云南纳板河热带季节雨林20 ha动态监测样地的树种组成与群落分类

大型森林动态监测样地是研究物种共存、群落演替等生态学核心问题的重要平台。纳板河流域国家级自然保护区管理局与中国科学院西双版纳热带植物园合作, 于2016-2017年参照美国史密森热带森林科学中心的技术标准, 在纳板河流域国家级自然保护区内建立了一块热带季节雨林20 ha动态监测样地。本研究分析了该样地的树种组成特征, 并进行了群落数量分类。结果表明: 该样地中DBH ≥ 1 cm的木本植物个体共有59,498株, 分属63科197属296种; 个体数超过1,000株的常见物种有15个, 个体数小于20株的稀有物种有126个。科的区系分布型以热带成分为主, 占总科数的65.08%, 温带成分占17.46%。属的区系分布型以热带成分为主, 占总属数的88.32%, 温带成分占10.66%。该样地群落类型的形成主要受海拔和凹凸度这两个地形因子的影响, 500个20 m × 20 m的样方可以分为4个群丛, 分别为: (1)灰毛浆果楝 + 粗糠柴 - 假山萝 + 番龙眼群丛(Cipadessa baccifera + Mallotus philippensis - Harpullia cupanioides + Pometia pinnata Association); (2)长梗三宝木 + 腋球苎麻 - 顶果木 + 番龙眼群丛(Trigonostemon thyrsoideus + Boehmeria glomerulifera - Acrocarpus fraxinifolius + Pometia pinnata Association); (3)云南银柴 + 大果山香圆 - 湄公锥 + 普文楠群丛(Aporusa yunnanensis + Turpinia pomifera - Castanopsis mekongensis + Phoebe puwenensis Association); (4)歪叶榕 + 密花火筒树 - 毒药树 + 番龙眼群丛(Ficus cyrtophylla + Leea compactiflora - Sladenia celastrifolia + Pometia pinnata Association)。     

Soil phosphorus heterogeneity promotes tree species diversity and phylogenetic clustering in a tropical seasonal rainforest

The niche theory predicts that environmental heterogeneity and species diversity are positively correlated in tropical forests, whereas the neutral theory suggests that stochastic processes are more important in determining species diversity. This study sought to investigate the effects of soil nutrient (nitrogen and phosphorus) heterogeneity on tree species diversity in the Xishuangbanna tropical seasonal rainforest in southwestern China. Thirty‐nine plots of 400 m² (20 × 20 m) were randomly located in the Xishuangbanna tropical seasonal rainforest. Within each plot, soil nutrient (nitrogen and phosphorus) availability and heterogeneity, tree species diversity, and community phylogenetic structure were measured. Soil phosphorus heterogeneity and tree species diversity in each plot were positively correlated, while phosphorus availability and tree species diversity were not. The trees in plots with low soil phosphorus heterogeneity were phylogenetically overdispersed, while the phylogenetic structure of trees within the plots became clustered as heterogeneity increased. Neither nitrogen availability nor its heterogeneity was correlated to tree species diversity or the phylogenetic structure of trees within the plots. The interspecific competition in the forest plots with low soil phosphorus heterogeneity could lead to an overdispersed community. However, as heterogeneity increase, more closely related species may be able to coexist together and lead to a clustered community. Our results indicate that soil phosphorus heterogeneity significantly affects tree diversity in the Xishuangbanna tropical seasonal rainforest, suggesting that deterministic processes are dominant in this tropical forest assembly.     

Buttress form of the central African rain forest tree Microberlinia bisulcata, and its possible role in nutrient acquisition

