Fire persistence traits can be used to predict vegetation response to changing fire regimes at expansive landscape scales – an Australian example

Aim Building on a substantial literature addressing the fire responses of woody plants, particularly under mediterranean climates, we assess the extent to which fire persistence traits can be used to predict vegetation responses to fire regime changes in fire‐prone arid and savanna landscape settings. Location Australia, applying data from arid central to monsoonal northern regions (11–26° S, 129–138° E). Methods With reference to a substantial sub‐continental floristics dataset, we first assigned the fire response (obligate seeder, resprouter) and seedbank persistence (transient, dormant) of rapid and longer‐maturing (> 3 years) woody taxa. Using logistic regression, we then modelled the proportions of taxa possessing these traits as a function of mean annual rainfall (highly correlated with fire frequency) and terrain roughness (a measure of topographic variability) in 0.25° × 0.25° and 1° × 1° grid cells. Separate assessments were undertaken with datasets for 1264 sclerophyll and 236 rain forest taxa. Results This woody flora is characterized by taxa exhibiting mostly resprouting and dormant seedbank traits that promote site persistence. While numbers of obligate seeder and resprouter taxa were related positively to both rainfall and roughness, the relative abundance of both sclerophyll and rain forest obligate seeders decreased significantly with rainfall. The relative abundance of sclerophyll (especially long‐lived) obligate seeders alone increased with topographic roughness. The proportion of taxa with transient seedbanks increased with rainfall in resprouters generally, and in rain forest obligate seeders alone. Main conclusions We find that resprouters are favoured on more productive, fire‐prone sites, and obligate seeders are favoured in less productive, more fire‐protected settings. Seedbank persistence responses are more variable. These findings concur generally with theoretical constructs, and support comparable assessments in Australian and other fire‐prone systems ranging from mediterranean to boreal environments. Our observations illustrate that resprouting and obligate seeding syndromes, but not necessarily seedbank persistence, are useful predictors of vegetation responses to changing fire regime conditions at large landscape scales.     

What predicts the richness of seeder and resprouter species in fire‐prone Cape fynbos: Rainfall reliability or vegetation density?

In ecosystems subject to regular canopy fires, woody species have evolved two general strategies of post‐fire regeneration. Seeder species are killed by fire and populations regenerate solely by post‐fire recruitment from a seed bank. Resprouter species survive fire and regenerate by vegetative regrowth from protected organs. Interestingly, the abundance of these strategies varies along environmental gradients and across regions. Two main hypotheses have been proposed to explain this spatial variation: the gap dependence and the environmental‐variability hypotheses. The gap‐dependence model predicts that seeders are favoured in sparse vegetation (vegetation gaps allowing effective post‐fire recruitment of seedlings), while resprouters are favoured in densely vegetated sites (seedlings being outcompeted by the rapid crown regrowth of resprouters). The environmental‐variability model predicts that seeders would prevail in reliable rainfall areas, whereas resprouters would be favoured in areas under highly variable rainfall that are prone to severe dry events (leading to high post‐fire seedling mortality). We tested these two models using distribution data, captured at the scale of quarter‐degree cells, for seeder and resprouter species of two speciose shrub genera (Aspalathus and Erica) common in fire‐prone fynbos ecosystems of the mediterranean‐climate part of the Cape Floristic Region. Contrary to the predictions of the gap‐dependence model, species number of both resprouters and seeders increased with values of the Normalized Difference Vegetation Index (a widely used surrogate for vegetation density), with a more marked increase for seeders. The predictions of the environmental‐variability hypothesis, by contrast, were not refuted by this study. Seeder and resprouter species of both genera showed highest richness in environments with high rainfall reliability. However, with decreasing reliability, seeder numbers dropped more quickly than those of resprouters. We conclude that the environmental‐variability model is better able to explain the abundance of woody seeder and resprouter species in Southern Hemisphere fire‐prone shrublands (fynbos and kwongan) than the gap‐dependence model.     

Relationship between leaf traits and fire-response strategies in shrub species of a mountainous region of south-eastern Australia

Background and Aims

Resprouting and seed recruitment are important ways in which plants respond to fire. However, the investments a plant makes into ensuring the success of post-fire resprouting or seedling recruitment can result in trade-offs that are manifested in a range of co-occurring morphological, life history and physiological traits. Relationships between fire-response strategies and other traits have been widely examined in fire-prone Mediterranean-type climates. In this paper, we aim to determine whether shrubs growing in a non-Mediterranean climate region exhibit relationships between their fire-response strategy and leaf traits.

