Enikő Magyari

Population dynamics and genetic changes of Picea abies in the South Carpathians revealed by pollen and ancient DNA analyses

BackgroundStudies on allele length polymorphism designate several glacial refugia for Norway spruce (Picea abies) in the South Carpathian Mountains, but infer only limited expansion from these refugia after the last glaciation. To better understand the genetic dynamics of a South Carpathian spruce lineage, we compared ancient DNA from 10,700 and 11,000-year-old spruce pollen and macrofossils retrieved from Holocene lake sediment in the Retezat Mountains with DNA extracted from extant material from the same site. We used eight primer pairs that amplified short and variable regions of the spruce cpDNA. In addition, from the same lake sediment we obtained a 15,000-years-long pollen accumulation rate (PAR) record for spruce that helped us to infer changes in population size at this site.ResultsWe obtained successful amplifications for Norway spruce from 17 out of 462 pollen grains tested, while the macrofossil material provided 22 DNA sequences. Two fossil sequences were found to be unique to the ancient material. Population genetic statistics showed higher genetic diversity in the ancient individuals compared to the extant ones. Similarly, statistically significant Ks and Kst values showed a considerable level of differentiation between extant and ancient populations at the same loci.Lateglacial and Holocene PAR values suggested that population size of the ancient population was small, in the range of 1/10 or 1/5 of the extant population. PAR analysis also detected two periods of rapid population growths (from ca. 11,100 and 3900 calibrated years before present (cal yr BP)) and three bottlenecks (around 9180, 7200 and 2200 cal yr BP), likely triggered by climatic change and human impact.ConclusionOur results suggest that the paternal lineages observed today in the Retezat Mountains persisted at this site at least since the early Holocene. Combination of the results from the genetic and the PAR analyses furthermore suggests that the higher level of genetic variation found in the ancient populations and the loss of ancient allele types detected in the extant individuals were likely due to the repeated bottlenecks during the Holocene; however our limited sample size did not allow us to exclude sampling effect.This study demonstrates how past population size changes inferred from PAR records can be efficiently used in combination with ancient DNA studies. The joint application of palaeoecological and population genetics analyses proved to be a powerful tool to understand the influence of past population demographic changes on the haplotype diversity and genetic composition of forest tree species.

A guide to screening charcoal peaks in macrocharcoal-area records for fire-episode reconstructions

Macroscopic charcoal records can be used to infer spatially explicit reconstructions of past fire history. However, a current deficiency in the charcoal-analysis toolbox has been the lack of a method to consider sampling variability and charcoal-particle area distributions for peak detection with charcoal-area records. We present a screening procedure specific for datasets comprising charcoal numbers and areas to screen the charcoal-area estimates with respect to the count sums. The rationale for screening charcoal-area peaks stems from the observation that although charcoal-area records can be more suitable in a statistical sense for peak detection (e.g. as established by the signal-to-noise index), charcoal-area peaks can be questionable if they are determined by just one or a few larger charcoal particles. Our method begins with a charcoal-area time series analysed by existing methods to identify peaks representing fire episodes. To screen these peaks, the method uses bootstrap resampling of charcoal-particle areas observed in a user-defined subsection of the record around each peak to obtain the range of likely charcoal areas for different counts. Peaks with total area within the likely range of bootstrapped samples (e.g. p > 0.05) are flagged as potentially unreliable, whereas samples with total area significantly greater than expected by chance are deemed robust indicators of past fire events. In an example application of the method to a charcoal record from Lake Brazi, Romania, several peaks failed to pass the screening suggesting that, as for count-based records, unscreened charcoal-area records may include spurious fire episodes and thus potentially underestimate past fire-return intervals.

Chironomid-inferred Holocene temperature changes in the South Carpathians (Romania)

