INVASION BY HERACLEUM-MANTEGAZZIANUM IN DIFFERENT HABITATS IN THE CZECH-REPUBLIC

Heracleum mantegazzianum, a tall forb from the western Caucasus invaded several different habitats in the Czech Republic. The relation between invasion success and type of recipient habitat was studied in the Slavkovsky les hilly ridge, Czech Republic. The vegetation of 14 habitat types a occurring in an area of ca. 25 km(2) was analysed using phytosociological releves, and the invasion success of Heracleum (in terms of number of localities, area covered and proportion of available area occupied) was recorded separately in each of them. Site conditions were expressed indirectly using Ellenberg indicator values. The hypothesis tested was that Heracleum spreads in the majority of vegetation types regardless of the properties of the recipient vegetation. Community invasibility appeared to be affected by site conditions and the composition of the recipient vegetation. The species is not found in acidic habitats. Disturbed habitats with good possibilities of dispersal for Heracleum seeds are more easily invaded. Communities with a higher proportion of phanerophytes and of species with CS (Competitive/Stress-tolerating) strategy were more resistant to invasion. The invasion success was bigger in sites with increased possibilities of spread for Heracleum diaspores. Communities invaded by Heracleum had a lower species diversity and a higher indicator value for nitrogen than not-invaded stands. It appears that species contributing to community resistance against invasion of Heracleum, or capable of persisting in Heracleum-invaded stands, have similar ecological requirements but a different life strategy to the invader.