Response of vascular epiphyte diversity to different land-use intensities in a neotropical montane wet forest

Although vascular epiphytes contribute substantially to the biodiversity of tropical montane forests, it is unclear how their diversity and community composition is affected by forest alteration. We studied the response of vascular epiphyte assemblages to different intensities of land-use in a montane wet forest of northeastern Ecuador: (1) unmanaged mature forest; (2) mature forest with mid- and understorey opened for cattle grazing; and (3) isolated remnant trees in cattle pastures. The numbers of individuals and species of epiphytes per host tree did not differ significantly between land-use types, neither did total epiphyte species richness (n = 30 trees). However, total species richness of pteridophytes was significantly lower on isolated remnant trees compared to unmanaged forest, whereas several taxa rich in xerotolerant species (Bromeliaceae, Orchidaceae, Piperaceae) exhibited the opposite trend. An analysis of floristic composition using ordination (NMS) and randomisation techniques (MRPP) showed that epiphyte assemblages on isolated remnant trees were significantly distinct from unmanaged forest while managed forest was intermediate between those two vegetation types. Ordination analysis further indicated reduced floristic heterogeneity in disturbed habitats. These results suggest considerable, rapid species turnover since land-use change 6 years prior to study, with pteridophytes being replaced by more xerotolerant taxa. We attribute this floristic turnover primarily to changes in microclimate towards higher levels of light and desiccation stress associated with forest disturbance. Our results support the notion that community composition offers a more sensitive indicator of human disturbance than species richness.     

Long-term understory recovery after mechanical fuel reduction in Mediterranean cork oak forests

In the Euro-Mediterranean region, mechanical fuel reduction is increasingly used in response to the mounting occurrence of catastrophic wildfires, yet their long-term ecological effects are poorly understood. Although Mediterranean vegetation is resilient to a range of disturbances, it is possible that widespread fuel management at short intervals may threaten forest structural complexity and the persistence of some plant species and functional types, with overall negative consequences for biodiversity. We used a chronosequence approach to infer woody vegetation changes in the first 70 years after understory clearing in upland cork oak (Quercus suber) forests, and to assess how these are affected by treatment frequency. Across the chronosequence there was a shift between plant communities with contrasting composition, structure and functional organization. Understory cover increased quickly after disturbance and a community dominated by pioneer seeder and dry-fruited shrubs (Cistus ladanifer, C. populifolius, Genista triacanthos, and Lavandula stoechas) developed during about 15 years, but this was slowly replaced by a community dominated by resprouters and fleshy-fruited species (Arbutus unedo, Erica arborea) >40 years after disturbance. During the first 15 years there were rapid increases in woody species richness, vertical structural diversity, cover by Q. suber juveniles and saplings, and shrub cover at <1.5 m strata, which levelled off or slightly declined thereafter. In contrast, tree species richness, tree density and density of arboreal A. unedo and E. arborea, vertical structural evenness, and cover at >1.5 m strata increased slowly for >50 years. Treatment frequency showed strongly negative relationships with species richness, structural diversity and evenness, and horizontal and vertical understory cover, particularly that of slowly recovering species. These findings suggest that fuel reduction programs involving widespread and recurrent understory clearing may lead to the elimination at the landscape scale of stands with complex multi-layered understory occupied by large resprouters and fleshy-fruited species, which take a long time to recover after disturbance. Fuel management programs thus need to balance the dual goals of fire hazard reduction and biodiversity conservation, recognizing the value of stands untreated for >50 years to retain ecological heterogeneity in Mediterranean forest landscapes.     