Buttressing is a trait special to tropical trees but explanations for its occurrence remain inconclusive. The two main hypotheses are that they provide structural support and/or promote nutrient acquisition. Studies of the first are common but the second has received much less attention. Architectural measurements were made on adult and juvenile trees of the ectomycorrhizal species Microberlinia bisulcata, in Korup (Cameroon). Buttressing on this species is highly distinctive with strong lateral extension of surface roots of the juveniles leading to a mature buttress system of a shallow spreading form on adults. This contrasts with more vertical buttresses, closer to the stem, found on many other tropical tree species. No clear relationship between main buttress and large branch distribution was found. Whilst this does not argue against the essential structural role of buttresses for these very large tropical trees, the form on M. bisulcata does suggest a likely second role, that of aiding nutrient acquisition. At the Korup site, with its deep sandy soils of very low phosphorus status, and where most nutrient cycling takes place in a thin surface layer of fine roots and mycorrhizas, it appears that buttress form could develop from soil-surface root exploration for nutrients by juvenile trees. It may accordingly allow M. bisulcata to attain the higher greater competitive ability, faster growth rate, and maximum tree size that it does compared with other co-occurring tree species. For sites across the tropics in general, the degree of shallowness and spatial extension of buttresses of the dominant species is hypothesized to increase with decreasing nutrient availability.     

Tree competition and species coexistence in a cool-temperate old-growth forest in southwestern Japan

Abstract. The growth dynamics and mode of competition between adult trees ≥ 4 cm in DBH (stem diameter at breast height 1.3 m) of eight abundant species occupying ca. 90 % of the total basal area were investigated in a 4-ha study plot (200 m × 200 m) of a cool-temperate, old-growth forest on Mount Daisen, southwestern Japan. In the study plot, 30 tree species with individuals ≥ 4.0 cm DBH co-occurred. A bimodal DBH distribution showing upper and lower-canopy layers was found for the most dominant and largest species, Fagus crenata (ca. 78 % of the total basal area), whilst other tree species showed unimodal DBH distributions corresponding mostly to the lower-canopy layer. We developed a model for individual growth incorporating both intra and interspecific competition and the degree of competitive asymmetry. Onesided interspecific competition was detected only from Fagus crenata (upper-canopy species) to Acer japonicum and Acanthopanax sciadophylloides (lower-canopy species) on the scale of the 4-ha study plot. Only Acanthopanax sciadophylloides showed symmetric intraspecific competition. However, a positive (non-competitive) interspecific relationship between adult trees prevailed over a competitive relationship; for example, individual DBH growth rate of Fagus crenata (especially lower-canopy trees) was correlated with the abundance of Acer mono. The positive relationship represented a group of species with similar habitat preference [soil type (mature or immature) caused by landslide disturbance and the presence/absence of Sasa dwarf bamboos in the understorey], where tree densities were not so high as to bring about competition. Competitive interactions between adult trees ≥ 4 cm in DBH occurred only locally between a few specific species and were suggested to be almost irrelevant to the variation in species coexistence on the 4-ha scale of cool-temperate forest. Rather, the coexistence of 30 tree species (species diversity) on this large scale was suggested to be governed by the regeneration pattern of each component species (habitat preference, seedling establishment, sapling competition) with respect to landslide disturbance.     

Insights into regional patterns of Amazonian forest structure,diversity, and dominance from three large terra-firme forest dynamics plots

We analyze forest structure, diversity, and dominance in three large-scale Amazonian forest dynamics plots located in Northwestern (Yasuni and Amacayacu) and central (Manaus) Amazonia, to evaluate their consistency with prevailing wisdom regarding geographic variation and the shape of species abundance distributions, and to assess the robustness of among-site patterns to plot area, minimum tree size, and treatment of morphospecies. We utilized data for 441,088 trees (DBH ≥1 cm) in three 25-ha forest dynamics plots. Manaus had significantly higher biomass and mean wood density than Yasuni and Amacayacu. At the 1-ha scale, species richness averaged 649 for trees ≥1 cm DBH, and was lower in Amacayacu than in Manaus or Yasuni; however, at the 25-ha scale the rankings shifted, with Yasuni < Amacayacu < Manaus. Within each site, Fisher’s alpha initially increased with plot area to 1–10 ha, and then showed divergent patterns at larger areas depending on the site and minimum size. Abundance distributions were better fit by lognormal than by logseries distributions. Results were robust to the treatment of morphospecies. Overall, regional patterns in Amazonian tree species diversity vary with the spatial scale of analysis and the minimum tree size. The minimum area to capture local diversity is 2 ha for trees ≥1 cm DBH, or 10 ha for trees ≥10 cm DBH. The underlying species abundance distribution for Amazonian tree communities is lognormal, consistent with the idea that the rarest species have not yet been sampled. Enhanced sampling intensity is needed to fill the still large voids we have in plant diversity in Amazon forests.     

