Fire-related Germination Cues Research Articles

Concurrent assessment of functional types in extant vegetation and soil seed banks informs environmental constraints and mechanisms of plant community turnover in temperate forests of south-eastern Australia

Our understanding of how environmental heterogeneity shapes plant community dynamics is largely based on above-ground diversity despite the importance of seed banks as reservoirs of genetic and taxonomic diversity that buffer plant populations and influence vegetation following disturbance. Using a plant functional trait approach, this study examined the importance of fire-related germination cues and environmental determinants of plant community turnover in wet forests of south-eastern Australia – forests of both high conservation value and the focus of current timber harvesting. We surveyed extant vegetation, soil seed banks, forest structure and edaphic properties across 62 sites burnt in 1939 and not subsequently affected by wildfire or logging. A total of 46 families, and 99 species were identified in extant vegetation with 43 and 126 respectively in the soil seed bank, with only 32% of species co-occurring in both species’ pools. Despite historically long fire return intervals, the soil seed bank demonstrated a clear positive response to fire-related germination cues (heat in combination with smoke) that were concentrated in hard-seeded species dispersed by ants. Seeds from early successional species showed no response to fire cues, while species typical of the wetter margins of these forests were killed by high heat. The soil seed bank was dominated by species associated with early successional stages, consistent with the initial floristics model of succession. Woody species were largely restricted to extant vegetation and replacement is most likely to occur from future seed rain. Spatially structured environmental heterogeneity shaped plant turnover with the relative strength of environmental controls differing among functional types and pools of diversity. Differential response of the combined species pool relative to extant vegetation demonstrates that the soil seed bank provides a storage effect. Forest management practices that generate patchy and heterogenous environments, including the intensity of regeneration burns and density of overstorey species, will benefit biodiversity conservation through overstorey structural controls on resource availability and diversity of understorey vegetation, that is transferred to soil seed banks via tight abiotic controls and seed inputs.

How fire history affects germination cues of three perennial grasses from the mountain steppes of Golestan National Park

Smoke and heat as germination cues are some of the most important drivers stimulating seed germination. However, the impact of germination factors from wildfire (i.e., smoke and heat) on the germination of species occurring in western Asia has rarely been investigated. We aimed to analyze the effects of different smoke and heat treatments on seed germination of three perennial grasses (Festuca valesiaca, Poa densa, and Stipa zalesskii) collected from two non-burned and burned environments of the mountain steppes in Golestan National Park, Iran. Seeds were germinated on filter paper following smoke (1:2000, 1:1000, and 1:500, v/v) or heat (50, 80, 100°C) treatments. Results showed that the germination of study species was reduced by heat treatments, whereas no particular response was observed with the smoke treatments.Interestingly, the fire history influenced magnitude of effects of fire-related germination cues, leading to slightly lower germination for F. valesiaca and P. densa and higher germination for S. zalesskii. Our results indicate that fire-related germination cues have different impacts on these grassland species. The consideration of the fire history of specific sites on germination ecology seems important to understand the effects of fire on the plant communities.

Fire effects on seed germination: Heat shock and smoke on permeable vs impermeable seed coats

Flammable ecosystems host plants with different strategies in response to fire, such as increasing germination after the exposure to smoke and dormancy breaking by heat shocks. Cerrado is a fire-prone ecosystem, but less is known about fire-related germination cues compared to Mediterranean-like ecosystems. Here, we hypothesize that seeds with a permeable tegument (Melastomataceae) respond positively to smoke (increase in germination), while species with physical dormancy (Fabaceae) have dormancy broken by exposure to high temperatures. We exposed seeds from Fabaceae and Melastomataceae species to high temperatures and smoke solution to simulate fire. Finally, we combined the two treatments (heat shock + smoke). Our results showed that seeds of two legumes (Harpalyce sp. and Mimosa leiocephala) had their physical dormancy broken when exposed to high temperatures, while one Fabaceae (Mimosa somnians) and two Melastomataceae showed an increase in germination when exposed to smoke solution. Lastly, four Fabaceae and two Melastomataceae species responded when combining heat shock and smoke. Contrary to our predictions, the responses to fire stimuli in Cerrado species did not show a clear response pattern, as those found in Mediterranean vegetation, probably due to differences in fire regime. However, we showed novel results about smoke stimulation for some species and positive effects of combined treatments. Thus, Cerrado seeds differ in response to fire, showing that cues for germination are more complex than previously thought, differing from other fire-prone ecosystems.

