larix chinensis is one of typical endemic species in China,only distributed in alpine and sub-alpine belt in Mt.Qinling,Shaanxi Province of China.It is also one of endangered species in Chinese Plant red Data Book.It is the only tree that forms the pure forest which has special functions to conserve water,firm mountain stone and maintain water and soil at the timberline area.Mountain peaks covered in ice and rocks,steep slopes,wild torrents,and fragile soil and vegetation cover characterize the topography, where the environmental risks are high and natural disasters(e.g.,flood,erosion,rock and land slides,avalanches etc.) are frequent.The sub-alpine vegetation belt is a very important buffer zone limiting potential threats in mountainous areas,and undisturbed sub-alpine forests can efficiently reduce the risks of natural disasters.However,this vegetation belt is also a sensitive area.Assessing and analyzing population characters and community dynamics are therefore prerequisites for understanding ecological processes and restoration of natural forests.The population characters and community dynamics of L. chinensis populations along the altitudinal gradient on the southern slope of Taibai Mountains were studied in this paper.The forest was divided into three transects,i.e., low-altitude(2900～3 000 m),mid-altitude(3100～3200 m) and high-altitude(3300～3400 m).Primary results of this paper were summarized as following:1 Age structure studies along an altitudinal gradient would be helpful in understanding the limiting factors on the regeneration of natural forests.L.chinensis individuals were defined as trees,saplings,or seedlings by their heights.Age of each individual was estimated by the age-height relationships of seedlings or saplings and the age-DBH(diameter at breast height) relationships of big trees.The age structures differed across altitude classes.The age structure in low-altitude transect and in mid-altitude was closed to bell-shaped,which was characterized by the dominance of adult trees. Multi-modal age distribution was found in the high altitude transect,and was caused by lack of young seedlings and saplings.This suggested that different limiting factors played important roles in shaping the age structure and forest regeneration at different altitudes. In the low altitude,density dependent interspecific and gap disturbance was probably the most important limiting factor.In the mid-altitudinal transect,density dependent intraspecific competition between trees and gap disturbance likely controlled regeneration of L.chinensis.We propose that limiting climatical factors,e.g.temperature,play an important role in determining the age structure of L.chinensis populations in high-altitude areas.2 Alpine timberlines are ecotones highly sensitive to disturbances and enviromental changes that have become a major focus of global climate change research.To explore the survival status of L.chinensis populations,one plot(100 m×100 m) were investigated and analyzed.Time-specific life tables or vertical life table curves of survival-mortality based and hazard based age structures were drawn.The results showed that:①The survival curve of the population tended to be the type between DeeveyⅡandⅢ;②There existed two peaks of mortality in the lifespan,one was adult stage(70～80 years) and the other in the old stage(180～190 years);③Most individuals of different age class had a clumped distribution at different scales.With the population age increased,the distribution pattern had a trend from clustering to random,and the clustering intensity decreased somewhat.3 In order to explore the functions of gaps on forest dynamics and biodiversity protection in the sub-alpine coniferous forest,the survey of gaps and community had been carried out in Taibai Mountain Nature Reserve.Natural disturbance regimes of gaps,and tree species regeneration responses to gaps were studied.The results showed that:①In low-altitude and in mid-altitude transect,the gap size class distributions were also similar and showed a strong positive skewness with a few large and many small gaps;gaps＜100 m~2 were most frequent and gaps＞150 m~2 were rare.In high-altitude,most of the gap size class distributions were large.②There were significant differences in the size and number of seedlings among the different sized gaps and understorey.③In low-altitude transect and in mid-altitude,the regeneration of L.chinensis in the different sized gaps were as follows:medium＞small＞large＞understorey;the regeneration of Abies fargesii in the different sized gaps were as follows:small＞medium＞large＞understorey.In the high-altitude,small gap was benefit for the regeneration of L.chinensis.Common tree species in a sub-alpine coniferous forest in Taibai Mountains exhibited different gap regeneration behaviors.Shade-tolerant A.fargesii vigorously regenerates in gaps from advance regenerations.L.chinensis may also regenerate in gaps from new individuals,but regeneration was infrequent or absent.Because L.chinensis usually requires both a canopy opening and exposed mineral soil surfaces for seedling establishment.Therefore,the lower frequency middle gap may explain the absence of the L.chinensis regeneration.4 The experiments were made with the seeding of L.chinensis.The results showed that:①It was studied that daily change of chlorophyll fluorescence of L.chinensis by PAM-2100.The results indicated that in sunny day,F_v/F_m、Yield and qP daily change of photosynthesis decreased and there is the lowest photosynthesis at 14:00.The non-photochemical quenching rate(qN) increased significantly.It was proved that the PSⅡwas damaged at the high temperature.②At high temperature(＞25℃) and low temperature(＜0℃),the maximum quantum yield(F_v/F_m) of photosystemⅡ(PSⅡ) sharp declined with the increasing of time.5 According to the forest-growth-cycle theory,forest communities are dynamic, mosaic systems composed of patches in different developmental phases.Based on an investigation in a sample of L.chinensis forest types on Taibai Mountain,China,four distinct growth phases or patch types were recognized and patterns of patch mosaics and changes in species diversity were studied.Diurnal changes in light and temperature regimes in different patch types of the forest growth cycle were measured and analyzed. Our results were as follows:①The percentages of different patch types within the sampled forest community in low-altitude,mid-altitude and high-altitude,were for the gap phase(32.3%、40.3%and 48.5%),building phase(24.5%、34.0%and 32.0%),mature phase(23.5%、17.2%and 12.3%) and degenerate phase(19.7%、8.5%and 7.2%);②The change of densities(number of individuals/ha) of trees in the forest growth cycle was mainly caused by the larger sized trees;③The changes of species diversity with the forest growth cycle showed a wave-like pattern;④The average DBH,average height,average basal area at DBH,and average volume of each individual and stand volume all increased with the forest cycle process;⑤The environmental factors changed significantly,both diurnally and with progress of the forest cycle.Light intensity and soil surface temperature changed more in the gap phase than the other three phases.A framework to explain the mechanism for maintaining biological diversity within the sub-alpine coniferous forest is described.From our study,we hypothesize the following as a framework to explain the mechanism for maintaining biological diversity within the Taibai subalpine coniferous forest:Disturbance factors(e.g.,wind,snow and pest) acting on the forest canopy and trees causing tree deaths.Gaps of different sizes forming after the death of canopy trees. Restoration and regeneration process of trees in gaps,initiating the process of the forest growth cycle.Variation in ecological factors in patches of different developmental phases, having selective effects for different species groups and different sized trees.Varying regeneration and recruitment densities of different species groups and different sizes in different patch types.Variations in growth response for each species group in different patch types within a forest community,and all species satisfying their life history requirements in the patch mosaics within the community.In a word,some measures should be taken to protect L.chinensis.In all,there were lack of young seedling and sapling in the forest.According to the heliophytic and xerophytic characteristics of L.chinensis,different management activities should be taken according to the population characters and community dynamics in different altitude,so as to promote optimal environmental conditions for seedling recruitment in the rare L. chinensis.We should foster the sapling and cut down the higher trees reasonably to reduce the competition intensity.We can offer space and abundant light to the sapling by producing gap,cutting non-target species,clearing herbs,or felling the longer boughs of higher trees.Of course,there are many problems needing our research.For the growth of seedlings,the temperature should be 5～20℃.The temperature is too high or too low, temperatures can affect the seedling of L.chinensis growth.As a result,seedlings should be protection(such as adding a cover,etc.) to prevent extreme temperatures caused by damage to the seedlings.更多还原