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.     

Temporal effects of agri-environment schemes on ditch bank plant species

Many of the agri-environment schemes (AES) implemented in the Western Peat District of the Netherlands have as their objective the conservation of the diversity of ditch bank plants. We investigated the effects of AES on ditch bank species in this area, using a dataset collected by 377 farmers who managed and monitored ditch banks during a 10-year period. We found that species richness has increased minimally over the last 10 years in ditch banks. Yet, we found no differences in increases in time between ditch banks with and without AES. In both ditch bank types plant species composition changed to species with higher nitrogen tolerance. Furthermore, species that disperse over long distances by water increased, whereas species with no capacity to disperse over long distances declined in both ditch bank types. This indicates that changes in vegetation composition in ditch banks are affected by other factors than AES.     

Management history affects grassland seed bank build-up

Disturbance in the form of different management regimes affects established vegetation, but how the same management affects the corresponding seed banks is poorly understood. We used the seedling emergence method to investigate how present and previous management intensity impacts the dynamics of established vegetation and corresponding seed bank in six semi-natural grasslands (three pastures and three road verges) in W Norway. The increased management intensity reduced seed bank species richness but increased seedling density and the fraction of species with a persistent seed bank. Higher intensity also increased the components’ floristic similarity, probably through formation of gaps where seeds may germinate. Moreover, the seed bank responded in parallel with the established vegetation to underlying environmental variables as well as to management intensity. Management intensity hence impacted directly on many aspects of seed bank—established vegetation relationships, and controlled established vegetation partly through seed bank dynamics involving both temporal and spatial dispersal.     

Seed bank,seed dispersal and vegetation cover: Colonization along a newly‐created river channel

Question : What is the relative importance of the initial seed bank and subsequent seed dispersal for floristic composition of bank vegetation two years after creation of a newly‐cut reach of a river channel? Location : River Cole, West Midlands, United Kingdom. Methods : We took bank and bed sediment samples from a 0.5‐km reach of a new river channel cut into intact flood‐plain. After river diversion, seed samples deposited on artificial turf mats placed on the river banks and flood‐plain edge were taken in summer and winter 2002 and 2003. Seed rain samples from funnel traps were taken during summer 2002 and 2003. We undertook greenhouse germination trials to assess viable seed species within these samples. In summer 2004, we surveyed river bank vegetation. Agglomerative cluster analysis was used to investigate floristic similarity between seed bank, seed rain, seed deposition samples and final bank vegetation cover. DCA was used to explore contrasts between the samples and to assess whether these reflected interpretable environmental gradients. Results : Seed rain samples contained a small subset of species in the summer depositional samples. 38 species were found within the final vegetation, the seed bank, and at least one of the four sets of depositional samples; a further 30 species not present in the seed‐bank samples were present in at least one of the four sets of depositional samples and the final vegetation. Floristic composition of the vegetation was most similar to the depositional samples from winter 2002 and 2003 and summer 2003. DCA axis 1 reflected a time sequence from seed‐bank samples through depositional samples to the final vegetation. Conclusions : Newly cut river banks were colonized rapidly. Seed remobilization and hydrochorous transport from the upstream catchment are important for colonization. Species richness was highest in samples deposited during winter when high river flows can remobilize and transport viable seeds from upstream. This process would also have enhanced the species richness of seed production along the banks during the second summer (2003).     

Influence of fire on critically endangered Swartland Shale Renosterveld in the Cape Floristic Region

Questions

The degree to which renosterveld shrublands are fire‐dependent is currently unclear. To address this issue, the following questions were asked: (1) does smoke stimulate germination of soil‐stored seeds in renosterveld; (2) does recently‐burned renosterveld display changed composition and higher diversity than unburned vegetation; and (3) how do the species compositions of renosterveld soil seed banks and standing vegetation compare?

Location

Swartland, Cape Floristic Region, South Africa.

