The effect of fire and ants on the seed-bank of a shrub in a semi-arid grassland

Abstract Invasion of grasslands by woody plants following the introduction of domestic stock is a worldwide phenomenon. Burning is frequently recommended as a remedial measure but for a pastoral enterprise it is costly and the frequency of the fires required is of critical economic importance. The size and longevity of the soil seed-bank is an essential part of the response of shrub populations to prescribed fire regimes. In this study the seed-bank of the semi-arid zone shrub Dodonaea attenuata in Eragrostis eriopoda tussock grassland was examined in relation to harvesting by ants and the burning history of the sites. On unburnt sites, more than 3500 seeds per m2 entered the seed-bank in the summer 1984–85 but sites burnt 5 years previously produced less than one-third of that number. Burnt shrubs did not flower for 5 years and no seeds survived in the soil through to 1985. Burning immediately prior to seed ripening destroyed the seed crop but burning after seed-fall stimulated a greater germination in the following spring than on unburnt treatments. Ants rapidly harvested most of the seeds produced and after 20 months the combined effects of ant harvesting and germination had reduced the seed-bank at unburnt sites to 8–21 seeds per m2 and at sites burnt 7 years previously to less than two seeds per m2. Seeds were initially harvested in summer by Pheidole spp. of ants for their elaiosome and then discarded in middens outside the entrance to the ant nest. During the subsequent cool season the seeds were taken back into the nest and stored at depths ranging from 2 to 30cm. It was concluded that ants provided short-range dispersal (< 10 m) and promoted the contagious distribution of D. attenuata, which is advantageous for a fire-susceptible, arid-zone shrub invading a grassland liable to be burnt: seedlings derived from seeds in ant storage chambers near the soil surface and in sparse grass situations caused by competition from shrubs may obtain some survival advantage. Prescribed fire has potential as a management tool for controlling population density of D. attenuata because, depending upon season and frequency, it reduces seed rain by killing shrubs, suppresses flowering activity and destroys seed crops on the plant. Under the influence of a regime of regular burning, such as prevailed prior to the European pastoral industry, the limited soil seed-bank would have been a major constraint on D. attenuata populations.     

Germination traits and seed-bank dynamics of a biennial plant,Oenothera glazioviana Micheli

A study was conducted on the germination traits and seed-bank dynamics ofOenothera glazioviana (=O. erythrosepala), which sets seed in August in sand-dune systems in Japan. More than 90% of freshly matured seeds germinated over a wide range of temperature in light, but less than 10% did so in continuous darkness. Stratification (chilling under moist conditions) was ineffective in diminishing the light-requirement for germination. When fresh seeds were imbibed for 24 h including a 12-h light period, followed by 7-day air-drying, 94% of them became germinable in the dark at 25°C, but remained dormant at less than 15°C. of seeds collected in March from capsules of dead plants, 58% germinated in the dark at 25°C. After four cycles of alternatc 1-day wetting followed by 2-day drying or 1.5-day wetting followed by 1.5-day drying under a 12-h photoperiod, the fraction of viable seeds declined from 76% to 40% and 22%, respectively, due to germination during the wet periods. Seed-bag experiments were conducted in the field, using seeds given and not given a light-stimulus. Forty percent of the light-stimulated seeds germinated in the soil, whereas the seeds without a light-stimulus remained dormant throughout the experiment. When seeds were placed on the soil surface or at a depth of 0.5-1 cm, the proportion of germinable seeds declined during late spring and autumn, but not during winter and early spring. The seed-bank size of a natural population just prior to current seed dispersal was 2–3% of the seed production in the previous year, suggesting a high turnover rate of the seed-bank.     

Effects of winter mowing on vegetation succession in a lakeshore fen

Abstract. To assess whether winter mowing in wetlands fulfils the aim of preventing succession towards drier communities, 34 permanent quadrats (15 m²) were surveyed annually from 1984–1985 to 2000 within large mown and unmown (control) areas (several ha) in a calcareous lake shore fen (W Switzerland). Three trends were noticed: decrease of aquatic species, spread of Cladium mariscus and establishment of woody species (especially Alnus glutinosa and Frangula alnus). None of these trends was prevented by mowing, but mowing did prevent the accumulation of C. mariscus litter and kept woody saplings small. Succession was generally slow and often occurred in the form of sudden, discrete changes. Plant species richness increased with mowing and remained constant without mowing. Soil disturbance by the mowing machine contributed more to the effects of management on species composition than the periodic removal of biomass. It is concluded that mowing every three years in winter is insufficient to preserve semi‐aquatic communities against succession but sufficient to maintain the plant species richness of a low productive, regularly flooded fen.     

