Palynological evidence for Holocene environmental change in the Changjiang (Yangtze River) Delta, China

Holocene vegetation changes in response to climate fluctuations and human impacts are reviewed on the basis of pollen analyses from borehole cores taken from the Changjiang (Yangtze River) delta, China, and other previously reported data. During the earliest Holocene (10,930−9000 cal yr BP), the climate was warm and wet, allowing thermophilous hardwoods to occupy mid- and low-elevations surrounding a palaeo-Changjiang estuary. The climate became gradually cooler, and cool-tolerant conifers, grasses and ferns became dominant until 7600 cal yr BP, when the estuary became a delta. A mid-Holocene climatic optimum occurred between 7600 and 4800 cal yr BP, when evergreen and broadleaved deciduous trees flourished at mid- and low-elevations surrounding the delta front-prodelta. After this time, climate became cooler again until 1340 cal yr BP. During this period, evergreen and broadleaved deciduous trees were replaced by conifers and grasses inhabiting the inter/subtidal flat-delta front. This development of conifer-grassland vegetation was shortly interrupted between 3860 and 3200 cal yr BP when thermophilous tree cover increased and open vegetation with scattered conifers was reduced. Since 1340 cal yr BP, the vegetation has been similar to that at present under warm, wet conditions. Human impacts are recognized by the first appearance of Fagopyrum and a sudden increase in herb pollen at 4500 and 1340 cal yr BP, respectively.     

白洋淀地区全新世以来植被演替和气候变化初探

 根据对白洋淀白4号孔的孢粉分析、放射性碳年代测定和野外考察研究表明,白洋淀形成于中全新世。晚全新世以来,随着气候的变凉变干,古白洋淀开始收缩和解体,但在人类活动的利用改造下,使逐渐解体的白洋淀得以保留下来。依据气候地层学的观点,并结合放射性碳年代测定,白洋淀地区的全新世地层可以划分为四期：即古全新世(距今11000—9000年),气候温和湿润;早全新世(距今9000—7500年),气候偏凉偏干;中全新世(距今7500—3000年),气候温暖湿润;晚全新世(距今3000年至今),气候温凉偏干。     

太湖东部平原平望孔全新世环境演变地层记录

通过对太湖东部平原平望钻孔的年代、有孔虫和孢粉分析,探讨了该区域全新世植被变化与环境特征。结果显示全新世(11.5 kaBP)以来,太湖东部平原未受到广泛海侵的影响,主要是以淡水湖泊-沼泽沉积为主。该区域在4 kaBP以后,才有大面积的水稻种植。11.0—9.1 kaBP,以常绿-落叶阔叶林为主,花粉浓度较小,木本植物和水生湿生植物花粉含量增加,整体环境温凉偏干,但湿度逐渐增大,指示东亚季风逐渐加强。9.1—5.8 kaBP,花粉浓度最大,木本植物花粉含量略有减小,草本植物含量明显增加,主要是水生、湿生花粉的含量增加明显,平均达到32%,藻类含量为整个钻孔最大,其中在8—7 kaBP前后常绿类花粉含量较大,水生湿生花粉、淡水藻类的含量达到整个剖面最大,推测此时区域湿度最大,东亚夏季风最为强盛。5.8—1.3 kaBP常绿阔叶林百分比含量增加,落叶阔叶花粉含量减少,陆生草本植物的含量增加,水生湿生草本的含量减小,主要以常绿-落叶阔叶林为主,环境较前一带略干,东亚夏季风减弱。     

中国东部森林植被带划分之我见

简要回顾了中国东部森林植被带划分研究的历史及当前存在的争论。提出了中国东部植被带划分应以植被本身的特征,特别是地带性的生物群落集为主要依据,同时参照它们的区系组成和气候指标。根据上述原则将中国东部划分为6个植被带∶北方针叶林带、凉温带针阔混交林带、温带落叶阔叶林带、暖温带常绿落叶阔叶混交林带、亚热带常绿阔叶林带和热带雨林、季雨林带,并对各植被带的特征作了简要的描述。阐述了对一些植被带名称、界线改动的原因,特别讨论了我国常绿落叶阔叶混交林以及常绿阔叶林生物气候带的归属问题,认为前者归属于暖温带植被,后者归属于亚热带植被为宜。     

