Acta Palaeobotanica 50(1): 65–76, 2010 Holocene history of Cladium mariscus (L.) Pohl in the Czech Republic. Implications for species population dynamics and palaeoecology PETR POKORNÝ 1, JIŘÍ SÁDLO 2 and ALEX BERNARDOVÁ 3 1 Institute of Archaeology, Academy of Sciences of the Czech Republic, Letenská 4, CZ-118 01 Praha, Czech Republic; e-mail: [email protected]; 2 Institute of Botany, Academy of Sciences of the Czech Republic, CZ-252 43, Průhonice, Czech Republic; e-mail: [email protected]; 3 Department of Botany, Faculty of Science, University of South Bohemia, Branišovská 31, CZ-370 05, České Budějovice, Czech Republic; e-mail: [email protected] Received 6 October 2009; accepted for publication 22 April 2010 ABSTRACT. The occurrence of Cladium mariscus (L.) Pohl (Cyperaceae), a rare species in the Czech Republic, is often considered a relict of earlier phases of the Holocene. Hitherto its relict status had only been assumed, based on analogies from other European countries. We confi rm this assumption to a high degree, based on palae obotanical fi nds. We argue that local occurrences of C. mariscus in the Czech Republic can be considered as part of an independent meta-population surviving over the entire Holocene, rather than a component of meta- populations stretching from other parts of Europe where the species is more common. In the Czech Republic Cladium mariscus has so far been found at 11 modern localities and at 5 fossil sites as macrofossils. Its recent localities are restricted to the last remnants of fen mires in the middle course of the Labe (Elbe) River, whereas the fossil sites occupy a much broader area. Also habitats for the species were more diverse during the past. The ecological strategies of C. mariscus are rather similar in the short-term perspective, as well as on a millennial scale. The species is a strong competitor forming in optimal conditions compact and uniform stands. Its clonal populations easily overcome the effect of weak or short-term disturbances such as mowing or burning. Although the occurrence of C. mariscus is centred on fens and fen swamps, the plant is not strictly calciphilous; rather it requires dissolved salts suppressing the accessibility of other nutrients. The spread of the species is considerably limited by its ineffi cient dispersal of fruits and low survival ratio of seedlings. The clear ability of C. mariscus to persist in existing localities is in sharp contrast with its diffi culties in colonizing new habitats. Moreover, parental populations are rare and poor at present in the Czech Republic – for this reason the species cannot still keep up with the changing patterns of appearance/disappearance of vacant sites suitable for colonization and growth of the species. KEYWORDS: pollen analysis, plant survival strategies, plant macrofossils, species extinctions, refuges, relic species, wetland palaeoecology, Czech Republic INTRODUCTION Great fen sedge, Cladium mariscus (L.) Pohl the Czech Republic, since the onset of botani- (Cyperaceae) is a rhizomatous and stoloniferous cal research in the fi rst half of the 19th century, graminoid forming tall and dense stands. It is the species has been already considered as very generally considered as a heliophilous and cal- rare. Now it is listed in the Red Data List of Vas- ciphilous plant of marshy fens (Conway 1942, cular Plants under “critically threatened taxa” Oberdorfer 1977, Buczek 2005). With the excep- (Holub & Procházka 2000) and its community tion of the arctic zone, the species is distributed (Cladietum marisci Zobrist 1935) is protected over the whole of Europe, but generally it seems as a Prirority Habitat according to EU Natura to be in full retreat at present (Hegi 1980). In 2000 legislation (Šumberová et al. 2001). 66 This paper aims to contribute to an under- 0.3% safranine and mounted in a glycerol-water (1:1) standing of the Holocene dynamics of the spe- mixture. In each sample at least 700 pollen grains cies using the examples from its occurrence in were counted. For pollen identifi cation a reference col- lection and the following keys were used: Beug (2004); the Czech Republic. Our palaeo- and actuo- Faegri & Iversen (1989); and Moore et al. (1991). Pollen ecological analyses focus on a study of long- nomenclature follows ALPADABA (Alpine Palynologi- term succession in fen mire habitats, with cal Data-Base), located at the Institute of Plant Sci- a special emphasis on plant survival strate- ences, Bern. According to some published keys (Moore et al. 1991, Beug 2004), Cladium mariscus pollen can gies. Until recently, records of fossil occur- be distinguished from other Cyperaceae pollen by the rences have been almost lacking in the region, presence of a fi nger-like projection on the pollen grain. with the exception of an indirect reference to According to our observations in reference pollen mate- data of Rudolph (Anonymous 1925) and a fi nd rial, this can also be a