Damage to the tree stands of the Elagin Island of St. Petersburg (Russia) caused by fungal pathogens (Agaricomycetes Doweld) and the effect of water regime on their distribution

Abstract

The general weakening and drying out of trees in the green stands of St. Petersburg in recent years has raised serious concerns. The majority of old-growth trees in particular has mechanical damages to the trunks and roots that are the gateways for the phytopathogen infection. The most common are wood-destroying fungi that cause stem and root rot, which leads to a decrease in the mechanical strength of wood that results in the occurrence of windblow and windbreak when the affected trees become a threat to visitors and the property. The greatest harm in stands is caused by the honey agarics, a collective fungi group belonging to agaricomycetes. The goal of the study is to examine the causes of tree damage by the honey agarics in the stands of Elagin Island, identification of the influence of the hydrological regime on the  development of the pathogen, and development of proposals for the improvement of standing timbers. To detect foci of the honey agarics and the degree of its influence on the condition of trees, exploratory and detailed surveys were carried out. Particular attention was paid to the compilation and analysis of the cartographic material on the location of the main foci of the pathogen. The occurrence of the honey agarics was recorded in the areas with different levels of ground water. It was found that development of the root rot also depends on the flooding of the trees' roots due to water regime deterioration in the soils of Elagin Island. The foci are located in the areas of excessive soil moisture and coastal zones. The reasons for the water stagnation on the island have been clarified. The proposed measures to improve the stands of the island should include not only phytosanitary measures but also efforts to improve the growing conditions of trees without changing the historical appearance of the park.