Diatom response to the Holocene climatic optimum on the North Icelandic shelf

A diatom record from core MD992275 on the North Icelandic shelf reveals palaeoclimatic and palaeoceanographic changes during the time interval 9000 to 5600 cal. year BP. The study period includes the Holocene Climate Optimum (HCO), as widely known in the North Atlantic region. A comparison with data for the last 2000 years and with the present-day surface sediment diatom assemblages shows that there was considerably stronger influence of Atlantic water masses in the area during the HCO than in the late Holocene and today. The results of cluster analysis and principal component analysis divide the studied period into three intervals, each characterised by a specific diatom assemblage. The assemblages indicate changes in the interaction of the relatively warm Irminger Current (IC) and the cold East Greenland Current (EGC) and East Icelandic Current (EIC). The North Icelandic shelf was strongly affected by the IC during the interval 8000–6800 cal. year BP, which may be the warmest period of the Holocene. During the intervals 9000–8000 and 6800–5600 cal. year BP, the influence of the IC was relatively weak and that of the EGC and EIC increased correspondingly. The well-known 8200 cal. year BP cooling event, shown in many records from the North Atlantic, is reflected by a relatively strong influence of the EGC and EIC between about 8300 and 8100 cal. year BP in our record. However, the diatom assemblages show that the inferred circulation change did not bring the strength of the IC down to the levels seen at present and during the last two millennia.     

云贵高原抚仙湖近13300年的花粉/炭屑记录*

抚仙湖是云贵高原著名的断陷深水湖,其沉积物蕴藏着流域地质历史时期丰富的环境信息。对钻取自该湖的900cm 湖泊沉积物岩芯进行花粉/炭屑分析及花粉数据的主成分分析表明,抚仙湖流域的植被、气候与火灾在过去的13 300年经历了5个阶段的变化：(1)13 300—10 400cal．a BP,植被以松林为主,伴有山地暗针叶林和常绿阔叶林,表明该时期气候较为冷湿,森林火灾多发,在后期随着温度和湿度的降低,森林火灾愈加频繁。(2)10 400—5 700cal．a BP,松林收缩,常绿阔叶林扩张,出现一定数量的落叶阔叶林,显示该时期气候偏暖偏干;此阶段早期随着气候变暖变干森林火灾的发生延续上阶段高发的状态,直到9 500cal．a BP后随着湿度的增加森林火灾明显减少。(3)5 700—1 800cal．a BP,松林变化较小,常绿/落叶阔叶林比重增大,首次出现了暖热性的枫香林,显示该时期暖湿的气候特征,火灾发生频率低。(4)1 800—500cal．a BP,松林扩张,阔叶林收缩,本阶段后期草本植被比重开始增加,显示该时期气候相对冷干,森林火灾发生频率较高。(5)500cal．a BP至今,松林收缩,落叶阔叶树种增多,草本植物花粉明显增多,显示该时期气候温凉偏干,森林火灾发生频率降低。     

Holocene vegetation history with implications of human impact in the Lake Chaohu area, Anhui Province, East China

Palynological analyses of Holocene deposits located about 2 km to the southwest of the Lake Chaohu, Anhui Province, documented well the local vegetation history, its inferred environment and human impacts for the first time. An evergreen and deciduous mixed broad-leaved forest dominated by Cyclobalanopsis and Quercus existed from ca. 10,500 cal b.p. and became fully developed between ca. 8,250 and 7,550 cal b.p. Notable fluctuations occurred in the main components of the flora indicated by the decline in Cyclobalanopsis and other arboreal plants (AP), and an increase in terrestrial herbs between ca. 7,550 and 3,750 cal b.p., inferring the progressive opening of the forest under considerable human interference, which largely agrees with the archaeological evidence. After ca. 3,750 cal b.p., the broad-leaved forest largely gave way to terrestrial herbs, and never again recovered. Pinus continued to rise alongside the majority of herbs between ca. 3,750 and 2,000 cal b.p., then also declined after ca. 2,000 cal b.p. Human influence on the natural vegetation displayed in the pollen diagram seems to increase greatly up the core. The disappearance of broad-leaved forest indicates significant human impact after ca. 3,750 cal b.p., which is consistent with both the archaeological evidence and historical records. From that time the natural environment in the study area was subjected to long-standing pressure from increasing farming and population.     

