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.     

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.     

Heat pre-treatment and the germination of soil- and canopy-stored seeds of south-western Australian species

The role of heat (shock) in stimulating the germination of soil-stored hard seeds from fire-following species is well known. However, the effects of high temperatures on germination of canopy-stored (serotinous) seeds are less well understood. In this study, we examined the effect of heat shock at four temperatures (60, 80, 100 and 120 °C) applied for 10 min on the germination of ten co-occurring Western Australian fire-following species (five hardseeded, five serotinous). Unlike previous studies, we distinguished between the effects of heat shock on germination rate, as well as total seedling emergence. In comparison with unheated controls, a heat pulse at one or more temperatures increased total germination and germination rate for three of the hardseeded species (Acacia pulchella, Daviesia cordata and Trymalium ledifolium). The precise pattern of germination response for D. cordata was influenced by whether we examined total germination or germination rate. Germination of four serotinous species (Calothamnus quadrifidus and three Hakea species) was unaffected by pre-treatments at one or more above-ambient temperatures. Only Allocasuarina humilis displayed both increased rate and total germination at higher temperatures. Our results show that germination in some serotinous species may respond favourably to, or at least be unaffected by, the passage of fire.     

Fire and flood: Soil‐stored seed bank and germination ecology in the endangered Carrington Falls Grevillea (Grevillea rivularis,Proteaceae)

Abstract Seed germination is dependent on the interaction between the dormancy state of a seed and the presence of favourable environmental conditions. Thus, the spectacular pulse of seedling recruitment in many Australian vegetation communities following disturbances such as fire can be attributed to changes in microsite conditions and/or the dormancy‐breaking effect of the disturbance on accumulated seed banks. Grevillea rivularis is a threatened species endemic to the area immediately above Carrington Falls in the NSW Southern Highlands. Most of the population is confined to the riparian vegetation zone in woodland and heath, and is therefore subject to periodic disturbance from fire and flood. For this species, a pulse of seedling recruitment has been recorded after fire, flood and mechanical soil disturbance. The aims of this study were to examine the density and vertical distribution of the soil‐stored seed bank and to investigate the role of heat and scarification as cues for germination of fresh and soil‐stored seed. There was a large seed bank under the canopies of established individuals (194 ± 73 seeds m^?2) and most seeds were found in the 0–2 cm and leaf‐litter layers of the soil profile. The germination response of soil‐stored and fresh seed was examined using a hierarchical series of laboratory experiments. Seeds of G. rivularis showed marked dormancy polymorphism. Thirty‐six percent of soil‐stored seed germinated without treatment, whereas no untreated fresh seeds germinated. Scarification or heating caused significant germination of dormant soil‐stored seed, but only scarification resulted in germination of dormant fresh seeds. These results highlight important differences in the dormancy state of soil‐stored and fresh seed. Thus, being a riparian species in a fire‐prone environment, the dormancy mechanisms in seeds of G. rivularis suit this species to disturbance by both fire and flood.     

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

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

A STUDY OF THE SEED BANK OF A SALT MARSH IN NORTHERN SAN FRANCISCO BAY

Abundance, species composition, and distribution of buried seeds in a San Francisco Bay salt marsh were studied by collecting soil samples in October and February and observing seedling emergence in the greenhouse. Results were compared with existing vegetation patterns and field germination. Average numbers of buried viable seed down to a 5-cm depth were 380/ m² in October and 700/m² in February, with field germination averaging 118/m². Salicornia virginica dominated the seed bank in the greenhouse and in field germination. Most other marsh species were present in the seed bank but numbers of seeds were low. A significant correlation was found between highest species diversity and proximity to channels. The nature of this low-diversity, low-density seed bank reflects dominance of long-lived perennial species, seed dispersal patterns and selective environmental pressures.     

