Influence of fire on critically endangered Swartland Shale Renosterveld in the Cape Floristic Region

Questions

The degree to which renosterveld shrublands are fire‐dependent is currently unclear. To address this issue, the following questions were asked: (1) does smoke stimulate germination of soil‐stored seeds in renosterveld; (2) does recently‐burned renosterveld display changed composition and higher diversity than unburned vegetation; and (3) how do the species compositions of renosterveld soil seed banks and standing vegetation compare?

Location

Swartland, Cape Floristic Region, South Africa.

Methods

Soil seed bank samples from a north‐ and south‐facing slope were smoke‐treated and germinated to test for smoke‐stimulated germination. Burned standing vegetation was surveyed 16 months post‐fire, as was unburned vegetation on the same slopes. Seed bank species richness and density were compared between smoke‐treated and untreated samples within and between slopes. Burned and unburned standing vegetation were compared within and between slopes in terms of species richness, abundance and aerial cover. Compositional similarity of the seed banks and standing vegetation was assessed.

Results

Seed banks were dominated by annuals and graminoids. Smoke treatment had no effect, except for driving significantly higher species richness and seedling density in south‐facing slope perennial shrubs. Species richness and seedling density were significantly higher in seed banks on the south‐facing slope compared to the north‐facing slope. Burned standing vegetation exhibited significantly higher diversity than unburned vegetation. Annuals and graminoids displayed significantly higher species richness and aerial cover in burned renosterveld. The north‐facing slope contained less than half the number of species/m² compared to the south‐facing slope. The seed banks and standing vegetation showed low to intermediate similarity (Sørensen = 31%–53%), but grouped close together on an NMDS plot, suggesting intermediate similarity overall.

Conclusions

Elevated germination of perennial shrubs in smoke‐treated seed bank samples and increased diversity of post‐fire standing vegetation suggest the renosterveld in this study shows elements of a fire‐driven system. Certain species only recruited in burned sites, suggesting fire‐stimulated germination. Aspect had a major influence on plant community composition, with the mesic south‐facing slope being more diverse than the xeric north‐facing slope. The similarity between the seed banks and standing vegetation was higher than previously shown for renosterveld, and appears to be higher than for fynbos.     

Soil seed bank and floristic diversity in a forest‐grassland mosaic in southern Spain

Abstract. Soil seed bank and floristic diversity were studied in a forest of Quercus suber, a forest of Quercus canariensis and a grassland, forming a vegetation mosaic in Los Alcornocales Natural Park, southern Spain. The soil seed bank was estimated by the germination technique. In each community patch, diversity, woody species cover and herbaceous species frequency was measured. Three biodiversity components – species richness, endemism and taxonomic singularity – were considered in the vegetation and the seed bank. Forest patches had a soil seed bank of ca. 11 200–14 100 seed.m^?2 and their composition had low resemblance to (epigeal) vegetation. The grassland patch had a more dense seed bank (ca. 31 800 seed.m^?2) and a higher index of similarity with vegetation, compared with the forests nearby. The complete forest diversity was 71–78 species on 0.1 ha, including 12–15 species found only in the seed bank; the grassland species richness was higher (113 species on 0.1 ha). We discuss the role of soil seed banks in the vegetation dynamics and in the complete plant biodiversity of the mosaic landscape studied.     

Composition,size and dynamics of the seed bank in a mediterranean shrubland of Chile

Abstract Analysis was performed of the richness and abundance of woody species, forbs, and annual grasses in the easily germinating soil seed bank (henceforth seed bank) in a mediterranean shrubland of central Chile. The effects of successional development after fire and by microsite type (underneath or outside shrubs) on the density of seeds in the soil, and the relationship of species abundance in the seed bank with its abundance in the above‐ground vegetation was examined. A total of 64 plant species were recorded in the seed bank, of which 44 were annual or biannual. Eight species were woody and another eight were perennial herbs. Four could not be identified to species level. The highest richness of established herbaceous species was recorded in late spring, with 31 species. The regeneration of the herbaceous vegetation was driven by the annual production of seeds and by a reserve of short‐lived propagules in the soil. Density of all germinating seeds was significantly higher during late spring and late summer. Density of grass seeds was greater during late spring, while that of all other species was greater during late summer. Annual grass seeds accumulated in higher proportion at exposed microsites rather than under woody canopy, and in young (< 5 years old) and intermediate‐age patches (10–20 years old) rather than in mature vegetation (30–50 years old). The abundance of established woody and herb species was uncorrelated with that of the seed bank.     