Vegetation structure characteristics and relationships of Kalahari woodlands and savannas

The Kalahari Transect is one of several International Geosphere–Biosphere Programme (IGBP) transects designed to address global change questions at the regional scale, in particular by exploiting natural parameter gradients ( Koch et al., 1995 ). In March 2000, we collected near‐synoptic vegetation structural data at five sites spanning the Kalahari's large precipitation gradient (about 300–1000 mm yr^?1) from southern Botswana (～24°S) to Zambia (～15°S). All sites were within the expansive Kalahari sandsheet. Common parameters, including plant area index (PAI), leaf area index (LAI) and canopy cover (CC), were measured or derived using several indirect instruments and at multiple spatial scales. Results show that CC and PAI increase with increasing mean annual precipitation. Canopy clumping, defined by the deviation of the gap size distribution from that of randomly distributed foliage, was fairly constant along the gradient. We provide empirical relationships relating these parameters to each other and to precipitation. These results, combined with those in companion Kalahari Transect studies, provide a unique and coherent test bed for ecological modeling. The data may be used to parameterize process models, as well as test internally predicted parameters and their variability in response to well‐characterized climatological differences.     

Vegetation structure: Fine scale relationships with soil in a cerrado site

There is a lack of understanding on factors influencing the occurrence of high species heterogeneity at fine scale in the Brazilian cerrado. Soil is a major determinant of vegetation in the Brazilian cerrado and an important candidate to influence species distribution at fine scales, since soil features vary at very small distances, whereas many environmental variables are relatively homogeneous at such scale. We tested plant-soil relationships at fine scales in a cerrado site. We placed 100 contiguous 25 m² plots, where we identified all woody individuals and measured several soil features. We did partial redundancy analysis, controlling for spatial autocorrelation, to test for relationships between soil features and floristic composition. We also did multiple regressions or spatial autoregressive models to test for relationships between soil features and: (1) the abundance of the five most common species, (2) total abundance, (3) richness, (4) evenness, and (5) diversity. We found weak relationships between soil and floristic composition, richness, and total abundance, which, coupled with also weak relationship found in another study with plant available water, indicate there is no major environmental variable influencing vegetation at fine scales, but several of them interacting. Organic matter was positively related with the abundance of Myrsine umbellata and was negatively related to evenness. Although a causal relationship cannot be inferred with certainty, the dominance of Myrsine umbellata seems to be related to a positive feedback with soil.     

The effect of water supply on seed-bank analysis using the seedling-emergence method

1. When using the seedling-emergence method to analyse a soil seed bank the greenhouse conditions should match the germination requirements of the species involved. Although the seedling-emergence method is common practice in ecological studies, the germination characteristics of many species are not known, or are only partly known.
2. Before carrying out a large-scale seed-bank study in a wet dune slack, we tested the water requirements of the species in the seed bank, comparing a waterlogged soil with a moist soil. Four species germinated in significantly larger numbers in a waterlogged soil, seven species in a moist soil and 11 species showed no significant difference. When a species was present in low densities, it was often missed using the less appropriate treatment.
3. These results emphasize the need for a preliminary study before carrying out a seed-bank analysis and show the danger of using a 'standard' method to analyse soil samples from different habitats.     

Climate change and lakeshore conservation: a model and review of management techniques

Climate change is expected to cause significant changes to the hydrology of lakes, reservoirs and other wetlands. In particular, there will be an increase in the level of disturbance produced by water-level fluctuations. This may have adverse consequences for biodiversity, water quality and human uses. Strategies to cope with these climate change impacts are currently poorly developed. This article proposes the use of Grime’s CSR theory as a framework to understand the potential impacts of climate change on shoreline vegetation. It is also used to recommend a series of practical management techniques that will contribute to the adaptation capacity of shoreline ecosystems. Four key areas are highlighted: hydrological controls, substrate conditions, shoreline topography and vegetation establishment.     

