Harvester ants (Messor barbarus) as disturbance agents in Mediterranean grasslands

Questions: 1. Do disturbances by harvester ants (Messor barbarus L.) affect soil properties? 2. Do they alter seed distribution? 3. Do they show a different species composition? 4 Are these changes related to seed size (length and weight)? Location: Mediterranean grasslands in central Spain, near Madrid. Methods: We recorded autumn seed banks and spring vegetation in middens, trunk trails and controls. Soil properties were also measured in middens and controls. The effect of seed weight and length was analysed after transforming data into phylogenetically independent contrasts. Results: Soil under middens is more silty and higher in potassium, organic matter and pH. Seed density and seed bank species richness increased greatly in middens, while vegetation species richness was significantly lower in comparison to control samples. Abundance changes in this disturbance type were positively correlated with seed weight, both in seed bank and vegetation. In contrast, we only detected a slight increase in bare ground on foraging trunk trails, with no clear effects on seed bank and vegetation composition. Conclusions: Midden development is a mechanism that generates heterogeneity which favours the survival of certain large‐seeded species mainly predated by ants in Mediterranean grasslands. This effect may partially neutralize the dominance of small seeded species expected from the seed predation process.     

The potential role of seed banks in the recovery of dune ecosystems after removal of invasive plant species

Question: How resilient is the seed bank of an invaded dune system? Is that resilience dependent on duration of invasion? How does the accumulated litter layer contribute to the soil seed bank? Location: Coastal sand dunes invaded by Acacia longifolia, Portugal. Methods: Seedling emergence was used to quantify and compare soil seed banks in long‐invaded, recently invaded and non‐invaded areas. Changes in seed banks were also compared with areas where A. longifolia and the litter layer were removed. Results: Species richness, seedling density and diversity were higher in non‐invaded and recently‐invaded areas than in long‐invaded areas. Although there was an apparent similarity between non‐invaded and recently‐invaded areas, analyses of species traits revealed differences. Non‐invaded areas had a wider array of traits. Exotic/invasive species dominated invaded seed banks while native species dominated non‐invaded seed banks. Life forms, growth forms, longevity and dispersal mode showed differences between areas, with cleared plots of long‐invaded areas being apparently the most similar to non‐invaded plots. Acacia longifolia seeds were most abundant in long‐invaded areas, particularly where the litter layer remained. Removal of A. longifolia plus the litter had little effect on the seed bank composition of recently‐invaded areas but resulted in noticeable changes in seed banks of long‐invaded areas. Conclusions: Long‐invaded areas are less resilient and show a higher reinvasion potential, despite severe alteration of the seed banks of both areas. Seed bank studies can be a useful tool to guide management, but can give misleading results when invasion periods are protracted.     

Effect of three mound-building ant species on the formation of soil seed bank in mountain grassland

The effect of three ant species (Lasius flavus, Formica spp., Tetramorium caespitum) on soil seed bank formation was studied in temperate mountain grassland. Seed removal experiments, analysis of soil seed content and seed survival experiments were carried out to evaluate the influence of ground ants on the seed fate. In the seed removal experiment seeds of 16 species, including 5 species with elaiosome-bearing seeds (myrmecochores), were exposed and their removal followed for 39 h. On average, ants removed 63.8% of myrmecochorous seeds and 10.9% of seeds without adaptation to ant dispersal. Analysis of soil seed content revealed that myrmecochores, in spite of expectations that they would accumulate in nests of seed dispersing ants, were most abundant in the soil of control plots. Evidence on seed relocation to the ant nests was obtained from a comparison of mounds of seed dispersing and seed non-dispersing ant species, as more seeds were found in the mounds of Formica spp. and Tetramorium caespitum (seed dispersers) in comparison with the mounds of Lasius favus (non-disperser).The soil seed bank of the compared microhabitats (control plots and mounds of 3 ant species) differed in their species composition, seed abundance and vertical distribution. The most distinct qualitative differences were between seed flora of control plots and mounds of Tetramorium caespitum. Control plots had approximately 30,000 propagules per m², which was double the number of seeds found in the ant mounds. In control plots, abundance and diversity of seeds steeply declined with depth; this trend was not observed in the mounds probably due to bioturbation. In the seed survival experiment, more seeds (2 out of 3 species) survived in control plots, which may also contribute to the higher seed abundance in this microhabitat.This study showed that seed relocation by ants does not contribute significantly to seed bank build-up at this study site. Ants may, however, increase the regeneration success of myrmecochores, mainly by dispersal for distance and placement in a larger spectrum of microsites, in contrast to species not adapted for myrmecochory.     

