Temporal patterns of genetic variation across a 9-year-old aerial seed bank of the shrub Banksia hookeriana (Proteaceae)

The pattern of accumulation of genetic variation over time in seed banks is poorly understood. We examined the genetic structure of the aerial seed bank of Banksia hookeriana within a single 15-year-old population in fire-prone southwestern Australia, and compared genetic variation between adults and each year of a 9-year-old seed bank using amplified fragment length polymorphism (AFLP). B. hookeriana is well suited to the study of seed bank dynamics due to the canopy storage of its seeds, and because each annual crop can be identified. A total of 304 seeds from nine crop years and five maternal plants were genotyped, along with 113 plants from the adult population. Genetic variation, as assessed by the proportion of polymorphic markers (P(p)) and Shannon's index (I), increased slightly within the seed bank over time, while gene diversity (H(j)), did not change. P(p), I, and H(j) all indicated that genetic variation within the seed bank quickly approached the maximal level detected. Analysis of molecular variance revealed that less than 4% of variation could be accounted for by variation among seeds produced in different years, whereas there was greater differentiation among maternal plants (12.7%), and among individual seeds produced by different maternal plants (83.4%). With increasing population age, offspring generated each year were slightly more outbred, as indicated by an increase in the mean number of nonmaternal markers per offspring. There were no significant differences for H(j) or I between adults and the seed bank. Viability of seeds decreased with age, such that the viability of 9-year-old seeds was half that of 2-year-old seeds. These results suggest that variable fire frequencies have only limited potential to influence the amount of genetic variation stored within the seed bank of B. hookeriana.     

Enhanced seed defenses potentially relax selection by seed predators against serotiny in lodgepole pine

Serotiny, the retention of seeds in a canopy seed bank until high temperatures cause seeds to be released, is an important life history trait for many woody plants in fire‐prone habitats. Serotiny provides a competitive advantage after fire but increases vulnerability to predispersal seed predation, due to the seeds being retained in clusters in predictable locations for extended periods. This creates opposing selection pressures. Serotiny is favored in areas of high fire frequency, but is selected against by predispersal seed predators. However, predation also selects for cone traits associated with seed defense that could reduce predation on serotinous cones and thereby relax selection against serotiny. This helps explain the elevated defenses in highly serotinous species. However, whether such interactions drive variation in seed defenses within variably serotinous populations has been studied rarely. We investigated the effects of phenotypic selection exerted by red squirrel (Tamiasciurus hudsonicus) predation on Rocky Mountain lodgepole pine (Pinus contorta latifolia) seeds. Squirrels preferentially harvested cones with more and larger seeds, indicating a preference for a higher food reward. We found evidence for stronger selection on trees with serotinous cones, which presumably accounts for the elevated defenses of and lower predation on serotinous compared to non‐serotinous cones. Lower levels of predation on serotinous cones in turn lessen selection against serotiny by squirrels. This has important implications because the frequency of serotiny in lodgepole pine has profound consequences for post‐fire communities and ecosystems widespread in the Rocky Mountains.     

Dispersal and recruitment dynamics in the fleshy‐fruited Persoonia lanceolata (Proteaceae)

Question: What is the role of dispersal, persistent soil seed banks and seedling recruitment in population persistence of fleshy‐fruited obligate seeding plant species in fire‐prone habitats? Location: Southeastern Australia. Methods: We used a long‐term study of a shrubby, fleshy‐fruited Persoonia species (Proteaceae) to examine (1) seed removal from beneath the canopy of adult plants; (2) seedling recruitment after fire; (3) the magnitude and location of the residual soil seed bank; and (4) the implications for fire management of obligate seeding species. We used demographic sampling techniques combined with Generalised Linear Modelling and regression to quantify population changes over time. Results: Most of the mature fruits (90%) on the ground below the canopy of plants were removed by Wallabia bicolor (Swamp wallaby) with 88% of seeds extracted from W. bicolor scats viable and dormant. Wallabies play an important role in moving seeds away from parent plants. Their role in occasional long distance dispersal events remains unknown. We detected almost no seed predation in situ under canopies (< 1%). Seedling recruitment was cued to fire, with post‐fire seedling densities 6‐7 times pre‐fire adult densities. After fire, a residual soil seed bank was present, as many seeds (77‐100%) remained dormant and viable at a soil depth where successful future seedling emergence is possible (0‐5 cm). Seedling survival was high (> 80%) with most mortality within 2 years of emergence. Plant growth averaged 17 cm per year. The primary juvenile period of plants was 7–8 years, within the period of likely return fire intervals in the study area. We predicted that the study population increased some five‐fold after the wildfire at the site. Conclusions: Residual soil seed banks are important, especially in species with long primary juvenile periods, to buffer the populations against the impact of a second fire occurring before the seed bank is replenished.     

