THE SEED BANK OF A FRESHWATER TIDAL MARSH

Presence of buried viable seeds at three depths in freshwater marsh soils was determined by observing seedling emergence in the greenhouse. These results were compared with field germination. For the greenhouse study soils were collected in December 1976, and March 1977, from six vegetation types in the Hamilton Marshes near Trenton, New Jersey. Three to five times more seeds and almost three times as many species germinated in the greenhouse than in the field. Of the ten most numerous species in greenhouse samples, 7.2 ± 0.2 SE species were also observed as seedlings at that site in the field. Annuals comprised seven of the ten most numerous species in both the greenhouse and in the field. Estimated seed densities for the top 10 cm of marsh soil ranged from 6,405 to 32,400 seeds m⁻². Germination in soils collected in March was 31% greater than for those collected in December. Decrease in species number with depth was significant for March soils. While seedling numbers also decreased with depth, considerable variability occurred and the differences were not significant. The seed bank profile suggests that viability and/or dormancy are prolonged in these freshwater tidal marsh soils.     

Field fate of Amaranthus patulus seeds subjected to leaf-canopy inhibition of germination

Summary The germination of seeds of Amaranthus patulus Bertol., is known to be sensitive to leaf-transmitted light. Seeds were enclosed in transparent polyester-mesh envelopes and placed horizontally in 10-cm deep soil or on the soil surface, beneath a closed vegetation cover in the field. Changes in the numbers of firm intact seeds and of germinable seeds were traced for up to 3 years by periodical retrievals and germination tests. Rapid loss of germinable seeds, mainly due to germination, was observed in the buried seed population, in which only 20% of seeds maintained their germinability after 1 year, and a negligible number after 3 years. In contrast, the seeds placed on the soil surface maintained germinability relatively well: over 80% of seeds remained germinable after 1 year and a low percentage still preserved their germinability after 3 years. Assuming exponential decay in germinability, the decay rates on and in the soil were calculated from the data of the 1-year experiment to be 0.21 and 0.84 year^-1 respectively. The fate of seeds that were exposed to canopy light on the soil for a month and then buried was shown to be almost the same as that of the seeds which had been continuously in 10-cm deep soil. Correspondingly, the possibility of the induction of secondary (induced) dormancy by exposure to canopy light was excluded in a laboratory experiment, in which it was found that the imbibed seeds suffering leaf-canopy inhibition of germination exuded some diffusible germination inhibitor responsible for apparent dormancy. Estimation of numbers of A. patulus in the seed bank of an early successional field showed that 3,500 seeds/m² remained in the soil to the depth of 10 cm after 3 years' exclusion of the species following the production of 700,000 seeds/m², by a population explosively established after experimental induction of secondary succession.     

Soil seed bank and community dynamics in an annual-dominated Mediterranean salt-marsh

Abstract. The seed bank in the soil and litter of an annual grassland in the upper salt marsh of the Guadalquivir delta (SW Spain) contained on average 49110 seeds/m²; 29 species were represented. Field censuses of the grassland, in two consecutive springs, yielded 7 410 and 9 520 plants/m² respectively. A combined Correspondence Analysis of the seed bank samples and field censuses showed differences in grassland composition between wet and dry years. The environmental changes induced different expressions of the soil seed bank, mediated by demographic processes. The effect of salinity (25 dS/m of NaCl) was studied on intact soil blocks transplanted to a greenhouse. Salinity did not affect the emergence of seedlings, but reduced the growth of the dominant species, Trisetaria panicea. The importance of the role of seed banks in community dynamics and their use for conservation management are discussed.     

