Altitudinal belts exhibit substantial variation across the world's mountains in number, typology, combination patterns, and vertical range. However, the conditions under which specific belts occur and the climatic factors influencing their vertical range remain poorly understood. Therefore, this study focuses on tropical African mountains, which are characterized by massive volcanic cones, rich biodiversity, and complete altitudinal belt structure, as a representative region. We compiled 23 spectra of altitudinal belts from published literature for 10 representative tropical African mountains. Integrating climatic data of WorldClim V2.0 and topographic data from SRTM 90 m DEM, we investigated the vertical ranges and combination structures of altitudinal belts, and analyzed their relevant driving climatic factors using stepwise regression. The results show that: (1) Tropical African mountains usually have five to eight altitudinal belts which constitute a complete altitudinal belt spectrum from tropical vegetation to nival zones. (2) The upper montane regions are typically characterized by the development of bamboo forest, cloud forest, and ericaceous forest belts, but with different patterns of single belt, dual belts and triple belts. (3) Climate-altitudinal belt regression models could well explain the vertical range of the highest forest belts (ericaceous forest) and low forest belt (monsoon rainforest) (R 2 = 0.72-0.75), and could moderately explain the vertical range of mountain forest belt, bamboo forest belt and cloud forest belt (R 2 = 0.31-0.44). (4) The normal establishment of a specific altitudinal belt primarily depends on annual hydrothermal conditions or on a compensatory interplay between temperature and precipitation under suboptimal conditions, while the vertical range of any altitudinal belt is closely associated with the intra-annual or seasonal variations of hydrothermal conditions. This study further highlights the complexity and diversity of tropical African mountains, providing a more solid scientific foundation for altitudinal belt theory development.

The Qinling-Daba Mountains (QDM), extending east-west in central China, span warm temperate and subtropical zones and are characterized by complex geographical transitions and high biodiversity. They actually also act as a significant ecological corridor between the Tibetan Plateau and East China plains, but this almost has not been addressed. This study uses plant species data of 40 national nature reserves within QDM and 18 in adjacent area, performs consensus clustering at the levels of species, genus, and areal type, traces the origins and dispersal routes of 89 Chinese endemic genera, and, finally, assesses the importance and areal differentiation of environmental factors on species distribution. The results show: (1) The QDM as a corridor contribute greatly to the high biodiversity in the study areas, particularly in the easternmost and westernmost sections. (2) The QDM promote species interactions and exchanges between west China and east China. The genera involved are classified into four main types of geographic origins: Central-East China components (41 genera) and North China components (8 genera) spread southwestward; Southwest components (24 genera) spread eastward and northeastward; while Northwest components (6 genera) show limited eastward spread. (3) Multi-year average precipitation, elevation, and coldest quarter temperature significantly influence plant distribution. (4) Elevation differences (peak, base, and average) under 1000 m among reserves enhance plant dispersal, resulting in obvious corridor effect. This study provides theoretical support for understanding the corridor effect in the study area and its contribution to biodiversity pattern of China.

The complexity of forest ecosystems leads to differences in the distribution patterns of different vegetation types along elevation gradients. This study aimed to explore the characteristics of AGB variations along elevation gradients for different forest types and tree species components in the Qinling–Daba Mountains. Based on 329 field vegetation survey plots, including four sampling transects and four representative mountains, individual tree AGB was calculated using allometric biomass equations. Further, generalized additive models (GAMs) were used to investigate the relationships between AGB and elevation for four forest types (broadleaf forests, coniferous forests, mixed coniferousbroadleaf forests, and shrublands) and three AGB components (total AGB (tAGB), broadleaf species AGB (bAGB), and coniferous species AGB (cAGB)) across eight vegetation survey regions. The results showed that the AGB of different forest types is significantly related to elevation (p < 0.05), with broadleaf forest AGB showing a unimodal pattern with elevation, coniferous forest and mixed forest AGB increasing with elevation, and shrubland AGB exhibiting a noticeable rise at higher elevations. The AGB components across different vegetation survey regions also showed significant relationships with elevation (p < 0.05), with broadleaf species AGB displaying a monotonically increasing trend in regions with a small elevation range and exhibiting a unimodal or bimodal distribution in regions with a large elevation range, while coniferous species AGB generally increased with elevation. Although elevation significantly influenced forest AGB, the variation in R2 values indicated that elevation is not the sole determinant of AGB variation. This study improves the understanding of spatial patterns of forest biomass along elevation gradients.

