Climate change is transforming the landscape of European forests, upsetting the traditional balance between trees and their parasites. But in an uneven way: even in the war between trees and insects there are winners and losers. In this case, the big losers are the coniferous forests, hit hard throughout Europe (including Italy) by an implacable enemy like the spruce bark beetle. On the other hand, the damage caused by insects that attack the foliage, which are usually more dangerous for broad-leaved forests, is reduced. A dynamic that could drastically redesign the geography of European greenery in the coming decades, as reported by research published in the journal Global Change Biology.
Insects and climate change
The harmful effects of climate change on woods and forests take many forms: the drier climate can favor fires, extreme weather events cause devastating storms. An indirect but increasingly prevalent effect, however, is mediated by parasites, which more easily affect dry or diseased trees due to adverse climatic conditions, and thus increase in number, causing epidemics that also affect healthy plants. It is a known dynamic, which mainly concerns xylophagous insects (which feed and dig burrows in the wood and bark) and sap-sucking insects, and less caterpillars and other parasites that feed on the leaves. And which has become increasingly common and dangerous: in recent years the damage caused by insects in European forests has for the first time exceeded that caused by fires and strong winds.
The study
The research was carried out by experts from 17 European universities and research institutes, using data collected by the forestry services of 15 nations on the continent. In total, the analyzed data covers a period of over 20 years, and describes the activity of over 50 species of herbivorous insects widespread in European forests. The researchers analyzed the ongoing trends by differentiating xylophagous and leaf-eating insects, the most affected tree species, and the different geographical areas of the continent. Confirming the role of insects as the main danger for European woods and forests in this phase characterized by important climate changes.
And bringing to light some inequalities: parasites that burrow into trunks are causing ever greater damage, while leaf eaters even seem to be in decline. Furthermore, the most damaged areas are those where the climate is becoming drier and hotter, demonstrating that climate change risks further exacerbating the problem in the coming years.
What the results say
“Our findings send a clear signal: coniferous forests are increasingly vulnerable to insects burrowing into wood and bark, particularly the spruce bark beetle, while deciduous tree species are suffering decreasing levels of damage from a more diverse group of insects,” underlines Tomáš Hlásny, from the Czech University of Life Sciences in Prague.
The results of the study indicate that it will be necessary, in the future, to take into account which species best resist predators when planning reforestation interventions, in order to make European forests more resilient. But also that the timber market will constantly be at risk of suffering sudden shocks, because the effects of climate change tend to be unpredictable – heat or cold waves, sudden storms, droughts – and the trees most affected are precisely those that dominate the European market: spruce, white fir, Scots pine.
The Italian case
The scenario photographed by the research should be quite familiar in our area, because it follows almost perfectly what happened recently in the woods of Northern Italy. In 2018, the 150 km/h winds of storm Vaia felled around 16 million trees in the provinces of Trento, Belluno and Vicenza, leaving more than 8 million cubic meters of wood on the ground and also damaging many of the plants that remained standing. The perfect conditions for the small bark beetle, an insect that feeds on the wood of old or diseased spruce trees. As a rule, its presence is beneficial for forests, because it helps to dispose of damaged trees and make room for new growth, without damaging healthy trees.
However, having a lot of wood felled by the winds at its disposal, the bark beetle has reproduced excessively, helped by the high summer temperatures. And it began to attack even healthy trees, causing an epidemic that affected almost all the spruce forests of Northern Italy. Clearly visible to anyone who has visited those areas in recent years, for the red and gray patches that dot the slopes of the mountains, patches of trees affected by the bark beetle, destined to dry out and die. The good news is that six years after the start of the epidemic, the small insect now seems to be under control in almost all Alpine provinces, thanks to the efforts of the forestry services, the growth of the bark beetle’s natural predators (also driven in their case by the overabundance of food) and the not too high temperatures of the summer of 2024, which limited the reproduction of the insect. The bad news, however, is that as the study just discussed shows, a new epidemic in the coming decades is a very real possibility, given that climate change shows no signs of stopping.