Methods

Field surveys were used to classify species into fire-response types. We then compared specific leaf area, leaf dry-matter content, leaf width, leaf nitrogen and carbon to nitrogen ratios between (a) obligate seeders and all other resprouters, and (b) obligate seeders, facultative resprouters and obligate resprouters.

Key Results

Leaf traits only varied between fire-response types when we considered facultative resprouters as a separate group to obligate resprouters, as observed after a large landscape-scale fire. We found no differences between obligate seeders and obligate resprouters, nor between obligate seeders and resprouters considered as one group.

Conclusions

The results suggest that facultative resprouters may require a strategy of rapid resource acquisition and fast growth in order to compete with species that either resprout, or recruit from seed. However, the overall lack of difference between obligate seeders and obligate resprouters suggests that environmental factors are exerting similar effects on species'' ecological strategies, irrespective of the constraints and trade-offs that may be associated with obligate seeding and obligate resprouting. These results highlight the limits to trait co-occurrences across different ecosystems and the difficulty in identifying global-scale relationships amongst traits.     

Ecological and evolutionary differences between Mediterranean seeders and resprouters

Abstract. Differences in allocation patterns between seeders and resprouters in several Mediterranean plant communities (Australia, California and South Africa) have led to the prediction that seedlings of seeders grow faster than those of resprouters. In the Mediterranean Basin, it has also been hypothesized that regeneration strategy of plants after fire is associated with several other life history traits. This paper tests both hypotheses for the dominant plants in the Mediterranean Basin from literature data. Results show that seeders from the Mediterranean Basin grow significantly faster and allocate more biomass to leaf plus paracotyledons than resprouters. Seeders are mainly non‐sclerophyllous, anemochorous, dry‐fruited, small‐seeded species that evolved in the Quaternary (post‐Pliocene) and are associated with earlier successional stages. Resprouters are mainly sclero‐phyllous, vertebrate‐dispersed, fleshy‐fruited, large‐seeded species that evolved in the Tertiary (pre‐Pliocene) and are associated with late successional stages.     

Patterns of storage tissue and starch distribution in the young taproot of obligate seeders and resprouters of Australian Proteaceae (Juss.): Possible evidence of homoplastic evolution

The ancient Gondwanan family Proteaceae has its greatest speciation in fire‐prone environments of Australia. Fire response is either by seedling recruitment from parent plants that succumb to fire (obligate seeders), or survival and resprouting from protected buds (resprouters). Starch is the main source of energy for resprouting and in roots is restricted to parenchyma tissue. This study compared the size and distribution of storage parenchyma and the magnitude of starch reserves in roots of several proteaceous species from different genera in relation to their fire response and taxonomy. Cross‐sections (2 μm) of roots of 51 resprouter and 42 seeder species from 12 genera were stained for starch. Areas of cortex and ray parenchyma along with starch grain density were measured using image analysis software (Assess 2.0) and comparable samples of root tissue were assayed chemically for starch. Starch, where present, predominated in ray and cortex tissue with a greater percentage in resprouters (13.4 ± 1.03) than seeders (1.8 ± 0.26); these results correlated significantly with the chemical assay for starch (r = 0.93, P < 0.0001). Resprouters also had more storage parenchyma (56.9 ± 1.72%) than seeders (41.9 ± 1.91%) mostly due to broader rays (17.5 ± 1.22%) compared with seeders (8.2 ± 0.16%). Percentage of cortex tissue was similar for seeders and resprouters (39.4 ± 2.24 and 33.7 ± 2.04 respectively). Anatomical preferences for storage site were consistent within genera and broad suprageneric groupings. This study shows that histological analysis of root starch is a reliable predictor of resprouting capacity in Proteaceae and that patterns of storage tissue within genera, together with the persistence of parenchyma devoid of starch in seeders, are consistent with response to fire and suggests homoplastic evolution of this response within the family.     

