| 1. |
- Ballesteros-Cánovas, Juan Antonio, et al.
(författare)
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Estimation of recent peat accumulation with tree saplings
- 2022
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Ingår i: Progress in Physical Geography. - : SAGE Publications. - 0309-1333. ; 46:4, s. 515-529
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this paper is to develop an approach to estimate peat accumulation rates (PAR) over recent decades based on the age and burial depths of roots from pine sapling and to use the newly developed approach to estimate spatial variations of PAR. To this end, we sampled 120 pine saplings growing in three plots at Rėkyva peatland in Lithuania and accounted for the microtopography around each specimen. In the lab, all saplings were cut into 1-cm segments, sanded and analysed. The counting of annual rings allowed dating the germination of each sapling with a yearly resolution and thus also enabled estimation of peat accumulation. The latter was derived by measuring the distance from the original root collar at germination to the ground level (or peat surface) at the time of sampling. The large number of samples selected from three plots also enabled determination of spatial variations in PAR. We obtain averaged PAR values of 1.6 ± 0.72 cm yr−1 across the three plots and over the last decades, but also observe strong spatial heterogeneity in PAR resulting from differences in local hydrology and vegetation. To validate the results, we compared tree-ring derived PAR with radiocarbon-based (14C) estimates at one of the plots. The results are consistent between the two approaches with PAR estimated to 0.8 and 0.79 cm yr−1, respectively, over the last 20 years. We conclude that PAR can be assessed accurately with tree-ring approaches and that they have clear advantages over radiocarbon dating for shorter timescales as they can be replicated more easily. For longer timescales and larger depths (> 15 cm), however, 14C dating remains the preferred approach.
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| 2. |
- Blanchet, Guillaume, et al.
(författare)
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Impacts of regional climatic fluctuations on radial growth of Siberian and Scots pine at Mukhrino mire (central-western Siberia)
- 2017
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Ingår i: Science of the Total Environment. - : Elsevier BV. - 1879-1026 .- 0048-9697. ; 574, s. 1209-1216
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Tidskriftsartikel (refereegranskat)abstract
- Ring width (TRW) chronologies from Siberian (Pinus sibirica) and Scots (Pinus sylvestris) pine trees were sampled at Mukhrino - a large mire complex in central-western Siberia - to evaluate the impacts of hydroclimatic variability on tree growth over the last three centuries. For this purpose, we compared climate-growth correlation profiles from trees growing on peat soils with those growing on adjacent mineral soils. Tree growth at both peat and mineral soils was positively correlated to air temperature during the vegetation period. This finding can be explained by (i) the positive influence of temperature on plant physiological processes (i.e. growth control) during the growing season and (ii) the indirect impact of air temperatures on water table fluctuations. We observe also a strong link between TRW and the winter Palmer Drought Severity Index (PDSI), especially in Siberian pine, reflecting the isolating effect of snow and limited freezing damage in roots. Significant negative relations were, by contrast, observed between bog TRW chronologies and hydroclimatic indices during spring and summer; they are considered an expression of the negative impacts of high water levels and moist peat soils on root development. Some unusually old bog pines - exhibiting >500 growth rings - apparently colonized the site at the beginning of the Little Ice Age, and therefore seem to confirm that (i) peat conditions may have been drier in Siberia than in most other regions of western Europe during this period. At the same time, the bog trees also point to (ii) their strong dependence on surface conditions.
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| 3. |
- Büntgen, Ulf, et al.
(författare)
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The influence of decision-making in tree ring-based climate reconstructions
- 2021
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 12
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Tidskriftsartikel (refereegranskat)abstract
- Tree-ring chronologies underpin the majority of annually-resolved reconstructions of Common Era climate. However, they are derived using different datasets and techniques, the ramifications of which have hitherto been little explored. Here, we report the results of a double-blind experiment that yielded 15 Northern Hemisphere summer temperature reconstructions from a common network of regional tree-ring width datasets. Taken together as an ensemble, the Common Era reconstruction mean correlates with instrumental temperatures from 1794–2016 CE at 0.79 (p < 0.001), reveals summer cooling in the years following large volcanic eruptions, and exhibits strong warming since the 1980s. Differing in their mean, variance, amplitude, sensitivity, and persistence, the ensemble members demonstrate the influence of subjectivity in the reconstruction process. We therefore recommend the routine use of ensemble reconstruction approaches to provide a moreconsensual picture of past climate variability.
