Invasive alien pests as the major threat to European woodland ecosystems: ash and elm as the examples

Lead Author Rimvys, Vasaitis
Institution Contact Swedish University of Agricultural Sciences
Theme Theme 1: Vulnerability of Arctic Environments
Session Name 1.7 Invasive species in Arctic ecosystems in the changing world: Is it a real threat?
Datetime Wed, Sep 14, 2016 10:30 AM - 10:50 AM
Presentation Type Oral
Abstract text In recent years, a number of invasive alien pests caused severe damage to woodlands of Europe. Those include Dothistroma-, Diplodia-, Fusarium circinatum- and pinewood nematode, each causing dieback of pine, Phytophthora diebacks on deciduous trees and larch. Chestnut blight caused by Cryphonectria parasitica and plane blight caused by Ceratocystis platani are typical examples of invasive aliens formerly and currently observed in southern Europe. More recently devastating disease of Buxus has emerged, the agent of which is Cylindrocladium buxicola, infections of which are often followed by a secondary infestation from Volutella buxi, another fungal blight. It is currently acknowledged, that due to increasing international trade with (potted) plants for planting, more alien pests are to come. In this presentation, lethal diseases caused by invasive alien fungi to ash and elm will be discussed, that are much actual to northern Europe.

Recently and nowadays, severe Ash DieBack (ADB) is observed in most European countries. This is an emerging disease caused by invasive alien fungus Hymenoscyphus fraxineus originating from Far East Asia. The disease results in massive ash mortality, and currently threatens the existence of tree species on a continental scale. Also Dutch Elm Disease (DED) is a lethal disease, which during the last 100 years has led to a massive mortality of elm trees in Europe, threatening the existence of the species over large geographical areas. DED is caused by invasive alien fungi from the genus Ophiostoma originating both from Asia and North America.

However, data from European clonal seed orchards of ash have demonstrated that different tree genotypes exhibit different levels of susceptibility to ADB. Reports from numerous countries indicate that there are individual ash trees without any symptoms in otherwise ADB devastated areas. Due to the fact that the massive amounts of pathogen spores are distributed by wind, all ash in such areas must have been about equally exposed to the disease. Therefore presence of symptomless ash would suggest tolerance or resistance to the disease. Consequently, breeding programs of ash against ADB have been recently initiated in many European countries. Moreover, it has been known for decades ago that different elm genotypes are not equally susceptible to DED, and trials for breeding of elms against DED in Europe have historical roots. As a result, recently a number of DED-resistant elm clones were developed and registered for practical use in horticulture and forestry, and are to be continued and expanded.

Therefore, the objectives for long-term strategy to control and restrict impact of those tree pests are: i) to create (GPS-mapped) pan-European database of ash and elm resistant / tolerant to ADB, respectively DED; ii) to exchange genetic material of resistant / tolerant between research groups; iii) to initiate breeding for resistance trials on a continental scale; iv) to establish pan-European network of seed orchards by planting available resistant genotypes of ash and elm; v) to initiate silvicultural trials by replanting resistant trees in affected ecosystems / woodlands; vi) to initiate the experiments for biological control of DED with viruses; vii) to continuously perform biodiversity studies in areas devastated by ADB and DED (focusing also on introduced Siberian ash and elm which are apparently resistant to ADB and DED), and mediate the results to society; x) to conduct demonstration meetings and seminars for stakeholders and general public. Already at this stage, there are two principal messages to European stakeholders and society: i) BOYCOTT imported plants for planting; ii) promote propagation, marketing and planting of locally produced plants.
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