Climate: what Forests Teach Us

From its site in the Massif de l'Étoile, the Climed platform overlooks Marseille. Spread over 2 hectares, 93 structures with gutters collect rain to study how the garrigue reacts to declining rainfall.

Here in the Forest of Fontblanche (south-east of the town of Aubagne) on a workshop-site belonging to the French National Institute for Agricultural Research (INRA), a sample core is being taken from an Aleppo pine . It will be used to determine the thickness of the tree’s growth rings and to analyze the conditions to which it has been subjected, such as lack of water.

Preparation of an Aleppo pine core taken from the forest of Fontblanche. It has been sanded to clearly reveal the rings, which will later be examined under a binocular microscope.

At the Observatory for downy oaks (O3HP), on the site of the Haute-Provence Observatory to the north of Marseille, researchers use rolling covers which they can open and close above the treetops. In this way, they are able to deflect part of the rainfall and simulate changes in the climate.

The O3HP platform also has walkways equipped with measuring instruments. Here, a branch has been enclosed in a sealed chamber to capture the volatile biogenic organic compounds emitted by oak trees under stress from water deprivation.

At ground level, gutters collect rainwater under forest cover (left) and clear of any cover (right) to determine the percentage of rainfall intercepted by trees. As it passes through the treetops, rain gathers mineral and organic elements that are also examined.

Nearby, the Icos tower (Integrated Carbon Observation System) rounds out the range of analyses, measuring atmospheric concentrations of greenhouse gases, particularly CO2. As part of a European network of measuring stations, it can study the contribution of Mediterranean forests to the carbon balance.

To set up the walkways among the treetops in 2009, scientists had to shuffle between oaks… The exercise was well worthwhile, as these measurements begin to yield their initial teachings which include the following: reduced rainfall greatly slows decomposition of the litter—comprising dead leaves and other plant detritus—a key process for the functioning of the ecosystem.