Sentiero Vaia di Maranza
The Vaia Storm
The Data
Between October 27 and 31, 2018, the northeastern part of Italy was struck by what is known as the "Vaia storm." The rainfall that fell over 72 hours was exceptional, reaching half of the annual rainfall in Trentino (with maximum peaks of 600 mm). The sirocco gusts reached 120 km/h, with peaks of 190 km/h.
The wind and rain caused significant damage to infrastructure, interrupting power lines as well as access to gas and drinking water.
Numerous landslides and collapses of roads and bridges occurred, but the greatest damage was inflicted on the forest stands. Here, on mount Marzola, between Povo and Villazzano, over 2,000 cubic meters of trees were blown down.
On a national level, the estimated damage was around 8.5 million cubic meters of windthrown timber and 42,000 hectares of affected forests. In Trentino alone, 19,800 hectares of forests were felled (mainly Norway spruce forests), corresponding to over 4 million cubic meters.
The "Vaia Storm" trail runs along the western slope of the mount Marzola, in the areas most affected by the storm, with a length of 3.1 km and a positive elevation gain of about 160 meters.
The Bark Beetle
In Norway spruce forests, one of the main secondary effects of large-scale disturbances like windthrows is the proliferation of the bark beetle.
The European spruce bark beetle (Ips typographus) is a cylindrical-shaped, brown-colored beetle from the Scolytidae family, measuring about 4-5 mm in length.
In spring, the males enter the trees and build a mating chamber, where they mate with two or three females. These females then tunnel galleries up to 15 cm long, parallel to the trunk axis, where they lay about 50 eggs. The larvae, while feeding, carve galleries 5-6 cm long, orthogonally to the trunk axis.
These intricate galleries interrupt the flow of sap in the phloem, preventing sugars from reaching the roots. Furthermore, when the adults enter the trunks, they carry pathogenic fungi that clog the water-conducting vessels in the xylem, causing the spruce to die.
The late signs of attack (which, however, do not allow for effective control) include discoloration of the needles, their fall while they’re still green, peeling of the bark, and woodpecker markings in search of food.
The Stumps
After the logging interventions for the windthrown trees, the forests are left with the stumps of trees uprooted by the wind.
In the past, forest management often aimed to reduce the presence of deadwood in forests, for both phytosanitary reasons and aesthetic reasons related to tourism.
However, deadwood serves many functions, such as protecting young seedlings in their first years of life. Additionally, deadwood is an important source of nutrition for insects, bacteria, and fungi. Microorganisms decompose the organic material, releasing nutrients stored in the wood for other life forms.
Sometimes in the woods, we can observe "spruces on stilts": a seed germinates on top of a stump, and its roots, while growing, descend along the sides until they touch the ground. The stump, once decayed, leaves a void between the soil and the plant, making it appear to be growing on "stilts."
Among the animals that benefit from the presence of deadwood are numerous birds that nest in the crevices of dead trees or feed on insects whose life cycle is linked to the presence of necromass. Some examples include the Crested Tit, the Alpine Woodpecker, and the Black Woodpecker.
The Effects of the Vaia Storm... and Now?
It is difficult to imagine how the forest can recover after a disturbance such as the Vaia storm.
However, forests know well where to start: the first species to emerge, among the herbaceous vegetation, are shrubs and heliophilous trees. These plants need a lot of light, poorly tolerate competition from larger trees, and are therefore perfect for post-disturbance conditions.
It is these species that, by claiming light, space, and nutrients in the soil, will pave the way for more stable stands, such as beech or spruce forests.
Often, these species, with their fruits, provide an excellent source of food for birds and mammals, while protecting young seedlings in their shade that will become the future forest.
Here, ecotone environments are formed, i.e., transition zones between one ecosystem and another, ideal for species like roe deer.
They may seem a bit disorderly, but within them, they hold a high biodiversity.