Non‐fire induced seed release ina weakly serotinous pine: climatic factors,maintenance costs or both?

The advantages of canopy seed retention (serotiny) for plants inhabiting fire‐prone ecosystems are well documented. However, very few species are completely serotinous and non‐fire induced opening of serotinous fruits is commonly observed (weak serotiny). Two non‐mutually exclusive causes are envisaged to contribute to this process: mechanical changes in serotinous fruits mediated by climatic conditions (e.g. drought) or the costs of maintenance for the plant of these long‐lasting structures. However, their relative contribution to the spontaneous opening of serotinous fruits remains elusive as well as the consequences for the build‐up of the canopy seed bank and inter‐individual differences in serotiny. In this study we monitored the dynamics of cone production and cone opening in the weakly serotinous Pinus halepensis for five years (2004–2008), including two severe drought episodes (2005, 2006). Drought decreased the production of conelets, increased the abortion of immature cones, reduced the seed quality in the cohorts of cones produced during these years, and increased the opening of serotinous cones. During the first drought episode, a higher proportion of serotinous cones opened in those pines bearing a larger crop of younger cones. This suggests that not only passive changes induced by drought but also competition among cones for resources (e.g. water) might be involved in this process. The opening of serotinous cones in pines bearing more cones made inter‐individual differences in the size of the canopy cone bank to narrow or even to reverse from 2004 to 2008. These results may help to understand the decrease in serotiny when pines grow and accumulate more cones and the large inter‐individual variability in the degree of serotiny observed in P. halepensis forests. In addition, the negative effects of drought episodes for the size of the canopy cone bank and the seeds contained can be an unexplored cause of post‐fire regeneration constraint.     

Limiting inbreeding in disjunct and isolated populations of a woody shrub

Pollen movements and mating patterns are key features that influence population genetic structure. When gene flow is low, small populations are prone to increased genetic drift and inbreeding, but naturally disjunct species may have features that reduce inbreeding and contribute to their persistence despite genetic isolation. Using microsatellite loci, we investigated outcrossing levels, family mating parameters, pollen dispersal, and spatial genetic structure in three populations of Hakea oldfieldii, a fire‐sensitive shrub with naturally disjunct, isolated populations prone to reduction in size and extinction following fires. We mapped and genotyped a sample of 102 plants from a large population, and all plants from two smaller populations (28 and 20 individuals), and genotyped 158–210 progeny from each population. We found high outcrossing despite the possibility of geitonogamous pollination, small amounts of biparental inbreeding, a limited number of successful pollen parents within populations, and significant correlated paternity. The number of pollen parents for each seed parent was moderate. There was low but significant spatial genetic structure up to 10 m around plants, but the majority of successful pollen came from outside this area including substantial proportions from distant plants within populations. Seed production varied among seven populations investigated but was not correlated with census population size. We suggest there may be a mechanism to prevent self‐pollination in H. oldfieldii and that high outcrossing and pollen dispersal within populations would promote genetic diversity among the relatively small amount of seed stored in the canopy. These features of the mating system would contribute to the persistence of genetically isolated populations prone to fluctuations in size.     