feature, unfortunately, of other published by Čulíková (1999). Using data from Cyperaceae pollen grains. We think, therefore, that pollen records themselves cannot be used as a defi ni- our (sub)recent population and palaeoecologi- tive proof of Cladium mariscus local fossil presence cal analyses, we propose some general hypoth- and that macrofossil fi nds of the species are necessary eses on the long-term dynamics of the species for a defi nite proof of local occurrence of the species. occurring in small-scale, ecologically-extreme Chemical analyses were performed in the Czech habitats. We recognize that such long-term Geological Institute in Prague (analyst: J. Veselý). Total concentrations of metals were determined by fl ame dynamics during the Holocene are somewhat atomic absorption spectroscopy (FAAS) or by volumet- separated from the more short-term perspec- ric titration (Al) after mineralization of homogenized tives of ‘recent’ population biology focused on samples with H2SO4, HNO3, and HF (200°C, 2 hours). a scale of months to tens of years. Total sulphur was determined by the Eschka method (ISO 334 International Standard). Silica concentration was calculated as the difference between 100% and the sum of all measured elements expressed as oxides. MATERIAL AND METHODS After subsampling for other analyses (pollen, sedi- ment chemistry), the remaining material was used for The paper is mostly based on a palaeoecological an investigation of plant macroremains: contiguous investigation of the valley-bottom fen mire Zahájí 10cm-long samples were cut and the volume of each situated in the lower Ohře River Basin (50°22′43″N, determined. Macrofossils were extracted by sieving 14°06′57″E; Fig. 1). The pollen and macrofossil record with running water, using sieves of mesh sizes 200 μm, from this site covers about the last 5000 years with- 300 μm and 700 μm. The residue was examined under out any apparent hiatus. The present local climate a dissecting stereomicroscope. For determination of of the site is relatively warm, dry, and continental macrofossils, a reference collection of seeds and fruits (8.3°C mean annual temperature, 496 mm mean and a published keys (Kats et al. 1965, Cappers et annual precipitation), as a result of its low elevation al. 2006) were used. The plant nomenclature used is (190 m a.s.l.) and its position under an orographic rain according to Flora Europaea (Tutin et al. 1964–1980). shadow. The site’s surroundings have been densely The numbers of macrofossil fi nds were recalculated to and continuously populated since at least the Neolithic a standard sediment volume of 300 ml. period (according to the regional component in the pol- len diagram and to regional large-scale archaeological investigations; Kuna 1998, Pokorný 2005). RESULTS The results of palaeoecological analyses of the stud- ied fossil record have given a complex picture of the development of vegetation in the surrounding region, PAST AND PRESENT DISTRIBUTION and these data have been published separately (Poko- OF CLADIUM MARISCUS rný 2004, 2005). The present article is devoted solely IN THE CZECH REPUBLIC to the interpretation of the Cladium mariscus macro- fossil fi nds at this site, so those interested in questions The sites of past and present distribution of of the exact absolute dating of the profi le, regional Cladium mariscus are shown together in Fig- vegetation development, chronology of human impact, ure 1. They form a closed area that is limited to etc., should consult the above-mentioned articles. soft carbonaceous sediments of Mesozoic age in Sediment sampling for pollen, sediment chemis- try and macroremains analyses were performed from the Central Bohemian Basin at altitudes under an open pit (profi le depth from 0 to 280 cm) and by 300 m a.s.l. The nearest neighbouring recent a Russian-type chamber-coring device (Jowsey 1966) localities lie at a distance of some 150–200 km from 280 cm to the bottom (570 cm). in eastern and southern Germany, Austria and Samples for pollen analyses were treated by acetol- Poland (Benkert et al. 1998, Haeupler et al. ysis. As most sediment contained some mineral parti- cles, the samples were pre-treated with concentrated 1988, Schönfelder et al. 1990, Zając & Zając (35%) cold hydrofl uoric acid (HF) for 24 hours (Moore 2001, Gałka et al. 2007). The characteristics of et al. 1991). Extracted microfossils were stained with individual sites in the Czech Republic and the 67 Fig. 1. Recent and historical occurrence (small star) and macrofossil fi nds (triangle) of Cladium mariscus on a map of the Bohemian Basin. Fossil sites are named chronologies of C. mariscus local populations layers near Lázně Bělohrad (eastern Bohemia, are listed in Appendix 1. see Fig. 1). This reference was only marginal For recent or subrecent localities, we have and the fi nd had been almost completely for- ascribed the beginning of the occurrence either gotten for more than 70 years.