The role of the soil seed bank in vegetation recovery on an oceanic island severely damaged by introduced goats

Question: Are the seed banks of an isolated subtropical oceanic island capable of naturally regenerating vegetation either with species of the historical forest community or with the existing grassland community after severe damage to the vegetation by goats? Location: Nakoudojima Island, Bonin Archipelago (Ogasawara Shoto), Japan. Methods: Soil samples were collected at 0–5 cm and 5–10 cm depths from seven plots in forests, grasslands, artificially matted areas and bare land. Soil seed banks were assessed using the seedling emergence method followed by the hand‐sorting of ungerminated seeds. We determined the size and composition of the seed banks in upper soil layers of plots and compared the seed banks to the standing vegetation. Results: A total of 12 220 seedlings belonging to 42 species from 20 families germinated. Total mean seed density (0–5 cm depth) was low in all plots within forest, grassland, and heavily degraded vegetation types (34.7 ± 8.6 to 693.5 ± 123.6, 58.6 ± 7.8 to 107.1 ± 10.0, and 1.1 ± 0.5 to 7.2 ± 2.3 seeds/m², respectively). Forbs and graminoids dominated the seed banks of grassland and forest plots including Cyperus brevifolius, Gnaphalium pensylvanicum, Oxalis corniculata and Solanum nigrum, and these alien species comprised 90% of the density of the seed bank. There was little correlation between seed banks and standing vegetation of the island (Sørensen similarity coefficient values 0.26 to 0.45). Conclusions: If natural regeneration occurs from the seed bank of the island, future vegetation will not move toward the original forest community, because the seed bank is dominated by non‐native herbaceous grassland species. Though isolated, a few forest remnants with low species richness could be an important source for the natural re‐establishment of forest on the island; however, seed availability may be limited by either poor dispersal or pollination so that woody species will probably recover very slowly on this goat‐impacted island.     

Seasonal dynamics of Mediterranean pasture seed banks along environmental gradients

The size and dynamics of seed banks were studied in grazed and ungrazed Mediterranean pastures at different altitudes and topography positions. The soil samples were collected in autumn and spring and the seed banks composition was determined by greenhouse germination over a 9-month period. The percentage of bare ground and the presence of new seedlings were recorded monthly from October to July in the field. A fall in seed density and species richness in the banks and a tendency for seeds to remain in the banks were linked to a rise in altitude. Germination in lower pastures mainly occurred in October in the numerous gaps left by the summer drought. At higher altitudes, the scarcity of gaps and the harsh climate led to an autumn–spring segregation of germination. On a local scale, the low slope positions and the ungrazed plots had a larger number of persistent seed bank species and a lower percentage of bare ground where seeds could germinate than their respective plots in the upper positions and grazed plots. A higher seed density in ungrazed than grazed plots was only detected in the three highest plots. No seed bank species richness trend was detected. In populations of the same species in different types of environments, the seasonal variation of seed numbers was environment-dependent for the majority of the species. In general, perennial grassland and its related low gaps availability appear to favour persistent seed banks.     

Relationships between seed banks and spatial heterogeneity of North American alvar vegetation

Abstract. This is the first quantitative study of seed bank characteristics in North American alvar habitats. We assessed seed bank density, species richness, and species composition in 75 plots distributed among five alvar sites in Bruce Peninsula National Park, Ontario, Canada, each of which displayed areas of high and low vegetation cover within the alvar and a fully forested perimeter area. Forested habitats immediately adjacent to alvar patches contained minimal seed banks for species restricted to the alvar patches. Open alvars contained less than 1% seeds from woody forest species. This suggests that forest is not invading adjacent alvar habitat via seeds and that adjacent forest does not contain a reservoir of alvar seeds. When compared to areas on the alvar with high vascular plant cover, areas with low cover contained a slightly smaller viable seed bank, but seed banks from high and low vegetation cover plots had similar species composition and species richness. High vegetation cover plots had slightly higher mean and maximum soil depths compared with low cover plots, but no differences in other physical and chemical parameters. Thus, spatial heterogeneity in plant cover is associated only weakly with heterogeneity in below‐ground factors. Despite the availability of seed and soil resources, vegetation dynamics are constrained in areas with low plant cover, and thus alvar community development seems to respond non‐linearly to resource availability.     

