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Presentazione orale

Santini A

Invasive alien pathogens: an increasing threat to forest ecosystems

Riassunto: Emerging infectious forest plant diseases (caused by fungi, viruses, bacteria and alike) cause significant losses to forest economy and ecology by decreasing the yield and quality of timber and causing losses in biodiversity at species or population level. Main factors able to cause the occurrence of an emerging infective disease are: (1) Arrival of a new pathogen in a new ecosystem, (2) movement of new virulent strains, or emergence of a new aggressive strain in an area where the pathogen existed, (3) introduction of new vectors that can transmit a pathogen efficiently, and (4) consistent change in climate in the short term. The first three factors are linked to the introduction of alien species into a new environment. During the last 100 yrs, human activities, especially international travel and trade, have circumvented the existing natural barriers as mountains and oceans, and species are invading new continents at an increasing rate, often causing substantial disturbance to forest ecosystem as well as severe socio-economic impacts (Liebhold at al., 1995). For this reason, in the frame of the EU Forthreats project a comprehensive database on invasive forest fungal pathogens, reported from 20 European countries, has been compiled. Aim of this work was to organize information relative to invasive alien forest pathogens in order to set up a reliable strategy to control the effects of old and new introductions into European territory. Ascomycetes were the most introduced class of pathogens and their arrivals increased from 1980s to 2000s. It follows Chromista, whose number of introductions was constant until 1990; afterwards they registered a booming increment. Expanding European pathogens were the main threats until 1940s; afterwards North America resulted as the main source of alien pathogens followed by Asia. An important recent phenomenon was the increasing appearance of new pathogens originated by natural hybridisation of resident and introduced species. All the introductions happened unintentionally, chiefly by trade of living plant material. Amenity trees are the most affected by alien fungi, followed by forest and nursery material. The introduced pathogens are above all agents of foliar diseases and cankers, the former until 1920 and the latter more conspicuously in recent times. Root rots are increasing since 1990s. An important amount of introduced pathogens is able to cause lethal diseases. None of the host forest species became extinct because of invasive alien pathogens, even if they went toward important numeric reductions or phenotypic modifications. Even if the link between species invasions and the extinction of natives is widely accepted by scientists as well as conservationists, the available data supporting invasion as a cause of extinctions are, in many cases, anecdotal, speculative and based upon limited observation (Gurevitch and Padilla, 2004). If their effect is not combined with that of other disturbances, aliens are not generally responsible for widespread extinctions or of severe genetic depauperation. On the other hand, they are able to cause the extinction of small marginal populations that could be rich of genetic diversity. The threat they cause is, therefore, to be intended at germplasm instead of species or genus level. For this reason these results should wake up silviculturists, ecologists and conservationists to fasten their attention on small marginal or fragmented populations, setting up specific strategies of in situ and ex situ conservation.

Citazione: Santini A (2009). Invasive alien pathogens: an increasing threat to forest ecosystems. In: VII Congresso Nazionale SISEF “Sviluppo e adattamento, naturalità e conservazione: opportunità per un sistema forestale in transizione“ (Università degli Studi del Molise, Isernia - Pesche (IS), 29 Settembre - 3 Ottobre 2009), Abstract-book, Contributo #c07.6.8. - [online] URL: https://congressi.sisef.org/?action=paper&id=1258

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