Snowbeds trapping seed rain—a comparison of methods

The possibility of assessing seed rain by deposits in snowbeds was investigated in the Abisko area in northernmost Swedish Lapland. In late summer the "grey blanket" on the snowbed surface was skimmed off, melted and sieved through a filter paper. The debris contained on average 741 seeds m², making up 6.5% of the total debris dry mass. A total of 11,909 seeds, representing 69 species, were encountered in the study. Phyllodoce coerulea, Carex bigelowii and Juncus trifldus were the most abundant. The efficiency of the snowbeds as diaspore traps was compared with a set of artificial traps. Data from two years were compared. The snowbed proved to be more efficient than artificial seed traps, in particular for trapping seeds of graminoids and herbs. Both methods revealed considerable among-year variation in seed output as a possible result of differences in summer climate. The results also suggest that snowbed can be used for assessing aeolian inorganic deposition, in the present study on average 9.0 g m².     

Seedling recruitment in semi-natural pastures: the effects of disturbance, seed size, phenology and seed bank

We examined recruitment patterns in semi-natural pastures and their relationships to disturbance and species composition at different spatial scales (0.01 m² up to 4 m²) of both the vegetation and the seed bank. Possible associations between seedling recruitment and phenology were also studied. The study was performed in four pastures with different management history. Seedling recruitment was generally enhanced by disturbance, with the greatest effect for small-seeded species that germinate in the autumn. The local species-pool contributed to a large extent to seedling recruitment; 83 % of the recruited species were found in the vegetation, whereas 44 % of the recruited species were found in the seed bank. There were a total of 88 species found in the vegetation at different spatial scales; 61 % were recorded at the smallest spatial scale (0.01 m²). The area sampled at this scale comprised 1.25% of the area examined, indicating a small scale structuring of diversity in the pastures. The species number in the vegetation varied between 7 and 14 for the smallest scale (0.01 m²), and between 23 and 42 for the largest scale (4 m²), in the four pastures. The species number in the seed bank was less variable. Like most studies of perennial grasslands, we found no close correspondence between species distribution in the vegetation and in the seed bank. Two of the pastures had a joint management history and exhibited a close similarity of species in the seed bank, despite that one of the pastures was abandoned already in the beginning of this century.     

Plant species diversity in an old, traditionally managed hay meadow compared to abandoned hay meadows in southwest Norway

A chronosequence, representing a successional series, was used for the comparison of a hay meadow site managed in an old traditional way for at least a hundred years, and hay meadow sites abandoned for about 10, 20 and 30 years, respectively. Old traditional management included grazing early and late in the growing season, mowing in August and light or no fertilizing. The tree cover was the most important factor deciding the composition of vegetation. Time since abandonment was not completely correlated to tree cover, as some plots had a dense canopy and others were situated in the open. The total species number decreased with number of years since abandonment in plots > 0.001 m²and <100 m². The highest species number in 1 m² plots was recorded in the managed site, with 38 species of phanerogams. Fourtyeight % of the indicators of traditional management present in the managed site was recorded in the site which had been abandoned for 30 years. Frequency — log area curves made it possible to group species according to persistence in the sward. As a result, a group of functional indicators of rare hay meadows in the region was distinguished.     

Relationship between seed and clonal growth in the reproduction of Carex rugulosa Kük. in riverside meadows