Multiple fire-related cues stimulate germination inChaenorhinum rubrifolium(Plantaginaceae), a rare annual in the Mediterranean Basin

AbstractIn Mediterranean fire-prone ecosystems, annual species specific to post-fire habitats should have a soil seed bank and should be able to germinate after a fire. Therefore, various fire-related cues can be expected to stimulate germination in post-fire annuals. Germination patterns of the rare annualChaenorhinum rubrifolium(Plantaginaceae) were examined in response to mechanical scarification, heat shock, aqueous smoke, nitrogenous compounds, gibberellic acid, karrikinolide (KAR1), and mandelonitrile (a cyanohydrin analogue, MAN) under dark and photoperiod conditions in the laboratory. Combinations of these treatments were also included in the experiment. Strong physiological dormancy in the seeds ofC. rubrifoliumwas partially broken by several fire-related germination cues, including smoke and nitrate, under light conditions. KAR1and MAN also stimulated germination, and the highest improvement in germination was achieved in the KAR1treatment in the presence of light. Heat shock + smoke and KAR1+ MAN combinations had positive synergetic and additive effects on germination under light conditions, respectively. The light played a crucial role in the promotion of germination. The results suggest that multiple fire-related cues operate to stimulate germination inC. rubrifolium, an annual species from the Mediterranean Basin. However, the species may have a broader germination niche than a fire-restricted one.

Fire-related cues and the germination of eight Conostylis (Haemodoraceae) taxa, when freshly collected, after burial and after laboratory storage

AbstractThe genus Conostylis (Haemodoraceae) is endemic to fire-prone south-western Australia. To gain an understanding of the effect of some fire-related germination cues, eight Conostylis taxa were tested in response to water, nitrate, smoke water and karrikinolide (KAR1) under light and dark conditions, when seeds were freshly collected and after a year of burial. The germination of all taxa tested was higher in response to smoke water and KAR1 than in water alone, whereas nitrate did not stimulate germination. Germination was higher in all taxa following 1 year of burial than in fresh seeds. Recently, glyceronitrile has been identified as another chemical in smoke water, apart from KAR1, that can stimulate the germination of certain species. The relative response of eight Conostylis taxa to KAR1, glyceronitrile and smoke water was examined in laboratory-stored seeds. Germination of these taxa was promoted by both smoke water and KAR1, except for C. neocymosa, which had high germination regardless of treatment. Four of the other seven taxa germinated to higher levels in at least one of the glyceronitrile concentrations tested (10, 50 or 100 μM) than in water alone. However, in only two of these taxa, C. aculeata subsp. septentrionora and C. juncea, was germination in glyceronitrile as high as that in smoke water. Thus, the response to glyceronitrile is not uniform across Conostylis taxa. Generally, germination was higher with KAR1 than glyceronitrile, suggesting that although some Conostylis taxa have the capacity to respond to glyceronitrile, KAR1 is the more important germination stimulant for this genus.

Effects of Fire on Germination of Ericameria fasciculata (Asteraceae), a Rare Maritime Chaparral Shrub

Knowledge gaps regarding the greenhouse propagation of rare, fire-adapted plant species can impede community level conservation efforts that require fire and active revegetation as management tools. Ericameria fasciculata is a rare shrub endemic to the maritime chaparral community of the central California coast and a listed species of concern. Prescribed burning is actively used in maritime chaparral to maintain community composition and conserve several species of concern with known affinities for fire-related conditions. No study has investigated the seed viability and germination requirements for E. fasciculata. The goal of this study was to ascertain the (1) greenhouse propagation potential of E. fasciculata for planned restoration efforts and (2) to determine if fire-related conditions inhibit or promote E. fasciculata germination. Seed dissection and viability testing indicated that a large percentage of seed were empty or inviable. A greenhouse study examined the potential for fire-related germination cues from heating, light, and charate. Heating and charate had negative effects on seed germination. The combination of heating and charate treatments were particularly lethal. Exposure to light or the addition of GA3 had no influence on germination rates. Results suggest that seed germination of E. fasciculata is inhibited by fire and, therefore, this species is dependent on seedling establishment between fire events.

Applying seed germination studies in fire management for biodiversity conservation in south-eastern Australia

Abstract. We examine the patterns of germination response to fire in the fire-prone flora of the Sydney basin, south-eastern Australia, using examples from several decades of research. The flora shows a strong response to fire-related germination cues. Most species show an interaction between heat and smoke, a number respond only to heat, whilst a few are likely to respond only to smoke. Many recruit in the first 12 months after fire and show no obvious seasonal patterns of recruitment, whilst several species have a strong seasonal germination requirement, even in this essentially aseasonal rainfall region. Key challenges remaining include designing future seed germination studies within the context of informing the germination response surface to smoke and heat interactions, and incorporation of the impact of varying soil moisture on seed germination post-fire, including its affect on resetting of seed dormancy. An understanding of the resilience of species to frequent fire also requires further work, to identify species and functional types most at risk. This work must ideally be integrated within the framework of the management of fire regimes that will change under a changing climate. We suggest that the functional classification of plant types in relation to fire could be enhanced by a consideration of both the type of germination response to fire (type of cues required) and the timing of the response (seasonally driven in response to seed dormancy characteristics, or independent of season). We provide a simplified version of such an addition to functional trait classification in relation to fire.

