The importance of traffic corridors as urban habitats for plants in Finland

Traffic corridors have been recognized as floristically rich with endangered and rare species included. The aim of this study is to treat traffic corridors as habitats and estimate their importance for diversity of vascular plants on municipal level. The material is derived from the comprehensive studies of urban floras in the cities of Vantaa, Kerava and Järvenpää during the 1990s in southern Finland. The material consists of over 190,000 species records (704–771 species). The material was divided in two groups: the ones with occurrences in traffic corridors (TC) and the others with no occurrences (NTC). The percentage of the traffic corridor plants of the total flora is almost the same in all the three cities: two thirds in traffic corridors and one third not in traffic corridors. The explanation may be the general floristic similarity of the cities. The two groups differ ecologically from each other. The association of plants with traffic corridors varies according to the ecology of the species. About 100 plants have more than 50% of their occurrences in traffic corridors. In Järvenpää, a group of four Carex-species was intensively mapped. 46 occurrences out of 50 were found in traffic corridors. A case study showed the difficulties in management of endangered species on a roadside site. The usual extensive management techniques were not sustainable for the survival of the species. Instead, a much more intensive management was needed.