Effects of experimental and real land use on seedling recruitment of six fen species

Seedling emergence and early establishment of six fen species differing in seed mass and growth form were investigated under experimental land use with changed vegetation structure and under real land use in a calcareous fen. Seeds of all six species were sown in plots with different experimental land-use treatments: summer and autumn mowing with or without litter removal, trampling and abandonment. Additionally, emergence and survival of experimentally sown seeds was investigated under real land use on adjacent sites managed by mowing, grazing, intense trampling or abandonment.On abandoned plots and on plots without litter removal of the land-use experiment, emergence rates of all species were negatively affected either by high litter and moss cover or by tall canopy. No differences were found between autumn and summer mowing. Gap creation by experimental trampling did not increase germination rate. Under real land use, establishment of seedlings of most species was positively affected by litter cover and tall canopy. Trampling, in contrast, had a severe negative effect on seedling survival.The investigated species differed in their germination ability which was tested in the germination chamber and in their response to land use. Succisa pratensis with the highest seed mass germinated well in the chamber and in the field more or less regardless of land use. The low germination rate of Parnassia palustris in the germination chamber indicated a limitation of viable seeds. In the field, however, seedling emergence was additionally limited by microsite availability. Seeds of Serratula tinctoria and Primula farinosa germinated well in the germination chamber, but seedling recruitment in the field was hampered in the presence of a high litter or moss cover. Seeds of Tofieldia calyculata and Pinguicula vulgaris were strongly dependent on the availability of suitable microsites in the field. They hardly germinated under natural conditions, in spite of a high number of germinable seeds in the germination chamber.     

Seedling recruitment in flood‐meadow species: The effects of gaps,litter and vegetation matrix

Question: Is the failure of establishment of rare flood‐meadow species in habitat restoration primarily due to seed or microsite limitation? How do sown species respond to artificially created gaps and added litter at two neighbouring sites with similar physical conditions but contrasting vegetation matrix (young arable fallow field vs species‐poor meadow sward)? Location: Upper Rhine valley, southwestern Germany, 85 m a.s.l . Methods: Seeds of six typical flood‐meadow species were sown in four treatment combinations of the factors gap creation and litter addition. Seedling recruitment was monitored for three years. Results: Five of the six species established successfully at both sites largely irrespective of treatments, indicating seed limitation. Only in the small‐seeded Arabis nemorensis, which was revealed to be strictly gap‐dependent at the meadow site, could an obvious microsite limitation be shown. The non‐significance of gap treatments in all other species at the relatively high productive meadow site is probably due to biomass removal by mowing in early summer. Only at the extremes of the seed size spectrum did the results meet predictions of plant ecological theory, such as the strict gap dependence of small‐seeded species in closed swards or the positive to neutral response of large‐seeded species to litter layers. Conclusions: Species identity was revealed to be the major factor influencing differences in recruitment. Due to the lack of a general trend in the response towards treatments the results support conceptual models that describe the interplay of facilitation and interference as a highly dynamic equilibrium, driven by variable abiotic and biotic marginal conditions.     

Does Germination Success Differ with Respect to Seed Mass and Germination Season? Experimental Testing of Plant Functional Trait Responses to Grassland Management

BACKGROUND AND AIMS: Plant functional trait responses to processes such as grassland management have been analysed frequently; however, the scaling-up from individual traits to the outcomes of vegetation dynamics has seldom been tested. In this experiment, germination success was studied with respect to the relationships between grassland management (mowing and grazing), as well as abandonment, and two traits that are relevant for seedling recruitment: seed mass and germination season. On the basis of discussions in the literature and indirect trait analyses in our previous studies, the following hypotheses are proposed: (1) with respect to seed mass, mowing and grazing favour the germination of small seeds, whereas after abandonment the germination success of larger seeds is higher; and (2) with respect to germination season, mowing and grazing favour autumn-germinating seeds, whereas succession promotes spring-germinating seeds. METHODS: The germination experiment took place in a semi-natural, dry grassland in north-east Germany. Seeds of eight herbaceous species that differ with respect to seed mass and germination season were sown in mown, grazed and abandoned plots. Germination success was documented during the following year. KEY RESULTS AND CONCLUSIONS: Contrary to the hypothesis, germination of small seeds was not promoted by mowing or grazing and they germinated relatively more often than expected in the abandoned plots. A relationship between abandonment and gaps of bare soil below the vegetation cover that favour germination of small seeds was likely, but could not be proved statistically. It is possible that the small seeds suffered less from predation. Mowing favoured autumn germination, which could be explained by the removal of biomass in late summer. Contrary to our expectation, there was relatively more spring germination after grazing than after mowing, yet vegetation height was smallest in spring. Generally, germination season was found to be related to the temporal occurrence of favourable light conditions.     

