Tree and shrub diversity and abundance in fragmented littoral forest of southeastern Madagascar

In the coastal littoral forest of extreme southeastern Madagascar, westudied tree diameter at breast height (DBH) 10 cm in 20, 50× 50 m plots in each of four forest fragments, andunderstorywoody vegetation (DBH < 10 cm, 1 m tall) in60,10 × 10 m plots in three of the fragments. Oneforestfragment was located in the highly degraded Lokaro region, and three in the nearbySainte-Luce forest. Atotal of 3476 trees, representing 169 species in 55 families, were recorded inthe50 × 50 m plots, and 10282 understory stems, representing195 species in 54 families, were found in the 10 × 10m plots. For each tree, DBH was recorded. Mean tree diameter andpatterns of tree size class distribution did not differ among the four forestfragments. However, the fragments differed significantly in both tree andunderstory stem densities, species richness and diversity values, and familyrichness values, with the Lokaro fragment having the lowest values for allmeasures. Furthermore, floristic patterns, family importance values, and communitysimilarity measures revealed that the species composition at theLokaro fragment was very different from the Sainte-Luce fragments. Anthropogenicdisturbance appears most pronounced in the isolated Lokaro forest, where bioticresources are limited to this single fragment.     

An ecological paradox: high species diversity and low position of the upper forest line in the Andean Depression

Systematic investigations of the upper forest line (UFL) primarily concentrate on mid and high latitudes of the Northern Hemisphere, whereas studies of Neotropical UFLs are still fragmentary. This article outlines the extraordinary high tree diversity at the UFL within the Andean Depression and unravels the links between the comparatively low position of the local UFL, high tree‐species diversity, and climate. On the basis of Gentry′s rapid inventory methodology for the tropics, vegetation sampling was conducted at 12 UFL sites, and local climate (temperature, wind, precipitation, and soil moisture) was investigated at six sites. Monotypic forests dominated by Polylepis were only found at the higher located margins of the Andean Depression while the lower situated core areas were characterized by a species‐rich forest, which lacked the elsewhere dominant tree‐species Polylepis. In total, a remarkably high tree‐species number of 255 tree species of 40 different plant families was found. Beta‐diversity was also high with more than two complete species turnovers. A non‐linear relationship between the floristic similarity of the investigated study sites and elevation was detected. Temperatures at the investigated study sites clearly exceeded 5.5°C, the postulated threshold value for the upper tree growth limit in the tropics. Instead, quasi‐permanent trade winds, high precipitation amounts, and high soil water contents affect the local position of the UFL in a negative way. Interestingly, most of the above‐mentioned factors are also contributing to the high species richness. The result is a combination of a clearly marked upper forest line depression combined with an extraordinary forest line complexity, which was an almost unknown paradox.     

西太平洋浮游动物种类多样性

西太平洋区是全球海洋生物种源中心,许多类群的最高物种多样性都出现于该区域,因此,在该区开展种类多样性的研究不仅重要和必要,而且具有在跨国尺度上进行综合管理和相互合作的迫切性。本文在西太平洋的浮游动物样品鉴定分类、编目、文献资料整理和分析的基础上,记录和编入西太平洋10个浮游动物类群2,658种(含亚种),隶属于206科675属,其中水螅水母类99科251属697种,栉水母类12科22属59种,浮游软体动物14科35属86种,介形类8科89属416种,桡足类51科156属908种,糠虾类4科58属202种,磷虾类2科8属56种,十足类8科22属105种,毛颚类5科8属48种,被囊类5科26属81种。     

Tree species composition and diversity of tropical mountain cloud forest in the Yunnan, southwestern China

Species composition, physiognomy, and plant diversity of the less known cloud forests in Yunnan were studied based on data collected from 35 sample plots at seven sites. In floristic composition, the cloud forests are mainly comprised of Fagaceae, Ericaceae, Vacciniaceae, Aceraceae, Magnoliaceae, Theaceae, Aquifoliaceae, Illiciaceae, Lauraceae, and Rosaceae. Physiognomically, the forests are dominated by tree and shrub species. Lianas are rare in the forests. The plants with microphyllous or nanophyllous leaves comprise 44.32–63.46% of the total species, and plants with an entire leaf margin account for more than 50% of the tree and shrub species. There are few tree and shrub species with a drip tip leaf apex and papery leaves. Evergreen species make up more than 75% of the total tree and shrub species. In a 2,500 m² sampling area, the number of vascular species ranged between 57 and 110; Simpson’s diversity index ranged from 0.7719 to 0.9544, Shannon–Winner’s diversity index from 1.8251 to 3.2905, and Pielou’s evenness index from 0.5836 to 0.8982 for trees. The cloud forests in Yunnan are physiognomically similar to the tropical cloud forests in America and Southeast Asia. They very much resemble the mountain dwarf mossy forest in Hainan Island, southeastern China, and the Mountain ericaceous forests in the Malay Peninsula. The cloud forests in Yunnan are considered to be developed, as are the tropical upper montane cloud forests in Asia.     