中度干扰对不同光照条件下草地物种多样性的影响

生物多样性保护是全球范围内的生态学问题,以往的观念是,人类活动是导致生物多样性急剧下降的主要原因,所以全球范围内都加快了生态环境的保护。但目前很多的森林、草地及自然资源出现了过度保护现象,导致生物多样性并没有随着环境保护的加强而增多。为了研究干扰对物种多样性的影响,本文设计了在不同光照条件下的人为干扰实验,运用Margalef丰富度指数、Sinmpson指数、Shannon-Winener指数和Pielou均匀度指数,研究了无人为干扰和中度干扰在不同光照条件下对物种多样性和植物生物量的影响,并以此为生态服务和生物多样性保护策略提供依据。结果表明,不同人为干扰强度和光照强度对物种的数量特征和分布特征产生了影响,有人为干扰样方中的物种多样性比无人为干扰样方中的高,中度干扰样方中物种数量多于轻度干扰样方。有光照的样方中物种数量比荫蔽样方中的物种数量要高。光照强度和人为干扰对地面现存生物量有影响,并且光照强度的影响要大于人为干扰。     

江南油杉人工林植物多样性与生境因子关系

为探寻江南油杉人工林林下植被生物多样性特征及生境因子对其的影响,对广西境内不同生境条件下的江南油杉人工林的植被状况进行了调查及生物多样性评价。结果表明:江南油杉人工林林下灌木层物种较草本层物种丰富,灌木层的Shanor-Wiener指数(H’)和Simpson指数(D)均明显高于草本层。草本层的Pielou指数(J)分布幅度(0.771~0.994)较灌木层的(0.841~0.945)宽。小乔木伴生树种较多,乔木种类与林地起源关系密切。不同森林郁闭度、坡度、坡向及坡位的江南油杉人工林林下植被多样性存在一定差异;随着郁闭度的上升,物种丰富度下降;阳坡灌木层植被丰富度略高于阴坡的;平坡的Shanor-Wiener指数和Simpson指数分布范围较斜坡的宽;中坡位的Shanor-Wiener指数和Simpson指数分布范围比上坡位和下坡位的低。     

人为经营干扰对人工雷竹林下植被多样性的影响

研究结果表明：（1）人为干扰导致了雷竹林群落层次结构简化，灌木层消失，草木层不明显。（2）不同干扰的雷竹林下植物变异大，群落相似系数低，优势种不同。（3）人为干扰强度增大，雷竹林下植物的丰富度，Shannon-Wiener和Simpson多样性指数随之减少。（4）同样的干扰强度对差的立地条件上群落物种多样性的影响更大。提出了保护生物多样性，发展持续稳定雷竹林的经营措施。     

间伐强度对云杉人工林下植物多样性的影响研究

调查了云杉人工林间伐后和未间伐的林分生长、林下植物种类、数量、盖度、高度,采用物种丰富度、Shannon-Wiener指数、Simpson指数和Pielou均匀度指数进行了多样性分析,以探讨间伐强度对云杉人工林下植物多样性的影响.结果表明：随着间伐强度的增大,保留木的生长显著优于对照区;林下植物种类、数量显著增加;不同间伐强度林下植物种类的多样性、丰富度、生物量、盖度、显著高于对照区,且随间伐强度的增强而增大,以重度间伐（＜450株/hm2）最为显著（灌木层多样性除外）.     

Tropical reptiles in pine forests: Assemblage responses to plantations and plantation management by burning

Worldwide, the land area devoted to timber plantations is expanding rapidly, especially in the tropics, where reptile diversity is high. The impacts of plantation forestry and its management on native species are poorly known, but are important, because plantation management goals often include protecting biodiversity. We examined the impact of pine (Pinus caribaea) plantations, and their management by fire, on the abundance and richness of reptiles, a significant proportion of the native biodiversity in tropical northern Australia, by (i) comparing abundance and diversity of reptiles among pine plantations (on land cleared specifically for plantation establishment), and two adjacent native forest types, eucalypt and Melaleuca woodlands, and (ii) comparing reptile abundance and richness in pine forest burnt one year prior to the study to remove understorey vegetation with pine forest burnt two years prior to the study. We also examined the influence of fire on reptile assemblages in native vegetation, by comparing eucalypt woodland burnt two years prior to the study and unburnt for eight years. To quantify mechanisms driving differences in reptile richness and abundance among forest types and management regimes, we measured forest structure, the temperatures used by reptiles (operative temperature) and solar radiation, at replicate sites in all forest types and management regimes. Compared to native forests, pine forests had taller trees, lower shrub cover in the understorey, more and deeper exotic litter (other than pine), and were cooler and shadier. Reptile assemblages in pine forests were as rich as those in native forests, but pine assemblages were composed mainly of species that typically use closed-canopy rainforest and prefer cooler, shadier habitats. Burning did not appear to influence the assemblage structure of reptiles in native forest, but burning under pine was associated with increased skink abundance and species richness. Burned pine was not warmer or sunnier than unburned pine, a common driver of reptile abundance, so the shift in lizard use after burning may have been driven by structural differences in understorey vegetation, especially amounts of non-native litter, which were reduced by burning. Thus, burning for management under pine increased the abundance and richness of lizard assemblages using pine. Pine plantations do not support the snake diversity common to sclerophyllous native forests, but pine may have the potential to complement rainforest lizard diversity if appropriately managed.     