Low allelopathic potential of an invasive forage grass on native grassland plants: a cause for encouragement?

Tall fescue (Festuca arundinacea Schreb.), a highly competitive European grass that invades US grasslands, is reportedly allelopathic to many agronomic plants, but its ability to inhibit the germination or growth of native grassland plants is unknown. In three factorial glasshouse experiments, we tested the potential allelopathic effects of endophyte-infected (E+) and uninfected (E−) tall fescue on native grasses and forbs from Midwestern tallgrass prairies. Relative to a water control, at least one extract made from ground seed, or ground whole plant tissue of E+ or E− tall fescue reduced the germination of 10 of 11 species in petri dishes. In addition, the emergence of two native grasses in potting soil was lower when sown with E+ and E− tall fescue seedlings than when sown with seeds of conspecifics or tall fescue. However, when seeds of 13 prairie species were sown in sterilized, field-collected soil and given water or one of the four tall fescue extracts daily, seedling emergence was lower in one extract relative to water for only one species, and subsequent height growth did not differ among treatments for any species. We conclude that if tall fescue is allelopathic, its inhibitory effects on the germination and seedling growth of native prairie plants are limited, irrespective of endophyte infection. On the other hand, the apparent inability of these plants to detect tall fescue in field soil could hinder prairie restoration efforts if germination near this strong competitor confers fitness consequences. We propose that lack of chemical recognition may be common among resident and recently introduced non-indigenous plants because of temporally limited ecological interactions, and offer a view that challenges the existing allelopathy paradigm. Lastly, we suggest that tall fescue removal will have immediate benefits to the establishment of native grassland plants.     

Factors limiting the distribution of the annual legumeKummerowia striata in a river floodplain

The annual legumeKummerowia striata often predominates in river floodplains forming a large population, but it is rare in gravelly areas adjacent to it. In order to clarify the factors limiting the distribution ofK. striata, its distribution pattern, germination and survival of seeds sown artificially were studied in the floodplain of the Ohta River. There was a positive correlation between the cover value ofK. striata and the percentage of fine particles (<0.2 mm) in the soil. In the winter season, there was a number of seeds (up to 47 seeds 20 cm⁻²) on the ground where aK. striata population had existed in the previous year, but they were very sparse in areas apart from the population. Only a small proportion of seeds sown in the gravelly area germinated. Many of the germinated individuals died before the first leaf unfolded, but the rest survived to maturity despite repeated floodings. Plants germinated in the gravelly area and those inoculated with soil from the gravelly area bore nodules, showing the presence ofRhizobium in the gravelly area. It was concluded that the colonization ofK. striata in the gravelly area was limited by slow dispersal, and by a low percentage of germination and high mortality in the early stage of establishment.     

Do seed and microsite limitation interact with seed size in determining invasion patterns in flooding Pampa grasslands?

Additive influences of the invasion ability of species (invasiveness) and the characteristics of the habitat which make it invasible (invasibility) cannot fully explain grassland invasion patterns. We tested the hypothesis that different species assemblages of grassland communities may partly result from interactive influences between the relative invasiveness of available species and community invasibility. During 10 months, we evaluated seed and microsite limitation of seedling emergence, survival, and recruitment of plants belonging to species with different seed size (large-seeded species vs. small-seeded species), with in a two-phase community mosaic typical of semi-natural grasslands in the southern flooding Pampa of Argentina. Seeds of large versus small-seeded species were sown either in species-poor patches dominated by a tall tussock grass (“pajonal”) or in species-rich patches dominated by short grasses (“matrix”), subjected to different levels of canopy disturbance (cut vs. uncut). Seed addition promoted seedling emergence for 7 out of the 10 species sown, and this effect was higher for large than for small-seeded species. After seed limitations were removed, interactive effects among seed size, community state and canopy disturbance reflected a strong positive influence of seed size on plant recruitment only in cut pajonal patches. Therefore, according to the stage of invasion process, relative species success may depend on non-interactive (seed-size effect on seed limitation to seedling emergence) or interactive influences among species invasibility and community invasiveness (from seedling emergence to plant recruitment). As a general conclusion, different assemblages of species are expected to successfully colonize spatially close grassland patches, according to both the available invasible species (seed size) and the community state and stage (species composition and canopy disturbance).     

