Foliar stable carbon and nitrogen isotopes in woody Mediterranean species with different life form and post-fire regeneration

Wildfire is an important ecological disturbance factor in most Mediterranean ecosystems. In the Mediterranean Basin, most shrub species can regenerate after fire by resprouting or seeding. Here, we hypothesize that post-fire regenerative syndromes may potentially co-vary with traits directly related to functional properties involved in resource use. Thus, seeders with a shorter life span and smaller size would have lower water-use efficiency (WUE) than re-sprouting species and would take up nutrients such as nitrogen from more superficial parts of the soil. To test this hypothesis, we compared leaf ¹³C and ¹⁵N signatures from 29 co-existing species with different post-fire regeneration strategies. We also considered life form as an additional explanatory variable of the differences between post-fire regenerative groups. Our data support the hypothesis that seeder species (which mostly evolved in the Quaternary under a Mediterranean climate) have lower WUE and less stomatal control than non-seeders (many of which evolved under different climatic conditions in the Tertiary) and consequently greater consumption of water per unit biomass. This would be related to their smaller life forms, which tend to have lower WUE and shorter life and leaf lifespan. Differences in ¹⁵N also support the hypothesis that resprouters have deeper root systems than non-resprouters. The study supports the hypothesis of an overlap between plant functional traits and plant attributes describing post-disturbance resilience.     

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).     

Adult root structure of mediterranean shrubs: relationship with post‐fire regenerative syndrome

Life‐history attributes can impose differences on root system structures and properties related to nutrient and water uptake. Here, we assess whether plants with different post‐fire regenerative strategies (resprouters, seeders and seeder–resprouters) differ in the topological and morphological properties of their root systems (external path, altitude, magnitude, topological index, specific root length, root length, root‐to‐shoot biomass ratio, length of the main axis of the root system and link length). To achieve these objectives, we sampled individuals from eight woody species in a shrubland located in the western Mediterranean Basin. We sampled the adult root systems using manual field excavation with the aid of an air compressor. The results indicate that resprouters have a higher root‐to‐shoot ratio, confirming their higher ability to store water, starch and nutrients and to invest in the belowground biomass. Moreover, this pattern would allow them to explore deeper parts of the soil layers. Seeder species would benefit from a higher specific root length, pointing to increased relative root growth and water uptake rates. This study confirms that seeders and resprouters may differ in nutrient and water uptake ability according to the characteristics of their root system. Species that can both resprout and establish seedlings after fire had different patterns of root system structure; in particular, root:shoot ratio was more similar to resprouters and specific root length was closer to seeders, supporting the distinct functional performance of this type of species.     

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.     

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.     

Linking post-fire regenerative strategy and leaf nutrient content in Mediterranean woody plants

We explored differences in leaf nutrient contents between species from Mediterranean shrublands with the ability to resprout after disturbances such as fire (resprouters) and others without this capacity (non-resprouters). Since it is to be expected that resprouting capacity is related to a more conservative use of nutrients, we hypothesize that resprouter and non-resprouter species will differ in their leaf nutrient concentrations.We measured the following leaf traits: leaf carbon content (LCC), leaf nitrogen content, leaf phosphorous content (LPC), leaf potassium content, leaf calcium content (LCaC), leaf magnesium content and leaf sodium content, in 30 woody species coexisting in a coastal shrubland. We also considered the influence of species’ taxonomic affiliation in our analysis.Non-resprouters had higher LPC and LCaC than resprouter species, and lower LCC, which could be related to their cell and life-history properties. This study also suggests that non-resprouter species have more P in their leaves and are less limited by P than resprouter species.Overall, the differences in leaf nutrient contents suggest that shifts in the proportion of resprouter and non-resprouter species resulting from changes in the fire regime may have effects on the functional properties of the ecosystem.     

