Population demography of rare sedges (Eriophorum gracile and Carex livida) north of the Arctic Circle in Murmansk Region and climate change impacts

Abstract

Species of Cyperaceae are little studied on the population level globally. Also in Murmansk Region, species from this family were not included in long-term population studies of rare plant species whereas other representatives from 21 families were put in [Blinova, 2009]. Experimental works with sedges is often neglected because of taxonomic difficulties and a lack of methods for study populations of this group [Kitamura et al., 2016; Sosnovska, Danylyk, 2017]. Such difficulties became obvious while the IUCN-red data book testing. Of rare sedges studied in this paper Eriophorum gracile is included in the regional Red data book [Kozhin, 2014] and Carex livida is in the Appendix of this book in the group Need of monitoring. 
 
 The Murmansk Region (6670 N), located in the north-eastern corner of Russian Fennoscandia, is a part of the Atlantic-Arctic zone of temperate belt with a rather mild climate. The region is very heterogeneous. Two latitudinal vegetation zones can be distinguished: tundra and taiga. So, many boreal plant species reach here their northern limit of distribution. Our field work has been conducted in the center part of the region in a recently found rich fen [Blinova, Petrovskij, 2014]. Both study species (Eriophorum gracile и Carex livida) have circumpolar distribution in wetlands of northern hemisphere [Hulten, Fries, 1986], and they are at the northern range in Murmansk Region [Kuzeneva, 1954; Chernov, 1954]. They are polycarpic perennials. An annual shoot has been selected as a counting unit (Fig. 1). In E. gracile only the number of generative shoots has been counted in the field. For non-destructive purposes, from herbarium data, the ratio between generative and vegetative shoots was defined as 1:1. The total population size for this species has been estimated from this ratio. In population of C. livida, the direct counting in the field has been done on 3-5 small plots (0.25*0.25 м2). Lately this value has been recalculated according to the area of population subset. Clusters and subsets have been distinguished in population structure according to suggested aggregation patterns of spatial structure in local plant populations [Blinova, 2018]. Marked population subsets have been monitored several times in the growing period in 2014-2016 years. In the field the boundaries and areas of rich fen and populations (including subsets) have been estimated with the help of GPS navigation device Garmin Dakota 20, in the lab all data are further processed using Garmin Software BaseCamp 4.2.5. Nomenclature for vascular plants is given according to S. K. Czerepanov [1995], for mosses after M. S. Ignatov O. M. Afonina [1992]. 
 
 Our results show that extremely low (0.2% for Eriophorum gracile) and relatively low (3.1% для Carex livida) population cover is characteristic for a large long-term monitored fen. Spatial aggregation of E. gracile population is structured on very small area (40 м2) whereas C. livida is established on relatively representative area (633 м2). E. gracile develops small population subsets (8 m2 on average) at a distance to next about 70 m in different parts of rich fen. Each such subset contains 9-10 mature individuals on average. C. livida has larger subsets (211 m2 on average) at 30 m away from the neighbor. The size of each subset makes c. 2500 generative shoots. The spatial population pattern of E. gracile shows isolated subsets with single clusters, whereas of C. livida represents isolated subsets with merged clusters. High fluctuations of population size and its subsets are revealed in E. gracile from year to year. The number of generative shoots and air temperature in the growing season (June-September) of the current year establish negative relationship.
 
 This study in one of the northernmost populations of Eriophorum gracile confirms other data from different parts of its distribution area that populations of this species are very fragmented and show high fluctuations in the number of generative shoots [Barr 1996; Ksermann, Moser, 1999; Dickenmann, Keel, 2004; Decker et al., 2006; Chatters, Sanderson, 2014]. An analysis of spatial structure of populations has been pointed out that anemochory of E. gracile could be a bottleneck for the population fitness in rich fens conditions, whereas baro- and hydrochory of C. livida promotes further seed germination and survival. Additionally, current climate-changed impacts could cause an extirpation of E. gracile from floristic composition of rich fens, whereas such a threat is minimal for C. livida. Both species need regional protection of their populations. An introduction into culture is essential for further ontogenetic studies and trigger examination of clonal division of labor.