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.     

Ecological aspects of soil seed-banks in relation to bauxite mining. II. Twelve year old rehabilitated mines

Abstract Germinable seed stores were estimated for 12–13 year old rehabilitation sites in the jarrah forest over two seasons (autumn and spring). Collected soils were subjected to combinations of smoking and heating treatments before the germination procedure was commenced. The mean topsoil seed reserve to a depth of 10 cm was 1938 seeds m^?2. Of this total reserve, more than 80% was found in the upper 5 cm of soil. The topsoil seed reserve of these rehabilitation areas was almost seven times that of the adjacent native jarrah forest (292 seeds m^?2; Ward et al. 1997). There was a seasonal effect with autumn-collected soils having significantly more germinable seeds (2723 seeds m^?2) than soils collected in spring (1153 seeds m^?2). More than half (53%) of the topsoil seed reserve in rehabilitated areas was composed of annual weed species, dominated by Aira caryophyllea, Centaurium erythraea and the native Levenhookia pusilla. Of the total of 70 species identified, 13 species showed significantly higher germination in smoked trays while 11 species exhibited significantly higher germination in heated trays. Species responding to the smoking treatment tended to be annuals while those responding to the heating treatment were typically legume shrub species. Examination of the topsoil seed reserve and the vegetation present in these areas showed that while the species composition was similar between the seed store and the vegetation, there was a large difference in densities, with species occurring at much higher densities in the topsoil than in the vegetation. However, the rankings of species were significantly correlated between the topsoil seed reserve and the vegetation present at the site. The implications of these results to prescribed burning of these rehabilitated areas is discussed.     

Can Managers Bank on Seed Banks When Restoring Pinus taeda L. Plantations in Southwest Georgia?

In the southeastern United States, private forestland managers are under increased pressure to provide wildlife habitat and biodiversity in addition to commercial products such as timber. This study used a stand classification scheme based on vegetation biodiversity from Hedman et al. to compare seed bank composition of benchmark (BM) and nonbenchmark (NBM) Loblolly pine ( Pinus taeda ) stands. In the Hedman et al. study, BM stands contained species associated with Longleaf pine ( P. palustris )/Wiregrass ( Aristida stricta ) communities, whereas NBM stands contained species associated with disturbed sites. The current vegetation of the BM and NBM stands had an average cover of 7.9%/m² and an average richness of 11 species/m². The intent for this study was to assist in understanding the potential role of the seed bank during stand development and restoration. We collected seed bank samples from six pine plantations in the winter of 2006. Seed bank samples yielded 2,885 germinants representing 56 unique species but only 4 were found in both current herbaceous vegetation plots and seed bank. The seed bank was dominated by native dicots. In BM stands, 76% of species were native, whereas in NBM stands, 69% were native. Seed bank samples from NBM stands had greater species richness ( p = 0.03) and total germinants ( p = 0.03) than BM stands. Although the seed bank in all stands was dominated by native species, our data suggest that the seed bank under P. taeda stands should not be viewed as the sole source of native species for most restoration goals.     

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.     

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.     

Two ways of trapping seeds in alpine environments, Lapland, Sweden

Seed dispersal in two habitats was investigated in the mid-alpine Latnjajaure valley, in northernmost Swedish Lapland. The seed rain size was measured using artificial seed traps and natural snowbed at a heath and a meadow site, c. 1000 m a.s.l. The average seed rain size trapped in the snowbeds varied from 18 seeds m^-2 at the heath site, to 96 seeds m-² at the meadow site. On average, the heath trap station had 177 seeds m-² and the meadow station, 218 seeds m². At each site, the vegetation was inventoried within a circular area with a radius of 20 m. Overall, the species assembly in the seed rain reflected the surrounding vegetation. However, there were additional species in the seed rain as well. At the seed trap station on the wind-exposed heath, 78% of the seeds originated from sites outside the homogeneous vegetation around the trap. These seeds were dispersed from locations at least 150 m from the trap site. By trapping a higher number of species than artificial traps and a higher number of seeds per unit area, snowbeds served as effective 'seed traps'. However, the location of the sampling spot in the snowbed is crucial due to a decrease in seed density towards the edge. In this study, with the aim of trapping the main dispersing species in the area, the optimal artificial seed trap size appears to be - 1.5–2.0 m². There was also a positive correlation between the mean July and August temperature, the seed rain size, and the number of species found. Thus, through brief visits to remote locations, the study of seed dispersal can be accomplished effectively when snowbeds are present on the landscape.     