秦巴山地是我国南北过渡带的主体,其地理位置和自然条件使其在生物地理分布上具有独特的地位与意义,是我国生物多样性关键地区之一.本研究通过对其自然保护地的现状进行梳理,发现秦巴山地自然保护地的空间分布整体上呈聚类型分布,在组成上以自然保护区、森林公园为主,以地质公园、湿地公园等为辅;在空间交叉重叠上,共有34处重叠区域,涉及60个自然保护地,主要分布在米仓山、西秦岭的太子山、神农架、伏牛山以及熊耳山等地;隶属于6种交叉重叠类型,以自然保护区—森林公园交叉重叠类型为主,反映了自然保护地设立早期的历史遗留问题.在此基础上,提出需要对规划不合理、存在空间重叠、碎片化的自然保护地予以重点关注和提升,从而促进秦巴山地自然保护地整合优化,形成科学合理的保护地布局.

东西向横穿中国中部的昆仑—秦岭巨型构造系使得我国自然环境产生了巨大的南北分异,但目前对于中国南北分界线的位置和南北过渡带范围的划分仍存在争议.本文对秦巴山地和江淮地区的自然地理结构与范围进行了深入的分析,从而确定了中国南北过渡带的范围和性质.研究表明,中国南北过渡带由西部的秦岭—大巴山系和东部的江淮低山平原两部分组成,以地带性的常绿落叶阔叶混交林为主要标志,与之对应的主要气候指标是最冷月均温0～4℃、极端最低气温为?10～?20℃;秦岭南坡下部常绿阔叶树种的出现不是亚热带开始的标志,而是南北植物交错区的开始或者严格意义上南北过渡的开始;江淮地区具有明显的夏季高温、冬季低温的特点,冬季气候指标比夏季温度指标更具控制作用;秦巴山地的存在和江淮地区冬季低温是我国南北过渡带形成的主要原因,从而发育了长约1750 km、平均宽度400 km、面积约70万km2的中国南北过渡带.南北过渡带的概念比南北分界线和北亚热带的提法更能够反映秦巴山地和江淮地区的自然地理特点,也更能体现我国自然地理格局的独特性质,对于认识中国地域系统结构与功能具有更重要的科学意义.

青藏高原巨大隆起不仅塑造了欧亚大陆的气候格局,也深远地影响了高原的地理生态格局.青藏高原巨大隆起而产生的山体效应不仅可对近地表温度产生显著影响,其对近地表层垂直大气亦可产生显著作用,然而目前仍缺乏这一方面的研究.因此,本研究基于MODIS大气廓线数据产品,以昼夜温差为切入点,分析了青藏高原不同季节、不同气压面(500～200 hPa)的昼夜温差差异.结果表明:①青藏高原内部不同季节、不同气压面高度处的昼夜温差均大于外部地区,整体符合山体效应的格局.②青藏高原海拔越高,不同季节的垂直层昼夜温差越大.③随着气压面高度的增加(500～200 hPa),海拔对冬季大气昼夜温差的影响逐渐降低,对春季、夏季和秋季的影响程度先升高后降低,作用最大处分别出现在300 hPa、250 hPa和300 hPa.