Influence of management on the seed production and seed bank of calcareous fen species

Abstract. The dynamics of the seed production and seed bank of two dominant perennial species of calcareous fens were investigated in response to different mowing frequency, fallow or pasture. The production of fertile shoots responded strongly to management practices. On sites where mowing alternated with fallow, autumn mowing led to an increase of fertile shoot density in Schoenus ferrugineus and a decrease in Molinia caerulea in the subsequent season. Repeated annual mowing after long-term fallow raised the density in Schoenus and inhibited initiation of flowering shoots in Molinia. Seed set and viability were influenced mainly by climatic or other factors. Variation of seed production between sites and in consecutive years at the same site could thus be large. The relationship between total seed production and seed bank was weak, but it improved when germination rates were included in the calculation. As the seed bank was generally smaller than the viable seed production, low survival and a high turnover of seeds in the upper soil layers is assumed for both species. Implications for recruitment strategies are discussed.     

Restoration of Prairie Community Structure and Ecosystem Function in an Abandoned Hayfield: A Sowing Experiment

Using a multispecies seed sowing experiment, we investigated the roles of seed and microsite limitation in constraining the restoration of native prairie diversity and ecosystem function in an abandoned upland hayfield in northeastern Kansas. Seeds of 32 native and naturalized plant species from the regional pool were sown into undisturbed and experimentally disturbed field plots. After six growing seasons, experimental sowing led to major shifts in species and functional group composition, increases in native species abundance and floristic quality, declines in abundance of non‐native species, and increases in plant diversity. These changes in community structure led to significant changes at the ecosystem level including increases in light capture, peak biomass, primary production, litter biomass, root biomass, and C storage in roots. Our findings reveal the importance of seed limitations in constraining the natural recovery of prairie vegetation, biodiversity, and ecosystem functioning in this grassland and confirm broadcast sowing as a useful tool for the restoration of upland hayfield sites.     

Restoring the Victorian Western (Basalt) Plains grassland. 1. Laboratory trials of viability and germination, and the implications for direct seeding

Summary   The Victorian Western (Basalt) Plains grassland is one of Australia's most threatened plant communities. Practitioners using seed for its restoration need to know whether seed can be sown fresh or whether it requires an after-ripening period. This study assessed the viability and germination of freshly harvested wild seed from 64 grassland species indigenous to the Basalt Plains of western Victoria. The seed was collected as part of a broader experiment that examined the potential of direct-sown complex seed mixes for the restoration of grassland communities. The germination of fresh seed at 25°C varied widely between species. Comparisons with tetrazolium viability tests for each species indicated varying levels of dormancy within the species pool. Germination separated into three broad responses at day 28. One-third of the species failed to germinate, one-third germinated at 1% to 50% and the remaining species germinated between 51% and 100%. Therefore, if the aim of a sowing was the rapid and synchronous establishment of most of the sown species, the use of fresh seed in restoration could be problematic. After 3 months of dry storage, eight species were re-tested for germination. Each of the selected species had shown high viability but low initial germination. Only two species significantly increased their total germination at 25°C. The annual species, Triptilodiscus pygmaeus , increased its total germination from 6% as fresh seed to 99% after dry storage. Testing the viability and germination capacity of freshly harvested seed from a large and diverse sample of native grassland species demonstrated that many of the species were unlikely to germinate rapidly or synchronously when sown in complex seed mixes soon after harvest. This finding has implications for the scheduling and management of restoration projects that rely on the use of such seed.     

