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.     

Fire,aridity and seed banks. What does seed bank composition reveal about community processes in fire‐prone desert?

Questions: The relationship between fire, aridity and seed banks is poorly understood in plant community ecology. We tested whether there was a close correspondence between the seed bank and standing vegetation composition with time‐since‐fire in a desert. We also examined whether longer‐lived species showed seed limitation relative to more ephemeral species, as this could influence grass‐woody ratios in a major biome. Location: Dune hummock grasslands/shrublands of central Australia. Methods: The effects of time‐since‐fire on floristic and functional group composition were examined by comparing plots unburned since 1984 against plots that had been burned in 2002. Three methods were used to quantify seed abundances: a germination trial using heat and smoke application, a flotation method, and a sieving method. Results: Seed bank densities were very low (<3000 m^?2). Species similarity between the seed bank and standing vegetation was high at sites recently burned (0.86) and low in sites long‐since burned (0.52). The relative abundance of ephemeral species in the seed bank peaked in recently burned plots, but the relative abundance of seeds of woody species did not match the pattern of abundance in the standing vegetation. Remarkably, the dominant perennial grasses and woody species were either absent from the seed bank or present at extremely low abundances. Discussion: Differences in the relative abundance of ephemeral species between standing vegetation and seed bank relate to the post‐fire succession process. The small soil pool of seed from woody species may be explained by allocation to belowground carbohydrate storage over seed production. Field observations suggest, however, that production of strongly dormant seed can be prolific and that high levels of seed predation make this system strongly seed‐limited. The discovery of this seed bank syndrome indicates that shifts in grass‐woody ratios can be driven by the juxtaposition of unpredictable seed rain and fire events in these desert dunes. However, estimates of grass‐woody ratios due to changing fire regimes will be difficult to predict.     

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.     

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.     

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.     

Regeneration of monsoon rain forest in northern Australia: the dormant seed bank

Abstract. As part of a wider study examining regeneration pathways in monsoon rain forest vegetation in northern Australia, the dormant component of the soil seed bank was assessed by storing soil samples for over six dry season months, before watering in shade-house trials. Six soil samples were collected from each of 34 sites broadly representative of the range of regional monsoon rain forest vegetation. Four floristic seed bank groups were derived through TWINSPAN classification. Mean group densities of germinants ranged from 25–144/m². Dormant seed banks were least dense, and most sparsely distributed, in sandy soils. Seed bank samples were dominated by woody pioneer monsoon rain forest species, especially figs; exotic weeds and savanna taxa (e.g. Poaceae) were relatively more common at seasonally dry sites. Dormant seed banks comprised species mostly present in the standing vegetation, although a small number of germinants represented species not growing at half the sites. Regeneration of woody pioneers from dormant seed banks is least likely to be of importance on infertile, seasonally dry sites.     

The Role of Soil Seed Banks in the Rehabilitation of Degraded Hillslopes in Southern Wello,Ethiopia1

The species composition in the soil seed bank of degraded hillslopes in southern Wello, Ethiopia, was assessed using the seedling emergence method and compared with that of the standing vegetation. Surface soils were sampled at 0‐to 5‐cm depth from 49 plots of four physiognomic vegetation classes (hereafter vegetation classes): forests, shrublands, grasslands, and degraded sites. Soils were spread on sterile sand in a glasshouse and watered. Emerging seedlings were recorded for five months until no new seedlings emerged. A total of 3969 seedlings belonging to 71 species and 30 families germinated. The species composition of the seed bank was dominated by 53 herb species (75%) compared to 2 tree species which accounted for only 3 percent of the total number of species. Seedling density differed significantly among vegetation classes and ranged from 391 to 7807 seeds/m². Mean species richness also differed significantly among the vegetation classes. Forty‐two species were found to be common to the seed banks and the standing vegetation; however, correspondence between species numbers and composition of the seed banks and the standing vegetation was poor. Although most of the species that germinated in the seed banks were herbs and grasses, they can develop a vegetative cover and contribute to reduction of soil erosion. Regeneration of the tree species (some of which have seed viability up to four years) however, requires both time and the presence of mature individuals. Together with hillside closure and soil conservation measures (e.g., terracing), planting of native woody seedlings might help to expedite rehabilitation of degraded hillslopes devoid of trees and shrubs.     