Reproductive traits of Pinus halepensis in the light of fire – a critical review

Fire is known to be a major factor in shaping plants and vegetation worldwide. Many plant traits have been described as adaptations for surviving fire, or regenerating after it. However, many of the traits are also advantageous for overcoming other disturbances. The fact that fire in the Mediterranean Basin has been almost exclusively of anthropogenic origin, and thus is of short duration in an evolutionary time scale, cast doubt on the possibility that fire can act as a selective force in the Mediterranean Basin. Our aim here is to review the ecological advantages of Pinus halepensis traits and their possibility to be selected by fire. The non-self pruning of cones and branches, and the high resin content increase the probability of canopy fires and consequent death of P. halepensis trees. Post-fire regeneration of P. halepensis depends totally upon its canopy-stored seed bank. The seedlings grow quickly and they first reproduce at an early age. Young reproductive trees function first as females with a high percentage of serotinous cones. Thus, young P. halepensistrees allocate many resources to seed production, reducing their `immaturity risk' in a case of an early successive fire. The proportion of serotinous cones is higher in post-fire naturally regenerating stands than in unburned stands, and seeds from serotinous cones germinate better under simulated post-fire conditions. The extremely high pH of the ash-bed under the burned canopies creates the post-fire regeneration niche of P. halepensis exactly under their parent trees. All these traits are advantageous for post-fire regeneration, but could they also be selected during the time scale of anthropogenic fires in the Mediterranean Basin? Pinus halepensis is a relatively short living tree with almost no recruitment under forest canopy. The longest estimated fire-return interval and generation length are about 125 years. The earliest solid evidence for the first hominid-controlled fire in the Mediterranean basin is 780,000 years ago, and thus the estimated number of post-fire generations is 6240. We suggest that such a number of generations is sufficient for the selection and radiation of fire adaptive traits in P. halepensis.

     

Organisation of the soil seed bank in mixed chaparral

Seed densities, estimated from germinations under glasshouse conditions, were determined for fire-treated and control soils sampled from north and south facing stands of mixedAdenostoma fasciculatum-Ceanothus greggii chaparral that last burned 10, 17, 36, 62 and 86 years before 1987. A total of 53 species was recorded. Total germinable seed density was not influenced by aspect nor by an experimental fire treatment, however, densities varied significantly, but not predictably, over the time since fire sequence. Species diversity was significantly lower in the 86 year old stand, but neither diversity or richness was influenced by the fire treatment. Soils from north facing slopes supported a higher species diversity overall, and seed densities of six species were significantly higher on north than on south slopes.We identify two functional groups in the seed bank on the basis of the direct effects of fire on seed densities: a fire-dependent group, comprising 6 species and about 21% of the total seed bank, in which germinable densities increased after the fire treatment, and a fire-independent group, made up of 11 species and almost two-thirds of the seed bank. The fire-independent group is further separated into two: a shrub-centred sub-group (Crassula erecta, Filago californica, Pterostegia drymarioides, Streptanthus heterophyllus andCryptantha intermedia) maintained larger seed banks in older stands and was associated with shrub cover; and an opportunistic sub-group (Camissonia hirtella, Gnaphalium chilense, Mimulus pilosus andSenecio vulgaris) tended to have larger seed banks in younger stands and was associated with canopy gaps.Overall, the soil seed assemblage from this mixed chaparral does not appear to be tightly coupled to fire-generated opportunities for recruitment. The reason for this is that the fire-dependent group represents only 6 species. In addition, among the fire-independent species, the shrub-centred group of 5 annuals made up almost 40% of total soil seed density. This group shows ecological and taxonomic affinities with desert annuals.     

Canopy seed bank structure in relation to: fire,tree size and density

To assess the canopy seed bank structure of Pinus halepensis, we measured the level of serotiny and the seed bank size and density of trees in unburned stands and post-fire regenerated stands in Israel. We analysed the effects of tree size, tree density and fire history on the level of serotiny. The level of serotiny decreased with an increase in tree height. The high level of serotiny in short trees could be explained by selection to increase regeneration chances after burning at pre-mature age. Also, limitation of long-distance seed dispersal opportunities in short trees may favour high serotiny levels. The level of serotiny was higher in post-fire stands than in unburned stands, suggesting a fast selection for serotiny by fire. Unburned stands had a higher total stand seed density than post-fire regenerated stands, but the proportion of seeds in serotinous cones of the total stand seed density was higher in post-fire regenerated stands. The fact that P. halepensis bears simultaneously serotinous and non-serotinous cones reflects its dual strategy as both a post-fire obligate seeder, mainly from serotinous cones and an early coloniser during fire-free periods, mainly from non-serotinous cones. The relative investment in these strategies is dependent on fire history and varies with tree height. Furthermore, mature brown cones can contribute to post-fire regeneration in case of spring fires, and serotinous cones are known to open partially also in dry spell events. Thus, post-fire regeneration and invasion are strategies, which seem to complement each other.     

