Beech decline in Central Europe driven by the interaction between Phytophthora infections and climatic extremes

Abstract

SummaryDuring the past decade, and in particular after the wet year 2002 and the dry year 2003, an increasing number of trees and stands of European beech (Fagus sylvatica L.) in Bavaria were showing symptoms typical for Phytophthora diseases: increased transparency and crown dieback, small-sized and often yellowish foliage, root and collar rot and aerial bleeding cankers up to stem heights of >20 m. Between 2003 and 2007 134 mature beech stands on a broad range of geological substrates were surveyed, and collar rot and aerial bleeding cankers were found in 116 (86.6%) stands. In most stands the majority of beech trees were declining and scattered or clustered mortality occurred. Bark and soil samples were taken from 314 trees in 112 stands, and 11 Phytophthora species were recovered from 253 trees (80.6%) in 104 stands (92.9%). The most frequent species were P. citricola, P. cambivora and P. cactorum. Primary Phytophthora lesions were soon infected by a series of secondary bark pathogens, including Nectria coccinea, and wood decay fungi. In addition, infected trees were often attacked by several bark and wood boring insects leading to rapid mortality. Bark necroses were examined for their probable age in order to determine whether the onset of the current Phytophthora epidemic was correlated to rainfall rates recorded at 22 Bavarian forest ecosystem monitoring stations. A small-scale survey in nine Bavarian nurseries demonstrated regular infestations of all beech fields with the same range of Phytophthora species. The results indicate that (1) Phytophthora species are regularly associated with beech decline and may also be involved in the complex of ÔBeech Bark DiseaseÕ, (2) excessive rainfalls and droughts are triggering the disease, and (3) widespread Phytophthora infestations of nursery stock might endanger current and future silvicultural projects aiming on the replacement of non-natural conifer stands by beech dominated mixed stands.

Occurrence of Phytophthora multivora and Phytophthora plurivora in the Czech Republic

“…The presented broad range of affected hosts and stands of P. plurivora are in accordance with extensive reports on its distribution ( Jung 2009;). The common distribution of P. plurivora in natural and seminatural riparian and forest stands raises much concern.…”

“…Therefore, P. multivora may also pose a potential risk to European forests, at least in Central and Mediterranean Europe, because the examined oak forest in South Moravia was highly affected by this species. The probable high impact of P. multivora and P. plurivora on oak lowland forests in South Moravia can be related to changes in temperature and rainfall (Jung 2009) and also to the canalisation of the Moravian lowland rivers in the 1970s and 1980s. These changes led to a significant decrease of the underground water table, to the ensuing water stress in the affected lowland forests, and to an increase of plants' susceptibility to fungal diseases (Čermák & Prax 2001).…”

Fishing for Phytophthora from Western Australia’s waterways: a distribution and diversity survey

“…Under favourable conditions some of these Clade 6 species, such as P. inundata, P. taxon PgChlamydo, P. gonapodyides and P. lacustris (e.g. Hansen and Delatour 1999;Greslebin et al 2005;Smith et al 2009;Randall 2011;Reeser et al 2011;Nechwatal et al 2012), can be aggressive tree pathogens (Brasier et al 2003b;Brown and Brasier 2007;Jung 2009). P. inundata has been isolated from dying native vegetation in Western Australia (WA) (Stukely et al 2007).…”

Robust cropping systems to tackle pests under climate change. A review

“…Root rot and canker disease caused by Phytophthora cinnamomi affects more than 1000 host species, especially in most temperate and subtropical areas of the globe (Sturrock et al 2011). Under climate change, this pathogen was reported to increase the instability and vulnerability of forest ecosystems by a shift toward central Europe (Jung 2009). Increasing temperatures were predicted to boost potential range expansion of P. cinnamomi along the western coast of Europe up to a few hundred kilometers eastward from the Atlantic coast within one century (Bergot et al 2004).…”