Seed germination ecology in southwestern Western Australia

Germination responses of species from the native plant communities of southwestern Western Australia can be related to syndromes of life history, fire response, and seed storage, and also to factors related to environmental stress. The Mediterranean-type climate of the region with periodic drought and recurrent fires affects the production of viable seeds in plants of limited stature and rooting depth. Fire response ephemerals and species cued to flower by fire tend to produce viable, readily germinable seeds, but there are instances where seed production is aborted in these predominantly herbaceous life forms. Clonal, rhizomatous species often produce mainly inviable seeds. Production of viable seeds in woody species of these highly diverse communities may also be restricted by limitations to cross pollination. Obligate post-fire seeding species tend to produce a greater proportion of viable seeds than species which are capable of resprouting following fire. Serotinous species, whether post-fire re-seeders or post-fire resprouting species, produce mainly viable seeds, which germinate readily once freed from protective fruits. Species of the legume families and a few others of the soil seed bank produce innately dormant seeds which can be germinated following heat shock treatments which simulate the effects of fire. Heat shock in these species appears mainly as a mechanism to crack the hard seed coats, but the effect of heat to denature seed coat inhibitors has not been eliminated. Western Australian species do not seem to break dormancy when exposed to leachates from burned wood as has been observed in comparable habitats in California and South Africa, but further research is advised. Germination in many native southwestern Australian species is cued by temperatures that correspond to the winter rainfall period. There are also indications that an after-ripening period of warm, dry storage increases percentage of germinable seeds. Stimulation of germination by hormones is almost unresearched in Western Australia, but germination percentages have been increased in a small number of species of horticultural potential. Stimulation of germination by soil nutrient concentrations is almost unresearched in Western Australia, except for the inhibitory effect of excess sodium chloride levels inEucalyptus andMelaleuca. These species only germinate when osmotic effects are reduced to lower levels as would occur when winter rains dilute soil salts. Application of research on seed germination has already enhanced the establishment of seedlings in the restoration of mine sites and is becoming important in aspects of the breeding and selection of native plants for the cut flower, bedding plant and essential oil industries.     

Seed longevity and fire: germination responses of an exotic perennial herb in NW Patagonian grasslands (Argentina)

Fire affects grassland composition by selectively influencing recruitment. Some exotic species can increase their abundance as a consequence of fire-stimulated seed germination, but response may depend on seed age. Rumex acetosella L. (Polygonaceae, sheep's sorrel) is a cosmopolitan herb that has invaded NW Patagonia's grasslands. This species forms persistent soil seed banks and increases after disturbances, particularly fire. We studied how fire and seed longevity influence R. acetosella germination. In 2008, we conducted laboratory experiments where we exposed different-aged seeds (up to 19 years old) to heat, smoke, charcoal, ash and control treatments. Total percentage germination and mean germination time depended on both seed age and fire treatment. Germination of younger seeds decreased with increasing temperature. There was no general pattern in germination responses of different-aged seeds to smoke, charcoal and ash. While smoke improved the germination of fresh seeds, charcoal decreased germination. Germination of untreated seeds was negatively correlated with seed age, and mean germination time increased with seed age. In most treatments, fresh seeds had lower germination than 1-5-year-old seeds, indicating an after-ripening requirement. Smoke stimulates R. acetosella germination, causing successful recruitment during post-fire conditions. Fresh seeds are particularly responsive to fire factors, possibly because they have not experienced physical degradation and are more receptive to environmental stimuli. Knowing the colonisation potential from the soil seed bank of this species during post-fire conditions will allow us to predict their impact on native communities.     

