Patterns of liana community diversity and structure in a tropical rainforest reserve,Ghana: effects of human disturbance

Most studies have concluded that liana diversity and structure increase with disturbance. However, a contradictory pattern has emerged recently calling for more research in the area. Liana diversity and structure were investigated in three forest types that differ in disturbance intensity (nondisturbed, moderately disturbed and heavily disturbed forest: NDF, MDF and HDF, respectively) in the Atewa Range Forest Reserve, Ghana. In each forest type, 10 square plots of 0.25 ha were demarcated. Lianas with diameter ≥1 cm located on trees with diameter ≥10 cm were enumerated. A total of 429 individuals representing 40 species, 29 genera and seventeen families were identified in the study. Shannon diversity and species richness of lianas were significantly lower in the HDF (P < 0.05). Liana density and basal area differed significantly across all forest types (P < 0.0001). The importance value index (IVI) of most liana species varied greatly across the forest types. The current study has provided evidence to support the pattern of decreasing liana diversity and structure with disturbance in some tropical forests. Further studies are recommended to gain more understanding of the factors that are responsible for the divergent liana responses to disturbance in tropical forests.     

Patterns of ferns community assemblages in some Malaysian and Nigerian tropical forests

Research on fern ecology has gained attention in the last decade, yet there is a paucity of information on the comparison of ferns communities across continents. This study focused on comparing the ferns community assemblages in some tropical forests of Malaysia and Nigeria, thereby assessing the patterns of species richness (SR) and phylogenetic diversity (PD) in relation to the bioclimatic drivers across the continents. The diversity and taxonomic compositions of ferns were assessed using 180 plots of 10 m × 10 m in each country. The species richness and other diversity indices were determined using the combined forests data for each country and for the individual forests. Also, the phylogenetic diversity of the ferns was assessed using the genus‐based molecular sequences downloaded from the GeneBank. The patterns of the ferns SR and PD in the two countries as driven by some bioclimatic factors were evaluated using the regression analysis. The observed and rarefied–extrapolated fern species richness is significantly higher in Malaysian forests than in Nigerian forests. Also, the other diversity indices are significantly higher in Malaysian forests except for the Shannon index which showed no significant difference between the two biogeographic regions. There is a very low similarity (7.41%) in the taxonomic composition of ferns between the two biogeographic areas, although the similarity in composition increased with increasing taxonomic levels (species: 7.41%, genus: 12.77%, family: 70.96%). Terrestrial and epiphytic ferns are more dominant than the other life forms in the two countries. The precipitation variables drive the phylogenetic structure of ferns in Nigeria, whereas both precipitation and temperature variables drive the phylogenetic structure of ferns in Malaysia. This indicates that ferns assemblages in Nigeria and Malaysia are driven by both climatic variables. Besides, we also hypothesize that these observed differences could be due to other historical and evolutionary processes.     

Floristic diversity of Mexican seasonally dry tropical forests

Studies of the variation in tropical plant species diversity and itsrelationship with environmental factors are largely based on research intropical moist/wet forests. Seasonally dry tropical forests (SDTFs), incontrast, have been poorly investigated. In this paper we present data from 20Mexican SDTF sites sampled to describe the magnitude of floristic diversity inthese forests and to address the following questions: (i) to what extent isspecies diversity related to rainfall? (ii) Are there other climatic variablesthat explain variation in species diversity in SDTFs? (iii) How does speciesidentity vary spatially (species turnover) within the country? We found thatspecies diversity was consistently greater (a ca. twofold difference) than wouldbe expected according to the sites' precipitation. Rainfall did notsignificantly explain the variation in species diversity. Likewise, the numberof dry and wet months per year was unrelated to species diversity. In contrast,a simple measure of potential evapotranspiration (Thornthwaite's index)significantly explained the variation in species diversity. In addition to thegreat diversity of species per site (local diversity), species turnover wasconsiderable: of a total of 917 sampled species, 72% were present only in asingle site and the average similarity (Sorensen's index) among sites wasonly 9%. These aspects of floristic diversity and the high deforestation ratesof these forests in Mexico indicate that conservation efforts should be directedto tropical forests growing in locations of low and seasonal rainfall.     