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| 4. |
- Edvardsson, Johannes, et al.
(författare)
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A multi-proxy reconstruction of moisture dynamics in a peatland ecosystem : A case study from Čepkeliai, Lithuania
- 2019
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Ingår i: Ecological Indicators. - : Elsevier BV. - 1470-160X. ; 106
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Tidskriftsartikel (refereegranskat)abstract
- In this study, six approaches were used to characterize hydrological changes in the Čepkeliai wetland complex (southeast Lithuania), namely (i) local water-table measurements (WTM), (ii) testate amoebae analysis, (iii) tree-ring width (TRW) series, (iv) peat stratigraphic data, (v) (hydro-) meteorological data (precipitation and river runoff), and (vi) a diachronic analysis of aerial photographs as well as historical maps. This multi-proxy framework provides complementary information on the hydrological evolution of the peatland and offers a unique opportunity to discuss the pros and cons of each approach. Local water-table measurements, for example, generated monthly resolved and precise (±0.01 m) hydrological information, but were limited to a 16-year period. On the other hand, the TRW data generated annually-resolved information linked to hydrological shifts over the period 1848–2018, but did not allow reconstruction of the amplitude of hydrological variations. Amongst the proxy records, the testate amoebae distribution is the only approach that gives a direct measurement of changes in water-table depths. At the same time, the approach is limited by chronological inaccuracies and weaker resolutions, similar to peat stratigraphic records. The meteorological data are theoretically representing the most highly resolved records. However, due to hydrological lags and feedbacks in peatlands, it was difficult to link regional changes observed in meteorological records to local changes in the peatland. The aerial photographs and historical maps offered an opportunity to document large-scale vegetation changes, which is useful for upscaling local results, but they may not capture rapid changes. Despite all these limitations, at Čepkeliai, most of the proxy records are in agreement with each other and suggest relatively moist conditions with water levels close to the peat surface during the late 1800s and early 1900s, followed by more detailed information towards the present showing shifts towards drier peat surface conditions during the 1930s and 1940s. The 1960s were dry, followed by a short, moist episode during the 1970s, and returning to drier conditions during the 1980s. A gradual change towards moister conditions was recorded over the 1990s and 2000s. The last decade in our records started with relatively wet conditions to end with lower water levels over the most recent years.
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| 5. |
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| 6. |
- Edvardsson, Johannes, et al.
(författare)
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Late-Holocene vegetation dynamics in response to a changing climate and anthropogenic influences – Insights from stratigraphic records and subfossil trees from southeast Lithuania
- 2018
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 185, s. 91-101
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Tidskriftsartikel (refereegranskat)abstract
- To increase our understanding of long-term climate dynamics and its effects on different ecosystems, palaeoclimatic and long-term botanical reconstructions need to be improved, in particular in underutilized geographical regions. In this study, vegetation, (hydro)climate, and land-use changes were documented at two southeast Lithuanian peatland complexes – Čepkeliai and Rieznyčia – for the Late-Holocene period. The documentation was based on a combination of pollen, plant macrofossils, peat stratigraphic records, and subfossil trees. Our results cover the last two millennia and reveal the existence of moist conditions in Southern Lithuania between 300 and 500 CE and from 950 to 1850 CE. Conversely, changes towards warmer and/or dryer conditions have been recorded in 100, 600, and 750 CE, and since the 1850s. Significant differences with other Baltic proxies prevent deriving a complete and precise long-term reconstruction of past hydroclimatic variability at the regional scale. Yet, our results provide an important cornerstone for an improved understanding of regional climate change, i.e. in a region for which only (i) few detailed palaeobotanical studies exist and which has, in addition, been considered as (ii) an ecologically sensitive region at the interface between the temperate and boreal bioclimatic zones.
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| 7. |
- Edvardsson, Johannes, et al.
