安太堡矿区复垦地植被恢复过程多样性变化

植被生态系统的重建是矿区复垦地恢复的主要环节之一。通过群落调查和实验分析,采用丰富度指数、物种多样性指数和均匀度指数,结合DCCA排序、多元线性回归和相关分析,研究了平朔安太堡矿区复垦地植被恢复过程中多样性的变化。群落多样性分析结果表明:(1)直接种植植被演替后期的植物种大大加速了原始植被演替进程;(2 )多样的人工配置群落比单一的人工配置群落更能促进群落向正向演替的方向发展;(3)能够适应矿区特殊生境的植被配置方式在恢复进程中与自然植被表现出一定的差异,这种差异只持续发生植被恢复的前3a,3a之后群落的演替与自然植被的演替表现出趋同性;(4)森林群落是较灌丛群落更适合安太堡矿区特殊生境的植被配置方式,其中刺槐和油松的混交效果较好。物种多样性的分析表明:(1)多样性偏高的群落与有机质和时间联系较为紧密,而多样性偏低的群落则与锰的联系较为紧密;(2 )制约矿区物种多样性变化的主要因素是土壤水分和演替时间;(3)锌对各多样性指数都有一定的影响(4)有机质、时间与丰富度指数相关显著;(5 )海拔与综合多样性指数相关显著;(6 )铜对均匀度指数的影响较大。方法的比较结果表明:(1)多元线性回归的灵敏度比相关分析高;(2 ) DCCA可以作为对定量分析的补充,解释那些在定量分析中不显著的因     

Understory Vegetation Dynamics of North American Boreal Forests

Understory vegetation is the most diverse and least understood component of North American boreal forests. Understory communities are important as they act as drivers of overstory succession and nutrient cycling. The objective of this review was to examine how understory vegetation abundance, composition, and diversity change with stand development after a major stand replacing disturbance. Understory vegetation abundance and diversity increase rapidly after fire, in response to abundant resources and an influx of disturbance adapted species. The highest diversity occurs within the first 40 years following fire, and declines indefinitely thereafter as a result of decreasing productivity and increased dominance of a small number of late successional feather mosses and woody plant species. Vascular plant and bryophyte/lichen communities undergo very different successional changes. Vascular plant communities are dynamic and change more dramatically with time after fire, whereas bryophyte and lichen communities are much slower to establish and change over time. Considerable variations in these processes exist depending on canopy composition, site condition, regional climate, and frequently occurring non-stand-replacing disturbances. Forest management practices represent a unique disturbance process and can result in different understory vegetation communities from those observed for natural processes, with potential implications for overstory succession and long-term productivity. Because of the importance of understory vegetation on nutrient cycling and overstory composition, post-harvest treatments emulating stand-replacing fire are required to maintain understory diversity, composition, and promote stand productivity in boreal forests.     

Intraspecific variation in plant size,secondary plant compounds,herbivory and parasitoid assemblages during secondary succession

During secondary succession on abandoned agricultural fields the diversity and abundance of insect communities often increases, whereas the performance and nutritional quality of early successional plants often declines. As the diversity and abundance of insects on a single plant are determined by characteristics of the environment as well as of the host plant, it is difficult to predict how insects associated with a single plant species will change during succession. We examined how plant characteristics of the early successional plant species ragwort (Jacobaea vulgaris), and the herbivores and parasitoids associated with these plants change during secondary succession. In ten grasslands that differed in time since abandonment (3–26 years), we measured the size and primary and secondary chemistry of individual ragwort plants. For each plant we also recorded the presence of herbivores in flowers, leaves and stems, and reared parasitoids from these plant parts. Ragwort plants were significantly larger but had lower nitrogen concentrations in recently abandoned sites than in older sites. Pyrrolizidine alkaloid (PA) composition varied among plants within sites but also differed significantly among sites. However, there was no relationship between the age of a site and PA composition. Even though plant size decreased with time since abandonment, the abundance of stem-boring insects and parasitoids emerging from stems significantly increased with site age. The proportion of plants with flower and leaf herbivory and the number of parasitoids emerging from flowers and leaves was not related to site age. Parasitoid diversity significantly increased with site age. The results of our study show that ragwort and insect characteristics both change during secondary succession, but that insect herbivore and parasitoid abundances are not directly related to plant size or nutritional quality.     