RELATIONSHIPS OF SEED BANKS TO PLANT DISTRIBUTION PATTERNS IN A FRESHWATER TIDAL WETLAND

Study of seed banks, field seedling emergence, and survival of macrophytes in four zones (steep bank—SB; gentle bank—GB; midbank—MB; high marsh —HM) along transects perpendicular to a stream channel in a freshwater tidal wetland showed that many species are widely distributed. Of the 35 species in the seed bank, 50% were common to all zones; of the 20 species emerging in the field, 77% were observed in all zones. Density of seeds, seedlings, and mature plants of most species, however, varied significantly with habitat. The seed bank of each zone reflected the dominant vegetation of that zone. Most species, even those with high potential for water dispersal, were not evenly distributed. Reciprocal transplants and survival persistence data of dominants corresponded with their habitat preferences. Seed bank densities differed from zone to zone (SB 1,717 m^-2; GB 1,645; MB 2,730; HM 3,620). In all zones the maximum field seedling density was less than the comparable seed bank one (SB 38% less; GB 33%; MB 46%; and HM 10%). These data, coupled with the higher proportion of the total seed bank and total field seedlings occurring in the HM, suggest that the stream channel sites were more stressful early in the growing season than the HM. Because of differential establishment and survival, importance of a species relative to the rest of the vegetation may change with time and occurrence of a species in the vegetation may greatly outweigh its importance in the seed bank or even the seedling stage. Although seeds of annual species were numerous with seven species making up 85% of the seed bank, annual species comprised only about half of the species recorded in the seed bank of each zone. It is not possible at our present level of understanding of seed banks in the freshwater tidal marsh to predict vegetation change. Various combinations of species attributes contribute to the zonation patterns observed in the freshwater tidal wetland.     

Temporary floating island formation maintains wetland plant species richness: The role of the seed bank

In wetlands, fluctuating water levels create opportunities for recruitment of new individuals from seed banks, and drawdown periods often favor the establishment of species adapted for life in shallow water. In this study, floating island formation functioned similarly to drawdowns in water level by creating patches of sediment that were less inundated relative to the surrounding deep water marsh. The disturbance of floating island formation (i.e., mats of sediment and vegetation rising vertically in the water column) also resulted in reduced cover of the dominant rooted, floating-leaved macrophyte, thereby creating temporary gaps for the establishment of other species. To assess how floating island formation influences species richness and composition of wetland plant assemblages relative to surrounding deep water marsh, field surveys of plant percent cover on and off of islands were conducted over 2 years, along with a controlled greenhouse seed bank experiment in which levels of inundation were manipulated. Five plant species were present in deep water marsh compared to 22 in surrounding on floating islands. Plant assemblages on floating islands consisted primarily of emergent species, while floating-leaved perennials dominated the deep water marsh. Species richness and assemblage composition in the greenhouse seed bank experiment differed among water level treatments in a manner consistent with differences observed in field surveys. Assemblages germinating under minimal inundation treatments were more species rich (3.5–4.3 species per sample) and contained more emergent species (>450 individuals m⁻²) than did those germinating under flooded conditions (2.8–2.9 species per sample and <405 individuals m⁻²). This study, in addition to being the only reported seed bank study of temporary (i.e., seasonal) floating islands, demonstrates that islands altered levels of inundation favoring the germination of more species-rich, emergent wetland plant assemblages. Because these islands persisted long enough for several species to set seed, their formation may be one mechanism by which the seed bank is replenished and populations of otherwise uncommon species are maintained.     

黄土丘陵沟壑区主要物种植冠种子库动态及其生态策略

植冠种子库是植物适应环境并应对外界干扰的种子生态策略之一,研究了黄土丘陵沟壑区12种主要植物植冠种子库动态,结果表明:杠柳不具有植冠种子库,其他11种植物均具有植冠种子库;除了黄刺玫种子在翌年5月达到脱落高峰,其他植物大部分种子在冬季脱落,其中杠柳、达乌里胡枝子、茭蒿、黄柏刺和水栒子的大部分种子脱落集中偏早,铁杆蒿和土庄绣线菊的大部分种子脱落集中偏晚;植冠宿存对大部分植物种子的萌发特性表现为促进作用;但不同植物种子的萌发时滞对植冠宿存响应差异较大;9种植物种子在植冠上宿存至翌年2月底,其种子活力仍能维持达60%以上;该区植物表现出不同的植冠种子库策略,通过不同的方式来减少干扰的威胁,提高成功萌发与更新的几率,它们或具有较大规模的宿存量、或调控种子萌发特性、或提高种子维持活力的百分比。此外,全面了解该区植物形成植冠种子库的机理及对应的生态策略还有待于全面、深入的研究。     

Regeneration of Cyperaceae, with particular reference to seed ecology and seed banks

