Early recovery signs of an Australian grassland following the management of Parthenium hysterophorus L.

Parthenium weed (Parthenium hysterophorus L.) is believed to reduce the above- and below-ground plant species diversity and the above-ground productivity in several ecosystems. We quantified the impact of this invasive weed upon species diversity in an Australian grassland and assessed the resulting shifts in plant community composition following management using two traditional approaches. A baseline plant community survey, prior to management, showed that the above-ground community was dominated by P. hysterophorus, stoloniferous grasses, with a further high frequency of species from Malvaceae, Chenopodiaceae and Amaranthaceae. In heavily invaded areas, P. hysterophorus abundance and biomass was found to negatively correlate with species diversity and native species abundance. Digitaria didactyla Willd. was present in high abundance when P. hysterophorus was not, with these two species, contributing most to the dissimilarity seen between areas. The application of selective broad leaf weed herbicides significantly reduced P. hysterophorus biomass under ungrazed conditions, but this management did not yet result in an increase in species diversity. In the above-ground community, P. hysterophorus was partly replaced by the introduced grass species Cynodon dactylon L. (Pers.) 1 year after management began, increasing the above-ground forage biomass production, while D. didactyla replaced P. hysterophorus in the below-ground community. This improvement in forage availability continued to strengthen over the time of the study resulting in a total increase of 80% after 2 years in the ungrazed treatment, demonstrating the stress that grazing was imposing upon this grassland-based agro-ecosystem and showing that it is necessary to remove grazing to obtain the best results from the chemical management approach.     

Seedling herbivory and the influence of plant species richness in seedling neighbourhoods

The aim of this experiment was to determine how increasing species richness within artificially created grassland gaps affected the overall magnitude of seedling losses to, and the selectivity of, seedling herbivores. Using chemical exclusion methods, the influence of molluscs the principal invertebrate herbivores in temperate grasslands, was assessed at three levels of plant species diversity (3, 6, and 12 species per gap). In comparison with ungrazed controls, mollusc herbivory significantly reduced seedling numbers. However, the total number of seedlings killed by molluscs was unrelated to the number of seedling species present in the gap. Furthermore, there was no evidence to suggest that seedling species diversity influenced rates of mollusc selection of the three individual species (Agrostis capillaris, Senecio jacobaeae, and Taraxacum officinale) present in each diversity treatment. This work highlights the preferential selection by molluscs of broad-leaved herb species over neighbouring grass seedlings. However the results also suggest that when presented with an increasing choice of different seedling species, the overall magnitude and selectivity of seedling removal by molluscs remains unchanged.     

The effect of mollusc grazing on seedling recruitment in artificially created grassland gaps

Two experiments conducted in spring and autumn 1992 examined the effect of mollusc grazing on seedling regeneration from natural grassland seedbanks by creating artificial gaps in plots in a grassland sward. Molluscs were excluded from half the gaps by application of molluscicide. Mollusc grazing in both the spring and autumn experiment significantly reduced seedling recruitment, though the intensity of grazing was greatest in autumn. Recruitment of five species was markedly influenced by molluscicide application. In spring, plots from which molluscs were excluded contained significantly more seedlings of Chenopodium polyspermum and Ranunculus acris. In the autumn, exclusion of molluscs resulted in increased populations of R. acris, Stellaria graminea and Rumex acetosa. Cerastium holosteoides populations were greatest in autumn grazed plots. Other species, notably the grasses Holcus lanatus and Agrostis capillaris and the legume Trifolium repens were unaffected by molluscicide application. Species diversity was significantly decreased by molluscicide application in the autumn. Gap size significantly affected the recruitment of two species. Ranunculus acris populations were significantly higher in small gaps in both spring and summer, while Chenopodium recruitment in the spring was greater in small gaps. Gap size also significantly influenced the risk of mollusc attack on Ranunculus as molluscs appeared to show an aggregative feeding response in the high seedling density small gaps. Selective grazing of vulnerable seedlings by molluscs may influence the eventual relative proportions of the species present and so provide a potent mechanism in shaping community composition in grasslands.     

