The Occurrence of Helianthus Tuberosus Species in the Nitra River Banks Vegetation Within the Topoľčany District
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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). Rivers represent material and energy arteries of the landscape greatly influenced and modified by human activities (Richardson et al., 2007) and their riparian vegetation is very susceptible to invasions of non-native species (Pyšek & Prach, 1994). Watercourses enable the transfer of diaspores in the direction of flow. The floods also distort riparian vegetation and thus creating new opportunities for colonization by invasive species and forming a source population for spreading invasive species into the surrounding landscape (Fehér, 2001). The term riparian vegetation means the strip of vegetation along the watercourse that is flooded about once a year and its width is determined by the surface flow on one side and the width of the bank on the other side (Novák et al., 1986). Many valuable works deal with the role of river corridors and their contribution to the occurrence and spread of invasive species in the environment. Assessing invasive behavior of plants in the river basin of the Nitra River is the topic in the work of Fehér (2001). There are many valuable works from the Czech Republic (Matějček, 2009). In Germany, the impact of river corridors on the spread of invasive plants was evaluated by Säumel & Kowarik (2010) and in Poland it is the work of Kolaczkowska (2010). The aim of the paper is to evaluate the occurrence and spread of invasive species of Helianthus tuberosus in riparian vegetation of the inter-embankment area of the Nitra River within the Topoľčany District. 2 Study Area The Nitra River forms the left-side tributary of the Váh River and Danube River. It springs on the southern slopes of Malá Fatra and the length of the river is 196.7 km (Porubský, 1991). The studied section of the river with the length of 23 km is delimited by the boundary of the Topoľčany District and it passes through the cadastral areas of 16 municipalities (Fig. 1). The 136 natural vegetation of the studied area is made of ash-elm-oak forests (hardwood alluvial forests) with species: Ulmus minor, Ulmus laevis, Quercus robur and lowland hygrophilous oak-hornbeam forest species: Quercus robur, Quercus cerris, Carpinus betulus, Ulmus minor, Ligustrum vulgare (Maglocký, 2002). Fig. 1 The area of interest within the Topoľčany District (Gális, 2012) 3 Material and Methods The Jerusalem artichoke (Helianthus tuberosus) is a perennial green to gray-green herb (Fig. 2) reaching the height of 60 - 250 cm. It came from North America to Europe in 1607 and it was gradually spread from France also to other countries. The most substantial site of occurrence includes riparian nitrophilic vegetation along watercourses, but also a variety of anthropogenic sites. It also occurs in the hydrophilic species of Convonvuletalia sepium and dominates in some of them. In the landscape, it spreads very aggressively and settles more and more areas. It is contributed not only by spreading through generative diaspores, but also by vegetative propagation of broken-off parts of corms washed away by water to new sites along the watercourse (Cvachová, et al., 2002). Mapping the sites of invasive species of Helianthus tuberosus was done during the vegetative period in the year of 2011 in the inter-embankment area of the Nitra River and on the 23 km long section. Fig. 2 Helianthus tuberosus individuals (Gális, 2012) The purpose of field survey was to identify the sites of occurrence and find abundance of species populations. The presence of the species was evaluated at 1 km long segments. The 137 research was conducted in the entire width of the inter-embankment area of the river, in terms of the work (Fehér & Končeková, 2001), divided into zones: (1) river bed and edge of the bank, (2) berm - mesophilic meadow species, (3) flood protection dike (Fig. 3). Fig. 3 Zones of the inter-embankment area of the Nitra river (Fehér, 2001) For each of the sites, we determined the size of population (Fehér, 2001): - semi- quantitative assessment in terms