Species Composition,Physiognomy and Plant Diversity of the Tropical Montane Evergreen Broad-leaved Forest in Southern Yunnan

Species composition, physiognomy and plant diversity of the less known tropical montane forests in southern Yunnan were studied based on the data from 15 sampling plots in three sites. These forests are mainly dominated by the families Theaceae, Fagaceae, Lauraceae and Euphorbiaceae in floristic composition, and dominated by evergreen phanerophytes with mesophyllous leaves. These forests are similar to lower montane rain forests in equatorial southeastern Asia in floristic composition and altitudinal distributions, but differ in physiognomy by having few epiphytes, but more lianas and more plants with compound leaves. These differences could be due to strongly seasonal climate and so-called mass elevation effect in southern Yunnan. They also differ from the tropical seasonal rain forests at lower altitudes in southern Yunnan by having conspicuously lower species richness, few epiphytes, fewer mega-mesophanerophytes, more abundant micro-nanophanerophytes and hemicryptophytes and more plants with microphyllous leaves. It is suggested that these forests could be termed tropical montane evergreen broad-leaved forests, and be a vegetation type from the northern margin of mainland southeastern Asia controlled by a strongly seasonal climate.     

Distinctive Phyllosphere Bacterial Communities in Tropical Trees

Recent work has suggested that in temperate and subtropical trees, leaf surface bacterial communities are distinctive to each individual tree species and dominated by Alpha- and Gammaproteobacteria. In order to understand how general this pattern is, we studied the phyllosphere bacterial community on leaves of six species of tropical trees at a rainforest arboretum in Malaysia. This represents the first detailed study of ‘true’ tropical lowland tree phyllosphere communities. Leaf surface DNA was extracted and pyrosequenced targeting the V1–V3 region of 16S rRNA gene. As was previously found in temperate and subtropical trees, each tree species had a distinctive bacterial community on its leaves, clustering separately from other tree species in an ordination analysis. Bacterial communities in the phyllosphere were unique to plant leaves in that very few operational taxonomic units (0.5%) co-occurred in the surrounding soil environment. A novel and distinctive aspect of tropical phyllosphere communities is that Acidobacteria were one of the most abundant phyla across all samples (on average, 17%), a pattern not previously recognized. Sequences belonging to Acidobacteria were classified into subgroups 1–6 among known 24 subdivisions, and subgroup 1 (84%) was the most abundant group, followed by subgroup 3 (15%). The high abundance of Acidobacteria on leaves of tropical trees indicates that there is a strong relationship between host plants and Acidobacteria in tropical rain forest, which needs to be investigated further. The similarity of phyllosphere bacterial communities amongst the tree species sampled shows a significant tendency to follow host plant phylogeny, with more similar communities on more closely related hosts.     

Preliminary Investigation of Extrafloral Nectaried Plants the Tropical Rainforests in Xishuangbanna,China

In order to understand the distribution pattern of the extrafloral nectaried plants in the tropical rainforest in Xishuangbanna, Yunnan , China, we investigated seven forest communities ( three primary forests and four secondary forests at different ages) in Xishuangbanna Nature Reserve . Fifty-two species belonging to 36 genera and 23 families accounting for 12.3% of 424 angiosperm species in the seven communities were found to bear extrafloral nectaries ( EFNs ). Among which, eight genera and 37 species were the first time to be recorded as plants to bear EFNs. The study indicated, (1)The EFN species mainly occurred in subclasses Dilleniidae, Rosidae and Asteridae of the Magnoliopsida , and the most common EFNs were flattened glands situated on leaf blades ; (2) The proportions of EFN species within the seven communities ranged from 9.5% ( Vatica guangxiensis forest ) to 18 .5% ( Macaranga denticulata forest ), and the EFN species appeared to be more abundant in the secondary forests than those in the primary forests; (3) EFN species were disproportionally distributed among different growth forms, with the abundance being: tree > shrub > liana > herb , and no epiphytic and parasitic plants were found to bear EFNs.     

