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(a) Pearson correlation coefficients r between PIMO and other MXD chronologies in Europe. MXD chronologies include all chronologies for Europe that date back prior to 1900 and are available in the International Tree-Ring Data Bank (ITRDB; Grissino-Mayer and Fritts, 1997; shttp://www.ncdc.noaa.gov/paleo/treering.html). PIHE MXD chronologies are indicated by squares. Absolute r-values higher than 0.2 are significant at the 95% confidence level (for n=100); (b) annual and decadally smoothed (10 yr smoothing spline) reconstructions of August temperature anomalies in Bulgaria (black) and of summer NAO (Folland et al., 2009; grey, inversed).
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The dominant atmospheric circulation pattern that governs European summer climate is a blocking-like pattern over the British Isles that co-occurs with a low over southeastern Europe. The meridionally oriented configuration of this circulation pattern favours the intrusion of warm air over the northeastern Mediterranean during one mode and over nor...
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Context 1
... chronologies were 55 years or longer after truncation at a sample replication of ten series. We were primarily interested in the high-frequency synoptic relation- ships across Europe and therefore the so-called residual chronolo- gies (with low-order autocorrelation removed from individual series before chronology compilation) were used for correlation analyses (Figure 6a). We found overall positive correlations with MXD time series in the Balkans, southern and central Italy, and the Carpathians. ...
Context 2
... et al. (2009) combined two of the MXD records from Scotland (Coulin and Inverey) with MXD and TRW records from western Norway for their reconstruction of the sNAO and PIMO correlates significantly negatively with this sNAO reconstruction over its full length ; r=−0.43; p<0.001; Figure 6b). The correlation is predominantly expressed in the high (interan- nual) frequency domain (r=−0.48; ...
Context 3
... is positively related to temperature reconstructions in the Balkans, Southern and Central Italy, and Western Turkey, whereas opposing temperature variability patterns are manifested over the British Isles, southern Scandinavia, and the Western European North Sea and Atlantic Coast. This spatial pattern is mimicked in a correlation map of PIMO with other MXD tree-ring records over Europe (Figure 6a). PIMO shows similar temporal variabil- ity patterns as other MXD records throughout the Balkans, Italy, and even Romania and Poland and the similarity is particularly strong for the three other PIHE records from Greece and Italy. ...
Context 4
... shows similar temporal variabil- ity patterns as other MXD records throughout the Balkans, Italy, and even Romania and Poland and the similarity is particularly strong for the three other PIHE records from Greece and Italy. The majority of MXD records from the UK and southern Scandi- navia are in anti-phase with PIMO and it thus comes as no sur- prise that PIMO correlates negatively with a sNAO reconstruction based on two of these records (Figure 6b). The relationship between the two reconstructions confirms the sNAO pattern as the main driver of the teleconnection between summer tempera- tures in southeastern versus northwestern Europe and this tele- connection is most pronounced on interannual (rather than decadal or lower frequency) timescales. ...
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... Cross-correlation analysis of the Lake Bâlea chironomid inferred T July record with the Scarisoara Ice Cave δ 18 O record ( Fig. 8; Perşoiu et al., 2017), which was recently re-interpreted to reflect fluctuations in the autumn/winter position of NAJ with more negative isotope ratios representing a more northerly position of NAJ (Warken et al., 2024), show moderately strong positive correlation (r = 0.44, Fig. S8A and B). This suggests the association of lower summer temperatures with more northerly position of the winter NAJ, and given the association of a more northerly summer NAJ with cooler summers in the Balkan (Trouet et al., 2012), low amplitude fluctuation in the geochemical and chironomid proxies may reflect changes in summer NAJ position between 7900 and 5500 cal yr BP (Fig. 8). The northward shift of summer NAJ influences regional temperatures via summer NAO and EA patterns today (Mellado-Cano et al., 2019). ...
... The northward shift of summer NAJ influences regional temperatures via summer NAO and EA patterns today (Mellado-Cano et al., 2019). Under these circumstances during summer, the British Isles (BI) are characterised by strongly positive geopotential heights, while geopotential heights are anomalously negative over the Balkan and the NE Mediterranean, including the Southern Carpathians (Trouet et al., 2012). These conditions result in cyclonic circulation (associated with the trough over SE Europe) tending to bring northerly or northwesterly winds over the Southern Carpathians that advect cooler maritime or continental polar air masses from higher latitudes leading to suppressed daily maximum temperatures. ...