Comparative seed germination ecology of Austrostipa compressa and Ehrharta calycina (Poaceae) in a Western Australian Banksia woodland

Austrostipa compressa, a native ephemeral of southwest Western Australia was stimulated to germinate under a range of temperatures, in the presence of light, and exposure to smoke-water. This combination of environmental cues results in winter-maximum germination in immediate postfire and disturbed-soil environments of this Mediterranean-type climate. In contrast, Ehrharta calycina, an introduced perennial grass from southern Africa that has invaded Banksia woodlands, germinated under a wide range of temperature and light conditions, but showed no promotive response to smoke-water. Although A. compressa seeds tolerated heat shock better than E. calycina, the self-burial mechanism of A. compressa seeds ensures protection from fire. High-intensity fire could have a greater impact on E. calycina, as the seeds of this species tend to accumulate in the top of the soil profile where they are more susceptible to high temperatures. Although seeds of E. calycina are more susceptible to high temperatures, survival of mature individuals by postfire resprouting ensures continued survival in native woodlands. Estimates of soil seed bank densities showed extreme variability, but some recently burnt areas of the Yule Brook Botany Reserve contained up to 8000 seed m^?2 of A. compressa and nearly 75 000 seeds m^?2 of E. calycina. Viable soil seed bank densities of A. compressa are reduced with time-since-last fire, but areas of greater than 45 years since the last fire, still contained up to 119 seeds m^?2. In both species, only about half their soil seed bank germinates following fire, thus ensuring the potential for later recruitment. Massive soil seed populations of E. calycina in native Banksia woodlands pose a major problem to management of this plant community type.     

Soil seed-bank components of the northern jarrah forest of Western Australia

The germinable soil seed-store of the northern jarrah (Eucalyptus marginata Donn ex Sm.) forest was found to average 767 seeds m^?2 (range:377–1579 seeds m^?2) over six randomly selected plots within a range of forest sites. A total of 68 different taxa of vascular plants were recognized following heating and glasshouse tray germination tests of field-collected soils. Both the qualitative and quantitative composition of the soil seed-bank were dominated by annuals and sub-shrubs. Because less than 10% of the seed of the soil was from species of the dominant tree and woody shrub strata, there were major floristic differences between the existing flora and the composition of the soil seed-bank. The influences of the soil seed-bank on rehabilitation of disturbed jarrah forest lands and current fire management are discussed.     

Natural regeneration of Spanish black pine [Pinus nigra Arn. ssp. salzmannii (Dunal) Franco] at contrasting altitudes in a Mediterranean mountain area

Information on plant seed dispersal, natural loss dynamics of seeds and germination are critical for understanding natural regeneration mechanisms. The aim of this study was to assess the effect of different forest stand densities on seedfall, seed predation, and seedling germination of two populations of the endangered Spanish black Pine forests located at lower (Central population) and higher elevation near the limit of the species?? range (peripheral population) in the Cuenca Mountains of Central Spain. The seed predation and germination experiment also included a nested site preparation treatment. Seed fall varied significantly between 2006 and 2005 or 2007 in both populations. During the only mast year of 2006, higher seedfall was observed at lower elevation and in higher density stands. Predation rates were influenced by the seed crop since predators consumed more than 75?% of seeds in years with lower production and less than 15?% in a mast year. Seed germination is influenced by forest habitat, stand density and soil scalping. For common habitat types, and in a high seed production year, better seed germination rates were observed in medium and dense stands (25?C30 and 35?C40?m²?ha^?1, respectively, in terms of basal area). No statistical difference in seed germination rate was found for Spanish black pine forest at its ecological distribution limit between lower and higher densities (15?C20 and 35?C40?m²?ha^?1, in terms of basal area). In both sites, closed stands with soil scalping exhibited higher germination rates.     