Experimental defaunation of terrestrial mammalian herbivores alters tropical rainforest understorey diversity

It has been suggested that tropical defaunation may unleash community-wide cascading effects, leading to reductions in plant diversity. However, experimental evidence establishing cause–effect relationships thereof is poor. Through a 5 year exclosure experiment, we tested the hypothesis that mammalian defaunation affects tree seedling/sapling community dynamics leading to reductions in understorey plant diversity. We established plot triplets (n = 25) representing three defaunation contexts: terrestrial-mammal exclosure (TE), medium/large mammal exclosure (PE) and open access controls (C). Seedlings/saplings 30–100 cm tall were marked and identified within each of these plots and re-censused three times to record survival and recruitment. In the periods 2010–2011 and 2011–2013, survival was greater in PE than in C plots and recruitment was higher in TE plots than in C plots. Overall, seedling density increased by 61% in TE plots and 23% in PE plots, whereas it decreased by 5% in C plots. Common species highly consumed by mammals (e.g. Brosimum alicastrum and Ampelocera hottlei) increased in their abundance in TE plots. Rarefaction curves showed that species diversity decreased in TE plots from 2008 to 2013, whereas it remained similar for C plots. Given the prevalence of tropical defaunation, we posit this is an anthropogenic effect threatening the maintenance of tropical forest diversity.     

热带森林中的斑块动态与物种多样性维持

斑块作为景观要素之一,直接到景观结构的空间格局及其内部各要素之间的相互关系,其动态也将导致景观格局的变化。异质性的斑块在自然森林中是普遍存在的,这就是说,顶极森林中仍然存在着由不同种类或不同生长时期的植物种群组成的森林斑块。由自然或人为干扰所驱动的森林生长循环导致敢这些斑块在空间上的镶嵌,对于持定的地域片段,也导致了不同生长时期的森林斑块的周期性循环。在热带森林中,森林的生长循环由林窗期（ｇａｐ     

不同恢复阶段热带森林土壤nirS型反硝化微生物群落结构及多样性特征

探明热带森林土壤反硝化微生物群落结构及多样性,对于理解反硝化引起的N₂O排放及缓解全球变暖具有重要意义。本研究以西双版纳3个不同恢复阶段热带森林类型[即白背桐（Mallotus paniculatus,MP）、崖豆藤（Millttia leptobotrya,ML）群落、群落及高檐蒲桃（Syzygium oblatum,SO）群落]为研究对象,揭示土壤nirS型反硝化微生物群落组成及多样性的干湿季变化,分析热带森林恢复过程中土壤理化环境变化对nirS型反硝化细菌群落的影响。结果表明,变形菌门（Proteobacteria）和酸杆菌门（Acidobacteria）相对丰度表现为恢复前期高于恢复后期,而脱氯单胞菌属（Dechloromonas）、嗜盐单胞菌属（Halomonas）和罗思河小杆菌属（Rhodanobacter）表现为恢复后期高于恢复前期;绿弯菌门（Chloroflexi）和放线菌门（Actinobacteria）均随恢复年限增加而增加,而贪铜菌属（Cupriavidus）和假单胞菌属（Pseudomonas）的相对丰度表现为随恢复年限增加而降低。9月份各样地新检测出的属数量表现为：SO （19种） > MP （13种） > ML （7种）。土壤nirS型反硝化微生物群落的Shannon多样性指数表现为：高檐蒲桃群落 > 崖豆藤群落 > 白背桐群落,且9月（湿季） > 3月（干季）。相关分析表明,热带森林恢复引起土壤N库（全氮、NH₄⁺、NO₃^-）、C有效性（微生物量碳、易氧化碳）及微气候（土壤含水率与温度）的改变,能够显著影响nirS型反硝化细菌群落的结构及多样性。主成分分析结果表明,土壤硝态氮、微生物量碳、全氮及易氧化碳是调控不同恢复阶段热带森林土壤nirS型反硝化细菌群落结构及多样性变化的主控因子,其次为土壤水分、温度、水解氮、pH、铵态氮、有机碳、容重及C/N。     

热带与亚热带森林分子生态学研究

当前 ,植物学家会有更多的方法和手段来从事植物学的研究 ,如分子生物学方法、遗传学的方法、植物生理学的方法、分类学方法等。其中分子生物学方法直接研究植物遗传物质ＤＮＡ ,从根本上揭示了生物体内涵 ,有着极其重要的作用[4 7] 。因此用分子生物学手段进行生态学的研究有着广泛应用前景和重要意义。分子生物学方法既节省时间和资金 ,又比传统方法解决了更多的问题[6 1] 。例如在动物学研究中 ,用少许的毛发就可以分析高山土拨鼠 (ＭａｒｍｏｔａｍａｒｍｏｔａＳｃｉｕｒｉｄａｅ)的交配系统[30 ] ;粪便所带的肠道粘膜细胞ＤＮＡ也可以…     

