Maximum Latewood Density Chronologies Research Articles

Tree-Ring Chronologies from the Upper Treeline in the Russian Altai Mountains Reveal Strong and Stable Summer Temperature Signals

Radial tree growth at high-elevation and high-latitude sites is predominantly controlled by changes in summer temperature. This relationship is, however, expected to weaken under projected global warming, which questions the reliability of tree-ring chronologies for climate reconstructions. Here, we examined the growth–climate response patterns of five tree-ring width (TRW) and maximum latewood density (MXD) chronologies of larch (Larix sibirica) from upper-treeline ecotones in the Altai Mountains, which is a key region for developing millennial-long dendroclimatic records in inner Eurasia. The TRW and MXD chronologies exhibited significant year-to-year coherency within and between the two parameters (p < 0.001). While TRW is mostly influenced by temperature changes during the first half of the growing season from June to July (r = 0.66), MXD is most strongly correlated with May–August temperatures (r = 0.73). All seasonal temperature signals are statistically significant at the 99% confidence level, temporally stable back to 1940 CE, the period with reliable instrumental measurements, and spatially representative for a vast area of inner Eurasia between northeastern Kazakhstan in the west, northern Mongolia in the east, southern Russia in the north and northwestern China in the south. Our findings demonstrate the paleoclimatic potential of TRW and especially MXD chronologies and reject any sign of the ´divergence problem´ at these high-elevation, mid-latitude larch sites.

Application of RCS and signal-free RCS to tree-ring width and maximum latewood density data

Dendroclimatic research faces the challenge of selecting appropriate detrending methods for retaining low-frequency signals in temperature reconstructions. Among the numerous methods available to dendrochronologists, regional curve standardisation (RCS) and the signal-free approach in combination with RCS (SF-RCS) are increasingly used to preserve the full spectrum of temperature variance in tree-ring data. Here, we apply RCS and SF-RCS to tree-ring width (TRW) and maximum latewood density (MXD) datasets composed of only living and combined living and relict trees from northern Scandinavia. Whereas RCS and SF-RCS produce highly similar chronologies when applied to composite (living-plus-relict) datasets, particularly for MXD, both methods fail to establish chronologies coherent with regional temperature trends when applied to living-tree datasets. Additional tests including pruning of well-replicated living-tree datasets, to approximate the heterogenous age-structure of composite datasets, reveal improved results and coherent trends in MXD. While this demonstrates the applicability of joint detrending and pruning techniques to retain meaningful low-frequency variance in living-tree MXD chronologies, similar improvements were not achieved with TRW, likely because of the much stronger age-trend inherent to this widely used proxy. Further tests with other tree species and in alpine environments are needed to verify these findings. However, such assessments require an adjustment of tree-ring sampling protocols to increase replication to 50+ trees per site including old and young individuals to facilitate data pruning.

Revising Alpine summer temperatures since 881 CE

Europe experienced severe heat waves during the last decade, which impacted ecological and societal systems and are likely to increase under projected global warming. A better understanding of pre-industrial warm-season changes is needed to contextualize these recent trends and extremes. Here, we introduce a network of 352 living and relict larch trees (Larix decidua Mill.) from the Matter and Simplon valleys in the Swiss Alps to develop a maximum latewood density (MXD) chronology calibrating at r = 0.8 (p > 0.05, 1901–2017 CE) against May–August temperatures over Western Europe. Machine learning is applied to identify historical wood samples aligning with growth characteristics of sites from elevations above 1900 m asl to extend the modern part of the chronology back to 881 CE. The new Alpine record reveals warmer conditions in the tenth century, followed by an extended cold period during the late Medieval times, a less-pronounced Little Ice Age culminating in the 1810s, and prolonged anthropogenic warming until present. The Samalas eruption likely triggered the coldest reconstructed summer in Western Europe in 1258 CE (-2.32 °C), which is in line with a recently published MXD-based reconstruction from the Spanish Pyrenees. Whereas the new Alpine reconstruction is potentially constrained in the lowest frequency, centennial timescale domain, it overcomes variance biases in existing state-of-the-art reconstructions and sets a new standard in site-control of historical samples and calibration/ verification statistics.

Evaluating the Effect of Vegetation Index Based on Multiple Tree-Ring Parameters in the Central Tianshan Mountains

