Distribution of alien plant species of the Middle Volga Region (South-East of the European part of Russia): a dataset

Abstract Background The dataset presented in the current study contains information regarding alien vascular plant species found in the Middle Volga Region (South-East of the European part of Russia). The dataset overall includes 413 species belonging to 247 genera and 67 families. The described dataset is based on the data published during floristic studies from 1851 to 2019. The dataset does not include alien vascular plant species that have presently disappeared from the territory of the region. It contains a total of 7,782 records of occurrences, extracted from the Salix system of information and analytics, developed in the Institute of Ecology of the Volga River Basin of the Russian Academy of Sciences. New information A total of 7,782 records were published on the occurrence of alien vascular plants in the Middle Volga Region. Each entry includes information regarding the place of occurrence of the alien plant species, the year of occurrence, the person who recorded the alien plant and who identified it, status of the species (introduced or invasive), link to the herbarium, which contains the specimen and the literary source. If it were impossible to establish the names of the persons who collected the samples and (or) their identification in the identifiedBy and recordedBy fields, the names of the authors of the publication given in the associatedReferences field were entered. The presented dataset supplements the information on the distribution of alien plant species in the whole European part of Russia and specifies the places of their findings in the Middle Volga Region.


Introduction
Currently, the invasion of alien plant species constitutes a large-scale phenomenon that poses a threat to the natural diversity and is regarded as one of the most serious environmental problems that mankind faces today (Lambdon et al. 2008, Vinogradova et al. 2010, Pyšek et al. 2017, Senator and Rozenberg 2017. The Middle Volga Region is one of the leading regions of Russia in terms of industrial development and economic infrastructure. The area of the Region is 99,000 km ; the population density is 48.6 per km . The position of the Middle Volga Region, situated in the intersection of large transport routes of both latitudinal and longitudinal directions, and the significant population density are determining factors for the richness of alien flora and the high rates of its dynamics (Rozenberg 2009). This article contains the dataset records on alien vascular plant species occurrences, published in GBIF as a Darwin Core Archive (Senator 2020), prepared in accordance with the concept of "data paper" (Penev et al. 2017).

General description
Purpose: The main purpose of this study is the presentation of a published dataset on the distribution and the composition of alien plant species of the Middle Volga Region (South-East of the European part of Russia) in the GBIF as a Darwin Core Archive. In addition, the study aims to provide accurate information on the global distribution of alien plant species, based on the records of their growth outside of their native ranges and enables the creation of large-scale plant invasion models. Study area description: The Middle Volga Region is located in the South-East of the European part of Russia. From the aspect of Regional Administration, it is considered as Samara and Ulyanovsk Oblasts of the Russian Federation (Fig. 1).

Design description:
The first step of the study was to create a checklist of alien plant species found in the Middle Volga Region (Senator and Vasjukov 2019). The conceptual basis of the study is the adoption of the idea of the invasive species as an alien plant naturalising into the natural and semi-natural plant communities (Richardson et al. 2010a, Baranova et al. 2018. Hence, all other alien plant species are either recognised as potentially invasive (established and successfully propagating in places where they are introduced, but not spreading into natural and semi-natural plant communities) or nonnaturalised.
The dataset is based on Samara and Ulyanovsk Oblasts' published data on the flora, which are confirmed through stored samples in Herbaria of the Lomonosov Moscow State University (MW), V.L. Komarov Botanical Institute of the Russian Academy of Sciences (LE), Institute of Ecology of the Volga River Basin of the Russian Academy of Sciences

Study extent:
The presented dataset is based on the published synopsis of alien plants species of the Middle Volga Region (Senator and Vasjukov 2019) and materials stored in the Salix system of information and analytics ). The dataset does not include alien vascular plant species that have presently disappeared from the territory of the Region, likewise species that are native in one part of the study Region, while in another they are found exclusively in disturbed habitats. The terms "introduced species" and "invasive species" are used in accordance with Richardson et al. (2010b) and the system of terms used in Russian-language scientific literature (Baranova et al. 2018).