Methods

Soil seed bank samples from a north‐ and south‐facing slope were smoke‐treated and germinated to test for smoke‐stimulated germination. Burned standing vegetation was surveyed 16 months post‐fire, as was unburned vegetation on the same slopes. Seed bank species richness and density were compared between smoke‐treated and untreated samples within and between slopes. Burned and unburned standing vegetation were compared within and between slopes in terms of species richness, abundance and aerial cover. Compositional similarity of the seed banks and standing vegetation was assessed.

Results

Seed banks were dominated by annuals and graminoids. Smoke treatment had no effect, except for driving significantly higher species richness and seedling density in south‐facing slope perennial shrubs. Species richness and seedling density were significantly higher in seed banks on the south‐facing slope compared to the north‐facing slope. Burned standing vegetation exhibited significantly higher diversity than unburned vegetation. Annuals and graminoids displayed significantly higher species richness and aerial cover in burned renosterveld. The north‐facing slope contained less than half the number of species/m² compared to the south‐facing slope. The seed banks and standing vegetation showed low to intermediate similarity (Sørensen = 31%–53%), but grouped close together on an NMDS plot, suggesting intermediate similarity overall.

Conclusions

Elevated germination of perennial shrubs in smoke‐treated seed bank samples and increased diversity of post‐fire standing vegetation suggest the renosterveld in this study shows elements of a fire‐driven system. Certain species only recruited in burned sites, suggesting fire‐stimulated germination. Aspect had a major influence on plant community composition, with the mesic south‐facing slope being more diverse than the xeric north‐facing slope. The similarity between the seed banks and standing vegetation was higher than previously shown for renosterveld, and appears to be higher than for fynbos.     

Influence of Grazing on Soil Seed Banks Determines the Restoration Potential of Aboveground Vegetation in a Semi‐arid Savanna of Ethiopia

Species composition, number of emerging seedlings, species diversity and functional group of the soil seed banks, and the influence of grazing on the similarity between the soil seed banks and aboveground vegetation, were studied in 2008 and 2009 in a semi‐arid savanna of Ethiopia. We tested whether the availability of persistent seeds in the soil could drive the transition from a degraded system under heavy grazing to healthy vegetation with ample perennial grasses. A total of 77 species emerged from the soil seed bank samples: 21 annual grasses, 12 perennial grasses, 4 herbaceous legumes, 39 forbs, and 1 woody species. Perennial grass species dominated the lightly grazed sites, whereas the heavily grazed sites were dominated by annual forbs. Heavy grazing reduced the number of seeds that can germinate in the seed bank. Species richness in the seed bank was, however, not affected by grazing. With increasing soil depth, the seed density and its species richness declined. There was a higher similarity in species composition between the soil seed bank and aboveground vegetation at the lightly grazed sites compared with the heavily grazed sites. The mean similarity between the seed banks and aboveground vegetation was relatively low, indicating the effect of heavy grazing. Moreover, seeds of perennial grasses were less abundant in the soil seed banks under heavy grazing. We concluded that restoration of grass and woody species from the soil seed banks in the heavily grazed areas could not be successful in semi‐arid savannas of Ethiopia.     

Impact of invasions by alien plants on soil seed bank communities: Emerging patterns

Much of our current understanding of the impact of invasive species on plant communities is based on patterns occurring in the above-ground vegetation, while only few studies have examined changes in soil seed banks associated with plant invasions, despite their important role as determinants of vegetation dynamics. Here, we reviewed the literature on the impact of plant invasions on the seed bank and we provide a quantitative synthesis using a meta-analysis approach. Specifically, (1) we quantified the impact of 18 invasive alien plants on (i) species richness and (ii) density of the seed banks of invaded communities, based on 58 pair-wise invaded-uninvaded comparisons (cases); we identified (2) the invasive taxa that are responsible for the largest changes in the seed bank; and (3) the habitats where substantial changes occur. Our study showed three major findings: (1) species richness (68% of cases) and density (58% of cases) were significantly lower in native seed banks invaded by alien plants; (2) species richness and density of native and alien species were remarkably lower in seed banks invaded by large, perennial herbs compared to uninvaded sites; and (3) invaded seed banks were often associated with a larger richness and/or abundance of alien species. This study indicates a need for additional seed bank data in invasion ecology to characterize species-specific and habitat-specific impacts of plant invasions, and to determine whether changes in the seed banks of native and alien species are a symptom of environmental degradation prior to a plant invasion or whether they are its direct result. The findings of this study help improve our capacity to predict the long-term implications of plant invasions, including limitations in the recruitment of native species from the seed bank and the potential for secondary invasions by seeds of other alien species.     

