Scirpus radicans (Cyperaceae), a newly-discovered native species in Lithuania: population, habitats and threats

Abstract

A previously unrecorded native species, Scirpus radicans (Cyperaceae), was discovered in the southern part of Lithuania in 2020. Although this species has a large distribution area in other parts of Eurasia, it is currently recognised as threatened in many European countries. Recordings of S. radicans in Lithuania had been expected, as these plants do occur or have been reported to occur in neighbouring regions. The aim of this study was to analyse the distribution of S. radicans in southern Lithuania, to determine the occupied areas and the size of populations, to study their capacity of vegetative reproduction, their habitats and associated plant communities, as well as to perform an assessment of the species' conservation status within the country. We studied S. radicans populations at two sites on the shores of Lake Pabezninkai and of Lake Netečius in the Varėna District (southern Lithuania), from August to October 2020. A total of 993 individuals of S. radicans were counted and their stands comprised 0.73 ha. The density of individuals in the studied plots ranged from 0.02 to 0.78 plants/m2. Only 0.5% of individuals at Lake Pabezninkai and 20.7% of individuals at Lake Netečius were at the stage of generative reproduction. Individuals at the stage of vegetative reproduction comprised 56.4%, whereas generative individuals amounted to 1.7% of all studied plants. One to seven stolons developed per plant and the mean number of rosettes per stolon was 2.8 ± 1.2. Potentially, a total of ca. 2860 rosettes could be expected from all individuals of the studied plots, but the actual realised rate of vegetative reproduction is unknown. A more detailed study of the reproductive capacities of S. radicans would be required for better understanding the causes of the lately observed decrease of this species in most of the countries of Central Europe. Our analysis of the associated plant communities has enabled us to confirm the presence of a Scirpetus radicantis Nowiński 1930 association previously not recorded in Lithuania. By assessing S. radicans in accordance with the IUCN Criteria, we conclude that this species should be classified as endangered (EN) in Lithuania. Based on this assessment, we propose to include this species on the list of legally protected species of Lithuania. Conservation of shallow lakes with sandy or muddy shores and with significant natural fluctuations of the water level is the main measure for ensuring the survival of S. radicans, as well as other rare and endangered species adapted to such a type of habitat.

Study on the Rare Semiaquatic Plant Elatine hydropiper (Elatinaceae) in Lithuania: Population Density, Seed Bank and Conservation Challenges

“…The lowest abundance of this species was found in the communities of Scirpetum radicantis Noviński 1930. These communities were recorded for the first time in Lithuania on the shores of this lake [35]. The occurrence of Scirpetum radicantis communities once again confirms the uniqueness and nature conservation value of this natural lake.…”

“…During investigations in southern Lithuania in 2020, we found a large and abundant population of Elatine hydropiper on the exposed shores of Lake Pabezninkai (Varėna district), where Scirpus radicans and Eleocharis ovata, previously unreported in the country, and several other protected plant species were found [35,36]. The discovery of the Elatine hydropiper population in Lake Pabezninkai and its shores prompted us to perform detailed studies with the aim of determining the status of the population and assessing its potential for long-term survival.…”

“…There are periodic fluctuations in water level. At the time of the lowest water level (by 1.5-1.6 m), the area of the lake decreases to 38.2 ha, exposing sandy or silty plains 30-80 m wide [35]. The water in the lake is brownish, with mean transparency of 0.87 ± 0.15 m (Secchi disk), with low concentration of dissolved minerals (con- ductivity 43 ± 4 µs cm −1 ) at pH 6.13 ± 0.4 [39].…”

“…Such communities are mostly found in fish-ponds, and Elatine hydropiper is sometimes referred to as a specific species of fishpond [56]. It should be added that Eleocharis ovata, a characteristic species of the Polygono-Eleocharitetum ovatae association, was also found in Lake Pabezninkai for the first time in Lithuania [35,36]. As the water level in Lake Pabezninkai has receded by about 1.5-1.6 m over the last four years, Elatine hydropiper was found in communities of different developmental stages.…”

“…There are no clear signs of pollution of Lake Pabezninkai at the present time, but until 1990 the lake was affected by pollution from nearby livestock farms. Despite the former pollution, the lake bottom sediments are not rich in nutrients, as the tall helophytes (Phragmites australis, Typha latifolia) grow fragmentary on the shores and the nitrophilous plants (Bidens, Persicaria) are scarce on the wet exposed shores [35,36].…”