Factors Affecting Seed Germination and Seedling Establishment of Fen-Meadow Species

Availability of seeds and provision of “safe sites” for seedling recruitment are essential for successful restoration of seminatural grassland communities. Inability to provide species‐specific conditions for seedling recruitment appears to be a major factor limiting establishment of fen‐meadow species on restoration sites. This contention was tested in the field for both germination and establishment conditions for a selection of fen‐meadow species. A Cirsio‐Molinietum fen meadow and an agriculturally semi‐improved species‐poor grass dominated rush pasture were used. Seeds of Carex ovalis, Cirsium dissectum, Molinia caerulea, Succisa pratensis, and Holcus lanatus were sown onto treatments comprising either irrigation or no irrigation, presence or absence of existing vegetation canopy, and presence or absence of soil disturbance. Germination of all except H. lanatus was higher in the fen meadow than in the rush pasture. The fen‐meadow site was less susceptible to drought, provided more light to the seed environment, and showed a stronger day–night variation in relative humidity compared with the rush pasture. All the fen‐meadow species responded strongly to the experimental treatments, whereas H. lanatus showed only a small response. Soil disturbance was the major factor that increased germination. Removal of the vegetation canopy improved germination only in S. pratensis. Conditions affecting survival of seedlings were different from those affecting seed germination. Seedling survival was greater on the fen‐meadow site than on the rush pasture. Canopy presence was the major factor that reduced seedling survival. Few seedlings survived in the presence of the rush pasture canopy. Irrigation and soil disturbance were of minor importance for seedling survival on both sites. Safe sites for seed germination and seedling establishment of fen‐meadow species existed on the fen meadow even without soil disturbance and gap creation. Safe sites for seedling recruitment were not present in the rush pasture. The need for species‐specific definition of safe site characteristics at the two stages of seedling recruitment (i.e., for seed germination and for seedling survival) was demonstrated. The implications of these findings for restoration of seminatural grasslands are discussed.     

Seed and microsite limitation in Rheum nobile,a rare and endemic plant from the subnival zone of Sino-Himalaya

Background: Species persistence, particularly in monocarpic species, depends on the successful recruitment of individuals. An understanding of the factors that limit the recruitment of rare monocarpic plant species is therefore vital for their conservation.

Aims: To identify the factors limiting the recruitment of Rheum nobile, a rare and highly specialised monocarpic giant herb endemic to the high eastern Himalayas.

Methods: Seed sowing (seeds added or not added) and seedling transplanting experiments were conducted in disturbed (vegetation removed) and undisturbed plots in the vicinity of established populations of R. nobile to explore the mechanisms of recruitment limitation. Four levels of photosynthetically active radiation (0, 15, 30 and 50 μmol m^?2 s^?1) and two sowing positions (beneath and above grass litter or moss layer) were manipulated in the laboratory to determine how ground cover limited seedling emergence.

Results: Seed addition increased seedling recruitment. Disturbance significantly increased seedling emergence and establishment. Seed germination significantly decreased with the reduction of light availability, but 31.7% of all seeds germinated in complete darkness. Seedling emergence was close to zero when seeds were sown on top of a layer of grass litter or moss, but rose to 34.5% when the seeds were sown beneath such layers.

Conclusions: Our results indicate that the recruitment of R. nobile is limited by a combination of seed and microsite availability. Therefore, in order to conserve this species, we suggest adding seeds to suitable sites and implementing soil disturbances in existing populations to create suitable microsites.     

Bryophyte Mats Inhibit Germination of Non-native Species in Burnt Temperate Native Grassland Remnants