Cyperaceae (sedges) are an important component of many ecosystems. To understand better their regeneration, we examined seed ecology, including dispersal, seed characteristics, and germination behavior that relate to seed bank development and persistence. We also evaluated sedge seed banks from 104 studies, representing a wide array of habitats. Sedge seed bank development and persistence were associated with germination and dormancy traits, namely: dormancy level, seasonal dormancy patterns, and requirement for light, alternating temperatures, and aerobic conditions. Interplay of traits appears to have resulted in low-risk germination strategies adapted to exploit infrequent occurrence of gaps and facilitate formation of persistent seed banks. A variety of dispersal modes and morphological adaptations occurred, but many species had no apparent specialized structures. The main dispersal vectors were water and then animals. About 216 species, in 21 genera, were recorded in the seed bank survey. High densities (>50,000 m⁻²) occurred occasionally in wet habitats, but generally values were low (<500 m⁻² in 70% of entries). Species richness was also generally low (mean 4.8 species study⁻¹), but ranged from 10 to 33 species in certain wetlands. Our studies showed varied reproductive strategies within habitats, persistence, and ability of many species to colonize disturbed habitats. Overall, seed banks tended to be persistent (>1 year). Maximum longevity ranged between 10 and 295 years, but for certain species viability was lost in <3 years. Seeds of many sedges occurred in deeper soil layers to depths >1 m. Seed production, low in rhizomatous species, ranged between 0 and 345,000 seeds m⁻² year⁻¹. Amphicarpy or pseudo-viviparous plantlets occurred in limited numbers of species. The relation between seed production, seed rain, and seed bank is largely obscure and awaits further investigation. For successful restoration and species conservation projects, seed banks (or a source of seeds) are necessary, combined with suitable germination and establishment conditions. Future seed bank studies are considered.     

Seed Stores for Restoration of Species-Rich Shrubland Vegetation Following Mining in Western Australia

The extreme species richness of native shrubland vegetation (kwongan) near Eneabba, Western Australia, presents a major problem in the restoration of sites following mineral sand mining. Seed sources available for post-mining restoration and those present in the native kwongan vegetation were quantified and compared. Canopy-borne seeds held in persistent woody fruits were the largest seed source of perennial species in the undisturbed native vegetation and also provided the most seeds for restoration. In undisturbed vegetation, the germinable soil seed store (140–174 seeds · m^?2) was only slightly less than the canopy-borne seed store (234–494 seeds · m^?2), but stockpiled topsoil provided only 9% of the germinable seeds applied to the post-mining habitat. The age of stockpiled soil was also important. In the three-year-old stockpiled topsoil, the seed bank was only 10.5 seeds · m^?2 in the surface 2.5 cm, compared to 56.1 to 127.6 seeds · m^?2 in fresh topsoil from undisturbed vegetation sites. In the stockpiled topsoil, most seeds were of annual species and 15–40% of the seeds were of non-native species. In the topsoil from undisturbed vegetation, over 80% of the seeds were of perennial species, and non-native species comprised only 2.7% of the seed bank. Additional seeds of native species were broadcast on restoration areas, and although this represented only 1% of the seed resources applied, the broadcast seed mix was an important resource for increasing post-mining species richness. Knowledge of the life-history characteristics of plant species may relate to seed germination patterns and assist in more accurate restoration where information on germination percentages of all species is not available.     

The dynamics of the soil seed bank after a fire event in a woody savanna in central Brazil

The seed-bank dynamics of cerrado, a savanna-like vegetation type in central Brazil, was monitored for a year after a fire event in the mid-dry season. Fifty paired soil and litter samples were collected 1 day before and 1 day after the fire to record the immediate effects on the seed bank, and thereafter at monthly intervals to investigate the post-fire seed bank dynamics. The samples were hand-sorted and the intact seeds were classified as monocot or dicot and counted. All seeds underwent germination trials in a germination chamber for 1 month. Seeds that did not germinate were checked for the presence and viability of the embryo. The sorted soil samples were placed in a greenhouse for 6 months, and the count of emerging seedlings was added to the number of germinated and dormant seeds from the germination trials to estimate the total number of viable seeds per sample. The fire did not affect the total seed-bank density: 63 ± 8 seeds m^?2 before the fire, and 83 ± 20 seeds m^?2 (mean ± se) immediately after it. Although monocots represented 65 % of the pre-fire seed bank, 1 year after the fire, the monocot seed density did not reach the pre-fire value, whereas the density of dicot seeds increased threefold. After the fire, the viable seed density and species richness, decreased with the onset of the rainy season coinciding with germination in the field. Therefore, post-fire recruitment increases genetic variability and contributes to the persistence of plant populations in cerrado communities.     