Beta diversity and oligarchic dominance in the tropical forests of Southern Costa Rica

Recent studies have reported a consistent pattern of strong dominance of a small subset of tree species in neotropical forests. These species have been called “hyperdominant” at large geographical scales and “oligarchs” at regional‐landscape scales when being abundant and frequent. Forest community assembly is shaped by environmental factors and stochastic processes, but so far the contribution of oligarchic species to the variation of community composition (i.e., beta diversity) remains poorly known. To that end, we established 20.1‐ha plots, that is, five sites with four forest types (ridge, slope and ravine primary forest, and secondary forest) per site, in humid lowland tropical forests of southwestern Costa Rica to (a) investigate how community composition responds to differences in topography, successional stage, and distance among plots for different groups of species (all, oligarch, common and rare/very rare species) and (b) identify oligarch species characterizing changes in community composition among forest types. From a total of 485 species of trees, lianas and palms recorded in this study only 27 species (i.e., 6%) were nominated as oligarch species. Oligarch species accounted for 37% of all recorded individuals and were present in at least half of the plots. Plant community composition significantly differed among forest types, thus contributing to beta diversity at the landscape scale. Oligarch species was the component best explained by geographical and topographic variables, allowing a confident characterization of the beta diversity among tropical lowland forest stands. Abstract in Spanish is available with online material.     

影响天然林下层植物物种多样性的林分因子的研究

以我国东北过伐林区3种典型森林类型为对象,用多元逐步回归方法来研究影响天然林下层植物多样性的林分因子,尤其是与森林经营有关的林分因子,从而通过经营来维持和增加物种多样性。研究表明,与经营有关的因子中对下层植物多样性有显著影响的有林分郁闭度、公顷株数和树种多样性。因此,在林分发展的一定阶段,应采取合理经营措施如采伐来控制林分密度,保持多树种的混交,来维持和增加树种多样性。     

Phylogenetic community patterns suggest Central Indian tropical dry forests are structured by montane climate refuges

Aim

We used an eco-phylogenetic approach to investigate the diversity and assembly patterns of tropical dry forests (TDFs) in Central India. We aimed at informing conservation and restoration practices in these anthropogenically disturbed forests by identifying potential habitats of conservation significance and elements of regional biodiversity most vulnerable to human impact and climate change.

Location

Tropical dry forests of Madhya Pradesh, Central India.

Methods

We analysed the species richness, stem density, basal area and phylogenetic structure (standardized effect size of MNTD, MPD, PD and community evolutionary distinctiveness cED) of 117 tree species assemblages distributed across a ~230 to ~940 m elevational gradient. We examined how these community measures and taxonomic (Sørensen) and phylogenetic (UniFrac) beta diversity varied with elevation, precipitation, temperature and climatic stress.

Results

Species richness, phylogenetic diversity, stem density and basal area were positively correlated with elevation, with high-elevation plots exhibiting cooler temperatures, higher precipitation and lower stress. High-elevation assemblages also trended towards greater phylogenetic dispersion, which diminished at lower elevations and in drier, more stressful plots. Phylogenetic turnover was observed across the elevation gradient, and species evolutionary distinctiveness increased at lower elevations and under harsher abiotic conditions.

Main Conclusions

Harsher abiotic conditions at low elevations may act as a selective filter on plant lineages, leading to phylogenetically clustered low-diversity assemblages. These assemblages contained more evolutionarily distinct species that may contribute disproportionately to biodiversity. Conversely, milder abiotic conditions at high elevations may serve as refuges for drought-sensitive species, resulting in more diverse assemblages. Conservation practices that prioritize both high- and low-elevation habitats could promote the persistence of evolutionarily distinct species and areas of high biodiversity within the Central Indian landscape. Establishing connectivity between these habitats may provide a range of climatic conditions for species to retreat to or persist within as climates change.     

The cost-effectiveness of biodiversity surveys in tropical forests

The identification of high-performance indicator taxa that combine practical feasibility and ecological value requires an understanding of the costs and benefits of surveying different taxa. We present a generic and novel framework for identifying such taxa, and illustrate our approach using a large-scale assessment of 14 different higher taxa across three forest types in the Brazilian Amazon, estimating both the standardized survey cost and the ecological and biodiversity indicator value for each taxon. Survey costs varied by three orders of magnitude, and dung beetles and birds were identified as especially suitable for evaluating and monitoring the ecological consequences of habitat change in our study region. However, an exclusive focus on such taxa occurs at the expense of understanding patterns of diversity in other groups. To improve the cost-effectiveness of biodiversity research we encourage a combination of clearer research goals and the use of an objective evidence-based approach to selecting study taxa.     