Effects of grazing on patch structure in a semi‐arid two‐phase vegetation mosaic

Abstract. Question: What are the grazing effects in the spatial organization and the internal structure of high and low cover patches from a two‐phase vegetation mosaic? Location: Patagonian steppe, Argentina. Methods: We mapped vegetation under three different grazing conditions: ungrazed, lightly grazed and heavily grazed. We analysed the spatial patterns of the dominant life forms. Also, in each patch type, we determined density, species composition, richness, diversity, size structure and dead biomass of grasses under different grazing conditions. Results: The vegetation was spatially organized in a two‐phase mosaic. High cover patches resulted from the association of grasses and shrubs and low cover patches were represented by scattered tussock grasses on bare ground. This spatial organization was not affected by grazing, but heavy grazing changed the grass species involved in high cover patches and reduced the density and cover of grasses in both patch types. Species richness and diversity in high cover patches decreased under grazing conditions, whereas in low cover patches it remained unchanged. Also, the decrease of palatable grasses was steeper in high cover patches than in low cover patches under grazing conditions. Conclusions: We suggest that although grazing promotes or inhibits particular species, it does not modify the mosaic structure of Patagonian steppe. The fact that the mosaic remained unchanged after 100 years of grazing suggests that grazing does not compromize population processes involved in maintaining patch structure, including seed dispersal, establishment or biotic interactions among life forms.     

Fire-type and forestry management effects on the early postfire vegetation dynamics of a Pinus pinaster woodland

The objective of this research was to study the effects of type of fire, prefire-, and postfire-management on the postfire vegetation dynamics of a Pinus pinaster woodland in Central Spain, burned at 15 yr of age. The effects of type of fire (crown-, or surface-fire), prefire-management (thinning out of trees and clearing of brush or no such actions) and postfire-management (removal of burned trees one year after the fire or no such action) on the postfire vegetation were studied during the first three years after the fire. Herbaceous plant abundance, species richness, and diversity, as well as abundance, growth and density of the dominant shrub species (Cistus ladanifer) were measured during the first three years after the fire. Our results show that the effects of the type of fire on the vegetation were minimal. Prefire-management effects were significant on the abundance of herbaceous species, mainly during the second and third year after fire, in particular for the Leguminosae species. Prefire managed areas were more diverse in species, and produced higher plant biomass than unmanaged areas. Postfire-management effects on the shrubs and herbs were minimal, except for the Leguminosae, which increased their cover where the trees had been removed. Plant dynamics were marked by the interaction between prefire-management and fire-type through the dynamics of the shrub cover. On most occasions, plots that resulted in lower cover of C. ladanifer had greater abundance of herbaceous plants and, in particular, of the Leguminosae. In general, our results show that irrespective of fire-type, prefire-, or postfire-management all areas tended to be very similar in their vegetation three years after the fire.     

Small mammal abundance in Mediterranean post-fire habitats: a role for predators?

We studied patterns of small mammal abundance and species richness in post-fire habitats by sampling 33 plots (225 m² each) representing different stages of vegetation recovery after fire. Small mammal abundance was estimated by live trapping during early spring 1999 and vegetation structure was sampled by visual estimation at the same plots. Recently–burnt areas were characterised by shrubby and herbaceous vegetation with low structural variability, and unburnt areas were characterised by well developed forest cover with high structural complexity. Small mammal abundance and species richness decreased with time elapsed since the last fire (from 5 to at least 50 years), and these differences were associated to the decreasing cover of short shrubs as the post-fire succession of plant communities advanced. However, relationships between vegetation structure and small mammals differed among areas burned in different times, with weak or negative relationship in recently burnt areas and positive and stronger relationship in unburnt areas. Furthermore, the abundance of small mammals was larger than expected from vegetation structure in plots burned recently whereas the contrary pattern was found in unburned areas. We hypothesised that the pattern observed could be related to the responses of small mammal predators to changes in vegetation and landscape structure promoted by fire. Fire-related fragmentation could have promoted the isolation of forest predators (owls and carnivores) in unburned forest patches, a fact that could have produced a higher predation pressure for small mammals. Conversely, small mammal populations would have been enhanced in early post-fire stages by lower predator numbers combined with better predator protection in areas covered by resprouting woody vegetation.     