抚仙湖窑泥沟人工湿地的除磷效果研究

为了减缓和控制抚仙湖局部湖湾水体富营养化趋势,在抚仙湖北岸建设了净化面积1 hm²的人工湿地.综合利用生物氧化塘、水平潜流人工湿地和表面流人工湿地治理技术,对入湖河道窑泥沟污水中磷的去除效果进行了试验研究.结果表明,该人工湿地系统对磷具有较强的去除能力.总磷去除率在57.7%～81.10%之间,平均去除率为54.9%.单位面积磷滞留量平均为26 mg·m^-2·d^-1,其中,湿地植物同化作用磷滞留量为26.1 mg·m^-2·d^-1,约占磷滞留总量的10%,大部分磷去除是通过基质吸附和沉降作用,但主要湿地植物水芹的季节变化对相应功能区的除磷效果会产生一定影响.试验期间,各功能区单位面积磷滞留量依次为水平潜流人工湿地＞生物氧化塘＞沉淀池＞表面流人工湿地.     

Effect of eutrophication on culm architecture of lakeshore Phragmites reeds

The eutrophication of lakes in central Europe has been assumed to be at least partly responsible for a widespread die-back of fringing Phragmites australis reeds. To test the ‘eutrophication hypothesis’ on a broad data basis, lakeshore reed stands at 41 lakes of known trophic status and 10 stands in waste water and sludge treatment plants in Denmark and north Germany (North data subset, n=26), and south Germany, Switzerland and Austria (South data subset, n=25) were investigated. A total of 24 culm performance variables in three different shoot classes were analyzed by two-way ANOVA with the geographic origin and the ‘relative trophic index’ as factors. The geographic origin had a pronounced influence on culm architecture, whereas the effect of the trophic level mostly failed to be significant in the ANOVA. The culms from the North reed stands showed a weaker performance throughout than those from the South stands for a given trophic level. However, some of the morphometric traits in the North stands were significant positively correlated with the trophic level but very few significant cases were observed in the South data subset. Three hypotheses are discussed to explain the geographic effect: climatic effects, geochemistry of lake water and sediments, and trophic history of the lakes. It is concluded that lake eutrophication does not influence the culm performance negatively and that eutrophication cannot be regarded as a general cause in reed decline.     

典型高原湖滨带底泥细菌群落结构及多样性特征

【背景】高原湖泊的富营养化日趋严重,而湖滨带作为湖泊的保护屏障对外源污染物具有拦截净化等作用,水环境变化则会对底泥细菌产生深刻影响。【目的】探究高原湖滨带底泥细菌群落结构特征及与水体富营养化之间的联系。【方法】基于16S rRNA基因高通量测序技术分析了阳宗海南岸湖滨带8个不同样点的底泥细菌群落结构及多样性,并结合样品水体环境因子,采用主成分分析(PCA)和冗余分析(redundancy analysis,RDA)探讨了水体富营养化对底泥细菌群落结构及丰富度的影响。【结果】湖滨带底泥细菌与水体富营养化程度存在响应关系,在水体富营养化程度高的区域(S3)细菌丰富度较高,操作分类单元(operationaltaxonomicunits,OTU)高达1473。反之,在富营养化程度低的区域(S1)细菌丰富度较低,OTU为730。阳宗海南岸湖滨带底泥中主要优势菌门为变形菌门(Proteobacteria)和绿弯菌门(Chloroflexi),含有少量的放线菌门(Actinobacteria)、酸杆菌门(Acidobacteria)和厚壁菌门(Firmicutes);绿弯菌门(Chloroflex...     