Landscape-level tree diversity assessment in tropical forests of southern Eastern Ghats,India

This large-scale, landscape-level study aims to assess tree species diversity, stem density and stand structure of six major tropical hill forests of southern Eastern Ghats, India, namely, Bodamalai (BM), Chitteri (CH), Kalrayan (KA), Kolli hills (KO), Pachaimalai (PM) and Shervarayan hills (SH). The Eastern Ghats of India is relatively under-studied compared with the Western Ghats biodiversity hotspot. The entire stretch of southern Eastern Ghats was divided into smaller grids of 6.25 km × 6.25 km, totaling to 120 grids. Within each grid, a belt transect of 0.5 ha (5 m × 1000 m) area was laid and all trees ≥30 cm girth at breast height (gbh) were enumerated. A total of 272 tree species (≥30 cm gbh) that belonged to 181 genera and 62 families were recorded in the total 60 ha area inventoried. Diversity indices such as Shannon, Simpson and Fisher's alpha indices were 2.44, 0.03 and 42.1, respectively, for the whole 60 ha area. One way ANOVA revealed that the species richness varied significantly across the six sites (F_(5,823) = 4.854, p < 0.0002). Also, the contribution of tree species to total species richness classified by three plant types viz. evergreen, brevi-deciduous and deciduous species varied significantly across the sites (One way ANOVA: F_(2,15) = 10.05, p < 0.002). Similarity indices such as Jaccard and Sørensen showed that sites CH and KA are more similar in terms of species composition. The total stand density and basal area for the total 60 ha area were 27,412 stems (457 stems ha⁻¹) and 1012.12 m² (16.9 m² ha⁻¹), respectively. The stand density and basal area for the six sites ranged from 290 (in site BM) to 527 stems ha⁻¹ (in site KA) and from 5.6 (in site BM) to 24.4 m² ha⁻¹ (in site KO), respectively. Stand density and basal area of tree species varied significantly across the six hill complexes (F_(5,823) = 4.85, p < 0.0002 and F_(5,823) = 2.71, p < 0.02, respectively). A positive correlation was obtained between stand density and species richness in sites PM (r_s = 0.65, p < 0.05) and SH (r_s = 0.67, p < 0.05), but not in other sites. The predominant tree species in the tropical forests of southern Eastern Ghats include Albizia amara, Euphorbia antiquorum, Canthium dicoccum var. dicoccum, Memecylon edule, Chloroxylon swietenia and Nothopegia heyneana. Taxonomically, Euphorbiaceae constituted the most diverse family with 25 species. Whereas, by tree abundance the Mimosaceae with 4126 stems enumerated from the 60 ha area formed the dominant family. Bray–Curtis cluster analysis, based on tree species composition and abundance revealed that the low-diverse site BM formed a separate entity from other hill complexes. This large-scale tree diversity inventory provides a baseline data for a variety of investigations and is expected to be useful for effective forest management and biodiversity conservation of southern Eastern Ghats region.     

热带森林植物多样性及其维持机制

热带森林具有地球上最丰富的植物多样性。关于热带森林植物多样性的维持机制,虽有众多假说,但均未形成完善的理论体系。不同的学者从不同的角度出发得出了许多结论,但也引起了不少争议。本文主要简述了4种经常被用来解释热带森林高植物多样性的机制：生态位分化、取食压力、生活史负相关和随机竞争,每一种机制都有大量的证据支持。热带森林植物沿微环境梯度的非随机空间分布表明其生态位分化很明显,并对其多样性起重要作用。动物的取食降低母树周围同种幼苗的生长率和存活率,为其他物种存活提供了机会,这就是取食压力假说,这是一个极有前景但仍需大量实验验证的假说。生活史负相关使得热带森林的许多植物能够共存。冠层植物的抑制使得随机性在林下植物的建立过程中起决定作用。     

我国丛赤壳类真菌分类研究

丛赤壳类真菌是具有经济重要性的生物类群。该文回顾了我国该类分类研究的简史,概述近年来取得的相关研究进展,揭示我国该类真菌的物种丰富程度,展示建立在分类学基础上的真菌DNA条形码探索以及分子系统学研究成果,表明资源和分类研究与真菌天然产物研究联手的新发现。     