We present a Holocene summer air temperature reconstruction based on fossil chironomids from Lake Brazi (1740 m.a.s.l.), a shallow mountain lake in the South Carpathians. Summer air temperature reconstruction was performed using transfer functions based on the Swiss (Sw-TF) and the merged Norwegian–Swiss calibration data set (NS-TF). Our results suggest that summer air temperatures increased rapidly from the onset of the early Holocene onwards (ca. 11,500–10,200 cal. yr BP), reaching close to present July air temperatures (~11.2°C). Between ca. 10,200 and 8500 cal. yr BP mean reconstructed temperatures increased further by 1.5–2.0°C. Later on, from ca. 8500 cal. yr BP, chironomid-based summer temperatures started to decrease, although mean values were still above present-day temperatures. The next time period (ca. 6000–3000 cal. yr BP) was cooler and with less variable temperature conditions than earlier. Afterwards (ca. 3000–2000 cal. yr BP), a sharp decrease occurred in inferred temperatures with values under present-day conditions by 1.8°C. Finally, in the last 2000 years, reconstructed temperatures showed again an increasing trend at Lake Brazi. Short-term temperature declines of 0.6–1.2°C were observed between ca. 10,350–10,190, 9750–9500, 8700–8500, 7600–7300, 7100–6900 and 4400–4000 cal. yr BP. These temperature declines are, however, within the estimated error of prediction of the chironomid-based inferences. Generally, our reconstructed temperatures complied with the summer insolation curve at 45°N, with other proxy-records (i.e. pollen and diatoms) from the same sediment and with other records from the Carpathians and from Western Europe.

Review of dated Late Quaternary palaeolimnological records in the Carpathian Region, east-central Europe

The Carpathian Region (including mountains and plains) has for a long time been lacking good palaeoenvironmental and especially palaeolimnological records, particularly for the Late Quaternary. In the last two decades, many new sedimentary sequences were obtained and studied using a wide range of palaeoproxies. This article reviews results from 123 sequences in the Carpathian Region, all dated by radiometric methods. Our aim was to pay attention to the existence of these data; many of them published in national periodicals and journals. Palaeoenvironmental records with at least two proxies and with palaeolimnological interpretation were compiled in both tabular form and on maps. Inspite of the density of examined sites, an assessment of the dataset led us to the following conclusions: (1) very few provide firm hydrological–limnological interpretation, such as lake level and mire water-depth fluctuation, lake productivity changes and pH changes; (2) only 47 of them are real multi-proxy studies (have at least two proxies employed on the same sediment core); (3) glacial lakes in Slovakia and Romania as well as in Ukraine are seriously under-investigated although they would be ideal objects of palaeolimnological works with the many proxies applicable on them; (4) the Hungarian lowland areas are dominated by shallow tectonic lakes or palaeochannels, often with unsatisfactory preservation of certain biological proxies (e.g. diatoms, chironomids, cladocerans). Consequently, palaeolimnological studies from this region have to apply a different combination of proxies and approach than mountain lake studies.

Holocene treeline and timberline changes in the South Carpathians (Romania): Climatic and anthropogenic drivers on the southern slopes of the Retezat Mountains

Two high-altitude lake-sediment sequences (Lake Lia, 1910 m a.s.l. and Lake Bucura, 2040 m a.s.l.) from the Retezat Mountains (South Carpathians, Romania) were analysed using multi-proxy methods to study responses of treeline, timberline and alpine/subalpine vegetation to climate change and human impact during the past 16,000 years. Woody species (Pinus mugo, Pinus cembra, Picea abies and Juniperus communis) reached Lake Lia between 12,000 and 11,800 cal. yr BP, whereas P. mugo colonised the shores of Lake Bucura at 9600 cal. yr BP. Lake Lia was in the timberline ecotone between 8000 and 3200 cal. yr BP, in semi-open P. cembra and Picea abies woodland, probably mixed with P. mugo on the steeper slopes. Lake Bucura was surrounded by the upper part of the krummholz zone during the mid-Holocene. The increase in P. cembra after c. 6000 cal. yr BP around Lake Lia suggests that the composition of the timberline forest changed. The disappearance of P. cembra and Picea abies around Lake Lia at ~3000 cal. yr BP reflects descent of the timberline. A large mean July temperature decline between 3300 and 2800 cal. yr BP may have driven or at least contributed to the descent of the Picea abies–P. cembra forests. An increase in human indicator pollen types in Lake Bucura around 4200 cal. yr BP may reflect human impact in the naturally open alpine zone in the Late Bronze Age. In contrast, human impact likely appeared considerably later, around 2650 cal. yr BP (Early Iron Age) around Lake Lia in the upper subalpine zone. Human impact likely intensified after 2200 cal. yr BP at both sites that resulted in the lowering of the krummholz zone. We conclude that climate change and human impact both played an important role in the lowering of the treeline and timberline in the late-Holocene.