Large-scale manipulation of plant litter and fertilizer in a managed successional temperate grassland

Plant litter may play an important role in herbaceous plant communities by limiting primary production and influencing plant species richness. However, it is not known how the effect of litter interacts with fertilization. We tested for the role of litter and fertilization in a large-scale experiment to investigate effects on diversity and biomass of plant species, growth forms, native vs. non-native groups, and abiotic ecosystem components (e.g., soil moisture, PAR). We manipulated plant litter (removed vs. left in situ) and nutrient availability (NPK-fertilized vs. unfertilized) for 4 years in 314-m² plots, replicated six times, in an old-field grassland. While many of our species-level results supported previously published studies and theory, our plant group results generally did not. Specifically, grass species richness and forb biomass was not affected by either fertilization or plant litter. Moreover, plant litter removal significantly increased non-native plant species richness. Relative to native plant species, all of our experimental manipulations significantly increased both the biomass and the species richness of non-native plant species. Thus, this grassland system was sensitive to management treatments through the facilitation of non-native plant species. We coupled biotic and abiotic components within a nonmetric multidimensional scaling (NMS) analysis to investigate treatment effects, which revealed that specific treatments altered ecosystem development. These results suggest that fertilization and plant litter may have larger impacts on plant communities and on ecosystem properties than previously understood, underscoring the need for larger-scale and longer-term experiments.     

Impact of different‐sized herbivores on recruitment opportunities for subordinate herbs in grasslands

Abstract. Potential effects of herbivores on plant species diversity depend on herbivore size, species and density. In this study we examine the effect of different‐sized herbivores (cattle and rabbits) on recruitment of subordinate herbs in grasslands. We show that in a grazed floodplain, grassland plant species richness is mainly determined by the presence of many species of subordinate herbs. These herbs experience high colonization and extinction rates. We conclude that the creation of colonization opportunities for subordinate herbs plays a crucial role in maintaining plant species richness in productive grasslands. We found that cattle disperse large amounts of seeds via their dung, over ten times more than rabbits. Rabbits create more and on average larger bare soil patches than cattle. In a field experiment artificial disturbances improved germination success tremendously for four tested herb species. We found that bare soil is the best regeneration site, while cattle dung gave a too strong nutrient stimulus, resulting in tall vegetation and therefore light limitation. These results can be confirmed with results from field monitoring plots where plant species richness was positively related to the occurrence of bare soil patches. Therefore both large and small herbivores have a major impact on dispersal and colonization, but for different reasons. Cattle are identified as most important for seed dispersal whereas rabbits have a main effect as creators of disturbances. These results emphasize the importance of distinguishing between herbivore species in assessing their (potential) effects.     

Mountain grassland biodiversity: Impact of site conditions versus management type

Grasslands of the Swiss Alps provide agricultural goods, ecological services, disaster protection, and scenic beauty. We identified influences of site conditions and management type on grassland biodiversity, and specifically evaluated the effectiveness of the agri-environmental programme in the Alps. Vascular plants and grasshoppers were mapped in conventionally managed cut meadows, cut meadows of the ecological compensation programme (ECA meadows), and conventionally managed pastures (n=324). We determined climatic and topographic site conditions, quantified the degree of remoteness of all plots in GIS, and estimated the habitat diversity in the vicinity of the sampling sites. The data were analysed by discriminant analysis, rank-correlation analysis, non-parametric ANOVA, general linear models, and ANCOVA. Plant biodiversity hot spots were in economically unattractive, remote sites. These were the typical site conditions of ECA meadows. Hence we concluded that the ecological compensation programme was effectively ensuring management at these sites, and thus protecting mountain grassland plant species richness. Grasshoppers seemed not to benefit from mountain ECA meadows, which were probably often situated at the climatic limit of several species. Pastures were the most species rich management type (plants and grasshoppers), but conversion from cut grassland to pastures should be limited, as negative economic and ecological effects have been reported. We propose that the co-existence of well-managed pastures and long-term ECA meadows might best conserve mountain grassland biodiversity.     

人为干扰对传粉昆虫群落物种多样性及其优势类群生态位的影响

物种多样性是群落功能复杂性和稳定性的重要量度指标,不同干扰强度下物种多样性和生态位特征不同,人为干扰对传粉群落的影响可以通过群落结构和物种多样性的变化直接表现出来。在巩义市选取24个采样点,3种景观类型(农田、灌丛、林地)进行取样,共捕获传粉昆虫18576头,分属于14目,147科,双翅目、膜翅目、鞘翅目、鳞翅目、半翅目与缨翅目6个传粉功能群。为了解研究区人为干扰对传粉昆虫类群传粉类群及其生态位的影响,本研究选取双翅目、膜翅目、鞘翅目3类主要传粉昆虫作为研究对象,在景观类型分类与实际情况的基础上,依据人为干扰指数赋值表和干扰强度计算公式,分析不同干扰强度下传粉昆虫优势种群生态位特征情况,结果表明:各传粉类群在不同的干扰条件下物种多样性不同;作为优势类群的蠓科、胡蜂科,生态位宽度和生态位重叠均均值高于其他几个类群,且中度干扰强度下值最大,但其生态宽度值与生态重叠值之间没有明显的相关关系。     