Plant species diversity, plant biomass and responses of the soil community on abandoned land across Europe: idiosyncracy or above-belowground time lags

We examined the relationship between plant species diversity, productivity and the development of the soil community during early secondary succession on former arable land across Europe. We tested the hypothesis that increasing the initial plant species diversity enhances the biomass production and consequently stimulates soil microbial biomass and abundance of soil invertebrates. We performed five identical field experiments on abandoned arable land in five European countries (CZ, NL, SE, SP and UK) which allowed us to test our hypothesis in a range of climate, soil and other environmental factors that varied between the experimental sites. The initial plant diversity was altered by sowing seed mixtures of mid-successional grassland species with two or five grass species, one or five legumes and one or five forbs. The results of low and high sown diversity treatments were compared with plots that were naturally colonized by species present in the seed bank. In three out of the five field sites, there was no correlation between plant species number and plant biomass production, one site had a positive and the other a negative relation. Treatments with a high diversity seed mixture had a higher biomass than the naturally colonized plots. However, there was no significant difference between high and low sown diversity plots at four out of five sites. The three-year study did not give any evidence of a general bottom-up effect from increased plant biomass on biomass of bacteria, saprophytic fungi or abundance of microarthropods. The biomass of arbuscular mycorrhizal was negatively related to plant biomass. The abundance of nematodes increased after abandonment and was related to plant biomass at four sites. Our results support the hypothesis that plant species diversity may have idiosyncratic effects on soil communities, even though studies on a longer term could reveal time lags in the response to changes in composition and biomass production of plant communities.     

Long‐term regeneration of a tropical plant community after sand mining

Sandy coastal plant communities in tropical regions have been historically under strong anthropic pressure. In Brazil, these systems shelter communities with highly plastic plant species. However, the potential of these systems to regenerate without human assistance after disturbances has hardly been examined. We determined the natural regeneration of a coastal sandy plain vegetation (restinga) in Brazil, 16 years after the end of sand removal. We inventoried 38 plots: 20 within a sand‐mined site and 18 in an adjacent undisturbed site. We expected lower diversity values in the sand‐mined site compared to the undisturbed site, but similar species composition between the two sites due to the spatial proximity of the two sites and the high plasticity of restinga species. Species were ranked using abundance and importance value index in both sites, and comparisons were performed using Rényi entropy profiles, rarefaction curves, principal component analysis, and redundancy analysis. Species composition and dominant species differed markedly between the two sites. Bromeliads and Clusia hilariana, well‐known nurse plants, dominated the undisturbed site but were almost absent in the regenerating site. Species richness did not differ between both sites, but diversity was higher in the undisturbed site. Within‐site composition differences in the mined area were associated with field characteristics. Interestingly, species classified as subordinate or rare in the undisturbed site became dominants in the regenerating site. These newer dominants in the sand‐mined site are not those known as nurse plants in other restingas, thus yielding strong implications for restoration.     

Aspen (<Emphasis Type="Italic">Populus tremuloides</Emphasis>) stands and their contribution to plant diversity in a semiarid coniferous landscape

We conducted a field study to determine the relative contributions of aspen (Populus tremuloides), meadow, and conifer communities to local and landscape-level plant species diversity in the Sierra Nevada and southern Cascade Range, northeastern California, USA. We surveyed plant assemblages at 30 sites that included adjacent aspen, conifer, and meadow communities across a 10,000-km² region. We statistically investigated patterns in local and landscape-scale plant diversity within and among the three vegetation types. Summing across sites, aspen stands supported more plant species overall and more unique plant species than either meadow or conifer communities. Local richness and diversity did not differ between aspen and meadow plots; conifer forest plots were significantly lower in both measures. Heterogeneity in species composition was higher for aspen forest than for meadows or conifer forest, both within sites and between sites. Plant communities in aspen stands shared less than 25% of their species with adjacent vegetation in conifer and meadow plots. Within aspen forest, we found a negative relationship between total canopy cover and plant diversity. Our results strongly support the idea that plant communities of aspen stands are compositionally distinct from adjacent meadows and conifer forest, and that aspen forests are a major contributor to plant species diversity in the study region. Current patterns of aspen stand succession to conifer forest on many sites in the semiarid western US are likely to reduce local and landscape-level plant species diversity, and may also have negative effects on other ecosystem functions and services provided by aspen forest.     

