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

Abstract

Abstract:The alien invasive pathogen Hymenoscyphus fraxineus causes large-scale decline of European ash (Fraxinus excelsior). We assessed ash dieback in Germany and identified factors that were associated with this disease. Our assessment was based on a 2015 sampling of national forest inventory plots that represent a supra-regional area. In the time from 2012 to 2015, the number of regrown ash trees corresponded to only 42% of the number of trees that had been harvested or died. Severe defoliation was recorded for almost 40% of the living trees in 2015, and more than half of the crowns mainly consisted of epicormic shoots. Necroses were present in 24% of root collars. A total of 14% of the trees were in sound condition, which sum up to only 7% of the timber volume. On average, trees of a higher social status or with a larger diameter at breast height were healthier. Collar necroses were less prevalent at sites with a higher inclination of terrain, but there was no evidence for an influence of climatic variables on collar necroses. The disease was less severe at sites with smaller proportions of the basal area of ash compared to the total basal area of all trees and in the north-eastern part of the area of investigation. The regeneration of ash decreased drastically.

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

“…Stronger plants had an improved chance of surviving either an H. fraxineus or Phytophthora attack (Table 3), which correlates with studies showing that damage to developed trees is less frequent [16,18]. A positive correlation was observed between the height and diameter of seedlings and their survival, and also the height/diameter interaction was strong and significant.…”

“…The mortality of seedlings in ash stands infected with H. fraxineus constitutes major damage and a threat to the existence of the species on the sites [16,52]. 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].…”

“…In the affected regions, damage caused by the fungus H. fraxineus was higher in younger stands than in older ones, ranging from ≥60% in Germany [16], 57% up to 80% in young stands in Norway [17], or 3% to 35% in older and younger stands in France, respectively [18], but even in the devastated areas, some trees showed good crown conditions and a high survival rate during an attack [19], indicating the presence of genetic resistance existing within the populations [15,20]. Individual resistance between resilient populations of Manchurian and susceptible European ash individua was ascribed to the presence of a chemical compound such as iridoid glycoside in the leaves of the more resistant trees [21,22].…”

Impact of Fraxinus excelsior dieback on biota of ash-associated lichen epiphytes at the landscape and community level

“…It started in north-eastern Poland and during the next years expanded to neighboring countries (Przybył 2002;Bakys et al 2009a;Pautasso et al 2013;Gross et al 2014a). Recently, a severe dieback of ash, which includes trees in all age stages (Gross et al 2014a;Needham et al 2016;Enderle et al 2018), can be observed in most European countries (Bakys et al 2009a, b;Kowalski and Holdenrieder 2009a, b;Allen et al 2010;Beck et al 2016;Coker et al 2019). It is caused mainly by the fungus Hymenoscyphus fraxineus, which induces wilting and loss of leaves, thinning of crowns, darkening of wood, necrosis and neoplastic changes on trunks and branches, and finally leads to the deaths of trees (Baral et al 2014;Gross et al 2014b), but other pathogens that weaken this tree are also reported, e.g.…”

The invasive forest pathogen Hymenoscyphus fraxineus boosts mortality and triggers niche replacement of European ash (Fraxinus excelsior)

“…Global warming and globalization put pressure on forests ecosystems and threaten their capacity to deliver goods and services to society 1,2 . In the last centuries, an increasing number of invasive pathogens have been introduced into forests 3 mainly by trade of living plants, which has created an unprecedented movement of species across continents [4][5][6] .…”