Fire effects on ecosystems range from destruction of aboveground vegetation to direct and indirect effects on belowground microorganisms. Although variation in such effects is expected to be related to fire severity, another potentially important and poorly understood factor is the effects of fire seasonality on soil microorganisms. We carried out a large-scale field experiment examining the effects of spring versus autumn burns on the community composition of soil fungi in a typical Mediterranean woodland. Although the intensity and severity of our prescribed burns were largely consistent between the two burning seasons, we detected differential fire season effects on the composition of the soil fungal community, driven by changes in the saprotrophic fungal guild. The community composition of ectomycorrhizal fungi, assayed both in pine seedling bioassays and from soil sequencing, appeared to be resilient to the variation inflicted by seasonal fires. Since changes in the soil saprotrophic fungal community can directly influence carbon emission and decomposition rates, we suggest that regardless of their intensity and severity, seasonal fires may cause changes in ecosystem functioning.

Aim: Plant species regenerate after fire either through vegetative growth (i.e., obligate resprouters) or seed germination (i.e., obligate seeders), with some species adopting both strategies (i.e., facultative seeders). Fire season can have important consequences for the relative abundance of plant species adopting these regeneration strategies. The present study aimed to test for differential effects of fire season on perennial plant community composition.Location: Eastern Mediterranean woodland in the Judea Mountains, Israel. Methods:We conducted, for the first time, a large-scale field experiment, involving prescribed spring and autumn burns in a typical eastern Mediterranean woodland.We sampled the perennial plant community before and after the burns, quantifying temporal changes in community composition caused by seasonal fires. Results:Although fire intensity and severity were consistent between the two seasonal fires, plant community composition differed between areas subjected to spring or autumn burns. The abundances of all common species, Pistacia lenticus (obligate resprouter), Cistus spp. (obligate seeders) and Teucrium divaricatum (facultative seeder), were all reduced by both fires. Yet, their dominance in the post-fire perennial plant community was retained.Differential fire season effects were detected only among obligate seeders, which experienced a stronger reduction in abundance after spring than after autumn burns. Conclusions:Differential fire season effects on the perennial plant community resulted from phenological rather than fire intensity/severity effects. Such changes in community composition may have important implications for plant community dynamics, because they affect the circle of "fire event-plant regeneration-fire reoccurrence", determining the probability and intensity of future fires. Furthermore, even though the eastern mediterranean ecosystem is considered highly resilient to disturbances, increased spatio-temporal variation in fire season, may result in a new vegetation mosaic, differing from the contemporary one, i.e., an alternative stable state. K E Y W O R D S community composition, facultative seeders, fire disturbance, obligate resprouters, obligate seeders, plant life form, plant regeneration strategy 116 | Applied Vegetation Science TSAFRIR eT Al.

Aims We explored if and how seasonal fires interact with microhabitat type (i.e., under Pistacia shrub, under Cistus shrub, or a canopy gap) to influence the composition of the germinable soil seed bank (GSSB) community in a typical eastern Mediterranean woodland. Methods We conducted a field experiment, involving prescribed spring and autumn burns, and thereafter quantified the seed germination patterns using soil samples collected from both burned and adjacent unburned control plots. Important Findings Soil temperature was significantly higher during autumn burns, while being more variable during spring burns. Fire caused overall reductions in GSSB density, richness and diversity. The reductions in GSSB richness and diversity were significantly stronger under Pistacia and Cistus shrubs located within plots subjected to autumn burns, and these patterns were mainly evident among annuals. GSSB density of dwarf shrubs was higher in samples collected from burned plots, and this pattern was more pronounced in samples collected under Pistacia and Cistus shrubs. Together with the appearance of unique species, seasonal fires led to significant changes in the composition of the GSSB community. Our results illustrate that seasonal fires interact with spatial heterogeneity to influence the composition of the GSSB community mostly via differential effects on the germination densities of annuals and dwarf shrubs. These findings imply that the increase in the frequency of seasonal fires, which has occurred in the eastern Mediterranean basin during the last few decades, may translate into a shift in eco-evolutionary selection pressures, operating on plants inhabiting this unique ecosystem.

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