Ecological integrity of tropical secondary forests: concepts and indicators

Naturally regenerating forests or secondary forests (SFs) are a promising strategy for restoring large expanses of tropical forests at low cost and with high environmental benefits. This expectation is supported by the high resilience of tropical forests after natural disturbances, yet this resilience can be severely reduced by human impacts. Assessing the characteristics of SFs and their ecological integrity (EI) is essential to evaluating their role for conservation, restoration, and provisioning of ecosystem services. In this study, we aim to propose a concept and indicators that allow the assessment and classification of the EI of SFs. To this end, we review the literature to assess how EI has been addressed in different ecosystems and which indicators of EI are most commonly used for tropical forests. Building upon this knowledge we propose a modification of the concept of EI to embrace SFs and suggest indicators of EI that can be applied to different successional stages or stand ages. Additionally, we relate these indicators to ecosystem service provision in order to support the practical application of the theory. EI is generally defined as the ability of ecosystems to support and maintain composition, structure and function similar to the reference conditions of an undisturbed ecosystem. This definition does not consider the temporal dynamics of recovering ecosystems, such as SFs. Therefore, we suggest incorporation of an optimal successional trajectory as a reference in addition to the old-growth forest reference. The optimal successional trajectory represents the maximum EI that can be attained at each successional stage in a given region and enables the evaluation of EI at any given age class. We further suggest a list of indicators, the main ones being: compositional indicators (species diversity/richness and indicator species); structural indicators (basal area, heterogeneity of basal area and canopy cover); function indicators (tree growth and mortality); and landscape proxies (landscape heterogeneity, landscape connectivity). Finally, we discuss how this approach can assist in defining the value of SF patches to provide ecosystem services, restore forests and contribute to ecosystem conservation.     

Wood decomposition is more strongly controlled by temperature than by tree species and decomposer diversity in highly species rich subtropical forests

While the number of studies on the role of biodiversity on ecosystem functioning is steadily increasing, a key component of biogeochemical cycling in forests, dead wood decay, has been largely neglected. It remains widely unknown whether and how dead wood decay is affected by diversity loss in forests. We studied the hierarchical effects of tree species diversity on wood decay rates in a subtropical forest landscape in southeast China via its influence on fungal OTU richness and invertebrate diversity using piecewise structural equation models. The experiment was conducted in natural forest plots that span a wide gradient of tree species diversity embedded in a heterogeneous topography. To account for interactions between macro‐invertebrates and fungi, that potentially modify the influence of tree biodiversity and climate on dead wood decay, we compared a macro‐invertebrate exclusion treatment with a control treatment that allowed access to all types of decomposers. Diversity effects of trees on wood decay rates were mostly negative and mediated by the diversity of macro‐invertebrates. However, the effects of tree species diversity or fungal OTU richness and macro‐invertebrate diversity on wood decay rates were comparatively weak. Temperature affected decay rates positively and had the strongest influence in all treatments. While the exclusion of macro‐invertebrates did not lead to a reduction of wood decay rates, our results suggest that they may however have a mediating role in the process. In the presence of invertebrates the predictability of wood decay rates was higher and we observed a tendency of a stronger temperature control. Our results suggest that there is evidence for diversity effects on wood decomposition, but the temperature control is still more important. Thus, an increase in mean annual temperature will increase carbon and nutrient turnover through wood decomposition in subtropical forest irrespective of biotic composition.     

Above-ground forest biomass is not consistently related to wood density in tropical forests

Aim  It is increasingly accepted that the mean wood density of trees within a forest is tightly coupled to above-ground forest biomass. It is unknown, however, if a positive relationship between forest biomass and mean community wood density is a general phenomenon across forests. Understanding spatial variation in biomass as a function of wood density both within and among forests is important for predicting changes in stored carbon in response to global change, and here we evaluated the generality of a positive biomass–wood density relationship within and among six tropical forests.
Location  Costa Rica, Panama, Puerto Rico and Ecuador.
Methods  Individual stem data, including diameter at breast height and spatial position, for six forest dynamics plots were merged with an extensive wood density database. Individual stem biomass values were calculated from these data using published statistical models. Total above ground biomass, total basal area and mean community wood density were also quantified across a range of subcommunity plot sizes within each forest.
Results  Among forests, biomass did not vary with mean community wood density. The relationship between subcommunity biomass and mean wood density within a forest varied from negative to null to positive depending on the size of subcommunities and forest identity. The direction of correlation was determined by the associated total basal area–mean wood density correlation, the slope of which increased strongly with whole forest mean wood density.
Main conclusions  There is no general relationship between forest biomass and wood density, and in some forests, stored carbon is highest where wood density is lowest. Our results suggest that declining wood density, due to global change, will result in decreased or increased stored carbon in forests with high or low mean wood density, respectively.