Forest pests are becoming increasingly aggressive because of global warming

Population of Pinus sylvestris with trees attacked by scolytids in Catalonia. It can be seen by the brown colour of the crowns Image: Luciana Jaime.
Population of Pinus sylvestris with trees attacked by scolytids in Catalonia. It can be seen by the brown colour of the crowns Image: Luciana Jaime.

The scientific community has already shown that forests growing in a climate unsuitable for them, such as a spruce in a dry climate, are easily more affected by forest diseases or pest attacks. However, according to the article recently published in Global Change Biologyclimate change is making it possible for even forests living in their most optimal environment to be affected by bore beetle infestation. Who is the main promotor? Drought. According to the research results, the great heat waves, together with the droughts that accompany them – such as those of 2015 and 2018 – put forests at the limit of their resistance and expose them more to the attack of insects, a detonating mixture that then causes pest mortality in large forest masses. In this way, the strength of a forest in the face of the attack of these insects depends largely on the drought and how intense and lasting it is. has been

 

“The effects of drought  are cumulative: forests have a memory and the more droughts in their history, the more likely they are to succumb.”

LUCIANA JAIME GONZÁLEZ,CREAF researcher and first author.

 

Global warming is leading to more and better development of some forest pests, such as pine borer beetles of the genera Tomicus i Ips ,and at the same time, it can lead to more severe droughts. According to the expert, the result of this combination is a lethal cocktail for conifers: and 6% have already died ”.

Scots pine (Pinus sylvestris) attacked by the borer beetle Tomicus minor. Image: Luciana Jaime.

The forests of northern, central and eastern Europe are at risk 

In recent years, Europe’s coniferous forests that have died directly or from causes associated with insect attacks have increased alarmingly. For this reason, this study led by CREAF and the Autonomous University of Barcelona (UAB), has investigades 130 plots across Europe monitored since 2010 to understand how trees respond to the attacking insect and which ones are most exposed

The scolitid species that are causing the most problems are those that complete more than one life cycle per year, because they take advantage of the warm weather to reproduce more.

The team counts also on Enric Batllori, CREAF researcher, Francisco Lloret, UAB Ecology Professor and CREAF Researcher, and Marco Ferretti of the Swiss Federal Institute (WSL) to understand how trees respond to the attacking insect and which ones are most exposed. They have found that central, northern and eastern Europe are the areas where pests become more aggressive and infest more forests. In particular, the species of scolitids that are causing the most problems are those that complete more than one life cycle per year, known as multivolts, because they take advantage of rising temperatures to reproduce more times a year. These data, “are very important to be able togenerate risk maps and hot spots where schoolchildren will be most favoredby the high temperatures and associated droughts and they can jeopardize the integrity of the forest, ”says the researcher.

In addition to drought and temperature, there are other factors that predispose trees to be attacked by these insect pests, such as the structure of the forest itself and the composition of its forest species. 

Reference article:
Jaime L, Batllori I, Ferretti M, Lloret F (2022). Climatic and stand drivers of forest resistance to recent bark beetle disturbance in European coniferous forests. Global Change Biology. DOI: 10.1111/gcb.16106.

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