Distribution of some synanthropic plant species in the historic center of Irkutsk (East Siberia)

The article is devoted to the results of the grid mapping of some synanthropic herbaceous plant species, i.e. four alien plants (Atriplex sagittata Borkh., Hordeum jubatum L., Impatiens glandulifera Royle, Sisymbrium officinale (L.) Scop.), and one indigenous apofit species (Potentilla paradoxa Nutt.) in the historic center of Irkutsk. For mapping, we used a geographical grid system. The territory of the center of Irkutsk (total area is 2183.7 hectares) was divided into squares of size 10''. In the field, every square was equal to 310 m in latitude and 190 m in longitude. We determined the abundance of species in every square by a three-point scale: 1 - sporadically, or several small groups of plants, 2 - infrequently, or several few square meter populations, 3 - frequently, or forming large clusters. For Impatiens glandulifera, cultivated and spontaneous populations were considered separately. In total, we investigated 368 squares. For constructing maps, we used the QGIS 2.12.0. We found that all four alien plant species were successfully naturalized. Most common species is Hordeum jubatum. We registered it in 31% of squares. This species is one of the most aggressive aliens in the region, but in Irkutsk center we found usually small and not numerous (per grid) populations. Obviously, the reason for this fact is a lack of large free vegetation sites, the most preferred habitat of the species. Impatiens glandulifera is the only species used by local people as a cultivated plant. Although, we found now cultivated populations in 12 squares only. Spontaneous populations of I. glandulifera are much more frequent; we found them in 26% of investigated squares. Sisymbrium officinale and Potentilla paradoxa are recorded in 24 and 21% of investigated squares, respectively. Both of them are presented by small and not abundant populations. Atriplex sagittata is found only in 36 squares (10% of investigated), but this species, as well as Impatiens glandulifera, is phytosociologically active, composing monodominant stands. In case of Potentilla paradoxa, we face a methodological problem of separation of indigenous and adventive fractions of flora. In many sources, this species is treated as alien for Baikal region, but there is no evidence of its introduction to the flora. This Asian and North American species was accounted already in the first comprehensive flora of the Baikal-Dahuria region, published in the middle of the XIX-th century by NS Turczaninow. It means that if P. paradoxa is adventous for the regional flora, it is an archeophyte species, but the problem of detection of archeophytes is hardly developed for North Asian regions of Russia. Therefore, we prefer to treat only neophytes as an alien fraction of flora, introduced to the region in the second half of the XIX-th century or later, and not counted by NS Turczaninow. Funding: This research was conducted in the framework of budget projects of VB Sochava Institute of geography, Siberian Branch of the Russian Academy of Sciences, projects No VIII.79.2.3 and VII.79.2.5. Acknowledgments: We are grateful to students of Irkutsk State University, G. Iljin and Ya. Sitnikova for participating in field investigations.

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