The effect of fire-related germination cues on the germination of a declining forest understorey species

Fire is an important component of most Australian terrestrial ecosystems and exerts a major influence on plant recruitment in these systems. Seeds of species from Australian heath, woodland and grassland systems have a diverse response to fire-related germination cues. Australian forests are also subject to fire events. However, for species of these forests, the diversity of germination responses to fire-related germination cues is poorly known. This study reports on the germination response of seed of Prostanthera askania Conn (Lamiaceae), a species restricted to eucalypt forests and eucalypt forest–rainforest boundaries. Smoke and heat shock negatively interact in relation to the germination level of P. askania seed. Thus, in this study, smoke elevated the germination level of P. askania seed only in the absence of applied heat treatments. P. askania seed also displayed high levels of dormancy, but unlike some related species, smoke effected a partial dormancy break. These results suggest that low-intensity fire may be optimal for the germination of this species. This is supported by an observed germination response of this species to a low-intensity fire and low-intensity fire may be a common feature of species of rainforest–eucalypt forest boundaries. However, other species in these systems have germination levels maximised by cues associated with high-intensity fire. Shifts in rainforest boundaries, reported effects of weed invasion on fire intensity in rainforests and the reported decline of species as a result of increased fire intensity suggest that P. askania may have been disadvantaged by a range of habitat changes associated with fire regimes since European settlement.

Influence of multiple fire-related germination cues on three Sydney Grevillea (Proteaceae) species

Influence of multiple fire-related germination cues on three Sydney Grevillea (Proteaceae) species

Germination response of seven east Australian Grevillea species (Proteaceae) to smoke, heat exposure and scarification

Seeds of plant species from fire-prone vegetation often show dormancy, and germinate in response to fire-related cues. Seeds of some east Australian Grevillea species were known from earlier studies to germinate in response to fires, but gave mixed results when heat shock was tested as a germination stimulus. In the current study, seeds of seven east Australian Grevillea species were tested for their germination response to smoke, to short heat exposure, and to scarification. Seeds were smoked in a chamber by using a mixture of native woodland vegetation as fuel. The smoking and heating treatments were administered to seeds in bulk: this meant that subsequent germination data for these two treatments were not independent. Cumulative germination in the laboratory was scored for up to 60 days. All three germination treatments, when administered singly, increased germination: smoke increased germination in all seven species, heat in four species, and scarification in a different four species. Pairwise combinations of the three treatments also increased germination in some species e.g. smoke and heat treatments combined led to the highest germination observed in four species, and to increased germination compared with either treatment singly, in another species. Some treatment combinations appeared to interact: heat and scarification combined led to decreased germination in three species. The role of heat exposure and scarification in increasing germination was not due to the breaking of an impermeable seed coat: water uptake of both scarified and unscarified seeds was rapid and equal (after 24 h) in all seven species. The results indicate that seeds of the Grevillea species investigated are responsive to one or more fire-related germination cues.

Germination ecology of six shrubs in fire-prone Cape fynbos

To explain the recruitment and coexistence of species which establish after fire, this study predicted that each species would have different germination cues as a component of different regeneration niches. Furthermore, for species subject to natural fire frequencies of 10–20 years, fire-related cues, seed dormancy, extended longevity and fire-related germination cues might be predicted. However, results indicated broadly similar germination requirements. Seeds subjected to two heat treatments and a charcoal extract failed to show significantly enhanced germination. Instead, highest germination successes were achieved under alternating diurnal temperatures which implied an indirect fire cue, viz. the removal of insulating vegetation. Leachate solution inhibited germination in two species suggesting allelopathic effects during inter-fire periods. Only two species showed dormancy and three species did not have extended longevity but showed declining germinability after three years. Finally, in order to determine the potential germination from a soil-stored seed bank, data analysis simulated a seed bank comprising three years' accumulation of seeds. In each species the proportion of germinable seeds varied each year over the three years. Also, the germinability in response to ageing varied for each year's seed production. This would explain the variation in densities of the six species after different fire events, and hence offers a better explanation for species' coexistence.