Evenness of soil organic carbon chemical components changes with tree species richness,composition and functional diversity across forests in China

Higher tree species richness generally increases the storage of soil organic carbon (SOC). However, less attention is paid to the influence of varied tree species composition on SOC storage. Recently, the perspectives for the stronger persistence of SOC caused by the higher molecular diversity of organic compounds were proposed. Therefore, the influences of tree species richness and composition on the molecular diversity of SOC need to be explored. In this study, an index of the evenness of diverse SOC chemical components was proposed to represent the potential resistance of SOC to decomposition under disturbances. Six natural forest types were selected encompassing a diversity gradient, ranging from cold temperate to tropical forests. We examined the correlations of tree species richness, composition, and functional diversity, with the evenness of SOC chemical components at a molecular level by ¹³C nuclear magnetic resonance. Across the range, tree species richness correlated to the evenness of SOC chemical components through tree species composition. The negative correlation of evenness of SOC chemical components with tree species composition, and the positive correlation of evenness of SOC chemical components with tree functional diversity were found. These indicate the larger difference in tree species composition and the lower community functional diversity resulted in the higher heterogeneity of SOC chemical components among the communities. The positive correlation of the evenness of SOC chemical components with the important value of indicator tree species, further revealed the specific tree species contributing to the higher evenness of SOC chemical components in each forest type. Soil fungal and bacterial α-diversity had effect on the evenness of SOC chemical components. These findings suggest that the indicator tree species conservation might be preferrable to simply increasing tree species richness, for enhancing the potential resistance of SOC to decomposition.     

Microbial community composition and functional diversity in the rhizosphere of maize

This study investigates the small-scale stratification of bacterial community composition and functional diversity in the rhizosphere of maize. Maize seedlings were grown in a microcosm with a horizontal mesh (53 M) creating a planar root mat and rhizosphere soil. An unplanted microcosm served as control. Thin slices of soil were cut at different distances from the mesh surface (0.2–5.0 mm) and analysed for bacterial community composition by PCR-DGGE (polymerase chain reaction-denaturing gradient gel electrophoresis) of 16S rDNA and tested for activities of different enzymes involved in C, N, P and S cycling. Bacterial community composition and microbial functional diversity were affected by the presence of the maize roots. The bacterial composition showed a clear gradient up to 2.2 mm from the root surface, while no such gradient was observed in the unplanted pot. Invertase and phosphatase activities were higher in the close vicinity of maize roots (0.2–0.8 mm), whereas xylanase activity was unaffected. This study shows that the changes in bacterial community composition and functional diversity induced by roots may extend several millimetres into the soil.     

Duration and frequency of non-flow periods affect the abundance and diversity of stream meiofauna

1. Intermittent streams (IS) comprise a large proportion of the drainage network in many parts of the world. The non-flow period of IS are known to impact stream biota because aquatic habitats dry out. However, less well understood are the relative effects of the temporal component of these drying events including their duration and frequency.
2. Here, we characterised effects of temporal component of drying events on abundant and species-rich meiofauna. The effects were assessed in 22 streams in the north-eastern Iberian Peninsula. The duration and frequency of non-flow events was characterized over a period of 250 days prior to sampling the sediment-dwelling meiofauna in riffle zones that completely dried out.
3. Overall, meiofauna abundances were amongst the highest ever reported for streambeds. Most meiofaunal taxa correlated positively with the frequency of drying events and correlated positively with the length of dry periods recorded shortly before sampling, suggesting that the community was able to recover quickly. Tardigrades were the only group to correlate positively with the longest dry periods, suggesting that they had the best resilience capabilities in streams that had experienced the longest droughts.
4. On average, nematodes made up half of the meiofauna. We identified a total of 113 different nematode species. The nematode community was more taxonomically diverse in IS, with a smaller proportion of bacterivores and a higher proportion of fungivore species such as Filenchus vulgaris. Thereby resembling the trophic structure commonly observed in soil ecosystems.
5. Our results show that most meiofauna were positively influenced by drying disturbance, that is being able to quickly recover after them. This suggests outstanding resilience capabilities, and points out meiofaunal organisms as key players for kick-starting stream food webs and functions once flow returns.

