Rivers As Dispersal Corridors for Primarily Expansion of Invasive Plant Species in Serbia
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Rivers as Dispersal Corridors for Primarily Expansion of Invasive Plant Species in Serbia Renata Gagić Serdar*1, Tomislav Stefanović1, Svetlana Bilibajkić 1, Zoran Poduška 1, Ilija Đorđević1, Ljubinko Rakonjac1,2, Goran Češljar 1, Radovan Nevenić,1,3 1 Department for Spatial Planning, GIS and Forest Policy, Institute of forestry, Belgrade, Serbia 1, 2 Institute of forestry, Belgrade, Serbia 1,3 Department for Spatial Planning, GIS and Forest Policy, Institute of forestry, Belgrade, Serbia [email protected] Abstract Invasive plant species are often more successful within introduced areas when compared to their natural ranges. These species represented a suite of successful invaders within a young forest as pioneer vegetation on surfaces made by various transformations of native habitats and land use (river flood surfaces). River valleys represent biologically rich corridors, characterized by natural disturbances that create moist and barren sites suitable for colonization by native riparian plants, but also by woody invasive weeds. The most common, high aggressive and hydrochoric invasive plant in riparian forests in Serbia is false indigo bush (Amorpha fruticosa L.). Pattern of water regimes fluctuations and its influences on populations and stands of A. fruticosa was observed for this introduced riparian woody species along law land as well as few other rivers in Serbia. It was registered that spontaneous spreading of this plant is at the same time followed by certain level of infested seed by bruchid seed-beetle (Coleoptera, Bruchidae, Bruchinae). This evidence indicate that the seed parasites are endophagous herbivores. The variable effects of theirs abundance were recognized due to persistence of seed banks, asexual reproduction of plants, seasonal reproduction of plants, low or incomplete damage on seeds by the seed predators and competition between bruchid beetle and parasite whose larvae also detected feeding in seeds of A. fruticosa; genera Oedaule (Hymenoptera: Chalcidoidea: Pteromalidae). Therefore, if these biological conditions of weeds and seed-predators are overcome, the probability of biological control of weedy plants by seed-predators will increase. In the case of A. fruticosa control by bruchid beetle and parasitic wasp, as a potential condition has not been fully investigated and must be subjected to close examination in the future. Significant level of infested seeds (approximately 30% of all examined pods from localities where water regimes range are stabile) leads to conclusion that these seed parasites could be important reducing factor in successful suppression of A. fruticosa in non-flooded forest habitats. There is a hypothesis which needs to be proven by investigations that until now have labeled the hydrologic regime as the most important extrinsic factor of water-dispersed seeds along riparian corridors. Directly, fluctuations affect mortality of seed predators in significant level and that in a goal of biological measures of weed control utility host plant pods could be i.e. collected during extreme floods. Our results also suggest that planting native tree species along river corridors together with monitoring with prevailing of ecological and entomological research would help prevent invasion risks and contribute implementing natural diversity protection principles with invasive tree species aggressive expansion in floodplains in different invasion stages to prevent further water-mediated dispersal. Keywords: Indigo bush, riparian corridors, expansion, native forests, seed predation, Serbia BALWOIS 2012 - Ohrid, Republic of Macedonia - 28 May, 2 June 2012 1 Introduction False indigo bush, Amorfa fruticosa L. Fabaceae: Papilionaceae: Astragalae is the woody shrub plant species which had been introduced in Europe from North American continent in 1724 (1) when human also unintentionally starts the transportation and introduction of alien species that eventually colonized compatible ecosystems across the globe. It was introduced in the Balkan Peninsula, especially within flooding ranges of major rivers (Sava and Danube), at the beginning of the twentieth century, precisely in 1900 (1). Fast-growing bushes with purple with orange pollen illuminative flowers at first had been purposed for enriching urban greenery as one of the exotic woody plant, where still grows in urban areas as a cultivated decorative shrub expressed in rich, abundant and an attractive flowering (2). It had been proved to be useful in a way of preventing landslides, supportive for railroads stabilization or in other common ameliorative usage (3). One of its useful characteristics is that A. fruticosa belong to group of woody species of honey