Effects of changes in the timing and duration of the wet season on the germination of the soil seed bank of a seeder-dominated Mediterranean shrubland

In seasonal climates, rainfall patterns are highly variable across years, and can control seed bank dependent regeneration. Here we asked how changing the timing and duration of the wet season would affect the germination of the soil seed bank of a 14-year-old seeder-dominated shrubland. Soil samples, subjected or not to a heat shock, simulating fire, were set to germinate in a chamber whose conditions (temperature and photoperiod) were successively changed to simulate autumn, winter, and spring. Irrigation was implemented to produce three wet season treatments, varying its timing and duration: long (14?weeks of irrigation, during autumn, winter, and spring), medium (8?weeks, late autumn to early spring) and short (4?weeks in winter). Wet season treatments significantly affected germination of shrubs and herbs, as well as species richness and diversity, whereby the later and shorter the season, the lower these variables. Dicots were more sensitive to the treatments than monocots. The timing of the wet season was also important, as similar significant differences were found when only the first 4 weeks of each simulated wet season treatment were considered; the later the season, the lower the germination and richness. Heating the soil generally increased germination but few significant effects were found. We document that a change in the timing and/or duration of the wet season can significantly affect soil seed bank germination. We discuss these results in a context of shifting rainfall patterns under climate change.     

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.     

Energy metabolism in green cells

Background: Although fire is an important factor in determining cerrado vegetation, information about its effect on seed banks is sparse. Cerrado fires are rapidly moving surface fires with low residence time, producing only short-term heating of the uppermost centimetres of the soil. However, the reduction in vegetation cover and deposition of ashes increases the daily amplitude of soil temperature by as much as 35 °C.

Aims: To assess the effect of post-fire daily soil temperatures on the germination of one alien and nine native grasses.

Methods: Seeds were stored at alternating temperatures of 45 ºC/10 ºC (10 h/14 h) for 7 d or 30 d, simulating two different storage times in the soil seed bank before the onset of the rainy season. Germination was monitored over 30 d.

Results: The variation in temperature had a significant effect on the rate of seed germination in some species, either enhancing it (Aristida setifolia) or reducing it (Schizachyrium sanguineum). Increased storage time reduced the viability of S. sanguineum and Echinolaena inflexa. The invasive Melinis minutiflora had the highest germination rate and it also showed the best toleration of post-fire conditions (45 ºC/10 ºC) after 7 d, with significant reduction in the germination time after 30 d.

Conclusions: Fire seems to have a significant effect in the early life of cerrado grasses. Some native species responded positively to temperature oscillation, suggesting that they should be better prepared to compete with alien species after a fire, with more of their seeds germinating and/or at a more rapid rate.     

Spatial relationships between the standing vegetation and the soil seed bank in a fire-prone encroached dehesa in Central Spain

Postfire vegetation regeneration in many fire-prone ecosystems is soil seed bank dependent. Although vegetation and seed bank may be spatially structured, the role of prefire vegetation patterns and fire in determining postfire vegetation patterns is poorly known. Here, we investigated the spatial patterning of species abundance and richness in the vegetation and seed bank of a Mediterranean encroached dehesa in Central Spain. The seed bank was studied with and without a heat shock simulating a spatially homogeneous fire. Semivariograms and cross-semivariograms showed that species richness in the vegetation was aggregated in patches, mainly of herbs, with highest values corresponding to high herb cover and low tree cover. Species richness in the seed bank was also structured in patches, but the spatial pattern was weak. Seedling density of germinates in the seed bank also showed weak spatial pattern. Heating increased overall germination and species richness, and the intensity of the spatial pattern of species richness, particularly of herbaceous species. However, seed bank density patterns disappeared after heat shock because of increased germination of shrubs without spatial pattern. Our results document that the spatial structure of plant richness in the vegetation may persist after fire due to the spatial patterns of herbaceous species in the seed bank, and that postfire species richness patterns can arise independently of fire intensity patterns. However, the spatial structure of the vegetation after fire can be altered by the feedback between shrub encroachment and an eventual fire because of the ubiquitous germination of shrubs.     