Carex rugulosa Kük. develops riverside vegetation in brackish marshes along the lower parts of rivers. Because the rhizomatous ramets grow densely (590–950/m²) in its developed population, it is expected that seedlings cannot get enough light to grow if seeds germinate in crowded ramets. We studied the reproductive contribution of seed in a marshy meadow of the Ohashi River, Japan. The number of seeds produced was 6900–14 200/m² in 2002. The number of buried seeds in the following germination season differed among sites from 1190 to 2690/m². No seedlings were observed at plots where the ramets from rhizomes grew densely. In contrast, seedlings appeared in plots where all rhizomatous ramets were artificially cut. The number of seedlings corresponded to 17.5–39.5% of that of buried seeds. All these seedlings were submerged and died when it rained heavily. In the genotype analysis using allozyme detection, one of the phosphoglucoisomerase loci ( Pgi-2 ) indicated a pair of alleles. Among eight plots (each plot was 50 or 60-cm square), four showed an excess of heterozygotes and two showed homozygote domination in the Pgi-2 genotype. These results suggest that: (i) seed germination is suppressed in crowded ramets; (ii) seedling survival is severely reduced by inundation; and (iii) the population is usually maintained by clonal growth. As germination is induced in open areas, it is hypothesized that the main role of seed is recovery after vegetation decline caused by environmental stresses or colonization to other areas without dense vegetation.     

Seed banks in Danish deciduous forests: species composition, seed influx and distribution pattern in soil

Samples of soil from six forest stands of different age and composition were collected, and the seedlings emerging during germination experiments were recorded Total seed bank densities varied between 2230 and 15,630 seeds m⁻² The seed bank size was positively correlated with the yearly seed influx, which constituted from 400 to 2720 seeds m⁻² Juncus effusus dominated the seed banks with generally 2000 to 3300 seeds m⁻², to exceptionally 10820 seeds m⁻² Seeds of Rubus idaeus, Betula pubescens and Carex spp were also abundant in the soil Similar numbers of species were present in the seed banks and vegetation, but only 7-48% were species in common Anemochorous species were more frequent in soil than above-ground, while zoochorous species were rare in soil but abundant in the vegetation A measure of the occurrence of seeds in relation to soil depth was designed Seeds of species with short-term survival in soil (e g Anemone nemorosa, Epilobium angustifolium, Oxalis acetosella and Stellaria holostea) were confined to the top soil, while many well known long-term survivors (e g Carex piluhfera, Poa annua, Rubus idaeus and Stellaria media) were found predominantly deep in the soil The horizontal distribution of seeds of herbaceous species forming short-term seed banks was largely random, while seeds of herbs capable of long-term survival in soil were significantly aggregated Except for one old and species-poor site, the dormant flora indicated generally high levels of disturbance in the past     

Effect of fire on the topsoil seed banks of rehabilitated bauxite mine sites in the jarrah forest of Western Australia

Summary Germinable seed stores of 5- and 8-year-old rehabilitated bauxite mine pits in south-west Western Australia were assessed before and after burning. These seed stores were compared to those of adjacent unmined Jarrah ( Eucalyptus marginata ) forest, to identify at what age fire can be reintroduced, in order to measure restoration success and reduce fire hazard. Soils were sampled in early summer (before fire) and late autumn (after fire). Before fire, the mean topsoil seed bank of 5-year-old sites was 2121 seeds per m² while 8-year-old sites had a mean of 1520 seeds per m². Only the 5-year-old sites were significantly different from the forest mean of 1478 seeds per m² for the same season. After summer burns (and possibly due to seasonal effects) topsoil seed banks of rehabilitated areas (sampled in autumn) decreased by an average of 53 per cent. Topsoil seed banks of 5–8-year-old sites were resistant to lower intensity burns, with 362 seeds per m² of native species surviving mild burns and 108 seeds per m² of native species surviving after an intense summer fire. The topsoil seed reserve of 5–8-year-old rehabilitated areas had a high proportion of annual weed species while the forest sites had high levels of subshrubs and native annuals. Low-intensity burns did not alter the composition of life-forms in the soil seed bank, while intense burns favoured annual weed and shrub species. The results indicate that it is not appropriate to introduce fire to rehabilitated areas before 8 years, due to limited fuel reduction benefits and possible adverse effects on obligate seeding species. The large proportion of weed species in the soil seed bank of young rehabilitated areas is a concern, and remains a major consideration for future disturbance of these areas.     