Effects of grazing on soil seed bank dynamics: An approach with functional groups

Abstract. The relationship between intensity and timing of cattle grazing on changes in the size and composition of the soil seed bank were investigated in a 3‐yr study in a Mediterranean grassland in northeastern Israel. Treatments included manipulations of stocking rates and of grazing regimes, in a factorial design. The retrieved soil seed bank community was rich in species, with 133 species accounting for 80% of the 166 species recorded at the site. Within the seed bank, 89% of the species were annuals. Seed bank dynamics was analysed in terms of plant functional groups and germination strategies. In terms of total seed bank density and including all functional groups, 42% of the seeds present in the soil did not germinate under watering conditions. The dormancy level differed greatly among functional groups. The seed bank of annual legumes, crucifers, annual thistles and annual forbs had a large fraction of non‐germinated seeds and characterized areas grazed early in the growing season under high and very high grazing intensity. These functional groups were considered to have a higher potential for persistent seed banks production. In contrast, short and tall annual grasses and tall perennial grasses, that were dominant in ungrazed or moderately grazed paddocks, generally had seed banks with a very small fraction of non‐germinated seeds. Seed bank densities varied widely between grazing treatments and years. Under continuous grazing, heavy grazing pressure reduced seed bank densities of grasses and crucifers in comparison to moderate grazing. The greatest reduction on the seed bank densities resulted from heavy grazing concentrated during the seed‐set stages.     

Effect of harvester ants of the genus Pogonomyrmex on the soil seed bank around their nests in the central Monte desert,Argentina

1. The abundance and composition of soil seed banks is a key determinant of plant community structure. Harvester ants can remove huge quantities of preferred seeds close to the nest affecting composition and spatial distribution of plants. 2. In the central Monte desert (Argentina) ants of the genus Pogonomyrmex have high seed removal rates, especially of the five main grasses. The aim of this study was to establish if their foraging activity affects spatial patterns of the soil seed bank around their nests. Our hypotheses were: (1) removal by ants decreases seed abundance of preferred species in the soil; and (2) the effect varies in time. 3. Soil seed abundance was assessed at different distances from Pogonomyrmex nests in the litter and in bare soil at the beginning, the middle, and the end of the season (late spring‐early autumn). 4. A lower seed abundance of preferred species was observed close to the nest in the litter at the end of the season. Non‐preferred species showed no distance gradient. 5. The lower foraging activity and seed consumption at the beginning of the season could explain the temporal variation of the spatial effect. This was only observed in the litter, probably because of the higher removal frequency in this substrate. 6. Colonies of Pogonomyrmex spp. could enhance the heterogeneity of soil seed banks in the central Monte desert from the summer to the beginning of the autumn. Implications for vegetation dynamics depend on the degree to which seed density limits perennial grasses recruitment after ant activity season.     

红壤侵蚀区植被恢复过程中土壤种子库变化特征

土壤侵蚀作为一种自然营力和自然干扰形式对土壤种子库的次分布与物种组成具有一定的影响。本研究对典型红壤侵蚀区裸地(Ⅰ号)、马尾松林地(Ⅱ、Ⅲ、Ⅳ号)和次生林(Ⅴ号)等5处不同植被恢复区的土壤种子库物种组成、储量及分布格局进行研究,探究在植被恢复过程中土壤侵蚀对土壤种子库的影响。结果表明: 研究区土壤种子库共统计到21种物种,物种丰富度低,以草本种类为主。各样地土壤种子库密度为56.7～793.3粒·m^-2,样地间差异显著,土壤种子库密度随着土壤侵蚀强度加重而明显下降。各样地浅层0～2 cm土壤种子库密度随着上坡-中坡-下坡的变化均呈增加趋势;剧烈侵蚀地和强烈侵蚀地土壤种子库主要分布在5～10 cm深层土壤内,且中上坡0～2 cm土层几乎没有种子。土壤侵蚀使得土壤种子库在土层中的分布呈现深层化,植被恢复后深层种子库积累仍需要较长的时间。     

Fire and regeneration: the role of seed banks in the dynamics of northern heathlands

