In the United States, oaks are drought tolerant

According to a study of Scottish pines, oak species show more resistance than previously imagined in the United States, or because they are more susceptible to severe episodes of drought, making trees more suitable for long periods of dry weather. “We thought oaks living in very arid environments were the most vulnerable,” explains AFP Sylvain Telson, a researcher at INRAE ​​at the University of Bordeaux who participated in the study and published in the latest edition. Processes of the American National Academy of Sciences. Mr Telson says 19 species of oak “established in the west of the US” are “extremely drought tolerant”, ranging from the humid temperate forests of Washington State in the north to the deserts of southern California. An intense heat wave is dangerous to any plant; In general, the water that feeds on it follows the circumference of the vessels from the roots to the leaves, where most evaporate.

As the lack of water in the soil and the increase in temperature accelerates its evaporation through the leaves, the pressure of the sap in the vessels decreases. On ships “we’re at a certain threshold, air bubbles appear”, in other words, an embolism, which ends up killing the plant by blocking the flow of soap, explains INRAE’s researcher. The oak species that the researchers studied “have a great deal of protection against embolism”, especially by creating highly resistant vessels. To measure this margin, the laboratory compares the moment when air bubbles appear in the vessels of a branch and emphasizes that the vessels of a tree subject to a severe episode of drought occur in the field.

According to Sylvain Telson, species studied over millions of years are “more tolerant of dry weather than current”. On the other hand, in the face of very rapid climate change, he says, “Can they adapt so quickly? Nothing seems less.”

In Scotland, a team of scientists led by Thomas Owenton of the University of Sterling studied the recovery potential of winter pine, also known as northern pine, following a severe drought. Extending their observations to nine years after this chapter – most studies covering two or three years – although the trees initially experienced stunted growth, most returned to normal four to five times. After many years. According to a study published in the Journal of Ecology last January, some have recorded “growth” for some years. “It never reached the level (of the trunk) they should have reached without a single episode of drought, but it did allow it to reduce the deficit,” Thomas Owenton told AFP. According to him, it is necessary to consider the effects of prolonged drought, and not to focus on the only growth deficit caused by this chapter.