Depth distribution and composition of seed‐banks in alien‐invaded and uninvaded fynbos vegetation

South African fynbos vegetation is threatened on a large scale by invasive woody plants. A major task facing nature conservation managers is to restore invaded areas. The aim of this study was to determine the restoration potential of fynbos following dense invasion by the Australian tree Acacia saligna. The impacts of dense invasion on seed‐bank composition and depth distribution were investigated to determine which fynbos guilds and species have the most persistent seed‐banks. Soil samples were excavated at three different depths for invaded and uninvaded vegetation at two sand plain and mountain fynbos sites. Seed‐banks were determined using the seedling emergence approach. Invasion caused a significant reduction in seed‐bank density and richness at all sites. There was a significant, but smaller, reduction in seed‐bank density and richness with soil depth at three sites. Seed‐bank composition and guild structure changed following invasion. Low persistence of long‐lived obligate seeders in sand plain fynbos seed‐banks indicates that this vegetation type will be difficult to restore from the seed‐bank alone following alien clearance. The dominance of short‐lived species, especially graminoids, forbs and ephemeral geophytes, suggests that regenerating vegetation will develop into a herbland rather than a shrubland. It is recommended that seed collecting and sowing form part of the restoration plan for densely invaded sand plain sites. As seed density remained higher towards the soil surface following invasion, there is no general advantage in applying a mechanical soil disturbance treatment. However, if the shallow soil seed‐bank becomes depleted, for example following a hot fire through dense alien slash, a soil disturbance treatment should be given to exhume the deeper viable seed‐bank and promote recruitment.     

Buried germinative seeds in mature beech forests with different herbaceous vegetation and soil types

The seed banks in the soils of seven mature beech forests in southern Sweden were examined using the seedling-emergence method. Seedling emergence in the field was also studied. In the studied forests, covering a wide range of vegetation and soil types, between 1020 and 4500 germinating seeds m⁻² were found in the seed bank. Seed abundance showed no apparent relationship with the type of soil or vegetation at the sites, but the highest number of species in the seed bank was found on the mull sites. The species diversity of germinative seeds increased strongly with increasing soil fertility.
Only a minor part (10–35%) of the species in the germinable part of the seed bank were represented in the vegetation. Soil samples from the oligotrophic sites mainly contained graminoids, notably Carex spp., while herbs dominated the seed banks of the rich mull sites. Seeds of e.g. Stellaria nemorum, Oxalis acetosella, Moehringia trinervia, Viola rivinianalreichenbachiana, Melica uniflora , and Milium effusum were especially abundant in the mull soils. Woody species were infrequent on all sites, and no representatives of the early spring flora were noted in the germination tests.
In the mor and moder soils most seeds were recovered from the mineral soil, and they were believed to originate from early stages in the succession of the forest. Several sites had comparatively large seed banks of species that typically occur in disturbed forests, e.g. Juncus effusus and Rubus idaeus , but very few germinating seeds belonged to species restricted to non-forest habitats. Emerging seedlings in the field were only observed on the mull and moder sites. With few exceptions they belonged to species, which were common both in the seed banks and in the vegetation.     

Soil seed bank in different vegetation types in the Loess Plateau region and its role in vegetation restoration

In the Loess Plateau region, soil erosion is a serious problem. Vegetation restoration is an effective approach to control soil erosion and improve ecosystems. The soil seed bank generally plays an important role in vegetation restoration after disturbance. Thus, we reviewed soil seed bank studies to reveal the soil seed bank characteristics and its role in vegetation restoration in three vegetation types (forest, forest‐steppe, and steppe). We selected 38 seed bank studies and analyzed several seed bank characteristics, such as seed density, species composition, and the relationship between seed size and seed bank. We also assessed the role of the soil seed bank in vegetation restoration. The soil seed bank density ranged from 2,331 ± 1,993 to 6,985 ± 4,047 seeds/m² among the different vegetation types. In the soil seed bank, perennial herbs and grasses accounted for 51.5% of the total species. Native species that were dominant or common in the standing vegetation usually had relatively high seed bank densities. Moreover, species with smaller seeds generally had higher soil seed bank densities. The present study indicates that the soil seed bank plays a significant role in spontaneous vegetation restoration, especially during the early successional stages in abandoned slope farmlands and grazing‐excluded grasslands. However, species with large seeds or transient soil seed banks should be reintroduced through seeding to accelerate target species restoration. More studies on soil seed banks need to be conducted to comprehensively reveal their characteristics.     

Fire severity affects vegetation and seed bank in a wetland

Questions: How does the severity of prescribed fires affect vegetation and seed bank in a wetland? Location: A fire‐prone reed swamp in northern Japan (250 ha, 40°49′N, 141°22′E, <10 m a.s.l.). Methods: Vegetation, biomass and seed bank were monitored for the 2 yr after annual prescribed fires were discontinued. Plant communities were placed into three categories based on fire severity: high (H) – fire consumed litter completely; moderate (M) – fire removed standing litter but left wet fallen litter; and low (L) – fire incompletely removed standing litter and did not remove fallen litter. Soil samples were collected in autumn 2007 and early summer 2008, and germinable seed bank was investigated by greenhouse trials. Results: High fire severity increased diversity in the next growing season by the establishment of short herbs in the standing vegetation. The biomass of forbs and grasses was greater in H where Phragmites australis biomass was reduced. The density of seed bank was >30 000 seeds m^?2 throughout all the treatments. Perennial plants were dominant in the vegetation, while annuals, biennials and rushes were dominant in the seed bank. Small seeds were more abundant in the soil than in the litter. Qualitative and quantitative similarities between seed bank and the vegetation were low, and tended to be higher in H. Conclusions: Fire contributed to the development of diverse standing vegetation via the positive effects on seed bank dynamics, and can be considered a tool to maintain species‐rich marshes.     