Species-rich native grasslands in western Victoria, Australia, are often small, have a high perimeter to area ratio and are surrounded by non-native species. Few non-native species, however, have invaded them. A feature of species-rich grasslands is the presence of a bryophyte mat (composed of mosses and liverworts) that carpets the intertussock spaces. I assessed the role of these mats in plant invasions by sowing three non-native species (Briza maxima, Hypochoeris radicata, Plantago lanceolata) in replicated disturbed (mats removed) and undisturbed (mats intact) microsites at three grassland remnants (two recently burnt, one unburnt for 3 years) and followed seedling emergence, survival and growth for 5 months. Three native species were also sown for comparison. The rate of germination and total percent germination of non-native species were significantly enhanced at both burnt sites when the mat was disturbed. The large-seeded Briza maxima failed to germinate at both burnt sites in the absence of soil disturbance. The native species generally did not show a strong germination or growth response to soil disturbance in burnt areas. At the unburnt site, where monthly percent soil moisture was highest, final percent germination of the non-native and native species was greatest of any site in both microsites, and germination was not significantly affected by soil disturbance. Differences in the seed morphology of native and non-native species may play an important role in their ability to establish on bryophyte mats in moisture-limiting environments. Any activity that disrupts the mats in the frequently burnt, species-rich grassland remnants is likely to significantly enhance the germination and subsequent growth by non-natives. However, where burning is infrequent, germination of some non-native species may be expected, regardless of disturbance, although growth will likely be favoured in disturbed areas.     

The effect of nutrient level on plant structure and production in a wet grassland: a field study

Since the 1950s, agricultural intensification has affected the structure and functioning of ecological systems including wet grasslands. Our study site, a wet grassland near Třeboň, Czech Republic, was historically a sedge meadow, but increased nutrient additions, a long-lasting flood in 2002 and changed mowing patterns resulted in domination by Phalaris arundinacea. The aim of the study was to determine how different nutrient conditions may affect plant structure and production in a wet grassland used for hay production. Species composition and percent cover were determined from line intercepts. Aboveground biomass was harvested six times each in 2007 and 2008 and primary production then calculated. Ingrowth core bags were used to determine belowground production. Aboveground production was two times greater in the high nutrient versus the low nutrient area in both years, while belowground production was very similar. The high nutrient area was still dominated by P. arundinacea, but Carex gracilis was now a co-dominant in the low nutrient area. However, other factors, such as water level and mowing regime, may interact with nutrient level to govern wet grassland structure and function.     

Stimulation of soil nitrification and denitrification by grazing in grasslands: do changes in plant species composition matter?

Stimulation of nitrification and denitrification by long term (from years to decades) grazing has commonly been reported in different grassland ecosystems. However, grazing generally induces important changes in plant species composition, and whether changes in nitrification and denitrification are primarily due to changes in vegetation composition has never been tested. We compared soil nitrification- and denitrification-enzyme activities (NEA and DEA, respectively) between semi-natural grassland sites experiencing intensive (IG) and light (LG) grazing/mowing regimes for 13 years. Mean NEA and DEA (i.e. observed from random soil sampling) were higher in IG than LG sites. The NEA/DEA ratio was higher in IG than LG sites, indicating a higher stimulation of nitrification. Marked changes in plant species composition were observed in response to the grazing/mowing regime. In particular, the specific phytomass volume of Elymus repens was lower in IG than LG sites, whereas the specific volume of Lolium perenne was higher in IG than LG sites. In contrast, the specific volume of Holcus lanatus, Poa trivialis and Arrhenatherum elatius were not significantly different between treatments. Soils sampled beneath grass tussocks of the last three species exhibited higher DEA, NEA and NEA/DEA ratio in IG than LG sites. For a given grazing regime, plant species did not affect significantly soil DEA, NEA and NEA/DEA ratio. The modification of plant species composition is thus not the primary factor driving changes in nitrification and denitrification in semi-natural grassland ecosystems experiencing long term intensive grazing. Factors such as trampling, N returned in animal excreta, and/or modification of N uptake and C exudation by frequently defoliated plants could be responsible for the enhanced microbial activities.     