北京地区全新世植被和气候变化研究进展

该文综述了北京地区全新世以来植被演替和气候变化的相关研究资料,这些资料反映了当前阶段对该地区该时段植被与气候环境格局特征的认识。北京地区全新世早期(约12 000–8 000 cal a B.P.)植被为森林草地和/或针叶树占主导的针阔混交林,森林中阔叶树类群逐渐增多,指示了气候由寒冷干燥转为温暖湿润;全新世中期(约8 000–2 000 cal a B.P.前后)植被为暖温带针阔混交林,指示暖湿气候;全新世晚期(约2 000 cal a B.P.以来)转为森林草地和/或针叶树占主导的针阔混交林,气候转向凉干。植被演替反映的湿润度变化与季风区其它地区变化趋势一致。值得注意的是,前人研究揭示北京地区山区与平原中植被类型和类群组成已经出现空间分异。今后如能深入开展定量古气候重建研究,有可能精确描述其气候变化的过程,增进中国不同地理单元同时期气候变化的对比。     

Palynological investigation of Holocene palaeoenvironmental changes in the coastal plain of Marathon (Attica, Greece)

The identification of Middle-Late Holocene palaeoenvironmental conditions of the Marathon coastal plain gained great interest in the last decades due to its high environmental and archaeological importance. Palynological analysis of samples from two boreholes and two trenches along a transect in the marshy area of the Marathon coastal plain, enabled the tracing of the vegetation and the main environmental changes for the last ∼6000 cal BP. Pollen data suggest a human disturbed environment with Pinus, Quercus, Juniperus and Ericaceae, while a general trend towards Mediterranean vegetation patterns is observed during the last ∼3000 cal BP. Pollen grains from aquatic and hydrophilous plants, dinoflagellate cysts, algal remains and other palynomorphs were used in order to determine the local depositional environment and its evolution through time.     

Vegetation and fire history with their implication for climatic change and fire events since the last deglacial in the Aso Valley, central Kyushu, southwestern Japan: new pollen and charcoal data

To better understand the response of forest vegetation to climate and fire regimes with reference to human activities over the last deglacial period in the Aso Caldera, central Kyushu, southwestern Japan, a 33.9 m long sediment core was examined in order to reconstruct the vegetational and fire history using pollen and charcoal analyses. The results show that a cool temperate broad-leaved deciduous forest, dominated by Quercus (deciduous oaks) with Carpinus and Fagus, prevailed in the Aso Valley from ca. 14.6 ka cal. b.p., indicating warming since the last glacial period. The landscape was presumably covered by a mosaic of deciduous Quercus forests and terrestrial Artemisia communities. Around 12.8–11.7 ka cal. b.p., Quercus dominated the forest and fires occurred frequently. Co-expansion of distinctive Ulmus–Zelkova and Celtis–Aphananthe forests coupled with a progressive retreat of Quercus in the early Holocene could reflect a strengthening of the East Asian summer monsoon under mild and humid climate conditions. Around 8 ka cal. b.p., significant increases in Cyclobalanopsis (evergreen oaks), Castanopsis/Castanea and Podocarpus indicate a further warming, in particular an increased winter temperature. Warm temperate lucidophyllous forests, dominated by Cyclobalanopsis, flourished after 7.3 ka cal. b.p., probably corresponding to the “Holocene Climatic Optimum” interval. Progressive expansion of Quercus at the expense of Cyclobalanopsis began around 6.4 ka cal. b.p. and paralleled an increase in charcoal until ca. 4.8 ka cal. b.p.; this could be evidence of fire disturbance induced by the early-middle Jomon people. The disturbed evergreen forest experienced a temporary recovery but then opened again from 3.6 ka cal. b.p. due to extensive fire deforestation, as suggested by the high charcoal levels during this time. Human exploitation and buckwheat (Fagopyrum) agriculture may have contributed to the opening of the forest, which allowed secondary forests (primarily Pinus and Quercus) and herbaceous communities (mainly Poaceae) to spread. These results are discussed in comparison with other high-resolution pollen data from western Japan to better elucidate the vegetation and fire history over the last deglacial in the Aso Caldera.     

