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

Heracleum mantegazzianum, a tall forb from the western Caucasus invade d several different habitats in the Czech Republic. The relation betwe en invasion success and type of recipient habitat was studied in the S lavkovsky les hilly ridge, Czech Republic. The vegetation of 14 habita t types a occurring in an area of ca. 25 km(2) was analysed using phyt osociological releves, and the invasion success of Heracleum (in terms of number of localities, area covered and proportion of available are a occupied) was recorded separately in each of them. Site conditions w ere expressed indirectly using Ellenberg indicator values. The hypothe sis tested was that Heracleum spreads in the majority of vegetation ty pes regardless of the properties of the recipient vegetation. Communit y invasibility appeared to be affected by site conditions and the comp osition of the recipient vegetation. The species is not found in acidi c habitats. Disturbed habitats with good possibilities of dispersal fo r Heracleum seeds are more easily invaded. Communities with a higher p roportion of phanerophytes and of species with CS (Competitive/Stress- tolerating) strategy were more resistant to invasion. The invasion suc cess was bigger in sites with increased possibilities of spread for He racleum diaspores. Communities invaded by Heracleum had a lower specie s 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-i nvaded stands, have similar ecological requirements but a different li fe strategy to the invader.