云南热带季雨林及其与热带雨林植被的比较

在中国植物学文献中, 对热带季雨林的解释和运用是不一致的, 特别是易于把季雨林与热带雨林相混淆。季雨林是在具有明显干、湿季变化的热带季风气候下发育的一种热带落叶森林植被, 是介于热带雨林与热带稀树草原(savanna)之间的一个植被类型。云南的热带季雨林在分布生境、生态外貌特征、植物种类组成和地理成分构成上, 均与热带雨林有明显区别, 季雨林主要分布在海拔1 000 m以下的几大河流开阔河段两岸和河谷盆地, 其群落结构相对简单, 乔木一般仅有1至2层, 上层树种在干季落叶或上层及下层树种在干季都落叶; 在生活型组成上, 季雨林的木质藤本相对较少, 大高位芽植物及地上芽植物很少, 但地面芽植物很丰富, 地下芽植物和一年生植物也相对丰富; 在叶级和叶型特征上, 季雨林植物的小叶和复叶比例相对较高, 分别占到24%和44%; 在植物区系地理成分构成上, 季雨林的热带分布属合计也占绝对优势, 但以泛热带分布属的比例相对较高, 约占到总属数的30%, 热带亚洲至热带非洲分布属的比例也较高, 约占总属数的12%。季雨林的地理成分更为多样性, 起源与发展历史也更复杂和古老。     

中国西南地区热带季节雨林及山地常绿阔叶林热值及能量分配格局

能量分配格局是研究生态系统能量流动的基础,但是由于热带森林结构的高度复杂性和物种多样性,对它的热值和能量分配格局的全面研究还很少。该文研究的热带季节雨林位于西双版纳,是分布于热带亚洲北缘的一种森林类型;山地常绿阔叶林位于云南省中部的哀牢山,属于我国西部亚热带地区的山地常绿阔叶林。该研究的目的是探讨这两种重要森林类型的热值和能量分配格局,验证Golley(1961,1969)提出的世界范围内植被的热值由低纬度向高纬度、由低海拔向高海拔升高的规律。热值的测定采用SDCM-Ⅲa氧弹测量仪。两个森林样地面积都是1 hm²,能量分配格局及年固定量根据生物量和生物量增量计算。研究结果表明,热带季节雨林样地的热值低于山地常绿阔叶林,乔木层的热值>灌木层>草本层,所有器官中叶片的热值较高。由于以前种植砂仁(Amomum villosum)的影响,热带季节雨林样地的能量现存量小于山地常绿阔叶林,但是因为地处高温高湿、光照充足的地区,热带季节雨林的能量年固定量高于山地常绿阔叶林。对于热带季节雨林样地来说,97%的能量储存在乔木层中;山地常绿阔叶林样地的乔木层储存了88%的能量,可见乔木层是维持森林能量结构的关键层。研究结果为Golley的结论提供了更加丰富的实验证据。     

Biodiversity correlates with regional patterns of forest litter pools

We compared litter pools of more than 1,000 forests differing in tree species diversity over a large scale in Catalonia (NE Spain). Monospecific forests always had smaller litter pools than mixed (from 2 to 5 tree species) forests. Whether there was a positive effect beyond two species mixtures depended on the species and functional identity of the dominant tree species. In sclerophyllous forests the positive effect of diversity was a step-function from one to more species. However, in conifers, litter pools increased constantly with tree diversity. The identity of the dominant tree species and functional type had also a significant effect on litter pools. For instance, forests dominated by sclerophyllous tree species had larger litter pools than forests dominated by deciduous and conifer tree species. When other forest structure parameters (i.e. tree basal area, wood production, successional stage, shrub cover and leaf area index) and environmental factors (i.e. mean annual temperature, mean annual precipitation, annual evapotranspiration and hillside position) where included in the analysis only leaf area index, basal area, wood production and mean temperature influenced litter pools positively. Our analysis emphasizes that at the regional scale, the litter compartment can be as influenced by biodiversity components as by other forest structure and climate components. In mixed forests, species and functional identity of the trees determine whether litter pools increase with tree diversity.     