Scale-dependent segregation of seeders and resprouters in cork oak (<Emphasis Type="Italic">Quercus suber</Emphasis>) forests

Recent studies showed that disturbances and water availability determine the richness among plants with different post-fire strategies of Mediterranean-type ecosystems. The aim of this study was to determine whether or not the scale of analysis has an influence on the effects of these factors and, therefore, on the segregation of the dominant post-fire strategies, obligate seeders and obligate resprouters, and facultative species. We recorded all woody species and geographical features on 94 (75 m²) plots of cork oak woodlands in the southern Iberian Peninsula. For each regenerative type (resprouters, seeders and species with both traits—facultative species), we tested the relationship between the number of species and the predictors using a generalised linear mixed model. The fixed predictor considered at the large scale was altitude, and fixed predictors considered at the local scale were aspect (north/south) and disturbance (fire and clearing by heavy machinery; yes/no). The random predictor was the factor of site. When this factor did not have significant effect for some regenerative types, these relationships was tested using a generalised linear model. Resprouting species were most represented at lower altitudes and in undisturbed sites, while seeders were also at lower altitudes but mostly on south-facing slopes, especially south-facing disturbed sites. For facultative species, site is the most important variable. The proportion of seeders from the total species is not related to altitude, but it is related to disturbance and aspect. These results suggest that there is no segregation of the richness of seeders and resprouters at the large scale (altitudinal gradient). Differences appeared at the local scale (aspect and disturbance).     

Impact of two wildfires on endemic granite outcrop vegetation in Western Australia

Abstract. In seasonally dry regions of the world fire is a recurring disturbance but little is known of how fire interacts with granite outcrop vegetation. We hypothesize that the floristic composition in granite vegetation, usually attributed to the edaphic environment, may also reflect the impact of disturbances such as fire. Dramatic differences in floristic composition and cover over 13 years and two fires were observed in vegetation on a Western Australian granite outcrop. This was very marked in the first year following the two fires, with annuals and geophytes showing the greatest turnover of species. Even among the perennial shrubs there was considerable turnover in a number of obligate seeders. After the first fire the number of species declined for woody perennials, herbaceous perennials and annuals, remained unchanged for perennial grasses and sedges, and varied with highest richness 4 yr after fire for geophytes. Demographic studies of two endemic woody obligate seeders and three endemic mallee eucalypt resprouters similarly showed dramatic differences within and between species in seedling recruitment following the two fires. Fire does have a significant impact on the floristic composition of semi‐arid granite outcrop vegetation communities. Studies on other granite outcrop systems are needed to test the generality of this conclusion.     

Costs of resprouting are traded off against reproduction in subtropical coastal dune forest trees

Resprouting can be an important means of regeneration for forest tree species resulting in multi-stemmed architecture, especially at less productive or frequently disturbed sites. However, the cost of resprouting may be traded off against growth or reproduction. In subtropical coastal forest in South Africa, trees grow on steep, sandy dunes with unstable soils and low to moderate nutrient availability. These coastal forests experience seasonally strong anticyclonic winds from August through October. We examined the hypothesis that basal resprouting resulting in multiple stems causes lower rates of sexual reproduction and recruitment by individuals. We examined whether trees traded off resprouting against seed output, seed size, seedling abundance and recruitment by seedlings. Species were designated as good and poor resprouters based on their frequency of multi-stemmed individuals at Cape Vidal. Good resprouters had more stems, produced less seed and had lower seed mass than poor resprouters, and had lower seedling abundance and fewer individuals in small diameter classes than large diameter classes. Seedling abundance in good resprouters was not influenced by the availability of understorey gaps. Good resprouters were most abundant on dune crests and seaward slopes that were exposed to sea winds. Persistence of established individuals by producing multiple stems from basal resprouts is important where a chronic disturbance regime potentially reduces the survivorship of single-stemmed individuals and thereby their opportunities for reproduction. Good resprouters appear to trade-off recruitment of new individuals for multiple stems that increase the persistence of established ones against disturbance. We conclude that multi-stemming arising from basal resprouts has evolved to promote individual persistence under low to moderate intensity but pervasive wind stress.     

Biogeography of seeder and resprouter Erica species in the Cape Floristic Region—Where are the resprouters?