西双版纳热带森林树洞丰富度及其分配特点

树洞是森林生态系统的重要结构,对动物多样性的维持起着重要作用。为研究热带森林树洞的数量特征及其分配特点,选取西双版纳20hm2热带森林动态监测样地为研究对象,采用地面观测法调查了样地内所有胸径≥5cm活立木上的树洞。结果表明:(1)该样地森林的树洞密度为108.4个·hm-2,具有树洞的树1725株(占树木总数的6.22%),隶属于208个种;(2)树木个体的树洞数量随径级增加而增加,并在种间变化不均匀;(3)树木出现空心的概率随胸径级的增加而显著增加,并且在树种间存在显著差异;(4)与其他纬度地区森林的树洞密度比较,本研究结果支持了Boyle等(2008)提出的低纬度森林具有较高树洞密度的推测。     

Possible influence of ramets on the population structure and distribution of the giant tree Warszewiczia uxpanapensis, Tilarán Mountain Range, Costa Rica

The distribution and population structure of Warszewiczia (=Elaeagia) uxpanapensis, a tree that reaches a height of 45 m, a DBH of 1.40 m and 8 m tall buttresses, was studied on two 1-ha plots of premontane pluvial forest. It had a frequency of 49 % and a mean dominance of 6.5 %. The adult distribution was random (mean distance to the nearest neighboring tree in plot 1, it was 14.26 m, n = 15; Clark-Evans Index (IC-E) = 1.07; in plot 2, it was 15.33 m, n = 18, IC-E = 1.34,). The seedlings represented 60.3 % of the sampled population (plot 1, n = 94; plot 2, n = 85). This species has a very high capability of propagating itself vegetatively through clones ("ramets"), which influence its distribution and population structure. With a ramet density in plot 1 of 0.8 and in plot 2 of 0.3/100 m2, its propagation could be from fallen trees or branches (which also create clearings in the forest) or from standing trees and even live branches that produce adventitious roots.     

Habitat specialization and phylogenetic structure of tree species in a coastal Brazilian white-sand forest

Aims The coastal Brazilian rainforest on white-sand (restinga) ranks among the most fragmented forest types in the tropics, owing to both the patchy distribution of sandy soils and widespread coastal development activities. Here we study the environmental and evolutionary determinants of a forest tree assemblage at a single restinga forest in Southeastern Brazil. We also explore the ability of competing hypotheses to explain the maintenance of species diversity in this forest type, which includes contrasting extremes of edaphic conditions associated with flooding stress.Methods The study was conducted in a white-sand forest permanent plot of 10.24 ha on the coastal plain of Southeastern Brazil. This plot was divided into 256 quadrats of 20×20 m, which were classified into two main edaphic habitats (flooded and drained). Trees with a diameter ≥1cm at breast height were identified. We assembled DNA sequence data for each of the 116 morphospecies recognized using two chloroplast markers (rbcL and matK). A phylogenetic tree was obtained using the maximum likelihood method, and a phylogenetic distance matrix was produced from an ultrametric tree. We analyzed similarity in floristic composition and structure between habitats and related them to cross-plot distances using permutation procedures. Null model torus shift simulations were performed to obtain a statistical significance level for habitat association for each species. The phylogenetic structure for the two habitats and for each 20×20 m quadrat was calculated using the mean phylogenetic distance weighted by species abundance and checked for significance using the standardized effect size generated by 5000 randomizations of phylogenetic tip labels.Important findings Our results indicate that partitioning among edaphic habitats is important for explaining species distributions and coexistence in restinga forests. Species distributions within the plot were found to be non-random: there was greater floristic similarity within than between habitats, and>40% of the more abundant species were positively or negatively associated with at least one habitat. Patterns of habitat association were not independent of phylogenetic relatedness: the community was overdispersed with respect to space and habitat type. Closely related species tended to occur in different habitats, while neighboring trees tended to belong to more distantly related species. We conclude that habitat specialization is important for the coexistence of species in restinga forests and that habitat heterogeneity is therefore an essential factor in explaining the maintenance of diversity of this unique but fragile and threatened type of forest.     