(författare)
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Periodicities in mid- to late-Holocene peatland hydrology identified from Swedish and Lithuanian tree-ring data
- 2016
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 137, s. 200-208
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Tidskriftsartikel (refereegranskat)abstract
- Twenty-five tree-ring width (TRW) chronologies, developed from moisture sensitive peatland trees in Sweden and Lithuania, and representing eight periods during the mid-Holocene to present, were analysed regarding common periodicities (cycles). Periods of 13e15, 20e22, and 30e35 years were found in most chronologies, while 8e10, 18e19, and 60e65 year periodicities were observed as well, but less commonly. Similar periodicities, especially about 15 and 30 years in duration, were detected in both living and subfossil trees, indicating that the trees have responded to similar forcing mechanisms on those timescales through time. Some of the detected periods may be related to solar variability and lunar nodal tides, but most of the detected periodicities are more likely linked to hydrological changes in the peatlands associated to atmospheric patterns such as the North Atlantic Oscillation (NAO), or variations in sea surface temperatures (i.e. the Atlantic Multidecadal Oscillation, AMO). However, no significant relationships between tree growth, NAO and AMO could be formally established, possibly due to hydrological lag and feedback effects which are typical for peatlands but render in-depth assessments rather difficult.
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| 8. |
- Rimkus, Egidijus, et al.
(författare)
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Scots pine radial growth response to climate and future projections at peat and mineral soils in the boreo-nemoral zone
- 2019
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Ingår i: Theoretical and Applied Climatology. - : Springer Science and Business Media LLC. - 0177-798X .- 1434-4483. ; 136:1-2, s. 639-650
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Tidskriftsartikel (refereegranskat)abstract
- This paper aims to study what influence different meteorological parameters have on the radial tree growth of Scots pine (Pinus sylvestris L.) in peat and mineral soils, as well as to make predictions of radial tree growth responses to changing climate based on various future climate projections. Four Lithuanian peatland complexes representing different geographical settings and hydrological conditions were studied. From each study site, two tree-ring width (TRW) series were derived, one from trees growing on peat soil and one from trees on mineral soil at the periphery of the peatland. The annual growth rings from trees grown on mineral soils, in different geographical regions in Lithuania, show synchronicity, whereas the correlation between the TRW series from different peatland sites was weak to absent. The main factor that explains radial tree growth at the mineral-soil sites was air temperature during early spring (February–March), which influences the onset and duration of the growing season. However, variations in radial tree growth on the peatland sites were also attributed to lagged hydrological responses relating to precipitation and evaporation over several years. Our future projections show that growth conditions for pine trees on mineral soils will improve in the twenty-first century in Lithuania following an increase of air temperature in early spring. The predictions for the trees growing on peat soils, however, rely on the groundwater-level changes governed by a combination of precipitation and evaporation changes. Towards the end of the twenty-first century, the groundwater level in most Lithuanian peatlands is expected to increase, which most likely will result in harsher growth conditions for the peatland trees. This assumption is, however, open for debate as the peatland trees appear to favour the current warming conditions. It may therefore be too early to precisely predict future growth responses for the peatland trees, but this study is a next step to better understand future climate dynamics and vegetation responses in the Baltic region.
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| 9. |
- Stančikaite, Migle, et al.
(författare)
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Holocene vegetation and hydroclimatic dynamics in SE Lithuania - Implications from a multi-proxy study of the Čepkeliai bog
- 2019
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Ingår i: Quaternary International. - : Elsevier BV. - 1040-6182. ; 501, s. 219-239
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Tidskriftsartikel (refereegranskat)abstract
- Due to the scarcity of reliable palaeoecological and climatic proxy records from the Eastern Baltic covering the Holocene, there has been increased interest for multi-proxy studies in the region to detect local to regional environmental changes. The Čepkeliai wetland complex, SE Lithuania, provides an uninterrupted Holocene sediment sequence, which is used here to reconstruct palaeoenvironmental history in the southern part of the Eastern Baltic. High-resolution lithological (LOI, magnetic susceptibility), palaeobotanical (pollen, plant macrofossil, tree rings), isotopic (14C) and geochemical data were employed to reconstruct the peculiarities of vegetation and hydroclimate dynamics, as well as to discuss results in a local to regional context. Temporal lags of environmental reactions to Holocene climatic warming were recorded both in lithostratigraphical and biostratigraphical data, thus confirming regional significance of this phenomenon. A deep meso- to eutrophic basin - influenced by high surface runoff and surrounded by early boreal forest - existed at the site until about 11,300 cal BP. Thereafter, immigration of thermophylous taxa such as Ulmus (since 10,700-10,800 cal BP), Corylus (since 10,400-10,300 cal BP), Tilia and Quercus (after 9500 cal BP) as well as changes in the limnic environment point to an amelioration of the environmental situation, i.e. to a predominance of a warm and dry climatic regime. Instability of palaeobotanical and lithological records suggests that environmental anomalies of the Early Holocene occurred at about 11,200-11,000 cal BP, 10,600-10,300 cal BP, and 8200-7800 cal BP. These anomalies are thus contemporaneous with the pronounced climatic shifts (i.e. dry and cool intervals) known at the continental scale. An expansion of Picea was facilitated by the 8200-7800 cal BP climatic shift whereas early establishment of Alnus glutinosa suggests an onset of a wet interval (10,200 cal BP) which was previously unknown in the area. The stepwise lowering of the water table noted at about 7300-7200 and 6600-6700 cal BP, with the termination of the lake-phase and change to telmatic environment after 6100 cal BP, proves the positive reaction of the site to the dry climatic reversals of the Middle Holocene. Following the decay of the broad-leaved thermophilous forest after 4500 cal BP, a cold climatic reversal favored the formation of a diverse mosaic-like vegetation which was then replaced by homogenous Pinus-Picea vegetation after 3400 cal BP. The climatic and site-specific factors have been playing a leading role in the development of the site whereas signals of human interference remain negligible.