Geographically, the Qinling-Daba Mountains serve as the main body of the north-south transitional zone of China. However, the transitional patterns of their plant species still need to be clarified. This study analyzed latitudinal variations of plant species richness, relative importance values (RIV), and plant species abundance based on plant community field survey data for 163 sample sites along three north-south transect lines in the eastern, middle, and western parts of the study areas. The difference in RIV between subtropical and temperate species (SND-RIV) was selected to reveal the latitudinal interlacing pattern of northern and southern plant species. Along the eastern (Sanmenxia-Yichang), middle (Xi’an-Dazhou), and western (Tianshui-Guangyuan) transects, the richness and RIV of subtropical plant species increased while those of temperate plant species decreased from north to south. In the eastern transect, temperate plant species richness and RIV were the highest at Shennongjia and Funiu Mountain, respectively, because of their high elevations. In the middle transect, subtropical plant species richness and RIV were the highest in the Daba Mountains. In the western transect, richness and RIV were higher for subtropical than temperate plant species from the south of Longnan. The crisscrossing areas of northern and southern plant species were ∼180 km, ∼100 km, and ∼60 km wide for the eastern, middle, and western transects, respectively, showing a narrowing trend from east to west. For the eastern and western transects, decreases in subtropical plant species distribution from south to north could be attributed to a decrease in mean annual precipitation in the same direction. However, for the middle transect, mean annual temperature had a slightly greater influence on plant species’ latitudinal distribution than the moisture index. This study provides a more solid scientific basis for future investigations of this key geographical boundary in China.

秦巴山地是我国典型的地理—生态过渡带,呈现出高度的复杂性、多样性、过渡性和敏感性.本文基于秦巴山区野外调查样方数据和收集的典型山地垂直带谱数据,从带幅的角度比较秦巴山地典型垂直带的多维变化和分异.结果表明:1)纬向上自北向南,落叶阔叶林带幅从2200 m逐渐减小至100 m,在唐家河地区消失;常绿落叶阔叶混交林带、针阔混交林带带幅呈线性增加趋势;针叶林带带幅从300 m增加到550～900 m.2)经向上自西向东,沿山脉走向,典型山地常绿阔叶林带幅从400 m增加至600 m,常绿落叶阔叶混交林带带幅从500 m增加至800 m,东部针阔混交林带比西部宽约100 m;落叶阔叶林带在秦巴山区中部较宽、东西较窄,而针叶林带则与之相反.3)坡向方面,大巴山对带幅的坡向分异作用比秦岭更加明显;就单独山体而言,南坡常绿落叶阔叶混交林带和针叶林带带幅通常比北坡更宽,而落叶阔叶林带在南坡更窄,针阔混交林带在秦岭南坡和大巴山北坡拥有比另一侧更宽的带幅,内外相差200～300 m.4)垂直带带幅是多种因素综合作用的结果,其中区域气候决定了基带的性质和垂直带谱的基本序列,山体基面高度对带幅有向上的挤压作用,山体相对高度决定了带幅发育的潜在空间分布范围.秦巴山地典型垂直带带幅的多维分异很好地体现了中国南北过渡带的过渡性和复杂性,研究结果可为秦巴山地自然保护区的植被垂直保护提供科学依据.

秦岭—大巴山作为中国暖温带和亚热带气候过渡区,是中国生物多样性研究的热点地区之一,气候对秦巴山地植物多样性空间分布影响巨大.本文基于秦巴山地及邻区种子植物物种数据库,首先分析了植物目、科、属、种多样性,乔木、灌木、草本多样性以及中国特有种多样性的空间分布规律,以阐明植物多样性在秦巴山地过渡带上的空间分布特点;其次,结合秦巴山地的气温和降水数据,对植物多样性和环境指标进行空间叠加分析,揭示其在空间分布上的协同变异规律;再次对植物目、科、属、种,乔木、灌木、草本以及中国特有种进行聚类,并将结果展布在空间上,以显示秦巴山地植物在空间上的聚类规律;最后总结植物多样性突变位置的气候特征,并据此确定亚热带和暖温带划分的植物指标.研究结果表明:1)该区目、科、属、物种多样性,乔木、灌木多样性均呈现由南到北逐渐减少的空间分布格局,植物科、属多样性具有较明确的分界线,物种多样性具有明显的过渡带,而这条分界线处和过渡带内气候指标的变化范围稳定,南多北少的分界线位置大致均在东部伏牛山(南召县、内乡县、商南县、郧县)—中部太白山以南(镇安县、石泉县、洋县)—西部秦岭南坡(勉县、武都区、文县、平武县);2)南多北少的过渡带覆盖东部伏牛山南坡—神农架北坡之间宽阔的地区,中部太白山南坡—米仓山北坡相对较窄的区域,西部几乎为一条线,与分界线位置基本重合;3)在中国特有种多样性方面,秦巴山地内部明显高于秦巴山地邻区,进一步印证了秦巴山地内部的过渡性强烈.本文的研究结果可为秦巴山地植物多样性保护提供科学依据,有助于人类理解生态环境对森林生态系统的影响.