Small-scale moisture availability increase during the 8.2-ka climatic event inferred from biotic proxy records in the South Carpathians (SE Romania)

In this paper, we present high-resolution early Holocene pollen, plant macrofossil, charcoal, diatom, biogenic silica, and loss-on-ignition records from a mountain lake in the South Carpathians in order to reveal ecosystem response to the 8.2-ka climatic oscillation. We found significant changes both in terrestrial vegetation and lake diatom assemblages in the northern slope of the Retezat Mts between c. 8300 and 8000 cal. yr BP. Rapid changes in relative frequencies and pollen accumulation rates of the major deciduous pollen types associated with peaks in microcharcoal accumulation rates suggested that vegetation disturbance mainly took place in the mixed-deciduous forest zone, where woodland fires partially destroyed the populations of Fraxinus excelsior, Quercus, and Corylus avellana and facilitated the establishment of Carpinus betulus in the forest openings. The diatom record furthermore showed the spread of a planktonic diatom species, Aulacoseira valida, at 8150 cal. yr BP, coincidently with a short-lived expansion of C. betulus. Since diatom blooms mainly occur in spring in the Retezat Mts, increased spring water depth and increased water turbulence were inferred from these data. The expansion of C. betulus against F. excelsior and C. avellana at the same time suggested a modest increase in available moisture during the growing season. Taken together, these data imply that during the 8.2-ka event, winter and spring season available moisture increased, while summers were characterized by alternating moist/cool and dry/warm conditions.

Drivers of Holocene treeline and timberline changes in the Retezat Mountains (South Carpathians, Romania)

Four high-altitude lake sediment sequences (Lake Brazi, 1740 m .as.l., Lake Gales 1990 m a.s.l., Lake Bucura, 2040 m a.s.l. and Lake Lia, 1910 m a.s.l.) were analyzed using multi-proxy methods (pollen, stomata, plant macrofossil and micro- and macrocharcoal) in order to study responses of treeline and alpine/subalpine vegetation to climate change and human impact during the last 15000 years. Observing and reconstructing the changes of the position and structure of the treeline can provide valuable information on biotic and other factors such as human activities. Sediment cores were taken from two lakes on the northern slope (Lake Brazi and Lake Gales) and two lakes from the southern slope (Lake Lia and Lake Bucura) in the Retezat Mountains, South Carpathians (Romania).

Fire on ice and frozen trees? Inappropriate radiocarbon dating leads to unrealistic reconstructions

Comment on Carcaillet & Blarquez (2017) ‘Fireecology of a tree glacial refugium on a nunatak with aview on Alpine glaciers’.

Rövid távú koraholocén (8200 év) klímafluktuációk vegetációra gyakorolt hatása a Déli-Kárpátok Retyezát-hegységében

Pál Ilona1* – Magyari Enikõ1 – Finsinger Walter2 – Braun Mihály3 – Pálfy József1 – Molnár Mihály4 – Buczkó Krisztina5 1 ELTE TTK Általános és Alkalmazott Földtani Tanszék, 1117 Budapest Pázmány Péter stny. 1/C. 2 Centre de Bio-Archeologie et d’Ecologie UMR 5059, Montpellier, France. 3 Debreceni Egyetem Szervetlen és Analitikai Kémiai Tanszék, 4032 Debrecen, Egyetem tér 1. Pf. 21. 4 MTA ATOMKI Hertelendi Ede Környezetanalitikai Laboratórium, 4001 Debrecen, Pf. 51. 5 Magyar Természettudományi Múzeum, 1087 Budapest, Könyves Kálmán krt. 40. * E-mail: palilona@caesar.elte.hu Rövid távú koraholocén (8200 év) klímafluktuációk vegetációra gyakorolt hatása a Déli-Kárpátok Retyezát-hegységében A Pécsi Tudományegyetem Földrajzi Intézetéből

The impact of the 8.2 ka rapid climate change event on the vegetation and lake ecosystem of the South Carpathian Mountains, Romania

Our research is based on pollen-based reconstruction of vegetation composition changes in the Shouthern Carpathians in response to rapid climate changes during the Early Holocene. We demonstrated vegetation response in the northern slope of Retezat Mountains focusing on Lake Brazi. Retezat has a particular importance because of its location and different climatic effects that prevail. Our aim was to examine the vegetation response due to climatic oscillations, which occurred during the Early Holocene. We paid particular attention to the climate change occurring 8200 years ago. We used pollen analysis for the Holocene section of the sediment of Lake Brazi. We investigated the sediment section which covers the so called climatic oscillation at higher resolution.