     

不同林型土壤微生物有机碳降解基因的多样性

应用寡聚核苷酸基因芯片,分析了米亚罗林区冷杉原始林（M—Y）和20世纪60年代云杉人工林（M-60）土壤微生物的功能基因多样性。该功能基因芯片含有与有机碳降解、碳固定、氮、磷、硫循环和金属抗性相关的1961个基因探针。在M—Y和M-60样地中分别检测到39和62个具有较强杂交信号（SNR≥2）的功能基因,其基因多样性水平指数分别为3．59和4．04,杂交信号强度总值分别为480280和630560。M—Y和M-60样地中分别检测到32个和37个有机碳降解基因,占总基因的82％和60％,这些基因分属于22个不同的基因类群,分别参与木质素、木聚糖、几丁质等有机碳的降解过程。有机碳降解基因在两个样地中存在较大的多样性和丰度差异。这些结果说明了大多数的土壤微生物直接参与了土壤有机碳的降解,同时,林型不同显著影响了土壤微生物群落结构和有机碳降解微生物的多样性。     

中亚热带几种针、阔叶树种凋落物混合分解对土壤微生物群落碳代谢多样性的影响

土壤微生物群落功能如何响应凋落物物种组成的改变,对于指导我国的人工林种植具有重要意义。通过小盆模拟试验,用BIOLOG微平板培养的方法研究了南方红壤丘陵区典型物种马尾松和湿地松的凋落物分别与白栎和青冈的凋落物混合,与单一针叶凋落物分解时相比,针阔混合凋落物分解过程中土壤微生物群落功能多样性的差异。结果表明：(1)针叶和阔叶混合分解提高了土壤微生物群落碳代谢的强度、丰富度以及多样性,针阔混合凋落物分解时土壤微生物群落的碳源代谢方式与单一针叶分解时差异显著;(2)凋落物分解前期土壤微生物群落碳代谢强度、丰富度和多样性与凋落物初始C/N呈显著负相关,分解后期土壤微生物群落碳代谢强度与凋落物初始木质素/N比呈显著负相关,碳代谢多样性与初始P含量呈显著正相关;(3)通过改变凋落物物种组成,进而改变凋落物元素组成(C/N、木质素/N和P),能显著影响土壤微生物群落的碳代谢强度和代谢多样性。在南方红壤丘陵区,针-阔叶混合的凋落物比单一针叶凋落物更有利于提高土壤微生物群落的功能。     

目标树抚育对亚热带天然次生灌丛群落结构和多样性的影响

在浙江省临安市选择典型天然次生灌丛,分别进行封禁和目标树抚育,探讨灌丛恢复为乔木林的可能性.结果表明: 4年后,与未管护(对照)相比,封禁和目标树抚育后群落平均胸径分别提高1.3和2.6倍,平均高度分别提高0.5和1.1倍;目标树抚育林木出现了对照林分没有的4.5～8.5 cm径阶和4.5～8.5 m树高阶,形成了4 m高的新林层;灌木层物种丰富度和多样性指数没有因抚育而下降;封禁管理维持了群落的树种组成,遵循原有的演替方向;目标树抚育显著改变了群落的树种组成,提高了目的树种的重要值,近期有可能恢复成为针阔混交林群落.与封禁相比,目标树抚育在优势林木胸径和高度生长、树种组成改善等方面更能达到预想的目标.在有条件经营的情况下,可以选择目标树抚育模式对天然次生灌丛进行管理,从而达到加快群落恢复演替形成乔木林的目的.     

南岭东西段植物群落物种组成及其树种多样性垂直格局的比较

根据沿海拔梯度设置的样地的调查资料,对南岭东段的莽山和西段的猫儿山植物群落乔木层物种多样性的垂直分布格局进行了比较研究。莽山和猫儿山的植被类型差异不大,但相同植被类型的物种组成有比较明显的差异。随海拔的上升,两山体乔木的最大树高均呈现显著下降趋势。猫儿山乔木的最大胸径、胸高断面积之和以及立木密度在海拔梯度上呈单峰曲线变化趋势。莽山乔木的最大胸径、胸高断面积之和与海拔呈明显的负相关性,而立木密度的变化规律不明显。这种单峰曲线格局或负相关关系与中尺度上的海拔高度以及小尺度上的土壤特性、小地形以及人为干扰强度等因素有关。在海拔1000m以下的常绿阔叶林群落和1700m以上的山顶矮林群落,莽山乔木的物种丰富度均明显高于猫儿山。两山体的乔木种数与海拔之间都显示出负相关性,但莽山由于高海拔群落受人为干扰的影响,这种相关性不显著。乔木层α多样性沿海拔梯度没有表现出明显的变化规律,并且在两山体之间也看不出明显的差别。本文最后还对两山脉低海拔区段的常绿阔叶林群落的物种组成和多样性进行了对比分析,结果表明人为干扰导致猫儿山常绿阔叶林的物种丰富度(S)和α多样性(H’)明显低于莽山的原生性常绿阔叶林群落,而且落叶阔叶树种和毛竹(Phyllostachys pubescens)开始入侵到群落中。     

