THE ECOLOGY OF THE CAUCASIAN HERBACEOUS PERENNIAL HERACLEUM-MANTEGAZZIANUM SOMM. ET LEV. (GIANT HOGWEED) IN CULTURAL ECOSYSTEMS OF CENTRAL-EUROPE

Heracleum mantegazzianum Somm. et Lev. (Giant Hogweed) is a herbaceous perennial from the subalpine zone of the western Caucasus Mountains. It was first introduced to Central Europe around 1850 as a horticultur al plant, and has subsequently attained a wide distribution through wi ldling spread (ergasiophygophyte). Heracleum has firmly established it self in Artemisietea phytosociological communities (nitrophytic herbac eous perennial communities), on fresh to moist sites' with good to ver y good nutrient levels, in lowland to submontane zones (epecophyte and agriophyte). These sites include those formerly used agriculturally o r horticulturally, eutrophied forest or copse edge ecotones, as well a s extensively or no longer managed road or railway verges. These are a ll sites where nutrient levels have been greatly altered or where eutr ophication has occurred, through anthropogenic influence. The document ation of the phenological development of a Heracleum stand on a river floodplain site, near the city of Giessen in the lowland zone of Centr al Hesse, has shown that the species is at least biennial, usually how ever triennial to perennial. Heracleum mantegazzianum spreads exclusiv ely in a generative fashion by seeds, individually contained within fr uiting bodies (mericarps), which are almost always found within a 250 cm radius around the senesced mother plant (passive autochory). The di aspores germinate predominantly in early spring (flowering period of T ussilago farfara), germination being possible only after the maturatio n of the embryo during a two to three month cold period. By the end of the growth period, only a few individuals have developed from the sev eral thousand germinated seedlings, namely those which have accumulate d sufficient nutrient reserves in the roots. This enables Heracleum ma ntegazzianum to develop a new vegetative body quickly and independentl y of weather conditions during the following growth period. Heracleum mantegazzianum has the property of being able to draw the vegetation p oint in the hypocotyl up to 10 cm into the soil by vertical contractio n of the central tap-root. This property facilitates rapid sprouting i n spring. Heracleum belongs to those perennial species with a juvenile phase, flowering and bearing fruit only once before senescing. This s enescence is caused by the depletion of nutrient and energy reserves, the reproductive organs competing with the vegetative organs for the r emaining nutrients. During the flowering and seed ripening phase, the vegetative structures shrivel up and the energy of the carbohydrates i n the roots is exhausted. Regenerative growth is possible during the v egetative growth phase, because the plant is able to draw on considera ble nutrient reserves in the roots. The regenerative capacity during t he generative growth phase is restricted however; only those plants di sturbed before full flowering are able to develop new inflorescences w ith lesser flower and seed quantities.