THE OCCURRENCE OF HELIANTHUS TUBEROSUS SPECIES IN THE NITRA RIVER BANKS VEGETATION WITHIN THE TOPOĽČANY DISTRICT Marek Gális Department of Ecology and Environmental Sciences, Faculty of Natural Sciences, Constantine the Philosopher University in Nitra, Tr. A. Hlinku 1, 949 74 Nitra, Slovakia Correspondig author:
[email protected] Abstract The presence of non-native plant species in natural floras is mostly linked to various kinds of human activities. In this article we introduce the results determined during the field survey of invasive neophyte occurrence in riparian vegetation of the Nitra River within the Topoľčany District, in 2011. The occurrence of Helianthus tuberosus was recorded in 23 segments (1km long parts of the river channel). The highest presence of this species was registered in the riparian vegetation of the Nitra River. Overall 155 locations, invaded by Helianthus tuberosus, were recorded in the surveyed area. Our results indicate that the river channel play very important role in the dispersion of non-native plant species in selected area and local expansion of this invasive herb is not yet finished. Next colonization within the river channel, cadastral area of town and villages and its surrounding is likely to occur especially in parts of the river channel linked with human activities. Key words: invasive plant species, Helianthus tuberosus, Nitra River, Topoľčany District 1 Introduction The success of the introduction of non-native plant species into the region, in which they have not occurred so far, largely depends on the possibility of spreading in the surrounding environment particularly through the linear sites (rivers, roads, railways) (Pyšek & Prach, 1993).