Heat in the forest - Oak leaves withstand surprisingly high temperatures
The leaves of oaks can withstand heat well, according to a study. A Swiss team measured the temperature on trees in Switzerland, France, and Spain last summer and came to "surprising" results, as reported by the Swiss Federal Research Institute for Forest, Snow and Landscape (WSL).
"Top leaves in the crowns reached temperatures of up to 50 degrees Celsius in August, which is quite incredible," said Charlotte Grossiord, a forest ecologist and lead author of the study. These values were measured at an air temperature of 40 to 42 degrees. The oaks survived the heat without the photosynthesis activity in the cells being destroyed. Plants use sunlight, water, and carbon dioxide to produce sugar for their growth through photosynthesis.
Heat test in a water bath
The research team found that European oaks can even withstand more heat. For this, they exposed leaves to increasing temperatures in a water bath. The leaves of Swiss European oaks survived up to 59 degrees, while those of other trees survived a bit less.
The trees have their own mechanism to keep the temperature of the leaves down in the summer, as the team found: the leaves constantly lose a little water, which evaporates at the surface and provides cooling.
The team recorded the temperatures in the top leaf layer using infrared thermal cameras on drones. To measure photosynthesis in the branches at the top and water loss, they used cranes in some cases.
Given the increasing frequency of heatwaves due to climate change, Grossiord recommends monitoring heat stress signals in forests using drones or satellites. Irrigation can cool the trees.
The study conducted by the Swiss team also revealed that European oaks in Spain demonstrated remarkable heat resistance. Despite the intense heat waves last summer, oaks in Spain maintained their integrity, showcasing Spain's oak trees' resilience.
The researchers further discovered that the oak trees in Spain employed an efficient water loss mechanism to regulate their leaf temperatures, contributing to their good heat tolerance.