Postglacial colonization history reflects in the genetic structure of natural populations of Festuca rubra in Europe

We conducted a large‐scale population genetic survey of genetic diversity of the host grass Festuca rubra s.l., which fitness can be highly dependent on its symbiotic fungus Epichloë festucae, to evaluate genetic variation and population structure across the European range. The 27 studied populations have previously been found to differ in frequencies of occurrence of the symbiotic fungus E. festucae and ploidy levels. As predicted, we found decreased genetic diversity in previously glaciated areas in comparison with nonglaciated regions and discovered three major maternal genetic groups: southern, northeastern, and northwestern Europe. Interestingly, host populations from Greenland were genetically similar to those from the Faroe Islands and Iceland, suggesting gene flow also between those areas. The level of variation among populations within regions is evidently highly dependent on the postglacial colonization history, in particular on the number of independent long‐distance seed colonization events. Yet, also anthropogenic effects may have affected the population structure in F. rubra. We did not observe higher fungal infection rates in grass populations with lower levels of genetic variability. In fact, the fungal infection rates of E. festucae in relation to genetic variability of the host populations varied widely among geographical areas, which indicate differences in population histories due to colonization events and possible costs of systemic fungi in harsh environmental conditions. We found that the plants of different ploidy levels are genetically closely related within geographic areas indicating independent formation of polyploids in different maternal lineages.     

Can a seed bank provide demographic and genetic rescue in a declining population of the endangered shrub <Emphasis Type="Italic">Acacia pinguifolia</Emphasis>?

Many threatened species suffer reduced genetic diversity as a result of small population size and isolation. However, species with a persistent seed bank may be buffered against genetic loss as seed banks are expected to accumulate the reproductive output of many seasons. For fire-dependent species in decline, prescribed ecological burning may be a means to stimulate germination and recover genetic diversity stored in the seed bank, providing a demographic and genetic rescue effect. Here we investigated the effectiveness of this strategy in a small, isolated and inbred population of the endangered shrub, Acacia pinguifolia. We surveyed genetic diversity and structure of remnant populations of A. pinguifolia and monitored regeneration before and after burning. Germination was stimulated by fire, but seedling numbers 18 months post-fire were low and barely above the number of adults killed by the fire. Genetic diversity was marginally higher in the post-fire seedling cohort than the pre-fire adults (H_E = 0.1 vs. 0.09, respectively). Outcrossing rates of open-pollinated seed from surrounding plants suggested moderately high levels of self-fertilisation (t _m  = 0.65) and analysis of fine-scale genetic structure implied pollen and seed dispersal over distances of several metres, suggesting that restricted gene flow and inbreeding may act to limit genetic diversity in the seed bank. We conclude that prescribed burning has not been immediately successful as a recovery strategy for this relictual population of A. pinguifolia, though future monitoring may detect additional recruits. Alternative conservation strategies, including performing inter-population crosses, may be required to restore genetic diversity and ameliorate extinction risks.     

Soil seed bank contributes significantly to genetic variation of Hypericum sinaicum in a changing environment

The contribution of soil seed bank of a desert endemic plant species in maintaining genetic diversity has been addressed in this paper through investigating the differences in genetic diversity and structure (using AFLP markers) between plants grown from soil seed bank and standing crop plants within and among five populations of H. sinaicum growing at St. Katherine Protectorate, southern Sinai, Egypt. Standard genetic diversity measures showed that the molecular variation within and among populations was highly significantly different between standing crop and soil seed bank. While soil seed bank had lower genetic diversity than standing crop populations, pooling soil seed bank with standing crop samples resulted in higher diversity. The results revealed also that soil seed bank had lower differentiation (7 %) than among populations of the standing crop (18 %). Results of neighbor-joining, Bayesian clustering and principal coordinate analysis showed that soil seed banks had a separate gene pool different from standing crop. The study came to the conclusion that the genetic variation of the soil seed bank contributes significantly to the genetic variation of the species. This also stresses the importance of elucidating the genetic diversity and structure of the soil seed bank for any sound and long-term conservation efforts for desert species. These have been growing in small-size populations for a long time that any estimates gained only from aboveground sampling of populations may be ambiguous.     