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.     

Small seed bank in grasslands and tree plantations in former grassland sites in the South Brazilian highlands

The soil seed bank can be an important source for vegetation regeneration, and data on the similarity between aboveground vegetation and the seed bank can provide information about successional pathways after disturbances or land-use change. We conducted this study in natural grasslands in the subtropical highland region in southern Brazil. We evaluated the effect of silviculture on richness, density, and composition of the seed bank at former grassland sites converted to pine plantations 25 years ago. We worked at six grassland sites and three pine plantation sites and used the seedling emergence method. Seed bank density and richness in grasslands were lower than those reported in similar environments in other regions. Species richness and density varied considerably within each vegetation type; therefore, richness and density were not statistically significant, while composition varied among vegetation types. In terms of species, the pine plantation seed bank was a small subset of the grassland seed bank. Seeds of typical grassland species were missing in the pine plantation, but also had only low abundances in the grassland, and similarity of seed bank and vegetation were low (less than 20%). The low seed density found in this study, including in grasslands areas, indicates that regeneration of species from the soil seed bank likely is of a limited role for the maintenance of plant populations after disturbances in this system. Our data further suggest that natural regeneration after tree planting in grasslands is reduced due to seed limitation.     

Seed banks are biodiversity reservoirs: species–area relationships above versus below ground

Soil seed banks offer plants the possibility to disperse through time. This has implications for population and community dynamics, as recognised by ecological and evolutionary theory. In contrast, the conservation and restoration literature often find seed banks to be depauperate, weedy and without much conservation value or restoration potential. One explanation for these contrasting views might lie in a systematic bias in the sampling of seed banks versus established plant communities. We use the species–area relationship as a tool to assess and compare the per‐area species richness and spatial structuring of the diversity of the established plant community versus soil seed banks. To allow this direct comparison we extensively survey the species–area relationship of the vegetation and underlying seed bank of a grassland community across twelve sites spanning regional bioclimatic gradients. We also compile a global dataset of established vegetation and seed banks from published sources. We find that seed banks have consistently higher intercepts and slopes of the relationship, and hence higher diversity at any given spatial scale, than the vegetation both in the field and literature study. This is consistent across habitat types, climate gradients, and biomes. Similarity indices are commonly used to compare vegetation and seed bank, and we find that sampling effort (% of the vegetation area sampled for seed bank) was the strongest predictor of vegetation–seed bank similarity for both the Sørensen (R² = 0.70) and the Raup–Crick (R² = 0.25) index. Our study suggests that the perception that seed banks are intrinsically less diverse than established plant communities has been based more on inadequate sampling than on biological reality. Across a range of ecosystems and climatic settings, we find high diversity in seed banks relative to the established community, suggesting potentially important roles of seed banks in population dynamics and diversity maintenance.     

Does invasion by an alien plant species affect the soil seed bank?

Questions: How does invasion affect old‐field seed bank species richness, composition and density? How consistent are these effects across sites? Does the soil seed bank match vegetation structure in old‐fields? Location: Menorca, Balearic Islands, Spain, western Mediterranean basin. Methods: We monitored seed germination in soils from old‐fields that were both uninvaded and invaded (legacy effect) by the annual geophyte Oxalis pes‐caprae. We also added O. pes‐caprae bulbs to uninvaded soils to test O. pes‐caprae interference with seedling emergence (competitive effect). We compared species composition in the seed bank with that of the vegetation. Results: Species richness in the seed bank and in the vegetation was not significantly different between invaded and uninvaded areas. Uninvaded areas did not have larger seed banks than invaded areas. More seedlings, especially of geophytes, emerged when O. pes‐caprae bulbs were added to the soil. Species similarity between invaded and uninvaded areas was higher in the seed bank (74%) than in the vegetation (49%). Differences in species composition were as important as differences among sites. The degree of species similarity between the seed bank and the vegetation was very low (17%). Conclusions: Despite invasion by O. pes‐caprae not affecting species richness, the variation in the seed bank species composition in invaded and uninvaded areas, and the differences between the seed bank and the mature vegetation, highlights that even if the invader could be eradicated the vegetation could not be restored back to the exact composition as found in uninvaded areas.     