Growth, water relations and photosynthesis of seedlings and resprouts after fire

Seasonal patterns of growth, water relations, photosynthesis and leaf characteristics were compared between obligate seeders (Cistus monspeliensis and Cistus ladanifer) and resprouters (Arbutus unedo and Pistacia lentiscus) from the first to the second year after fire. We hypothesized that seedlings would be more water-limited than resprouts due to their shallower root systems. Regarding water use strategies, Cistus species are drought semi-deciduous and A. unedo and P. lentiscus are evergreen sclerophylls, therefore, comparisons were based on the relative deviation from mature conspecific plants. Seedlings and resprouts had higher shoot elongation and leaf production than mature plants, and over an extended period. Differences from mature plants were larger in resprouts, with two-fold transpiration, leaf conductance and photosynthesis in late spring/early summer. Seedlings of C. monspeliensis exhibited higher transpiration and leaf conductance than mature plants, while those of C. ladanifer only exhibited higher water potential. Growth increments and ameliorated water relations and photosynthesis after fire were attributed to an increase in water and nutrient availability. The small differences in water relations and photosynthesis between seedlings and mature conspecifics are in accordance with the prediction of seedlings experiencing higher water limitation than resprouts. We attribute these results to differences in root systems: resprouters benefited from an increase in root/shoot ratios and the presence of deep roots whereas Cistus seedlings relied on very shallow roots, which cannot provide assess to deep water during summer. Nevertheless, seedlings did not show evidence of experiencing a more severe water limitation than mature conspecifics, which we attributed to the presence of efficient mechanisms of avoiding and tolerating water stress. The results are discussed in relation to post-fire demography of seeders and resprouters in Mediterranean communities.     

Leaf physiological traits in relation to resprouter ability in the Mediterranean Basin

In Mediterranean ecosystems, fire is a strong selective agent among plants, and the different post-fire regeneration strategies (e.g. resprouting and non-resprouting) have implications for other plant traits. Because young plants of non-resprouters need to grow quickly and mature well before the next fire, we predict that they should possess leaf traits related to increased efficiency in growth and resource acquisition compared with resprouter species. To test this hypothesis, we measured specific leaf area, leaf nitrogen and carbon concentrations and leaf physiological traits, including gas exchange parameters and chlorophyll fluorescence, in 19 Mediterranean species cultivated in a common garden. Both cross-species and phylogenetically informed analyses suggest that non-resprouters have better physiological performance at the leaf level (i.e. higher photosynthetic capacity) than resprouters. All these results suggest that non-resprouter species are able to take greater advantage for vegetative growth and carbon fixation than resprouters during periods when water is readily available. The contrasted physiological differences between resprouters and non-resprouters reinforce the idea that these two syndromes are functionally different (i.e. they are functional types).     

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.     

Fire regenerative syndromes of forest woody species across fire and climatic gradients

Community resilience after fire is determined by species’ ability to regenerate through two main mechanisms growth of new sprouts (resprouter species) and germination from surviving seed banks or from seeds arriving from neighbouring populations (seeder species). Both the mechanisms are present in Mediterranean communities. The occurrence of both the types in a community depends on fire history and the bio-geographical history determining the available species pool. Regenerative traits also covary with other functional attributes associated with resource acquisition and stress tolerance. As post-fire regenerative responses can be related to various ecological factors other than fire, we tested the hypothesis of a different proportional representation of post-fire regenerative syndromes in forest woody species along a climatic gradient in Catalonia (NE Spain) ranging from Mediterranean to temperate-boreal climates. Specifically, we expected seeder species to become less common with colder and moister conditions while resprouters would not be so influenced by the climatic gradient. We also tested the hypothesis of change in the relative abundance of regenerative syndromes in relation to recent fire history. We analysed a large database obtained from extensive forestry surveys and remote sensing fire records. After correction for spatial autocorrelation, we found an increase in the proportion of seeder species under more Mediterranean conditions and a decrease in fire-sensitive species (with no efficient mechanisms of post-fire recovery) in moister conditions. Resprouter species were similarly present across the whole gradient. A similar pattern was observed after excluding recently burnt plots. Therefore, post-fire regenerative syndromes segregate along the climatic gradient. Recent fires reduced the occurrence of fire-sensitive species and increased the proportion of seeder species. No significant effect was observed on resprouter species. Fire has a sorting effect, shaping the occurrence of species with different regenerative traits. Overall, fire seems to explain better the variability of the proportion of fire-sensitive species and climate the variability of seeder species. In addition, other factors (forestry practices and the covariation between regenerative and functional attributes) are likely to contribute to the regional pattern of regenerative syndromes.     

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.     

