The conclusion is simple : in the forests of the Landes, the young pines do not make old bones, which hinders the renewal of massive. And it took four years of research for scientists to understand what was happening. "We had a gaggle of suspects," says Laurent Augusto, a researcher at the Inrae (national research Institute for agriculture, food and the environment), " disease, climate, water stress, soil depletion ". "Several studies have been carried out in parallel. In the end, there is a guilty party, the climate. And of the accomplices, the animals ", continues the researcher.
summers increasingly dry
The forest of the Landes stretches over one million hectares, of which 10 % in forest dunes, along the coastline. Planted in the Nineteenth century to prevent the silting up of settlements, it provides today the industry of the paper pulp, the wood panel or the palette and numerous sawmills. "In Aquitaine, the timber industry is the second largest provider of jobs after the wine ", recalls Francis Maugard, head of research and development at the agency Landes Nord-Aquitaine (Office national des forêts (ONF). The pine, a symbol of the Moors, " is the only species that can grow on poor areas such as the forest dune ", he adds. The tree is so necessary to the stability of the dune that" essential " for logging purposes, impossible during the winter on the plateau landais, too wet for machinery, according to the NFB.
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Two concurrent factors have been discovered : a microclimate is dry and the growing presence of herbivores such as deer and small rodents, many more, who are dealing with young pines. "The evolution of summers a little warmer and a little drier, has contributed to what the young pines do not pass the summer, said the researcher. The concern was that this trend will gradually extend to other sectors of the landes forest. "At the same time, the teams have revived a technique of reforestation, abandoned since the 1960s.
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This is not to cut but to maintain after the cut " several mature trees which will provide a partial shade and less drying of the air during the day." This allows " for the young seedlings to better withstand the aridity of the summer ", he says. With these constraints : "It is necessary to provide a second harvest delicate for the large trees maintained with no damage to the young trees that have been so hard to grow," adds Laurent Augusto. The technique, called natural regeneration or partial harvesting, is still used in Spain, but the study could also be of interest to other massive european forest plagued with difficulties of renewal.