Does the urban heat island determine the distribution of Fallopia taxa in cities? – preliminary study from Wrocław (Central Europe)

Abstract

Among the invasive plant species found in Europe and North America, particular attention is paid to the Fallopia (Reynoutria) genus: Fallopia japonica, Fallopia sachalinensis and the hybrid created as a result of their crossing - Fallopia × bohemica. Many works describe the extraordinary expansiveness of knotweeds, in anthropogenic habitats, especially in large cities, the representatives from the Fallopia genus are already a permanent element of the local flora. The specific ecological properties of the cities can favour the expansion of Fallopia genus. The goal of this work was to answering the question - is there a relationship between the spread of knotweeds in the city and the local climatic conditions in the form of the so-called urban heat island? The field work was carried out in Wrocław, which is the fifth largest city in Poland, with an area of 292.82 km2 . The study showed that despite the potentially broad thermal amplitude, Fallopia japonica prefers the areas in the city with the highest temperature. The invasion of this species proceeds most intensively in the warmest regions of the city. Similar tendencies are observed in the case of the interspecies hybrid - Fallopia × bohemica. The third taxon - Fallopia sachalinensis - clearly prefers slightly colder parts of the city. It is worth noting that representatives of the Fallopia genus do not appear in the coldest parts of Wrocław. This is quite puzzling, because in these city areas, there are some types of semi-natural habitats which the invasive knotweeds usually willingly occupy. The preliminary study shown that in the urban ecosystem, the thermal factor influences the spread of the Fallopia genus. Research in this area regarding the all Fallopia taxa will continue.