of Evidenčný list mapovania inváznych druhov rastlín [Registration Sheet for Mapping Invasive Plant Species] (Cvachová & Gojdičová, 2002): J (Jedinec) - individual, SJ (Skupina jedincov) - a group of individuals, MS (Malé skupiny) - small groups, VZP (Veľký zapojený porast) - big involved vegetation. Invasive plant species were classified according to Zoznam nepôvodných, inváznych a expanzívnych cievnatých rastlín Slovenska 2 [List of Non-native, Invasive and Expansive Vascular Plants of Slovakia 2] (Cvachová, Gojdičová & Karasová, 2002) and determined according to Príručka na určovanie vybraných inváznych druhov rastlín [Handbook on Determination of Selected Invasive Plant Species] (Cvachová et al., 2002). Nomenclature of taxa was unified according to the work of Marhold & Hindák (1998). 4 Results and discussion During the field survey in delimited section of the Nitra River with a length of 23 km, we found in the inter-embankment area 155 sites of occurrence of Helianthus tuberosus individuals. From the 3 evaluated zones (river bed and edge of the bank, berm, dike), the sites with the occurrence of invasive species to the greatest extent (45 %) occurred in the zone of the river bed and the edge of the bank (Fig. 4). In the berm zone (mesophilic meadows), it occurred in 37 % proportion of the recorded sites of invaded species of Helianthus tuberosus. In the zone of flood protection dike, it was recorded only 18 % share of the species occurrence. 50 45 40 35 45 37 % 30 25 20 15 18 10 5 0 kyneta a hrana brehu berma protipovodňová hrádza Fig. 4 Occurrence of target species within the inter-embankment area (Gális, 2012) The graph shows that the biggest number of individuals of Helianthus tuberosus species is tied directly to nitrophilic riparian vegetation along the watercourse. The relatively high 138 proportion (37 %) was recorded also in the berm zone mainly due to the river segments with mass occurrence of the species often forming impassable vegetation in the entire width of the zone. Lower total abundance within this zone was caused by the maintenance of vegetation in the river segments which intervene in the inner town and villages. The flood protection dike contained the smallest proportion of sites invaded by the species of Helianthus tuberosus. Also in this zone, there is a regular maintenance of vegetation and with increasing distance from the watercourse, the site conditions changes and loses possibility of more significant transfer of diaspores in the direction of flow. Spatial expansion of invasive species of Helianthus tuberosus along the Nitra River was evaluated in 23 segments, each with a length of 1 km. Based on the selected distribution, we could evaluate to what extent is the delimited section of the river invaded and thus determine the expansion of the species along the entire length of the studied section (Tab. 1). Tab. 1 The occurence of Helianthus tuberosus species in the segments (Gális, 2012) Segments Population size Cadastral area River km 1 J Práznovce 98 2 SJ Práznovce, Topoľčany 97 3 MS Topoľčany 96 4 SJ Topoľčany 95 5 MS,VZP Topoľčany, Nitrianska Streda 94 6 MS,VZP Solčany, Nitrianska Streda 93 7 MS,VZP Nitrianska Streda 92 8 J,SJ Nitrianska Streda 91 9 MS Čeľadince, Chrabrany 90 10 SJ,MS Kovarce 89 11 MS Kovarce 88 12 SJ Kovarce 87 13 MS Kovarce 86 14 MS Dvorany nad Nitrou, Súlovce 85 15 SJ Oponice, Ludanice 84 16 SJ Kamanová, Oponice 83 17 J Oponice, Preseľany, Belince 82 18 J Preseľany 81 19 SJ Preseľany 80 20 J Hrušovany 79 21 J Hrušovany 78 22 J Koniarovce 77 23 J Koniarovce 76 Notes: J - individual, SJ - a group of individuals, MS - small groups, VZP - big involved vegetation From the results shown in the table, we can concluded that the most representative area of the invasive species of Helianthus tuberosus (MS - small groups, VZP - big involved vegetation) was recorded in segments 5-7 located in the northern part of the delimited section of the river. Gradually, towards the south part of the Nitra River, the occurrence of the species had variable character forming smaller populations (J - individual, SJ - a group of individuals) regarding the number and area in segments 17-23.