Replacing coniferous monocultures with mixed-species production stands: An assessment of the potential benefits for forest biodiversity in northern Europe

Conifer dominated plantations in central and northern Europe are associated with relatively low ecological values, and in some cases, may be vulnerable to disturbances caused by anthropogenic climate change. This has prompted the consideration of alternative tree species compositions for use in production forestry in this region. Here we evaluate the likely biodiversity costs and benefits of supplanting Norway spruce (Picea abies) monocultures with polycultures of spruce and birch (Betula spp.) in southern Sweden. This polyculture alternative has previously been evaluated in terms of economic, recreational, and silvicultural benefits. By also assessing the ecological implications we fill a gap in our understanding of the range of socio-ecological benefits that can be achieved from a single polyculture alternative. We project likely broad scale changes to species richness and abundance within production stands for five taxonomic groups including ground vegetation, tree-living bryophytes, lichens, saproxylic beetles, and birds. Our research leads us to three key findings. First, the replacement of spruce monocultures with spruce–birch polycultures in the managed forest landscapes of southern Sweden can be expected to result in an increase in biological diversity for most but not all taxa assessed, but it is unlikely to improve conditions for many red-listed forest species. Second, modification of other aspects of forest management (i.e. rotation length, dead wood and green tree retention, thinning regimes) is likely to contribute to further biodiversity gains using spruce–birch polycultures than spruce monocultures. Third, the paucity of empirical research which directly compares the biodiversity of different types of managed production stands, limits the extent to which policy relevant conclusions can be extracted from the scientific literature. We discuss the wider implications of our findings, which indicate that some climate change adaptation strategies, such as risk-spreading, can be readily integrated with the economic, environmental and social goals of multi-use forestry.     

Relationships between <Emphasis Type="Italic">Artemisia ordosica</Emphasis> communities and environmental factors following sand-dune stabilization in the Mu Us desert,northwest China

Artemisia ordosica is an excellent sand-fixing shrub for sand stabilization in northwestern China. Sand dune stabilization, a critically important process, leads changes in abiotic factors, such as soil structure and nutrient contents. However, the effects of factors on an A. ordosica community following sand stabilization remain unclear. In this study, we used canonical correspondence analysis (CCA) to examine the relationships between A. ordosica communities and environmental factors at three habitats: semi-fixed dune (SF), fixed dune with low-coverage biological soil crust (F), and fixed dune with high-coverage biological soil crust (FC) in Mu Us desert. The mean height and coverage of plants increased with sand stabilization, while species diversity and richness increased initially and then reduced significantly. Correlation analysis and CCA revealed that slope, soil organic carbon, and nutrient contents, proportion of fine soil particles, soil moisture, and thickness of biological soil crust were all highly correlated with vegetation characteristics. These environmental factors could explain 40.42 % of the vegetation–environment relationships at the three habitats. The distribution of plant species was positively related to soil moisture in the SF dune. Soil moisture, soil nutrient, and fine-particle contents mainly affected plants distribution in the F dune. In the FC dune, distribution of plant species was positively and negatively correlated with the thickness of biological soil crust and soil moisture at a depth 0–20 cm, respectively. The dominance value of typical steppe species increased significantly following sand-dune stabilization and relations between species and samples in CCA ordination bi-plots showed that perennial grasses could invade the A. ordosica community on FC, indicating A. ordosica communities had a tendency to change into typical steppe vegetation with the further fixation. We conclude that the significant differentiation not only occurred in community characteristics, but also in the relationships between vegetation and environmental factors among the three stages of dune fixation. So, restoration of degraded dune ecosystems should be based on habitat conditions and ecological needs.     