Role of heat tolerance and cone protection of seeds in the response of three pine species to wildfires

The post-fire regenerative ability of Pinus halepensis, Pinus nigra and Pinus sylvestris, three of the most important pine species present in the West Mediterranean basin, has been analyzed in the light of seed tolerance to different temperatures and times of exposure, and of seed position during the fire event (seeds inside cones versus free seeds). The combination of different fire intensities and degrees of seed protection allows us to draw different scenarios during the fire event: canopy scenarios (seeds inside cones), surface scenarios (seeds on the ground surface), and soil scenarios (seeds in the top soil layers). There were interspecific differences in the pattern of cone opening under the different heat treatments: cones of P. nigra and P. sylvestris showed similar percentages of opening, but considerably higher than those of P. halepensis. In the three species, seeds inside cones showed higher percentages of germination than those that were free, emphasizing the important role of cones in the protection of pine seeds from high temperatures. The percentage of germination decreased when both the temperature and the time of exposure increased, and there was also a significant species effect: P. halepensis showed higher germination rates than P. nigra, and both were higher than P. sylvestris. The overall scores of seed germination of these three pine species under the conditions tested suggests that their regeneration after fire should come either from the soil bank, or from the canopy bank, but rarely from the ground surface. As the existence of a permanent seed bank in Mediterranean pines is probably limited or nil, pine recruitment after fire appears to be mainly controlled by the existence of a canopy seed bank. The contribution of this canopy bank to the differences in postfire regeneration success of the three pine species is discussed in the light of their seeding phenology and the effects of fire severity on cone opening. The results obtained in this study contribute to explain the successful regeneration of P. halepensis, and the failure of P. nigra and P. sylvestris after fire.     

Can Soil Seed Banks Serve as Genetic Memory? A Study of Three Species with Contrasting Life History Strategies

We attempted to confirm that seed banks can be viewed as an important genetic reservoir by testing the hypothesis that standing (aboveground) plants represent a nonrandom sample of the seed bank. We sampled multilocus allozyme genotypes from three species with different life history strategies: Amaranthus retroflexus, Carduus acanthoides, Pastinaca sativa. In four populations of each species we analysed the extent to which allele and genotype frequencies vary in consecutive life history stages including the summer seed bank, which has been overlooked up to now. We compared the winter seed bank (i.e., seeds collected before the spring germination peak), seedlings, rosettes, the summer seed bank (i.e., seeds collected after the spring germination peak) and fruiting plants. We found that: (1) All three species partitioned most of their genetic diversity within life history stages and less among stages within populations and among populations. (2) All genetic diversity parameters, except for allele frequencies, were similar among all life history stages across all populations in different species. (3) There were differences in allele frequencies among life history stages at all localities in Amaranthus retroflexus and at three localities in both Carduus acanthoides and Pastinaca sativa. (4) Allele frequencies did not differ between the winter and summer seed bank in most Carduus acanthoides and Pastinaca sativa populations, but there was a marked difference in Amaranthus retroflexus. In conclusion, we have shown that the summer seed bank is not genetically depleted by spring germination and that a majority of genetic diversity remains in the soil through summer. We suggest that seed banks in the species investigated play an important role by maintaining genetic diversity sufficient for recovery rather than by accumulating new genetic diversity at each locality.     

Patch to landscape patterns in post fire recruitment of a serotinous conifer

Obligate seeding species are highly specialized to fire disturbance and many conifers such as cypress, which are adapted to high intensity stand-replacing fires, have canopy seed banks stored in serotinous cones. Resilience of these trees to fire disturbance is a function of disturbance frequency and one focus of this study was to determine the effect of patch age on postfire recruitment. A second focus was to determine the extent to which fire induced a landscape level change in the location of the forest boundary. Prior to a fire in 1994, a large Cupressus sargentii forest was a mosaic landscape of different aged patches of nearly pure cypress bordered by chaparral. Patches less than 60 years of age were relatively dense with roughly one tree every 1–2 m² but older patches had thinned to one tree every 3–15 m². Older trees had substantially greater canopy cone crops but the stand level seed bank size was not significantly correlated with stand age. Fire-dependent obligate seeding species are sensitive to fire return interval because of potential changes in the size of seed banks – facing both a potential `immaturity risk' and a `senescence risk'. At our site, C. sargentii regeneration was substantial in stands as young as 20 years, suggesting that fire return interval would need to be shorter than this to pose any significant risk. Reduced seedling recruitment in stands nearly 100 years of age may indicate risk from senescence is greater, however, even the lowest density seedling recruitment was many times greater than the density of mature forests – thus this cypress would appear to be resilient to a wide range of fire return intervals. Changes in landscape patterning of forest and chaparral are unlikely except after fire. Factors that inhibit tree establishment within the shrubland, as well as factors that affect shrub establishment within the forest border likely affect the `permeability' of this ecotone. After the 1994 fire this boundary appeared to be stable in that cypress recruited best within the shadow of burned canopies and cypress were weak invaders of adjacent shrublands.     