Small-scale patterns of species richness in Swedish semi-natural grasslands: the effects of community species pools

Temperate semi-natural grasslands are known for their high plant species richness at small spatial scales. We examined the variation in small-scale species richness in a sample of 63 sites from Swedish semi-natural grasslands, located as fragments in the modem landscape dominated by forest and agricultural land. Data were obtained from two spatial scales at each site. 1 dm² and 4 m². Using an analysis based on a Monte Carlo simulation, we found support for the species-pool hypothesis: a high species richness at the I dm- scale was associated with high species richness at the 4 m2 scale. The conclusion from this pattern analysis would, however, be considerably strengthened if we could reduce the likelihood that other mechanisms than sampling from species pools of unequal size influence the pattern of small-scale species richness. Additional analyses were made in order to identify such mechanisms. We examined whether four putative key traits: seed size, seed production, plant size and reproductive allocation were different among species at comparatively species-rich vs species-poor I dm' plots. We found only a little evidence for such differences. There was a weak tendency that species in the plots with high species richness possessed larger (and fewer) seeds than species from species-poor plots. Our results are congruent with the main prediction of the species pool model: variation in small-scale species richness (1 dm²- scale) is basically a result of sampling from unequally sized community species pools (4 m² scale). Variation in species richness between the 4 nr semi-natural grassland "patches" may thus be sought for among mechanisms operating al larger spatial scales than 4 m². We briefly discuss such mechanisms, based on other studies performed in the same study area.     

Regeneration by seeds in alpine meadow and heath vegetation in sub‐arctic Finland

Abstract. This paper compares the regeneration by seeds of heath and meadow and studies relationships between the floristic composition of phases in the regeneration pathway. Seed densities in the seed rain and seed bank as well as the densities of emerged seedlings in gaps and in closed vegetation were greater in the meadow than in the heath. In the heath, environmental constraints hindered seedling emergence almost completely so seeds accumulated in the seed bank. In the meadow, the decrease in the seed bank was due to high seedling emergence. Within both plant communities, seedling emergence in gaps and in closed vegetation was comparable. In the meadow, the seed rain and seedling emergence in gaps, as well as the seed bank and seedling emergence in gaps were positively correlated. Differences in seed and adult plant sizes were reasons for the low correlation between the standing vegetation and the other phases. In DCA ordination the first axis separated the phase of seedling emergence in closed vegetation and seed bank. The second axis separated the standing vegetation from the other phases. The structure of the seed rain was more heterogeneous than that of other phases. In the heath, the standing vegetation and the seed rain were positively correlated. The ordination of these phases reflected the patchiness of standing vegetation and the ability of the diaspores of Betula nana to disperse over long distances.     

Functional Plant Traits and Species Assemblage in Pyrenean Snowbeds

In mid-latitude mountains, snowbeds often consist of small, scattered alpine belt units that host many plants of high biogeographic interest. Because most snowbed species are weak competitors, it is important to study the dissemination and persistence of their seeds to better understand their population dynamics. This study analyzed the snowbed flora of the Central Pyrenees using 11 morpho-functional traits, mostly related to seed function. The seeds of most plants found in snowbeds are small or very small, they have ovoid to elliptical shapes, and have no attributes related to dispersal. When only snowbed specialists (i.e., with a phytosociological optimum in snowbed habitats) are considered, three strategy groups become apparent: i) annuals or pauciennials producing abundant small seeds prone to accumulate in the soil; ii) chamaephytes or hemicryptophytes that produce anemochorous seeds; and iii) other perennials – mainly hemicryptophytes – with no specific seed traits. In the first two groups, the extant populations are maintained either by permanent soil seed banks or by means of vegetative persistence and dispersal. The lack of specific traits in the third group suggests that these plants could be more sensitive to direct competitive exclusion from non-chionophilous species under a changing climatic scenario in which snowbeds tend to disappear.     