Soil seed bank and floristic diversity in a forest‐grassland mosaic in southern Spain

Abstract. Soil seed bank and floristic diversity were studied in a forest of Quercus suber, a forest of Quercus canariensis and a grassland, forming a vegetation mosaic in Los Alcornocales Natural Park, southern Spain. The soil seed bank was estimated by the germination technique. In each community patch, diversity, woody species cover and herbaceous species frequency was measured. Three biodiversity components – species richness, endemism and taxonomic singularity – were considered in the vegetation and the seed bank. Forest patches had a soil seed bank of ca. 11 200–14 100 seed.m^?2 and their composition had low resemblance to (epigeal) vegetation. The grassland patch had a more dense seed bank (ca. 31 800 seed.m^?2) and a higher index of similarity with vegetation, compared with the forests nearby. The complete forest diversity was 71–78 species on 0.1 ha, including 12–15 species found only in the seed bank; the grassland species richness was higher (113 species on 0.1 ha). We discuss the role of soil seed banks in the vegetation dynamics and in the complete plant biodiversity of the mosaic landscape studied.     

荒漠草原土壤种子库对草地管理方式的响应

以宁夏中部不同封育年限(封育1a、3a、5a和7a)、不同放牧方式(中等强度自由放牧、中等强度4区轮牧)、补播改良(2006年补播沙打旺Astragalus adsurgens和紫花苜蓿Alfalfa stiva)及未封育等管理方式下的荒漠草原为研究对象,采用空间梯度代替时间梯度法,于2012年3月下旬用样线法采集土壤样品,采用温室萌发法,统计土壤种子库物种组成和种子数,研究了不同草地管理方式下的种子库与地上植被相似性、多样性等特征。结果表明:1)宁夏荒漠草原土壤种子库中共出现14种植物,分属6科14属,除牛枝子(Lespedeza potanimii)为半灌木外其余均为草本植物。多年生植物占土壤种子库植物总数的65.3%,一年生植物占土壤种子库植物总数的35.7%;多年生植物种子数量随封育年限增加而表现为下降趋势,封育1a和未封育草地最多;2)不同管理方式下土壤种子库和地上植被的共有物种数为2—6种,封育时间延长导致土壤种子库物种与地上植被相似性下降,土壤种子库和地上植被共有物种数有减少趋势,自由放牧降低了土壤种子库和地上植被的共有物种数,补播恢复的草地土壤种子库中未出现补播物种;3)种子库物种多样性与管理方式无明显的相关性;种子库物种多样性指数4区轮牧草地最高,封育7a草地最低,物种丰富度指数封育1a草地最高,均匀度指数自由放牧草地最高,补播草地最低。若荒漠草原仅依靠土壤种子库恢复自然植被,则不建议封育时间过久,需间以适当的干扰(放牧);补播外来种未对荒漠草原土壤种子库产生贡献,反而对乡土种产生了一定限制。     

Soil seed bank dynamics in alpine wetland succession on the Tibetan Plateau

The primary goal was to address several questions with regard to how soil seed banks change in a successional series. How does the composition of the viable seed bank change, and how does the relationship of the soil seed bank and vegetation change with succession? Can the seed bank be regarded as a potential as a source of seeds for wetland restoration? We collected soil seed bank samples and sampled the vegetation in four different successional stages and used the NMDS (nonmetric multidimensional scaling) to evaluate the relationship of species composition between the seed banks and vegetation. The difference of seed density and species richness in different habitats and soil depths also was compared. Viable seeds of half (37) the species in the early-successional stage were found in all the successional stages. Similarity between seed bank and vegetation increased with succession. Both seed density and species richness in the seed bank increased with successional age and decreased with soil depth. The majority of species from the early-successional stage produced long-lived seeds. Seed density and species richness increased with succession, mainly as a result of increasing seed production, and hypotheses predicting decreasing density of buried seeds and species richness were not confirmed. Seed banks play a minor role in contributing to the regeneration of vegetation, and managers cannot rely on soil-stored seed banks for restoration of wetlands.     