The genus Erica L., with more than 600 species, and a high number of endemics, represents the most remarkable example of floristic diversity in the Cape Floristic Region (CFR). It is largely confined to nutrient-poor, acidic, sandy soils, being one of the most characteristic element of fynbos. The ability to survive fires, resprouting from a lignotuber, is a common trait among Euro-mediterranean Erica species. In contrast, resprouting is fairly uncommon among ericas in the CFR (less than 10%). Most of them are killed by fire, regenerating only but readily by seed germination. An extensive survey on the resprouting ability of South African Erica species was carried out and the pattern of geographical distribution of resprouters and seeders in the CFR was determined. The geographical distribution of these two regeneration classes was related to a climatic gradient of seasonality along the CFR. A pattern of higher proportions of resprouter species towards the mediterranean, strongly seasonal northwestern CFR and the non-seasonal eastern CFR and summer rainfall area outside the CFR was identified. The number of resprouter species reaches a maximum in the eastern CFR and is lower in the southwestern CFR despite the overall higher concentration of species in this subregion. Summer drought strongly influences the effectiveness of post-fire regeneration and growth (i.e. new recruits plus survivors) of Erica species, and is the major selective force accounting for the pattern of distribution of seeders and resprouters in the CFR. A mild mediterranean climate with reliable autumn-winter rains and a short summer drought, typical of the mountain areas of the southwestern CFR, favours recruitment of seeders but hampers recruitment of resprouters. Resprouter species persist and become dominant under harsh conditions for recruitment (severe summer drought) and would coexist with seeders under situations of no summer stress. Diversification is associated with seeder lineages. Hence, number of seeder species will be higher than number of resprouters, especially in the southwestern CFR, where favourable conditions for recruitment allow a massive concentration of seeder species, many of them narrow endemics.     

Burning phylogenies: fire, molecular evolutionary rates, and diversification

Mediterranean-type ecosystems are among the most remarkable plant biodiversity "hot spots" on the earth, and fire has traditionally been invoked as one of the evolutionary forces explaining this exceptional diversity. In these ecosystems, adult plants of some species are able to survive after fire (resprouters), whereas in other species fire kills the adults and populations are only maintained by an effective post-fire recruitment (seeders). Seeders tend to have shorter generation times than resprouters, particularly under short fire return intervals, thus potentially increasing their molecular evolutionary rates and, ultimately, their diversification. We explored whether seeder lineages actually have higher rates of molecular evolution and diversification than resprouters. Molecular evolutionary rates in different DNA regions were compared in 45 phylogenetically paired congeneric taxa from fire-prone Mediterranean-type ecosystems with contrasting seeder and resprouter life histories. Differential diversification was analyzed with both topological and chronological approaches in five genera (Banksia, Daviesia, Lachnaea, Leucadendron, and Thamnochortus) from two fire-prone regions (Australia and South Africa). We found that seeders had neither higher molecular rates nor higher diversification than resprouters. Such lack of differences in molecular rates between seeders and resprouters-which did not agree with theoretical predictions-may occur if (1) the timing of the switch from seeding to resprouting (or vice versa) occurs near the branch tip, so that most of the branch length evolves under the opposite life-history form; (2) resprouters suffer more somatic mutations and therefore counterbalancing the replication-induced mutations of seeders; and (3) the rate of mutations is not related to shorter generation times because plants do not undergo determinate germ-line replication. The absence of differential diversification is to be expected if seeders and resprouters do not differ from each other in their molecular evolutionary rate, which is the fuel for speciation. Although other factors such as the formation of isolated populations may trigger diversification, we can conclude that fire acting as a throttle for diversification is by no means the rule in fire-prone ecosystems.     

Legume seeders of the Cape Floristic Region inhabit more fertile soils than congeneric resprouters—sometimes

In fire-prone ecosystems, plants for the most part persist via either soil-stored seed banks (seeders) or below-ground storage structures (resprouters). Given their greater allocation of resources above ground to growth and reproduction, seeders are likely to have a higher nutrient requirement than resprouters. This may result in discernable differences in habitat nutrition and leaf morphology. These differences are probably accentuated in Cape legumes given their poor adaptation to low-P soils. It was hypothesized that legume seeders occupy habitats with greater fertility and possess larger, less sclerophyllous leaves than resprouters. Site nutrition and leaf morphologies were compared between seeders and resprouters in the genera Otholobium and Psoralea. There were no differences in leaf morphology between seeders and resprouters. Seeders sites had a higher total [N], exchangeable [Ca] and [Mg], and CEC, but lower [Fe] than resprouters. Only within Otholobium, did seeder sites have a higher Bray II [P]. This genus-specific variation in available P is probably a consequence of greater variation in soil type and precipitation between seeders and resprouters. Conversely, niche construction may contribute to the differences in soil fertility between seeders and resprouters in Psoralea. Thus, our data showed a general tendency for seeders to inhabit more fertile sites than resprouters. Caution is required, however, in generalizing these results, as our data indicate a difference in factors affecting soil nutrient availability between legume genera. Changes in soil fertility post-fire may limit legume persistence beyond the early stages of succession.     