Growth and mortality of trees in Amazonian tropical rain forest in Ecuador

Abstract. Structural changes are analysed in four samples representing 4 ha, two line transects and two hectare plots, of Amazonian tropical lowland rain forest in northern Ecuador. Only trees with a DBH ≥ 10 cm were included. A sample of floodplain forest in Añangu represents the largest turnover found in tropical forests (stand half-life = 23 yr). The line transect and hectare plot both of tierra firme forest in Añangu have the same turnover (37 yr) and were balanced for death and in-growth of both individuals and wood (basal area). The 1-ha tierra firme sample in Cuyabeno had a turnover of 67 yr and was in a growing phase. The floodplain line transect in Añangu was in a phase of structural breakdown. However, the floodplain line transect had the largest growth of basal area per tree (23.4 cm²/yr). The tierra firme samples had a growth of 9.6, 10.1, and 13.6 cm²/yr. Most of the dead trees fell with some uprooting in three of the four samples. However, no significant difference in the distribution of mode of death was found between the four samples. Death was independent of topography and the dead trees were randomly distributed. As the trees grow up they occupy more space and larger trees (DBH ≥ 15 cm) become more uniformly distributed, whereas smaller trees (DBH ≤ 15 cm) were randomly distributed. Our study confirms that plots of 1 ha are not sufficient to include representative samples of different stages of forest structure.     

Differential survival among life stages contributes to co‐dominance of Abies mariesii and Abies veitchii in a sub‐alpine old‐growth forest

Questions: Are there interspecific differences in mortality and recruitment rates across life stages between two shade‐tolerant dominant trees in a sub‐alpine old‐growth forest? Do such differences in demography contribute to the coexistence and co‐dominance of the two species? Location: Sub‐alpine, old‐growth forest on Mt. Ontake, central Honshu, Japan. Methods: From 1980 to 2005, we recorded DBH and status (alive or dead) of all Abies mariesii and A. veitchii individuals (DBH ≥ 5 cm) in a 0.44‐ha plot. Based on this 25 year census, we quantified mortality and recruitment rates of the two species in three life stages (small tree, 5 cm ≤ DBH < 10 cm; subcanopy tree, 10 cm ≤ DBH < 20 cm; canopy tree, DBH ≥ 20 cm). Results: Significant interspecific differences in mortality and recruitment rates were observed in both the small tree and sub‐canopy tree stages. In this forest, saplings (< 5 cm DBH) are mostly buried by snow‐pack during winter. As a consequence, saplings of A. mariesii, which is snow and shade tolerant, show higher rates of recruitment into the small tree stage than do those of A. veitchii. Above the snow‐pack, trees must tolerate dry, cold temperatures. A. veitchii, which can more readily endure such climate conditions, showed lower mortality rate at the subcanopy stage and a higher recruitment rate into the canopy tree stage. This differential mortality and recruitment among life‐stages determines relative dominance of the two species in the canopy. Conclusion: Differential growth conditions along a vertical gradient in this old forest determine survival of the two species prior to reaching the canopy, and consequently allow co‐dominance at the canopy stage.     

宝天曼国家级自然保护区落叶阔叶林密度制约效应对树木存活的影响

密度制约对物种共存起着重要作用。随着密度制约效应研究的深入, 亲缘关系较近的物种间表现出的密度制约效应逐渐被人们认识。本研究基于2009和2014年对宝天曼1 ha落叶阔叶林样地的2次调查数据, 利用广义线性混合模型分析了重要值排名前11位的物种不同邻域尺度的密度制约效应对不同径级(小径级(1 cm ≤ DBH < 5 cm)、中径级(5 cm ≤ DBH < 10 cm)、大径级(DBH ≥ 10 cm))目标个体存活的影响。研究表明: (1) 5年间样地中DBH ≥ 1 cm的所有个体的年均死亡率和增员率分别为5.85%和0.27%; (2)有5个物种的个体存活率与同种邻体个体数及同种邻体胸高断面积显著负相关; (3)小径级个体的存活在5 m的邻域范围内受同种密度制约和谱系密度制约的影响都很显著; 中径级个体在3个尺度上受到的密度制约和谱系密度制约的影响都不大; 大径级个体在7.5 m、10 m邻域范围内受谱系密度制约影响显著。结果表明, 同种密度制约和谱系密度制约效应对宝天曼落叶阔叶林不同生长阶段的树木个体影响不同。     

