Fire risk: close-up on habitat–forest interfaces

In Aix-en-Provence, Cemagref has developed a quasi-automatic method to map habitat–forest interfaces. This tool is of primary interest to land use managers and the actors involved in the fight against forest fires to prevent risk as well as to protect populations and property in case of fire.

“He who lives in isolation lives blissfully.” This is the principle adopted by a growing number of city dwellers, who, searching for the sun, open spaces, and privacy, are building homes on the edges or in the heart of the Mediterranean mountainous forest areas. According to statistics, this phenomenon should continue to develop, with 20% population growth for the South of France before 20201 . Thus, new land use configurations marked by substantial human activity in contact with combustible vegetation are appearing. These spaces, now called habitat–forest interfaces, are sensitive sources of forest fire start-ups. In addition, because of the presence of property and people that require protection, they are zones of increased vulnerability.

In her doctoral dissertation at Aix-en-Provence, Corinne Lampin-Maillet has designed a simple, rapid, and effective method to map the habitat–forest interfaces on large surface areas and on a large scale. The tool defines the type of interface of any zone considered. This information makes it possible to better define the uses of these spaces according to their sensitivity to fire and therefore to control their development.

1 Diren and DRAF PACA, 1999

– Clearly define the notion of interface

The first studies of habitat–forest interfaces appeared in the United States, Canada, and Australia, after the great forest fires of 1985. Other studies have followed in the European Mediterranean countries and at Cemagref over the last decade. The strong point of Corinne Lampin-Maillet’s dissertation is its development of a land use reading method that translates the organization of construction development in interaction with the natural environment as simply as possible. She compared bibliographic data and the opinions of experts of safety services and land use managers, then proposed a relevant definition of the notion of habitat–forest interface to the national context before developing her reading tool. Thus, a construction is said to be “in the habitat–forest interface” if clearing brush is legally required by the French forestry orientation law of 11 July 2001. This concerns constructions located less than 200 m from forests, garrigues, or scrubland. As for the habitat–forest interface zone, it is delimited by the space within a radius of 100 m around these constructions.

– Toward a complete decision-support system

Based on this definition, this scientist has established a method founded on teledetection and a spatial analysis tool to map the habitat–forest interfaces over large surfaces. The spatial analysis of inhabited zones takes into account criteria such as the distance between constructions and how they are grouped. Information relative to the horizontal structure of the vegetation in contact with the construction is added, which reflects it capacity to propagate fire. Depending on the vegetation’s structure and the type of habitat, as many as 12 types of interface have been identified. The method has been successfully applied to two study zones, one located in the Maures massif covering ten towns and the other in the Bouches-du-Rhône department, covering 30 towns.

At the request of the Ministry of Ecology, a methodological aide was written up in 2007; it set out the principles to describe the habitat–forest interfaces as well as the mapping process, which were particularly useful when elaborating the PPRIF². Since January 2008, the tool has been made available to any person or organization that wishes to apply and test it on a real-life scale. Trials are already planned on the department scale in the South of France and in Aquitaine.

Today, research is continuing so that the habitat–forest interface map can evolve toward a global tool for evaluating risk. Thus, other parameters can be taken into account such as wind, the topographic situation of a given zone, the road network, and the vegetation’s vertical structure.

²Plan for prevention of forest fire risks