Bryophyte species and communities on various roofing materials, Estonia

Considering the recent growth of interest in using mosses in creating vegetated green roofs, we set the aim of our study to get an overview of the variety of moss and liverwort species and communities growing spontaneously on roofs. Data were collected from 67 roofs of five different types of materials: fibre cement, bitumen, stone, thatched and steel from Tallinn and rural areas on Hiiumaa Island and in South Estonia. Indicator species analysis, MRPP, cluster analysis and ordination methods (DCA, CCA) were used for data analysis. As a result of this research, generalist bryophytes occurring on all types of roofing materials were studied and bryophyte species characteristics for certain material types were identified. The thatched roofs differed most clearly from the other roof types in their species composition and had the highest species diversity. Stone and fibre cement roofs had similar species composition. The results revealed significant dependence of the composition of the bryophyte flora on roofs on the density of the bryophyte carpet formed over time on the roof and the presence of a tree canopy above the roof. Other important factors were roof relief, the height of the roof from the ground and the indicator of environmental pollution NOx. However, the studied roofs in Tallinn and rural areas did not show significant differences in the species composition of bryophytes. Five communities were delimited: (1) Syntrichia ruralis – Schistidium apocarpum; (2) Orthotrichum speciosum – Bryum argenteum; (3) Brachythecium rutabulum – Hypnum cupressiforme; (4) Ceratodon purpureus – Rhytidiadelphus squarrosus; and (5) Pleurozium schreberi – Dicranum scoparium. The mentioned communities inhabited locations that differed in environmental conditions. The findings of this research can help choose the roofing material and species suitable for a certain location in creating moss greenery on roofs.