Drought during a key post-fire stage for recovery success filters plants with enhanced fitness under water stress in a Mediterranean obligate seeder

BACKGROUND AND AIMS: Climate change in Mediterranean ecosystems is lengthening summer droughts towards the wet seasons (autumn and/or spring). These seasonal rains are crucial to ensure post-fire recovery, especially for obligate-seeder species, because they rely exclusively on germination success. Although shifts in drought seasonality after fire could constrain regeneration, drought events can filter out more drought-tolerant species in adult communities. Yet the role of drought as a selective filter during the first wet seasons after fire in obligate seeders remains unclear. METHODS: We did an experimental fire on three sites. Then, we experimentally extended post-fire summer drought either by delaying its end into autumn or by advancing its onset into the following spring. Four and six years after the fire, we measured key life-history (height and fruit production) and leaf traits related to water-use strategy in the most abundant post-fire species found, Cistus albidus. KEY RESULTS: Four years after the fire, plants surviving autumn drought were taller and produced more fruits than those subjected to spring drought. Despite this higher resource investment, 6 years after the fire these individuals also exhibited leaf traits (e.g. specific leaf area) that enhanced drought tolerance. Furthermore, the advanced summer drought to spring led to opposite results. Further analysis revealed that drought treatments had a more relevant role than, for example, plant density, in explaining outcomes in key traits, such as specific leaf area. CONCLUSIONS: Our findings suggest that a drought during the first post-fire autumn can filter individuals with traits directly related to fitness and survival under drought. Moreover, we conclude that, more than drought during recovery, the timing of drought in this phase is crucial to generate intrapopulation filtering. This mechanism could have important implications for obligate seeders, which rely on replenishing their seedbank to persist in the face of disturbances.