Using testate amoebae to infer Holocene palaeohydrological history in the Northern Carpathians, Romania

We used radiocarbon dating, testate amoebae (TA) and pollen analysis of a peat profile extracted from an ombrotrophic bog (Tăul Muced) located in the Rodna National Park, Romania, to identify major changes in the wet-dry ecological gradient over the last 8000 years. We performed a quantitative reconstruction of the local depth to water table (DWT) and pH variation using the transfer function developed on a Polish modern testate amoebae data set and compared our reconstruction with other palaeohydrological studies in this region. The pollen record was used to determine regional vegetation dynamics as well as the potential impact of humans on peatland dynamic

How Joannites’ economy eradicated primeval forest and created anthroecosystems in medieval Central Europe

During European states’ development, various past societies utilized natural resources, but their impact was not uniformly spatially and temporally distributed. Considerable changes resulted in landscape fragmentation, especially during the Middle Ages. Changes in state advances that affected the local economy significantly drove trajectories of ecosystems’ development. The legacy of major changes from pristine forest to farming is visible in natural archives as novel ecosystems. Here, we present a high-resolution densely dated multi-proxy study covering the last 1500 years from a peatland located in CE Europe. The economic activity of medieval societies was highly modified by new rulers—the Joannites (the Order of St. John of Jerusalem, Knights Hospitaller). We studied the record of these directorial changes noted in the peat profile. Our research revealed a rapid critical land-use transition in the late Middle Ages and its consequences on the peatland ecosystem. The shift from the virgin forest with regular local fires to agriculture correlates well with the raising of local economy and deforestations. Along with the emerging openness, the wetland switched from alkaline wet fen state to acidic, drier Sphagnum-dominated peatland. Our data show how closely the ecological state of wetlands relates to forest microclimate. We identified a significant impact of the Joannites who used the novel farming organization. Our results revealed the surprisingly fast rate of how feudal economy eliminated pristine nature from the studied area and created novel anthroecosystems

Holocene wildfire regimes in forested peatlands in western Siberia: interaction between peatland moisture conditions and the composition of plant functional types

Wildfire is the most common disturbance type inboreal forests and can trigger significant changes in forestcomposition. Waterlogging in peatlands determines the degree of tree cover and the depth of the burnt horizon associated with wildfires. However, interactions between peatland moisture, vegetation composition and flammability, andfire regime in forest and forested peatland in Eurasia remain largely unexplored, despite their huge extent in borealregions. To address this knowledge gap, we reconstructedthe Holocene fire regime, vegetation composition, and peatland hydrology at two sites located in predominantly lighttaiga (Pinus sylvestris Betula) with interspersed dark taigacommunities (Pinus sibirica, Picea obovata, Abies sibirica)in western Siberia in the Tomsk Oblast, Russia. We foundmarked shifts in past water levels over the Holocene. Theprobability of fire occurrence and the intensification of firefrequency and severity increased at times of low water table(drier conditions), enhanced fuel dryness, and an intermediate dark-to-light taiga ratio. High water level, and thus wetpeat surface conditions, prevented fires from spreading onpeatland and surrounding forests. Deciduous trees (i.e. Betula) and Sphagnum were more abundant under wetter peatland conditions, and conifers and denser forests were moreprevalent under drier peatland conditions. On a Holocenescale, severe fires were recorded between 7.5 and 4.5 ka withan increased proportion of dark taiga and fire avoiders (Pinussibirica at Rybnaya and Abies sibirica at Ulukh–Chayakh)in a predominantly light taiga and fire-resister communitycharacterised by Pinus sylvestris and lower local water level.Severe fires also occurred over the last 1.5 kyr and were associated with a declining abundance of dark taiga and fireavoiders, an expansion of fire invaders (Betula), and fluctuating water tables. These findings suggest that frequent,high-severity fires can lead to compositional and structuralchanges in forests when trees fail to reach reproductive maturity between fire events or where extensive forest gaps limitseed dispersal. This study also shows prolonged periods ofsynchronous fire activity across the sites, particularly duringthe early to mid-Holocene, suggesting a regional imprint ofcentennial- to millennial-scale Holocene climate variabilityon wildfire activity. Humans may have affected vegetationand fire from the Neolithic; however, increasing human presence in the region, particularly at the Ulukh–Chayakh Mireover the last 4 centuries, drastically enhanced ignitions compared to natural background levels. Frequent warm and dryspells predicted by climate change scenarios for Siberia inthe future will enhance peatland drying and may convey acompetitive advantage to conifer taxa. However, dry conditions will probably exacerbate the frequency and severityof wildfire, disrupt conifers’ successional pathway, and accelerate shifts towards deciduous broadleaf tree cover. Furthermore, climate–disturbance–fire feedbacks will acceleratechanges in the carbon balance of boreal peatlands and affecttheir overall future resilience to climate chang