Do tropical forest leaves suffer more insect herbivory? A comparison of tropical versus temperate herbivory,estimated from leaf litter

It is generally believed that tropical forests suffer more herbivory, as a proportion of leaf area, than do temperate forests. Reviews so far have compared studies performed by different authors using very different methodologies. Here we carried out studies on 125 samples at 86 localities in eastern North America and on 75 samples taken at five localities in Malaysia and Singapore, including both mature secondary and primary forest. Samples in North America were spread over 3 years. In tropical Asia, the samples were taken at four time slices at least 8 months apart, scattered over a 4-year period. Total herbivore damage during the lifetime of tree leaves was estimated from the percentage area damaged in recently fallen, undecayed leaves from the forest floor, using scanner-linked software. In terms of percentage damage per leaf, the results suggest that lowland tropical forest has significantly higher leaf herbivory (5.82%) than temperate forest (5.48%). This is in accord with the general expectation that aseasonal tropical forests should have more herbivory damage. However, when percentage damage ‘per unit time of growing season’ is calculated based on an estimate of leaf lifetime in the tropics, tropical lowland herbivory damage turns out to be a fraction (about one half) of that in the temperate zone. Thus, these results tend to put in question the widely held view that herbivore damage is markedly more intense in the tropics. Over total leaf lifetime, the intensity of damage in the tropical area is only slightly higher than temperate regions. In terms of intensity of herbivory on leaves per unit of time, the opposite seems to be the case. It is uncertain which index should be taken as more significant in interpreting the selection pressure for anti-herbivore defenses in the tropics.     

太白山北坡落叶阔叶林物种多样性特征

对太白山北坡落叶阔叶林从不同类型,层次的丰富度,均匀度和物种多样性指数及其与环境梯度的关系等方面进行了分析。结果表明,处于中山带的锐齿槲栎林及辽东栎林的多样性较高,高海拔与低海拔处的群落多样性较低。水热梯度对物种多样性有很大影响。植物生长型与物种多样性的关系表现为灌木层的多样性指数（Ｄ）和均匀度大于草本层,而草本层大于乔木层,草木层物种丰富度最大,灌木层次之,乔木层最小,不同群落间灌木层各多样性测     

滇南勐宋热带山地雨林的物种多样性与生态学特征

 研究了鲜为人知的滇南勐宋地区的原始山地雨林植被, 根据分布生境、群落结构和种类组成特征,可将该山地雨林区分为沟谷和山坡两个类型, 分别定义为八蕊单室茱萸(Mastixia euonymoides)-大萼楠(Phoebe megacalyx)林和云南拟单性木兰(Parachmeria yunnanensis)-云南裸花(Gymnanthes remota)林。该山地雨林的外貌仍以单叶、革质、全缘、中叶为主的常绿中、小高位芽植物组成为特征,层间木质藤本植物仍较丰富,草本高位芽植物和附生植物丰富,但板根和茎花现象少见,属于热带山地垂直带上低山雨林或山地雨林植被类型。与该地区的典型热带季节雨林和赤道热带雨林相比, 勐宋的山地雨林群落中的大、中高位芽植物和藤本高位芽植物比例相对减少, 小、矮高位芽植物和草本高位芽植物比例相对增加,单叶、革质、非全缘叶和小叶比例相对增加,板根现象少见。与中国热带北缘-南亚热带地区（季风）常绿阔叶林比较, 勐宋的山地雨林有较多的附生植物和草本高位芽植物,相对较少的小高位芽植物和矮高位芽植物,小叶比例亦较少,非全缘叶和革质叶比例相对较低。故勐宋山地雨林是滇南热带北缘山地的一种较湿润生境的植被类型, 与所谓的季风常绿阔叶林不同。在物种多样性上,勐宋热带山地雨林在单位面积植物种数上并不比该地区的热带季节雨林低, 物种多样性指数与低丘季节雨林相当,比沟谷季节雨林低, 明显高于季风常绿阔叶林。     

