URBAN TREE ROOT SYSTEMS AND TREE SURVIVAL NEAR SEWERS AND OTHER STRUCTURES

摘要

We can expect an increasing number of problems for urban greenery associated with reconstruction of linear parts of municipal infrastructure in the nearest future. Especially reconstruction of sewer networks made of inert materials (existing sewers are usually old and of a poor functional state) represents a great risk for fully-grown urban greenery, because such structures are laid deep and require opening of wide areas of the ground surface, often planted with woody species. Fully-grown urban greenery is an unavoidable part of human environment and should be protected the same way as other systems of local infrastructure. However, recognising the current density of engineering infrastructure networks in streets (not housed in ducts), there is no area left for planting new greenery. After cutting down the existing trees, it is not possible, according to the valid spatial directives, to replant them in the same areas. Minimal distances of trees from sewers and other installations, such as urban drainage structures and water supply networks, given in the corresponding National Standards (1.5-2.5 m) represent only a simplified and schematic empirical solution of spatial problems. They lack background information about tree root systems and their development, which was not available during their earlier preparation. New instrumental methods applicable to whole tree root system investigations provide such information, and therefore enable measurements of entire "tree-construction systems" and their interactions. This can be achieved through modified water balance calculations, which are especially important in spatially limited urban locations. Such objectively determined spatial requirements are needed for assuring sustainable co-existence of urban structures and fully-grown greenery with long life-span (including minimum distances), and should serve for the management of greenery in urban areas. The minimum life space for urban greenery should be protected legislatively as well as by special technical means (e.g., plastic walls or underground containers) and also by assuring corresponding maintenance operations including regular water control, eventual fertilisation and periodical health control. For example, the City of Brno included in the above-ground tree part monitoring the Viridis system. It should work even better if it is combined with the newest instrumental methods visualizing the underground tree part.