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.     

Short-term thermal acclimation induces adaptive changes in the inner mitochondrial membranes of fish skeletal muscle

In the oxidative muscles (musculi laterales superficiales) of crucian carp Carassius carassius acclimated for 6 weeks to either 5 or 25° C, the volume density and the surface density of fibres per tissue did not differ significantly between the control and experimental groups. The correlation ratio (μ²) for these values was below 50, 39·3 and 43·9 respectively. After acclimation to 5° C, the surface density of outer mitochondrial membrane per fibre increased significantly from 0·93 to 1·23m² cm⁻³ in the summer population but dropped from 0·94 to 0·67 m² cm⁻³ in the winter population. The surface density of outer mitochondrial membrane per mitochondrion increased from 3·24 to 4·52 m² cm⁻³ in summer fish. After acclimation to 25° C, the surface density of inner mitochondrial membranes per muscle fibre decreased from 4·04 to 1·79 m² cm⁻³ in summer fish and from 3·86 to 1·07 m² cm⁻³ in winter fish. The surface density of inner mitochondrial membranes per mitochondrion increased from 14·17 to 15·60 m²cm⁻³ in summer fish but dropped from 13·91 to 10·67 m² cm⁻³ in winter fish. Correlation matrices demonstrate a negative correlation of the surface density of outer mitochondrial membrane per mitochondrion with the volume density of mitochondria per fibre and temperature, suggesting cold-induced proliferation of small mitochondria. It was concluded that short-term cold acclimation increased surface area of the inner mitochondrial membranes in summer fish.     

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.     

The effects of burning on the understorey composition of 11–13 year-old rehabilitated bauxite mines in Western Australia – Vegetation characteristics

Alcoa of Australia Limited has been rehabilitating bauxite mines in the jarrah (Eucalyptus marginata) forest of Western Australia for more than 30 years. Mines rehabilitated in the early 1980s using out-dated methods have built up substantial fuel loads that may be reduced through prescribed burning. The vegetation response of 11–13 year-old rehabilitated bauxite mines to fire regimes differing in intensity and season over the first two years of post-burn succession is compared to the native jarrah forest. A total of 243 species from 137 genera and 56 families were identified in the native forest reference sites and in the 11–13 year-old rehabilitated areas before and after burning. The vegetation of the pre-burn rehabilitated areas was very different to that of the native jarrah forest. While total live plant cover, Acacia density, non-native eucalypt seedling density, weed density and the evenness index were similar between the two areas, total plant density, live Acacia cover, the proportion of weeds, native species numbers and diversity were significantly different. However, the greatest difference between the vegetation of the pre-burn rehabilitated sites and the native jarrah forest was the higher dominance of seeding species (plants killed by fire) in rehabilitated areas. In contrast, native jarrah forest was dominated by resprouting species (plants that survive fire). Burning the rehabilitated sites was successful in making the areas more similar to the forest in terms of total plant density, live Acacia cover and native species numbers but decreased their similarity in terms of live plant cover, Acacia density, non-native eucalypt seedling density, weed density and evenness. The vegetation response of the rehabilitated areas to different seasons of burning showed that autumn burning led to a greater increase in plant establishment than spring burning. Autumn burning also resulted in an undesirable increase in the density of non-native eucalypt seedlings that was not observed following spring burning. Although burning these 11–13 year-old rehabilitated sites will increase similarity to the native forest, it is unlikely that they will resemble the native jarrah forest without further management intervention.     

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.     

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.     