The challenge of plant regeneration after fire in the Mediterranean Basin: scientific gaps in our knowledge on plant strategies and evolution of traits

Though observations on re-colonisation of post-fire sites in the Mediterranean Basin are plentiful, there still is an ongoing debate on the interrelation of fire regimes and species traits related to fire adaptation. Most of the studies found are restricted to particular species or claim to present community attributes. Therefore they often lack information for the evaluation of evolutionary evidence and historical contingency of the local fire regime and other abiotic conditions, which may act as selective pressure for plant regeneration strategies. Indeed, knowledge about the success of regeneration mechanisms and their interrelation with ecological factors is essential for the interpretation of the high spatio-temporal variability found in post-fire species performance. Such knowledge would be necessary to assess the potential of different regeneration mechanisms to cope with ongoing land-use and climate change—a crucial scientific challenge. A summary is given of the knowledge about the limits and potential of plant regeneration mechanisms after fire in the Mediterranean Basin, along with corresponding studies conducted in other parts of the world with similar climatic conditions in order to present the fullest possible picture. Moreover, the positive or negative impacts of particular parameters of a fire regime on different regeneration strategies (post-fire seeders, resprouters, and facultative resprouters) are explained and discussed in the light of published literature. To conclude, reference is made to scientific gaps that need to be filled in order to analyse species resistance and community resilience absorbing possible climate or land use changes.     

Persistence on inselbergs: the role of obligate seeders and resprouters

Aim To investigate if the current theories associated with recruitment strategies are sufficient to explain differences in the proportions of obligate seeders and resprouters on inselbergs and in the matrix. Location The New England Batholith of eastern Australia. Methods The importance of life form and regenerative response of flora species are compared for twenty‐four archipelagos of inselbergs habitat islands and for their adjacent matrix. Forward stepwise multiple linear regression is used to correlate measured and modelled variables with differences in the proportional abundance of obligate seeders on inselbergs at three levels of sampling. Results A total of 216 inselbergs were surveyed and information on 826 vascular plant species was collated. Herbs were the most common life form both on and off inselbergs. There were generally more shrubs on inselbergs than in the matrix. Resprouters were more common everywhere. However, obligate seeders were proportionately more common on inselbergs. The degree of insularity of outcrop floras accounted for 23–37% of the variance in the proportional abundance of obligate seeders at three sampling scales. Main conclusions A model is proposed whereby the mechanisms that influence the abundances of obligate seeders and resprouters are different on inselbergs and in the matrix. Inselberg environments are harsh, arid, have limited safe recruitment sites and below ground resources, but are not light limited. In such habitats, obligate seeders with persistence life‐history traits are favoured. Within the matrix in eastern Australia frequent biomass removal disturbances occur (such as fire) and resprouting is advantageous. High turnover obligate seeders with no persistence life‐history traits can be favoured in the matrix with a reduced disturbance regime and where competition for light still occurs. Some of these matrix obligate seeders occur on inselbergs due to their infrequent disturbance regimes.     

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.     

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.     

Relationships between leaf morphological traits, nutrient concentrations and isotopic signatures for Mediterranean woody plant species and communities

Background and aims

Soil factors are driving forces that influence spatial distribution and functional traits of plant species. We test whether two anchor morphological traits—leaf mass per area (LMA) and leaf dry matter content (LDMC)—are significantly related to a broad range of leaf nutrient concentrations in Mediterranean woody plant species. We also explore the main environmental filters (light availability, soil moisture and soil nutrients) that determine the patterns of these functional traits in a forest stand.

Methods

Four morphological and 19 chemical leaf traits (macronutrients and trace elements and δ¹³C and δ¹⁵N signatures) were analysed in 17 woody plant species. Community-weighted leaf traits were calculated for 57 plots within the forest. Links between LMA, LDMC and other leaf traits were analysed at the species and the community level using standardised major axis (SMA) regressions

Results

LMA and LDMC were significantly related to many leaf nutrient concentrations, but only when using abundance-weighted values at community level. Among-traits links were much weaker for the cross-species analysis. Nitrogen isotopic signatures were useful to understand different resource-use strategies. Community-weighted LMA and LDMC were negatively related to light availability, contrary to what was expected.

Conclusion

Community leaf traits have parallel shifts along the environmental factors that determine the community assembly, even though they are weakly related across individual taxa. Light availability is the main environmental factor determining this convergence of the community leaf traits.     

