| 1. |
- Diego Galvan, J., et al.
(författare)
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Drought-induced weakening of growth-temperature associations in high-elevation Iberian pines
- 2015
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Ingår i: Global and Planetary Change. - : Elsevier BV. - 0921-8181 .- 1872-6364. ; 124, s. 95-106
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Tidskriftsartikel (refereegranskat)abstract
- The growth/climate relationship of theoretically temperature-controlled high-elevation forests has been demonstrated to weaken over recent decades. This is likely due to new tree growth limiting factors, such as an increasing drought risk for ecosystem functioning and productivity across the Mediterranean Basin. In addition, declining tree growth sensitivity to spring temperature may emerge in response to increasing drought stress. Here, we evaluate these ideas by assessing the growth/climate sensitivity of 1500 tree-ring width (TRW) and 102 maximum density (MXD) measurement series from 711 and 74 Pinus uncinata trees, respectively, sampled at 28 high-elevation forest sites across the Pyrenees and two relict populations of the Iberian System. Different dendroclimatological standardization and split period approaches were used to assess the high- to low-frequency behavior of 20th century tree growth in response to temperature means, precipitation totals and drought indices. Long-term variations in TRW track summer temperatures until about 1970 but diverge afterwards, whereas MXD captures the recent temperature increase in the low-frequency domain fairly well. On the other hand summer drought has increasingly driven TRW along the 20th century. Our results suggest fading temperature sensitivity of Iberian high-elevation P. uncinata forest growth, and reveal the importance of summer drought that is becoming the emergent limiting factor of tree ring width formation in many parts of the Mediterranean Basin.
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| 2. |
- Esper, Jan, et al.
(författare)
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European summer temperature response to annually dated volcanic eruptions over the past nine centuries
- 2013
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Ingår i: Bulletin of Volcanology. - : Springer Science and Business Media LLC. - 0258-8900 .- 1432-0819. ; 75:7, s. 736-
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Tidskriftsartikel (refereegranskat)abstract
- The drop in temperature following large volcanic eruptions has been identified as an important component of natural climate variability. However, due to the limited number of large eruptions that occurred during the period of instrumental observations, the precise amplitude of post-volcanic cooling is not well constrained. Here we present new evidence on summer temperature cooling over Europe in years following volcanic eruptions. We compile and analyze an updated network of tree-ring maximum latewood density chronologies, spanning the past nine centuries, and compare cooling signatures in this network with exceptionally long instrumental station records and state-of-the-art general circulation models. Results indicate post-volcanic June-August cooling is strongest in Northern Europe 2 years after an eruption (-0.52 +/- 0.05 degrees C), whereas in Central Europe the temperature response is smaller and occurs 1 year after an eruption (-0.18 +/- 0.07 degrees C). We validate these estimates by comparison with the shorter instrumental network and evaluate the statistical significance of post-volcanic summer temperature cooling in the context of natural climate variability over the past nine centuries. Finding no significant post-volcanic temperature cooling lasting longer than 2 years, our results question the ability of large eruptions to initiate long-term temperature changes through feedback mechanisms in the climate system. We discuss the implications of these findings with respect to the response seen in general circulation models and emphasize the importance of considering well-documented, annually dated eruptions when assessing the significance of volcanic forcing on continental-scale temperature variations.
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| 3. |
- Esper, Jan, et al.
(författare)
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LONG-TERM SUMMER TEMPERATURE VARIATIONS IN THE PYRENEES FROM DETRENDED STABLE CARBON ISOTOPES
- 2015
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Ingår i: Geochronometria. - : Walter de Gruyter GmbH. - 1733-8387 .- 1897-1695. ; 42:1, s. 53-59
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Tidskriftsartikel (refereegranskat)abstract
- Substantial effort has recently been put into the development of climate reconstructions from tree-ring stable carbon isotopes, though the interpretation of long-term trends retained in such timeseries remains challenging. Here we use detrended delta C-13 measurements in Pinus uncinata tree-rings, from the Spanish Pyrenees, to reconstruct decadal variations in summer temperature back to the 13th century. The June-August temperature signal of this reconstruction is attributed using decadally as well as annually resolved, 20th century delta C-13 data. Results indicate that late 20th century warming has not been unique within the context of the past 750 years. Our reconstruction contains greater amplitude than previous reconstructions derived from traditional tree-ring density data, and describes particularly cool conditions during the late 19th century. Some of these differences, including early warm periods in the 14th and 17th centuries, have been retained via d13C timeseries detrending - a novel approach in tree-ring stable isotope chronology development. The overall reduced variance in earlier studies points to an underestimation of pre-instrumental summer temperature variability derived from traditional tree-ring parameters.