Plant community response to loss of large herbivores: comparing consequences in a South African and a North American grassland

Loss of biodiversity poses one of the greatest threats to natural ecosystems throughout the world. However, a comprehensive understanding of the impacts of species losses from upper trophic levels is still emerging. Here we compare the impacts of large mammalian herbivore species loss on grassland plant community structure and composition in a South African and North American grassland. Herbaceous plant communities were surveyed at sites without large mammalian herbivores present and at sites with a single species of herbivore present in both locations, and additionally at one site in South Africa with multiple herbivore species. At both the North American and South African locations, plant communities on sites with a single herbivore species were more diverse and species rich than on sites with no herbivores. At the multi-herbivore site in South Africa, plant diversity and richness were comparable to that of the single herbivore site early in the growing season and to the no herbivore site late in the growing season. Analyses of plant community composition, however, indicated strong differences between the multi-herbivore site and the single and no herbivore sites, which were more similar to each other. In moderate to high-productivity ecosystems with one or a few species of large herbivores, loss of herbivores can cause a significant decrease in plant diversity and richness, and can have pronounced impacts on grassland plant community composition. In ecosystems with higher herbivore richness, species loss may also significantly alter plant community structure and composition, although standard metrics of community structure may obscure these differences.     

Plants and insects in early old-field succession: comparison of an English site and an American site

The plant and insect communities of early, secondary succession beginning with bare ground in an Old World site (southern Britain) and a New World site (Iowa, U.S.A.) shared a number of characteristics. Both sites showed similar temporal patterns of plant species cover and species richness, although overall richness was greater at the Old World site. Annuals dominated at both sites during the first year of succession and were largely replaced by perennials in the second year. Monocotyledons were more abundant at the Old World site, especially in the second year. The two sites differed markedly in the contribution of native and introduced plant species, with the Old World site dominated by natives and the New World site by alien plant species. Insect herbivore load was greater at the Old World site, when expressed in terms of structural complexity of the vegetation, suggesting that there may be major differences in the influence of herbivores on the direction and rate of succession at the two sites.     

Plant species diversity and composition of wetlands within an upland forest

Though often overlooked, small wetlands in an upland matrix can support diverse plant communities that increase both local and regional species richness. Here we characterize the full range of wetland vegetation within an upland forest landscape and compare the diversity and composition of different wetland plant communities. In an old-growth forest reserve in southern Quebec, Canada, we sampled wet habitats including lakeshores, permanent and seasonal ponds, swamps, glades, and streamsides. We used clustering, indicator species analysis, and nonmetric multidimensional scaling ordination to identify and compare vegetation types. The wetlands contained 280 species of vascular plants, 45% of the reserve's flora, in only 1.1% of its area. Local diversity averaged 24 ± 0.7 species per 7 m(2), much higher than in the surrounding upland forests. Plant communities sorted into five types, whose strongest indicator species were Osmunda regalis, Glyceria striata, O. cinnamomea, Deparia acrostichoides, and Matteuccia struthiopteris, respectively. Both local species richness and compositional variation among sites differed among the vegetation types. By combining species representative of the region's major wetlands with species from the upland forest matrix, the plant assemblages of these wetlands make disproportionately important contributions to landscape-level diversity.     

Responses to fertility and disturbance in a low-diversity grassland

We examined variation in species composition in a low-diversity, anthropogenic grassland in response to 11 years of nitrogen (N) manipulation and disturbance. The species-poor grassland (2–3 species/0.5 m²) represents a wide spread vegetation type (>10 million ha in North America) dominated by the introduced perennial grasses Bromus inermis and Agropyron cristatum. Four levels of N and three of soil disturbance were applied in all combinations to plots (5 × 15 m, N = 120) in a completely randomized design each year. Seeds or transplants of 47 species were added to ensure that dispersal was not a barrier to changes in species composition. After 11 years of treatment, all but the most disturbed plots continued to be dominated by B. inermis. The cover of the second-most abundant species, A. cristatum, decreased with disturbance but did not vary significantly with N. Despite the lack of changes in the identity of the dominant species, our environmental manipulations strongly influenced ecosystem characteristics. Added N increased soil available N, and decreased the cover of bare ground and light availability. Soil disturbance decreased aboveground biomass, and increased the cover of bare ground and light availability. Sawdust application, designed to decrease N availability, significantly reduced community biomass, and increased light availability and the cover of bare ground, but did not alter nutrient availability or species composition. The results highlight the difficulty of restoring diversity in species-poor, anthropogenic communities dominated by introduced species, and thus the importance of conserving remnants of diverse natural grasslands.     