内蒙古大青山调角海子地区全新世气候与环境重建研究

以全封闭湖泊调角海子湖相沉积的高分辨率采样为基本分析材料,采用孢粉分析、沉积地球化学分析、     

广西金钟山自然保护区主要植被类型的特征

金钟山自然保护区计有种子植物101科273属514种,落叶栎林分布面积最广。随海拔升高,植被依次呈现出4个分布带:沟谷落叶阔叶林、沟谷常绿阔叶林、常绿落叶阔叶混交林和落叶阔叶林、山地苔藓矮林和山地常绿阔叶林。该区主要有4个分布区类型:世界分布、热带分布、温带分布和中国特有分布,其中热带分布占总属数的75.21%,表明本保护区的植物分布具有热带性质。其天然植被类型可划分为5个植被型组,7个植被型含暖性针叶林、暖性落叶阔叶林、常绿落叶阔叶混交林、常绿阔叶林、竹林和草丛,2个植被亚型含南亚热带山地常绿阔叶林、山顶阔叶矮林,以及33个群系。     

An Ecogeographical Regionalization for Biodiversity in China

Ecogeographical regionalization is the basis for spatial differentiation of biodiversity research. In view of the principle of international ecogeographical regionalization, this study has applied multivariate analysis and GIS method and based on some ecogeographical attributes limited to the distribution of plant and vegetation, including climatic factors, such as minimum temperature, mean temperature of the coldest month, mean temperature of the wannest month, annual average temperature, precipitation of the coldest month, precipitation of the wannest month, annual precipitation, CV of annual precipitation, biological factors such as vegetation types, vegetation division types, NPP, fiorisitic types, fauna types, abundance of plant species, genus and endemic genus; soil factors such as soil types, soil pH;topographical factors as longitude, latitude and altitude etc. The ecogeographical regionalization for biodiversity in China was made synthetically by using fuzzy cluster method. Four classes of division were used, viz., biodomain, subbiodomain, biome and bioregion. Five biodomains, seven subbiodomains and eighteen biomes were divided in China as follows: Ⅰ Boreal forest biodomain. Ⅰ A Eurasian boreal forest subbiodomain. Ⅰ A1 Southern Taiga mountain cold-temperate coniferous forest biome; Ⅰ A2 North Asian mixed coniferous-broad-leaved forest biome. Ⅱ Northern steppe and desert biodomain. Ⅱ B Eurasian steppe subbiodomain. Ⅱ BI Inner Asian temperate grass steppe biome; Ⅱ B2 Loess Plateau warm-temperate forest/shmb steppe biome. Ⅱ C Asia-Mrica desert subbiodomain. Ⅱ C1 Mid-Asian temperate desert biome; Ⅱ C2 Mongolian/Inner Asian temperate desert biome. Ⅲ East Asian biodomain. Ⅲ D East Asian deciduous broad-leaved forest subbiodomain. Ⅲ D1 East Asian deciduous broad-leaved forest biome, Ⅲ E East Asian evergreen broad-leaved forest subbiodomain. Ⅲ El East Asian mixed deciduous-evergreen broad-leaved forest biome; Ⅲ E2 East Asian evergreen broad-leaved forest biome; Ⅲ E3 East Asian monsoon evergreen broad-leaved forest biome; Ⅲ FA Western East Asian mountain evergreen broadleaved forest biome. Ⅳ Palaeotropical subdomain. IV F India-Malaysian tropical forest subbiodomain.Ⅳ Fl Northern tropical rain forest/seasonal rain forest biome; Ⅳ F2 Tropical island coral reef vegetation biome. Ⅴ Asian plateau biodomain. Ⅴ G Tibet Plateau subbiodomain. Ⅴ G1 Tibet alpine highcold shrub meadow biome;Ⅴ G2 Tibet alpine high-cold steppe biome; Ⅴ G3 Tibet alpine high-cold desert biome; Ⅴ G4 Tibet alpine temperate steppe biome; Ⅴ G5 Tibet alpine temperate desert biome.     