Biogeography of vascular plants on habitat islands, peninsulas and mainlands in an eascentral Swedish agricultural landscape

The increase of island species richness with area can be explained by an increase in habitat diversity or by an equilibrium of species immigration and extinction. We examined vascular plant species richness in 39 sites (24 habitat islands, 7 'habitat peninsulas' and 8 comparable 'mainland' sites). We sampled at three scales: whole sites, meadows within sites and quadrats (4 m × 4 m) within meadows. All sites (10–10⁴ m²) contained natural vegetation within arable fields in eascentral Sweden. There was a strong correlation between species richness and area for whole sites and for meadows There was no correlation, however, between species richness in quadrats and site area. The difference between site and meadow results on one side and quadrat results on the other suggests that species richness increases with whole site area primarily because large sites are more diverse than smaller ones. Speciearea relationships did not differ between islands, peninsula and mainland sites. Thus, patterns of species richness on our sites were more consistent with habitat diversity than an immigratioextinction equilibrium.     

Effect of Bat Exclusion on Patterns of Seed Rain in Tropical Rain Forest in French Guiana

To assess the impact of bats on seed dispersal in a tropical mature forest (Nouragues, French Guiana), we conducted a bat exclusion experiment and tested the hypotheses that an artificial reduction in the abundance of bats would result in: (1) a decrease in seed species diversity, at the community level; and (2) an increase in seed limitation (a failure of seeds to reach all suitable sites for germination) at the species level. Seed rain was sampled in two contiguous forest plots for a total of 120 d, using 49 seed traps (1 m²) arranged in 7 × 7 grids and spaced at 5-m intervals. Using mist nets, bat activity was reduced in one forest plot for a total of 60 nights. Thirty-nine plant species, or species groups, likely to be consumed and dispersed by bats, were collected within a total sample of 50,063 seeds. The overall seed rain was dominated by epiphytic Araceae and Cyclanthaceae (83.3%) and tree species within the genera Cecropia and Ficus (16.0%). Seeds from bat-dispersed shrubs and treelets ( Piper , Solanum , and Vismia ) were relatively rare (0.7%). The bat exclusion resulted in a 30.5 percent reduction in seed species richness and increased seed limitation for most of the species sampled. Seed limitation was caused mainly by a reduced seed rain (seed source limitation) rather than a decrease in seed dispersal uniformity (seed dispersal limitation). Therefore, bat-dispersed plants with low seed production are likely to be particularly affected by a decline in bat abundance, as a result of anthropogenic change.     

Frugivory and seed dispersal by redwings Turdus iliacus in southwest Iceland

We studied consumption of wild fruits by redwings Turdus thacus coburnt at two sites on the southwest coast of Iceland, just prior to the autumn migration During this period the principal study site offers c 800000 fruits ha⁻¹ most of these are of Empetrum nigrum (c 90% of fresh weight), but fruits of Vaccimum uliginosum. Arctostaphylos uva-ursi, Vaccimum myrtillus and Rubus saxatilis are also present Redwings regularly consumed the fruits of all these species except R saxatilis At both study sites E nigrum fruits were the most important component of the redwing diet (70 - 80% of fruits ingested), followed by V uliginosum (c 20%) Neither species was consumed as predicted on the basis either of overall relative abundance of fruits or of relative frequency of occurrence of fruiting plants in two hundred 0 3 m² plots In another forty 0 3 m² plots, the number of E nigrum fruits consumed over a seven-day penod was not significantly correlated with the number of fruits initially present Empetrum nigrum seed width is positively correlated with fruit size, and the mean width of seeds in droppings suggests that redwings prefer large E nigrum fruits (which have a higher pulp-to-seed weight ratio) to small E nigrum fruits Despite the predominance of E nigrum, redwing droppings tend to contain a mix of seeds of different species, the most frequent combination being E nigrum and V uliginosum     

Floristic composition, structure, and dynamics of an upper montane rain forest in Southern Ecuador