Feedbacks of plant identity and diversity on the diversity and community composition of rhizosphere microbiomes from a long‐term biodiversity experiment

Soil microbes are known to be key drivers of several essential ecosystem processes such as nutrient cycling, plant productivity and the maintenance of plant species diversity. However, how plant species diversity and identity affect soil microbial diversity and community composition in the rhizosphere is largely unknown. We tested whether, over the course of 11 years, distinct soil bacterial communities developed under plant monocultures and mixtures, and if over this time frame plants with a monoculture or mixture history changed in the bacterial communities they associated with. For eight species, we grew offspring of plants that had been grown for 11 years in the same field monocultures or mixtures (plant history in monoculture vs. mixture) in pots inoculated with microbes extracted from the field monoculture and mixture soils attached to the roots of the host plants (soil legacy). After 5 months of growth in the glasshouse, we collected rhizosphere soil from each plant and used 16S rRNA gene sequencing to determine the community composition and diversity of the bacterial communities. Bacterial community structure in the plant rhizosphere was primarily determined by soil legacy and by plant species identity, but not by plant history. In seven of the eight plant species the number of individual operational taxonomic units with increased abundance was larger when inoculated with microbes from mixture soil. We conclude that plant species richness can affect below‐ground community composition and diversity, feeding back to the assemblage of rhizosphere bacterial communities in newly establishing plants via the legacy in soil.     

Effects of ungulates on epigeal arthropods in Sierra Nevada National Park (southeast Spain)

This paper examines the effect of ungulates on epigeal arthropod communities in two common plant communities of the high mountains of the Sierra Nevada (southeast Spain). We have compared the abundance, biomass, diversity and specific composition of arthropod communities in grazed and ungrazed plots experimentally excluded from ungulates. In general, we found that arthropods were more abundant and diverse in grazed than in ungrazed plots. However, the effect of ungulates depended on the variable considered (diversity versus abundance versus biomass). Moreover, ungulates also affected species composition. This means that without affecting diversity, ungulates can still have a strong effect on arthropod communities by changing species composition. Also, the relationship between ungulates and arthropods differed depending on the year of study and the sampling period. In conclusion, our study indicates that to extrapolate the results obtained for a group of insects, a habitat or a sampling period is not appropriate for the conservation of arthropod communities.     

Vegetation structure,species life span,and exotic status elucidate plant succession in a limestone quarry reclamation

An understanding of the processes involved in plant succession is pivotal in achieving an effective site restoration. In a former limestone quarry (northeastern Italy), we explored the effects of a technical reclamation on the plant community using changes in cover of vegetation layers and two sensitive plant traits (i.e. exotic status and life span), with a chronosequence approach. Four reclaimed areas of different ages (from 8 to 35 years old) and natural vegetation in the surroundings were investigated with seven permanent plots each, for a total of 35. Changes in vegetation layers and species richness of both exotic status and life span were analyzed by generalized linear (mixed) models. Relations with plant community assembly were also considered, using a multivariate approach. Both vegetation layers and plant traits were affected by the age of reclaimed areas, evidencing the main changes in plant succession. Annual and exotic species decreased toward the mature stages of reclamation and target vegetation, whereas overall plant diversity (species richness) was stable. Our findings show that both vegetation layer changes and plant traits can be used to assess the degree to which reclamation efforts produce results that approach the restoration of a natural vegetation reference. Implementation of management practices aimed at favoring native perennial species (e.g. appropriate seed mixtures, mowing, tree, and shrub planting) could limit weed‐control efforts, representing a reasonable trade‐off between biodiversity promotion and invasive plant control.     