Questions: How do species composition and abundance of soil seed bank and standing vegetation vary over the course of a post‐fire succession in northern heathlands? What is the role of seed banks – do they act as a refuge for early successional species or can they simply be seen as a spillover from the extant local vegetation? Location: Coastal Calluna heathlands, Western Norway. Methods: We analysed vegetation and seed bank along a 24‐year post‐fire chronosequence. Patterns in community composition, similarity and abundances were tested using multivariate analyses, Sørensen's index of similarity, vegetation cover (%) and seedling counts. Results: The total diversity of vegetation and seed bank were 60 and 54 vascular plant taxa, respectively, with 39 shared species, resulting in 68% similarity overall. Over 24 years, the heathland community progressed from open newly burned ground via species rich graminoid‐ and herb‐dominated vegetation to mature Calluna heath. Post‐fire succession was not reflected in the seed bank. The 10 most abundant species constituted 98% of the germinated seeds. The most abundant were Calluna vulgaris (49%; 12 018 seeds m^?2) and Erica tetralix (34%; 8 414 seeds m^?2). Calluna showed significantly higher germination the first 2 years following fire. Conclusions: Vegetation species richness, ranging from 23 to 46 species yr^?1, showed a unimodal pattern over the post‐fire succession. In contrast, the seed bank species richness, ranging from 21 to 31 species yr^?1, showed no trend. This suggests that the seed bank act as a refuge; providing a constant source of recruits for species that colonise newly burned areas. The traditional management regime has not depleted or destroyed the seed banks and continued management is needed to ensure sustainability of northern heathlands.     

The role of the seed bank,seed rain and the timing of disturbance in gap regeneration

Abstract. Question: Does the degree and timing of disturbance contribute significantly to the pattern and process of regeneration in plant communities as a consequence of the availability and number of species of propagules present? Location: Acid grassland at 230 m a.s.l., eastern Scotland, UK. Methods : Plots were surface disturbed or had their soil profile inverted at monthly intervals at 12 dates during a year. Seed bank and seed rain were assessed at each treatment time. The effect of disturbance intensity and timing on the regenerating vegetation was assessed. Results: Removing the seed bank significantly slowed regeneration, as it contributed 43 % of developing cover after one year where it was present. At an individual seed level, seed in the seed rain had a much higher likelihood of contributing to the regenerating vegetation than a seed in the seed bank. Some species showed a reliance on the seed bank for regeneration, and hence there was a significant difference in the vegetation that developed between plots with the seed bank intact and those where it was removed. Winter disturbed plots (little seed rain) had slower rates of re‐vegetation than summer disturbed plots. Timing had little effect on species composition, though a significantly higher cover of perennial forb species developed on the winter disturbed plots. Conclusion: Removing the contribution of the seed bank had a greater effect on the composition of regenerating vegetation than the effect of seasonal variation on the seed rain.     

Impact of Formica exsecta Nyl. on seed bank and vegetation patterns in a subalpine grassland ecosystem

The mound building ant Formica exsecta Nyl. is widely distributed in grassland ecosystems of the Central European Alps. We studied the impact of these ants on seed bank and vegetation patterns in a 11 ha subalpine grassland, where we counted over 700 active ant mounds. The mounds showed a distinct spatial distribution with most of them being located in tall‐grass, which was rarely visited by ungulates (red deer; Cervus elaphus L.). Heavily grazed short‐grass, in contrast, seemed to be completely avoided by ants as only few mounds were found in this vegetation type. The species composition of the ant mound and grassland seed banks was quite similar, i.e. from 15 common plant species 12 were found in both seed bank types. We found the same proportions of myrmecochorous seeds in ant mound and grassland soil samples. In contrast, the number of seeds was 15 times higher in mound compared with the grassland soil samples. Also, the vegetation growing on ant mounds significantly differed from the vegetation outside the mounds: graminoids dominated on ant mounds, herbaceous and myrmecochorous species in the grassland vegetation. We found significant continuous changes in vegetation composition on gradients from the ant mound centre to 1 m away from the mound edge. Overall, F. exsecta was found to have a considerable impact on seed bank and vegetation patterns in the grassland ecosystem studied. These insects not only altered grassland characteristics in the close surrounding of their mounds, but also seem to affect the entire ecosystem including, for example, the spatial use of the grassland by red deer.     

Size traits and site conditions determine changes in seed bank structure caused by grazing exclusion in semiarid annual plant communities

