Bark Beetles unhindered by infusing tree diversity

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For decades, bark beetles have ravaged America’s forests. In an effort tackle this menace, conservationists are turning to new approaches, one of which is to diversify the woodlands with a variety of tree species.

Hopeful research on this approach has been done in the past by scientists looking into invasive pests like the hemlock wooly adelgid and emerald ash borer. Some of these studies even indicate that infestations of those species may be tempered by this technique.

Unfortunately, bark beetles don’t seem to be similarly put off.

At least this seems to be the finding of researchers from the University of Freiburg, who set up a roughly one-hectare experimental observation area testing out whether or not tree diversity hampers bark beetle infestations. In their work area, they placed six native deciduous and coniferous tree species from Europe and six deciduous and coniferous tree species from North America. Each of these were planted in different mono- and mixed plots.

After a severe drought three years ago, they then observed that bark beetles mainly attacked the native species: which were in this case the European spruce and the European larch. While measuring the infestation, the researchers also found that the position within the experimental site was important, with the trees at the outer edges getting hammered the hardest.

But did they arrest the infestation? Not really. As reported on the University of Freiburg website:

Until now, the researchers assumed that tree diversity reduces the infestation of insect pests such as the bark beetle. But their experiment shows that “increasing tree diversity can reduce the risk of bark beetle infestation for species that are susceptible to high infestation rates, such as larch and spruce. But the risk for less preferred species such as pine or exotic trees may increase with tree diversity, as beetles, once attracted, also attack these trees,” Berthelot says. Although the study indicates that non-native tree species are less attacked because the bark beetles are unfamiliar with these species. “However, this effect may weaken over the years,” she said. As a result, the risk of infestation in mixed forests is redistributed among tree species rather than reduced for all.”

To read the story on the University of Freiburg website, click here.

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