... In addition, the presence of a quasi-stationary upper-level trough leads to enhanced mid-level instability and persistent cloud formation bringing more rain. Overall, the BI ridge blocks zonal flow leading to stationary trough over SE Europe, which promotes air mass ascent leading to cloudiness and rainfall, N/NW winds and cool air advection that lower the daily temperatures (Bladé et al., 2012;Trouet et al., 2012). After 5500 cal yr BP, T July decreases in the high alpine zone from 9.8 to 8.9 • C, while only a smaller decrease (from 11 to 10.5 • C) is observed in the subalpine zone (Fig. 8). ...
The Southern Carpathians, a pivotal yet understudied transition zone between Atlantic and continental climate regimes, lack high-resolution summer temperature reconstructions critical for deciphering North Atlantic Oscillation (NAO) and North Atlantic Jet (NAJ)-driven Holocene climate variability. In this multi-proxy study, we use subfossil chironomids, pollen, loss-on-ignition, magnetic susceptibility, as well as major and trace element
analyses from the sediments of a high alpine lake, Balea (2034 m a.s.l.), to reconstruct sub-century scale Holocene climate variability and environmental change. Chironomid-inferred average TJuly at the lake is 9.3 C today. The lowest temperatures around 6 C were found in the Lateglacial (~13,600 cal yr BP). In the Holocene (since 8330 cal yr BP), TJuly ranged from 7.5 to 10.4 C with cooler periods between 5500 and 4800 cal yr BP (~8.9 C) and around 4200 cal yr BP (~9 C). After 4200 cal yr BP, ln(Rb/K) ratios suggested increasing precipitation that likely affected the sediment composition of the lake. Our findings support the NAJ’s summer impact in Eastern Central Europe by showing a ~0.5–1 C multi-decadal summer cooling in periods with a more northerly position of the summer NAJ. Chironomid assemblage composition change at 4200 cal yr BP involved the increase of Micropsectra insignilobus-type and Heterotrissocladius marcidus-type, while Micropsectra radialis-type declined. In addition, the overall chironomid population size declined pointing to decreasing lake productivity. The dominant taxon of the early- and mid-Holocene assemblages, Micropsectra radialis-type, disappeared at 2750 cal yr BP. We explained this faunal change with lake substrate change and proved the bias of the inferred increase in TJuly after 2750 cal yr BP.
... PILO TRW variability is also influenced by memory effects and by subtle micro-topographical effects Bunn et al., 2011;Tran et al., 2017), which makes an annually resolved temperature reconstruction from the PILO TRW archive challenging. At both high latitudes (Briffa et al., 1988;Esper et al., 2018) and mid latitudes (Büntgen et al., 2010;Klippel et al., 2020;Trouet et al., 2012), maximum latewood density (MXD) has been shown to be a better proxy for summer temperature than TRW. MXD captures the temperature signal at the end of the growing season, when smaller and thicker-walled latewood cells are formed (Rathgeber, 2017). ...
... Lower latitude tree-ring collections are thus predominantly used for hydroclimate reconstructions (Belmecheri et al., 2016). However, sampling of highelevation sites in these regions increases the strength of the temperature signal (Kipfmueller & Salzer, 2010), which is even more explicitly the case for MXD data (Büntgen et al., 2010;Klippel et al., 2019;Trouet et al., 2012) and confirmed in our study (Figure 2c). MXD RBAR values (Figure 2b) are rather low compared to TRW-based RBAR values from PILO (Salzer, Larson, et al., 2014), which is also observed in other studies, for example, MXD records from the European Alps (Lopez-Saez et al., 2023) or blue intensity records in the Southern Rocky Mountains (Heeter et al., 2020). ...
