Contents lists available at ScienceDirect Urban Forestry & Urban Greening journal homepage: www.elsevier.com/locate/ufug Floristic diversity, composition and invasibility of riparian habitats with Amorpha fruticosa: A case study from Belgrade (Southeast Europe) Nataša Radovanović, Nevena Kuzmanović, Snežana Vukojičić, Dmitar Lakušić, Slobodan Jovanović ⁎ University of Belgrade, Faculty of Biology, Institute of Botany and Botanical Garden, Takovska 43, 11000 Belgrade, Serbia ARTICLE INFO Keywords: City forests Flooded lowland meadows Invasive neophytes Invasibility-coverage index relations Species richness Willow and poplar forests ABSTRACT Amorpha fruticosa L. represents one of the most dangerous invasive neophytes spreading quickly in many countries and cities of southeastern Europe where it aggressively penetrates into newly invaded sites and establishes permanently. It prefers moist and periodically flooded terrains, being therefore a serious threat for fragile wet habitats. Considering this, the main aim of this research was to determine the floristic diversity, composition and level of invasibility of urban and suburban riparian forests and open habitats with domination of A. fruticosa at the mouth of the Sava and Danube Rivers in Belgrade, and to assess the impact of all invasive neophytes in the analyzed habitats. Two hundred fifty seven (257) relevés, made according to Braun-Blanquet (1964) methodology, were subjected to different statistical analyses. The obtained results showed that urban wet habitats with domination of A. fruticosa were differentiated into 7 coenological groups, with the total of 222 registered taxa, out of which 29 (13.06%) were invasive neophytes. These coenoses are developed within willow and poplar habitats, wet lowland meadows and reedbed habitats. We found a direct negative correlation between the change in the number of species and the proportion of invasive species i.e. their coverage indexes in the analysed stands. The identified coenological group with domination of Rubus caesius and A. fruticosa represents the most dangerous hotspot of invasive species, which might seriously threaten native species and their urban riparian habitats, as well as similar habitats downstream. 1. Introduction It is well-known that river floodplains are among the most threatened habitats (Pyšek and Prach, 1994; Hood and Naiman, 2000; Schnitzler et al., 2007). Namely, within the group of the plant species that grow almost exclusively in the corridors of large rivers (river corridor plants), we can find a high proportion of threatened species (Burkart, 2001). However, rivers also transport vegetative parts and seeds of some hydrophilic invasive plants, which can develop very quickly in the fertile riparian zones (Gallé et al., 1995; Säumel and Kowarik, 2010; Pedashenko et al., 2012). In this sense, the Danube with its characteristics is absolutely one of the most important routes for spreading these species in Europe (Pedashenko et al., 2012). Amorpha fruticosa L. (false indigo or indigo bush) is a deciduous shrub which originates from central and eastern part of North America and was introduced into Europe in 1724 as an ornamental species. It was brought to the Balkan Peninsula at the beginning of the twentieth century when it started to colonise alluvial forests and other habitats in large lowland river valleys (Gagić-Serdar et al., 2013), seriously threatening the ecological balance of native ecosystems (Krpan and Benko, 2009). Although Weber and Gut (2004) assessed that A. fruticosa represents a potentially invasive plant species in central Europe, nowadays it is one of the most dangerous invasive neophytes spreading rapidly in many countries and cities of south-eastern Europe as well (Anastasiu et al., 2007; Grbić et al., 2007; Pedashenko et al., 2012; Anačkov et al., 2013). The false indigo, growing mainly in wet habitats, is becoming very dangerous especially in fragile wet habitats of protected areas (Török et al., 2003; Botta-Dukát and Mihály, 2006; Dumitraşcu et al., 2012; Batanjski et al., 2016), e.g. the Danube Delta, one of the most important Ramsar sites of Europe (Protopopova et al., 2006; Anastasiu et al., 2007). As a semi-aquatic species, A. fruticosa prefers moist and periodically flooded habitats regardless of the level of their degradation (Doroftei, 2009; Anačkov et al., 2013). As it can reproduce both generatively and vegetatively, it is growing faster than most forest-cultural species (Tucović and Isajev, 2000; Gagić-Serdar et al., 2013). Amorpha fruticosa aggressively penetrates into newly invaded sites, where it establishes permanently (Radulović et al., 2008). http://dx.doi.org/10.1016/j.ufug.2017.04.006 Received 25 October 2016; Received in revised form 7 April 2017; Accepted 8 April 2017 ⁎ Corresponding author. E-mail address: sjov@bio.bg.ac.rs (S. Jovanović). Urban Forestry & Urban Greening 24 (2017) 101–108 Available online 10 April 2017 1618-8667/ © 2017 Elsevier GmbH. All rights reserved. MARK