弄岗北热带喀斯特季节性雨林15hm2动态监测样地树木死亡特征分析

以广西弄岗北热带喀斯特季节性雨林15 hm²森林动态监测样地为对象,结合2011年和2016年两次调查数据,分析5年间样地树木死亡个体的数量、径级结构和空间格局特征等。结果显示:2011年至2016年,样地有86.5%的树种出现了个体死亡的现象,死亡个体占个体总数的14.4%;死亡个体的聚集程度随空间尺度的增大而逐渐减弱;小径级个体死亡与周边邻体和环境的关联性较大;竞争是影响弄岗北热带喀斯特季节性云林树木死亡的主要因素。综合来看,北热带喀斯特季节性雨林内树木死亡并非是一个完全随机的过程,而是树木本身特征和生物与非生物环境共同作用的结果。     

Plant functional traits explain interspecific differences in immediate cyclone damage to trees of an endangered rainforest community in north Queensland

Abstract Cyclones cause profound immediate impacts on tropical rainforest trees, including defoliation, limb loss, snapping of stems and uprooting. Some studies have shown that plant functional traits such as tree size, buttress roots and wood density are correlated with these forms of cyclone damage. On 20 March 2006, Severe Tropical Cyclone Larry crossed the north Queensland coast and proceeded inland across the Atherton Tablelands, impacting the critically endangered Mabi Type 5b rainforest. We investigated the effects of Cyclone Larry on common tree species by categorizing damage to trees as uprooted, snapped, limbs damaged (light, moderate, severe) or upright and estimating levels of defoliation. Damage was then related to functional traits including tree size, presence of buttress roots, wood density, and leaf size and strength. Levels of damage differed between species. Tree size (diameter at breast height) and the presence of buttress roots were not related to damage levels. Wood density was significantly negatively correlated to proportion of trees with snapped stems and significantly positively correlated with the proportion of trees upright with no or light limb damage. Levels of defoliation were significantly related to leaf strength (specific leaf area – SLA) and to leaf width, but not other components of leaf size (area or length) or petiole length. Species with high wood density and low SLA (e.g. Argyrodendron spp.) were found to have high cyclone resistance, the ability to resist damage, while species with low wood density and high SLA (e.g. Dendrocnide photinophylla) exhibited low resistance. However, traits related to low resistance are also those linked to rapid growth and high cyclone resilience, the ability to recover from damage, so it is unlikely that the Mabi forest will experience long‐term changes in floristic composition following Cyclone Larry.     

西双版纳热带季节雨林的树种组成和群落结构动态

研究了西双版纳热带季节雨林1 hm2(hectare)动态监测样地1993年与2007年之间树种组成和群落结构的变化。对样地中胸径≥5 cm的乔木进行了每木调查。目前其树种组成的热带分布科、属所占比例分别为91%和94%,具有较高比例的热带植物区系性质。在1993年与2007年两次调查之间,树种数量由145种增至179种,仅有1到2个个体的稀有树种所占比例从54%降为51.1%。从森林的垂直结构来看,A、B、C三层的个体死亡率分别为12.8%、12.9%和19.0%,各层树木的增长率分别为-8.5%、-1.4%和44.8%。与此相对应,C层小径级的树木所占比例有较大提高。虽然小径级的树木在种类和数量上比例增大,但个体数量和种类组成相对稳定的A、B层优势树种变化不大,维持了群落结构的稳定性。14 a间,群落中新增加的具有先锋性质的树种不超过5个。1993年时,A、B两层尚有先锋树种存在,2007年已经从A、B两层中退出。因此,从14 a间树种组成和群落结构的变化来看,虽然具有树木的死亡和增补,但其物种成分和群落结构的总体格局没有明显的变化,处于动态平衡过程中。     

