Decline of European Beech in Austria: Involvement of Phytophthora spp. and Contributing Biotic and Abiotic Factors

Abstract

A severe decline and dieback of European beech (Fagus sylvatica L.) stands have been observed in Austria in recent decades. From 2008 to 2010, the distribution and diversity of Phytophthora species and pathogenic fungi and pests were surveyed in 34 beech forest stands in Lower Austria, and analyses performed to assess the relationships between Phytophthora presence and various parameters, i.e. root condition, crown damage, ectomycorrhizal abundance and site conditions. In total, 6464 trees were surveyed, and Phytophthora-associated collar rot and aerial bark cankers were detected on 133 trees (2.1%) in 25 stands (73.5%). Isolations tests were performed from 103 trees in 27 stands and seven Phytophthora species were isolated from bleeding bark cankers and/or from the rhizosphere soil of 49 trees (47.6%) in 25 stands (92.6%). The most common species were P. ×cambivora (16 stands) followed by P. plurivora (eight stands) and P. cactorum (four stands), while P. gonapodyides, P. syringae, P. psychrophila and P. tubulina were each found in only one stand. Geological substrate had a significant effect on the distribution of P. ×cambivora and P. plurivora while P. cactorum showed no site preferences. In addition, 21 fungal species were identified on beech bark, of which 19 and five species were associated with collar rot and aerial bark cankers, respectively. Four tested fine root parameters showed differences between declining and non-declining beech trees in both Phytophthora-infested and Phytophthora-free stands. In both stand categories, ectomycorrhizal frequency of fine root tips was significantly higher in non-declining than in declining trees. This study confirmed the involvement of Phytophthora species in European beech decline and underlines the need of more research on the root condition of beech stands and other biotic and abiotic factors interacting with Phytophthora infections or causing beech decline in absence of Phytophthora.