Recent climate change has driven divergent hydrological shifts in high-latitude peatlands

A recent synthesis study found 54% of the high-latitude peatlands have been drying and 32% have been wetting over the past centuries, illustrating their complex ecohydrological dynamics and highly uncertain responses to a warming climate. High-latitude peatlands are changing rapidly in response to climate change, including permafrost thaw. Here, we reconstruct hydrological conditions since the seventeenth century using testate amoeba data from 103 high-latitude peat archives. We show that 54% of the peatlands have been drying and 32% have been wetting over this period, illustrating the complex ecohydrological dynamics of high latitude peatlands and their highly uncertain responses to a warming climate.Peer reviewe

Fire hazard modulation by long-term dynamics in land cover and dominant forest type in eastern and central Europe

Wildfire occurrence is influenced by climate, vegetation and human activities. A key challenge for understanding the risk of fires is quantifying the mediating effect of vegetation on fire regimes. Here, we explore the relative importance of Holocene land cover, land use, dominant functional forest type, and climate dynamics on biomass burning in temperate and boreo-nemoral regions of central and eastern Europe over the past 12 kyr. We used an extensive data set of Holocene pollen and sedimentary charcoal records, in combination with climate simulations and statistical modelling. Biomass burning was highest during the early Holocene and lowest during the mid-Holocene in all three ecoregions (Atlantic, continental and boreo-nemoral) but was more spatially variable over the past 3–4 kyr. Although climate explained a significant variance in biomass burning during the early Holocene, tree cover was consistently the highest predictor of past biomass burning over the past 8 kyr. In temperate forests, biomass burning was high at ~ 45% tree cover and decreased to a minimum at between 60% and 70% tree cover. In needleleaf-dominated forests, biomass burning was highest at ~60 %–65%tree cover and steeply declined at > 65% tree cover. Biomass burning also increased when arable lands and grasslands reached ~15 %–20 %, although this relationship was variable depending on land use practice via ignition sources, fuel type and quantities. Higher tree cover reduced the amount of solar radiation reaching the forest floor and could provide moister, more wind-protected microclimates underneath canopies, thereby decreasing fuel flammability. Tree cover at which biomass burning increased appears to be driven by warmer and drier summer conditions during the early Holocene and by increasing human influence on land cover during the late Holocene. We suggest that longterm fire hazard may be effectively reduced through land cover management, given that land cover has controlled fire regimes under the dynamic climates of the Holocene

How warm? How wet? Hydroclimate reconstruction of the past 7500 years in northern Carpathians, Romania

As natural and anthropogenic ecosystems are dependent on the local water availability, understanding past changes in hydroclimate represents a priority in research concerning past climate variability. Here, we used testate amoebae (TA) and chironomid analysis on a radiocarbon dated complex of small pond and peat bog sediment profiles from an ombrotrophic bog (Taut Muced, northern Carpathians, Romania) to quantitatively determine major hydrological changes and July air temperature over the last 7500 years.Wet mire surface conditions with a pH between 23 and 4.5 were inferred for the periods 4500-2700 and 1300400 cal yr BP by the occurrence of Archerella flavum, Amphitrema wrightianum and Hyalosphenia papilio. Dry phases in mire surface conditions and a pH between 2.5 and 5 were inferred for 7550-4500, 2750-1300 and 0 cal yr BP-present by the dominance of Nebela militaris, Difflugia pulex and Phryganella acropodia. The quantitative reconstruction of mean July temperature based on the chironomid communities suggests low summer temperatures for the periods 6550-5600, 4500-3150 and 1550-600 cal yr BP, while periods of slightly higher summer temperatures were observed for 5600-4500,3150-1550 and 100 cal yr BP-present. There is a generally good agreement between drier phases of the peat surface conditions with higher July temperature, suggesting that temperature may have been a controlling factor for water table fluctuation.Our quantitative reconstructions, among the first for central eastern Europe, show a relatively good agreement with other palaeohydrological studies from central eastern Europe, but contrast with others estimates from north-west Europe. Another important aspect of our study is that it provides valuable information on changes in local hydrology and the potential effect of the mean summer temperature over these changes. (C) 2017 Elsevier B.V. All rights reserved

