Europe’s forests are facing a growing threat from pests due to global trade and climate change, but researchers are developing technologies that can provide an early warning of infestations to combat harmful insects and diseases.
Pests are responsible for damaging 35 million hectares of forest around the world every year. In the Mediterranean region alone, an area the size of Slovakia – five million hectares – is affected annually by pests, according to the United Nations Food and Agriculture Organization (FAO).
And the threat from insects and pathogens seems to be growing. Climate change means that some native pests can breed more often, while international trade spreads exotic insects and pathogens more.
Only a small number of exotic pests that arrive in Europe damage trees. “But these are very harmful, and there are more and more (of them),” said Dr Hervé Jactel, director of forest anthomology and biodiversity research at the French National Research Institute for Agriculture, Food and the Environment.
On average, six new species of tree pests are introduced to Europe every year, up from two a year in the 1950s, says Dr. Jactel. They arrive in potted plants and wood products or packaging.
Many of the new threats to Europe’s forests originate in Asia.
For example, the ash drill spread from Asia to the United States, where it killed more than 150 million trees and may have cost more than $ 10 billion in the last decade. Europe’s door is now knocking.
“We know it will kill all the boxes, or most of them,” said Dr. Jactel, which is the coordinator of the HOMED project that develops new ways to detect such exotic pests early.
The polyphagic bullet holes are another major threat. It can attack almost all deciduous tree species in Europe, says Dr. Jactel.
“It’s a very, very dangerous little beetle,” he said. “This is probably the next big issue for Europe.”
This small insect has its origins in Asia, spread to Israel, California and then South Africa where it has killed hundreds of thousands of trees. In April this year, it was first discovered in Italy, in a tropical garden. There is no sign that it has spread elsewhere in Europe.
Despite the fact that all countries affected by the beetle were on guard for it, no one could detect it until it had already caused damage, says Dr. Jactel. The problem is detecting exotic pests and pathogens before they start attacking trees.
Hundreds of thousands of containers filled with goods arrive at Europe’s ports and airports every day. Small insects or spores from fungal diseases can be stored in transports that contain wood products, pallets or packaging or live plants. The large number of transports is considering the sanitary inspectors’ resources for detecting insects and spores, says Dr. Jactel.
“It’s like finding a needle in a haystack.”
When the containers are opened, pests can easily escape to nearby trees. So increasing the monitoring of trees that grow around ports and airports is a good starting point, says Dr. Jactel.
Finding solutions to these pests is crucial. Forests cover 43% of the EU’s land area – a total of 182 million hectares – and are growing. The forestry sector accounts for about 1% of EU GDP and provides jobs for about 2.6 million people. If the pest is allowed to run – without the natural predators found in their original habitats and among trees that have not developed defenses against them – the pests can be devastating.
But new tools are also needed to warn inspectors of the presence of pests in containers before they can escape, he adds.
The HOMED team develops generic traps to attract a variety of insects. These will be placed in freight containers before departing from their country of origin and at airports, ports and train stations where imports arrive.
The team also develops traps for fungal spores and DNA tools and databases of species to identify whether a spore is local or imported.
The project also plants “sentinel” European trees in Asia, North America and elsewhere that can help researchers identify early on which pests may pose a particular threat to European trees.
For pests that have already taken hold in Europe, a possible solution is to import pests’ natural enemies from their country of origin, says Dr. Jactel.
Researchers in France and Switzerland are investigating whether the natural enemies of the destructive lamb tree template – which has spread from China across Europe – can be imported and used to contain it. But releasing this parasitic wasp to target the moths can cause other problems.
“We have to be very careful to make sure that the Chinese parasitoids will not affect European species,” said Dr. Jactel.
However, many threats to Europe’s forests are closer to home. A warming climate in many regions is helping some native pests to become more common.
The beetle is one of the most damaging pests currently attacking Europe’s forests and destroying spruces in Central Europe.
The Czech Republic has had to kill so many infected trees in recent years that the price of wood has fallen when the resulting timber has been sold, says Dr. Julia Yagüe, project manager for My Sustainable Forest (MSF), which monitors the health of Europe’s forests. Spruces take up to 140 years to grow fully, so the loss of so many trees will be felt for a long time.
This is largely due to the fact that the warming temperatures have allowed the beetles to breed more often.
“About 20 years ago we would have one breeding cycle per summer, but today we have up to four breeding cycles of bark beetle in the Czech Republic and southern Germany,” said Dr. Yague.
Warmer, longer and drier summers also mean that trees are more vulnerable to attacks because the conditions make them less able to withstand pests, she says.
Researchers are creating varieties of native spruce trees, which they hope will be more resistant to higher temperatures and drought and thus better able to fight attacks from pests.
But in the meantime, forests urgently need closer monitoring, says Dr. Yague. Forest managers usually take an inventory every five to ten years.
“Because climate change is putting so much pressure, we need to update our data on forests much more often,” she said.
The most effective way to monitor large forests is with satellite observations, which can help detect the early warning signs on trees that are under water or heat stress, and so are more susceptible to attacks.
They can also allow forest managers to detect the first signs of an infestation, such as dryness, loss of foliage or door.
“With remote sensing from satellites, we can detect this disease before even the human eye can detect it,” says Dr. Yagüe, who is a reading expert at the Spanish airline GMV.
MSF’s work to collect data became easier with the launch of Europe’s Copernicus satellites in 2014 and the development of technology that could process huge amounts of information.
MSF now receives snapshots of Europe’s forests every five days instead of every 15 to 30 days before Copernicus. “We get this information for free,” says Dr. Yague.
But there is another crucial element in improving the health of Europe’s forests, which are much closer to home.
Many of Europe’s forests have been abandoned. While they were once carefully managed landscapes, when people moved to cities, “the knowledge of living with nature has been lost,” said Dr. Yague. “Restoring this is extremely important.”
Trees in the United States face devastating threats due to invasive species
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