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

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

Seasonal variation in seed bank composition and its interaction with nutrient enrichment in the Everglades wetlands

In the Florida Everglades, nutrient enrichment from agricultural outflow and the change in hydrology have collectively contributed to the expansion of cattails (Typha spp.). To assess the effectiveness of prescribed fire in controlling cattails and to predict vegetation dynamics after the fire, it is important to understand the seasonal variation of the soil seed bank and how the seed bank is affected by nutrient enrichment and fire. This paper investigates the effects of season, nutrient enrichment, and fire on soil seed bank species composition, richness, and density along a nutrient gradient in Water Conservation Area 2A (WCA 2A) of the Florida Everglades. Species richness was significantly affected by nutrient enrichment and season but not their interaction. Total seed density, however, was significantly affected by the interaction between nutrient enrichment and season. Yet, at species level, the relationship between seed density, nutrient enrichment and season varied. The highest seed density of cattail occurred in summer at highly enriched sites, but that of sawgrass occurred in fall regardless of enrichment; the seed density of water lily was very low regardless of season and nutrient enrichment, and the highest Amarathus seed density occurred at highly enriched sites year round. Moreover, germination timing differed greatly among species. While cattail seeds had a short incubation period and started to germinate 2–3 days after initiation of the germination assay, sawgrass seeds generally started to germinate 4 weeks later. Further, both the prescribed summer fire at the highly enriched site and the natural winter fire at the moderately enriched site reduced the seed density of cattail but not of sawgrass. Our results suggest that fire application for vegetation recovery in WCA 2A would benefit from explicitly considering seasonal dynamics of the seed bank.     

Comparative seed biology and co-existence of two fynbos shrub species

Abstract. Fire-prone fynbos communities include numerous species which are difficult to distinguish in terms of conventional niche axes since they are morphologically similar and share the same broad life-history traits. These species compete for space after each fire and lottery theory predicts that those with dissimilar per capita regeneration would not co-exist in the long-term. We studied seed production, soil seed bank dynamics, germination and post-fire seedling establishment and mortality of two obligate reseeding, morphologically similar shrubs which co-occur in dune fynbos throughout the southwestern Cape. Passerina paleacea produced 30 x more plump seeds and maintained soil seed banks between 1.5 x (pre-dispersal) and 2.6 x (post-dispersal) times larger than Phylica ericoides. Seeds of both species showed a high degree of dormancy although germination was stimulated by direct fire-related cues for Phylica only. Approximately 4 x more Passerina seedlings than Phylica seedlings were counted at the end of the winter germination period after a mild autumn fire. However, seedling mortality in the first five months of the dry summer was more than twice as high for Passerina than for Phylica. We suggest that the long-term co-existence of these two species does not result from similar post-fire regeneration success but rather from population instabilities arising from differential regeneration in relation to fire regime. The results predict that hot fires followed by dry summers would favour Phylica over Passerina as the former has fire-stimulated germination and greater drought tolerance; cool fires followed by moist summers would favour Passerina.     

Fire as a stimulant of shrub recruitment in northwestern Patagonian (Argentina) grasslands

One strategy of plant survival during post-fire succession is to persist and regenerate by recruiting new individuals from a fire-resistant seed bank. The heat, smoke, and charcoal released during plant combustion may act (individually or in combination) as a cue for post-fire seed germination. Fabiana imbricata is a shrub that forms persistent seed banks in the northwestern Patagonian grasslands and shows a high recruitment from seeds during post-fire succession. Mathematical models showed that this species is advancing over the grasslands in response to fires. To corroborate these findings, we studied the role of fire on F. imbricata seed germination. In order to achieve this, a factorial experiment was designed in laboratory conditions to study the effect of heat, charcoal, smoke, scarification, and their interactions on F. imbricata seed germination. Seeds treated with the higher temperatures required a longer period of time to germinate, thus, significantly affecting the mean germination time. Total germination percentages in F. imbricata were significantly enhanced by smoke and scarification, but the interaction of heat, smoke, and scarification was more important than the effect of each fire factor alone. The positive response to fire cues exhibited by F. imbricata indicates that this species would have an adaptive advantage to colonize these grasslands if fire frequency increased, as predicted for this environment. Hence, fire will contribute to the grassland encroachment by this species and, therefore, to the loss of biodiversity and productivity of northwestern Patagonian grasslands.     