Historic DNA reveals genetic consequences of fragmentation in an endangered,endemic mustard

Understanding how anthropogenic disturbance affects genetic diversity is essential to appropriately incorporating genetic considerations into conservation plans. Unfortunately, we rarely have information about a population’s genetic diversity before it becomes imperiled. Here we reconstruct the historic range of the naturally rare annual mustard Streptanthus glandulosus subsp. niger (Sgn) and use herbarium specimens to quantify pre-disturbance genetic diversity. We compare this to the genetic diversity in the contemporary plant populations and to plants in the seed bank. We conclude that Sgn was recently a single, panmictic population composed of orders of magnitude more plants than exist today but experienced recent and abrupt declines following housing development. Today Sgn persists as two disjunct populations, the larger of which has retained historic levels of diversity although there is a downward trend in all measures. The smaller population has lost 21–28% of the diversity that was present only 50 years ago with an N_e?~?5–16. The contemporary populations have differentiated from each other due to drift. The seed bank contained no novel alleles and had high levels of homozygosity, indicating that it is incapable of providing genetic rescue. This novel combination of hDNA, the aboveground plant population and the seed bank can be used to design high impact conservation plans that appropriately incorporate genetic diversity for this and other imperiled species.

     

Genetic comparisons between seed bank and <Emphasis Type="Italic">Stipa krylovii</Emphasis> plant populations

The soil seed bank represents the potential plant population since it is the source for population replacement. The genetic structure of a Stipa kryiovii (Roshev.) plant population and its soil seed bank was investigated in the Xilinguole Steppe of Inner Mongolia using random amplified polymorphic DNA (RAPD) analyses. The population was sampled at two sites that were in close proximity to each other (0.5 km apart). Thirty plants and 18 seed bank samples were taken from each site to determine the genetic diversity between sites and between sources (plant or seed). The material was analyzed using 13 primers to produce 92 loci. Eighty-six were multi-loci, of which 23 loci (26.74%) of allele frequencies showed significant differences (P ≤ 0.05). The genetic similarity between two seed bank sites was 0.9843 while the genetic similarity between two plant sites was 0.9619. Their similarities were all greater than that between the seed bank and plant populations. An analysis of their genetic structure showed that 87.86% of total variation was derived by two-loci. Genetic structures between plant and soil seed bank populations in S. krylovii were different due to the variance of mean gametic disequilibria and mean gene diversity. AMOVA results showed that the majority of variance (88.62%) occurred within sites, 12.75% was from between-groups. Further research is needed to investigate the selective function in maintaining the genetic diversity of Stipa krylovii plant populations.     

Recovery after African Olive invasion: can a ‘bottom‐up’ approach to ecological restoration work?

African Olive (Olea europaea ssp. cuspidata) is a densely crowned evergreen small tree, native to eastern Africa that is highly invasive in areas where it has been introduced, including Hawaii and Australia. Invasion by African Olive threatens Cumberland Plain Woodland, a critically endangered grassy eucalypt woodland from western Sydney, Australia, through the formation of a dense mid‐canopy excluding the regeneration of native species. We established a 3‐year field experiment to determine the effectiveness of direct seeding and fire, as techniques for early stage restoration of a 2 ha historically cleared and degraded Cumberland Plain Woodland site after the removal of African Olive. Direct seeding was able to re‐establish a native perennial grass cover which was resistant to subsequent weed invasion and could be managed as an important first stage in woodland restoration with fire and selective herbicide. Fire was able to stimulate some germination of colonising native species from the soil seed bank after 15 years of African Olive invasion; however, germination and establishment of native shrubs from the applied seed mix was poor. We propose a ‘bottom‐up’ model of ecological restoration in such highly degraded sites that uses a combination of direct seeding and stimulation of the soil seed bank by fire, which could be applicable to other degraded grassy woodland sites and plant communities.     