Vegetation and environmental heterogeneity relationships in a Neotropical swamp forest in southeastern Brazil (Itirapina, SP)

Patterns in substrate, canopy openness, tree species composition and structure were studied in a swamp forest in southeastern Brazil (Itirapina, SP), using a fine spatial scale (∼0.05 km²). Sixty quadrats of 10 m × 10 m were divided into three sample plots, located in the centre and at both ends of the forest remnant (upstream and downstream), encompassing different environmental conditions. In each quadrat we quantified and identified individuals with CBH (circumference at breast height) ≥ 10 cm, the chemical properties of the soil, the drainage (flooded area) and the percentage of canopy openness. We keep 5124 individuals distributed over 37 species and 25 families. The downstream site presented a lower frequency of flooding, canopy openness, species richness (15 species) and density of individuals. In the central site we found different patterns of drainage and light incidence, the greatest species richness (31 species) and density of individuals, but smaller trees both in height and in diameter. The upstream site was subject to higher frequency of flooding, with intermediate values for density and species richness (27 species). Floristic and structural variation between and within sites reflects the different environmental conditions related to substrate and canopy openness. However, a larger number of species were correlated with drainage pattern (21 species) rather than with canopy openness (14 species), suggesting that the main factor responsible for the spatial organization of the plant community in swamp forests is soil drainage.     

Vegetation:environment relationships and water management in Shark Slough,Everglades National Park

The hydrologic regime of Shark Slough, the most extensive long hydroperiod marsh in Everglades National Park, is largely controlled by the location, volume, and timing of water delivered to it through several control structures from Water Conservation Areas north of the Park. Where natural or anthropogenic barriers to water flow are present, water management practices in this highly regulated system may result in an uneven distribution of water in the marsh, which may impact regional vegetation patterns. In this paper, we use data from 569 sampling locations along five cross-Slough transects to examine regional vegetation distribution, and to test and describe the association of marsh vegetation with several hydrologic and edaphic parameters. Analysis of vegetation:environment relationships yielded estimates of both mean and variance in soil depth, as well as annual hydroperiod, mean water depth, and 30-day maximum water depth within each cover type during the 1990's. We found that rank abundances of the three major marsh cover types (Tall Sawgrass, Sparse Sawgrass, and Spikerush Marsh) were identical in all portions of Shark Slough, but regional trends in the relative abundance of individual communities were present. Analysis also indicated clear and consistent differences in the hydrologic regime of three marsh cover types, with hydroperiod and water depths increasing in the order Tall Sawgrass < Sparse Sawgrass < Spikerush Marsh. In contrast, soil depth decreased in the same order. Locally, these differences were quite subtle; within a management unit of Shark Slough, mean annual values for the two water depth parameters varied less than 15 cm among types, and hydroperiods varied by 65 days or less. More significantly, regional variation in hydrology equaled or exceeded the variation attributable to cover type within a small area. For instance, estimated hydroperiods for Tall Sawgrass in Northern Shark Slough were longer than for Spikerush Marsh in any of the other regions. Although some of this regional variation may reflect a natural gradient within the Slough, a large proportion is the result of compartmentalization due to current water management practices within the marsh. We conclude that hydroperiod or water depth are the most important influences on vegetation within management units, and attribute larger scale differences in vegetation pattern to the interactions among soil development, hydrology and fire regime in this pivotal portion of Everglades.     

宁夏近20年来植被覆盖度及其与气温降水的关系

利用1981—2004年的植被指数(NDVI)资料,结合实地植被调查资料,将宁夏植被类型划分4个区域,确定了各地植被指数与覆盖度的关系,分析了宁夏各区域植被覆盖度的年际变化、季节变化、植被覆盖度的面积变化及其与气温和降水量的关系。结果表明:24年来宁夏贺兰山与贺兰山东麓的年植被覆盖度呈下降趋势,中部干旱带植被覆盖度呈上升趋势;近4年来,贺兰山植被状况整体变好;贺兰山东麓植被状况整体变差;中部干旱带的植被状况夏季变差,秋季变好;南部山区的植被覆盖度整体变好。宁夏春夏季降水量是影响植被覆盖度的关键性因子,气温对植被覆盖度的影响不显著。     

Ecological fish production in Long Pond,a lakeshore lagoon on Long Point,Lake Erie