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.     

Changes along a disturbance gradient in the density and composition of propagule banks in floodplain aquatic habitats

This study used germination methods to examine the density, species composition and functional composition of propagule banks in a series of riverine wetland aquatic habitats subject to varying degrees of hydrological and management-related disturbance. Under permanent inundation (the conditions prevailing at most sites during the growing season) propagule germination and species richness was low, with floodplain perennials and helophytes particularly affected. Densities of floodplain annuals were largely maintained through continued germination of a few flooding tolerant species. On damp mud (conditions associated with hydrological instability) total seedling number and species richness increased significantly, but species richness of germinating hydrophytes declined. Mean seedling density at 0–0.1m depth was 15450 ± 4400 m–2, reaching a maximum (162 050 m–2) in temporary backwaters. Annual (e.g., Lindernia dubia, Cyperus fuscus) and facultative ruderal species (e.g., Lythrum salicaria and Alisma plantago-aquatica) predominated. Vertical zonation of the propagule bank was weakly developed. The numbers of individuals and species germinating varied significantly between sites. The seasonal, most intensely disturbed sites (temporary backwaters) supported a numerically large, species-rich propagule bank based on floodplain annuals, while the permanent, less disturbed sites (ditches and an oxbow pond) had a small, species-poor propagule bank composed of hydrophytes and helophytes supplemented by allochthonous seed inputs. Sites intermediate on the gradient had a propagule bank dominated by facultative amphibious, ruderal hydrophytes. The composition of the seed bank and the established vegetation was most similar at the heavily disturbed sites where the seed bank was maintained by vigorously fruiting annuals and supplemented by inputs from temporary habitats upstream. At permanent sites much of the propagule bank composition could be accounted for by inputs of floodborne seed from the immediately adjacent floodplain. The established vegetation at such sites appeared to be maintained mainly by vegetative propagation with recruitment from the propagule bank likely only after severe disturbance. The potential contribution of functionally diverse propagule banks to sucessional processes within fluvially dynamic floodplain aquatic habitats is emphasised.     

Spatial relationships between the standing vegetation and the soil seed bank in a fire-prone encroached dehesa in Central Spain

Postfire vegetation regeneration in many fire-prone ecosystems is soil seed bank dependent. Although vegetation and seed bank may be spatially structured, the role of prefire vegetation patterns and fire in determining postfire vegetation patterns is poorly known. Here, we investigated the spatial patterning of species abundance and richness in the vegetation and seed bank of a Mediterranean encroached dehesa in Central Spain. The seed bank was studied with and without a heat shock simulating a spatially homogeneous fire. Semivariograms and cross-semivariograms showed that species richness in the vegetation was aggregated in patches, mainly of herbs, with highest values corresponding to high herb cover and low tree cover. Species richness in the seed bank was also structured in patches, but the spatial pattern was weak. Seedling density of germinates in the seed bank also showed weak spatial pattern. Heating increased overall germination and species richness, and the intensity of the spatial pattern of species richness, particularly of herbaceous species. However, seed bank density patterns disappeared after heat shock because of increased germination of shrubs without spatial pattern. Our results document that the spatial structure of plant richness in the vegetation may persist after fire due to the spatial patterns of herbaceous species in the seed bank, and that postfire species richness patterns can arise independently of fire intensity patterns. However, the spatial structure of the vegetation after fire can be altered by the feedback between shrub encroachment and an eventual fire because of the ubiquitous germination of shrubs.     

