Aleppo pine regeneration after fire

A French paper was published in the journal "Forêt Méditerranéenne" on several unknown or unrecognised aspects of Aleppo pine regeneration after fire.

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Photo: Siala / Pixabay
Photo: Siala / Pixabay

The paper accurately measured seed rain intensity and duration in relation with stand characteristics at many places. For the seeds, the dissemination was studied not only when first released from the cones, depending on wind speed, but also later on the soil with wind gusts, often on longer distances than their initial flight. Mechanisms of seed burrowing showed the importance of seed weight and shape, and soil surface roughness, and predation also interfered with seed spatial distribution.

The extreme temperatures (up to >70°C) and their daily regimes (potentially several hours over 65°C) at soil surface and at low depth in superficial soil layers, were characterised according to the many aggravating or mitigating factors: sun light angle (month), slope and orientation, soil and ashes color and texture, soil surface stoniness, soil cover by dry needles, remaining shade from burned stands (highly dependent on vegetation density and fire severity) and the shade of obstacles on the soil (stumps, rocks) depending of their size.

Finally, the resistance of seed germinative capacity to extreme thermal regimes for various periods was assessed by experiments both in the field and in the lab. Aleppo pine seeds lose progressively their germination capacity only after more than one week at soil surface with 4 hours daily at 70°C. Some can still germinate after 4 to 5 weeks with such a treatment, but most seedlings in this case develop very slowly or incompletely and are not viable. Several of the studied factors, particularly the duration of extreme temperatures at soil surface, and the ability for seeds to burry rapidly in depth, may explain the high spatial and temporal variability of Aleppo pine regeneration after fire.

Full reference: Vennetier M. 2020. Quelques aspects méconnus de la régénération du pin d’Alep après incendie. Forêt Méditerranéenne, 41(2). P101-120