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🇫🇷 France /Disasters & Emergencies

Summer Could Be Catastrophic for French Trees Already Weakened by Heatwaves

From Le Figaro · () French

Translated from French, summarized and contextualized by DistantNews.

At a glance

News Named sources Context piece
  • French forests have so far withstood heatwaves in May and June, but researchers warn that repeated heat and drought this summer could be catastrophic.
  • Trees, which can consume hundreds of liters of water daily, risk "hydraulic rupture" leading to desiccation or death if soil water reserves are depleted.
  • Differences in trees' heat adaptation abilities are altering forest composition, favoring southern species while causing mortality among less resilient ones like pedunculate oaks.

French forests have shown resilience against recent heatwaves, but researchers from the National Research Institute for Agriculture, Food and Environment (Inrae) caution that a repeat of extreme heat combined with drought this summer could prove devastating. While trees have adapted by adjusting transpiration, their survival hinges on soil water reserves, which were still abundant in May but less so in June.

Neither foliar desiccation, nor branch mortality, nor even individual deaths have been observed following the two heatwaves of 2026.

— Sylvain DelzonResearcher at the National Research Institute for Agriculture, Food and Environment (Inrae), noting the initial resilience of French forests.

An adult oak can use hundreds of liters of water on a 40-degree day. However, excessive water extraction from the soil can lead to "hydraulic rupture," a phenomenon where air bubbles form in the vascular system, causing desiccation and potentially tree death. In southwestern France, some species, like ash trees, are already nearing critical thresholds for this "vascular embolism."

hydraulic rupture

— Sylvain DelzonResearcher at Inrae, describing the critical condition trees face when drawing too much water from the soil.

After trees depleted much of their reserves during the June heatwave, a dry July could trigger an "exceptional drought" far more lethal than previous events. Such severe droughts have been known to cause massive tree mortality one to three years after the initial climate shock, as observed after the 2022 drought.

vascular embolism

— Sylvain DelzonResearcher at Inrae, referring to the critical threshold some trees are nearing due to water stress.

Trees also adapt by altering leaf-out timing, with oaks gaining a week's advantage per degree Celsius increase, compared to two days for beech. These differing adaptation capacities disrupt forest competition, favoring more tolerant species. Inrae notes a "Mediterraneanization" of forests, with southern species like holm oaks moving north. Conversely, less resilient species, such as pedunculate oaks, are experiencing high mortality rates in southwestern France, leading to their contraction in the region.

exceptional drought

— Sylvain DelzonResearcher at Inrae, warning of the potential consequences of a dry July following recent heatwaves.
DistantNews Editorial

Originally published by Le Figaro in French. Translated, summarized, and contextualized by our editorial team with added local perspective. Read our editorial standards.

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