Managing disturbance regimes to maintain biological diversity in forested ecosystems of the Pacific Northwest

Managing for biodiversity in Pacific Northwest forest ecosystems requires a means to predict the interactive effects of natural, introduced, and altered disturbance regimes. Although disturbances are known to be a determinant of patterns of biological diversity, disturbance and diversity principles have not been consistently applied in management of forest ecosystems in the Pacific Northwest. Here we review disturbance and diversity theory and develop a synthetic conceptual model for use in predicting the effects of disturbances of any origin on biodiversity, focusing on the Pacific Northwest. Disturbance principles have traditionally been applied to understanding patterns of species diversity, but they can also be applied to understanding the broader concept of biodiversity. Our conceptual model integrates these principles, illustrating relationships among mechanisms that limit species diversity and those that enhance it. Diversity-limiting factors are: environmental stress due to high levels of disturbance relative to productivity, and competitive exclusion that can arise where disturbance has been suppressed or managed to favor a particular species’ dominance. Conversely, biological diversity will be enhanced by disturbances that are not too frequent to be stressful, and that create functional heterogeneity (spatial and temporal variation in habitat structure and biological legacies that are vital for post-disturbance reproduction and growth). The three disturbance-related mechanisms that determine diversity operate over local to landscape spatial scales and ecological time scales and thus can be readily influenced by management. By comprehensively evaluating existing disturbance regimes and how they are influencing these factors, managers can help maintain or restore the ecological foundation for biodiversity. We describe management approaches to improve this foundation focusing on forests managed for multiple goals in the Pacific Northwest, where there is considerable potential for and interest in maintaining and enhancing biodiversity.     

藏东南川滇高山栎群落物种多样性格局

通过样方调查,采用物种多样性指数和DCCA排序方法,并结合种间联结、种间协变和系统聚类分析,对藏东南川滇高山栎(Quercus aquifolioides)群落的物种多样性及其分布格局进行了研究。结果表明:1)川滇高山栎群落物种数(丰富度)随海拔增高而降低,一定程度的人为干扰(即中度干扰)、较大的林分郁闭度和较矮的林冠层有利于群落物种多样性的增加;另外干旱河谷现象对群落物种多样性格局也有影响。2)群落各层次间物种多样性呈现出草本层>灌木层>乔木层的特征。3)群落种间较高的正负关联比理论上说明川滇高山栎群落结构较为稳定,生态习性和分布差异造就了种间的联结和协变格局。海拔梯度和年均降水量是影响各种群空间分布的主要因素。4)结合种-环境DCCA排序结果、种间关系和聚类分析结果可将川滇高山栎群落中除川滇高山栎之外的48个主要物种划分为4个生态种组。     

Effects of habitat type, vegetation structure, and proximity to forests on bird species richness in a forest–agricultural landscape of West Java, Indonesia

To halt biodiversity loss in the humid tropics of developing countries, it is crucial to understand the roles and effects of human-modified landscapes with fragmented forest remnants in maintaining biodiversity while fulfilling the demands of local communities and reducing poverty. To implement appropriate landscape planning for conserving biodiversity and ecosystem functioning, appropriate information is required about parameters of habitat suitability among various anthropogenic habitats with a range of distances to forests and vegetation characteristics, but such information is limited. We examined differences in avian communities between a remnant forest and four types of man-made forest (two mature plantations and two agroforests) in a forest–agricultural landscape of West Java, and we analyzed the effects of both local and landscape factors on various types of species richness in this landscape. The results from non-metric multidimensional scaling revealed avifauna in the two types of agroforest was clustered separately from that in the remnant forest, mainly because drastic declines in the abundance of forest specialists (including IUCN red-listed species) and their replacement with open-habitat generalists. The mixed-tree agroforests were colonized by 30 % of forest specialists and forest-edge species found in the remnant forest, and maintained the highest richness of species endemic to Indonesia among man-made forests, implying that some forest specialists and endemics might have adapted to ancient landscape heterogeneity. High proportion of insectivorous birds was found in the remnant forest (more than 50 %) and drastically decline in man-made forests, although the species richness of insectivores did not decline significantly in broad-leaved plantations. We concluded that protection of remnant forests should be prioritized to conserve forest bird diversity. However, as different environmental factors affected the richness values of different ecological groups, appropriate landscape design and habitat management could improve functional diversity in forest–agricultural landscapes in the tropics.     