Sampling description:
In 2017, the Salix database was created in order to store floristic information for the Middle Volga Region. The database contains records of all plant species growing in the area of the study. Each entry contains a link to a literary source or a herbarium specimen confirming the findings. The publication of the synopsis of alien plant species in the Middle Volga Region (Senator and Vasjukov 2019) made it possible to highlight and identify the alien plant species. The information about the collectors of herbarium specimens is presented in Table 1. There are 1472 occurrences in the dataset with coordinate uncertainty of 100 km. This is due to the fact that, in the literary sources of the late 19th and early 20th centuries, there is no exact geolocation. Instead, it is specified, for example, "Western part of Buguruslansky Uyezd" or "neighbourhood of Sergievsk". This collection could be made within a radius of 100 km or more from a settlement. At the same time, such data are of interest from the point of view of identifying the dynamics of the appearance of alien species in the study area.
Quality control: During the development process of the dataset, the records obtained from primary sources were examined by the first author, as some names of the species did not correspond to the modern nomenclature. The herbarium samples were collected and identified by scientists from the Institute of Ecology of the Volga River Basin of the Russian Academy of Sciences and are stored in the PVB herbarium. The accuracy of the determination of some samples was confirmed by taxonomists from the Lomonosov Moscow State University (MW) and V.L. Komarov Botanical Institute of the Russian Academy of Sciences (LE). For the purposes of publishing the dataset in the GBIF network, the records have been adjusted to match the Darwin Core specifications (Wieczorek et al. 2012).
Step description: 1. The initial data for this standardised dataset are the information stored in the Salix system of information and analytics, available at https://саликс.рф/Salix/. This information is updated regularly.
2. The Salix system of information and analytics enables us to generate a report in an Excel table form with the necessary dataset. For the purposes of the report, the fields «Species name», «Family», «Administrative Oblast», «District», «Location», «Geographical coordinates», unique identifiers for each taxon and bibliographic references were generated, containing the necessary information regarding the findings. In cases of an absence of a reference, a herbarium sample collector is specified.
3. The scientific names of plants were adjusted in accordance with the GBIF Taxonomic Backbone.

Geographic coverage
Description: The Middle Volga Region is a region located in the South-East of the European part of Russia. In botanical-geographical terms, it is located on the border of the European broad-leaved forest area and the Eurasian steppe area. The area of the region is 99,000 km ; the population density is 48.6 per km . From the aspect of Regional Administration, it is considered as Samara and Ulyanovsk Oblasts of the Russian The climate is temperate-continental, with peculiar seasonal circulation, characterised by sharp temperature contrasts between cold and warm seasons, a rapid transition from cold winter to hot summer, moisture deficiency, high evaporation rate and abundance of sunlight. The continentality of the climate increases from west to east. The average January temperature is -11 --13.5°С, in July -+19°С -+21.0°С. The frost-free period lasts 118-157 days. On the territory of the Region, there is a zonal decrease in annual precipitation from north to south from 540 to 370 mm. The largest part of the area of study is located in the forest-steppe zone, characterised by the presence of typical chernozem soil, an alternation of broad-leaved forests and a rich variety of steppe grasslands. The extreme south point of the territory is occupied by a steppe zone with forb-fescue-feather grass steppes on ordinary and southern chernozem soils.
The largest number of the records was made in the Ulyanovsk Oblast (4052 records or 52%), the smallest in the Samara Oblast (3730 records or 48%).

Taxonomic coverage
Description: The dataset includes records of expansion on alien plant species in two groups (Pinophyta and Magnoliophyta), 67 families, 247 genera and 413 species (Senator 2020). The majority of the records is occupied by the Magnoliophyta group. The highest number of the records refer to the Dicotyledones (90%), followed by the Monocotyledones (9.7%). The Pinophyta group is represented by a single family of Pinaceae, one genus and one species Larix sibirica (0.3% of records).
The Asteraceae, Poaceae, Brassicaceae, Rosaceae, Fabaceae, Amaranthaceae, Lamiaceae, Solanaceae, Caryophyllaceae and Apiaceae families have a wide range of multi-species and hold the maximum number of records, totalling 255 species that comprise 67% of the records (  A total of 18 families contain a small number of records (less than 10). In this case, the families Cleomaceae, Commelinaceae, Linaceae and Verbenaceae are represented by only one species and one occurrence.

Temporal coverage
Notes: 1851 -2019 The presented dataset contains information on the occurrences of alien plants since 1851, with the most recent findings recorded in 2019. Fig. 3 shows that, in the 19th century and in early 20th century, the number of findings of alien plant species in that period was small.  The species with the largest number of occurrences (species with more than 900 records are shown). Description: The presented dataset (Senator 2020) contains information about alien vascular plant species found in the Middle Volga Region (South-East of the European part of Russia). In total, this dataset includes 413 species belonging to 247 genera and 67 families. The study is based on data published during floristic studies from 1851 to 2019. At the same time, the study does not include alien vascular plant species that have now disappeared from the territory of the Region. In total, the dataset contains 7782 occurrence records which were extracted from the Salix information and analytical system developed at the Institute of Ecology of the Volga River Basin of the Russian Academy of Sciences .

Author contributions
Stepan Senator -alien plants sample collection, species identification, data preparation, manuscript editing Alyona Tretyakova -data preparation, manuscript editing Dmitry Vorontsov -data preparation, georeferencing, manuscript editing