Bristlecone pine (Pinus longaeva) (PILO) trees exhibit exceptional longevity. Their tree‐ring width (TRW) series offer valuable insights into climatic variability. Maximum latewood density (MXD) typically correlates better with temperature variations than TRW, yet PILO MXD records are non‐existent due to methodological challenges related to tree‐ring structure. Here, we used an X‐ray Computed Tomography (X‐ray CT) toolchain on 51 PILO cores from the California White Mountains to build a chronology that correlates significantly (r = 0.66, p < 0.01) with warm‐season (March‐September) temperature over a large spatial extent. This led to the first X‐ray CT‐based temperature reconstruction (1625–2005 CE). Good reconstruction skill (RE = 0.51, CE = 0.32) shows that extending MXD records across the full length of the PILO archive could yield a robust warm‐season temperature proxy for the American Southwest over millennia. This breakthrough opens avenues for measuring MXD in other challenging conifers, increasing our understanding of past climate further, particularly in lower latitudes.
... PILO TRW variability is also influenced by memory effects and by subtle micro-topographical effects Bunn et al., 2011;Tran et al., 2017), which makes an annually resolved temperature reconstruction from the PILO TRW archive challenging. At both high latitudes (Briffa et al., 1988;Esper et al., 2018) and mid latitudes (Büntgen et al., 2010;Klippel et al., 2020;Trouet et al., 2012), maximum latewood density (MXD) has been shown to be a better proxy for summer temperature than TRW. MXD captures the temperature signal at the end of the growing season, when smaller and thicker-walled latewood cells are formed (Rathgeber, 2017). ...
... Lower latitude tree-ring collections are thus predominantly used for hydroclimate reconstructions (Belmecheri et al., 2016). However, sampling of highelevation sites in these regions increases the strength of the temperature signal (Kipfmueller & Salzer, 2010), which is even more explicitly the case for MXD data (Büntgen et al., 2010;Klippel et al., 2019;Trouet et al., 2012) and confirmed in our study (Figure 2c). MXD RBAR values (Figure 2b) are rather low compared to TRW-based RBAR values from PILO (Salzer, Larson, et al., 2014), which is also observed in other studies, for example, MXD records from the European Alps (Lopez-Saez et al., 2023) or blue intensity records in the Southern Rocky Mountains (Heeter et al., 2020). ...
Bristlecone pine (Pinus longaeva) (PILO) trees exhibit exceptional longevity. Their tree-ring width (TRW) series offer valuable insights into climatic variability. Maximum latewood density (MXD) typically correlates better with temperature variations than TRW, yet PILO MXD records are non-existent due to methodological challenges related to their tree-ring structure. Here, we used an X-ray Computed Tomography (X-ray CT) toolchain on 51 PILO cores from the California White Mountains to build a chronology that correlates significantly (r=0.66, p<0.01) with warm-season (March-September) temperature over a large spatial extent. This led to the first X-ray CT-based temperature reconstruction (1625 – 2005 CE). Good reconstruction skill (RE=0.51, CE=0.32) shows that extending MXD records across the full length of the PILO archive could yield a robust warm-season temperature proxy for the American Southwest over millennia. This breakthrough opens avenues for measuring MXD in other challenging conifers, increasing our understanding of past climate further, particularly in lower latitudes.
... The variability of macroclimate, one of the most critical factors influencing growth, can determine similar and synchronous growth trends of trees across large areas (St. George, 2014;Trouet et al., 2012). Growth synchrony can be used as an EWS to predict stressful conditions in forest ecosystems . ...
... These climate changes for the Northern Hemisphere had a different local spatial and temporal manifestation. Keeping in mind that in Southeast Europe a number of climate changes show a different and even opposite trend compared to Western and Northern Europe (Luterbacher et al., 2004;Xoplaki et al., 2005;Brazdil et al., 2022;Trouet et al., 2012;Klesse et al., 2015), climate changes in Bulgaria and the neighboring countries in the Balkans are the most indicative. ...
This study aims to present and analyse several descriptions of snow cover conditions on Vitosha Mountain over the last five centuries. It uses the written historical sources and diachronic method. They are discussed in the context of available climate and environmental data for Bulgaria and the adjacent areas of the Balkans during the Little Ice Age (LIA). It can be concluded from the presented descriptions of Vitosha during the LIA that probably in the 17th and early 18th centuries Vitosha had significantly longer snow retention with the presence of permanent or semi-permanent snow patches, a situation that is significantly different from the present environmental conditions. The analysis of the climatic conditions during the LIA in other regions of Bulgaria, as well as in neighboring countries in the Balkans, shows that during this period, especially in the southern parts of the Balkan Peninsula, there was a significant climate cooling. Future studies of the (high resolution) natural archives in Bulgaria are needed to provide more information about the nature of climatic and environmental changes during the LIA.
http://www.dgt.uns.ac.rs/dokumentacija/zbornik/51-2/en/01en.pdf
... The variability of macroclimate, one of the most critical factors influencing growth, can determine similar and synchronous growth trends of trees across large areas (St. George, 2014;Trouet et al., 2012). Growth synchrony can be used as an EWS to predict stressful conditions in forest ecosystems . ...