天坑森林植物群落叶功能性状、物种多样性和功能多样性特征

以天坑内部-边缘-外部森林植物群落为研究对象,通过调查植物的群落结构、叶功能性状,探究天坑内外森林植物群落叶功能性状、物种多样性和功能多样性变化特征及其内在关联,为深入了解负地形森林生态系统的功能和恢复退化喀斯特地区的植被提供一定参考。研究结果如下：（1）比叶面积（SLA: 198.75 cm2/g)）、叶面积（LA: 42.70 cm2）、叶磷含量（LPC: 1.70 g/kg）和叶钾含量（LKC: 10.27 g/kg）在天坑内部最高,叶组织密度（LTD: 0.32 g/cm3）和叶干物质含量（LDMC: 0.41 g/g）在天坑外部最高,天坑内外森林均易受到磷限制,表明随天坑内部-边缘-外部生境变化,植物对环境的适应机制和生存策略发生了部分调整,物种的防御策略增强,生长投入策略减弱。（2）Shannon-Wiener指数（2.82）、Simpson指数（0.92）和Pielou’s均匀度指数（0.87）均以天坑外部最高,功能丰富度（1.05）、功能离散度（1.88）和Rao’s二次熵（4.52）以天坑内部最高,表明随天坑内部-边缘-外部生境的变化,植物功能性状的差异减少,物种分布及其功能性状分布总体上更为均匀、物种数量增多。（3）物种多样性指数之间、功能多样性指数之间存在较强的相关性,表明物种多样性指数之间、功能多样性指数之间存在不同的制约关系。（4）叶功能性状与物种多样性、功能多样性的相关性强,物种多样性和功能多样性之间相关性较弱,表明叶性状对生态学过程的变化较为敏感,叶功能性状与物种多样性之间存在较强的耦合关系。     

Tree diversity drives abundance and spatiotemporal β‐diversity of true bugs (Heteroptera)

1. Spatiotemporal patterns of canopy true bug diversity in forests of different tree species diversity have not yet been disentangled, although plant diversity has been shown to strongly impact the diversity and distribution of many insect communities. 2. Here we compare species richness of canopy true bugs across a tree diversity gradient ranging from simple beech to mixed forest stands. We analyse changes in community composition by additive partitioning of species diversity, for communities on various tree species, as well as for communities dwelling on beech alone. 3. Total species richness (γ‐diversity) and α‐diversity, and abundance of true bugs increased across the tree diversity gradient, while diversity changes were mediated by increased true bug abundance in the highly diverse forest stands. The same pattern was found for γ‐diversity in most functional guilds (e.g. forest specialists, herbivores, predators). Temporal and even more, spatial turnover (β‐diversity) among trees was closely related to tree diversity and accounted for ～90% of total γ‐diversity. 4. Results for beech alone were similar, but species turnover could not be related to the tree diversity gradient, and monthly turnover was higher compared to turnover among trees. 5. Our findings support the hypothesis that with increasing tree diversity and thereby increasing habitat heterogeneity, enhanced resource availability supports a greater number of individuals and species of true bugs. Tree species identity and the dissimilarity of true bug communities from tree to tree determine community patterns. 6. In conclusion, understanding diversity and distribution of insect communities in deciduous forests needs a perspective on patterns of spatiotemporal turnover. Heterogeneity among sites, tree species, as well as tree individuals contributed greatly to overall bug diversity.     

