A conspicuous decline of macromycetes, especially in ectomycorrhizal species, has been described in the last decade in various parts of temperate Europe. It has been argued that changes in population of these fungi can be attributed to direct or indirect effects of air pollution. In view of the fact that in central Europe these changes preceded a visual damaging of forest or even its decline, it seems that many ectomycorrhizal fungi are very suitable bioindicators of the disturbance of forest ectotrophic stability. Defined stages of this disturbance can be linked directly to particular phases of impoverishment of ectomycorrhizal mycocoenoses and of enrichment of lignicolous rnycocoenoses. These conclusions have been obtained from long-term research in permanent plots (1000-2500 m2) in spruce and recently also in oak and beech forests in the Czech Republic, but it seems that they are valid generally, at least in temperate forests. The analyses of proper mycorrhizae from the same plots confirmed data obtained from fruiting bodies. Both the percentage of ectomycorrhizal species and the ratio of active mycorrhizae are highly sensitive to some outer impact to forest ecosystems (air pollution, acidification, fertilization); their decrease is in negative correlation to the strong defoliation of trees and can be used for the prediction of next development in locality, at least in comparable stands, i.e., in the case of similar density of active mycorrhizae and analogous water stress.RCsumC : Au cours des dernikres dCcades, on a dCcrit, dans diffkrentes partie de l'Europe, tempCree, une diminution tvidente des espkces de champignons ectomycorhiziens. Des discussions sur les changements des populations de ces champignons suggkrent que ceci pourrait Ctre directement ou indirectement causC par la pollution atmosphkrique. Considerant qu'en Europe centrale ces changements ont prCcCdC les dommages visibles aux forCts ou mCme leur dCclin, il semble que plusieurs champignons ectomycorhiziens pourraient Ctre des indicateurs utiles de la perturbation de la stabilitC des forCts ectotrophes. Des Ctapes prCcises de cette perturbation peuvent Ctre reliCes directement 2 des Ctapes particulikres d'appauvrissement des mycocoenoses ectomycorhiziennes et de l'enrichissement des mycocoenoses lignicoles. Ces conclusions proviennent de recherches a long terme conduites dans des parcelles permanentes (1000-2500 m2) dans des forCts d'kpinette, et plus rCcemment de chCne et de hCtre dans la rCpublique TchCque, mais il semble qu'elles soient gknkralement valables, du moins pour les forCts tempCrCes. Les analyses conduites sur les mycorhizes propres B une mCme parcelle confirment les donnCes obtenues B partir des fructifications. Le pourcentage des espkces ectomycorhiziennes aussi bien que le rapport des mycorhizes actives sont fortement sensibles B certains impacts frappant les Ccosystkmes forestiers (pollution de l'air, acidification, fertilisation); leur diminution est en corrClation inverse avec les fortes dCfoliations des arbres et peut Ctre u...

Summary The impact of ash dieback caused by Hymenoscyphus fraxineus on 17 provenances of Fraxinus excelsior and one provenance of Fraxinus angustifolia was studied in an extensive field trial established in the Czech Republic prior to the H. fraxineus invasion in 1999. A difference in the level of resistance to ash dieback between the species was found: F. angustifolia was significantly less affected by the disease than F. excelsior. Moreover, particular provenances of F. excelsior showed important differences in the level of resistance to H. fraxineus. A relationship between the impact of ash dieback and altitude was also discovered – the provenances from altitudes above 600 m a.s.l. were less affected by the pathogen than were the provenances from lower areas. No difference in the impact of the disease among provenances of F. excelsior from different ecotopes (ravine, calcareous ravine and alluvial) was found. Substantial among‐tree variability in resistance to H. fraxineus was observed throughout the trial – promising genotypes (with crown defoliation up to 5%) were identified in all 18 tested provenances. In regard to this finding, it appears that the main source of resistance to the pathogen is probably at the individual genotype level in the trial. A secondary but massive attack by Hylesinus fraxini was identified in the trees that had been greatly damaged by ash dieback, and the beetle caused their health to deteriorate significantly. A significant negative effect of the presence of collar necroses caused by H. fraxineus and browse damage was also identified.

No abstract

Oak decline presenting symptoms of tracheomycosis have been observed globally over long periods of time. Since the 1990s, oak decline has been considered to be a multifactorial process where abiotic predisposing factors play a significant role. Nevertheless, biotic factors, such as subcortical insects and fungal pathogens, may influence the decline process, as some insect species transmit spores of tracheomycotic pathogens. We investigated biotic agents (subcortical insects, Ophiostoma spp. and Phytophthora spp.) in six declining oak stands located within mesophytic and thermophytic zones in the Czech Republic, where five dry years occurred from 2015 to 2019. The spectrum of insect pests of oak stands was investigated using two methods: reared from logs from each stand and window traps. The presence of Ophiostoma fungi was assessed from cultivated woodblocks; Phytophthora pathogens were isolated from soil samples. In total, 2931 subcortical insect individuals were captured during the 2021 vegetation period. The most species-rich group of the subcortical insect complex involved in oak decline consisted of the families Cerambycidae: Xylotrechus antilope; Curculionidae: Scolytus intricatus, Xyleborus monographus; and Buprestidae: Agrilus biguttatus, A. sulcicollis. The presence of Ophiostoma was detected in all stands with different intensities between tree parts. Several important oak pests were positively correlated with the occurrence of Ophiostoma. On the contrary, from all soil samples, Phytophthora plurivora was found at only one studied oak stand. Based on the results, a new modified model of biotic and abiotic factors involved in the oak decline is proposed.