... Charred particles are formed during fires, whose occurrence requires ignition (caused by lightning or human activities), suitable (dry) weather conditions, and fuel; the latter two factors control the fire spread [31,32]. Dry conditions favouring the fire spread are common in the Mediterranean regions: over the last 1850 years, there have been several dry periods of varying severity [33]. The main factor limiting the fire spread in this region is thus the availability of fuel, and woody cover in particular. ...
Highlights
The peat age was late Holocene, and less than 1900 years old.
The peat contained no charcoal, probably due to the lack of woody cover at the site for 1900 years.
Depth profiles of clay and nutrients (P, K, Ca, Mg) revealed an increase in atmospheric inputs over time, while nitrogen is homogeneously sequestrated in depth.
The dominant metallic trace elements (MTE) were cadmium, which peaked during the Roman epoch, then lead and mercury concentrated during the modern period, but decreasing onwards.
Peat geochemistry is strongly influenced by local and regional human activities, revealing a peat modified by social imprints.
Abstract
Sedimentological and biogeochemical measurements were conducted on minerotrophic peat in a wilderness area on a granitic plateau to reconstruct the local ecosystem’s history and clarify the peat’s response to local and global changes. The peat is less than 1900 years old. Its clay and iron (Fe) concentration profiles revealed an increasing atmospheric influx over time, whereas the levels of its nutrients (P, K, Ca, Mg) have increased since the 19th century. Additionally, changes in the relative abundance of amorphous aluminium indicated a gradual decrease in soil weathering. The dominant metallic trace elements were cadmium during the Roman epoch and early Middle Ages, then lead and mercury during the modern and the industrial eras. Unexpectedly, the peat proved to be sub-modern and lacks wildfire proxies, probably indicating an absence of nearby woodlands over the last 1900 years. Its concentrations of Ca and Mg indicate that airborne transport of particles released by soil erosion in lowland agricultural plains has strongly affected the peat’s composition since the 18th–19th century. The site has also been heavily influenced by metallic contamination due to regional metallurgy and agriculture, producing a peat that has been modified by social imprints over several centuries.
... Physiological studies carried out with saplings of Rila oak, Strandzha oak and Turkey oak (Q. cerris L.) at warmer conditions (Sofia city) and different drought regimes showed (Trouet et al., 2012) (TR) and regional summer scPDSI record from Cook et al. (OWDA) (2015); ** The listed "Narrow" years were not detected by the pointer years detection scripts. However, these were years with very low values compared to other neighboring years and in the Raw (not-detrended) tree-ring width chronologies they deviated with more than 1 standard deviation from the average tree-ring width value of the chronology (Fig. 2). ...
Quercus protoroburoides Donchev and Bouzov ex Tashev and Tsavkov (Rila oak) is a species with extremely limited and localized distribution. It is found only on several locations on slopes above Rila Monastery in Rila Mountains (Bulgaria) at elevations between 1500 m and 1750 m a.s.l. The trees are in small groups or scattered, usually situated on ridges slightly higher than the local population of sessile oak (Quercus petraea (Matt.) Liebl.) and above mixed fir-beech forests. The species was first discovered and described in 1968 by Boris Buzov, but was officially validated in 2017 by Tashev and Tsavkov. Up to this moment there were no dendrochronological studies of the species and there is general lack of data on how climate affects growth. Our aim was to contribute to filling this knowledge gap.