上海大金山岛植被分类与制图——基于网格化清查方法

网格化清查方法有助于准确诊断一个地区的植被性质,并为探索植被分类方法提供支持。该研究以上海大金山岛为对象,借助航拍影像等间距地将其划分为140个清查网格(40 m × 40 m),按照统计样方法逐网格调查植物群落特征,综合运用列表法和双向指示种法,进行植被分类并绘制现状植被图。按照新修订的植被三级分类系统进行分类:一级单位根据植被型,大金山岛植被划分为落叶阔叶林、常绿落叶阔叶混交林、常绿阔叶林、落叶阔叶灌丛、常绿落叶阔叶混交灌丛、常绿阔叶灌丛和草丛; 二级单位根据优势种和植物区系特征,可划分出15种群丛或群落类型; 三级单位根据群落年龄和外貌可划分为22种群落类型。以上结果表明,大金山岛不仅是上海市物种多样性最高的区域,也拥有华东海岛最典型、最多样的自然半自然森林群落。就植被状态而言,地带性森林群落处于演替中后期,但少数次生植被处于演替前期,且面临着猴群干扰导致的植被发育停滞不前等生态问题。关于植被分类方法,网格化清查方法可充分揭示植物群丛连续性中包含间断性和过渡性群落的现象。     

Altitudinal zonation of human-disturbed vegetation on Mt. Tianmu,eastern China

Much of the primary vegetation at low altitudes has been greatly altered or destroyed by a long history of human activities. This is particularly true in eastern China, where low-altitude areas are now dominated by secondary forests or plantations. Altitudinal vegetation zonation of this region is often based on these secondary forests, resulting in seral vegetation with an obscure zonal sequence. Here, we deduced the potential climax vegetation according to the regeneration patterns of the dominant species of the secondary forests at low altitudes (below 1,000 m a.s.l.) on Mt. Tianmu (1,506 m a.s.l., 30°18′30″–30°21′37″N, 119°24′11″–119°27′11″E). Based on the potential climax vegetation combined with the floristic composition and community structure, three vegetation zones were identified, viz: (1) evergreen broad-leaved forest zone (400–950 m a.s.l.); (2) evergreen and deciduous broad-leaved mixed forest zone (950–1,100 m a.s.l.); (3) deciduous broad-leaved forest zone (1,100–1,506 m a.s.l.). The altitudinal vegetation zones identified in this study correspond with the thermal conditions on Mt. Tianmu. The distribution of vegetation on Mt. Tianmu was limited by lower temperatures in winter, and the altitudinal thermal vegetation zones on this mountain were more similar to the thermal vegetation of Japan than to that of China. The vertical distributions and roles of conifers were different between the eastern and the western regions along 30°N latitude in humid East Asia. Cryptomeria fortunei formed the emergent layer, towering above the broad-leaved canopy at middle altitudes as C. japonica on Yakushima, but disappeared at high altitudes with hydrothermal limitation on Mt. Tianmu.     

