New experiments aim to save pine forests in Bordeaux from climate challenge

A 10-year experiment is about to start near Bordeaux to select a new generation of maritime pine trees able to resist drought.

Maritime pine trees make up most of the vast Landes forest, the largest in Europe, which stretches down from Bordeaux to the Basque Country.

It was created in the 19th century, when geologists and engineers discovered how to drill through a relatively thin layer of rock and drain the swamps which used to cover the region.

“The pines planted in the former swamps, were all maritime pine species which were found in the area,” said Dr Sylvain Delzon, a researcher with the INRAE state research agency, who also runs his own laboratory at the University of Bordeaux.

In around 1960 a second generation of trees were planted, developed by researchers for their fast growth and straight trunks, and then a third generation, with improved growth and straightness.

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“We will be looking for characteristics which will enable trees to grow and resist drought, because all the forecasts are that the region will be up to 60% dryer in the next 50 years.”

Limited rain experiment

During the experiment, eight different variations of maritime pine trees will be monitored in an open-sided structure with a roof, which closes automatically after 10 minutes of rain.

Plexiglass shields have been dug into the ground around the structure to limit rain runoff and the amount of water getting into the planting plot through capillary action.

“We estimate that the conditions in the shelter mean that the trees will get 60% less rain than usual for the region, which will enable us to see how they react,” said Dr Delzon.

The eight varieties have already been tested in the lab, with trees from Portugal and from around Barcelona showing the best drought-resistant characteristics.

“But until we have tests in the ground, we do not know if the lab results will be replicated,” said Dr Delzon.

He said maritime pines already in the forest were “incredibly resistant” to drought, with even very small, newly planted saplings surviving recent heatwave and drought episodes.

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Storm and fire risk to trees

The pine forests, which were an important source of resin for turpentine until around 40 years ago when production moved mainly to Asia, are now harvested every 50 years. The wood is mainly used for wood pulp for paper, in insulation boards or for biomass fuel.

Originally a 60-year harvest cycle was the norm, but owners have cut that by a decade to reduce the risk of mature trees being lost in storms and fires.

Other varieties of pine from different areas are more suitable for building, but maritime pine from the Landes is sometimes used for panelling in houses, where the knots in the wood give a rustic finish to a room.

The large fires south of Bordeaux in 2022 were the worst since 1949, but Dr Delzon said it is likely that maritime pine will be used to replant the devastated areas.

“The soil in the region is very poor and sandy, and not many other trees can grow well in it,” he said.

“I forecast that the forest will stay looking pretty much as it is for a long time in the future.”

While some people find the long stretch of pine forests south of Bordeaux monotonous to drive through, it does provide inspiration for others.

Former French prime minister and presidential hopeful, Alain Juppé, who was mayor of Bordeaux, has written eloquently about getting off the main road and deep into the quiet forest on hot days, where the perfume of the resin is “intoxicating”.

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