Two 1 ha plots of undisturbed upper montane rain forest in southern Ecuador were sampled for all trees with a dbh ≥ 5 cm. An extraordinarily high α-diversity for a forest near treeline is described. The "non-ridge forest" plot at 2900 m elevation has 75 species and 28 families ha^-1 and is believed to represent an advanced stage of succession whereas, the "ridge forest" plot at 2700 m elevation with 90 species and 38 families ha^-1 has a more rapid turn-over rate probably due to a more unstable environment. Downslope forces (soil creep) are discussed as a possible cause for 32–44% of all trees being inclined more than 30° in the moderately steep terrain (average slope 20° in both study plots). The plot of "non-ridge forest" is characterized by a much greater biomass whether expressed as basal area (44 m² versus 15 m²) or stem volume (214 m³ versus 52 m³), while the density is equally high (2310 versus 2090 trees ha^-1) in both plots. Families with Family Importance Value >25 / ha^-1 are Clusiaceae, Cunoniaceae, Melastomataceae, Myrsinaceae, and Ternstroemiaceae.     

Seed bank dynamics in abandoned meadows during a 20-year period in the Białowieża National Park

1 The relationship between size and floristic composition of the seed bank and vegetation dynamics was studied between 1976 and 1996 in 0.75 ha of an abandoned Cirsietum rivularis meadow. The plot was divided into 100-m² (10 × 10 m) quadrats and sampled 5-yearly to map the vegetation and determine the soil seed bank.
2 Densities of seeds in the soil fluctuated as succession proceeded. The initially small seed bank trebled by 15 years after abandonment, before falling, after 20 years, to approximately the same as in the initial stage.
3 The floristic richness of the seed bank decreased during succession, with the number of species falling from 38 to 25. The diversity of life forms, however, increased in later periods, with tall herbs, shrubs and trees appearing after 10 years.
4 Seed bank floristic composition is apparently both a product of the species composition of the current vegetation and a record of the long-term substitution of species. Other factors, including the structure of the vegetation, also influence the accumulation of seeds in the soil.
5 Although changes in number of species show a directional pattern, the seed bank size fluctuated in the course of succession on these fertile wet meadows.     

Phenology of the environmental weed Achillea millefolium (Asteraceae) along altitudinal and disturbance gradients in the Snowy Mountains, Australia

This study examined the phenology of the weed Achillea millefolium over a growing season in the Snowy Mountains. Vegetative and reproductive characteristics of plants in 1 m² quadrats were compared among sites at four different altitudes (medium and high montane, low and high subalpine) and three types of infrastructure (primary road, secondary road and building, total 12 sites). Altitude, infrastructure and time of year did not affect percentage cover of vegetation. Flowering started earlier and lasted longer in the low montane sites compared to high subalpine sites. The type of infrastructure only affected the number of reproductive structures at the peak of flowering, with A. millefolium growing next to buildings having two to three times more inflorescences per m² than along primary and secondary road verges. At the peak for each reproductive stage, there was an average of 1.47 developing inflorescences, 21 inflorescences in bud, 24 inflorescences in flower, 4 inflorescences setting seed, and 3 releasing seed. Based on the maximum number of inflorescences present at any time at each site, there was an average of 36 inflorescences, giving an estimate potential seed production of 51 400 seed per one m² for A. millefolium in the Snowy Mountains. If the climate changes in the Snowy Mountains as predicted, then it is likely that yarrow will produce more inflorescences and seed in the higher altitude sites.     

Relationship between the seed rain and the establishment of vegetation in two areas abandoned after peat harvesting

In this study the number and species composition of diaspores dispersing into two newly abandoned peat harvesting areas in Finland were investigated. In an area abandoned six years earlier a total of 2978 living seeds m⁻², representing 18 species, was captured by using water-filled traps during two summers. In a one-year-old succession area the total number of living seeds m⁻² was 2241, representing 16 plant species. The soil seed banks were found to be empty of viable seeds. In neither area there appeared to be any relation between number of dispersing seeds and of plant individuals of the same species in the pioneer vegetation. It is suggested that unfavourable conditions on the soil surface for seed germination and seedling growth of most dispersed species are majors factor in determining the structure of the established vegetation.     