Seasonal leaf dynamics across a tree density gradient in a Brazilian savanna

Interactions between trees and grasses that influence leaf area index (LAI) have important consequences for savanna ecosystem processes through their controls on water, carbon, and energy fluxes as well as fire regimes. We measured LAI, of the groundlayer (herbaceous and woody plants <1-m tall) and shrub and tree layer (woody plants >1-m tall), in the Brazilian cerrado over a range of tree densities from open shrub savanna to closed woodland through the annual cycle. During the dry season, soil water potential was strongly and positively correlated with grass LAI, and less strongly with tree and shrub LAI. By the end of the dry season, LAI of grasses, groundlayer dicots and trees declined to 28, 60, and 68% of mean wet-season values, respectively. We compared the data to remotely sensed vegetation indices, finding that field measurements were more strongly correlated to the enhanced vegetation index (EVI, r ²=0.71) than to the normalized difference vegetation index (NDVI, r ²=0.49). Although the latter has been more widely used in quantifying leaf dynamics of tropical savannas, EVI appears better suited for this purpose. Our ground-based measurements demonstrate that groundlayer LAI declines with increasing tree density across sites, with savanna grasses being excluded at a tree LAI of approximately 3.3. LAI averaged 4.2 in nearby gallery (riparian) forest, so savanna grasses were absent, thereby greatly reducing fire risk and permitting survival of fire-sensitive forest tree species. Although edaphic conditions may partly explain the larger tree LAI of forests, relative to savanna, biological differences between savanna and forest tree species play an important role. Overall, forest tree species had 48% greater LAI than congeneric savanna trees under similar growing conditions. Savanna and forest species play distinct roles in the structure and dynamics of savanna–forest boundaries, contributing to the differences in fire regimes, microclimate, and nutrient cycling between savanna and forest ecosystems.     

浙江古田山自然保护区木荷群落研究

通过对木荷群落特征进行分析,结果表明:木荷群落植物种类丰富,科属组成分散,区系成分复杂。从属的地理成分来看,热带分布的属多于温带分布的属。群落的生活型以高位芽植物为主,地下芽植物次之。该群落叶的性质以小型叶、单叶、草质、非全缘为主。群落垂直结构复杂,地上成层现象明显,可分为乔木层、灌木层和草本层,并有一定数量的层间植物。乔木层、灌木层和草本层的物种多样性大小依次为灌木层> 乔木层> 草本层。     

Sapling herbivory,invertebrate herbivores and predators across a natural tree diversity gradient in Germany’s largest connected deciduous forest

Tree species-rich forests are hypothesised to be less susceptible to insect herbivores, but so far herbivory–diversity relationships have rarely been tested for tree saplings, and no such study has been published for deciduous forests in Central Europe. We expected that diverse tree communities reduce the probability of detection of host plants and increase abundance of predators, thereby reducing herbivory. We examined levels of herbivory suffered by beech (Fagus sylvatica L.) and maple saplings (Acer pseudoplatanus L. and Acer platanoides L.) across a tree species diversity gradient within Germany’s largest remaining deciduous forest area, and investigated whether simple beech or mixed stands were less prone to damage caused by herbivorous insects. Leaf area loss and the frequency of galls and mines were recorded for 1,040 saplings (>13,000 leaves) in June and August 2006. In addition, relative abundance of predators was assessed to test for potential top-down control. Leaf area loss was generally higher in the two species of maple compared to beech saplings, while only beech showed a decline in damage caused by leaf-chewing herbivores across the tree diversity gradient. No significant patterns were found for galls and mines. Relative abundance of predators on beech showed a seasonal response and increased on species-rich plots in June, suggesting higher biological control. We conclude that, in temperate deciduous forests, herbivory–tree diversity relationships are significant, but are tree species-dependent with bottom-up and top-down control as possible mechanisms. In contrast to maple, beech profits from growing in a neighbourhood of higher tree richness, which implies that species identity effects may be of greater importance than tree diversity effects per se. Hence, herbivory on beech appeared to be mediated bottom-up by resource concentration in the sampled forest stands, as well as regulated top-down through biocontrol by natural enemies. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorised users.     

