In recent years, foresters have been able to observe it up close: First, prolonged drought weakens the trees, then bark beetles and other pests attack.
In recent years, foresters have been able to observe it up close: First, prolonged drought weakens the trees, then bark beetles and other pests attack. While healthy trees keep the invaders away with resin, stressed ones are virtually defenseless. Freiburg scientist Sylvie Berthelot and her team of researchers from the Faculty of Environment and Natural Resources and the Faculty of Biology are studying the importance of tree diversity on bark beetle infestation. They are investigating whether the composition of tree species affects bark beetle feeding behavior. The team recently published their findings in the Journal of Ecology.
In a 1.1 hectare experimental set-up in Freiburg, six native deciduous and coniferous tree species from Europe and six deciduous and coniferous tree species from North America were each planted in different mono- and mixed plots. After the severe drought in the summer of 2018, the Sixtoothed spruce bark beetle mainly attacked the native species: the European spruce and the European larch. “We were surprised that the beetles exhibited only a slight interest in the exotic conifer species, such as the American spruce,” Berthelot says.
While measuring the infestation, the researchers found that the position within the experimental site was also crucial. The trees at the edge were attacked the most. Therefore, Berthelot suspects that the bark beetle entered the testing plot from outside. “In addition, environmental influences weaken the unprotected outer trees more, so they are more susceptible.”
Read more at: University of Freiburg
Aerial view of the IDENT tree diversity experiment near Freiburg before (left) and after (right) the 2018 drought and bark beetle infestation (Photo Credit: K. R. Kovach, Sixtoothed spruce bark beetle photo by U. Schmidt)