Grassland restoration on former croplands in Europe: an assessment of applicability of techniques and costs

Grasslands used to be vital landscape elements throughout Europe. Nowadays, the area of grasslands is dramatically reduced, especially in industrial countries. Grassland restoration is widely applied to increase the naturalness of the landscape and preserve biodiversity. We reviewed the most frequently used restoration techniques (spontaneous succession, sowing seed mixtures, transfer of plant material, topsoil removal and transfer) and techniques used to improve species richness (planting, grazing and mowing) to recover natural-like grasslands from ex-arable lands. We focus on the usefulness of methods in restoring biodiversity, their practical feasibility and costs. We conclude that the success of each technique depends on the site conditions, history, availability of propagules and/or donor sites, and on the budget and time available for restoration. Spontaneous succession can be an option for restoration when no rapid result is expected, and is likely to lead to the target in areas with high availability of propagules. Sowing low-diversity seed mixtures is recommended when we aim at to create basic grassland vegetation in large areas and/or in a short time. The compilation of high-diversity seed mixtures for large sites is rather difficult and expensive; thus, it may be applied rather on smaller areas. We recommend combining the two kinds of seed sowing methods by sowing low-diversity mixtures in a large area and high-diversity mixtures in small blocks to create species-rich source patches for the spontaneous colonization of nearby areas. When proper local hay sources are available, the restoration with plant material transfer can be a fast and effective method for restoration.     

Recovery of native grass biodiversity by sowing on former croplands: Is weed suppression a feasible goal for grassland restoration?

Grassland restoration on former croplands offers good opportunity to mitigate the loss of grassland biodiversity. Weed suppression can be another benefit, which becomes increasingly important because of the high recent rate of abandonment of arable lands in Central and Eastern Europe. Our aim was to evaluate the usefulness of sowing two low-diversity seed mixtures followed by annual mowing, a frequently used restoration technique, in weed suppression. We found that rapidly forming cover of sown grasses effectively suppressed short-lived weeds and their germination except in the first year. The detected dense seed bank of short-lived weeds points out the possibility and threat of later weed infestation. In the short run perennial weeds cannot be suppressed easily by sowing and annual mowing. We found that the effectiveness of seed sowing followed by mowing in weed suppression can be different on sites with different history or seed mixture. Rapidly establishing perennial weeds, such as Agropyron species were only detected in former alfalfa fields; Cirsium arvense was found in former cereal and sunflower fields but not in former alfalfa fields. We found that the rate of weed suppression and success was influenced by the seed mixtures used. In several alkali restorations the high proportion of perennial weeds was detected in year 3. In loess restorations, much lower scores were typical. This was likely caused by the different seed mixture used. The loess seed mixture contained seeds of a clonally spreading tall-grass, Bromus inermis, which could compete more effectively with clonally spreading weeds, than could short grass species with or without tussock forming. Our findings indicate that post-restoration management require carefully designed actions that are fine-tuned addressing specific threats at the site level.     

Biodiversity and invasibility in grassland microcosms

In the years since Charles Elton proposed that more diverse communities should be less susceptible to invasion by exotic species, empirical studies have both supported and refuted Elton's hypothesis. Here, I use grassland community microcosms to test the effect of functional diversity on the success of an invasive annual weed (Centaurea solstitialis L.). I found that high functional diversity reduced the success of Centaurea by reducing resource availability. An equally important, but unstudied, question is whether diversity can buffer a community against the impacts of invasive species. In this experiment, although species diversity (independent of functional diversity) did not affect the success of the invader, the invader suppressed growth of species-poor communities more strongly. Invasion of Centaurea also increased summer evapotranspiration in species-poor communities. These results suggest that loss of species diversity alone does not affect community invasibility, but that communities with fewer species may be more likely to decline as a consequence of invasion.     

Influence of late season fire on early successional vegetation of an Oklahoma prairie

Abstract. The study of vegetation dynamics in tallgrass prairie in response to fire has focused on dormant season fire in late successional prairies. Our objective was to determine if late season fire of varying frequency results in divergent successional patterns in an early successional tallgrass prairie disturbed by grazing and cultivation. Specifically, we evaluated the influence of late‐summer fires of varying frequency on community composition and species richness. We collected vegetation and environmental data on two sites burned in the late growing‐season at varying frequencies. These communities differed in composition depending primarily on edaphic factors, time since the last burn, and year‐to‐year variation. We interpret the time effect as related to changes in species composition accompanying plant succession that followed disturbance either from cropping and heavy grazing on the loamy site or heavy grazing on the shallow site. Other unidentified factors also have a role in vegetation dynamics on this prairie. Community composition and species richness were not consistently responsive to frequency of growing‐season fires.     