Changes in forest vegetation and arbuscular mycorrhizae along a steep elevation gradient in Arizona

We assessed species composition, richness and abundance of understory vegetation, as well as arbuscular mycorrhizal (AM) inoculum potential on the San Francisco Peaks, tallest mountains in Arizona, crossing a steep, south-facing elevational gradient. These mountains have a high conservation value due to their rare habitats but previous vegetation studies have been limited. Because mature trees in the Pinaceae do not form associations with AM fungi, there may be more variation in plant community and AM fungal associations in coniferous forest than in ecosystems where all species associate with AM fungi. Differences in species composition between forest types reflected differences in the historical disturbance regimes. Species richness was highest in ponderosa pine forest (32.6 ± 1.4 per 1000 m² plot), although plant abundance was highest in aspen forest (49.4 ± 3.8%). Ponderosa pine and bristlecone pine forest were both high in species richness and contained species which were tolerant of frequent, low-intensity fire. Exotic species richness and abundance were highest in the lower elevations, which were also areas of high species richness and greater anthropogenic disturbance. Arbuscular mycorrhizal inoculum potential varied widely (1.2–80.1%), decreasing with increases in tree cover. We suggest indicator species that may be of use in monitoring these forests under changing climate and fire regimes.     

Edge effects on soil seed banks and understory vegetation in subtropical and tropical forests in Yunnan,SW China

Human-induced forest edges are common in many forest landscapes throughout the world. Forest management requires an understanding of their ecological consequences. This study addressed the responses of three ecological groups (non-forest species, secondary forest species and primary forest species) in edge soil seed banks and edge understory vegetation, and explored the relationship between the invasion of non-forest species in edge understory vegetation and the accumulation of their seeds in edge soil seed banks. The soil seed banks and understory vegetation were sampled along transects established at the edges of a continuous subtropical evergreen broad-leaved forest tract (Lithocarpus xylocarpus forest) bordering anthropogenic grasslands and three tropical seasonal rain forest fragments (Shorea wantianshuea forest) bordering fallows. Species composition in both soil seed banks and understory vegetation showed great difference among edge sites. In soil seed banks, the dominance (relative abundance and relative richness) of each ecological group did not change significantly along the edge to interior gradient. In understory vegetation, the invasion of non-forest species concentrated on the first several meters along the edge to interior gradient. The dominance of secondary forest species decreased with distance from the edge, while the dominance of primary forest species increased with distance from the edge. In forest edge zones, the invasion of a majority of non-forest species in understory vegetation lags behind the accumulation of their seeds in soil seed banks. Forest edges do not act as a good barrier for the penetration of non-forest species seeds. The lack of non-forest species in understory vegetation must then be due to conditions that are not appropriate for their establishment. Therefore, to prevent germination and survival of non-forest species further into the forest, management should focus on maintaining interior forest conditions.     

Avian assemblages in eucalypt forests,plantations and pastures in northern NSW,Australia