中国南北过渡带主要的自然地理属性之一就是发育了常绿落叶阔叶混交林,但对于该类混交林的内部结构及地理地带性的认识一直存在较多分歧.根据国家科技基础资源调查专项"中国南北过渡带综合科学考察"获取的野外植被样地调查数据,分析了秦岭—大巴山地区 1 条东西向样线及 3 条南北向样线(三门峡—神农架;西安—达州;天水—广元)木本植物的组成结构变化.结果表明:东西方向上,秦岭南麓仅在旬阳段常绿阔叶成分比较多(重要值 27.57%),其余各段都很低,尤其是最西端的迭部—白龙江段以及人类活动集中的汉中—洋县段,常绿阔叶成分重要值几乎为零;南北方向上,常绿阔叶木本植物的物种数、多度比例和重要值 3 个指标自北向南都具有缓慢增加的趋势.总体上,秦巴山地的落叶阔叶树种占据绝对优势,常绿阔叶树种仅在大巴山南部出现较多,但重要值在 20%以下.因而,从植被组成结构来看,秦巴山地植被呈现强烈的过渡性质,且树种组成成分更偏向于暖温带属性.秦巴山地以东的淮河两岸广大区域,更容易受到冬季低温的影响,致使在中国大陆中部形成内部结构复杂、过渡性非常强烈的宽大的气候-植被过渡带,明显区别于暖温带落叶阔叶林地带和亚热带常绿阔叶林地带,具有最高级自然地带的属性特征.

山地垂直带谱是气候和植被水平地带变化和更替的缩影,垂直带的带幅、带间过渡方式、带内结构和垂直带组合方式都表现出高度的异质性和复杂性.本文发现在中国南北过渡带中部太白山发育了世界上最宽的山地垂直带——山地落叶阔叶林垂直带.该垂直带从基带到典型垂直带再到先锋性垂直带皆为山地落叶阔叶林,3种本来可以独立存在的垂直带,连续分布形成了包含3个栎林亚带、2个桦林亚带的"三层五亚带"超级垂直带,远远超过正常情况下山地垂直带1000 m的阈值,且其上限达到了海拔2800 m.它的形成与秦岭所处的过渡性地理位置、秦岭中部垂直带谱的完整性、丰富的落叶木本植物种群及其形成的强大群落竞争优势等因素紧密相关.超级垂直带的发现有多方面的意义:它是中国南北过渡带又一重要的标志性自然地理特征;它表明山地垂直带在特殊的山地环境中可以具有非常复杂的内部结构和宽大带幅,这扩展了我们对山地垂直带谱结构及机理认识的广度,对于创建山地垂直带谱结构理论具有十分重要的意义;超级垂直带的发现,也说明中国南北过渡带还有很多科学内容有待我们去探索和发现,希望本文能起到抛砖引玉的作用,引起学界对超级垂直带形成的气候和生物多样性因素、地理过渡带的结构和生态效应等重大问题进行深入研究.