Soil seed bank dynamics of fire-prone wooded grassland, woodland and dry forest ecosystems in Ethiopia

In order to reveal the role of soil seed banks in vegetation recovery after fire in savanna, the spatial distribution and temporal changes in the soil seed banks of regularly burning savanna in Gambella, western Ethiopia, was studied. The seedling emergence technique was employed to determine the species composition and density of the soil seed bank of six sites ranging in fire severity from wooded grassland with frequent fires over woodland with intermediate fire frequency to forest with absence of fires. Species composition and density of seeds in the soil were compared between seasons, depths and sites with different types of standing vegetation. Fourteen plant species were recorded in the soil seed bank from the grassland and woodland sites and 6 from the dry forests; 60 % of the taxa in the soil seed bank were annuals and 40 % were perennials. The soil seed banks were largely dominated by graminoids and 48–97 % of the soil seed bank in the grasslands and woodlands was of a single grass species, Hyparrhenia confinis , which was absent from the dry forests. The soil seed pools ranged from less than 100 to 4700 seeds per m² depending upon the season. The soil seed bank of graminoids was nearly empty after the onset of the rainy season whereas seeds of broadleaved herbs and woody species able to germinate were still found after this time. Floristic composition, representation of life forms and density of seeds in soil did not correspond closely with that of the standing vegetation, but within graminoids there was a strong similarity between the soil seed bank and the standing vegetation. The current fire regime of Ethiopian savanna woodlands appears to maintain the dominance of graminoids over broadleaved herbs and woody plants both as seeds in the soil and in the standing vegetation.     

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.     

Fruit and seed ecology of wild robusta coffee (Coffea canephora Froehner) in Kibale National Park, Uganda

Coffee fruit production, frugivorous activities and seed longevity were investigated during two seasons. The average densities of fruiting coffee trees during the first sampling period ranged from four to seven per 25 m² and during the second sampling period, four fruiting trees per 25 m² were estimated. Fruiting coffee trees were significantly less than the non-fruiting trees ( P < 0.05, t -test). Periods of maximum coffee fruit fall coincided with those of lowest rainfall. Coffee fruit yield per tree from ground collections was 7–40 m⁻² in 1992 and 16–38 m⁻² in 1993/1994. Split coffee berries ranged between 71.7% and 83.6% of all fruits collected from the forest floor in the 1993/94 sampling period. Coffee seeds collected from the forest floor were mostly undamaged. Black and white colobus and redtail monkeys were observed to feed on ripe coffee fruits but did not crush the seeds. Coffee seed viability declined rapidly during storage. Seeds left on the forest floor survived longest, those stored under laboratory conditions lost viability fastest, and those in cold storage showed intermediate longevity.     

An automated greenhouse sand culture system suitable for studies of P nutrition

Abstract. Maintenance of realistically low solution P concentrations under controlled conditions is a major difficulty in studies of P nutrition. In this report, we describe a relatively simple and economical sand culture system capable of sustaining plant growth to maturity under controlled yet realistic P regimes. The system uses Al₂O₃ as a solid-phase P buffer, and modern process control technology to control irrigation and addition of other mineral nutrients. Aspects of the design, use and potential applications of automated solid-phase systems are discussed. The system was used to grow Phaseolus vulgaris to matarity at 0.4 mmol m³, 1.0 mmol m³ and 27 mmol m³ P with and without mycorrhizal inoculation. At flowering, low solution P concentrations were associated with reduced leaf concentrations of P in nonmycorrhizal plants, and reduced leaf concentrations of Ca in both mycorrhizal and nonmycorrhizal plants. Mycorrhizal inoculation increased leaf P, K, Mg and Mn concentrations, but reduced leaf N concentration. Low P regimes reduced final seed yield by diminishing both the number of pods per plant and the number of seeds per pod. Mycorrhizal inoculation significantly enhanced seed yield under low P regimes by increasing seed weight, the number of pods per plant, and the number of seeds per pod.