Synopsis Long Pond, a recently formed 2.4 ha lagoon on Long Point, Lake Erie (Canada), was treated with piscicide and found to contain 47,768 fishes of 22 species. Nine dominant species (Notropis heterolepis, Pimephales notatus, Notemigonus crysoleucas, Lepomis gibbosus, L. macrochirus, Perca flavescens, Cyprinus carpio, Micropeterus salmoides and Carassius auratus) comprised 91% and 97% of total numbers and standing crop respectively. Age, growth and production were determined giving a total fish production estimate (corrected for all species) of 87.5 kg ha^–1 y^–1 for this lagoon. Dominant species were deemed either invaders (Cyprinus carpio, Carassius auratus), which had entered the lagoon to spawn and been trapped, or residents. The invaders comprised 82% of the 277.8 kg ha^–1 total standing crop. Their successful spawning and subsequent escape of the young from the lagoon would have resulted in some 615 kg y^–1 of fish production outside the lagoon. Resident stocks were dominated by young fishes, a characteristic of exploitation or early colonization. This may have been due to the recent formation and subsequent expansion of the lagoon or high annual mortality due to extreme physical conditions but was most likely the result of excessive predation by Micropterus salmoides. Relationship between biomass and production show that the chance inclusion of the invaders produces an immediate shift from a characteristically early to a characteristically late phase of ecological development.     

Vegetation restoration patterns and their relationships with disturbance on the Giant Panda Corridor of Tudiling, Southwest China

Human activities such as deforestation, cultivation, and overgrazing have contributed to the destruction of forest ecosystems in the upper Minjiang River basin for a long time, which has led to the reduction in forest coverage and biodiversity. On the Giant Panda Corridor of Tudiling in this basin, the effects of the existing disturbance regimes on plant communities after the vegetation restoration in the 1980s were assessed, and the community composition, the species diversity and their relationships with environmental factors significantly associated with the disturbance were analyzed using the transect sampling method, the two-way indicator species analysis (TWINSPAN) and the detrended canonical correspondence analysis (DCCA). The results were as follows: communities could be classified into six types, and species were clustered into four functional groups (responsive to disturbance, retarded disturbance, resistant to intermediate disturbance, and resistant to heavy disturbance) based on both TWINSPAN and DCCA. DCCA with species composition of plots is similar to that with species diversity of plots. The communities were separated into distinct groups along the DCCA axis, and this pattern was significantly correlated with environmental factors. Elevation differences, shape, slope, distance to roads, and the number of paths in the plots had an evident influence on the distribution of the species and communities. Environmental factors including slope, distance to roads, and the number of paths revealed the gradient of disturbance among the communities along the DCCA axis. High disturbance intensity caused significantly lower species diversity and inhibited the regeneration of vegetation compared with the more diverse undisturbed communities. Artificial restoration was more effective than natural restoration in maintaining high species diversity. The process of succession was inhibited in natural restoration because of the failure of tree establishment, growth, and survival during regeneration.     

Vegetation restoration patterns and their relationships with disturbance on the Giant Panda Corridor of Tudiling, Southwest China

Human activities such as deforestation, cultivation, and overgrazing have contributed to the destruction of forest ecosystems in the upper Minjiang River basin for a long time, which has led to the reduction in forest coverage and biodiversity. On the Giant Panda Corridor of Tudiling in this basin, the effects of the existing disturbance regimes on plant communities after the vegetation restoration in the 1980s were assessed, and the community composition, the species diversity and their relationships with environmental factors significantly associated with the disturbance were analyzed using the transect sampling method, the two-way indicator species analysis (TWINSPAN) and the detrended canonical correspondence analysis (DCCA). The results were as follows: communities could be classified into six types, and species were clustered into four functional groups (responsive to disturbance, retarded disturbance, resistant to intermediate disturbance, and resistant to heavy disturbance) based on both TWINSPAN and DCCA. DCCA with species composition of plots is similar to that with species diversity of plots. The communities were separated into distinct groups along the DCCA axis, and this pattern was significantly correlated with environmental factors. Elevation differences, shape, slope, distance to roads, and the number of paths in the plots had an evident influence on the distribution of the species and communities. Environmental factors including slope, distance to roads, and the number of paths revealed the gradient of disturbance among the communities along the DCCA axis. High disturbance intensity caused significantly lower species diversity and inhibited the regeneration of vegetation compared with the more diverse undisturbed communities. Artificial restoration was more effective than natural restoration in maintaining high species diversity. The process of succession was inhibited in natural restoration because of the failure of tree establishment, growth, and survival during regeneration.