Seed dynamics during forest succession in Costa Rica

Soil seed banks and current seed inputs each play a role in tropical succession. We compared the abundance and floristic composition of seeds from these two sources at a Costa Rican site by germinating seeds from the soil, measuring seed inputs for 3 yr, and monitoring the earliest colonists in a forest clearing.There were an estimated 6800 viable seeds/m² in the soil of 3.3-yr-old vegetation, 9500 seeds/m² in 11-yr-old vegetation, and 7000 seeds/m² in a 75-yr-old forest. An estimated 10100 seeds/m² fell on the soil surface of the young successional vegetation during 3 yr and 3700 seeds/m² fell during that same time in the forest.Locally produced seeds accounted for about 75% of the seed input to the soil surface early in succession. Seeds dispersed out of young successional vegetation increased the quantity and species richness of the seed input and storage in an adjacent forest. Much of the species richness of the young successional vegetation resulted from seeds dispersed there from other communities by animals.Deforestation stimulated germination of most seeds in the surface soil of the old forest, including seeds of the dominant canopy tree. The recruitment of seedlings from the soil seed bank numerically overwhelmed that from post-disturbance seed rain and sprouts.We evaluated patterns of soil seed storage during succession and predicted the ability of vegetation of differing ages to respond to disturbance. Immediately after disturbance the number of seeds in the soil plummeted due to mortality, low inputs, and germination. As the vegetation regrew, the soil seed bank increased to a peak after 4 to 7 yr, then gradually decreased to its pre-disturbance size. High-frequency pulses of disturbance should result in reduced species richness, dominance by species with long-lived seeds, and fast recovery by seedling recruitment from the soil seed bank.Journal series number 6459 from the Institute of Food and Agricultural Sciences, University of Florida, Gainesville, Florida 32611, USA.Reprint requests to J. J. E. at Florida.     

RECOLONIZATION OF SMALL DISTURBANCE PATCHES IN A NEW ENGLAND SALT MARSH

Availability of colonizers and edaphic conditions were tested in relation to rates of recolonization of open patches in salt marsh vegetation. The density of buried viable seeds was estimated by counting seedlings in undisturbed vegetation and germinating seeds in the laboratory. A low density of viable seeds (<50 per m²) found in these salt marsh soils indicated the absence of an important viable seed bank in this system. Rates of recolonization in natural open patches were monitored for three years. Vegetative expansion of Spartina alterniflora, at approximately 12 cm per year, accounted for most of the recolonization of open patches, although some colonization of annual Salicornia spp. occurred from seeds. Salinity and sulfide and ammonium concentrations were measured in pore water samples from depths of 2–7 cm and 10–15 cm of soil. Comparison of the concentrations from disturbed and undisturbed plots in the marsh did not show significant differences, indicating that none of the edaphic conditions measured would be more inhibitory to plant growth in the disturbed than the undisturbed plots. Therefore, the rate at which small open patches become recolonized is primarily controlled by proximity of Spartina alterniflora and its capacity for vegetative expansion.     

Dormancy cycling and persistence of seeds in soil of a cold desert halophyte shrub

Background and Aims

Formation of seed banks and dormancy cycling are well known in annual species, but not in woody species. In this study it was hypothesized that the long-lived halophytic cold desert shrub Kalidium gracile has a seed bank and dormancy cycling, which help restrict germination to a favourable time for seedling survival.

Methods

Fresh seeds were buried in November 2009 and exhumed and tested for germination monthly from May 2010 to December 2011 over a range of temperatures and salinities. Germination recovery and viability were determined after exposure to salinity and water stress. Seedling emergence and dynamics of the soil seed bank were investigated in the field.

Key Results

Seeds of K. gracile had a soil seed bank of 7030 seeds m⁻² at the beginning of the growing season. About 72 % of the seeds were depleted from the soil seed bank during a growing season, and only 1·4 % of them gave rise to seedlings that germinated early enough to reach a stage of growth at which they could survive to overwinter. About 28 % of the seeds became part of a persistent soil seed bank. Buried seeds exhibited an annual non-dormancy/conditional dormancy (ND/CD) cycle, and germination varied in sensitivity to salinity during the cycle. Dormancy cycling is coordinated with seasonal environmental conditions in such a way that the seeds germinate in summer, when there is sufficient precipitation for seedling establishment.