Eucalypt plantations are expanding rapidly in Australia, and their value for native fauna requires investigation. The relative conservation value of young eucalypt plantations was investigated through assessment of avifauna richness, abundance and composition using transect surveys incorporating point counts in five broad habitat types—dryland forests, riparian forests, dryland plantations, riparian plantations, and riparian pastures (strips of riparian vegetation surrounded by pastures). A total of 73 species were recorded during formal surveys. Species richness and abundance were comparable among all habitat types except dryland plantations, which supported fewer species and in lower numbers. The avifauna assemblage differed according to broad habitat types. Forest habitats (dryland and riparian) harboured more forest- and woodland-dependent species, and a greater abundance of nectarivores and insectivores. Riparian plantations supported a similar number of forest- and woodland-dependent species to forest habitats, but also retained some open-country species. Riparian pastures had the highest cumulative species richness, reflecting a diverse mix of forest- and woodland-dependent birds and open-country species. It was the preferred habitat type for granivores and vertebrate eaters. Dryland plantations were dominated by common species and omnivores, and supported fewer forest- and woodland-dependent birds, insectivores and frugivores compared with other habitat types. The presence of riparian strips increased avifauna diversity and abundance in plantations and pastures to a greater extent than predicted by the proportional area of riparian habitat. The importance of riparian habitats needs to be recognised and incorporated into management policies if biodiversity conservation is to be an objective of plantation establishment.     

Strategic studies on the biodiversity sustainability in Yunnan Province, Southwest China

With an area of 394,000 km2 (4.1% of China's total area) and specific diversified geographical environments, Yunnan houses over 18,000 species of higher plants (51.6% of China's total), 1,836 vertebrate species (54.8% of China's total) and multitu-dinous species of rare, endemic and epibiotic wildlife, ranking first in species richness value and endemicity rate of China's biodiver-sity, thus becoming a rare gene bank of wildlife species with the most concentrated distribution of important wildlife taxa and a key terrestrial biodiversity region of global significance. Despite its evident abundance and endemism, however, the biodiversity is faced with threats of ecological fragility and human disturbances in socioeconomic development resulting in attenuation of biodiversity, degradation of ecosystems and serious loss of species, thus, it needs to be carefully studied for its sustainability. Based on the analy-ses of the geographical diversity, the macro material bases of Yunnan's biodiversity were reviewed and six characteristics of the pro-vincial biodiversity were described in the ecosystems, forest types, species compositions, endemic species, genetic resources, etc. By appraising the present status of the provincial biodiversity conservation, the facts that the biodiversity coexisted with fragility were revealed so that eight key disadvantageous factors in the provincial ecological fragility causing serious biodiversity loss were sum-marized and described in this paper. In order to satisfy the two-fold needs of biodiversity sustainability and socioeconomic develop-ment, eight strategies for the sustainable development were intensively elaborated by borrowing certain theories in modern conserva-tion biology, recycling economics and some successful innovations, and by giving comprehensive consideration to the ecological fragility mechanism, nature reserve construction, environmental protection and the exploitability of resources for biodiversity sus-tainability and socioeconomic development. Accordingly, relevant targets, principles, tactics and measures for effective biodiversity conservation and sustainability were suggested to lay a solid theoretical foundation and reliable scientific basis for the biodiversity and socioeconomic sustainable development.     

Structure of aquatic insect communities in tank-bromeliads in a East-Amazonian rainforest in French Guiana

Tank-bromeliads are discrete habitats which contain distinct aquatic communities, and which commonly occur in the neotropics. Because they span a broad range of ecological gradients in terms of habitat structure and amount of resources, researchers study the associations between the biodiversity of communities and these gradients in rainforests, where the very high species richness and densities within other continuous habitats makes it difficult to quantify animal communities. We analysed the diversity of aquatic insect communities in relation to different tank-bromeliad species in a primary rainforest (French Guiana) using artificial intelligence and complex optimization techniques to classify communities and model their determinants. First, the self-organizing map (neural network) was used to classify 158 bromeliads according to the quantitative structure of the insect communities. Catopsis berteroniana and Guzmania lingulata formed separate clusters of plants on the virtual map, while Vriesea splendens, Vriesea pleiosticha and Aechmea melinonii were grouped together in the remaining clusters. Some insect taxa occurred in all bromeliads, while other taxa were specific to a given species. Second, general linear modelling allowed us to specify the influence of the bromeliad species; water volume and volume of fine particulate organic matter inside of the tank; elevation above the ground; and sampling site on taxonomic richness and insect abundance. The number of taxa and individuals per plant increased with greater water volume, but the slope of the relationships depended on the bromeliad species. The significant influence of bromeliad species suggested that at similar water volumes different plant species had different taxon richness and insect abundance. Greater amounts of fine particulate organic matter were detrimental to community diversity in the tanks, probably because they decreased available space by clogging it and/or affected oxygen concentrations. The influence of tank-bromeliad species on the aquatic insect community was primarily related to their physical (and probably chemical) features rather than to species-specific associations sensu stricto. The classification of bromeliads with respect to animal species is likely to provide referential schemes for those biodiversity patterns to be expected under certain conditions, and may help to target model communities for subsequent experimental research.     