The influence of environmental factors and management methods on the vegetation of mesic grasslands in a central European mountain range

We examined how environmental factors combined with the diverse ways of the extensive management of mesic mountain grasslands affect species composition and diversity in the Polish part of Central Sudetes Mts. Based on the data from 100 research plots altitude, organic matter content and exchangeable magnesium in the soil, as well as the maximum soil water capacity and amount of sand fraction significantly affected species composition. Among the management methods, a significant effect on the differentiation of species composition was observed following the cessation of usage and mowing. Mown meadows had the highest share of forbs in the biomass, whereas those abandoned ones were dominated by tall and expansive grasses, mainly Calamagrostis epigejos. The species richest grasslands occurred in areas with soils of high water capacity, containing high concentrations of calcium and low amounts of total nitrogen. No significant effect of management methods on the total number of species as well as on the number of forb species was observed. Mown pastures had the highest mean value of the Shannon–Wiener diversity index.     

Interactive community responses to disturbance in streams: disturbance history moderates the influence of disturbance types

Both disturbance history and disturbance type act to structure communities through selecting for particular species traits but they may also interact. For example, flooding selects for species with flood‐resistant traits in streams, but those traits could make communities susceptible to other disturbances and so could cause shifts in community composition due to anthropogenic climate change. To better understand the interactive influences of disturbance history and type on community composition, we investigated the response of macroinvertebrate communities to disturbance using in‐stream channels. Using a split‐plot design, individual channels in five ‘stable’ streams and five ‘frequently disturbed’ streams (disturbance history) were subject to different disturbance type treatments (flooding, drying and a control). Disturbance type independently drove effects on species diversity, but all other effects of disturbance type depended on disturbance history. In particular, the interaction of disturbance type and history determined overall community response. Both disturbance types tested produced similar community responses in frequently disturbed streams, including changes in community composition and alterations to the abundance of less mobile taxa, but low‐flow had a significantly greater effect in stable streams. Macroinvertebrate drift was greatest in the rock‐rolling treatments and significantly less in the low‐flow treatment for both disturbance histories. Therefore, disturbance history moderated the effects of disturbance type and determined the mechanism of community response by determining how well species were adapted to disturbance. This outcome suggests that previous disturbances strongly influence how vulnerable communities are to changes in disturbance, and so should be considered when predicting how changes in disturbance regimes will affect future community composition.     

Species properties and recovery from disturbance: Forest herbs buried by volcanic tephra

Question: How do forest herb species differ from each other in their spatial and temporal dynamics during recovery from volcanic disturbance, and how are dynamics related to species traits? Location: Northeast of Mount St. Helens, Washington, USA. Methods: Following deposition of volcanic tephra in 1980, we measured herb density and cover in permanent 1‐m² plots during 1980‐2005 in three old‐growth forests with differing tephra depths. For 26 species, we calculated the frequency of plots with residuals (individuals that survived the eruption) versus re‐establishment on the tephra, timing of establishment, turnover, influence of nearby conspecific plants, importance of three components of cover increase, and relationship of flowering frequency to succession. Results: Tephra depth affected species behavior. Deep tephra produced fewer residuals, a greater increase in shoot size, and more shoot turnover; favored species that established late; and allowed establishment of early seral herbs. Nearby presence of conspecifics increased permanence of first establishment and rate of plot occupancy. Most species spread significantly in deep tephra but not in shallow tephra. Among species, frequency of flowering increased with fewer residuals, later establishment, and higher turnover. Species behavior seldom differed among growth forms based on leaf longevity and vegetative spread. Conclusion: Population dynamics at the small‐plot scale differed from those of the entire population. The timing and permanency of establishment and mechanism of expansion differed among species and with tephra depth. There was some consistency among species with similar habitat breadth and degree of flowering, but little consistency associated with the usual growth form classification.     