Soil seed bank dynamics in post-fire heathland succession in south-eastern Australia

Soil seed banks can exert a strong influence on the path of vegetation succession following fire, with species varying in their capacity to persist in the seed bank over time, leading to changes in seed bank composition and propagules available for post-fire colonisation. This study examined the effect of time since fire on soil seed bank dynamics in a chronosequence of seven sites spanning 26 years in a south-eastern Australian sand heathland. No significant change was evident in the species richness and density of the germinable soil seed bank, but species composition differed significantly among young (0–6 years since fire), intermediate (10–17 years since fire) and old-aged (24–26 years since fire) sites (using presence/absence data). No significant trend was observed in the similarity between the extant vegetation and the soil seed bank with time since fire. A total of 32% of the species recorded in the soil seed bank were not present in the above-ground vegetation at the same site, which suggests that species requiring fire for germination may be present in the seed bank. Most species present in the extant vegetation were not recorded (63%) or were in very low abundances in the soil seed bank (29%). The mode of regeneration appears to be the major determinant of species absence in the soil seed bank, as 66% of species occurring in the extant vegetation but not in the seed bank have the capacity to regenerate by resprouting. This study shows that a major shift in the successional pathway after fire due to altered seed bank composition is unlikely in this vegetation; most species not recorded in the seed bank are either resprouters (obligate or facultative) or serotinous, suggesting that they will readily regenerate following fire. Unless fire frequencies are high and kill fire-sensitive obligate seeders before they reach maturity, the chance that the soil seed bank could substantially alter vegetation composition within the study area after fire is low. However, it is unclear how successional pathways may alter in response to severe fires with the potential to kill both seeders and resprouters.     

Fire severity drives variation in post-fire recruitment and residual seed bank size of <Emphasis Type="Italic">Acacia</Emphasis> species

Very high-severity fires are a component of many fire-prone ecosystems, yet are often viewed as detrimental to vegetation. However, species in such systems are likely to have adapted to persist under a fire regime that includes high-severity fires. We examined how fire severity affects post-fire recruitment and residual seed banks of Acacia species and whether severity may affect plant responses to fire intervals. Nine sites of either high or low burn severity were identified after a large-scale mixed-severity fire in Warrumbungle National Park, south-eastern Australia. Transects were used to sample above-ground woody plant density. Seed bank size was surveyed by soil extraction from two depths and manual searching for seeds. Residual soil seed bank and recruitment were compared across the two burn severities. Acacia seedling density was higher in areas burnt at high severity, indicating that increased severity triggers increased germination from the seed bank. Size of residual seed bank was smaller after high-severity fire, but varied between species, with few Acacia cheelii seeds remaining despite high above-ground abundance. In contrast, A. penninervis retained a small residual seed bank. There was little evidence of negative effects on populations of Acacia species after high-severity burns. However, we found that high fire severity may impact on the ability of a species to persist in response to a subsequent short fire interval. Fire management for maintaining biodiversity needs to consider other key aspects of the fire regime, including severity and season, rather than focusing solely on fire frequency.     

Effects of seed burial and fire on seedling and sapling recruitment, survival and growth of African savanna woody plant species

Seed predation and seedling mortality can act as strong demographic “bottlenecks” to sapling recruitment in African savanna woodlands. Fire also limits tree recruitment from saplings by suppressing their growth. I conducted field experiments with 13 woody plant species to assess the effects of seed burial on seedling emergence rates and effects of fire on seedling and sapling survival and growth rates over a period of 8 years at a savanna plot in central Zambia, southern Africa. Seed removal rates by small rodents varied among years and buried seeds had significantly higher emergence rates than seeds exposed to predators in most but not all the species. Annual burning reduced sapling growth in some species but in other species saplings experienced successive shoot die back even in the absence of fire. The findings show that for some woody species, seed predation is an important constraint to seedling recruitment but not for others and annual fires are important hindrances to demography and growth for some species but not others. Thus, demographic “bottlenecks” occur at different life history stages in different savanna woody species and these have the potential to alter woody tree competitive relationships and ultimately savanna structure.     

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.     

The effects of three years of fencing enclosure on soil seed banks and the relationship with above-ground vegetation of degraded alpine grasslands of the Tibetan plateau

Background and Aims

Fenced enclosures have become an important method for re-establishing degraded grassland on the Tibetan plateau, and examination of soil seed banks may provide useful insights to understanding the effects and mechanisms of fencing enclosure on the restoration.