1. Contrasting patterns of change in the seed bank of natural grasslands are frequently found in response to grazing by domestic herbivores. Here, we studied the hypotheses that a) patterns of change in seed bank density and composition in response to grazing depend on spatial variation in resource availability and productivity, and b) that variation among species in patterns of seed bank response to grazing is linked to differences in species size traits (i.e. size of plant, dispersal unit and seed). 2. Effects of sheep grazing exclusion on the seed bank were followed during five years in a semiarid Mediterranean annual plant community in Israel. Seed bank density and composition were measured in autumn, before the rainy season, inside and outside fenced exclosures in four neighboring topographic sites differing in vegetation characteristics, soil resources and primary productivity: Wadi (dry stream terraces, high productive site), Hilltop, South‐ and North‐facing slopes (less productive sites). 3. Topographic sites differed in seed density (range ca 2500–18000 seed m^?2) and in seed bank response to grazing exclusion. Fencing increased seed density by 78, 51 and 18% in the Wadi, South‐ and North‐facing slopes, respectively, but had no effect in the Hilltop. At the species level, grazing exclusion interacted with site conditions in determining species seed bank density, with larger or opposite changes in the high productive Wadi compared to the other less productive sites. 4. Changes in seed bank structure after grazing exclusion were strongly related to species size traits. Grazing exclusion favored species with large size traits in all sites, while seed density of tiny species decreased strongly in the high productive Wadi. Species with medium and small size traits showed lesser or no responses. 5. The size of plants, dispersal units and seeds were strongly correlated to each other, thus confounding the evaluation of the relative importance of each trait in the response of species to grazing and site conditions. We propose that the relative importance of plant size vs seed size in the response to grazing changes with productivity level.     

Vegetation and soil seed bank in a 23-year grazing exclusion chronosequence in a Mediterranean dry grassland

Long-term grazing shaped plant diversity in dry Mediterranean grasslands. Abandonment of grazing affects plant diversity especially in the northern Mediterranean. Considerable efforts are, therefore, under way for grassland conservation and restoration. Yet, we do not know at which temporal scales impacts of grazing abandonment appear and in particular how soil seed banks evolve after longer grazing abandonment. Here, we provide detailed data from one of the very few long-term experiments available. These experiments provide data for up to 23 years (1982–2005) of grazing exclusion built in 1982, 1989, 2000 and 2001. Grazing exclusion decreased species richness, modified vegetation structure and changed soil parameters. Decline in species richness appears in communities that experienced 16 and 23 years of grazing exclusion. Only four to nine plant species of this Mediterranean grassland built persistent soil seed banks appearing after grazing exclusion, compared to 40–50 species in the established vegetation of grazed plots. Hence, similarity between vegetation and soil seed bank decreased with time of grazing exclusion. Even 23 years after abandonment, no woody plants colonised the experiments. We conclude that vegetation will recover fast from grazing abandonment in the short-term. Nevertheless, longer abandonment will impact diversity due to reduced soil seed banks.     

Characteristics of the soil seed bank in Mediterranean temporary ponds and its role in ecosystem dynamics

Species in temporary ponds overcome periods of unfavorable weather conditions by building up a large seed bank. With this strategy, the species diversity of ponds is preserved and information on their dynamics and structure is retained. Little is known about the characteristics, spatial patterns and role in the vegetation dynamics of the soil seed banks of Mediterranean temporary ponds, which are regarded as priority habitats under protection. We studied two sites of western Crete: Omalos, a mountain plateau at 1,060 m a.s.l. and Elafonisos, located near the coast at 60 m a.s.l. The seed bank was surveyed along transects using the germination method. Aboveground vegetation was measured on quadrats along the same transects. Canonical Correspondence Analysis (CCA) was run to define the zonation patterns. High density and species richness were recorded in both sites, with an average of 75,662 seeds/m² found in Omalos and 22,941 seeds/m² in Elafonisos. The community composition of both sites was remarkably different but in both locations perennial species were inconspicuous while annuals, prevailed in the seed banks. An important array of protected or rare species as well as several others which were absent from the vegetation were hosted in the soil seed banks, thereby rendering a low similarity between their composition. Soil seed banks in these ecosystems indicated a spatial heterogeneity that mirrored the aboveground vegetation distribution, sorted along the moisture gradient by their tolerance to flooding. Soil seed banks play a key role in the vegetation recovery after summer drought. The acts of preserving the soil seed bank and ensuring a transient flooding regime are essential to protect the unique vegetation communities of Mediterranean temporary ponds.     