秦岭—大巴山是中国重要的南北地理分界线和生态过渡带,建立秦巴山地南北方向上植物种类组成及重要值的详细变化序列和过渡模式,对于深入认识中国南北过渡带的过渡性、复杂性及暖温带与亚热带分界线具有十分重要的科学意义.本文通过野外实地调查获取秦巴山地东、中、西部3条南北穿越样线163个采样点的植被序列数据,分析了物种丰富度、相对重要值及优势种多度的纬向变化,并将亚热带与温带物种相对重要值的差值(SND-RIV)用于表现南北方物种的优势程度,以分析和归纳植物的空间变化模式.结果表明:①东部(三门峡—宜昌)、中部(西安—达州)、西部(天水—广元)亚热带物种丰富度及相对重要值自北向南递增,温带物种自北向南递减.东部温带物种丰富度及相对重要值在神农架和伏牛山由于海拔高度的影响出现两个峰值,中部亚热带物种在大巴山地区最高,西部亚热带物种在陇南以南超过温带物种;②东部南北方物种的交错过渡带最宽,约180 km;中部大约在秦岭南坡至大巴山北坡之间,约100 km;西部交错过渡带偏南,约50～60 km.③东、中、西部山地植物纬向过渡模式和驱动因子有明显差异.东、西部自南向北亚热带物种的减少主要与年均降水量减少有关,年平均气温影响较小;中部年平均气温的作用比湿润指数稍大.本文揭示了秦巴山地东、中、西部植物的南北变化及过渡模式,提升了对中国南北过渡带复杂性和多样性的科学认识.

The Qinling-Daba Mountains span subtropical and warm temperate zones and are one of the most remarkable biodiversity hotspots in China. Establishing a complete checklist of seed plants organized by nature reserves in the Qinling-Daba Mountains and adjacent areas is an important basis for managing and utilizing plant resources. First, we collected seed plant species data from published checklists representing 58 nature reserves in the Qinling-Daba Mountains and adjacent areas; second, we comprehensively and systematically sorted and integrated these data; third, we proofread and revised the data with the help of the R language and Flora of China dataset; and finally, we set up a seed plant database containing 96148 records, including the name, order, family, genus, life form, and endemism of each species for the entirety of the Qinling-Daba Mountains. The database contains 9491 species of seed plants belonging to 1729 genera, 211 families, and 59 orders, accounting for 39% of China's seed plants.

The Qinling-Daba Mountains (QBM), which are a major feature of China's north–south transitional zone, play important roles in the geographical and ecological patterns of China. The spatiotemporal changes in winter evergreen vegetation in the QBM are closely related to the protection of vegetation in China and have profound impacts on the sustainable development of vegetation in North and South China. This study aimed to introduce geographical distribution measurement methods into vegetation cover research by geographically characterizing evergreen vegetation, temperature, and precipitation. We used gravity centre analysis and standard deviation ellipse (SDE) methods to statistically analyse the concentration tendency, principal orientation, dispersion trend, and distribution differences of the winter normalized difference vegetation index (WNDVI), average temperature in winter (WAT), and accumulated precipitation in winter (WAP) in 1986–1990, 1991–1995, 1996–2000, 2001–2005, 2006–2010, and 2011–2015. The results show that (1) the gravity centres of the WNDVI and WAT in the QBM moved northwards, indicating that winter temperature is the main factor driving the northwards movement of evergreen vegetation in the QBM. (2) The angle between the development orientations of the WNDVI and the WAT remained basically stable, at close to horizontal, indicating that the development orientation of evergreen vegetation is mainly affected by winter temperature in the QBM. (3) The spatial differentiation coefficient between the WNDVI and the WAP decreased from 0.21 to 0.07; thus, the spatial distribution difference between evergreen vegetation and winter precipitation decreased gradually. These results confirm that in the QBM, winter temperature is the main factor affecting the overall evolution and development orientation of winter evergreen vegetation and that winter precipitation is the main factor affecting the internal distribution pattern of winter evergreen vegetation. The results of this study have reference value for evaluating the spatial distribution of evergreen vegetation development and resource management in the QBM.

The altitude of alpine timberline elevation has been considered to correlate with certain climatic factors. Many related isotherms (e.g., warmest month 10 °C isotherm) have been proposed to explain the altitudinal distribution of alpine timberline at the global scale. However, any climatic index actually has a wide range at the alpine timberline position worldwide. The altitudinal position of the alpine timberline is related to far more than just one climatic factor. Therefore, we developed a multivariable model for timberline elevation variability by collecting data from 473 timberline sites on the Eurasian continent. We analyzed 12 climatic variables that potentially account for timberline variation. Principal component and regression analyses were used to mine four climatic variables. The mean temperature of the warmest month (MTWM), mean temperature of the coldest month (MTCM), climatic continentality (K), and annual precipitation (AP) explained 95% of the variability of timberline elevation. MTWM, MTCM, K, and AP contributed 18%, 41.28%, 34.9%, and 5.82%, respectively, to the altitudinal distribution of alpine timberline on the whole continent; 20%, 44%, 28.86%, and 7.14% in the eastern continent; and 17.71%, 39.79%, 40.21%, and 2.29% in the western continent. We showed that MTWM, MTCM, K, and AP are deterministic factors for the altitudinal distribution of alpine timberline in the Eurasian continent. MTCM and K contributed to explaining the altitudinal distribution of timberline both in the entire, eastern, and western parts of the Eurasian continent. Our research highlights the significance of MTCM for the altitudinal distribution of timberline.