Late Holocene palaeohydrological changes in a \u3ci\u3eSphagnum\u3c/i\u3e peat bog from NW Romania based on testate amoebae

This paper investigates the possibility of reconstructing the palaeohydrological changes in an active Sphagnum peat bog from north-western Romania using testate amoebae fauna and organic matter content determined by loss on ignition (LOI). In total 28 taxa of testate amoebae were identified of which 11 were frequent enough to present a remarkable ecological significance. Based on the relative abundance of these taxa nine zones were identified, crossing from very wet to dry climate conditions. The wet periods identified are characterized by taxa like Centropyxis cassis, Amphitrema flavum and Hyalosphenia papilio, while in the dry periods Difflugia pulex and Nebela militaris thrive. We showed that combining qualitative information regarding hydrological preferences with the quantitative percentage data from the fossil record it is possible to obtain information regarding major surface moisture changes from the peat bog surface. Furthermore we identified a link between distribution of testate amoebae assemblages, organic matter variation and minerogenic material

Late Holocene palaeohydrological changes in a Sphagnum peat bog from NW Romania based on testate amoebae

This paper investigates the possibility of reconstructing the palaeohydrological changes in an active Sphagnum peat bog from north-western Romania using testate amoebae fauna and organic matter content determined by loss on ignition (LOI). In total 28 taxa of testate amoebae were identified of which 11 were frequent enough to present a remarkable ecological significance. Based on the relative abundance of these taxa nine zones were identified, crossing from very wet to dry climate conditions. The wet periods identified are characterized by taxa like Centropyxis cassis, Amphitrema flavum and Hyalosphenia papilio, while in the dry periods Difflugia pulex and Nebela militaris thrive. We showed that combining qualitative information regarding hydrological preferences with the quantitative percentage data from the fossil record it is possible to obtain information regarding major surface moisture changes from the peat bog surface. Furthermore we identified a link between distribution of testate amoebae assemblages, organic matter variation and minerogenic material

How warm? How wet? Hydroclimate reconstruction of the past 7500 years in northern Carpathians, Romania

As natural and anthropogenic ecosystems are dependent on the local water availability, understanding past changes in hydroclimate represents a priority in research concerning past climate variability. Here, we used testate amoebae (TA) and chironomid analysis on a radiocarbon dated complex of small pond and peat bog sediment profiles from an ombrotrophic bog (Taut Muced, northern Carpathians, Romania) to quantitatively determine major hydrological changes and July air temperature over the last 7500 years.Wet mire surface conditions with a pH between 23 and 4.5 were inferred for the periods 4500-2700 and 1300400 cal yr BP by the occurrence of Archerella flavum, Amphitrema wrightianum and Hyalosphenia papilio. Dry phases in mire surface conditions and a pH between 2.5 and 5 were inferred for 7550-4500, 2750-1300 and 0 cal yr BP-present by the dominance of Nebela militaris, Difflugia pulex and Phryganella acropodia. The quantitative reconstruction of mean July temperature based on the chironomid communities suggests low summer temperatures for the periods 6550-5600, 4500-3150 and 1550-600 cal yr BP, while periods of slightly higher summer temperatures were observed for 5600-4500,3150-1550 and 100 cal yr BP-present. There is a generally good agreement between drier phases of the peat surface conditions with higher July temperature, suggesting that temperature may have been a controlling factor for water table fluctuation.Our quantitative reconstructions, among the first for central eastern Europe, show a relatively good agreement with other palaeohydrological studies from central eastern Europe, but contrast with others estimates from north-west Europe. Another important aspect of our study is that it provides valuable information on changes in local hydrology and the potential effect of the mean summer temperature over these changes. (C) 2017 Elsevier B.V. All rights reserved