Sandfly distribution and abundance in a tropical rain forest

1. The distribution patterns of sandflies (Diptera: Psychodidae) upon tree buttresses were studied in tropical rain forest at Finca la Selva in the Caribbean lowlands of Costa Rica. 2. Four species of sandfly, Lutzomyia shannoni Dyar, L. trapidoi F. & H., L. ylephiletor F. & H. and L. vespertilionis F. & H. comprising 97% of those caught, used tree buttresses as diurnal resting sites. Their distribution on the buttresses was aggregated. 3. During the dry season tree species had no significant effect upon the distribution of the sandflies. However, during the wet season the distributions of two of the species, L. trapidoi and L. ylephiletor, were significantly affected by the species of tree; it is suggested that some species of tree may provide greater protection from rainfall than others. 4. L. vespertilionis was restricted to a single buttress on each positive tree. Distribution of this species is evidently determined by the distribution of its host animal, the bat (Emballonuridae). Female flies feed upon the bat's blood and male flies may be attracted to the bat as it provides a source of female sandflies. It is suggested, therefore, that tree buttresses serve as sandfly swarming sites. 5. Within a large buttress the sandflies are not randomly distributed but are aggregated in particular areas. Within these aggregations, the sandflies are vertically zoned upon the buttress with a shift in species composition with height. Two hypothesis were suggested to account for this distribution pattern: a response to an environmental gradient or an interaction between the four species of fly.     

Patterns of sandfly distribution in tropical forest: a causal hypothesis

1. In tropical rain forest, phlebotomine sandflies (Diptera: Psychodidae), such as Lutzomyia vespertilionis and L.ylephiletor, have an aggregated distribution on their tree buttress diurnal resting sites, as studied during 1987-88 at Finca la Selva in the Caribbean lowlands of Costa Rica. 2. Experimental transfer of flies to trees not used as resting sites indicated that many apparently suitable sites remain unoccupied. 3. Observations of sandflies on the buttresses revealed that males and females are juxtaposed more frequently than expected by chance alone. Courtship behaviour by three of the four species of sandfly studied was observed on the buttresses. 4. It is suggested that the use of buttresses as swarming sites for mating behaviour is more likely to account for the observed distribution patterns of sandflies than their use of buttresses simply as diurnal resting sites.     

西双版纳热带季节雨林土壤养分空间异质性对乔木树种多样性的影响

生态位理论认为,养分空间异质性分布会减少种间竞争排斥而有助于物种共存;而中性理论则认为群落树种呈独立于环境特征的随机分布。为研究土壤养分异质性与乔木树种多样性的联系,在西双版纳热带季节雨林随机设置了16个1 hm~2样方,调查了各样方乔木树种多样性,计算了各样方土壤有效氮(AN)、有效磷(EP)、有效钾(EK)、有机质(OM)、p H、总氮(TN)、总磷(TP)、总钾(TK)的变异系数以代表各样方土壤养分空间异质性分布的相对水平。Pearson相关分析表明,TK变异系数与乔木树种丰富度、Shannon-wiener指数呈显著正相关(P0.05),表明该区域不同植物可能在钾资源的利用上存在明显的生态位分化,钾的异质性有助于树种共存;OM、AN变异系数与Pielou均匀度指数呈明显正相关(P0.1),在一定程度上说明了这些养分的空间异质性缓解了种间竞争压力,树种多度分布相对均匀,有助于树种共存。除TK外,其它土壤指标的变异系数与乔木树种多样性的正相关性均不显著(P0.05),表明这些养分的空间异质性分布对乔木树种多样性的影响相对较小,中性或其它生态学过程可能掩盖了这些养分的空间异质性分布对乔木树种多样性的影响。这说明,土壤养分空间异质性可能在一定程度上促进了树种共存,但同时应当重视中性过程等在西双版纳热带雨林群落构建中的作用。     

Liana community and functional trait analysis in tropical dry evergreen forest of India

