The impact of pest and pathogen invasions on the compositional integrity of landscape architecture objects in St. Petersburg

This paper examines the spread of invasive organisms that cause the weakening and death of elm and ash trees in the historic parks of St. Petersburg. The spread of the Dutch elm disease pathogen Ophiostoma novo-ulmi and the elm bark beetle Scolytus spp. has led to the widespread death of elms in St. Petersburg. The emergence of outbreaks caused by the fungus Hymenoscyphus fraxineus and, in particular, the spread of the emerald ash borer Agrilus planipennis are the cause of ash dieback in the Petrodvorets district. The main objects of study are Alexandria Park (144 hectares) and the Memorial to the Defense of the City in 1941–1944, part of the “Green Belt of Glory of Leningrad” complex. An analysis of the volumetric-spatial structure was conducted based on historical and archival data and field surveys. The degree of preservation of compositional integrity was determined using N.N. Gusev's scale for assessing the preservation of the historical (memorial) appearance of trees and shrubs. The death of elm and ash trees as a result of pest and pathogen activity was established. The species composition of the Alexandria Park plantings corresponds to the historical one by more than 50%, but their placement does not correspond to this historical pattern. At the memorial complex commemorating the defense of the city, the species composition corresponds to less than 50%, and the placement also does not correspond to the historical pattern. At all surveyed sites, measures are necessary to preserve the historical appearance of the cultural heritage site, namely, the restoration of the compositional structure. Adaptation of the plantings to the effects of invasive pathogens and pests is recommended for the territory of the memorial complex. Preserving the compositional structure of parks by replacing woody plant species with the most similar visual characteristics, while ash and elm trees are rapidly dying due to the spread of invasive pests and pathogens, is a key task in preserving St. Petersburg's historic parks. However, to avoid the permanent loss of key landscape components, this task must be accompanied by a search for ways to control the numbers and spread of invasive pathogens and pests. 

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