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Soil seed banks play a major role in the post-fire regeneration of Mediterranean shrublands. They vary throughout the year in species composition, abundance, and readiness to germinate. After fire, germination occurs mainly during the following fall to spring. Time of germination can determine recruitment success. It is unclear what factors control postfire germination and its timing. We tested the effects of season and fire on the readily germinable soil seed bank of a seeder-dominated shrubland. Plots were burned early and late in the summer season (ES, LS). Soil samples were collected before and after fire, and germinated in a chamber simulating successively autumn, winter, and spring conditions. Samples were kept moistened at all times. Fire intensity was similar between ES and LS. Several species of Cistus and herbs, mostly annuals, were dominant. Most germination occurred during the simulated-autumn period, with little subsequent germination during the following two periods. Germination speed (T 50 ) during simulated-autumn was similar for shrubs and herbs, and independent of season or fire. Germination was lower for two shrubs (Rosmarinus officinalis, Cistus salvifolius) and higher for herbaceous dicots in LS than in ES soils. Fire reduced monocots and enhanced Cistus. Germination period significantly interacted with fire and season in some groups or species, altering the simulated-autumn germination peak. We demonstrate that the seed bank can germinate swiftly under simulated-autumn conditions. Hence, water availability is the main controlling factor of germination. Fire season differentially affected some species or groups, and could affect the post-fire regeneration.

Question: What are the short-term (first 4 yrs) dynamics of a Mediterranean heathland following burning during the early-vs the late-fire season?Location: Serra da Lousã, Central Portugal. Methods:The vegetation studied was a 16-year old heathland with Erica australis (resprouter), Pterospartum tridentatum (resprouter/seeder) and Erica umbellata (seeder) among the dominant species. Four blocks, each with three 50 m 9 40 m plots, were established. One plot per block was burned during the early season (ES) and one during the late season (LS), and the third remained unburned. Prior to, and during the first 4 yrs after burning, each burned plot was sampled for species abundance, vigour and richness. The effects of fire through time were tested using random blocks repeated measures ANOVA. Recruitment was modelled as a function of percentage of post-fire soil covered by litter (%). MANOVA was used to test changes in the relative dominance of the woody species due to fire. Community dynamics were assessed by NMDS ordination analysis.Results: Fire severity was higher and the percentage of post-fire soil covered by litter lower in ES than LS burns. The post-fire plant dynamics were dominated by the resprouting response. Resprouting was not affected by burning season, but ES fires resulted in higher seedling recruitment than LS fires, particularly in the dominant seeder E. umbellata. Seedling recruitment was negatively related to post-fire soil covered by litter. Additionally, seedling emergence was delayed by nearly 1 yr in LS fires with respect to ES fires. Species richness was higher in ES than LS fires. Fire did not globally affect the relative abundance of the dominant species, although the seeder E. umbellata decreased its relative cover with respect to the other dominant species. Ordination analysis showed that the postfire dynamics of the vegetation were on a track of convergence with the community existing before fire.Conclusion: Burning season differentially affected regeneration, mainly by its effect on seeding, with little effect on resprouting. Burning season and associated changes in fire severity and soil covered by litter could alter the short-term regeneration dynamics, which can have important implications for managing this highly flammable vegetation.

Question: In a seeder-dominated shrubland, does burning season affect postfire regeneration? Are herbs and shrubs similarly affected? Is the dominance of the main species modified by burning and its timing?Location: Los Puntales, Sierra Morena (C ordoba, southern Spain). Methods:The shrubland was 12 yr old, dominated by several species of Cistus, among the main seeders. Four blocks, each containing plots of 25 9 25 m, were burned in late May (early season, ES) and late September (late season, LS) with similar fire intensity. Woody plant density and woody and herbaceous cover and richness were monitored during the first three post-fire years and compared to pre-fire using ANOVA and ordination techniques.Results: Burning season did not affect cover of the herbaceous or woody species in general, nor cover of the main groups (monocots, dicots, annuals and perennials) or density of the main woody species 3 yr after fire. Fire, however, differentially affected the relative abundance of the main shrub species. Ordination analysis showed that, while succession of herbaceous species was on track to convergence with the pre-fire vegetation, this was not the case for the woody species.Conclusions: Burning season was not a significant factor in altering the postfire regeneration in this seeder-dominated shrubland. Thus, the temporal window for prescribed fires is large, and both seasons could equally be used for management purposes. However, changes in the relative dominance of species due to fire indicate that managers should be alert when this shrubland burns.

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