Bone-seed (

Bone-seed, Chrysanthemoides monilifera ssp. monilifera (L.), is an environmental weed of coastal vegetation communities scattered throughout New Zealand. To assess the long-term implications for native forest regeneration in sites where bone-seed is present, we selected four study sites around Wellington, New Zealand, where bone-seed was abundant. We compared seed bank composition in bone-seed-invaded sites with nearby native forest patches, and monitored bone-seed and native seedling recruitment with and without control of mature bone-seed plants. We also tested the potential effects of fire on bone-seed recruitment in these communities by heating seeds prior to germination. Bone-seed, gorse (Ulex europaeus), and native species emerged from seed bank samples taken from bone-seed-invaded sites, but only native species and (less) gorse emerged from seed bank samples taken from native forest patches. Gorse germination was strongly promoted by heat but bone-seed germination was less affected by heat. Bone-seed seedling abundance increased dramatically following canopy removal, whereas native seedling abundance decreased dramatically. This suggests that disturbance of any form is likely to favour recruitment of bone-seed (and gorse) over native species, although in the long term, native seedlings can establish beneath the canopy of mature bone-seed plants. It is not yet known if, in the absence of further disturbance, regenerating native vegetation will eventually replace bone-seed in New Zealand.     

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     

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.     

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 Bushmeat Harvest Alters Seedling Banks by Favoring Lianas, Large Seeds, and Seeds Dispersed by Bats, Birds, and Wind

We evaluated predictions that hunters favor lianas, large seeds, and seeds dispersed by bats, small birds, and mechanical means for seedling banks in central Panama. We censused 3201 trees in 20 1-ha plots and 38,250 seedlings in the central 64 m² of each plot. We found significant differences in the species composition of the seedling bank between nine protected sites in the Barro Colorado Nature Monument and 11 hunted sites in the contiguous Parque Nacional Soberanía. Lianas, species with large seeds, and species with seeds dispersed by bats, small birds, and mechanical means were all overrepresented at hunted sites. The latter two findings could also be evaluated relative to the species composition of reproductively mature adults for canopy trees. The tree species present in the seedling bank had significantly heavier seeds than the tree species present as adults at hunted sites but not at protected sites. The representation of seed dispersal modes among the species present in the seedling bank did not reflect pre-existing differences in the local species composition of adults. We hypothesize that hunting large seed predators favors large seeds by reducing predation and increasing survival. We also hypothesize that the harvest of large birds and mammals that disperse many seeds favors other species whose seeds are dispersed by bats, small birds, and mechanical means. This process also favors lianas because the seeds of disproportionate numbers of liana species are dispersed by wind.     

Relative abundance and growth of mussels (Mollusca: Eulamellibranchia) in pools 8,9 and 10 of the Mississippi River

SUMMARY. Twenty-three species of unionid mussels were sampled during the summer of 1975 from a 76-mile reach of the Upper Mississippi River; this represented eight species fewer than were recorded in a 1930–31 survey for the same section of the river. Of the 244 sites sampled in 1975, mussels were found at 116 sites and the ten most productive sites accounted for 40.8% of the 1205 mussels collected. There were as many as thirteen different mussel species taken from one sampling site. The two most abundant species ( Amblema peruviana and Megalonaias gigantea ) constituted 54.5% of the mussels sampled in 1975; these two species made up only 8.3% of the 1930–31 survey. Individuals of the twelve most abundant mussel species were aged, and shell-length growth equations were determined. In addition, shell-free dry weight growth rate and shell weight growth rate was determined for Amblema peruviana . The calculated annual production for A. peruviana (assuming a mean density of 1 per m²) was 482 mg/m² shell-free dry weight, and 14.471 g/m² shell weight.     

The forest of Vorsø, Denmark: Succession towards a natural, decidous boreal forest influenced by breeding cormorants

The forest on the strictly protected island Vorsø in Horsens Fjord has since 1952 been examined every ten years to discover the number, basal area, wood volume and aboveground biomass of the species. This paper describes the results from 1982 and the development up to that. The dominating species are Fraxinus excelsior, Ulmus glabra and Fagus sylvatica. The two forests, "Vesterskov" (6.09 ha) and "Østerskov" (2.48 ha) respectively, were, in 1982, still immature. Their number of stems per ha were: 756 and 509; basal area: 38 m² and 45 m². volume: 544 m³ and 615 m³; biomass 207 t and 268 t. The annual increase 1972–1982 was respectively 8.8 m³/ha and 0.3 m³/ha. The impact of the cormorant ( Phalacrocorax carbo sinensis ) is especially in "Østerskov" increasing, since the colony here was established in 1976. The succession of the forest is discussed in relation to the disturbance by the cormorants.     

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.