Effects of biological soil crusts on seed germination of four endangered herbs in a xeric Florida shrubland during drought

Soil crusts of rosemary scrubs in south-central Florida were examined for effects on seed germination of four herbs that are killed by fire and must recruit from seed: Eryngium cuneifolium (Apiaceae), Hypericum cumulicola (Hypericaceae), Polygonella basiramia (Polygonaceae), and Paronychia chartacea ssp. chartacea (Caryophyllaceae). Biological soil crusts in these sites are dominated by algae, cyanobacteria, fungi, and bacteria. Because crusts can change soil stability, water, and nutrients, they can affect seed germination. A series of greenhouse and field experiments were designed to first examine the effects of crusts in isolation and then to determine their role in the context of other environmental factors – time since fire and distance to the dominant shrub in this system, Ceratiola ericoides. In the greenhouse experiment, germination in autoclaved crusts was dramatically reduced relative to germination in living crusts for all but P. basiramia. In four field experiments where crusts were left intact, disturbed (mechanically or by flaming), or completely removed, the effects of crusts were variable and species-specific, but were significant enough to impact aboveground population sizes. More germination was consistently observed in recently burned sites away from C. ericoides shrubs. Overall rates of germination were generally very low during this study, possibly as a result of seasonal droughts that could have reduced germination, increased seed dormancy, and/or decreased seed viability. The importance of water for germination was confirmed in an experiment with two watering regimes and three crust treatments designed to create a gradient of soil water availability. Germination was significantly greater in the high water treatment and unaffected by soil crust moisture. Dry years are not uncommon in scrub and the results of this study help us to understand how scrub herbs fare during drought and what role biological soil crusts play in germination.     

Effect of fire on hard-coated Cistaceae seed banks and its influence on techniques for quantifying seed banks

The impact of fire on hard-coated Cistaceae (Halimium ocymoides, Cistus ladanifer, and C. salvifolius) soil seed banks in a Mediterranean 'maquis' shrubland, and its effect on seed germinability were studied. The study also contrasts the effectiveness of two widely used techniques for quantifying seed banks, the seedling emergence and the physical separation methods, in relation to fire. The null hypothesis that a massive enhancement of physically-dormant Cistaceae seed germination by fire would make use of the time-consuming physical separation technique unnecessary was tested. Fire reduced Cistaceae seed banks in the 0–2 cm deep soil layer by both seed fire-consumption and lethal temperatures, revealed by the significant decreasing of the seed bank density and by the increase of apparently-intact but soft-unviable seeds, respectively. In contrast, no damage was recorded in the 2–5 cm soil layer. A dramatic seed bank depletion (> 90%) in both soil layers was recorded one year after fire in the burnt area, coinciding with a significant increase of seedling density confined to the first post-fire year. The ecological consequences of this massive post-fire seed bank input are discussed. A germinability test revealed that germination of surviving Cistaceae seeds was significantly enhanced in all cases except for the C. salvifolious seed bank in the deeper soil layer. However, final germination levels (60–75%) did not correspond to the magnitude of seed bank depletion, especially for C. salvifolious, which suggests that other environmental factors not exclusively associated with fire may also be important in softening Cistaceae seeds. Germination enhancement by fire soil-heating was not high enough to reject the physical separation technique, at least in the deeper soil layer. The simultaneous use of both seedling emergence and physical separation is recommended for reliable seed bank estimates when a physically-dormant hard-seeded component can be expected in the soil, as in many Mediterranean ecosystems, regardless of fire occurrence.     