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| 4. |
- Esper, Jan, et al.
(författare)
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Northern European summer temperature variations over the Common Era from integrated tree-ring density records
- 2014
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Ingår i: Journal of Quaternary Science. - : Wiley. - 0267-8179 .- 1099-1417. ; 29:5, s. 487-494
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Tidskriftsartikel (refereegranskat)abstract
- Tree-ring chronologies of maximum latewood density are most suitable to reconstruct annually resolved summer temperature variations of the late Holocene. The two longest such chronologies have been developed in northern Europe stretching back to the 2nd century BC, and the 5th century AD. We show where similarities between the two chronologies exist, and combine portions of both into a new summer temperature reconstruction for the Common Era. To minimize the transfer of potential biases, we assess the contribution of the candidate reconstructions' measurements, and exclude data (i) from exceptionally young and old trees, and (ii) produced by different laboratory technologies. Our new composite reconstruction reveals warmer conditions during Roman, Medieval and recent times, separated by prolonged cooling during the Migration period and Little Ice Age. Twentieth century warmth, as indicated in one of the existing density records, is reduced in the new reconstruction, also affecting the overall, millennial-scale, cooling trend over the late Holocene (-0.30 degrees C per 1000 years). Due to the reduced biological memory, typical for tree-ring density measurements, the new reconstruction is most suitable for evaluating the rate and speed of abrupt summer cooling following large volcanic eruptions.
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| 5. |
- Esper, Jan, et al.
(författare)
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Testing the hypothesis of post-volcanic missing rings in temperature sensitive dendrochronological data
- 2013
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Ingår i: Dendrochronologia. - : Elsevier BV. - 1125-7865 .- 1612-0051. ; 31:3, s. 216-222
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Tidskriftsartikel (refereegranskat)abstract
- The precise, annual dating control, inherent to dendrochronology, has recently been questioned through a combined analysis of tree-growth and coupled climate models (Mann et al. (2012; hereafter MAN12)) suggesting single tree-rings in temperature limited environments are missing following large volcanic events. We test this hypothesis of missing, post-volcanic rings by using a compilation of maximum late-wood density (MXD) records that are typically used for reconstructing temperature and the detection of volcanic events, together with a unique set of long instrumental station data from Europe reaching back into the early 18th century. We investigate the temporal coherence between tree-ring MXD and observed summer temperatures before and after the most significant, precisely dated, volcanic event of the past 1000 years, the 1815 Tambora eruption widely known as the cause for the 1816 year without a summer. Comparison of existing and newly developed MXD chronologies from cold environments in Northern Scandinavia ((r) over bar North = 0.70, N=3) and the European Alps, including the Pyrenees, ((r) over bar central = 0.46, N=4) reveals significant interseries correlations over the 1722-1976 common period, suggesting coherence among these independently developed timeseries. Comparisons of these data with observed JJA temperatures - from 1722 to 1976, a 94-year pre-Tambora (1722-1815), and a 94-year post-Tambora (1817-1910) period - reveals significant and temporally stable correlations ranging from 0.32 to 0.68. However, if we assume the 1816 ring is missing in the MXD chronologies (i.e., shift the pre-Tambora data by one year), all proxy/instrumental correlations fall apart approaching zero. Results from an additional experiment, where the long instrumental record is replaced by an annually resolved, 500-year, summer temperature reconstruction derived from documentary evidence, corroborates the findings from the first experiment: significant positive correlations with the unmolested chronologies and zero correlation with the perturbed chronologies back to 1500 AD. These elementary analyses indicate that either the tree-ring chronologies are correctly dated, i.e., no is ring missing in the year without a summer, or that both the long instrumental and documentary records contain dating uncertainties. As the latter is unlikely, we conclude the MAN12 hypothesis on post-volcanic missing rings can be rejected based on simple comparisons of tree-ring, instrumental and documentary data over the past 300-500 years from Central and Northern Europe.