Strong signature of selection in seeder populations but not in resprouters of the fynbos heath Erica coccinea (Ericaceae)

A higher frequency of natural selection is expected in populations of organisms with shorter generation times. In fire‐prone ecosystems, populations of seeder plants behave as functionally semelparous populations, with short generation times compared to populations of resprouter plants, which are truly iteroparous. Therefore, a stronger signature of natural selection should be detected in seeder populations, favoured by their shorter generation times and higher rates of population turnover. Here we test this idea in Erica coccinea from the Cape Floristic Region, which is dimorphic for post‐fire regeneration mode. We measured three floral traits supposedly subject to natural selection in seeder and resprouter populations. We then compared phenotypic trait variation with neutral genetic variation in each group of populations using P_ST–F_ST comparisons to detect signatures of natural selection in seeders and resprouters. We found a strong signature of selection in seeder populations, but not in resprouters. Furthermore, anthers of seeders were more exserted (and larger) than those of resprouters. These differences were maintained at sites where seeders and resprouters co‐occurred, suggesting that phenotypic plasticity or adaptation to different growth environments are unlikely explanations for trait variation. These results provide empirical support for the hypothesis that the genetic signature of natural selection is certainly more intense in seeder than in resprouter populations, favoured by their comparatively faster generation turnovers. Increased frequency of natural selection would increase differentiation among populations, thus promoting speciation in pyrophytic seeder lineages of the Cape flora.     

Seed bank patterns in Restionaceae and Epacridaceae after wildfire in kwongan in southwestern Australia

Abstract. Post-fire seed germination, seedling mortality and seed banks were investigated in scrub-heath (kwongan) in SW Australia. Study species included herbaceous and woody, obligate seeders and resprouters in two non-bradysporous but significant plant families (Restionaceae and Epacridaceae). In all species, seedlings were recruited only in the first autumn-spring after fire and occurred in similar densities as the estimated germinable annual seed input. Seedlings were absent from unburnt vegetation. Although most species retained some residual seeds after fire, tests (excised embryo culture) indicated that a negligible number of seeds were germinable. Regardless of fire response or species, there appeared to be a large loss of seeds each year and in most cases, only a small proportion of the annual seed production was used in post-fire recovery of plants. Based on seedling: parent ratios, all species had the capacity to reconstitute parent densities from germinants in the first year after fire, but high seedling mortality and no further recruitment resulted in less seedlings than replacements for four resprouter Restionaceae and three Epacridaceae (all obligate seeders) at the end of the third year after fire.     

Long-term post-fire vegetation dynamics in Pinus halepensis forests of Central Greece: A functional group approach

A hierarchical approach for plant functional classification was applied to describe long-term vegetation change in Pinus halepensis burned forests. Plant species were initially grouped according to their growth form and afterwards data on species modes of regeneration, persistence and dispersal, together with some other specific competitive advantages were explored, resulting in the identification of 29 different functional groups, 14 for woody and 15 for herbaceous species. Three types of Pinus halepensis forests were identified, according to the structure of the understorey. For each forest type, a post-fire chronosequence of communities was selected for sampling. Data sampling was performed for at least two consecutive years in each community, so as to reduce the shortcomings of the synchronic approach and to increase the age range of each chronosequence. Even though the vast majority of the functional groups proved to be persistent throughout the post-fire development of vegetation, their species richness and abundance did not remain stable. An increase of annual herb richness and abundance was recorded in the first years after the fire, with the leguminous species forming the dominant functional group. For perennial herbs, the most abundant group was of species with vivid lateral growth, while the group of species with subterranean resource organs included the highest number of species. Finally, as far as the woody species are concerned, the groups that played the most important role in defining vegetation structure were the mono-specific group of the pine, the group of resprouting sclerophyllous tall shrubs and the group of obligate seeder short shrubs (with Cistusspp., among others). A negative relationship between the abundance of woody obligate resprouters and the regeneration of woody obligate seeders was found. The advantage of the proposed functional group approach over classical floristic or structural approaches for the long-term study of communities is discussed, together with the applicability of this approach in studies of vegetation risk assessments due to fire regime alterations.     