Different types of vegetation patches are alternately and randomly distributed in a timberline ecotone where the upper limit is the treeline and the lower limit is the timberline. However, most studies on timberline/treeline altitudinal distributions have simplified timberline or treeline as continuous curves and disregarded the fuzziness of timberline/treeline and the randomness of different vegetation patch distributions in a timberline ecotone. To study the altitudinal distribution characteristics of timberline and treeline from the perspective of uncertainty theory, we constructed the timberline and treeline elevation cloud models in Mt. Namjagbarwa in east Himalayas. Subsequently, we established multiple linear regression models by using nine influencing factors, namely, aspect, slope, topographic relief, dryness index, average temperature in January and July, latitude, summit syndrome (represented by the vertical distance from the peak), and snow effect (represented by the nearest distance from the snow) as independent variables, and the elevations of timberline/treeline as dependent variables. Then we compared the contributions of the nine factors in timberline, treeline, and the core and peripheral areas of timberline and treeline. The results show that 1) the timberline/treeline elevation cloud model can represent the overall characteristics (especially the uncertainty) of the altitudinal distributions of the timberline/treeline well. The uncertainty of treeline’s altitudinal distribution is higher than that of timberline (entropy and hyper entropy: 207.59 m and 70.36 m for treeline elevation cloud; entropy and hyper entropy: 191.17 m and 50.13 m for timberline elevation cloud). 2) The influence of climate and topography on timberline and treeline are similar. The average temperature in July has a significant negative correlation with the timberline/treeline elevation in Mt. Namjagbarwa, which is the most critical factor that affects timberline and treeline elevation, explaining the altitudinal distribution of 44.01% timberline and 46.74% treeline. However, the contributions of the nine factors in core and peripheral areas of timberline and treeline area are evidently different.

Mountain biodiversity is under unprecedented threat due to climate change and excessive human activity. Although protected areas (PAs) are the cornerstone of nature conservation, it is increasingly hard for isolated PAs to maintain the species and ecological processes they depend on in the long term. Linking nature reserves to form a large and connected conservation network is regarded as the optimal measure, but research in this field is lacking in China. We mapped PAs in the Qinling-Daba Mountains in China and identified corridors among PAs and the corridors’ key nodes using a least-cost analysis and circuit theory to model an ecological connectivity conservation network for the region. The results showed that this large ecological network has 46 habitat patches connected by 88 corridors, with 69 pinchpoints, 86 barriers and 37 stepping stones in and around the corridors. In this study, 34.86% of suitable habitats have little or no protection and, in the future, these areas should be developed with caution, with more emphasis on protecting their ecological connectivity. This study used connectivity analysis to construct large ecological corridors based on PAs, providing a framework for connectivity conservation at the biogeographic scale and a scientific reference for further, subsequent conservation actions.