Importance of the soil seed bank of disturbed sites in Chilean matorral in early secondary succession

Abstract. The dynamics of the seed bank may provide clues to the process of recovery of the vegetation of disturbed sites. The role of the seed bank may be more important in areas with a seasonal climate than in areas where seedling recruitment is not limited to one season. We studied the seed bank and the seed rain in three sites of the Chilean mediterranean-climate region (33° 48'S) which differed in the degree of anthropic disturbance: a closed-canopy, second-growth forest; an open matorral; and an old-field. Additionally, we tested the germination of seeds from the soil and from the current-year seed crop. The seed bank varied considerably between the two years of study, although no change in the vegetation could be observed. Seed density and species richness were lower in 1989 than in 1988. The seed bank of the second-growth forest changed less between years, while the old-field showed the largest change. The highest seed rain occurred under shrub patches in the open matorral, while few seeds fell in the spaces between shrub clumps or in the old-field. In the forest, seed rain was low and correlated with species cover. Germination was low (0 - 15%) in tests using either soil samples or fresh seeds. These results indicate that matorral succession is a very slow process, limited mainly by low germination and low arrival of propagules to open areas. Most woody species have animal-disseminated fleshy propagules. The presence of established shrubs which may serve as perches or refuges for animals increases species richness in the seed rain and the seed bank.     

Soil seed bank in a patchy vegetation of coastal sandy plains in southeastern Brazil

Large seed banks have been found in tropical dry forests and also in habitats with high seasonality in rainfall. However, patchily structured vegetation could induce great spatial variation in the seed bank. We characterized the seed bank in a patchy vegetation of restinga, a common type of coastal vegetation found in the Atlantic forest biome. We also evaluated whether there is any spatial variation between the litter and soil layer, bare sand, and the edge and center of vegetation patches with distinct species dominance. We found 104 seeds/m² in the seed bank using a 5‐cm‐depth sampling. Seven out of 16 species found in the restinga seed bank germinated; two of these were found in the early stages of vegetation patches. We found a higher number of seeds at the edge than in the center of vegetation patches. However, there were no significant differences in the number of seeds in the seed bank between the litter and soil layer, and between vegetation patches with distinct species dominance. Bare sandy soils had lower seed bank densities than vegetation patches. A small seed bank size might be explained by the low proportion of seeds from herbaceous and woody species, which are pioneers in the Atlantic forest. However, seed bank might play an important role in the early stages of the successional process, due to the occurrence of the few species that are able to colonize new young vegetation patches.     

Postfire seed bank dynamics in semiarid grasslands

We evaluated the combined effects of fire after drought on the seed bank composition and its role in the postfire recovery of NW Patagonia grasslands. During three years, we monitored the seed bank and the aboveground vegetation. Species were arranged in functional groups and Detrended Correspondence Analysis was used to separate sites according to species and functional groups. Similarity between aboveground vegetation and seed bank was calculated with SØrensen Index. In the first year, the seed density was similar in the control and burned sites and was lower than following years in all the sites. The species that survived the high temperatures were all annuals with the exception of the perennial species Fabiana imbricata and Rumex acetosella. In the second postfire year, the diversity and seed density increased due to the contribution of fugitive species (rare in the community) and exotic annual species. Seed bank of perennial species was the most affected by fire and just recovered in the third year. Drought did not affect the similarity between the seed bank and vegetation. Fire had low impact on the total seed bank, probably due to the heat buffering nature of the soil, whereas drought reduced significantly seed bank size and richness. Seed bank contributes to grassland richness maintenance.     

Competitive abilities of three narrowly endemic plant species in experimental neighborhoods along a fire gradient

We conducted field experiments manipulating lichens, shrubs, and herbs along a time-since-fire gradient and assessing effects on three endemic herbaceous species of Florida scrub: Eryngium cuneifolium, Hypericum cumulicola, and Polygonella basiramia. Responses included seed germination, survival, biomass, and fecundity. Transplants into recently burned patches generally had higher survival, larger biomass, and greater reproductive output than transplants into long-unburned patches. Open areas and sites near oaks frequently were more favorable than sites near Florida rosemary. Ground lichens did not affect germination but increased mortality rate of seedlings. Neighboring small shrubby and herbaceous species did not affect the performance of these species. Of the three species, naturally occurring E. cuneifolium were farthest from large shrubs, and their microhabitats had the least ground lichens and shrubs. Eryngium cuneifolium and H. cumulicola are capable of forming persistent seed banks and their recruitment after fire depends mostly on these dormant seeds. Polygonella basiramia relies on seed dispersal and immediate seed germination to colonize recently burned patches. Management for these species should involve variable fire regimes to allow all three species to persist along with many other scrub endemics.     

