Evaluating the impact of Hymenoscyphus fraxineus in Trentino (Alps, Northern Italy): first investigations

Abstract

The spread of Hymenoscyphus fraxineus has been causing great concern regarding the survival of European ash (Fraxinus excelsior) throughout Europe since the 1990s. The disease was first recorded in Trentino (southern Alps, Italy) in 2012 and has spread throughout the mountain landscape, where ash trees are scattered in small and isolated stands in different valleys. The status of the disease was checked by monitoring the damage to natural regeneration and adult trees in 90 sites spread over the whole region. The survey confirmed the complete colonization by the pathogen of the whole investigated area, with high levels of damage to both young and adult ash trees. Regeneration (both seedlings and saplings) was observed to be affected by the fungus in 88 plots out of 90. Out of 4486 examined young European ashes, 2261 (50.4%) were affected and 789 (17.6%) were already dead. Ten of the 384 assayed flowering ashes (Fraxinus ornus) showed symptoms on branches and apical stems, similar to those observed for European ash. Isolation and molecular analysis proved the presence of the fungus on both symptomatic European and flowering ashes. The examined 386 adult trees showed different levels of damage, sometimes reaching more than 75% of the crown. Some individual trees (42) growing close to severely damaged trees appeared fully healthy, which suggests the possible existence of some resistant/tolerant individuals in the examined populations.

Ash Dieback on Sample Points of the National Forest Inventory in South-Western Germany

“…This is contrary to observations in northern Italy, where ash dieback is still in a relatively early epidemical stage and where dominated trees were in the poorest condition [37]. We assume that the disease-induced decline occurs faster in dominated trees and many of these individuals already died, which may have led to the higher proportion of rather healthy or resistant individuals among the remaining population in this stratum.…”

Survival of European Ash Seedlings Treated with Phosphite after Infection with the Hymenoscyphus fraxineus and Phytophthora Species

“…The regeneration of ash on heavily infested sites is endangered both by infestation and a lower production of seed [53], and by a high infection rate of seedlings [54]. The survival rate of young trees is very low because of the small crown volume and girdling of the main stem [18,55], while in older trees, this process is slower and takes time to be observed while the disease progressively develops on the shoots [56][57][58].…”

Diplodia fraxini and Diplodia subglobosa: The Main Species Associated with Cankers and Dieback of Fraxinus excelsior in North-Eastern Italy

“…The disease was observed for the first time in north-eastern Poland [4], and has now become widespread in forest ecosystems and nurseries in over 20 European countries [5,6]. In Italy, the disease was detected in 2009 in Friuli-Venezia Giulia along the border with Slovenia and in a few years, it spread quickly to the Alpine valleys of Veneto and Trentino, and in ash formations of the Apennines [7][8][9].…”