Long‐term seed bank dynamics in a temperate forest under conversion from coppice‐with‐standards to high forest management

Questions: How do changes in forest management, i.e. in disturbance type and frequency, influence species diversity, abundance and composition of the seed bank? How does the relationship between seed bank and vegetation change? What are the implications for seed bank dynamics? Location: An ancient Quercus petraea — Carpinus betulus forest in conversion from coppice‐with‐standards to regular Quercus high forest near Montargis, France. Methods: Seed bank and vegetation were sampled in six replicated stand types, forming a chronosequence along the conversion pathway. The stand types represented mid‐successional stages of stands in transition from coppice‐with‐standards (to high forest (16 plots) and early‐ and mid‐successional high forest stands (32 plots). Results: Seed bank density and species richness decreased with time since last disturbance. Adjusting for seed density effects obscured species richness differences between stand types, but species of later seres were nested subsets of earlier seres, implying concomitant shifts in species richness and composition with time since disturbance. Later seres were characterized by species with low seed weight and high seed longevity. Seed banks of early seres were more similar to vegetation than to later seres. Conclusions: Abandonment of the coppice‐with‐standards regime altered the seed bank characteristics, as well as its relationship with vegetation. Longer management cycles under high forest yield impoverished seed banks. For their persistence, seed bank species will increasingly rely on management of permanently open areas in the forest landscape. Thus, revegetation at the beginning of new high‐forest cycles may increasingly depend on inflow from seed sources.     

Effects of the litter layer of Pteridium aquilinum on seed banks under experimental restoration

Questions: Does the litter layer of Pteridium aquilinum (bracken) act as a barrier to certain species in the seed bank? Does bracken control/restoration treatment affect seed transfer through the litter layer? Location: Five experiments at three sites across the UK covering two major vegetation types; acid‐grassland and heath‐land. Methods: At each experiment a range of bracken control and vegetation restoration treatments were applied for about ten years. The seed bank was sampled in both the bracken litter and the soil. The cover (%) of each species in the vegetation and the bracken litter abundance (cover and depth) was also estimated. Results: The bracken litter layer acts as an inert barrier as it contained a large proportion of seeds available in the litter‐soil profile (38%– 67% of the total). Bracken litter depth and cover also influenced significantly the seed bank composition in both the bracken litter and the soil. These effects were site‐specific, and species‐specific. The application of treatments changed significantly the balance between seed inputs and outputs in the bracken litter layer for some species. This was either a positive or negative response relative to the untreated control plots. Conclusion: For heathland and acid‐grassland restoration, the bracken litter layer may be an important seed source, but it must be disturbed particularly before seed addition.     

Red crabs in rainforest on Christmas Island,Indian Ocean: No effect on the soil seed bank

Red land crabs (Gecarcoidea natalis) are both abundant and widespread in intact rainforest on Christmas Island, Indian Ocean, occurring at densities of ~ 1 crab m^–2. We used an on-going exclusion experiment to test the hypothesis that through their activities as seed predators and soil disturbers, these omnivores are important determinants of the density and relative species abundance of seeds in the soil seed bank of undisturbed primary rainforest. After 6.5 y of continuous crab exclusion, there was no significant difference in the density of seeds in the top 3 cm of soil between the control (3671 ± 517 seeds/0.19 m²) and exclusion plots (3285 ± 801 seeds/0.19 m²), nor was there any significant treatment difference in relative species composition. There were also no significant treatment differences when Muntingia calabura, which accounted for 91.9% of all seeds in the seed bank, was excluded from the analyses. We attribute the lack of a significant impact of red crabs to their probable inability to handle the very small seeds which occurred in the seed bank, and the low level of soil disturbance at the study site. We conclude that the observed impact of red crabs on the abundance and diversity of successional species in natural light gaps on Christmas Island is due to their impact on germinating seedlings alone, rather than any additional impact on the soil seed bank.     

Hidden biodiversity in the Arctic – a study of soil seed banks at Disko Island,Qeqertarsuaq, West Greenland

Seed dispersal is a key process in plant community dynamics, and soil seed banks represent seed dispersal in time rather than in space. Despite their potential importance, seed bank dynamics in the Arctic are poorly understood. We investigated soil seed banks and corresponding plant community composition in three contrasting vegetation types in West Greenland, viz. dwarf shrub heaths, herb slopes and fell‐fields. Through germination testing, 31 species were documented in soil seed banks. All of these were herbaceous, while no dwarf‐shrub species, which represents the dominating growth form in the above‐ground vegetation, were emerging from the seed bank. Consequently, across vegetation types, the lowest similarity between seed bank and above‐ground vegetation was found in dwarf shrub heath. Nine plant species were exclusively found in seed bank, all of which were non‐clonal forbs. Seed bank size (total number of seeds) and species richness seemed to increase with the level of natural disturbance. Additionally, we examined the effect of different experimental light and temperature conditions on the quantity and diversity of germinating seeds. The difference in diversity in vegetation and seed bank at the species level will impact population dynamics, regeneration of vegetation after disturbances and its potential to respond to climate change.     

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.