Наукові праці Лісівничої академії наук України (Oct 2018)
Risk of birch disappearance in Zhytomyr Polissya of Ukraine
Abstract
The studies have established a number of causes of birch stand dieback in the Zhytomyr Polissya of Ukraine. Attention is focused on the deep pathology of the birch, caused by a complex of factors and, first of all, associated with bacterial etiology. It is established that the wetwood in the trunk of birch trees is of bacterial origin. The samples of wood and exudate have been selected for laboratory studies of plants, which had pronounced signs of pathology (cracks, swelling). It has been experimentally proven that the causative agent of birch dieback is the phytopathogenic bacteria Enterobacter nimipressuralis Carter, which causes dropsy of coniferous and deciduous forest trees. It has been established that the symptoms of bacterial dropsy are directly related to the saturation of the moisture of the tissues of the trunk and the shoots of the birch, the formation of the wet pathological nucleus in the plant, the cracks and ulcers on the trunks, the periderm during the active phase of the disease, necrotic wet ulcers in the places of external penetration of the infection, abundant fluxes exudate in the affected trees on the trunks are formed numerous water shoots. It was observed that in some mature birches the pathological core never came out with sapwood in the form of a crack, remaining inside the trunk during the whole ontogenesis. The plant's vitality was ensured by the activity of the last year's annual layers of wood and cambium, which were not affected by bacterial dropsy and annually set aside annual radial growth. This testified to the deep pathology of birch. It has been established that the composition of stand somewhat affects the dieback of birch trees. Complex and mixed tree stands are more resistant to bacteriosis. The prevalence of bacterial dropsy in birch stands of different age groups increases with their age and decrease in fullness. The unequal level of bacterial dropsy of various groups of plant associations was noted: blueberry, cereal, green-moss and heather. When examining the trunks of model trees, a pattern of altitude location of lesions was discovered. The data on the type of lesion and the density of wounds on the trunk are given, the species composition and the level of dominance of tremex, which are ecologically and trophically associated with birch, are analysed . Tremex are carriers of the causative agent of bacterial dropsy. Moreover, they are the source of accumulation and an important vector of inoculum spread in birch stands. It is also important that the pathogen is biologically inert to xylophagous insects.
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