Methods

An investigation was conducted into the effects of enclosure for 3 years on the soil seed banks of degraded natural and sown grasslands at eight study sites. Species composition, soil seed bank density and the relationships with above-ground vegetation were analysed based on 4800 soil core samples and counting of seeds extracted from soil samples.

Results

After 3 years of fencing enclosure, soil seed banks differed between the different communities across the study sites. Species numbers and seed density in soil seed banks decreased from natural grassland to sown grassland, with most seeds occurring in the upper 5 cm soil layer. In these alpine grasslands, relatively few species produced high numbers of seeds, although their occurrence across the eight study sites was variable. Total vegetation cover increased with enclosure due to the colonization capacity of the vegetation rather than soil seed banks.

Conclusions

This study provided evidence that soil seed banks do not play an important role in the restoration of degraded alpine grassland when using fencing enclosures. Further studies conducted over longer periods are needed to address this subject.     

Germinable soil seed banks in a tropical savanna: seasonal dynamics and effects of fire.

Abstract The germinable soil seed bank of a tropical eucalypt savanna of north‐eastern Australia was found to be dominated by grasses and forbs, with seed bank density ranging from 58 to 792 seeds per square metre, from a total of 53 species. Late dry season fires and the fire‐related cues, heat shock and smoke, broke the seed dormancy of a range of tropical savanna species. Heat shock promoted the germination of the species groups natives, exotics, subshrubs, ephemeral and twining perennial forbs, and the common species Indigofera hirsuta, Pycnospora lutescens and Triumfetta rhomboidea. Exposure to smoke at ambient temperature promoted germination from the soil seed bank of the species groups combined natives, upright perennial forbs and grasses, as well as the common grasses Digitaria breviglumis and Heteropogon triticeus. The germinable soil seed bank varied seasonally, increasing from the mid wet season (February) and early dry season (May) to a maximum in the late dry season (October). The effect of recent fire history on soil seed bank dynamics was limited to the immediate release of some seed from dormancy; a reduction in seed densities of subshrubs and monocots, other than grasses, in recently burnt savanna; and enhanced seed density of the ephemeral I. hirsuta in the year following fire. The seed banks of most savanna species were replenished in the year following burning.     

河水漫溢对塔里木河下游荒漠河岸林地表植被与土壤种子库的影响

采用种子萌发法,研究了河水漫溢对塔里木河下游荒漠河岸林地表植被与土壤种子库的影响.结果表明：塔里木河下游漫溢区地表植被分属8科13属14种,非漫溢区为10科21属26种植物;与非漫溢区相比,漫溢区地表植被中出现了一些浅根系和喜湿的草本植物;漫溢区单位面积物种数、植被盖度、植株密度、物种多样性指数和丰富度指数均比非漫溢区有明显增加.漫溢区土壤种子库中有物种19种,比非漫溢区增加了5种;漫溢区土壤种子库总密度比非漫溢区增加了3.94倍;与非漫溢区相比,漫溢区1年生草本植物种子的比例增加了23.07%,而灌木植物种子比例减少了20.99%;多年生草本的变化则不明显;河水漫溢提高了土壤种子库的生物多样性.漫溢区和非漫溢区土壤种子库与地表植被的共有物种分别为18和9种,土壤种子库与地表植被的相似性系数分别为0.842和 0.667.     

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.     

The Role of Soil Seed Banks in Natural Restoration of the Degraded Hunshandak Sandlands, Northern China

The density of seeds in soil seed banks and the species composition of both seed banks and aboveground vegetation were examined in naturally restored sites (NRS) and aerially seeded sites (ASS) in the Hunshandak sandlands of northern China. Five sites were naturally restored 1, 2, 4, 8, and 15 years ago and four sites were aerially seeded 1, 2, 5, and 7 years ago. In total, 36 species were recorded in the seed bank and 41 species in the aboveground vegetation for all NRS, whereas the numbers were 17 and 19, respectively, for ASS, indicating that the NRS can support higher diversity of species than the ASS. During the initial 2 years of restoration, introduced alien shrubs by aerial seeding dominated the vegetation of ASS, although there were indigenous pioneer species in the seed bank which failed to establish in the community. In contrast, indigenous species were dominant components in both the seed bank and the vegetation at the NRS. These findings suggest that the establishment of introduced species might have restricted the germination of certain indigenous pioneer species. Seed bank density of NRS significantly increased with time from 459 ± 76 seeds m⁻² at NRS2 to 3,351 ± 694 seeds m⁻² at NRS15, showing that the seed bank in degraded grassland is large enough to allow natural restoration. It is not always necessary to actively introduce seeds to enhance vegetation diversity.