Percularities of forming of phytobiota formation of the flat green roofs of extensive type in the city of Lviv

Abstract

The taxonomic composition, bioecological and chorological characteristics of cultural plant species of flat green roofs of extensive type in the city of Lviv were investigated. The structural features of the flora of cultivated species were identified, the levels of their frost-resistance and winter hardiness and USDA-zoning, and and the vertical distribution of green roofs types were studied. It was found that five design types are used for greening roofs in Lviv - "Sedum carpet", " Rooftop lawn", "Fragrant herbs", "Cereals garden" and "Garden on the roof". Most of the implemented projects were carried out according to technology and using substrates, lawn mixtures and a list of plants from the German company "ZinCo GmbH". The exceptions are objects of collective and private property in low-rise buildings, where individual projects were implemented for roof greening, and the list of plants was selected according to project proposals. Most green roofs are created on buildings with a height of 10-20 m (45% green roofs). Also, popular is greening of high-rise 10-storey and higher apartment buildings (22% green roofs). It was found that 230 species of plants and 105 of their cultivars were used for greening flat roofs. The spectrum of viable forms is dominated by phanerophytes (129 species, 44%) and hemicryptophytes (98 species, 33%). Most plant species grow naturally in Southeast Asia - 56 species (24%), Europe (50 species, 22%), North America (39, 17%), and Eurasia (32,14%). 11 species (5%) are of hybrid origin. Among coniferous cultivars, dwarf and blue-colored conifers predominate - Chamaecyparis lawsoniana ‘Minima Glauca’, Juniperus horizontalis ‘Blue Chip’, J. procumbens ‘Nana’, J. squamata ‘Blue Carpet’, Picea glauca ‘Conica’, P. omorika ‘Nana’, Pinus heldreichii ‘Compact Gem’, P. mugo ‘Gnom’, P. m. ‘Mops’, Taxus cuspidata ‘Nana’, Thuja occidentalis ‘Globosa’, Th. o. ‘Hoseri’. Variegated-leaved plants are often used (Cornus alba ‘Elegantissima’, Lonicera ligustrina var. pileata ‘Variegata’, Euonymus fortunei ‘Emerald ‘n’ Gold’, Weigela florida ‘Nana Variegata’), limbate (Cornus alba‘ Argenteo-marginata’) and purple-leaved forms (Acer platanoides ‘Crimson King’, Berberis thunbergii ‘Atropurpurea’, B. th. ‘Atropurpurea Nana’, Cotinus coggygria ‘Royal Purple’, Phuopsis stylosa ‘Purpurea’). Annual plants are practically not used in roof greening, with the exception of Begonia cucullata, Liatris spicata ‘Alba’, L. s. ‘Kobol’, Matricaria breviradiata, Salvia splendens, which are annually planted in the "pockets" of compositions to create a color accent. Of uncommon species and new varieties of plants on green roofs the following species are found: Azorella trifurcata, Betula utilis ‘Doorenbos’, Caryopteris incana, Cornus kousa ‘Milky Way’, Cytisus × kewensis, Kniphofia uvaria, Leontopodium nivale, Nothofagus antarctica, Vitis californica ’Roger’s Red’. Rooftop lawns are made mainly by sowing with grass mixtures of low-growth cereals and micro-clover that do not require frequent mowing (Lilliputian, Canada Green and Gnome) or using a roll lawn. The territory of Lviv belongs to the 6 USDA-zone; however, the roof greening uses species regionalized for other USDA-zones. It is shown that the majority of species planted on flat roofs belong to the 5 USDA-zone (96 species, 33%); species of the 4 zone (69 species, 23%) and 3 zone (61 species, 21%) are also widely represented. Almost never are used species of zones 8 (5 species, 2%), 9 (1 species, 1%), and 10 (2 species, 1%). The analysis of winter hardiness of the species showed that species from the mountainous regions of Central and East Asia, where the continental climate dominates, pass the winter on green roofs best. But species from European mountains have lower winter hardiness. It was found that cultivars also have lower winter hardiness than the species from which they were derived. For high-quality, durable, ecologically and economically feasible greening of flat roofs in Lviv, it is essential to select winter- and frost-resistant plant species that belong to higher USDA-zones than the territory of the city of Lviv, as well as to use plant species from the mountains of Central and East Asia. It is necessary to take into account the height of the building, which creates a vertical zonation of vegetation.

Keywords

• roof greening; species composition; cultivars; biomorphological structure; frost resistance; usda-zones.