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The article assumes that, the areas of dark coniferous forests with disturbed and lost stability are catastrophically expanding in Siberian regions in the modern period. This fully applies to the plantations with a prevalence of Abies sibirica Ledeb., located in the southern part of the Yenisei Siberia (territory of the Krasnoyarsk Region). The research was carried out in the spruce and fir plantations of the Biryusinsky district forestry of the KGU “Emelyanovskoye lesnichestvo” in order to clarify the role of the main biotic factors of the sanitary state violation and drying out of dark coniferous plantations. The method of research is route and detailed forest pathological inspection with the subsequent integral evaluation of the sanitary and forest pathological state of forest plantations. On the basis of all indicators of the state and tree falling parameters, a slight disturbance of the stability of the forest plantations Picea obovata Ledeb. was established; weak-strong disturbance until the loss of stability of A. sibirica plantation with their progressive drying out. The main biotic factors in the accumulation of pathological tree fallings and degradation of fir stands are the root pathogen Armillaria mellea s. l. and the invasive xylophage Polygraphus proximus Blandford in association with the micromycete Grosmannia aoshimae, that have a concomitant negative effect on trees. Additional factors of weakening, less often drying of fir trees are necrotic rust diseases; they are bacterial dropsy (pathogen is an association of phytopathogenic bacteria) and blister rust (pathogen is Melampsorella caryophyllacearum G. Schrot.), genus Monochamus.

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Scots pine blister rust and red ring rot are common diseases on Scots pine throughout its entire range. Many specialists have studied these diseases in various aspects. Nevertheless, the cenotic patterns of incidence in pine forests, primarily for Scots pine blister rust, have been studied to a lesser extent. The study is aimed to establish the peculiarities of incidence of Scots pine blister rust and red ring rot in pine forests at the dendrocenosis-level in the context of forest conditions and the biology of pathogens. We studied the pine forests of the Dzerzhinskoe forestry located in the Krasnoyarsk Krai. Research methods included detailed forest pathological examination, macroscopic diagnostics of diseases, determination of indicators proving disease manifestation, and analysis of the series of diameter-related distribution of trees. Scots pine blister rust was proved to be of high injuriousness for trees and entire forest stand in case of hotspot emergency. Red ring rot does not play such a significant role in the plant community since trees with signs of rot retain their activity for a long time as part of the cenopopulation. Diameter-related distribution of the affected trees mainly corresponds to the general stand structure. Nevertheless, in red ring rot hotspots, there is a certain predominance of large specimens in the affected part of the stand, which is associated with a reduced immunity in such trees. Scots pine blister rust in herb-rich pine forests often damages trees with diameters below average. Scots pine blister rust pathogen completes different stages of its life cycle on different plants infecting intermediate host from various species of herbaceous growing in the ground cover of herb-rich pine forests.

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