ECOLOGICAL AND GEOGRAPHICAL ANALYSIS OF DISTRIBUTION OF <i>HERACLEUM PERSICUM</i>, <i>H. MANTEGAZZIANUM</i> AND <i>H. SOSNOWSKYI</i> ON THE NORTHERN LIMIT OF ITS SECONDARY RANGE IN EUROPE
The group of plants known as giant hogweeds: Heracleum mantegazzianum, H. persicum and H. sosnowskyi are widely recognized as dangerous alien species in Europe. We have analyzed the climatic conditions on the northern boundary of the secondary range of giant hogweeds group species in Northern Europe. The northernmost areas of growth of H. persicum are localized in the coastal regions of the northern and central parts of the Scandinavian Peninsula (up to 71° NL). Within Fennoscandia, the plants H. mantegazzianum and H. sosnowskyi were found up to 69° NL. The natural gradient of climatic parameters within the subarctic and temperate zones in Northern Europe allowed us to assess the ranges of climatic conditions required for the plants in this territory. We have found that the minimum sum of active temperatures values required for these alien plants are >1150 °С (for temperatures above 5 °C) and >450 °С (for temperatures above 10 °C). The heat resource exceeding this level ensures successful growth, development and reproduction of giant hogweeds group species in the climatic conditions of Subarctic Europe. The presence of stable snow cover on the territories with very low air temperatures during winter period prevents buds and seedlings cold damage. Climatic indices calculated as ratio of air temperature and snow depth or winter precipitation can serve as markers reflecting climatic constraints for the expansion of alien giant hogweeds group species in north direction. The main climatic parameters limiting the distribution of these species in Northern Europe are: insufficient sum of active temperatures, seasonal freezing of soils to temperatures critical for wintering organs of plants, late spring and early autumn frosts.