In our study we analyzed 42 series (22 trees) from Q. protoroburoides from two locations (Drushlyavitsa and Brichebor) and compared them to cores from Q. petraea from the same region. The Rila oak trees varied in age from 30 to 170 years. Nearly half of them were about 50 years old. The composed tree-ring chronology spans from 1856 to 2019 with more than 5 included series after 1870. The sessile oak trees were generally older and the chronology spanned from 1743, having more than 4 series after 1786. The climate-growth analysis with local and gridded data revealed positive effects on growth of previous August and current April-June precipitation, positive correlations with previous May-June temperatures and negative with August temperatures. Most of the pointer years with low growth were characterized by extreme climate conditions, such as summer droughts, unusually cold summers or delayed start of the vegetation period due to late frost events at the end of May or early June. Our data indicate that Q. protoroburoides and Q. petraea trees at this unusually high location for oaks are sensitive to climate conditions including summer droughts.
... Bosnian pine forms very old stands, including the oldest scientifically dated tree in Europe [22,23]. Due to its longevity, the species has been widely used for climate reconstruction, e.g., [24][25][26][27][28][29][30][31][32][33][34][35][36][37], while up to our knowledge there are no studies using those long-developed chronologies for dating historical timber. Given its very resinous and resistant to decay and decomposition wood [34] and its suitability as a timber species for general construction, housing, carving, cooperage, dairying, and storage of goods [21,27,38], the lack of dendroarchaeological studies may be possibly attributed to its limited distribution and the non-exploration of the historical timber within or around the distribution area of the species. ...
(1) Background: Pinus heldreichii is a long-living tree subalpine species commonly used for climate reconstruction. Nevertheless, its potential for dendroarchaeology and dating of historical timber remains unknown. In Metsovo and in the surrounding area of Pindus National Park (Northern Greece) it is commonly used for the construction of buildings and wooden objects and artifacts. (2) Methods: We examined timber found in historical buildings within the study area and we tried to date it using local reference chronologies of Bosnian and Black pines. (3) Results: Bosnian pine chronologies can be used to date timber from historical buildings, while they can also be used as reference chronologies against Black pines, giving very high cross-dating values. Therefore, and since the macroscopic identification of the two species’ timber is impossible, the analysis of wood anatomy is necessary to distinguish the two species in the case of historical wood. (4) Conclusions: The current paper presents the first application of dendroarchaeology for Bosnian pine and highlights the potential of the species in studying cultural heritage and the human past.
... Numerous dendrochronological studies have been performed with Bosnian pine over the Balkan Peninsula and Italy, most of which focus on the species' response to climatic variability (Todaro et al. 2007;Panayotov et al. 2010;Seim et al. 2012;Klippel et al. 2017) and anthropogenic activity (Todaro et al. 2007). Long tree-ring chronologies have also been used for climate reconstruction (Touchan et al. 2005b(Touchan et al. , 2014a(Touchan et al. , 2014bTrouet et al. 2012;Klesse et al. 2015;Klippel et al. 2018;Esper et al. 2020Esper et al. , 2021). An application of blue intensity, a relatively new measurement technique based on image analysis used as a proxy for treering density (Campbell et al. 2007;Buckley et al. 2018), illustrated positive correlations with August and August-July temperatures in Bosnian pines as shown by Tsvetanov et al. (2020). ...
Key message
Long Bosnian pine chronologies from different mountains are shaped by different climatic parameters and can help identify past drought events and reconstruct landscape histories.
Abstract
We developed a 735-year-long Pinus heldreichii chronology from the southern distribution limit of the species, expanding the available database of long Bosnian pine chronologies. Tree-ring growth was mainly positively correlated with growing degree days (GDD: r 1950–2018 = 0.476) while higher temperatures during both winter and growing season also enhanced growth ( T WT : r 1950–2018 = 0.361 and T GS : 0.289, respectively). Annual precipitation, during both calendar and water years, had a negative but weaker impact on annual tree growth. The newly developed chronology correlates well with chronologies developed from the neighboring mountains. The years with ring width index (RWI) lower than the average were found to correspond to cool years with dry summers. Still, the newly developed chronology was able to capture severe drought events, such as those in 1660, 1687, and 1725. Several old living trees had internal scars presumably caused by fires. Therefore, old mature trees could be used for fire history reconstruction in addition to climate reconstruction. Although the presence of lightning scars indicates an important natural agent of fire ignition, human activities associated with animal grazing could also be an underlying reason for fires in the region.
