Provenance and seed mass determine seed tolerance to high temperatures associated to forest fires in Pinus pinaster

We show that Pinus pinaster provenance affects both seed germination and seedling recruitment after fire. This information is crucial for managers to select the best seed-provisioning populations when implementing reforestation programs to assist the natural post-fire regeneration of the species. Reforestation programs to assist natural regeneration of maritime pine (Pinus pinaster Aiton) forests after wildfires very often neglect the fire-adaptive traits of the selected seed-source populations, threatening future stand resilience to fire. We investigate the influence of seed provenance and weight on the rate and timing of seed germination, and on early seedling growth of P. pinaster after fire. We simulated conditions during fire by experimentally submitting free seeds from three P. pinaster provenances with contrasting levels of serotiny (from < 6 to > 58 % of trees bearing serotinous cones within the population) to six combinations of temperature and exposure time. We fitted GLMs and LMs to test for differences among provenances in reproductive performance after the thermal shock treatments. Heavy seeds derived from the very low serotinous population exhibited greater tolerance to heat (higher germination rate, lower germination time, and higher seedling length) than the lighter ones from the highly serotinous population. The seeds enclosed in serotinous cones are, however, the only ones protected from high fire-induced temperatures, delaying release until favourable post-burn conditions for germination and seedling establishment. Therefore, selecting the best fire-adapted populations with the optimal serotiny level as seed-provisioning sources should be encouraged to ensure forest regrowth in fire-prone areas.