Vegetation classification of East China with multi-temporal NOAA-AVHRR data

East China lies in the subtropical monsoon climatic zone and is dominated by subtropical evergreen broad-leaved forests, a unique vegetation type mainly distributed in East Asia with the largest distribution in China. It is important to be able to monitor and estimate forest biomass and production, regional carbon storage, and global climate change impacts on these important vegetation types. In this paper, we used coarse resolution remote sensing data to identify the vegetation types in East China and developed a map of the spatial distribution of vegetation types in this region. Nineteen maximum normalized difference vegetation index (NDVI) composite images (acquisition time span of 7 months from February to August), which were derived from 10 days National Oceanographic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR) channel 1 and channel 2 observations, an unsupervised classification method, and the ISODATA algorithm were employed to identify the vegetation types. To reduce the dimensions of the dataset resulted in a total of 28 spectral clusters of land-cover of which two clusters were urban/bare soil and water, the images were processed using principal component analysis (PCA). The 26 remaining spectral clusters were merged into six vegetation types using the Chinese vegetation taxonomy system: evergreen broad-leaved forest, coniferous forest, bamboo forest, shrub-grass, aquatic vegetation, and agricultural vegetation. The spatial distribution and areal extent for the coniferous forests, shrub-grass, evergreen broad-leaved forests, and agricultural vegetation were calculated and compared with the Vegetation Atlas of China at a 1:1,000,000 scale. The spatial accuracy and the area accuracy for coniferous forests, shrub-grass, evergreen broad-leaved forests, and agricultural vegetation were 79.2%, 91.3%, 68.2% and 95.9% and 92.1%, 95.9%, 63.8% and 90.5%, respectively. The spatial accuracy and area accuracy of the bamboo forest were 28.7% and 96.5%, respectively; the spatial accuracy of aquatic vegetation was 69.6%, but there was a significant difference in its area accuracy because image acquisition did not cover the full year. Our study demonstrated the feasibility of using NOAA-AVHRR to identify the different vegetation types in the subtropical evergreen broad-leaved forest zone in East China. The spatial location of the six identified vegetation types agreed with the actual geographical distribution of the vegetation types in East China. __________ Translated from Acta Phytoecologica Sinica, 2005, 29(3): 436–443 [译自: 植物生态学报, 2005, 29(3): 436–443]     

广东季雨林的几个问题

 季雨林是分布在具有明显干湿季节变化热带地区,在干季或多或少,甚至全部落叶的森林植被;是介于热带雨林向热带稀疏林过渡的居间类型,而不是由热带雨林向亚热带常绿阔叶林过渡的植被类型。应归属于经向地带性植被,而非纬度地带性植被。并且,在广东南部沿海地区的气候条件下,也不会有季雨林发育。广东南部沿海地区的榕树+香蒲桃+野苹婆(Ficus microcarpa+Syzygium odoratum+Sterculia lanceolata)群落等类型不是季雨林,而是热带季节雨林,属广义的热带雨林范畴。     

Holocene vegetation and water level history in two bogs of the Cordillera de Talamanca, Costa Rica

Pollen records of Holocene sediment cores from the Costa Rican Cordillera de Talamanca (La Chonta bog, 2310 m and La Trinidad bog, 2700 m) show the postglacial development of the montane oak forest zone from ca. 9500 to 1500 yr BP. During the early Holocene (ca. 9500–700 yr BP), alder vegetation covered the La Chonta and La Trinidad bogs and their adjacent hills. The upper forest line is inferred to be at 2800–3000 m elevation. A Podocarpus-Quercus forest characterised the middle Holocene (ca. 7000–4500 yr BP). The upper forest line is located at >3000 m reaching the present-day altitudinal distribution. A Quercus forest characterised the late Holocene (ca. 4500–1500 yr BP). Compared to modern conditions, the early Holocene has similar average temperatures, but the moisture level was probably higher. Pollen evidence for the late Holocene indicates drier environmental conditions than today. In order to improve the paleoecological interpretation, we described the local vegetation and used moss samples as pollen traps at both montane bogs along strong soil moisture gradients.The Netherlands Centre for Geo-ecological Research, ICG     

