Repeated periods of heat and drought causing some trees to die – study

Climate change is causing apparently healthy trees to die after periods of heat and drought. Many may not die immediately but repeated periods of hot weather seem to increase the vulnerability of some species more than others.

Researchers studied 20 species of conifers planted 100 years ago in the same place in the Netherlands, taking tree ring samples to see how they did in droughts between 1970 and 2013. From the distance between the rings it is possible to tell how much each species’ growth was affected.

After the hot, dry summers from 2018 to 2020 the scientists returned and found that some of the plantation had not just lost growth but been unable to survive at all. Some species had all come through but in others seven out of 10 trees had died.

Rather surprisingly it was not the different ability of trees to find water in the soil that caused the deaths but leaf damage. Some pine species renew their needles each year while others keep them for a decade or even longer, something that would normally save the tree energy and effort. But in this case the species that had heat-damaged needles but could replace them quickly survived, while those that did not have that ability gradually died.