Fire persistence traits of plants along a productivity and disturbance gradient in mediterranean shrublands of south-east Australia

Aim To understand changes in fire persistence traits of plants along a latitudinal gradient, considering the interactions between productivity, community (fuel) structure and fire regime. Location A gradient in the south of Australia (latitude 33–37° S; longitude 140–143° E), including: Little Desert National Park (VIC), Big Desert Wilderness Park (VIC), Murray‐Sunset National Park (VIC), Danggali Conservation Park (SA) and Tarawi Nature Reserve (NSW). Methods We selected four areas along a latitudinal gradient for which information on fire history and vegetation was available. Then, we tested to what extent the four selected areas have different climate and different fire regimes. Plant cover values of different life forms provided an indication of the plant community structure and flammability, and the proportion of species with different fire persistence traits (resprouting, seedbank persistence) informed us on the trait selection. Results Precipitation decreases and temperature increases from south to north. Thus the selected sites represent a gradient from high productivity (low aridity) in the south to low productivity (high aridity) in the north. Fire statistics suggest that fire frequency parallels productivity. There is a tendency for life form dominance and community structure to shift in such a way that fuel connectivity is reduced towards the north. Resprouting species increase and obligate seeders decrease along the fire–productivity gradient. Main conclusions Changes in plant traits are difficult to understand without simultaneous consideration of both the disturbance and the productivity gradients. In our study area, fire regime and productivity interact in such a way that decreases in productivity imply changes in fuel structure that produce a reduction in fire frequency. Resprouting species are better represented at the high fire–productivity part of the gradient, while obligate seeders are better represented at the opposite end of the gradient. The results also emphasize the importance of considering not only climate changes but also changes in fuel structure to predict future fire regimes.     

Influence of summer marine fog and low cloud stratus on water relations of evergreen woody shrubs (Arctostaphylos: Ericaceae) in the chaparral of central California

Mediterranean-type climate (MTC) regions around the world are notable for cool, wet winters and hot, dry summers. A dominant vegetation type in all five MTC regions is evergreen, sclerophyllous shrubland, called chaparral in California. The extreme summer dry season in California is moderated by a persistent low-elevation layer of marine fog and cloud cover along the margin of the Pacific coast. We tested whether late dry season water potentials (Ψ(min)) of chaparral shrubs, such as Arctostaphylos species in central California, are influenced by this coast-to-interior climate gradient. Lowland coastal (maritime) shrubs were found to have significantly less negative Ψ(min) than upland interior shrubs (interior), and stable isotope (δ(13)C) values exhibited greater water use efficiency in the interior. Post-fire resprouter shrubs (resprouters) had significantly less negative Ψ(min) than co-occurring obligate seeder shrubs (seeders) in interior and transitional chaparral, possibly because resprouters have deeper root systems with better access to subsurface water than shallow-rooted seeders. Unexpectedly, maritime resprouters and seeders did not differ significantly in their Ψ(min), possibly reflecting more favorable water availability for shrubs influenced by the summer marine layer. Microclimate and soil data also suggest that maritime habitats have more favorable water availability than the interior. While maritime seeders constitute the majority of local Arctostaphylos endemics, they exhibited significantly greater vulnerability to xylem cavitation than interior seeders. Because rare seeders in maritime chaparral are more vulnerable to xylem cavitation than interior seeders, the potential breakdown of the summer marine layer along the coast is of potential conservation concern.     

Demography of woody plants in relation to fire: Banksia serrata Lf. and Isopogon anemonifolius (Salisb.) Knight

Banksia serrata and Isopogon anemonifolius are serotinous resprouters (single-stemmed tree, multi-stemmed shrub, respectively) found in forests within the Sydney region. Studies were conducted to predict the population dynamics of these species. Seed production and survival and the accumulation of seed-bank within cones were estimated in relation to time since fire. Emergence, survival and development of lignotubers were measured in young juveniles and the time taken to reach adulthood was estimated. This information and published data on survival were used to estimate the amount of recruitment of adults and juveniles necessary for stands to remain in a stable state under frequent (<16 years), high and low intensity fire regimes. The effects of longer intervals (up to 80 years) between fires were also estimated. It was predicted that B. serrata populations will decline in numbers when the interval between high intensity fires is <9 years, while under low intensity fires the critical interval was 12–13 years. In I. anemonifolius the predicted intervals were 14 and 16 years, respectively. When fires are timed so that maximum seed-bank is available (about 30 year interval), it is unlikely that resprouters will dominate communities because the seed-banks and rates of growth of seedlings of obligate seeder shrubs are greater than these resprouters. Populations of these resprouters may be more able to persist than obligate seeders when the fire frequency is either very high (<6 years) or low (>50years), though the density of resprouter populations may slowly decline under such fire regimes.     