Dormancy and the fire-centric focus: germination of three Leucopogon species (Ericaceae) from South-eastern Australia

BACKGROUND AND AIMS: Germination studies of species from fire-prone habitats are often focused on the role that fire plays in breaking dormancy. However, for some plant groups in these habitats, such as the genus Leucopogon (Ericaceae), dormancy of fresh seeds is not broken by fire cues. In the field, these same species display a flush of seedling emergence post-fire. Dormancy and germination mechanisms therefore appear complex and mostly unknown. This study aimed to identify these mechanisms by establishing dormancy class and testing the effects of a set of typical germination cues, including those directly related to fire and entirely independent of fire. METHODS: To classify dormancy, we assessed seed permeability and embryo morphology, and conducted germination experiments at seasonal temperatures in incubators. To test the effects of fire cues on germination, factorial combinations of smoke, heat and dark treatments were applied. Ageing treatments, using burial and seasonal incubation, were also tested. Germination phenology was established. KEY RESULTS: Seeds were dormant at release and had underdeveloped embryos. Primary dormancy of the study species was classified as morphophysiological. Seasonal temperature changes overcame primary dormancy and controlled timing of germination. Fire cues did not break primary dormancy, but there was a trend for smoke to enhance germination once this dormancy was overcome. CONCLUSIONS: Despite the fact that fire is a predominant disturbance and that many species display a flush of emergence post-fire, seasonal temperatures broke the primary physiological dormancy of the study species. It is important to distinguish between fire being responsible for breaking dormancy and solely having a role in enhancing levels of post-fire germination for seeds in which dormancy has been overcome by other factors. Biogeographical evidence suggests that morphological and physiological factors, and therefore seasonal temperatures, are likely to be important in controlling the dormancy and patterns of post-fire germination of many species in fire-prone regions.     

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.     

Burning grasses,poor seeds: post-fire reproduction of early-flowering Neotropical savanna grasses produces low-quality seeds

Fire is a key factor triggering ecological processes in old-growth grasslands and savannas and could have strong implications for reproduction via seeds for the herbaceous layer. In the Neotropical savannas, grasses show strong synchronous post-fire flowering, and their reproduction is often considered fire-dependent, with their massive post-fire seed production being suggested as a source of population maintenance. However, literature lacks studies to provide evidence of fire-dependent flowering and no study has assessed the quality of the post-fire seed production. Therefore, we aimed to describe a phenological pattern across early-flowering Neotropical savanna grasses in both recently burnt and unburnt cerrado communities addressing three questions: (1) Do the early-flowering species rely on fire for reproduction via seeds? (2) If no, what are the effects of fire on their reproductive phenology? (3) Does the massive seed production in post-fire cerrado communities lead to high-quality seeds? We recorded the reproductive phenology of nine early-flowering grasses for 17 weeks in unburnt and recently burnt cerrado communities. We collected the seeds, estimated the production of fertile seeds, and tested germination. No species showed a pattern of fire-dependent reproduction. Fire stimulated earlier flowering while reproduction in the unburnt community was related to continuous rainfall. Seed production following fire was of low quality, and no species produced?>?7% fertile seeds. Seed germination remained below 50% for most species. Post-fire seed production of early-flowering species led to poor seed quality, suggesting a constraint to the recruitment of new individuals of early-flowering Neotropical savanna grasses in recently burnt cerrados.

     

Fire severity affects vegetation and seed bank in a wetland

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

Germination response to various temperature regimes of four Mediterranean seeder shrubs across a range of altitudes

