Soil pH and Organic Matter Content Affects European Ash (Fraxinus excelsior L.) Crown Defoliation and Its Impact on Understory Vegetation

Abstract

European ash (Fraxinus excelsior L.) dieback caused by the fungus Hymenoscyphus fraxineus (T. Kowalski) Baral, Queloz, and Hosoya has been affecting European forests since 1992. The disease drives severe crown defoliation, branch loss, and finally tree mortality in European ash. The environmental factors affecting the disease process are still not fully recognized. We hypothesized that the level of crown defoliation in ash, as well as its impact on understory vegetation, will differ along the pH gradient in soil. We examined 27 ash stands in western Poland. We assessed the crown defoliation of 15 dominant and co-dominant trees, soil parameters (pH and soil organic matter contents; SOM), and also recorded the understory vegetation species composition. Most moderately and severely damaged trees occurred within the plots with a high SOM content (>7.5%) and neutral to slightly alkaline soil pH (>7.0) in the A horizon. We noted significantly lower crown defoliation in mesic sites with acidic soils and lower SOM contents. The results also showed the influence of ash crown defoliation on the species functional composition. Ash dieback led to the creation of gaps, and their colonization by other species frequently found in forest sites, especially forest-edge tall herbs.

A Novel Plant Resistance Inducer for the Protection of European Ash (Fraxinus excelsior L.) against Hymenoscyphus fraxineus—Preliminary Studies

“…Other studies have indicated also that soil may indirectly affect ADB by the promotion of fungus inoculation because of high soil moisture and soil reaction variability [4,6,32]. Among the soil factors affecting the mortality rates of ash are soil pH, calcium carbonate content, high air humidity, and shallow groundwater table level [5,33]. These soil conditions occur in alder-ash forest chosen to collect ash saplings for our experiment.…”

Disturbance by invasive pathogenic fungus alters arthropod predator–prey food‐webs in ash plantations

“…The observed results agree with previous studies showing that H . fraxineus induces changes in habitat structure and that these changes interact with plantation age (Erfmeier et al., 2019; Turczański et al, 2020). Due to leaf and branch loss, the tree canopy thinned and created gaps that were colonized by shrubs.…”

“…The lethal disease is thus often referred to as ash-dieback. Mortality opens tree canopies in forests, increasing light availability and promoting the growth of understorey vegetation (Turczański et al, 2020). Although the impact of H. fraxineus on the forest physical structure may superficially resemble impacts of other disturbance types (Heilmann-Clausen et al 2013;Swanson et al 2011), a mathematical model has indicated that the ash-dieback would lead to extinction cascades of many ash-associated species across several trophic levels (Hultberg et al 2020).…”

“…The lethal disease is thus often referred to as ash‐dieback. Mortality opens tree canopies in forests, increasing light availability and promoting the growth of understorey vegetation (Turczański et al, 2020). Although the impact of H. fraxineus on the forest physical structure may superficially resemble impacts of other disturbance types (Heilmann‐Clausen et al.…”

“…We hypothesized that the open tree canopy and increased density of understorey vegetation along the infestation gradient (Turczański et al, 2020) will increase the number of attachment points for web‐building spiders to construct their webs (Vasconcellos‐Neto et al., 2017). This will increase the proportion of large orb‐web and space‐web spiders because these species respond more intensively to habitat complexity than sheet‐web spiders (Rypstra, 1983).…”