Plant species diversity in cape fynbos: Gamma and delta diversity

Summary This paper reports the number of plant species on circumscribed fynbos areas (gamma diversity), ranging in size from 0.27 km² (a site with 364 species) to 471 km² (2351 species). The composition of the floras of four of these sites was analysed to measure delta diversity, the change in flora from one site to the next. Maximum gamma diversity values fitted a species-area curve log S=2.69+0.25 log A. Gamma diversity is apparently higher than in any of the world's biogeographic zones except perhaps the tropical rain forest, and in other South African sites of areas around 1.0 km², which have about as many species. High delta diversities are reflected in differences between fynbos floras of 50 to 70 %, in spite of relative proximity; this degree of diversity is apparently unmatched anywhere. The results support the conventional view that fynbos plant diversity is partly a consequence of the peculiar geography of the zone, and of palaeo-climatic change, which have favoured geographic speciation.This paper would not have been possible without the conscientious work of staff at Jonkershoek, especially that of R.A. Haynes and E.F. Kruger. The information on the floras of each area studied here has been built up through decades of field work by various collectors. Identifications of the many difficult taxa are due to taxonomists at the National Herbarium, at the Compton Herbarium, Kirstenbosch and at the Bolus Herbarium, University of Cape Town. M. F. Thompson and E. E. Esterhuysen contributed materially in this respect.Paper presented at the Annual Congress of the South African Association of Botanists, Stellenbosch, January 1979.This work is based partly on the results of the conservation research programme of the South African Department of Forestry and the Botanical Research Institute's programme on fynbos phytosociology, and is published with permission of our respective heads of Departments.     

The shape of things to come: woodland herb niche contraction begins during recruitment in mesic forest microhabitat

Natural abundance is shaped by the abiotic requirements and biotic interactions that shape a species' niche, yet these influences are rarely decoupled. Moreover, most plant mortality occurs during early life stages, making seed recruitment critical in structuring plant populations. We find that natural abundance of two woodland herbs, Hexastylis arifolia and Hepatica nobilis, peaks at intermediate resource levels, a pattern probably formed by concurrent abiotic and biotic interactions. To determine how this abundance patterning reflects intrinsic physiological optima and extrinsic biotic interactions, we translocate adults and seeds to novel locations across experimentally extended abiotic gradients. These experiments indicate that the plant distributions probably reflect biotic interactions as much as physiological requirements, and that adult abundance provides a poor indication of the underlying niche requirements. The positive response exhibited by adult transplants in the wettest conditions is offset by increased fungal attack on buried seeds consistent with peak natural abundance where soil moisture is intermediate. This contraction of niche space is best described by Connell's model--species are limited by physiological tolerances where resources are low and biotic interactions where resources are high.     

Modeling the effects of grassland management intensity on biodiversity

A growing food demand and advanced agricultural techniques increasingly affect farmland ecosystems, threatening invertebrate populations with cascading effects along the food chain upon insectivorous vertebrates. Supporting farmland biodiversity thus optimally requires the delineation of species hotspots at multiple trophic levels to prioritize conservation management. The goal of this study was to investigate the links between grassland management intensity and orthopteran density at the field scale and to upscale this information to the landscape in order to guide management action at landscape scale. More specifically, we investigated the relationships between grassland management intensity, floral indicator species, and orthopteran abundance in grasslands with different land use in the SW Swiss Alps. Field vegetation surveys of indicator plant species were used to generate a management intensity proxy, to which field assessments of orthopterans were related. Orthopteran abundance showed a hump‐shaped response to management intensity, with low values in intensified, nutrient‐rich grasslands and in nutrient‐poor, xeric grasslands, while it peaked in middle‐intensity grasslands. Combined with remote‐sensed data about grassland gross primary productivity, the above proxy was used to build landscape‐wide, spatially explicit projections of the potential distribution of orthopteran‐rich grasslands as possible foraging grounds for insectivorous vertebrates. This spatially explicit multitrophic approach enables the delineation of focal farmland areas in order to prioritize conservation action.     