Ant-mediated expansion of an obligate seeder species during the first years after fire

Most obligate seeder species build up a soil seed bank that is associated with massive seed germination in the year immediately after a fire. These species are also shade‐intolerant and disappear when vegetation cover closes, creating unsuitable conditions for seedling recruitment. The only way for these plants to expand their populations is when habitats suitable for seedling recruitment arise (i.e. in years immediately after a fire). However, short primary seed dispersal of obligate seeders does not allow these plants to colonise the suitable habitats, and these habitats can only be colonised by secondary seed dispersion. We hypothesised that Fumana ericoides, an obligate‐seeding small shrub, not only establishes abundantly in the first year after fire, but also expands its local range in the following years due to secondary dispersal by ants while suitable habitats are still available. We tested this hypothesis using experimental studies and a simulation model of potential population expansion in a recently burned area. Results showed that F. ericoides not only established prolifically in the year immediately after fire, but was also able to recruit new individuals and expand its population in the years following the fire, despite a low germination rate and short primary seed dispersal. Ant‐mediated seed dispersal and availability of suitable habitats were key factors in this phenomenon: ants redistributed seeds in suitable habitats while they were available, which accelerated the expansion of F. ericoides because new plants established far away from the core population.     

Population structure and reproductive status of two Banksia shrubs at various times after fire

Populations of the obligate-seeder, Banksia ericifolia, were even-aged. Seedling recruitment occurred only after fire. Mean genet size (height + canopy diameter; H+D) increased progressively with elapsed time since fire in stands last burnt 2–23 years before 1981. Populations of a co-occurring resprouter, B. oblongifolia, were mixed-aged. Genet size varied significantly between stands, but this variation was not explained by regressions of H+D on years since fire. In addition B. oblongifolia seedlings were recruited both after fire and in patches of heath unburnt for 16 years.Most flower and seed production in B. oblongifolia occurred in the stands last burnt less than 10 years previously. More than 30% of genets had not produced cones since the last fire, irrespective of how many years had elapsed. In contrast, few B. ericifolia genets had produced cones five years after fire, but by 16 years after fire nearly 100% had. Overall, about 51% of B. ericifolia inflorescences and about 28% of B. oblongifolia inflorescences set seed. The number of seeds in seed-bearing cones was not significantly different between species.Resprouting B. oblongifolia genets began flowering sooner after fire, but B. ericifolia subsequently overtook them in accumulating a bank of serotinous seeds. In the stand unburnt for 23 years the largest B. ericifolia genets had more than twice as many cones as the largest co-occurring B. oblongifolia. However, when accumulated cone production was compared for genets of equal H+D over all stands, there was no difference between species.We thank the New South Wales National Parks & Wildlife Service for permission to do this work in Ku-ring-gai Chase National Park. We are grateful to Don Adamson, Lynn Day, David Haig and James Sim for constructive comments on earlier drafts.     

Canopy effects of the invasive shrub Pyracantha angustifolia on seed bank composition,richness and density in a montane shrubland (Córdoba,Argentina)

Abstract Invasive woody species frequently change the composition of the established vegetation and the properties of the soil under their canopies. Accordingly, invasion may well affect regenerative phases of the community, especially at the seed bank level, likely influencing community restoration. Pyracantha angustifolia (Rosaceae) is an invasive shrub in central Argentina that affects woody recruitment, particularly enhancing the recruitment of other exotic woody species. There is though no information regarding its effect on the soil seed bank within the invaded community. The present study was set up to gain further insight into the canopy effects of P. angustifolia. We aimed to assess whether the invasive shrub affects seed bank composition, richness and seed density as compared with the dominant native shrub Condalia montana (Rhamnaceae), and to relate the observed seed bank patterns with those of the established vegetation. We evaluated the composition of the germinable seed bank and the established vegetation under the canopy of 16 shrubs of P. angustifolia, 16 shrubs of C. montana, and in 16 control plots (10 m²) without shrub cover. The floristic composition of the seed bank differed among canopy treatments. However, seed bank richness did not differ significantly. There was an overall high seed density of exotic species throughout the study site, though exotic forbs showed significantly lower seed densities under the invasive shrub. Pyracantha angustifolia would not promote the incorporation of new species into the seed bank of the invaded community but rather favour the establishment of woody species that do not depend on seed banks. The absence of dominant woody species in the seed bank, the dominance of exotic forbs, and the high similarity between established exotic species and those present in the seed bank may surely affect community restoration following the main disturbances events observed in the region.