Fire and runoff as complementary ecological filters shaping dormancy release and recruitment in Cistus albidus L.

Physical dormancy in Mediterranean Cistaceae is commonly interpreted as a fire-related adaptation. Yet in semi-arid catchments, hard-coated seeds are also exposed to sediment-laden runoff, where abrasion, transport and water availability may occur together. This raises a broader ecological question: are dormancy release and recruitment in Mediterranean obligate seeders filtered mainly by fire, or by interacting thermal and hydrological disturbance processes? We addressed this question in Cistus albidus L., a widespread western Mediterranean shrub, by comparing dry heat, simulated wildfire, runoff-driven scarification, manual scarification and one-year natural ageing using seeds from six mother plants. A complementary establishment trial assessed whether germination translated into early seedling survival under contrasting seasonal conditions. Fresh seeds germinated well after all dormancy-breaking treatments. Final germination did not differ significantly among replicated fresh-seed treatments, reaching 80.7% after dry heat, 72.6% after simulated wildfire and 73.9% after manual scarification. Runoff scarification, interpreted descriptively because seeds were processed as a single composite batch, produced similarly high germination (78.4%). Simulated wildfire mainly accelerated germination: seeds reached 50% germination faster than after dry heat, but final germination was not higher. One-year-old seeds retained substantial viability but showed low germination after 12-h hydration, indicating that physical dormancy persisted after one year; extended hydration partly increased germination within the aged cohort. Seedling emergence was high in both establishment trials, but survival was strongly seasonal. Summer cohorts showed near-complete post-emergence mortality, whereas autumn cohorts maintained high survival after 60 days. Regeneration in C. albidus is not adequately explained by strict fire dependence. Heat exposure provides a rapid dormancy-breaking cue, whereas the runoff simulation provides evidence for a plausible hydrological pathway in which seed-coat abrasion and water exposure are coupled. Fire and runoff may therefore act as complementary recruitment filters with different temporal consequences. These findings support an interpretation of C. albidus as a flexible obligate seeder whose recruitment depends on the alignment between dormancy release, hydration and post-emergence conditions. Mediterranean shrubland models should incorporate hydrological scarification, seasonal establishment bottlenecks and the increasing mismatch between fire and rainfall regimes.