On the relationship between plant species diversity and genetic diversity of Plantago lanceolata (Plantaginaceae) within and between grassland communities

Aims and Methods The relationship between genetic diversity and species diversity and the underlying mechanisms are of both fundamental and applied interest. We used amplified fragment length polymorphism (AFLP) and vegetation records to investigate the association between genetic diversity of Plantago lanceolata and plant species diversity using 15 grassland communities in central Germany. We used correlation and partial correlation analyses to examine whether relationships between genetic and species diversity were direct or mediated by environmental differences between habitats.Important findings Both within- and between-population genetic diversity of P. lanceolata were significantly positively correlated with plant species diversity within and between sites. Simple and partial correlations revealed that the positive correlations indirectly resulted from the effects of abiotic habitat characteristics on plant species diversity and, via abundance, on genetic diversity of P. lanceolata. Thus, they did not reflect a direct causal relationship between plant species diversity and genetic diversity of P. lanceolata, as would have been expected based on the hypothesis of a positive relationship between plant species diversity and niche diversity.     

Impact of flooding on potential and realised grassland species richness

In order to reduce flood risk, river management policies advise floodplain restoration and the recreation of water retention areas. These measures may also offer opportunities for the restoration of species-rich floodplain habitats through rewetting and the restoration of flood dynamics. The potential to enhance biodiversity in such flood restoration areas is, however, still subject to debate. In this paper we investigate whether flooding along a small altered lowland river can contribute to the potential and realised species richness of semi-natural meadows. We compare the seed bank and vegetation composition of flooded and non-flooded semi-natural meadows and test the hypothesis that flooding contributes to an input of diaspores into the meadow seed banks, thereby promoting seed density and potential species richness. Furthermore we hypothesise that, where habitat conditions are suitable, flooding leads to a higher realised species richness. Results showed that seed densities in flooded meadows were significantly higher than in non-flooded meadows. The seed banks of flooded meadows also contained a higher proportion of exclusively hydrochorous species. However, the seed bank species richness, as well as the species richness realised in the vegetation did not differ significantly between flooded and non-flooded meadows. Finally, the seed bank and standing vegetation of flooded sites showed larger differences in species composition and Ellenberg nitrogen distribution than non-flooded sites. From these results we conclude that, although flooding does contribute to the density and composition of the seed bank, most imported seeds belong to only a few species. Therefore, it is unlikely that flooding substantially enhances the potential species richness. Furthermore, even if new species are imported as seeds into the seed bank, it seems unlikely that they would be able to establish in the standing vegetation. However, it is unclear which factors impede the establishment of imported species in the vegetation. The implications of our findings for flood meadow restoration are discussed.     

Seed germination and seedling performance of two Mediterranean tree species,holm oak (shape Quercus ilex L.) and Aleppo pine (shape Pinus halepensis Mill.): a multifactor experimental approach

A two-level multifactor experimental approach was used to compare seed germination and seedling performance of two Mediterranean tree species: the early successional Aleppo pine (Pinus halepensis Mill.) and the late successional holm oak (Quercus ilex L.). In a first experiment germination rate was evaluated under the combined effects of shade, nitrogen availability, and pine or holm oak leaf litter. In a second experiment we tested for the effects of shade, nutrient availability, and litter type on seedling survival, growth and biomass allocation. Holm oak showed higher germination rates under shaded than under unshaded conditions, while Aleppo pine showed no differences between shaded and unshaded conditions. Nitrogen availability and litter type had no significant effect on germination of either species. Both species showed increased RGR, but also higher mortality rates, when grown in an enriched nutrient environment. While Aleppo pine showed no differences in RGR and mortality rate under different shading levels, RGR decreased and mortality increased for holm oak in full light. Increased radiation decreased LAR, SLA and height:diameter ratio, and increased RWR and R/S in both species, although Aleppo pine showed more pronounced changes. Unlike Aleppo pine, holm oak responded to increased nutrient availability by decreasing R/S and increasing LAR. From these results, no seed-seedling conflicts were found in either species, but a trade-off does seem to exist for holm oak between biomass allocation traits deployed in response to increased nutrient availability and radiation. Aleppo pine outperformed holm oak under most environmental conditions tested and showed a wider regeneration niche.     

Population structure and succession in temperate forests of southwestern Japan

In the temperate forests of southwestern Japan, the population density of woody plants in the community increases in the early stage of secondary succession, reaches a peak in the old oak-chestnut forest, and decreases towards the climax beech forest. The species richness and diversity of woody plants also show a trend similar to that of the population density. The canopy-tree population decreases in the course of the succession while the basal area increases, showing a self-thinning process. The species richness, diversity and population density of herbaceous plants are much influenced by the dominance of the bamboo, Sasa palmata. The life-history traits of trees, lower trees and shrubs are discussed in relation to their shoot system, reproductive pattern and successional processes.