The soil seed bank and understorey regeneration in Eucalyptus regnans forest,Victoria

Abstract The soil seed bank and its relation to the extant vegetation in a Eucalyptus regnans F. Muell. forest in the Central Highlands of Victoria were examined. The average seed density was 430 germinable seeds m^?2 to a depth of 2 cm. There was a polynomial regression relationship between the density and species richness of seeds in soil and forest age (0. 6–54 years). Species richness was not significantly different among soil depths (0- 2 , 2- 5 , 5–10 and 10–20 cm) in the forest stand of 54 years old. More seeds germinated from the 5–10 cm depth than from the other depths. Forbs accounted for 73% of the total germinable seeds and there was no germination of E. regnans. The number of species, particularly woody plant species, germinating from the soil seed bank were significantly lower than in the extant vegetation. However, almost all species present in the soil seed bank were present in the vegetation. The soil seed bank provides an important source for the rapid regeneration of understorey vegetation following clear-cutting and slash-burning in the E. regnans forest. The rapid understorey establishment may play an important role in protecting soil from erosion, in nutrient conservation, replacement and redistribution. The soil seed bank may also be a necessary source of maintaining genetic diversity in the forest over the long term.     

Fire and regeneration: the role of seed banks in the dynamics of northern heathlands

Questions: How do species composition and abundance of soil seed bank and standing vegetation vary over the course of a post‐fire succession in northern heathlands? What is the role of seed banks – do they act as a refuge for early successional species or can they simply be seen as a spillover from the extant local vegetation? Location: Coastal Calluna heathlands, Western Norway. Methods: We analysed vegetation and seed bank along a 24‐year post‐fire chronosequence. Patterns in community composition, similarity and abundances were tested using multivariate analyses, Sørensen's index of similarity, vegetation cover (%) and seedling counts. Results: The total diversity of vegetation and seed bank were 60 and 54 vascular plant taxa, respectively, with 39 shared species, resulting in 68% similarity overall. Over 24 years, the heathland community progressed from open newly burned ground via species rich graminoid‐ and herb‐dominated vegetation to mature Calluna heath. Post‐fire succession was not reflected in the seed bank. The 10 most abundant species constituted 98% of the germinated seeds. The most abundant were Calluna vulgaris (49%; 12 018 seeds m^?2) and Erica tetralix (34%; 8 414 seeds m^?2). Calluna showed significantly higher germination the first 2 years following fire. Conclusions: Vegetation species richness, ranging from 23 to 46 species yr^?1, showed a unimodal pattern over the post‐fire succession. In contrast, the seed bank species richness, ranging from 21 to 31 species yr^?1, showed no trend. This suggests that the seed bank act as a refuge; providing a constant source of recruits for species that colonise newly burned areas. The traditional management regime has not depleted or destroyed the seed banks and continued management is needed to ensure sustainability of northern heathlands.     

Effects of ethylene and some other environmental factors on different stages of germination in red root pigweed (Amaranthus retroflexus L.) seeds*

Abstract. Ethylene was found to promote two distinct processes during germination of redroot pigweed (Amarantus retroflexus L.) seeds: embryo expansion that splits the seed coat (incomplete germination), and radicle penetration through the more elastic endosperm (complete germination). The two events can be separated in time by subjecting seeds to low water potential or low CO₂ levels, which arrest germination of some seeds at the incomplete stage. Ethylene applications to incompletely germinated seeds promote complete germination, with a response threshold near 0.02 cm³ m^?3 and saturation near 0.5 cm³ m^?3. Higher ethylene concentrations (0.5 to 50 cm³ m^?3) given during the first day of seed imbibition also increase the percentage of seeds which initiate embryo expansion and split the seed coat. Light and elevated CO₂ also promote radicle penetration of the endosperm in seeds incubated under water stress. The results support the view that the germination pause at the incomplete stage is an adaptation to environmental stresses that can be overcome with exogenous ethylene or certain other stimuli.     