In dry-summer seasonal climates, the beginning of the rainy season can prompt germination under different temperatures, depending on altitude. Understanding germination responses to temperature with altitude is important in fire-prone environments for species regenerating after fire from seeds (seeders), particularly under changing climate. Here we investigated the role of temperature in four Mediterranean seeder shrubs from Central Spain. Seeds from 17 sites (285–1,253 m altitude), of two hard-seeded nanophanerophytes (Cistus ladanifer and C. salviifolius) and two soft-seeded chamaephytes (Lavandula pedunculata and Thymus mastichina) were investigated. Intact and heat shock treated seeds were set to germinate under four temperature regimes, including a treatment simulating future warming. GLM with binomial or gamma functions were used to test treatment effects using altitude as a covariate. Altitude was a significant covariate only in L. pedunculata. Temperature did not affect final germination in either Cistus, but it significantly affected T. mastichina, and interacted with altitude in L. pedunculata, whereby the higher the altitude the less it germinated with decreasing temperature. Germination speed (T₅₀) was lower at colder temperatures in all but C. salviifolius that was insensitive to our treatments. Heat shock significantly increased final germination in both Cistus and T. mastichina, but did not interact with temperature or altitude. We conclude that germination response to temperature, including varying sensitivity with altitude, differed among these species; thus, changes in the timing of the onset of the rainy season will diversely affect populations at various altitudes. We discuss our results in a context of changing climate and fire.     

Evidence for direct effects of fire‐cues on germination of some perennial forbs common in grassy ecosystems

In grassy ecosystems of south‐eastern Australia, fire maintains richness of native forbs. It is commonly thought that fire promotes regeneration indirectly by reducing competition for light and providing gaps for recruitment, rather than directly stimulating germination. However, physiological dormancy and morphophysiological dormancy are common, and few studies have explored responses to fire‐cues among dormant or hard‐to‐germinate forbs. Recent studies from other fire‐prone ecosystems suggest that in some cases, fire‐cues may not alleviate physiological or morphophysiological dormancy, but instead promote germination in combination with treatments which alleviate dormancy. We experimentally tested the prevailing hypothesis that perennial forbs common in south‐eastern Australian grassy ecosystems do not germinate in direct response to fire. Responses to fire‐cues both inherently and in combination with treatments which alleviate dormancy were investigated for seven species. Two fire‐cues (smoke and heat) plus a treatment of both heat + smoke were applied to fresh seed at three temperatures (35/25°C, 30/20°C and 25/15°C). Following this, the effect of fire‐cues on seed that had undergone warm stratification, cold stratification and dry‐after‐ripening was investigated. Three species — Arthropodium strictum, Cheiranthera cyanea and Dianella revoluta — responded to fire‐cues inherently, although germination in C. cyanea was low. High germination of D. revoluta was found when fire‐cues were combined with warm stratification. Fire‐cues had no effect on germination of Brunonia australis, Burchardia umbellata and Eryngium ovinum. Germination of Stypandra glauca was zero following all treatment combinations. Our finding that fire‐cues promote germination of three of the seven study species did not provide sufficient evidence to reject the current hypothesis that germination of perennial forbs is not typically promoted by fire‐cues. However, this study highlights the important direct role fire‐cues can play in promoting germination of some perennial forbs both inherently and in combination with treatments used to alleviate physiological dormancy.     

Early post-fire regeneration of a Pinus halepensis forest on Mount Párnis,Greece

Abstract. The post-fire regeneration of a 45-yr-old Pinus halepensis (Aleppo pine) forest, burned in July 1989, has been studied on Mount Párnis, Attiki, Greece. Four experimental plots at various slopes and exposures were established at altitudes of 400 - 450 m, and monitored for 3 yr at 3-month intervals. Early regeneration took place abundantly, through both resprouting and seed germination of mostly hard-seeded herbs and shrubs; the floristic richness was high with 80 taxa. Pine seedling emergence took place during the winter of the first post-fire year. The mean pine seedling density by the end of the recruitment period (March 1990) was 5–6 seedlings/m². This density decreased slightly during late spring and considerably during summer. During the second post-fire year only a relatively slight decline was observed; thereafter the density was stabilized to 1 - 2 seedlings/m². Mortality follows a negative exponential curve that levels off at ca. 20 %. Height distributions throughout the three post-fire years were all positively skewed as a result of the presence of few very tall saplings. A considerable fraction (20 %) of very short (5–15 cm) saplings were still alive 39 months after the fire; these may constitute the sapling bank. Based on the analysis of height distribution curves, it is concluded that the taller seedlings survived significantly better than the shorter ones.     

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

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