Trees as templates for tropical litter arthropod diversity

Increased tree species diversity in the tropics is associated with even greater herbivore diversity, but few tests of tree effects on litter arthropod diversity exist. We studied whether tree species influence patchiness in diversity and abundance of three common soil arthropod taxa (ants, gamasid mites, and oribatid mites) in a Panama forest. The tree specialization hypothesis proposes that tree-driven habitat heterogeneity maintains litter arthropod diversity. We tested whether tree species differed in resource quality and quantity of their leaf litter and whether more heterogeneous litter supports more arthropod species. Alternatively, the abundance–extinction hypothesis states that arthropod diversity increases with arthropod abundance, which in turn tracks resource quantity (e.g., litter depth). We found little support for the hypothesis that tropical trees are templates for litter arthropod diversity. Ten tree species differed in litter depth, chemistry, and structural variability. However, the extent of specialization of invertebrates on particular tree taxa was low and the more heterogeneous litter between trees failed to support higher arthropod diversity. Furthermore, arthropod diversity did not track abundance or litter depth. The lack of association between tree species and litter arthropods suggests that factors other than tree species diversity may better explain the high arthropod diversity in tropical forests.     

Ecological and biogeographical studies on the tropical rain forest of south Yunnan,SW China with a special reference to its relation with rain forests of tropical Asia

Abstract. Ecological and biogeographic analyses of the tropical rain forest in south Yunnan were made using data from seventeen sample plots and floristic inventories of about 1000 species of seed plants. The rain forest is shown to be a type of true tropical rain forest because it has almost the same profile, physiognomic characteristics, species richness per unit area, numbers of individuals in each tree species and diameter classes of trees as classic lowland tropical rain forests. As the area is at the northern margin of monsoonal tropics, the rain forest differs from equatorial lowland rain forests in having some deciduous trees in the canopy layer, fewer megaphanaerophytes and epiphytes but more species of lianas as well as more species of microphylls. In its floristic composition, about 80% of total families. 94% of total genera and more than 90% of total species are tropical, of which about 38% of genera and 74% of species are tropical Asian. Furthermore, the rain forest has not only almost the same families and genera, but also the same families rank in the top ten both in species richness and in dominance of stems, as lowland forests in southeast Asia. It is indisputable that the flora of the rain forest is part of the tropical Asian flora. However, most of the tropical families and genera have their northern limits in south Yunnan and most have their centre of species diversity in Malesia. More strictly tropical families and genera have relatively lower species richness and importance compared with lowland rain forests in tropical southeast Asia. Thus, the flora also shows characteristics of being at the margin of the tropics. Based mainly on physiognomy and floristic composition the tropical rain forest of Yunnan is classified into two types, i.e. seasonal rain forest and wet seasonal rain forest, the latter is further divided into two subtypes, i.e. mixed rain forest and dipterocarp rain forest. From analysis of geographic elements it is also shown that the tropical rain forest of Yunnan occurs at a geographical nexus with its flora coming mainly from four sources, i.e. Malesia, south Himalayas, Indochina and China.     

Deciduousness in a seasonal tropical forest in western Thailand: interannual and intraspecific variation in timing, duration and environmental cues

Seasonal tropical forests exhibit a great diversity of leaf exchange patterns. Within these forests variation in the timing and intensity of leaf exchange may occur within and among individual trees and species, as well as from year to year. Understanding what generates this diversity of phenological behaviour requires a mechanistic model that incorporates rate-limiting physiological conditions, environmental cues, and their interactions. In this study we examined long-term patterns of leaf flushing for a large proportion of the hundreds of tree species that co-occur in a seasonal tropical forest community in western Thailand. We used the data to examine community-wide variation in deciduousness and tested competing hypotheses regarding the timing and triggers of leaf flushing in seasonal tropical forests. We developed metrics to quantify the nature of deciduousness (its magnitude, timing and duration) and its variability among survey years and across a range of taxonomic levels. Tree species varied widely in the magnitude, duration, and variability of leaf loss within species and across years. The magnitude of deciduousness ranged from complete crown loss to no crown loss. Among species that lost most of their crown, the duration of deciduousness ranged from 2 to 21 weeks. The duration of deciduousness in the majority of species was considerably shorter than in neotropical forests with similar rainfall periodicity. While the timing of leaf flushing varied among species, most (∼70%) flushed during the dry season. Leaf flushing was associated with changes in photoperiod in some species and the timing of rainfall in other species. However, more than a third of species showed no clear association with either photoperiod or rainfall, despite the considerable length and depth of the dataset. Further progress in resolving the underlying internal and external mechanisms controlling leaf exchange will require targeting these species for detailed physiological and microclimatic studies.     