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| 6. |
- Konter, Oliver, et al.
(författare)
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Climate sensitivity and parameter coherency in annually resolved delta C-13 and delta O-18 from Pinus uncinata tree-ring data in the Spanish Pyrenees
- 2014
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Ingår i: Chemical Geology. - : Elsevier BV. - 0009-2541 .- 1872-6836. ; 377, s. 12-19
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Tidskriftsartikel (refereegranskat)abstract
- We explore the 20th century climate sensitivity of annually resolved carbon and oxygen isotope ratios in five Pinus uncinata individuals from the upper treeline in similar to 2400 m asl of the Spanish Pyrenees. Time series of delta C-13 and delta O-18 are calibrated against temperature, precipitation, and drought indices over the period 1901-2009. Negative correlations of delta C-13 with summer precipitation and drought indices, as well as positive correlations with summer temperatures, confirm previous evidence from similar habitats in the Pyrenees. In contrast to this summer climate signal in the carbon isotopes, the delta O-18 record reveals mainly negative correlations with spring precipitation and drought. We explore the coherence between delta C-13 and delta O-18 time series derived from individual trees and assess the influence of widely applied delta C-13 correction procedures on the climate signal strength. Spatial correlation patterns and decomposition of the time series into high-and low-frequency components are used to develop a calibration setup for carbon and oxygen isotope ratios, which will improve long-term climate reconstructions in a region, where classical tree-ring width and density data are limited.
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| 7. |
- Lendvay, Bertalan, et al.
(författare)
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Improved recovery of ancient DNA from subfossil wood - application to the world's oldest Late Glacial pine forest
- 2018
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Ingår i: New Phytologist. - : Wiley. - 0028-646X .- 1469-8137. ; 217:4, s. 1737-1748
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Tidskriftsartikel (refereegranskat)abstract
- Ancient DNA from historical and subfossil wood has a great potential to provide new insights into the history of tree populations. However, its extraction and analysis have not become routine, mainly because contamination of the wood with modern plant material can complicate the verification of genetic information. Here, we used sapwood tissue from 22 subfossil pines that were growing c. 13000yr bp in Zurich, Switzerland. We developed and evaluated protocols to eliminate surface contamination, and we tested ancient DNA authenticity based on plastid DNA metabarcoding and the assessment of post-mortem DNA damage. A novel approach using laser irradiation coupled with bleaching and surface removal was most efficient in eliminating contaminating DNA. DNA metabarcoding confirmed which ancient DNA samples repeatedly amplified pine DNA and were free of exogenous plant taxa. Pine DNA sequences of these samples showed a high degree of cytosine to thymine mismatches, typical of post-mortem damage. Stringent decontamination of wood surfaces combined with DNA metabarcoding and assessment of post-mortem DNA damage allowed us to authenticate ancient DNA retrieved from the oldest Late Glacial pine forest. These techniques can be applied to any subfossil wood and are likely to improve the accessibility of relict wood for genome-scale ancient DNA studies.
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| 8. |
- Seim, Andrea, et al.