plants. These were also one of its initial using purposes, but very soon Indigo bush had reached out of planting controlled cultivation and spontaneously started spreading all over territory of Serbia in different forest habitats (4). Primarily in aquatic ecosystems in Serbia formed a numerous stands with outstanding abundant populations. False Indigo bush do not form such abundant populations in all law land forests communities in Serbia (4). It achieves self- reproductive forests, such as riparian forests of Pedunkulate oak, Ash, Ash- White Alder forests, Oak- Elm- Ash and Willow-Poplar forests. Localities where process of aggressively spreading of A. fruicosa were observed and where collecting of pods and other plant material was performed during period 2006-2011 were selected according to regarding self-reproductive key criteria. Degradation level of endangered phytocenological communities in great river planes (river Sava and river Danube), considering their natural regeneration attributes are in synecology and dinamics of abundance of A. fruicosa populations (5).Threatened influence of invasive species to native ecosystems and environment as global planetary disturbing phenomenon blocks the continuity of natural processes, even though the legislation in this area is very precise (6, 7). Permanent disruption of diversity and existing native food chains resulting with huge number of extinct species due to changed competitive species interrelationships as just some of the consequences is still actual and more progressive (6, 7). Surfaces of different land use were abundantly colonized with A. fruticosa during last few decades, on the territory of whole Republic of Serbia, especially in the valleys of large lowland rivers, with the broad indicative flood zones (8). For centuries forests had not been managed in a goal of intruder’s evident rising problem solving, and surfaces of occupied stands are constantly increasing. Changes happened in habitats crossed the critical values after alien population quantities. River flood surfaces and river valleys represent biologically rich corridors characterized by natural disturbances that create moist and barren sites suitable for colonization by native riparian plants, and also by woody invasive weeds. This paper are dealing with only sustainable development addressed method, use bio potential of bruchid beetle – indigo bush weevil (11, 12), recorded feeding in A. fruticosa seeds (pods) in Serbia in 2006 (12). Spontaneous spreading of this plant is, at the same time followed by certain level of infested seed by mentioned bruchid seed-beetle, Acanthoscelides pallidipennis (Motschulsky) Coleoptera: Bruchidae: Bruchinae. Native genera of parasite wasp Oedaule (Hymenoptera: Chalcidoidea: Pteromalidae) larvae had been found in significantly lower share of infested pods also determinated as seed predators of A. fruticosa. Previous hypothesis (9), that wasp was ektoparasitoid and predator of bruchid beetle larvae has been dismissed. Final conclusions is establishing of parasitoid complex of host plant – parasites system (A. fruicosa – A. pallidipennis; Oedaule sp.).This evidence may indicate that the seed parasites are endophagous herbivores, first registered in Serbia as indigo bush weevil, with the same origin as its host. It is assumed that it was introduced in the Balkan Peninsula at the beginning of the twentieth century, together with host plant, and its significant seed percentage predation were also established in previous studies. (9, 10). Pods yield natural insect toxic chemical (13), which indicate that this insects are resistant. Research findings are ecological performances of this positive useful insect in correlation with different environment parameters. The most effective on A. fruticosa growth and development are riparian microclimate conditions (specially moderate water level fluctuations in bank corridor formation stands and riparian cultures where Indigo bush is dominant in middle forest floor. Presence of light (if it reaches the ground conditions are ideal), and soil type are closely linked with the most common forest communities where A. fruticosa present serious harmful factor. It affects unsecured survival or much more fully unpossible growth and natural BALWOIS 2012 - Ohrid, Republic of Macedonia - 28 May, 2 June 2012 2 regeneration of law land forests, especially with Quercus robur L. as dominant young tree in competition to (8). The research of the above representatives of entomofauna with the life cycle of this insect in Serbia started in 2006 in the aim of finding candidates for biological control and strategy of integral suppression of host plant. From late summer 2006, to October 2011 the pods had been collected from more than 20 localities in Vojvodina, Mačva, the vicinity of Belgrade, in Đerdap Gorge, Central Serbia