Evaluating strategies for facilitating native plant establishment in northern Nevada crested wheatgrass seedings

Non‐native crested wheatgrasses (Agropyron cristatum and A. desertorum) were used historically within the Great Basin for the purpose of competing with weed species and increasing livestock forage. These species continue to be used in some areas, especially after wildfires occurring in low elevation/precipitation, formerly Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis)/herbaceous communities. Seeding native species in these sites is often unsuccessful, and lack of establishment results in invasion and site dominance by exotic annuals. However, crested wheatgrass often forms dense monocultures that interfere competitively with the establishment of desirable native vegetation and do not provide the plant structure and habitat diversity for wildlife species equivalent to native‐dominated sagebrush plant communities. During a 5‐year study, we conducted trials to evaluate chemical and mechanical methods for reducing crested wheatgrass and the effectiveness of seeding native species into these sites after crested wheatgrass suppression. We determined that discing treatments were ineffective in reducing crested wheatgrass cover and even increased crested wheatgrass density in some cases. Glyphosate treatments initially reduced crested wheatgrass cover, but weeds increased in many treated plots and seeded species diminished over time as crested wheatgrass recovered. We concluded that, although increases in native species could possibly be obtained by repeating crested wheatgrass control treatments, reducing crested wheatgrass opens a window for invasion by exotic weed species.     

Phylogenetic and functional structures of succession in plant communities on mounds of Marmota himalayana in alpine regions on the northeast edge of the Qinghai–Tibet Plateau

Few studies have examined the succession of plant communities in the alpine zone. Studying the succession of plant communities is helpful to understand how species diversity is formed and maintained. In this study, we used species inventories, a molecular phylogeny, and trait data to detect patterns of phylogenetic and functional community structure in successional plant communities growing on the mounds of Himalayan marmots (Marmota himalayana) on the southeast edge of the Qinghai-Tibet Plateau. We found that phylogenetic and functional diversities of plant communities on marmot mounds tended to cluster during the early to medium stages of succession, then trended toward overdispersion from medium to late stages. Alpine species in early and late stages of succession were phylogenetically and functionally overdispersed, suggesting that such communities were assembled mainly through species interactions, especially competition. At the medium and late stages of succession, alpine communities growing on marmot mounds were phylogenetically and functionally clustered, implying that the communities were primarily structured by environmental filtering. During the medium and late stages of succession the phylogenetic and functional structures of plant communities on marmot mounds differed significantly from those on neighboring sites. Our results indicate that environmental filtering and species interactions can change plant community composition at different successional stages. Assembly of plant communities on marmot mounds was promoted by a combination of traits that may provide advantages for survival and adaptation during periods of environmental change.     

Site fertility drives temporal turnover of vegetation at high latitudes

Experimental evidence shows that site fertility is a key modulator underlying plant community changes under climate change. Communities on fertile sites, with species having fast dynamics, have been found to react more strongly to climate change than communities on infertile sites with slow dynamics. However, it is still unclear whether this generally applies to high‐latitude plant communities in natural environments at broad spatial scales. We tested a hypothesis that vegetation of fertile sites experiences greater changes over several decades and thus would be more responsive under contemporary climate change compared to infertile sites that are expected to show more resistance. We resurveyed understorey communities (vascular plants, bryophytes, and lichens) of four infertile and four fertile forest sites along a latitudinal bioclimatic gradient. Sites had remained outside direct human disturbance. We analyzed the magnitude of temporal community turnover, changes in the abundances of plant morphological groups and strategy classes, and changes in species diversity. In agreement with our hypothesis, temporal turnover of communities was consistently greater on fertile sites compared to infertile sites. However, our results suggest that the larger turnover of fertile communities is not primarily related to the direct effects of climatic warming. Furthermore, community changes in both fertile and infertile sites showed remarkable variation in terms of shares of plant functional groups and strategy classes and measures of species diversity. This further emphasizes the essential role of baseline environmental conditions and nonclimatic drivers underlying vegetation changes. Our results show that site fertility is a key determinant of the overall rate of high‐latitude vegetation changes but the composition of plant communities in different ecological contexts is variously impacted by nonclimatic drivers over time.