Seed bank dynamics in tall‐tussock grasslands along an altitudinal gradient

Abstract. We studied the germinable soil seed bank of tall‐tussock grasslands along an altitudinal gradient in the mountains of central Argentina. We selected 10 sampling plots at three altitudinal levels (1200 m, 1600 m and 2200 m). We assessed the composition of the established vegetation and took ten compound soil samples (0 ‐ 5 cm depth) at each plot in autumn and spring. The soil samples were sieved, chilled, and incubated in a glasshouse to assess the composition of the seed bank. The similarity between the composition of the seed bank flora and that of the established vegetation was low throughout the gradient. Most species did not change their seed bank strategy along the gradient. Seed bank richness and density increased with altitude. Most species had a persistent seed bank at all altitudinal levels, and the proportion of such species increased with altitude. These results suggest that a cold climate directly and/or indirectly favours the formation of seed banks and seed persistence in the soil.     

The relationship between soil seed bank,above‐ground vegetation and disturbance intensity on old‐field successional permanent plots

Questions: How does disturbance and successional age influence richness, size and composition of the soil seed bank? What is the potential contribution of the soil seed bank to the plant community composition on sites differing in their successional age or disturbance intensity? Location: Experimental Botanical Garden of Göttingen University, central Germany. Methods: Above‐ground vegetation and soil seed bank were studied on formerly arable fields in a 36‐year‐old permanent plot study with five disturbance intensities, ranging from yearly ploughing via mowing to long‐term uninterrupted succession. We compared species compositions, seed densities and functional features of the seed bank and above‐ground vegetation by using several methods in parallel. Results: The seed bank was mainly composed of early successional species typical of strongly disturbed habitats. The difference between seed bank composition and above‐ground vegetation decreased with increasing disturbance intensity. The species of greatest quantitative importance in the seed bank was the non‐native forb Solidago canadensis. Conclusions: The ability of a plant community to regenerate from the soil seed bank dramatically decreases with increasing time since abandonment (successional age) and with decreasing disturbance intensity. The present study underlines that plant species typical of grasslands and woodlands are limited by dispersal capacity, owing to low capacity for accumulation of seeds in the soil and the fact that most species do not build up persistent seed banks. Rare and target species were almost absent from the seed bank and will, after local elimination, depend on reintroduction for continuation of their presence.     

Diversity,composition and guild structure relationships between soil-stored seed banks and mature vegetation in alien plant-invaded South African fynbos shrublands

We investigated vegetation-seed bank relationships at three fynbos sites on the Cape Peninsula, South Africa, and the impacts to these sites of invasion by the alien tree Acacia saligna. Soil-stored seed banks in uninvaded fynbos were of a similar density to those previously measured in fynbos (ca. 1100–1500 seeds m^-2) and were dominated by mostly short-lived species. Lack of similarity between mature vegetation and seed banks, suggests that seed banks are poor predictors of mature vegetation composition and structure in fynbos. This lack of correspondence was attributed to the ephemerals (present only in the soil seed bank) and the dominance of serotinous (aerial seed bank) and sprouting (soil seed bank low to absent) species, in mature vegetation. Long-lived seeders were among the 10 most abundant species in the seed banks at all sites and at two sites shrub species contributed more to seed bank richness than any other growth form. Soil-stored seed banks, therefore, boost species richness and diversity both in early post-fire and later seral stages.There was a decline in fynbos species richness, diversity and abundance both in the standing vegetation and seed banks with increasing duration of invasion by the alien tree, Acacia saligna. However, the rate of decline was higher for the vegetation than the seed banks, suggesting that many fynbos species have long-term persistent seed banks. At two sites, there was no obvious shift in community composition associated with Acacia invasion: invaded sites were depauperate versions of the uninvaded site. However, at a third site, the vegetation composition shifted towards a community dominated by bird-dispersed thicket species and its seed bank shifted towards a community dominated by wind-dispersed perennials. Community composition of the soil seed banks under dense, recent Acacia was very similar to that of the corresponding uninvaded fynbos at all sites, indicating that there is good potential to return to species-rich fynbos vegetation after removal of the alien Acacia. Most seed bank species persisted in the soil seed bank of the long-invaded fynbos at low frequency and density, indicating high seed longevity in many species. We suggest that either a thick Acacia litter layer or a deep (>5 cm) burial moderated the fire and ambient temperature effects, preventing these seeds from germinating after fire and thus preventing loss from the seed bank.