论滇南西双版纳的森林植被分类

本文基于多年研究成果的总结,对西双版纳森林植被的分类、主要植被类型及其特征进行了系统归纳,并讨论了它们与世界类似热带森林植被的关系。以群落的生态外貌与结构、种类组成和生境特征相结合作为植被分类的原则和依据,可以将西双版纳的热带森林植被分类为热带雨林、热带季节性湿润林、热带季雨林和热带山地常绿阔叶林四个主要的植被型,包括有至少二十个群系。热带雨林包括热带季节雨林和热带山地(低山)雨林二个植被亚型。热带季节雨林具有与赤道低地热带雨林几乎一样的群落结构和生态外貌特征,是亚洲热带雨林的一个类型,但由于发生在季风热带北缘纬度和海拔的极限条件下,受到季节性干旱和热量不足的影响,在其林冠层中有一定比例的落叶树种存在,大高位芽植物和附生植物较逊色而藤本植物和在叶级谱上的小叶型植物更丰富,这些特征又有别于赤道低地的热带雨林。热带山地雨林是热带雨林的山地亚型,是该地区热带山地较湿润生境的一种森林类型,它在植物区系组成和生态外貌特征上类似于热带亚洲的低山雨林,隶属于广义热带雨林植被型下的低山雨林亚型。热带季节性湿润林分布在石灰岩山坡中、上部,在群落外貌上类似热带山地常绿阔叶林但在植物区系组成上与后者不同,它是石灰岩山地垂直带上的一种植被类型。热带季雨林是分布在该地区开阔河谷盆地及河岸受季风影响强烈的生境的一种热带落叶森林,是介于热带雨林与萨王纳之间的植被类型。热带山地常绿阔叶林(季风常绿阔叶林)是西双版纳的主要山地植被类型,它分布在热带季节雨林带之上偏干的山地生境。它在植物区系组成上不同于该地区的热带季节雨林,在生态外貌特征上亦不同于热带山地雨林,是发育在受地区性季风气候强烈影响的热带山地的一种森林植被类型。     

On the Classification of Forest Vegetation in Xishuangbanna,Southern Yunnnan

Xishuangbanna of southern Yunnan is a region of extremely interest to biologists and also a hotspot for biodiversity conservation . It is located in a transitional zone from tropical Southeast Asia to temperate East Asia biogeographically. The present paper reviewed vegetation types of Xishuangbanna and suggested a revised classification system based on theupdated study results over the last two decades . By combining physiognomic and floristic characteristics with ecological performances and habitats , the primary forest vegetation in Xishuangbanna can be organized into four main vegetation types: tropical rain forest, tropical seasonal moist forest, tropical montane evergreen broad-leaved forest and tropical monsoon forest. The tropical rain forest can be classified into two subtypes , i. e. tropical seasonal rain forest in the lowlands and tropical montane rain forest on higher elevations. The tropical seasonal rain forest in this region shows similar forest profile and physiognomic characteristics to those of equatorial lowland rain forests and is a type of world tropical rain forest. Because of conspicuous similarity on floristic composition , the tropical seasonal rain forest in Xishuangbanna is a type of tropical Asian rain forest . However , since the tropical seasonal rain forest occurs at the northern edge of tropical SE Asia, it differs from typical lowland rain forests in equatorial areas in maintaining some deciduous trees in the canopy layer , fewer megaphanerophytes and epiphytes but more abundant lianas and more plants with microphyll . It is a type of semi-evergreen rain forest at the northern edge of the tropical zone . The tropical montane rain forest occurs in wet montane habitats and is similar to the lower montane rain forests in equatorial Asia in floristic composition and physiognomy . It is a variety of lower montane rain forests at the northern tropical edges of tropical rain forests . The tropical seasonal moist forest occurs on middle and upper limestone mountains and is similar to the tropical montane evergreen broad-leaved forest of the region in physiognomy, but it differs from the latter in floristic composition. The monsoon forest in Xishuangbanna is a tropical deciduous forest under the influence of a strong monsoon climate and is considered to be a transitional vegetation type between tropical rain forest and savanna in physiognomy and distribution. The tropical montane evergreen broad- leaved forest is the main vegetation type in mountain areas . It is dominated by the tree species of Fagaceae , Euphorbiaceae , Theaceae and Lauraceae in majority. It differs from the tropical montane rain forests in lack of epiphytes and having more abundant lianas and plants with compound leaves . It is considered to be a distinct vegetation type in the northern margin of mainland southeastern Asia controlling by a strong monsoon climate, based on its floristic and physiognomic characteristics.