天然气管道工程对云南乌蒙山国家级自然保护区生物多样性的影响评价

为准确评价天然气输送管道工程建设对乌蒙山国家级自然保护区生物多样性造成的影响程度及其可控性,全面调查评价区域的生物多样性现状。文中重点阐述了建设项目对评价区景观(生态系统)、生物群落(栖息地)、物种(种群)、主要保护对象和生物安全的影响评价。评价结果认为,拟建的天然气输送管道项目对保护区生物多样性的影响程度为"较小影响",并针对项目建设实际提出进一步优化施工方案,加强对施工人员的生物多样性保护意识培训,聘请生态监理,施工结束后恢复当地原有森林植被等建议。     

Mangrove community recovery potential after catastrophic disturbances in Bangladesh

The objective of this study was to compare the variation in the soil seed banks and the aboveground vegetation in relation to three habitats, i.e., swamp forests, grassland and sand dunes within the Sundarbans mangrove forests of Bangladesh. We collected vegetation data (species and their percentage cover) by using quadrat sampling: 10 m × 10 m for swamp forests and 5 m × 5 m for grassland and sand dunes. We estimated the density of viable seeds of species in the seed bank by counting germinants from soil cores in a germination chamber. Species richness and composition of both aboveground vegetation and the soil seed banks differed significantly among habitats. We identified a total of 23 species from the soil seed bank. Of these, two were true mangrove species and the remaining were non-mangrove species, including halophytic grasses, herbs and mangrove associate species. Our results confirm that mangrove species do not possess a persistent soil seed bank. The presence of high-density non-mangrove and associated mangrove species in the soil seed bank implies that after frequent catastrophic disturbances which limit incoming propagules from adjacent forest stand, large canopy gaps can easily become invaded by non-mangrove and mangrove associate species. This would result in the formation of a cover of non-mangrove species and cryptic ecological degradation in mangrove habitats. We suggest that forest managers should actively consider gap plantations with mangrove species in the large canopy gaps created after catastrophic disturbances to counteract the invasion of non-mangrove species and cryptic ecological degradation.     

埃塞俄比亚东南部Dello Menna森林植被的植物区系和结构分析(英文)

描述了埃塞俄比亚东南部Dello Menna森林植被的植物区系组成和植被结构。鉴定和描述了50个20m×20m的样方的植物群落类型、物种多样性、丰富度和均匀性,分析了已鉴定植物群落类型与环境因子的相关性,还描述了木本植物种群结构。每个样方内,均记录木本植物的物种、丰富度、高度和胸径以及海拔、坡度。利用PC-ORD软件对植被进行分类。用Sorensen相似性系数探测群落之间的差异性。计算Shannon-Wiener多样性指数、物种丰富度、Shannon均匀性来描述各种植物群落的物种多样性。共记录了53个科的171个维管植物种。豆科植物是主要的优势植物科系,包括13个属26种(1 5%),其次依次是菊科、唇形科和槭树科,各包括8个物种(4.6%)。根据植物分类结果,识别并描述了3个植物群落(Dalbergia microphylla群落、Grewia bicolar-Acaciabrevispica群落、Combretum molle-Combretum collinum群落)。植物区系之间的物种丰富度、多样性和均匀性存在差异。物种丰富度和多样性随海拔变化呈现出贝尔型分布。群落间植物随海拔梯度有一定的变化,表明海拔是决定植物群落分布的重要因素之一。Dalbergia microphylla群落物种丰富度和多样性均最高。优势种群落结构呈现出各种模型。植被可持续利用是今后的研究方向。