Rodent seed predation and seedling recruitment in mesic grassland

Seedling recruitment of two grasses (Arrhenatherum elatius and Festuca rubra) and two herbs (Centaurea nigra and Rumex acetosa) was measured in areas with and without rodents to which seeds of each species were sown at three seed densities (1000, 10,000 and 50,000 seeds m⁻²) in two seasons (spring and autumn 1995). Seed removal was measured for 10-day periods and the fate of seedlings was followed for 15 months after sowing. The proportion of seed removed ranged from 6 to 85% and increased with increasing seed density for each species. Rodents had no effect on seedling emergence or survival in the spring sowing. In the autumn sowing, rodents reduced seedling emergence of all four species sown at 1000 and 10,000 seeds m⁻² but had no impact at 50,000 seeds m⁻², presumably because of microsite limitation. We suggest the difference between spring and autumn arose because emergence was seed limited in autumn but microsite limited in spring; microsite availability was higher in autumn because a summer drought killed plants, reduced plant biomass and opened up the sward. Fifteen months after the autumn sowing, fewer A. elatius and C. nigra seedlings survived on plots exposed to rodents. This result reflected not only the reduced seedling emergence but also increased seedling mortality (seedling herbivory) in sites exposed to rodents. In contrast, F. rubra and R.acteosa showed density-dependent seedling survival which compensated for initial differences in seedling emergence, so that no effect of rodents remained after 15 months. The results suggest that rodent seed predation and seedling herbivory exert strong effects on seedling recruitment of A.elatius and C. nigra when recruitment conditions are favourable (conditions that lead to high microsite availability) and may contribute to both species being maintained at low densities in the grassland. The results also demonstrate that highly significant impacts of rodent seed predation at the seedling emergence stage can disappear by the time of plant maturation. Received: 2 March 1998 / Accepted: 28 September 1998     

不同刈割频度对大针茅草原群落特征及土壤元素含量的影响

在草原生态系统中,土壤是植物生长发育最重要的基质,对植物群落动态有显著的影响。刈割是内蒙古典型草原区除放牧外最重要的利用方式。研究不同刈割频度对典型草原区群落特征和若干土壤性质的影响及土壤因子与群落特征的相关性,旨在得出对群落多样性最有利并最适宜生产利用的刈割频度。研究区设置在内蒙古锡林浩特市东部以大针茅建群的典型草原;在2009—2013年进行不同频度的刈割处理,共设置处理,一年两次刈割、一年一次刈割、两年一次(割一年休一年)刈割、围封,在2013年8月采集测定土壤养分的样品。刈割对群落多样性影响显著,割一年休一年Shannon-Wiener多样性指数、Pielou均匀度指数、丰富度指数均高于其他刈割处理(P0.05);不同频度刈割下,一年两次刈割处理下土壤20—30cm和30—40cm的有机质含量显著高于其他处理(P0.05);不同频度刈割处理下土壤中的速效磷和速效氮的含量没有显著差异;一年两次处理的土壤全氮含量显著高于其他处理(P0.05)。Shannon-Wiener多样性指数与有机质含量、全氮含量呈显著负相关;Pielou均匀度指数与土壤元素间无显著相关关系;Richness指数与有机质含量呈显著负相关,与全氮含量为极显著负相关关系。割一年休一年刈割处理下土壤元素含量呈现更好的状态,结合群落物种多样性及生产利用的角度,割一年休一年为最合理的刈割频度。     

Effects of plant competition,seed predation,and nutrient limitation on seedling survivorship of spotted knapweed (<Emphasis Type="Italic">Centaurea stoebe</Emphasis>)

We measured seed germination and seedling survivorship of spotted knapweed, Centaurea stoebe, in a series of laboratory and field experiments to evaluate the efficacy of seed limitation as a management focus. This work was initiated 6 years after introduction of several biological control agents. The soil seed bank of the site used in this study contained a mean density of 5,848 seeds/m² (ranging from 0 to 16,364 seeds/m²), and 92% of the seeds isolated from soils were shriveled, discolored, and/or partially decayed. Additionally, none of the intact seeds germinated, suggesting that the viable seed bank at our field study site has been exhausted. Centaurea stoebe seeds were planted into pots under a range of soil nitrogen (N) availability, with half of the pots containing a single density of previously established seedlings of a native cool-season grass, slender wheatgrass (Elymus trachycaulus). A watering regime mimicking local precipitation was applied. Spotted knapweed exhibited large biomass responses to N addition, but the presence of grasses suppressed the ability to exploit this N. Surprisingly, low soil N conditions improved knapweed survivorship in the presence of grasses. Nevertheless, recruitment and biomass were still far below the levels reached in the absence of competition. To evaluate the effect of density on successful recruitment, Centaurea stoebe seed was introduced into a meadow at three densities matching reduced levels of seed production under the constraints of seed predators. These densities were sown with or without a seed mixture of native species, into an existing plant community lacking C. stoebe, and seedling recruitment was recorded over 2.5 years. Across all plots and densities sown (568–2,272 seeds m⁻² year⁻¹), seedling recruitment was less than 1%. The invasion potential of spotted knapweed was greatly diminished when realistic levels of plant competition and biological control limit seed production. We therefore conclude that a combination of seed limitation and shortage of ‘safe sites’ within undisturbed vegetation can limit densities of C. stoebe.     

