Reciprocal contamination by invasive plants: analysis of trade exchange between Slovakia and Romania.
In this work, potential contamination by invasive plant propagules as a result of trade exchange between Slovakia and Romania, was assessed. National lists, describing biology and ecology of 30 worst invasive plant taxa, were formulated, and trading in period 2006-2010 between countries analysed. Using norms for commodity impurity level, information on species habitat occupancy and literature data dealing with seed/fruit attachment on roads we calculated then potential invasive plant propagule export (PE) for each taxon. We found three fold higher total good export from Slovakia than in opposite direction, increasing export of commodities potentially containing invasive plant propagules exported from Romania to Slovakia and rise of road compared to railway transport. PEs for Slovak invasive plant taxa were one-two orders higher than those for Romanian ones. Potentially most exported taxa for Slovakia were: Amaranthus sp., Ambrosia artemisiifolia, Galinsoga sp., Kochia scoparia and Sorghum halepense (tens to hundreds tonnes each). And these could mostly be exported from Romania: Amaranthus sp., Ambrosia artemisiifolia, Artemisia annua, Conyza canadensis, Cuscuta campestris, Datura stramonium, Erigeron annus, Galinsoga sp., Iva xanthiifolia, Kochia scoparia, Lycium barbarum, Sorghum halepense, Veronica persica and Xanthium orientale subsp. italicum (units to tens tonnes each). High PE was significantly associated with cereals export. Our formula for PE is applicable for any inter- and intra-continental trade exchange.