Experimental forest near Bordeaux

An experimental forest was planted near Bordeaux in 2021 to study the effects of drought on trees. Researchers wanted to understand how different tree species respond to water scarcity and extreme heat.

Canopy walkway installed

A walkway allowing access to the canopy was installed on the site this autumn. This structure enables scientists to study the upper parts of trees and observe how they react to environmental stress, including temperature changes and water availability.

Tree species nearing critical thresholds

The data collected from the experimental forest, currently being analyzed as of 2026, shows that certain tree species have already reached their critical threshold. Species like the ash and the pedunculate oak are showing signs of decline, including crown shedding and branch mortality.

Vascular system under study

Researchers at Bordeaux are studying the vascular system of trees, that is, how they transport water through their vessels and what happens during heatwaves. This research aims to understand the mechanisms that allow trees to survive or fail under extreme conditions.

Impact of climate change on crops

Questions about the effects of climate change and its extreme events such as droughts on trees and crops, and whether they can adapt, are being explored by the teams of Sylvain Delzon, a research director at INRAE (National Institute of Agronomic Research) and the University of Bordeaux.

Branch heating system added

After the installation of an experimental forest in Floirac, near Bordeaux, in 2021, depriving some trees of rainwater, a walkway was recently installed this autumn to study the canopy. A branch heating system has been installed at the top of the walkway and allows researchers to observe the impact of two additional degrees on the development of leaves and buds.

Mediterranean species moving north

The sensors installed several years ago already clearly show that there are species that are very close to their decline threshold or have crossed it. For the same reasons, we see Mediterranean species that are moving up and expanding their range, such as the holm oak.

Vascular embolisms in ash trees

For the ash in particular, the researcher describes the spread of vascular embolisms, that is, air bubbles that spread through these vessels and make them unsuitable for water transport, leading to branch, organ drying and individual mortality.

Droughts and forest fires

The episodes of 2022 and 2026 have significantly dried out the soils and undergrowth and created fuel. Result: two unprecedented fires in 2022 and 2026. It is still too early to comment on the mortality caused by the 2026 drought.

Rapeseed crops affected

We have to wait until spring 2027 to see if the trees are able to produce leaves. However, according to the first elements, while the 2022 drought defoliated thousands of hectares of trees, the researcher estimates that large crops have suffered more this year.

Rapeseed supply concerns

He expects that records for soil drought have been broken this year. There are about 1.5 million hectares of rapeseed sown annually in France, making it the leading oilseed crop in the Hexagon. However, 40 percent of these plantings this year are very poor to very degraded, and therefore we will have problems with the supply of oilseed seeds in 2027.

Spring crops severely impacted

He believes that we can then question whether it is worth continuing to grow rapeseed south of the Loire. Drought waves began early, in May, and were coupled with heatwaves that consumed the soil water. We see that spring crops such as maize, sunflower, soybean, sorghum have been impacted by almost 50 percent in terms of production.

Plant mortality and unharvested fields

We have even observed mortality among soybean and maize plants in our trials as early as July. The situation was so degraded that there was both plant mortality and unharvested fields.

Understanding resistance to drought

The INRAE teams want to understand what explains why certain species resist better to water stress and from what threshold this constitutes a threat. This requires following forests over the long term and this is what we are doing here, but also setting up predictive models to try to predict the evolution, the forest dynamics for the end of the century.

Adapting forest management

Their mission to help managers make the right choices and adapt the way to manage the future forest appears completely vital after a summer with infernal temperatures.