盐磷胁迫对木麻黄和台湾相思种子萌发及幼苗生长的影响

恶劣环境下,人工海防林因面临养分胁迫而经营困难。为探讨盐、磷胁迫对主要海防林树种木麻黄和台湾相思种子萌发及生长的影响,该研究分别用不同浓度的NaCl(盐)和KH₂PO₄(磷)溶液处理种子和浇灌幼苗,测定种子萌发和幼苗生长指标。结果表明：(1)高盐胁迫显著抑制种子萌发,对幼苗生长有一定影响,但两种植物影响程度不同;台湾相思种子萌发耐盐性高于木麻黄,前者相对盐害率最大值为23.03%,后者为89.15%;随着盐浓度增加,木麻黄和台湾相思种子的发芽率、发芽势、发芽指数和活力指数均降低,对应最大值分别为38.70%、34.67%、18.70、0.055和76.67%、62.22%、48.46、6.11。(2)两种植物的株高和根长随盐浓度增加而降低,木麻黄和台湾相思株高分别为12.29～6.01 mm和48.27～17.33 mm,根长分别为8.57～1.45 mm和33.41～5.88 mm;台湾相思根、茎、叶生物量及根冠比均随盐浓度的增加逐渐减小,木麻黄各处理差异较小。(3)台湾相思的种子和幼苗较木麻黄更耐低磷环境,二者最适磷浓度存在差异;木麻黄种...     

Role of nitrate in regulating germination of Sinapis arvensis L. (wild mustard)

Abstract Depending on the applied concentration, nitrate can either stimulate or inhibit germination of dormant seeds of Sinapis arvensis L. (wild mustard). Seed NO^?₃ levels that corresponded to the maximal germination frequencies recorded, ranged from 0.3 to 4.4 nmol seed^?1 for applied NO^?₃ concentrations between 2.5 and 20 mol m^?3. Germination was significantly lower in seeds containing more than 5 nmol NO^?₃. Although the presence of NO^?₃ within the seed was required to promote germination, seed NO^?₃ levels were 5 to 15 times less than levels calculated from the volume of solution taken up by the seeds. Seed NO^?₃ levels also responded in a passive fashion to the external NO₃^? concentration when the seeds were incubated on filter paper or in soil. In a representative soil containing 26 mg NO^?₃-N per kg dry weight and 8 to 16% water by weight, the amount of NO^?₃ taken up by the seeds reached inhibitory levels. Our results suggest that levels of inorganic nitrogen (NO^?₃, NH⁺₄) in managed soils may play an important role in regulating germination of dormant S. arvensis seeds.     

Seed dynamics during forest succession in Costa Rica

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

The role of Rhytidoponera metallica (Hymenoptera,Formicidae) in facilitating post‐fire seed germination of three ant‐dispersed legume species

The fire avoidance hypothesis proposes that a benefit of seed dispersal by ants (myrmecochory) is to protect seeds from being killed during fire and to facilitate post‐fire germination of seeds that require heat shock to break their physical dormancy. The aim of this study was to quantify the effect of fire and seed burial by a predominant seed‐dispersing ant, Rhytidoponera metallica (subfamily: Ectatomminae) on germination levels of three ant‐dispersed legume species (Pultenaea daphnoides, Acacia myrtifolia and Acacia pycnantha). Experimental burial of seeds within aluminium cans at a site prior to being burnt and at an adjacent unburnt site showed that fire increased germination levels, particularly for seeds buried at 1‐ and 2‐cm deep and that overall, germination levels differed among the three plant species. To quantify seed burial depths and post‐fire germination levels facilitated by R. metallica ants, seeds were fed to colonies prior to fire at the burnt and unburnt sites. Of the seeds buried within nests that were recovered, between 45% and 75% occurred within the upper 6 cm of the soil profile, although unexpectedly, greater percentages of seeds were recovered from the upper 0–2 cm of nests in the unburnt site compared with nests in the burnt site. Germination levels of buried seeds associated with R. metallica nests ranged from 21.2% to 29.5% in the burnt site compared with 3.1–14.8% in the unburnt site. While increased seed germination levels were associated with R. metallica nests following fire, most seeds were buried at depths below those where optimal temperatures for breaking seed dormancy occurred during the fire. We suggest that R. metallica ants may provide fire avoidance benefits to myrmecochorous seeds by burying them at a range of depths within a potential germination zone defined by intra‐ and inter‐fire variation in levels of soil heating.     