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| 10. |
- Taminskas, Julius, et al.
(författare)
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Combining multiple proxies to investigate water table fluctuations in wetlands : A case study from the Rėkyva wetland complex, Lithuania
- 2019
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Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182. ; 514, s. 453-463
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Tidskriftsartikel (refereegranskat)abstract
- The impact climate and land-use changes have on the hydrological conditions in peat bogs and lakes is often complex, but of great importance for the carbon budget and biodiversity in these ecosystems. Links and feedbacks between raised bog water table depth, lake level, net precipitation, hydrometeorological indices, and radial tree growth have been studied and identified in the Rėkyva wetland complex, Lithuania. Moreover, several statistically significant correlations between raised bog water table depths, lake level, local river runoff, and tree growth were observed. The changes of raised bog water table, lake level, and tree growth show synchronous trends despite variations in the absolute values. Our results show decreasing water table in the Rėkyva wetland complex over the last 100 years, especially in the middle of the 20th century. This study also shows a potential for reconstructing water table fluctuations in wetland complexes using multi-indicator approaches. Our observations and reconstruction show consistency with several regional studies and reconstructions of moisture variations in Baltic raised bogs, at least for periods without strong anthropogenic influences.
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| 11. |
- Tamkevičiūtė, Marija, et al.
(författare)
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Scots pine (Pinus sylvestris L.) based reconstruction of 130 years of water table fluctuations in a peatland and its relevance for moisture variability assessments
- 2018
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Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694. ; 558, s. 509-519
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Tidskriftsartikel (refereegranskat)abstract
- Continuous water-table (WT) measurements from peatlands are scarce and – if existing at all –very short. Consequently, proxy indicators are critically needed to simulate hydrological changes in peatlands over longer time periods. In this study, we demonstrate that tree-ring width (TRW) records of Scots pine (Pinus sylvestris L.) growing in the Čepkeliai peatland (southern Lithuania) can be used as a proxy to reconstruct hydrological variability in a raised bog environment. A two-step modelling procedure was applied to extend existing measurements and to develop a new and longer peatland WT time series. To this end, we used instrumental WT measurements extending back to 2002, meteorological records, a P-PET (difference between precipitation and potential evapotranspiration) series covering the period 1935–2014, so as to construct a tree-ring based time series of WT fluctuations at the site for the period 1870–2014. Strongest correlations were obtained between average annual WT measured at the bog margin and total P-PET over 7 years (r = 0.923, p < 0.00001), as well as between modelled WT and standardized TRW data with a two years lag (r = −0.602, p < 0.001) for those periods where WT fluctuated at the level of pine roots which is typically at <50 cm depth below the peat surface. Our results suggest that moisture is a limiting factor for tree growth at peatlands, but below a certain WT level (<50 cm under the soil surface), drought becomes a limiting factor instead. To validate the WT reconstruction from the Čepkeliai bog, results were compared to Nemunas river runoff since CE 1812 (r = 0.39, p < 0.00001, 1870–2014). We conclude that peatlands can act both as sinks and sources of greenhouse gases in case that hydrological conditions change, but that hydrological lags and complex feedbacks still hamper our understanding of several processes affecting the hydrology and carbon budget in peatlands. We therefore call for the development of further proxy records of water-table variability in peatlands to improve our understanding of peatland responses to climatic changes.
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