Reynoutria niche modelling and protected area prioritization for restoration and protection from invasion: A Southeastern Europe case study

An important step in managing invasive species is determining the factors responsible for their current and potential distribution, especially when species distribution is climatically determined like in Reynoutria taxa case. The main aim of this paper was to integrate all available distribution data of the Reynoutria taxa in SE Europe and to predict in which habitats and along which corridors its future spread can be expected. Distribution data of the Reynoutria taxa were obtained from extensive field studies in the period from 2006 to 2016, as well as from the literature and herbarium sources. A total of 4081 localities in Serbia and the Kosovo region, Montenegro, Slovenia, Croatia, Bosnia and Herzegovina, Bulgaria and Romania have been recorded, most frequently in riparian and human-made habitats. Ecologically suitable ranges for the Reynoutria taxa were predicted using the MaxEnt program and 19 bioclimatic variables which were derived from the WorldClim data set. Results of this study showed that the most frequent Reynoutria taxa in SE Europe are R. japonica var. japonica and hybrid R. × bohemica. The most suitable geographical areas for R. japonica and R. sachalinensis are mostly located in the north, while for R. × bohemica the central part of SE Europe is suitable. The precipitation of the warmest quarter had a high influence on the potential distribution modelling of these closely related species. Potential distribution modelling revealed R. × bohemica's high temperature tolerance in different seasons with high durability of drought (up to 60 mm per year less precipitation than parental species). Moreover, this research predicts which areas are most likely to be invaded, and makes suggestions where to focus management efforts for survey and removal of these invaders, especially in protected areas. According to the future climate analysis R. japonica and R. × bohemica could expand their range in riparian habitats up to 30-40%. Consequently, invasion in Slovenia's and Croatia's rivers requires urgent preventative measures. This study provides empirical evidence that these plants could become widespread throughout SE Europe within 25 years under the current trend and emphasizes that regionally specific management plans should be implemented to prevent further spread of these taxa.