Leaf litter of <Emphasis Type="Italic">Kageneckia angustifolia</Emphasis> D. Don (Rosaceae) inhibits seed germination in sclerophyllous montane woodlands of central Chile

Leaf litter accumulation can have either positive, negative or neutral effects on seed germination and seedling recruitment. In montane woodlands of the Mediterranean zone of central Chile, large amounts of leaf litter accumulate beneath the crowns of the summer semi-deciduous tree Kageneckia angustifolia and no regeneration of this or other plant species has been observed beneath this tree throughout the year. In a sample plot of 5000 m² we selected ten K. angustifolia trees and measured (1) leaf litter accumulation beneath and outside canopy; (2) the effects of time elapsed since burial on viability of K. angustifolia seeds with and without a leaf litter cover; (3) field seed germination with presence or absence of leaf litter and (4) the possible chemical effects of K. angustifolia leaf litter leachates on seed germination of its own seeds and of other two co-occurring native shrubs species (Guindilia trinervis and Solanum ligustrinum). Our results show that a considerable accumulation of leaf litter occurred beneath K. angustifolia, and litter negatively affected seed viability and germination of this species in the field. Under laboratory conditions, K. angustifolia leaf litter leachates inhibited seed germination of its own seeds and of the two native shrub species. Chemical effects are likely involved in the negative effects of leaf litter on the recruitment of K. angustifolia in the montane sclerophyllous woodland of central Chile.     

Effects of smoke,heat and charred wood on the germination of dormant soil‐stored seeds from a Eucalyptus baxteri heathy‐woodland in Victoria,SE Australia

The effects of dry heat, wet heat, charred wood and smoke on the germination of dormant soil‐stored seeds from a Eucalyptus woodland in western Victoria were tested by using a glasshouse seed‐bank germination experiment. Seedling density, species richness and species composition were compared between replicated treated and control samples. A total of 5922 seedlings, comprising 59 plant species, was recorded from the soil samples over a period of 150 days. While a few species dominated (including Centrolepis strigosa, Wahlenbergia gracilenta and Ixodia achillaeoides), 26 species were represented by fewer than five seedlings and 18 species were restricted to single treatment types. With the exception of charred wood, all treatments led to a significant increase in seed germination relative to the control. The highest number of germinants was obtained for the smoke treatment, with a mean (± SE) of 12 547 ± 449 seedlings m^–2. Heat treatments yielded intermediate densities, with means (± SE) varying between 7445 ± 234 and 9133 ± 445 seedlings m^–2. In comparison with the estimates of seed‐bank sizes from other fire‐prone ecosystems, these densities are high. Species richness differed significantly among treatments. Highest mean richness was recorded in the smoke treatment and lowest for the control and charred wood treatments. There were significant differences in seed‐bank species composition between treatment types based on analysis of similarity (Anosim) using Bray–Curtis similarity. While heat was a specific requirement for triggering germination in hard‐seeded species (e.g. Fabaceae), smoke was the most effective trigger for species from a broad range of other families. The potentially confounding effect of physical and chemical mechanisms of germination stimulation in heated bulk soil samples is raised as an issue requiring further investigation in relation to the role of smoke as a germination trigger.     

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

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

Soil seed banks in different environments: initial forest,mature forest,Pinus and Eucalyptus abandoned stands

Abstract

Different environments (initial forest, mature forest, Pinus and Eucalyptus stands) found in Seasonal Semideciduous Forest fragments affect the density of viable seeds, as well as the floristic similarity, diversity, and richness of tree species in soil seed banks. This hypothesis was tested in the current study. Soil seed bank samples were collected in the aforementioned environments during rainy and dry seasons, and taken to a shade house, where they remained under favorable seed germination conditions. Tree seedling emergence was measured, and sample species were identified every 15?days, for six months, in each sampling period. In total, 97 individuals m^?2 and 23 species emerged in all environments and periods. The highest density of viable seeds of tree species in the soil seed bank was found in the initial forest stretch, mature forest stretch and abandoned Eucalyptus stand. Only the Pinus stand seed bank in the dry season had different floristic and lower viable seed density than the mature forest seed bank. Thus, all environments, except the abandoned Pinus stand, can preserved Seasonal Semideciduous Forest fragments.