Dominant Drivers of Seedling Establishment in a Fire-Dependent Obligate Seeder: Climate or Fire Regimes?

Climate change is causing fire regime shifts in ecosystems worldwide. Plant species with regeneration strategies strongly linked to a fire regime, such as obligate seeders, may be particularly threatened by these changes. It is unclear whether changes in fire regimes or the direct effects of climate change will be the dominant threats to obligate seeders in future. We investigated the relative importance of fire-related variables (fire return interval and fire severity) and environmental factors (climate and topography) on seedling establishment in the world’s tallest angiosperm, an obligate seeder, Eucalyptus regnans. Throughout its range, this species dominates the wet montane forests of south-eastern Australia and plays a keystone role in forest structure. Following major wildfires, we investigated seedling establishment in E. regnans within 1 year of fire as this is a critical stage in the regeneration niche of obligate seeders. Seedling presence and abundance were strongly related to the occurrence of fire but not to variation in fire severity (moderate vs. high severity). Seedling abundance increased with increasing fire return interval (range 26–300 years). First-year seedling establishment was also strongly associated with low temperatures and with high elevations, high precipitation and persistent soil water availability. Our results show that both climate and fire regimes are strong drivers of E. regnans seedling establishment. The predicted warming and drying of the climate might reduce the regeneration potential for some obligate seeders in future and these threats are likely to be compounded by changes in fire regimes, particularly increases in fire frequency.     

Post‐fire regeneration of Mediterranean plant communities at a regional scale is dependent on vegetation type and dryness

Question: We tested whether (1) the change in composition and structure of whole plant communities after fire is directly related to regeneration of the dominant tree species in the canopy; (2) the change in structure and composition of plant communities several years after fire decreases with the proportion of obligate seeders and (3) the proportion of obligate seeders in plant communities increases with the dryness gradient. Location: Catalonia (NE Spain) Methods: We measured floristic differences between burned and long‐since burned sites in eight vegetation types across a climate gradient. We compared 22 sites burnt in 1994 in paired plots with 22 sites that had not been burnt since the 1940s. In each site we placed plots in burned and long‐since burned areas, where we identified the presence and abundance of all plant species. Results: When the tree canopy recovers, structure and composition of the vegetation also return to the long‐since burned community; when tree canopy does not recover, composition of the post‐fire community varies compared to the long‐since burned one. A higher proportion of obligate seeders in the pre‐fire community promotes quicker regeneration of the original community. The proportion of obligate seeders increased along the dryness gradient. Conclusions: Regeneration of plant communities after fire depends on the vegetation type before the fire. Regeneration increases when the dominant tree or shrub species persists after fire and with a higher proportion of obligate seeders in the pre‐fire community. The proportion of obligate seeders varies along the dryness gradient, which suggests that vegetation in drier areas (when seeders are more abundant) recovers earlier than in moister areas.     

Woody species tolerance to expansion of the perennial tussock grass Ampelodesmos mauritanica after fire

Abstract. In Mediterranean shrublands, post‐fire accumulation of above‐ground biomass of resprouters is faster than that of seeders. This suggests that resprouters may have a competitive advantage. To test this hypothesis, we used a removal experiment to study the effect of the presence of the dominant tussock‐grass Ampelodesmos mauritanica on the resprouting shrubs Erica multiflora and Globularia alypum and on the seeders Rosmarinus officinalis and Pinus halepensis three and four years after a wildfire. Water potential of target plants was also measured to see if Ampelodesmos removal increased water availability. Ampelodesmos marginally reduced growth of all target species but did not influence survival or water potential of any target species. Our results suggest that the effect of climatically influenced water stress was stronger than the effect of Ampelodesmos neighbours. Plant‐plant interactions in this Mediterranean community are weak after fire and the magnitude of the Ampelodesmos effect does not differ between seeders and resprouters.