The role of soil seed banks in the restoration of dry acidic dune grassland after burning of Ulex europaeus scrub

Question: Can the seed bank play a significant role in the restoration of plant communities of dry acidic dune grassland where fire has destroyed Ulex europaeus scrub? Location: Northern French Atlantic coast. Methods: One year after the fire, the seed bank and vegetation were sampled in 1 m × 1 m plots along three transects from the oldest scrub vegetation towards the grassland. Differences in species richness, seed density and contribution of ecological groups in the seed bank and vegetation along the transects were analysed. Results: Seed density and species richness in the seed bank decreased significantly from the grassland towards the centre of the scrub vegetation; 50% of the seed bank consisted of core species of the target plant community, such as Carex arenaria, Aira praecox, Rumex acetosella and Agrostis capillaris. Seeds of these species were also found in the deeper soil layers beneath the oldest scrub vegetation, indicating that they can be considered to be long‐term persistent. Beneath the youngest scrub vegetation, seeds of rare satellite target species also occurred. However, no target species were established on the burned site after one year, resulting in a large discrepancy between seed bank and vegetation. Conclusions: Although the seeds present in the soil indicate that restoration of the acidic grassland based on the seed bank is possible, additional management actions such as mowing and soil disturbance may be necessary to restrict resprouting of Ulex and to stimulate the germination of seeds of target species in the deeper soil layers.     

Influence of Seed Mixture and Hydrological Regime on the Establishment of a Diverse Grassland Sward at a Site with High Phosphorus Availability

Abstract Three experiments were undertaken to investigate the influence of seed mixture on the establishment of a target grassland community on a site with high available phosphorus. In the first experiment autumn‐ and spring‐sown commercial seed mixtures were compared with seed harvested from a nature reserve with respect to their ability to produce an inundation grassland community similar to that described by the British National Vegetation Classification (NVC) as Agrostis stolonifera–Alopecurus geniculatus grassland (MG13). In the second experiment the composition and sowing rate of a commercial seed mixture were altered to investigate whether these factors were significant in the establishment of a sward similar to MG13. Similarly, in the third experiment the composition of a commercial seed mixture designed to achieve an alternative community, Cynosurus cristatus–Caltha palustris grassland (NVC code MG8), was sown. The vegetation resulting from each of these treatments was monitored with permanent quadrats for a 3‐year period, and the hydrological regime of each quadrat location was modeled and quantified. The results showed that seed mixture, timing of sowing, and seeding rate had an initial effect on the vegetation that established. However, by the third year of monitoring there were no significant differences between these treatments, and hydrological regime had become the most important factor in determining the distribution of species. The vegetation was less diverse than predicted from germination tests and decreased in diversity over the monitoring period. It is suggested that this may be a result of the hydrological regime being unsuitable for several of the sown species or due to the extremely high available phosphorus concentration in the soil. This study highlights the need to understand the soil and hydrological conditions of a site before choosing a target community and designing a seed mixture.     

Influence of soil salt,at levels characteristic of some roadside environments,on the germination of certain tree seeds

Summary Tree seeds were germinated in a greenhouse soil mix amended with varying amounts of sodium chloride. The salt was added in amounts approximating certain roadside soil environments.Betula alleghaniensis, Catalpha bignonioides, Quercus coccinea andQ. cerris seed exhibited reduced germination percentage at the highest salt concentrations. Germination ofRobinia pseudoacacia seed was delayed as salt concentration was increased. Except for slight germination percentage reduction, seed ofAilanthus altissima, Pinus rigida andGleditsia triacanthos were uninfluenced by the salt treatments.