Understanding the variation patterns of mountain plant species diversity is becoming increasingly important in forest ecosystem management and protection. However, the research on plant species diversity has mainly focused on changes in whole plant species. Therefore, an in-depth study of the change mode of plant species via different classification methods and its impact on the overall change in plant diversity is very important for forestland restoration and biodiversity protection. In this study, the Qinling-Daba Mountains, a major feature of China's north–south transitional zone, were selected as the study area. Based on the floristic data of 58 nature reserves in the Qinling-Daba Mountains and its adjacent areas, the north–south change patterns of plant orders, families, genera and species diversity were first analyzed. Second, plant species were divided into different groups according to taxonomic group (orders, families and genera), life form (trees, shrubs and herbs) and endemism (species endemic and nonendemic to China). The change patterns of each group in the north–south direction were analyzed. Finally, the effects of different groups on the north–south change patterns of whole species are discussed. The species diversity of orders, genera and species exhibited a typical latitudinal gradient pattern, specifically, it gradually decreases from south to north, but the species diversity is relatively scattered. According to the north–south variation in species diversity in each order, families and genus, 5% of the orders, 2% of the families and 6% of the genera were positively correlated with latitude, and the rest were negatively correlated or uncorrelated. According to the north–south variation patterns of different life forms, the diversity of trees and shrubs showed a bimodal Gaussian distribution with latitude. According to the north–south variation patterns of plant endemism, the diversity of endemic species showed a Gaussian distribution with latitude, but the diversity of nonendemic species was negatively correlated with latitude. The dispersion of whole species diversity is caused by species in a few orders, families and genera, trees and shrubs, and endemic species. They may be more strongly affected by the vertical zonality of the mountains, which is inconsistent with the typical latitude gradient model. Our research will provide a basis for forestland management, nature reserve establishment and biodiversity conservation.

The Qinling-Daba Mountains are the main body of China’s North-South Transitional Zone. Analysis of the north-south gradual variation of vegetation components is significant for understanding the structural diversity and complexity of this transitional zone. In this study, based on survey data of plant communities, the eastern Qinling-Daba Mountains is divided into four geographic units: the north flank of eastern Qinling Mts., south flank of eastern Qinling Mts., north flank of eastern Daba Mts. and south flank of eastern Daba Mts. We also explore division of regional climate according to areal differentiation of plant-species, community structure and species-richness, respectively. The results show that, (1) at plant-species level, there are mainly northern plants in north flank of eastern Qinling Mts. with evergreen species and fewer northern plants in south flank of eastern Qinling Mts.; there are mainly southern plants in eastern Daba Mts. (2) At community structure level, there are 4 formations (3 northern formations and 1 widespread formation) in north flank of eastern Qinling, 6 formations (3 northern formations, 1 southern formation, and 2 widespread formations) in south flank of eastern Qinling, 4 formations (2 southern formations and 2 widespread formations) in north flank of eastern Daba Mts., and 3 formations (3 southern formations) in south flank of eastern Daba Mts. In terms of the numbers and properties of formations, there is a mixture of northern and southern formations only in the south flank of eastern Qinling Mts. (3) At species-richness level, the diversity of families, genera and species decreased with increasing latitude, but the mixing of northern plants and the southern plants began to occur in south flank of eastern Qinling Mts. This means that the south flank of the eastern Qinling Mts. serves more suitably as the dividing line between China’s warm temperate and subtropical zones.

西秦岭是指嘉陵江以西的秦岭-大巴山,是我国南北过渡带的西段,被作为青藏高原与秦巴山地的过渡区域,地质和地貌结构复杂,气候类型多样,亚热带、温带和高山气候交错分布,形成我国生物多样性最为丰富和保护地最集中的地区之一,特别是包含了我国大熊猫国家公园四大片区中分布在中间的岷山和白水江两大片区.西秦岭又是我国南、北方特有属的主要分界线和特有属的分布中心之一,更是西南向华中、华东及华北特有属扩展的关键通道,对于我国生物多样性格局的形成具有重要意义.这里也是我国秦汉唐时期人类活动重要的南北通道和场所,对于民族的统一和文化的传播意义非凡.此外,以成徽盆地为核心的西汉水流域,气候冷暖适度、地形和缓、洞穴发育,具有上古时代人类生存的理想条件;古昆仑山的原型、大禹治水地点以及炎黄活动区域这些中华上古文明发生的关键地点和事件,极有可能就发生在西秦岭内部.因此,西秦岭的自然保护不仅要做好自然保护地体系,特别是大熊猫国家公园的设计、完善和有效保护,更要研究西秦岭的自然保护对中华文明起源和发展的重要意义,严格保护好此地的珍贵历史文化景观资源.