• Reduce text

    Reduce text
  • Restore text size

    Restore text size
  • Increase the text

    Increase the text
  • Print

    Print

European pines display good fire resistance

Of the pine trees that populate the Mediterranean forests that are so exposed to fire, the Canary Island pine, maritime pine and parasol pine are the best equipped to survive. This ranking, established in the context of the European Fire Paradox research programme1 in which INRA is involved, will serve as a decision-making aid for the more rational management of forests, before or after fires, and for the control of prescribed burning.

L’un des majestueux pins laricio du domaine qui jouxte le bâtiment de l’unité INRA-URFM occupé par des membres de l’équipe, Domaine Saint Paul, Pôle Agroparc, Avignon – Montfavet,Il a fait tourné la tête du photographe,Vue en contre plongée, 29 juillet 2008,. © INRA, SLAGMULDER Christian
By Press Office
Updated on 10/03/2014
Published on 08/05/2009

Every year, fires affect 500,000 hectares of Mediterranean forests, mainly in Spain, Portugal, France, Italy and Greece, because of climatic conditions and the type of vegetation. But these are not the only causes, as fires are also started by agricultural or forest burning, open waste dumps, high voltage power lines, changes of use in forest regions and carelessness. High winds can also enhance the risk of fire by increasing the quantity of dead, flammable timber on the ground and hampering access for the fire services. Thus fire also affects western France2, Poland and, further north, Finland and Sweden.
"95% of these forest fires are caused by human activities. We must therefore learn to live with them, by exploiting the findings of scientists. This is the challenge of Fire Paradox, a European research consortium designed to improve the control of the ever-growing number of Mediterranean forest fires", explains Eric Rigolot, deputy coordinator of the programme, deputy director of the INRA Ecology of Mediterranean Forests Unit and a specialist in fire ecology, the science that studies the effects of fire on ecosystems.

Organising scientific knowledge

Prescribed burning used preventively for scrub clearance.. © INRA, LEGRAND C.
Prescribed burning used preventively for scrub clearance. © INRA, LEGRAND C.
With his Portuguese and Spanish partners, the researcher compared the principal pine species found in European forests as a function of their fire resistance: Aleppo pine (Pinus halepensis), Monterey pine (P. radiata), parasol or stone pine (P. pinea), maritime pine (P. pinaster), Canary Island pine (P. canariensis), black pine (P. nigra) and Norway pine (P. sylvestris). Their initial classification was based on the morphology of different pine trees, this data being collected from observations or experiments by the international scientific community.

On the one hand, the classification includes individual tree traits: bark thickness (the bark protects living tissues and ensures tree diameter growth); foliage3, in this case needles; bud-bearing branches, the organs for length growth (protected from thermal shock by scales of varying thickness and a sleeve of green needles); tree architecture (tree shape can protect vital organs (such as buds and seeds contained in cones) from flames), etc. On the other hand, this classification takes account of the reproductive characteristics of different species. How does a species regenerate itself? Will it benefit from the passage of a fire? In this respect, pines are notable in that they only reproduce from seed, and build up seed banks in their cones. These numerous seeds survive for several years, protected by a state of "dormancy" and remaining physiologically inactive. Another specificity is serotiny, observed in the Aleppo pine and maritime pine: their cones are coated with resin. By melting this resin, a fire opens the scales of the cone and the seeds are released. These two specificities are indicative of the evolutionary adaptation of pine trees to frequent fires.

Furthermore, the severity of fire-related injuries to foliage or the trunk, which markedly influences tree mortality, must also be taken into account when classifying the fire resistance of pines. For this reason, researchers have developed a model for each species that calculates their chances of survival following a fire. This model integrates how the intensity of a fire, its residence time at the foot of a tree and the length of flames, damage the tree.

European pines, adapted to attack from fire

Overall, among the seven pines thus classified, the Canary Island Pine (the only one to regenerate by budding4, which is an advantage), the maritime pine and then the parasol pine are the best adapted to surviving a fire. However, a low intensity fire can be well-tolerated, even by species reputed to be fire-susceptible, such as the Aleppo and Monterey pines. If the fire is intense, all trees die, but their ability to regenerate remains considerable; pines are the first species to recolonise a fire-affected area. In full light and in a soil fertilised by ash, the young plants develop rapidly and well. They benefit greatly from the scrub clearing effect of fire, when compared with deciduous trees. This natural regeneration does not usually require replanting.

"By introducing rationality where empiricism previously prevailed, this classification helps to guide the choices of foresters, notably when they need to select trees to be conserved after a fire", continues Rigolot. Thus, for example, following a fire in a forest made up of parasol and Aleppo pines, and despite apparently similar damage, it is not necessary to cut down the parasol pines because they have a greater chance of survival. And in the context of organising preventive fire breaks, foresters could preferentially remove species with the lowest resistance to fire, such as Aleppo pines. These conclusions are also essential with respect to prescribed burning, which is easier to implement under the most fire-resistant pines.

(1) An innovative approach to integrated wildland fire management: http://www.fireparadox.org

(2) In Gascony, the Landes forest covers a million hectares of maritime pines.

(3) The term "foliage", like those of crown or leafing, indicate all leafy parts of the tree.

(4) The Canary Island pine can generate a bud directly on its trunk, i.e. from cells that are normally programmed to ensure diameter growth rather than length growth!

Contact(s)
Scientific contact(s):

  • Éric Rigolot, François Pimont. Ecology of Mediterranean Forests Unit (URFM)
Associated Division(s):
Forest, Grassland and Freshwater Ecology
Associated Centre(s):
Provence-Alpes-Côte d'Azur

Deciphering the paradoxes of fire

The aim of Fire Paradox, a European scientific project, is to obtain efficient tools to combat (increasingly common) fires in Mediterranean forests, to improve the management of these forests and establish the foundations for new regulations. To achieve this, it is necessary to understand all aspects of fire: the circumstances under which it occurs, its behaviour, its effects on trees and its socioeconomic impacts.

The originality of the project resides in accepting the paradox of fire. It can thus be both destructive and beneficial: indeed, it can be used preventively for scrub clearance by prescribed burning and also as a counter-fire to put an end to an outbreak.
36 partners from 16 countries affected by forest fires are involved in this project which started in 2006 and will be completed in 2010.

Reference

Fire resistance of European pines, Paulo M. Fernandes, José A. Vega, Enrique Jiménez, Eric Rigolot, Forest Ecology and Management, 256 (2008) 246-255.