Interactive effects of radiation,temperature and salinity on different life history stages of the Arctic kelp <Emphasis Type="Italic">Alaria esculenta</Emphasis> (Phaeophyceae)

Vegetative resprouting, soil or canopy-stored seed banks, post-fire seed dispersal and germination are the major strategies by which plants regenerate after fires. Post-fire regeneration modes of plants are commonly based on the presence or absence of post-fire recruitment as well as the presence or absence of post-fire resprouting. High temperatures, smoke and ash are characteristics of fire and the post-fire environment. We hypothesized that heat, smoke, ash and pH will have differential effects on seed germination depending on species’ post-fire regeneration strategies: serotinous vs. nonserotinous (which may have soil seed banks) and resprouters vs. nonresprouters (which may be obligate seeders). Here we examined the effects of these factors on the germination of 27 common east Australian species. Most serotinous species supported our hypothesis by showing no effect or reduced germination in response to heat. However, contrary to our prediction, all nonserotinous nonresprouting species also showed no effect or reduced germination in response to heat. Smoke, contrary to our hypothesis, had a negative or no effect on all serotinous and nonresprouting species, but no clear directional effect on serotinous and resprouting species. Supporting our hypotheses, ash and high pH showed positive or nonsignificant effects on the germination of all serotinous resprouting species, and a negative or no effect on nonserotinous resprouting species. However, contrary to our prediction, it had a negative or no effect on the serotinous nonresprouting species and no clear effect on nonserotinous nonresprouting species. We also discovered large differences in germination responses between conspecific populations that varied in their degree of resprouting. Although our data confirmed several of our predictions, the overall conclusion is that the responses of seeds to heat, smoke, ash and pH are not tightly associated with post-fire regeneration functional types. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

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.     

Long-term post-fire dynamics of co-occurring woody species in Pinus brutia forests: the role of regeneration mode

Regeneration mode is one of the key attributes determining population structure and dynamics of plant species. We investigated long-term patterns after fire in the cover of plant species in a 100-year chronosequence of burned Pinus brutia forests in a humid Mediterranean climate region in Turkey. Significant trends were present in the change of cover in major species through post-fire chronosequence, and species with similar trends were clustered in relation to their regeneration modes. Obligate resprouters increased their cover from the early post-fire years to the later stages, while cover of obligate seeders with a soil seed bank increased in the early years, but then decreased through time. Facultative resprouters were at an intermediate position, with an increase in cover until mid-successional stages and then a decrease through time. The cover of the only obligate seeder with a canopy seed bank (P. brutia) followed a linear increasing trend during the succession. When species with the same regeneration mode were grouped, the same trends were observed with more explained variances. A few life-history traits were enough to explain the observed trends. Our study shows that regeneration mode is an explanatory functional grouping system for describing long-term post-fire dynamics of Mediterranean Basin woody species. We suggest that regeneration mode must be a major component of any vegetation or forest stand dynamics model in the Mediterranean Basin. This result has important implications for the management of Mediterranean Basin ecosystems, and can potentially be extrapolated to other Mediterranean-type fire-prone ecosystems.     

不同沙丘生境主要植物比叶面积和叶干物质含量的比较

研究了生长在不同沙丘生境中 (流动沙丘 ,半固定沙丘和固定沙丘 ) 2 0个植物种 (10个 1年生植物种和 10个多年生植物种 )的比叶面积 (SL A)和叶干物质含量 (L DMC)的变化 ,并且分析了各个沙丘生境的土壤养分特征。结果表明 ,各个植物种的平均 SL A和 L DMC在植物种之间差异显著 ;多数在两种或 3种沙丘生境均有分布的植物其 SL A在不同沙丘生境之间差异显著 ,但是仅有 6个植物种的 L DMC在不同沙丘生境之间表现出差异 (p<0 .0 5 )。与许多研究结果类似 ,1年生植物的 SL A显著大于多年生植物的 SL A,而且两者之间 L DMC存在一定的差异。 1年生植物 SL A和 L DMC之间相关性不显著 ,但多年生植物SL A和 L DMC之间呈显著负相关。综合所有 2 0个植物种可以发现 ,SL A增大时 ,L DMC有下降的趋势