Fire and regeneration: the role of seed banks in the dynamics of northern heathlands

Questions: How do species composition and abundance of soil seed bank and standing vegetation vary over the course of a post‐fire succession in northern heathlands? What is the role of seed banks – do they act as a refuge for early successional species or can they simply be seen as a spillover from the extant local vegetation? Location: Coastal Calluna heathlands, Western Norway. Methods: We analysed vegetation and seed bank along a 24‐year post‐fire chronosequence. Patterns in community composition, similarity and abundances were tested using multivariate analyses, Sørensen's index of similarity, vegetation cover (%) and seedling counts. Results: The total diversity of vegetation and seed bank were 60 and 54 vascular plant taxa, respectively, with 39 shared species, resulting in 68% similarity overall. Over 24 years, the heathland community progressed from open newly burned ground via species rich graminoid‐ and herb‐dominated vegetation to mature Calluna heath. Post‐fire succession was not reflected in the seed bank. The 10 most abundant species constituted 98% of the germinated seeds. The most abundant were Calluna vulgaris (49%; 12 018 seeds m^?2) and Erica tetralix (34%; 8 414 seeds m^?2). Calluna showed significantly higher germination the first 2 years following fire. Conclusions: Vegetation species richness, ranging from 23 to 46 species yr^?1, showed a unimodal pattern over the post‐fire succession. In contrast, the seed bank species richness, ranging from 21 to 31 species yr^?1, showed no trend. This suggests that the seed bank act as a refuge; providing a constant source of recruits for species that colonise newly burned areas. The traditional management regime has not depleted or destroyed the seed banks and continued management is needed to ensure sustainability of northern heathlands.     

Composition and diversity of herbaceous patches in woody vegetation: The effects of grazing,soil seed bank,patch spatial properties and scale

Herbaceous plants contribute much to plant diversity in Mediterranean-type ecosystems though mostly occupying relatively small patches within the dense woody vegetation. While studying species diversity in the herbaceous patches, we hypothesized that grazing, soil seed bank, and spatial properties of the patch affect plant diversity and composition at different spatial scales. The study site was in an LTER site located in the Mediterranean region in north Israel. We determined herbaceous species composition in: (1) randomly sampled quadrats in herbaceous patches in grazed and un-grazed plots; (2) soil seed bank samples taken from the same patches and germinated under optimal greenhouse conditions; (3) quadrats in the same patches sown with a homogenous mixture of local soil samples. Using GIS methods, we determined small-scale spatial characteristics of the herbaceous patches. Alpha and beta diversities were calculated at the patch and plot scales using Shannon's entropy H. Grazing increased alpha diversity of local untreated seed bank samples but decreased alpha diversity of the artificial homogenous soil seed bank mixture at both patch and plot scales. Positive relation between alpha diversity and patch area was detected only under grazing. Grazing increased beta diversity in all three treatments at the patch scale. Grazing decreased the similarity in species composition between above-ground vegetation and soil seed bank. The results indicate that moderate cattle-grazing affects species diversity in the herbaceous patches within the dense maquis. This effect is scale-dependent, and interacts with the effects of soil seed bank and patch spatial-properties: without grazing soil seed bank plays a more important role than patch spatial properties, but under grazing the size and the accessibility of the patch are more important in the determination of herbaceous species composition.     

Relationships between seed banks and spatial heterogeneity of North American alvar vegetation

Abstract. This is the first quantitative study of seed bank characteristics in North American alvar habitats. We assessed seed bank density, species richness, and species composition in 75 plots distributed among five alvar sites in Bruce Peninsula National Park, Ontario, Canada, each of which displayed areas of high and low vegetation cover within the alvar and a fully forested perimeter area. Forested habitats immediately adjacent to alvar patches contained minimal seed banks for species restricted to the alvar patches. Open alvars contained less than 1% seeds from woody forest species. This suggests that forest is not invading adjacent alvar habitat via seeds and that adjacent forest does not contain a reservoir of alvar seeds. When compared to areas on the alvar with high vascular plant cover, areas with low cover contained a slightly smaller viable seed bank, but seed banks from high and low vegetation cover plots had similar species composition and species richness. High vegetation cover plots had slightly higher mean and maximum soil depths compared with low cover plots, but no differences in other physical and chemical parameters. Thus, spatial heterogeneity in plant cover is associated only weakly with heterogeneity in below‐ground factors. Despite the availability of seed and soil resources, vegetation dynamics are constrained in areas with low plant cover, and thus alvar community development seems to respond non‐linearly to resource availability.     