Conclusions

Kalidium gracile has three life history traits that help ensure persistence at a site: a polycarpic perennial life cycle, a persistent seed bank and dormancy cycling. The annual ND/CD cycle in seeds of K. gracile contributes to seedling establishment of this species in the unpredictable desert environment and to maintenance of a persistent soil seed bank. This is the first report of a seed dormancy cycle in a cold desert shrub.     

Plant recruitment in the High Arctic: Seed bank and seedling emergence on Svalbard

Abstract. Composition and density of the soil seed banks, together with seedling emergence in the field, were examined on Svalbard. 1213 soil samples were collected from six drymesic habitats in three regions representing various stages of colonization from bare moraines to full vegetation cover and spanning a range of typical nutrient and thermal regimes. Of the 165 vascular plant species native to Svalbard, 72 were present as mature plants at the study sites and of these 70% germinated seed. Proglacial soil had 12 seedlings per m², disturbed Dryas heath 131, intact Dryas heath 91, polar heath 715, thermophilic heath 3113, and a bird cliff 10437 seedlings. Highest seed bank species richness was at the thermophilic heath (26 species). Seedlings of 27 species emerged in the field, with fewer seedlings in disturbed habitats (60 seedlings per m²) than in intact Dryas heath (142), suggesting that an absence of ‘safe sites’ limited seedling establishment in disturbed habitats. Measurement of seedling emergence in the field increased awareness of which species are able to germinate naturally. This may be underestimated by up to 31% if greenhouse trials alone are used, owing partly to unsuitability of greenhouse conditions for germination of some species and also to practical limitations of amount of soil sampled. Most thermophilic species failed to germinate and some species present at several sites only germinated from the thermophilic heath seed bank, suggesting that climate constrains recruitment from seeds in the High Arctic.     

Seed dispersal and germination patternsin a rare Mediterranean island endemic (Anchusa crispa Viv., Boraginaceae)

We analyse and discuss patterns of seed dispersal and germination of a rare endemic plant species, Anchusa crispa Viv. (Boraginaceae) from Corsica and Sardinia. This coastal plant inhabits dunes and back-dunes, and currently numbers only a few thousand individuals which generally occur in isolated populations. This study included experiments conducted in the field in Corsica and also under controlled conditions in the laboratory. Short-distance dispersal of A. crispa is performed by ants, both by myrmecochory and dyszoochory. The invasion of an exotic species of ant, Linepithema humile, could locally modify the dispersal system and possibly the population dynamics of A. crispa. Long-distance dispersal may occur by water transport since seeds can germinate after at least 1 week of immersion in seawater and readily float on the surface. Burial of seeds is favourable for germination, percentage germination being maximised at a depth of 1–2 cm below the soil surface. A. crispa has a seed bank of about ten viable seeds per m², which may contribute to the survival of this species which exists in small populations with a short life span. Due to its seed dispersal and germination patterns, the conservation of this species will necessitate that human disturbance, which can destabilise the surface of the sand is prevented and that new populations are introduced to favourable sites.     

Vertical structure of seed banks and the impact of depth of burial on recruitment in two temporary marshes

The structure of the seed bank (including Chara oospores), in relation to depth within the sediment and disturbance, was studied in two Rhône delta temporary marshes for two years. The seeds of all species were concentrated in the top 2 cm of sediment with very low numbers beeing found below 4 cm. When an exclosure eliminated disturbances of the sediment by animals, the vertical repartition of seeds at site 2 was more pronounced than outside the exclosure.In experiment 1, the emergence capacity of seeds from different depths and buried under layers of sterile equivalent to those in the field was measured. Depending of the species, 22 to 98% of the seeds germinated from unburied seeds in the top 2 cm. Only 1% of the oospores of Chara (from site 2) at 2 to 4 cm depth in the sediment emerged.In experiment 2, surface seed bank samples were placed under 0, 2 or 4 cm sterile sediment depth. The samples contained numerous recent seeds and the emergence percentage reached 41% (for Ruppia maritima). Only the seeds of Zannichellia spp failed to germinate from a depth of 2 cm or more. The emergence percentage from 2 cm depth or more was always lower than at the surface. These experiments showed that both burial and ageing of seeds decrease germination capacity.The majority of the active seeds located at the surface germinate when the marsh is flooded. Seeds located between 2 and 4 cm can be brought back to the surface by disturbances and play the role of a reserve involved in maintenance of populations that go without seed production for one or some years.     