Aim Lianas are abundant and diverse throughout the world and constitute an important structural and functional component of tropical forests. This study aims to investigate liana diversity, abundance and their functional traits in Indian tropical dry evergreen forest (TDEF).Methods A total of ten 1-ha plots, one each in 10 Indian TDEF sites were demarcated. Each 1-ha plot was divided into one-hundred 10- × 10-m quadrats to facilitate woody species inventory. All lianas ≥1cm diameter measured at 130cm from the rooting point and all trees ≥10-cm girth at breast height (gbh) were recorded from the study sites to analyze the patterns of liana diversity and abundance and also to compare the contribution of lianas to the total woody species richness, density and basal area. Liana variables across the study sites were compared using one-way analysis of variance. The qualitative functional traits of inventoried lianas and trees were assessed on the field and referring to pertinent field manuals.Important findings A total of 9237 liana individuals (ranged from 408–1658 individuals ha^-1) representing 52 species, 45 genera and 28 families were encountered from the 10 study sites. Liana species richness ranged from 11–31 species ha^-1 in 10 sites, which averaged 23.4 (±5.7) species ha^-1. The total basal area of lianas in the study sites was 7. 3 m 2 (0.20–1.76 m 2 ha^-1). There was a significant variation in liana species richness, density and basal area across the studied sites. On the whole, lianas contributed 52%, 49.3% and 4.1% to the total woody species (lianas and trees) richness, density and basal area, respectively. Liana trait analysis revealed the majority (50%) of lianas belonged to brevi-deciduous type. Stem twining was the chief climbing mechanism, exhibited by 21 species (52.6% of total abundance). More than half of the liana species (34 species; 6925 individuals) had microphyllous leaves. Fleshy-fruited lianas mostly bearing berries and drupes constituted the major fruit type in the studied sites. Zoochory was the predominant dispersal mode observed in 63.4% of species. Considering the ecological and functional role of lianas in Indian TDEF, the need for conservation is emphasized.     

Climatic correlates of phylogenetic relatedness of woody angiosperms in forest communities along a tropical elevational gradient in South America

Aims This study assesses the relationship between phylogenetic relatedness of angiosperm tree species and climatic variables in local forests distributed along a tropical elevational gradient in South America. In particular, this paper addresses two questions: Is phylogenetic relatedness of plant species in communities related to temperature variables more strongly than to water variables for tropical elevational gradients? Is phylogenetic relatedness of plant species in communities driven by extreme climatic conditions (e.g. minimum temperature (MT) and water deficit) more strongly than by climatic seasonal variability (e.g. temperature seasonality and precipitation seasonality)?Methods I used a set of 34 angiosperm woody plant assemblages along an elevational gradient in the Andes within less than 5 degrees of the equator. Phylogenetic relatedness was quantified as net relatedness index (NRI) and nearest taxon index (NTI) and was related to major climatic variables. Correlation analysis and structure equation modeling approach were used to assess the relationships between phylogenetic relatedness and climatic variables.Important findings Phylogenetic relatedness of angiosperm woody species in the local forest communities is more strongly associated with temperature-related variables than with water-related variables, is positively correlated with mean annual temperature (MAT) and MT, and is related with extreme cold temperature more strongly than with seasonal temperature variability. NTI was related with elevation, MAT and MT more strongly than was NRI. Niche convergence, rather than niche conservatism, has played a primary role in driving community assembly in local forests along the tropical elevational gradient examined. Negative correlations of phylogenetic relatedness with elevation and higher correlations of phylogenetic relatedness with elevation and temperature for NTI than for NRI indicate that evolution of cold tolerance at high elevations in tropical regions primarily occurred at recent (terminal) phylogenetic nodes widely distributed among major clades.     

Biomechanics of buttressed trees: bending strains and stresses

The different hypotheses about buttress function and formation mainly involve mechanical theory. Forces were applied to two trees of Sloanea spp., a tropical genus that develops typical thin buttresses, and the three-dimensional strains were measured at different parts of the trunk base. Risks of failure were greater on the buttress sides, where shear and tangential stresses are greater, not on the ridges, in spite of high longitudinal (parallel to the grain) stresses. A simple beam model, computed from the second moment of area of digitized cross sections, is consistent with longitudinal strain variations but cannot predict accurately variations with height. Patterns of longitudinal strain variation along ridges are very different in the two individuals, owing to a pronounced lateral curvature in one specimen. The constant stress hypothesis is discussed based on these results. Without chronological data during the development of the tree, it cannot be proved that buttress formation is activated by stress or strain.