Response of plant species and life form diversity to variable fire histories and biomass in the jarrah forest of south‐west Australia

Frequent fires reduce the abundance of woody plant species and favour herbaceous species. Plant species richness also tends to increase with decreasing vegetation biomass and cover due to reduced competition for light. We assessed the influence of variable fire histories and site biomass on the following diversity measures: woody and herbaceous species richness, overall species richness and evenness, and life form evenness (i.e. the relative abundance or dominance among six herbaceous and six woody plant life forms), across 16 mixed jarrah (Eucalyptus marginata) and marri (Corymbia calophylla) forest stands in south‐west Australia. Fire frequency was defined as the total number of fires over a 30‐year period. Overall species richness and species evenness did not vary with fire frequency or biomass. However, there were more herbaceous species (particularly rushes, geophytes and herbs) where there were fewer shrubs and low biomass, suggesting that more herbaceous species coexist where dominance by shrubs is low. Frequently burnt plots also had lower number and abundance of shrub species. Life form evenness was also higher at both high fire frequency and low biomass sites. These results suggest that the impact of fire frequency and biomass on vegetation composition is mediated by local interactions among different life forms rather than among individual species. Our results demonstrate that measuring the variation in the relative diversity of different woody and herbaceous life forms is crucial to understanding the compositional response of forests and other structurally complex vegetation communities to changes in disturbance regime such as increased fire frequency.     

Nested spatial patterns in seed bank and vegetation of Mediterranean old-fields

A nested sampling design was used to describe the spatial patterns for the species richness and composition in the seed bank and vegetation of three Mediterranean old-fields (1, 7, and 15 yr after the last ploughing). Three scales were examined hierarchically: sampling units within plots of 0.25 m² for the vegetation and of 0.05 m² for the seed bank, 100 m² plots within fields, and fields of 1000 m². In spite of the strong spatial variation among sampling units, species richness and composition of both seed bank and vegetation showed hierarchically structured patterns of heterogeneity, while each old-field was a homogeneous entity. These spatial patterns tended to be partially masked when the data were aggregated at the scale of the plot. Such results stress the use of a nested sampling design for studying variation in species richness and taxonomic composition in both vegetation and seed bank. This design, in combination with CCA, also showed that the vegetation showed a coarser grain than the seed bank, probably in relation to seed clumping.     

Driving factors of small-scale variability in a savanna plant population after a fire

The severity of fire impacts on fire-prone vegetation is often spatially heterogeneous, and may lead to small-scale patchiness in the structure of plant populations by affecting mortality, topkill, and reproduction. This patchiness, however, is not usually taken into account in fire ecology studies. We show that a dry-season fire may result in small-scale patchiness in the population structure of the common shrub Miconia albicans, mostly by differential topkill and resprouting. We related fire severity to population structure parameters of the study species and assessed the effects of fire on its soil seed bank. Basal area of non-woody live stems and of dead stems increased with fire severity, whereas that of woody live stems decreased, indicating topkill and resprouting. However, there was no relationship between fire severity and the total number of live or dead plants, showing that mortality in the fire was low. We found very few seedlings, indicating that resprouting, not germination from the soil seed bank, is the main recovery strategy of this species. The fire also affected the soil seed bank, as there were fewer seedlings emerging from soil collected in burned patches. Although this study was performed with a single species, it is likely that other species, especially those with basal resprouting, will show similar patterns of post-fire patchiness in population structure. This patchiness, in turn, may affect the spatial distribution of future fires, and should be taken into account in studies of fire ecology.     

Fire enhances litter decomposition and reduces vegetation cover influences on decomposition in a dry woodland