天山中部天山云杉林土壤种子库年际变化

通过定点采样,采用萌发法对天山中部天山云杉(Picea schrenkiana Fisch.et Mey.)近熟林(101-120a)和成熟林(121-160a) 2004-2011年(8a)土壤种子库物种组成、种子密度的年际变化和不同间隔年限土壤种子库物种组成的相似性进行了分析.结果表明:(1)土壤种子库中共萌发鉴定出种子植物87种,隶属29科70属,其中乔木种子植物2种,灌木种子植物2种,草本种子植物83种,土壤种子库中草本植物种子密度远远大于木本植物种子密度;8个采样年份土壤种子库恒有种仅有6种;(2)土壤种子库种子密度及其中天山云杉种子密度存在巨大的年际变动,且不具有同步性;土壤种子库种子密度最大(2009年)值为(953.75±66.12)粒/m2,最小(2008年)值为(186.50±20.37)粒/m2,其中天山云杉种子密度最高(2006年)达到(584.50±53.58)粒/m2,最低(2005年)仅有(0.25±0.26)粒/m2;(3)天山云杉林土壤种子库年际间物种组成的相似性不高,Czekanowski相似系数均值仅为0.344,并随间隔年限的增加呈现减小—增大—减小的变化趋势.天山云杉林土壤种子库物种组成和种子密度稳定性差,年际间相差悬殊,物种组成的相似性不高,种子库中天山云杉种子密度主要受其种子库采样前一年天山云杉结实丰歉的影响,属间断型.土壤种子库年际变化特征可为天山森林的更新恢复和可持续经营提供科学依据.     

Disturbance regimes as determinants of seed banks in coastal dune vegetation of the southeastern Cape

Soil-stored seed banks of grassland, fynbos and thicket, all growing on calcareous dunes and each subject to different disturbance regimes, were examined. Seed banks were determined from counts of germinants from 50 soil cores from each type. Aboveground estimates of plant species cover in 10 1-m² plots were used in determining vegetation/seed bank similarities. There was no evidence for seed bank densities to be markedly higher in the most frequently disturbed community (grassland -4273 seeds/m²) than the least disturbed community (thicket - 3417 seeds/m²). Highest similarity between seed bank and above-ground vegetation composition in terms of species and growth form/life-span classes was recorded for grassland (CC = 50%). Lowest similarity (CC = 13%) was found in the less frequently disturbed thicket where no seeds of climax trees were recorded in the seed bank. A fynbos community on a north-facing (warm, dry) slope had intermediate-sized seed banks (1683 seeds/m²) with intermediate vegetation/seed bank similarity (CC = 46%). However, on the south-facing slope, which has a large post-fire ephemeral herb component, seed banks were larger (4518 seeds/m²) but less similar to above-ground vegetation (CC = 39%o). Ordination (DCA) of vegetation data from the four communities was different from an ordination of their seed bank data. Fynbos shrub species were absent from seed banks of both grassland and thicket, even though secondary succession proceeds from grassland, through fynbos to thicket. Their seed banks appear less persistent than those of European heath or Californian chaparral shrubs.     

Size and longevity of seed banks of alpine gentian (Gentiana nivalis L.)

Summary

The alpine gentian (Gentiana nivalis L.) is a mountain rarity found at only two localities in Britain. It is an annual, establishing anew from seed each year and so the size and persistence of its seed bank is important for survival. Seed bank size was measured in summer, before seeds were shed, by sampling from soils at two sites where the alpine gentian is common. As the seeds do not germinate readily in the laboratory, it was assumed that all apparently healthy seeds extracted from the soils were alive and viable. This assumption was corroborated when 95–97% of seeds buried experimentally for 9–12 years germinated after repeated applications of gibberellic acid solution over a period of 6 months.

Densities of naturally buried alpine gentian seeds at the two sites ranged from 1.3 to 6.8 × 10³ seeds m^-2 and they comprised a major component of the community seed bank, disproportionately greater than the abundance of parent plants in the vegetation. The half-life of experimentally buried seeds was estimated as 15 or 32 years, depending on depth of burial and soil type. The findings explain why alpine gentian numbers can recover quickly after a population crash and emphasise the importance of the seed bank to the species' long-term survival in the montane environment.     

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.     

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.