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Quelques aspects méconnus de la régénération du pin d’Alep après incendie

Abstract : The dominant conifers in Mediterranean forests are adapted for regeneration after wildfire. They are resilient thanks to serotinous cones protecting the seeds during the fire, liberating them soon after into a habitat free of most competition, thus favoring germination and seedlings survival. However, this strategy of obligate seeder sometimes fails or gives uneven results over time and space even for similar stands. This article provides a synthesis of long-term research aiming at disentangling the many phenomena which could explain such an irregularity in the regeneration. We studied : (i) seed pre-fire availability, seed rain intensity and spatial patterns, the first dissemination of winged seeds in the air, and their later journey on the ground with wind gusts, which can be longer than the initial flight, their burial mechanisms, and animal predation; (ii) soil temperature in the months following fire, seeds being exposed to extreme heat on the black soil surface, in an ash layer and at low depth (60°C to more than 70°C for 4 to 6 hours per sunny day), along with the factors driving these temperatures (solar energy, cloudiness, slope and aspect, shade from remaining trees and obstacles on the ground, soil color and texture, cover of unburned needles or leaves falling after fire); (iii) Finally, we studied the resistance of the Aleppo pine seeds to such long lasting exposure to heat. Aleppo pine seeds progressively lose their germination capacity only after more than one week at 60°C-70°C for 4hrs per day. A significant percentage of seeds can germinate, though far more slowly, after 4-5 weeks of such a heat regime, but they hardly give viable seedlings. All factors cited above reducing sun light intensity and those helping seed to bury at least a few centimeters in the soil (biological activity, animals) help releasing heat stress for seeds and contribute to a higher germination rate. Conclusion: Aleppo pine seeds are adapted to regeneration after wildfire thanks to their resistance to very high temperatures at ground level. However, a residence period of several weeks on the hot ground with few shade, or just slightly buried, reduces germination rate and speed, and inhibits the seeding development. Climate factors driving seed availability before fire, and many factors regulating soil temperature, interact to explain regeneration spatial and temporal patterns
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Contributor : Michel Vennetier <>
Submitted on : Monday, January 4, 2021 - 10:47:22 PM
Last modification on : Friday, March 5, 2021 - 3:27:00 AM
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  • HAL Id : hal-03096312, version 1



Michel Vennetier. Quelques aspects méconnus de la régénération du pin d’Alep après incendie. Forêt Méditerranéenne, 2020, 41 (2), pp.101-120. ⟨hal-03096312⟩



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