Dry woodlands frequently experience fire, and the heterogeneous spatial patterning of vegetation cover and fire behavior in these systems can lead to interspersed burned and unburned patches of different vegetation cover types. Biogeochemical processes may differ due to fire and vegetation cover influences on biotic and abiotic conditions, but these persistent influences of fire in the months or years following fire are not as well understood as the immediate impacts of fire. In particular, leaf litter decomposition, a process controlling nutrient availability and soil organic matter accumulation, is poorly understood in drylands but may be sensitive to vegetation cover and fire history. Decomposition is responsive to changes in abiotic drivers or interactions between abiotic conditions and biotic drivers, suggesting that decomposition rates may differ with vegetation cover and fire. The objective of this study was to assess the role of vegetation cover and fire on leaf litter decomposition in a semi-arid pinyon-juniper woodland in southern New Mexico, USA, where prescribed fire is used to combat increasing woody cover. A spatially heterogeneous prescribed burn led to closely co-located but discrete burned and unburned patches of all three dominant vegetation cover types (grass, shrub, tree). Decomposition rates of leaf litter from two species were measured in mesh litterbags deployed in factorial combination of the three vegetation cover types and two fire treatments (burned and unburned patches). For both litter types, decomposition was lower for unburned trees than for unburned grass or shrubs, perhaps due to greater soil–litter mixing and solar radiation away from tree canopies. Fire enhanced litter mass loss under trees, making decomposition rates similarly rapid in burned patches of all three vegetation cover types. Understanding decomposition dynamics in spatially heterogeneous vegetation cover of dry woodlands is critical for understanding biogeochemical process responses to fire in these systems.     

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

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

Composition and seasonal flux of the soil seed bank of species-rich Themeda triandra grasslands in relation to burning history

Abstract. Most species-rich grasslands dominated by Themeda triandra in southeastern Australia have been ungrazed and frequently burnt for decades. The seedling emergence technique was used to determine the size and taxonomic composition of the soil seed bank of five grasslands that had different fire histories (i.e. burnt at 1 yr, 3 yr and > 10 yr intervals) and this was compared to the standing vegetation at each site. A nested sampling design (subplot, plot, site) was used to determine the effect of spatial scale on the patterns observed in both the vegetation and the seed bank. Temporal variation in the seed bank was assessed by repeated soil sampling over a two year period. 61 native and 30 exotic species were recorded in the vegetation. Richness varied more between sites than within sites. Sites were therefore internally homogeneous for species richness. However, no correlation between burning frequency and richness was found. DCA ordination separated the sites into distinct groups, but sites with similar fire history did not necessarily group closely. 60 taxa germinated from the soil seed bank, comprising 32 native and 28 exotic species; 11 species, mostly therophytes, were restricted to the seed bank. The richness of the seed bank was significantly lower than the vegetation at all spatial scales. No correlation between seed bank richness and fire history was found. The seed bank of species-rich grasslands is dominated by a limited number of widespread, highly clumped, annual, native and exotic monocots. Most native hemicryptophytes, and perennials in general, were represented in the soil by a transient seed bank. Only 12 % of study species, all therophytes, were considered to form large, persistent seed banks, the size of which was greater in unburnt grasslands at all times of the year. The distinct floristic patterns observed in the vegetation are less clearly represented in the seed bank. The seed bank represents a floristically distinct (and less variable) component of the vegetation when compared to the standing flora. The size of the long-term soil seed bank suggests that it has little functional importance for many native species and probably contributes little to seedling regeneration processes following disturbance. Altering established fire regimes is likely to only change the composition and small-scale richness of the existing site vegetation and will not re-integrate species previously lost from the vegetation due to past management. It is suggested that the maintenance of vegetation remnants and processes that encompass a range of long-term burning histories will be necessary if the flora is to be conserved in situ. Restoration of degraded grasslands cannot rely on the soil seed bank but rather, will be dependent on the reintroduction of propagules.     

Effects of fire regime shift in Mediterranean Basin ecosystems: changes in soil seed bank composition among functional types

We studied the soil seed bank in a possible scenario of fire regime shift and asked: (1) Does high fire frequency impact the density of seeds stored, species richness and evenness? (2) Overall, does high fire frequency produce changes in the presence–absence and abundance of species? The study was implemented in a Mediterranean Basin ecosystem in plots with increasing fire frequency (unburned, burned once and burned twice in the last 66 years). The number of seeds increased with fire frequency for all life forms (shrub, scrub, perennial forb, annual forb and perennial graminoid). Species richness of annual forbs also increased. Evenness of shrubs diminished because the number of seeds in all the species decreased, except C. albidus, which increased. Overall, differences in the abundance of species were found, mainly by depleting shrubs and increasing forbs. There were no differences in the presence–absence data. In conclusion, high fire frequencies act as a filtering factor for species of a larger size and advanced maturity age. In contrast, life forms of small size and rapid onset of reproductive maturity can be enhanced. This community conversion from woody to herbaceous soil seed banks is fundamental to identify vegetation changes in future regimes of high fire frequency.