The beetle now also attacks standing trees. Towards killing for a radius of fifty meters around the outbreaks
AGORDO. There is another Vaia storm lurking. “It could be worse than it was three years ago,” sighs with concern, Professor Andrea Battisti, Professor of Entomology at the University of Padua. These days he is hiking through the woods of the Belluno area and the Asiago plateau.
“The bark beetle advances, attacking twice as many trees as a year ago, even those standing,” is his alarm cry. The results of the monitoring conducted with pheromone traps show that in the areas affected by Vaia the density of the insect – the bark beetle – had reached alarming levels of about 8-9,000 individuals per trap last year. “This summer”, reports the expert, “we have reached 20,000”.
The Region has installed 80 traps, almost one per valley, in the mountains of Belluno, Treviso (Grappa) and Vicentino. “The traps are devices to measure the quantity of individuals in a specific area”, explains Federico Vianello, “and based on the checks, the experts will decide how to intervene”. The only possible intervention is the cutting of the standing plants, if they have also been infested, as is happening. The abatement plans have not been decided, but beware. The outbreaks are in fact about eighty, at least. Not all that disruptive. But the satin cut usually concerns a circumference with a radius of 50 meters. It is easy to imagine what the result will be. And the trees, once felled, will have to be skinned immediately, if they are not immediately removed.
The 2018 Vaia storm, with winds of almost 200 km per hour and average cumulative rainfall between 600 and 700 mm, caused damage to the woods for about 8.5 million cubic meters crashed. In an alpine environment, this event, which in Veneto particularly affected the provinces of Belluno, Treviso and Vicenza, was associated with increasingly unfavorable climatic conditions for conifers (mild winters and drought summers) due to global warming. Under these conditions, in 2019 the populations of bark beetle beetles, specifically the bark beetle of the spruce and that of the Scots pine, developed in the large mass of fallen or stressed trees, starting an exponential population growth that partly affected the survival also trees not directly affected by the storm.
Is the fault, therefore, of the trees on the ground left to rot on the spot due to the delays in the construction sites? It did not happen in Cansiglio and on the Asiago plateau, elsewhere yes. «I would not speak of negligence», Battisti replies, «but of objective delays, due to the many inaccessible sites, the pandemic, the difficulty of finding businesses. Of course, in the province of Bolzano it was possible to reclaim 90% of the crashed areas, here with us 60%, in some areas more (Asiago and Val Visdende, in others less). But now we have to run. Where the insect attacks, it is necessary to cut “.
But, the bark beetle is not the only problem. In Vigo di Cadore, on the white alder it was reported for the first once the presence of Phytophthora plurivora and on the green alder the Phytophthora alpina, a new species. In recent years there has been a series of growing problems caused by the arrival of some exotic bark beetles originating from Southeast Asia and belonging to the genus Xylosandrus. Among these X. germanus and X. crassiusculus capable of attacking various woody species of forest interest (mainly broad-leaved trees) both cultivated and spontaneous, including chestnut groves on the border between the provinces of Treviso and Belluno. For the foothills, along the phytoclimatic belt of Castanetum, the galligena wasp of the chestnut Dryocosmus kuriphilus (chestnut beetle), an alien species native to China, is now widespread. «Most of our forests are still in very good health», Battisti admits, «but when the right time comes, we need to cut the right tree. Regardless. But you have to run. If we don’t win the game in four years, we lose it definitively ».