The incidence and implications of clouds for cloud forest plant water relations

Although clouds are the most recognisable and defining feature of tropical montane cloud forests, little research has focussed on how clouds affect plant functioning. We used satellite and ground‐based observations to study cloud and leaf wetting patterns in contrasting tropical montane and pre‐montane cloud forests. We then studied the consequences of leaf wetting for the direct uptake of water accumulated on leaf surfaces into the leaves themselves. During the dry season, the montane forest experienced higher precipitation, cloud cover and leaf wetting events of longer duration than the pre‐montane forest. Leaf wetting events resulted in foliar water uptake in all species studied. The capacity for foliar water uptake differed significantly between the montane and pre‐montane forest plant communities, as well as among species within a forest. Our results indicate that foliar water uptake is common in these forest plants and improves plant water status during the dry season.     

Fungal endophyte communities in two tropical forests of southern India: diversity and host affiliation

Fifteen tree species from a tropical dry thorn forest and fifteen tree species from a tropical dry deciduous forest in the Mudumalai Wildlife Sanctuary, Nilgiri Biosphere Reserve, southern India, were surveyed for their foliar endophyte communities during the dry and wet seasons. Surface sterilized leaf segments of uniform dimension were plated on nutrient agar and culturable endophytes growing from the segments were identified. Endophyte diversity was greater in the dry thorn forest than in the dry deciduous forest in the dry season. Although the isolation frequency of culturable endophytes increased for both forests during the wet season, the assemblages were represented not by any unique fungal species but by the commonly occurring ones. Furthermore, although individual leaves were densely colonized by endophytes, only a few species of endophytes colonized the whole leaves; and, only a few fungal species dominated the foliar endophytic communities and were common for both forests during both dry and wet seasons. Thus, even under wet conditions that favour dispersal and infection by fungi, the endophyte diversity increased only marginally, an indication that certain tropical forests are not hyperdiverse with reference to fungal endophytes. This should be considered when using culturable endophyte diversity as a surrogate for estimating global fungal diversity.     

Estimating leaf inclination and G-function from leveled digital camera photography in broadleaf canopies

The effectiveness of using leveled digital camera for measuring leaf inclination angles was investigated in this study as an inexpensive and convenient alternative to existing approaches. The new method is validated with manual leaf angle measurements for various broadleaf tree species common to hemi-boreal region of Estonia and the tropical forests of Hawai’i Islands. The acquired leaf angle distributions suggest that planophile case might be more appropriate than the commonly assumed spherical as the general approximation of leaf orientation while modeling the radiation transmission through the canopies of (hemi)-boreal broadleaf stands. However, direct leaf inclination measurements should be obtained whenever possible, as there will always exist a large variety of leaf orientation, both among different species and in the space–time domain within a single species. The camera method tested in this study provides a new robust and affordable tool to obtain this information.     

Species richness,endemism, and conservation of American tree ferns (Cyatheales)

Analyses of richness and endemism of Cyatheales (tree ferns) in tropical America were performed and evidence of a diversity gradient is presented. For this, the occurrence ranges of 239 species were plotted into a 5° × 5° grid-cell map and then analyzed using species richness and endemism indices. Here we show that species richness and endemism are not distributed randomly over the landscape, but do aggregate into defined regions of high diversity in tropical America: the northern Andes, lower Central America, upper Central America and Mexico, the Guyana Highlands, southeastern Brazil, and the Antilles. These distributional patterns are congruent with the geographical distribution of cloud forest, which in turn is determined by topography, high humidity, and persistent cloud immersion. The mountain regions of tropical America, especially the cloud forests, harbour most of the species of American Cyatheales and have high levels of habitat loss and climatic fragility. Conservation policies for Cyatheales are centred on the local use and trade of many tree fern species, but none such policies focus on cloud forest habitat loss. This makes tree ferns a critically endangered group of plants. In the face of the current environmental crisis and global climate change, the presence of Cyatheales in these regions sounds the alarm on their conservation priorities.