俄罗期平原针—阔林过渡带森林群落组成结构与物种多样性的研究

俄罗斯平原针-阔林过渡带森林群落的物种多样性的研究表明,该地区的物种多样性类同于许多类型的过渡带,即群落的过渡带（针阔混交林）比相邻群落（针叶林和阔叶林）具有更高的多样性。针阔混交林群落的组成结构较好地反映了其特殊的过渡性。在该过渡带较高的物种多样性并不证明群落稳定性的增加。因此,在探讨多样性与群落稳定性关系时,综合包括均匀度在内的多个指数才可能作出较为客观的结论。     

Soil Effects on Forest Structure and Diversity in a Moist and a Dry Tropical Forest

Soil characteristics are important drivers of variation in wet tropical forest structure and diversity, but few studies have evaluated these relationships in drier forest types. Using tree and soil data from 48 and 32 1 ha plots, respectively, in a Bolivian moist and dry forest, we asked how soil conditions affect forest structure and diversity within each of the two forest types. After correcting for spatial effects, soil‐vegetation relationships differed between the dry and the moist forest, being strongest in the dry forest. Furthermore, we hypothesized that soil nutrients would play a more important role in the moist forest than in the dry forest because vegetation in the moist forest is less constrained by water availability and thus can show its full potential response to soil fertility. However, contrary to our expectations, we found that soil fertility explained a larger number of forest variables in the dry forest (50 percent) than in the moist forest (17 percent). Shannon diversity declined with soil fertility at both sites, probably because the most dominant, shade‐tolerant species strongly increased in abundance as soil fertility increased.     

Land use change alters functional gene diversity,composition and abundance in Amazon forest soil microbial communities

Land use change in the Amazon rainforest alters the taxonomic structure of soil microbial communities, but whether it alters their functional gene composition is unknown. We used the highly parallel microarray technology GeoChip 4.0, which contains 83 992 probes specific for genes linked nutrient cycling and other processes, to evaluate how the diversity, abundance and similarity of the targeted genes responded to forest‐to‐pasture conversion. We also evaluated whether these parameters were reestablished with secondary forest growth. A spatially nested scheme was employed to sample a primary forest, two pastures (6 and 38 years old) and a secondary forest. Both pastures had significantly lower microbial functional genes richness and diversity when compared to the primary forest. Gene composition and turnover were also significantly modified with land use change. Edaphic traits associated with soil acidity, iron availability, soil texture and organic matter concentration were correlated with these gene changes. Although primary and secondary forests showed similar functional gene richness and diversity, there were differences in gene composition and turnover, suggesting that community recovery was not complete in the secondary forest. Gene association analysis revealed that response to ecosystem conversion varied significantly across functional gene groups, with genes linked to carbon and nitrogen cycling mostly altered. This study indicates that diversity and abundance of numerous environmentally important genes respond to forest‐to‐pasture conversion and hence have the potential to affect the related processes at an ecosystem scale.     

Regeneration Potential of Floodplain Forests Under the Influence of Nonnative Tree Species: Soil Seed Bank Analysis in Northern Italy

Soil seed banks are the ecological memory of plant communities and might represent their regeneration potential. This study examines the soil seed bank in hardwood floodplain forests of the biosphere reserve “Valle del Ticino” (Northern Italy) to find out whether the natural forest vegetation can potentially be restored by the soil seed bank. We compared near natural forests of the phytosociological association Polygonato multiflori–Quercetum roboris with stands dominated by the nonnative tree species Robinia pseudoacacia and Prunus serotina in order to investigate whether the composition of the soil seed bank is significantly influenced by the composition of the main canopy tree species and soil properties. Soil seed bank samples were taken from 20 randomly selected plots in stands that were differentiated into four groups related to the dominant forest canopy species. The germinated plants were counted and their species determined. A total of 2,427 plants belonging to 84 species were recorded. The composition of the dominant tree species and soil parameters significantly influence the composition of the seed bank. The similarity with the standing vegetation was very low. Only 13% of the species in the soil seed bank represent the target vegetation. The low percentage of target species and the high percentage of nonnative species imply that the regeneration of near‐natural forest vegetation from the soil seed bank is not feasible. Consequently, disturbances that may activate the soil seed bank should be minimized. Thus, we recommend stopping the mechanical removal of the nonnative tree species in the Ticino Park .     

Tree diversity,tree height and environmental harshness in eastern and western North America

Does variation in environmental harshness explain local and regional species diversity gradients? We hypothesise that for a given life form like trees, greater harshness leads to a smaller range of traits that are viable and thereby also to lower species diversity. On the basis of a strong dependence of maximum tree height on site productivity and other measures of site quality, we propose maximum tree height as an inverse measure of environmental harshness for trees. Our results show that tree species richness is strongly positively correlated with maximum tree height across multiple spatial scales in forests of both eastern and western North America. Maximum tree height co‐varied with species richness along gradients from benign to harsh environmental conditions, which supports the hypothesis that harshness may be a general mechanism limiting local diversity and explaining diversity gradients within a biogeographic region.