Effect of fungal pathogens and climatic factors on production, biodiversity and health status of ash mountain forests

Abstract

European ash (Fraxinus excelsior L.) is a broad-leaved fast-growing tree species common in most parts of Europe, highly-valued for its ecological properties and occurrence in many forest site types. Its future is threatened, especially by an invasive fungal pathogen Hymenoscyphus fraxineus causing disintegration of E. ash stands throughout all Europe. This paper deals with changes in stand structure, biodiversity and production parameters in mixed European ash stands in the Krkonoše Mountains National park, Czech Republic, with respect to ash dieback progress for period 2009–2015. Studied four permanent research plots (0.25 ha) showed negative dynamics of stand structural and production parameters. Volume of ash ranged between 98–376 m3 ha–1 (stand volume 378–613 m3 ha–1), which indicates a decrease by 2.7% during 6 years. Detected fungi caused mean deterioration of foliage by 22.9%, canopy by 15.8% and mortality reached 15.2%. The earlier ash dieback symptoms were detected at suppressed and intermediate trees, especially on waterlogged sites and at low altitude. Conversely, ash dieback was reflected less intensively at higher-elevated sloping stands, although low temperature (particularly severe frosts at the beginning of the year) was prevailing limiting factor for radial growth of ash in these mountain areas. The biodiversity indices of tree layer indicate mostly medium values with a decreasing tendency (to 22.4%). Relationship between spatial pattern of trees without dieback symptoms and infected trees was positive at small distances (to 7 m) or random. In terms of preventive silvicultural practices, strong systematic thinning is recommended to maintain the vitality of ash stands.