(författare)
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Climate sensitivity of Mediterranean pine growth reveals distinct east-west dipole
- 2015
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Ingår i: International Journal of Climatology. - : Wiley. - 0899-8418 .- 1097-0088. ; 35:9, s. 2503-2513
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Tidskriftsartikel (refereegranskat)abstract
- The European Mediterranean region is governed by a characteristic climate of summer drought that is likely to increase in duration and intensity under predicted climate change. However, large-scale network analyses investigating spatial aspects of pre-instrumental drought variability for this biogeographic zone are still scarce. In this study we introduce 54 mid- to high-elevation tree-ring width (TRW) chronologies comprising 2186 individual series from pine trees (Pinus spp.). This compilation spans a 4000-km east-west transect from Spain to Turkey, and was subjected to quality control and standardization prior to the development of site chronologies. A principal component analysis (PCA) was applied to identify spatial growth patterns during the network's common period 1862-1976, and new composite TRW chronologies were developed and investigated. The PCA reveals a common variance of 19.7% over the 54 Mediterranean pine chronologies. More interestingly, a dipole pattern in growth variability is found between the western (15% explained variance) and eastern (9.6%) sites, persisting back to 1330 AD. Pine growth on the Iberian Peninsula and Italy favours warm early growing seasons, but summer drought is most critical for ring width formation in the eastern Mediterranean region. Synoptic climate dynamics that have been in operation for the last seven centuries have been identified as the driving mechanism of a distinct east-west dipole in the growth variability of Mediterranean pines.
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| 9. |
- Treydte, Kerstin, et al.
(författare)
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Recent human-induced atmospheric drying across Europe unprecedented in the last 400 years
- 2024
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Ingår i: NATURE GEOSCIENCE. - 1752-0894 .- 1752-0908. ; 17, s. 58-65
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Tidskriftsartikel (refereegranskat)abstract
- The vapor pressure deficit reflects the difference between how much moisture the atmosphere could and actually does hold, a factor that fundamentally affects evapotranspiration, ecosystem functioning, and vegetation carbon uptake. Its spatial variability and long-term trends under natural versus human-influenced climate are poorly known despite being essential for predicting future effects on natural ecosystems and human societies such as crop yield, wildfires, and health. Here we combine regionally distinct reconstructions of pre-industrial summer vapor pressure deficit variability from Europe's largest oxygen-isotope network of tree-ring cellulose with observational records and Earth system model simulations with and without human forcing included. We demonstrate that an intensification of atmospheric drying during the recent decades across different European target regions is unprecedented in a pre-industrial context and that it is attributed to human influence with more than 98% probability. The magnitude of this trend is largest in Western and Central Europe, the Alps and Pyrenees region, and the smallest in southern Fennoscandia. In view of the extreme drought and compound events of the recent years, further atmospheric drying poses an enhanced risk to vegetation, specifically in the densely populated areas of the European temperate lowlands. The atmosphere has dried across most regions of Europe in recent decades, a trend that can be attributed primarily to human impacts, according to tree ring records spanning 400 years and Earth system model simulations.
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| 10. |
- Wilson, Rob, et al.
(författare)
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Last millennium northern hemisphere summer temperatures from tree rings : Part I
- 2016
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 134, s. 1-18
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Forskningsöversikt (refereegranskat)abstract
- Large-scale millennial length Northern Hemisphere (NH) temperature reconstructions have been progressively improved over the last 20 years as new datasets have been developed. This paper, and its companion (Part II, Anchukaitis et al. in prep), details the latest tree-ring (TR) based NH land air temperature reconstruction from a temporal and spatial perspective. This work is the first product of a consortium called N-TREND (Northern Hemisphere Tree-Ring Network Development) which brings together dendroclimatologists to identify a collective strategy for improving large-scale summer temperature reconstructions. The new reconstruction, N-TREND2015, utilises 54 records, a significant expansion compared with previous TR studies, and yields an improved reconstruction with stronger statistical calibration metrics. N-TREND2015 is relatively insensitive to the compositing method and spatial weighting used and validation metrics indicate that the new record portrays reasonable coherence with large scale summer temperatures and is robust at all time-scales from 918 to 2004 where at least 3 TR records exist from each major continental mass. N-TREND2015 indicates a longer and warmer medieval period (similar to 900 1170) than portrayed by previous TR NH reconstructions and by the CMIP5 model ensemble, but with better overall agreement between records for the last 600 years. Future dendroclimatic projects should focus on developing new long records from data-sparse regions such as North America and eastern Eurasia as well as ensuring the measurement of parameters related to latewood density to complement ring-width records which can improve local based calibration substantially.
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