Combining tree ring data with remote sensing data can help to gain a deeper understanding of the driving factors that influence vegetation change, identify climate events that lead to vegetation change, and improve the parameters of global vegetation index reconstruction models. However, it is currently not well understood how climate change at different elevations in the central Tianshan Mountains affects radial tree growth and the dynamics of forest canopy growth. We selected Schrenk spruce (Picea schrenkiana) tree core samples from different elevations in the central Tianshan Mountains. We analyzed the relationships of various tree-ring parameters, including tree-ring width, maximum latewood density (MXD), and minimum earlywood density (MID) chronologies, with 1982–2012 GIMMS (Global Inventory Modelling and Mapping Studies) NDVI (Normalized Difference Vegetation Index), 2001–2012 MODIS (moderate resolution imaging spectroradiometer) NDVI, and meteorological data. (1) There were strong correlations between tree-ring width chronologies and the lowest temperatures, especially in July. Tree-ring width chronologies at higher altitudes were positively correlated with temperature; the opposite pattern was observed at lower altitudes. MID chronologies were positively correlated with July temperature in high-altitude areas and mean temperature and highest temperature from May to September in low-altitude areas, and negatively correlated with precipitation during this period. MXD chronologies were mainly negatively correlated with precipitation. MXD chronologies were mainly positively correlated with temperature in April and May. (2) The correlations between MXD chronologies at each sampling point and NDVI in each month of the growing season were strong. Both MID and MXD chronologies were negatively correlated with GIMMS NDVI in July. The overall correlations between tree-ring parameters and MODIS NDVI were stronger than the correlations between tree-ring parameters and GIMMS NDVI in high-altitude areas; the opposite pattern was observed in low-altitude areas. Drought stress may be the main factor affecting tree ring parameters and NDVI. In the future, we should combine tree ring parameters with vegetation index to investigate a larger scale of forests.

Regional Characteristics of the Climatic Response of Tree-Ring Maximum Density in the Northern Hemisphere

The maximum latewood density (MXD) of tree rings can reflect the temperature of the growing season, but the timing of the response differs among regions. We selected 152 maximum latewood density chronologies from the Northern Hemisphere that showed a significant response to temperature. Based on a cluster analysis and the sensitivity of MXD to the monthly mean temperature, the chronologies were classified into six clusters. The clusters showed distinct regional characteristics, and the period and peak month of significant response of the chronologies in each cluster to temperature were different. Spatial synchronization of the MXDs revealed that the two clusters distributed in Europe showed the most consistency and the strongest response to the April–September monthly mean temperature compared with the other clusters. Temperature accounted for more than 40% of the total MXD variance in all clusters, whereas the effect of precipitation was much smaller. In addition to climatic factors, the random effect of the latitude and longitude of sampling sites, elevation, and tree species was a major factor contributing to the variance in MXD in each cluster. Latitude and longitude had the strongest influence among the three random effects, and tree species had the weakest influence, except at high latitudes. The MXD of each cluster showed sensitivity to temperature within a certain interval, with a positive linear response, and the sensitivity interval was greatest at high latitudes. Certain clusters showed a negative linear sensitivity to precipitation. The results provide a reference for studying the climatic threshold of large-scale tree-ring density formation.

Impacts of Atlantic Multidecadal Oscillation and Volcanic Forcing on the Late Summer Temperature of the Southern Tibetan Plateau

Abstract In this paper, we present a late summer (August–September) temperature reconstruction over the period 1792–2020 based on a tree-ring maximum latewood density (MXD) chronology for the southern Tibetan Plateau (TP). The reconstruction explained 66.2% of the variance in the instrumental temperature records during the calibration period 1960–2020 and captured the warming trend since the 1960s, which would support the current warming on the TP. In addition, a warming hiatus existed during 2001–12 and the last 20 years (2000–20) were the warmest period in the past two centuries. The reconstruction matched other MXD- and mean latewood density (LWD)-based late summer temperature reconstructions from neighboring regions, and fluctuated in synchrony with the Climatic Research Unit (CRU) Northern Hemisphere land surface temperature during 1850–2020. Multitaper method analysis and wavelet analysis revealed significant periodicities of 2–3, 20–30, and 40–60 years in the reconstructed series. Our reconstructed series was very consistent and highly correlated with the Atlantic multidecadal oscillation (AMO). During the warm phase of the AMO, higher pressure and divergent horizontal winds over the TP contribute to warmer summers in the region. In addition, we found that the southern TP experienced the lowest temperature and downward solar radiation in the second year following large volcanic eruptions. The decrease in downward solar radiation may be directly responsible for the occurrence of the lowest temperatures. The results indicate that the AMO and large volcanic eruptions were impacting factors on temperature in our study area.

Pine Maximum Latewood Density in Semi‐Arid Northern China Records Hydroclimate Rather Than Temperature

AbstractLong records of tree‐ring maximum latewood density (MXD) measurements in conifers have been successfully employed to reconstruct summer temperature changes globally. Yet, the potential of MXD as a proxy in semi‐arid, low‐latitude regions for reconstructing either temperature or hydroclimate variability remains largely unexplored. Here, we developed a MXD data set of Chinese pine from semi‐arid northern China, and investigated its sensitivity to different climate variables. We found that the annual self‐calibrated Palmer Drought Severity Index from previous August to current July displays the strongest influence on the MXD variation. The entire MXD chronology (covering 1736–2020) is highly consistent with nearby tree‐ring‐based annual precipitation and drought reconstructions at decadal timescales, confirming a temporally stable hydroclimate signal in our MXD record. In particular, the rapid wetting trend during the 2010–2020 period is well captured by the MXD data. This novel study has wide implications for future use of tree‐ring density data to reconstruct past climate changes globally.

Tree-ring anatomy of Pinus cembra trees opens new avenues for climate reconstructions in the European Alps

Tree rings form the backbone of high-resolution palaeoclimatology and represent one of the most frequently used proxy to reconstruct climate variability of the Common Era. In the European Alps, reconstructions were often based on tree-ring width (TRW) and maximum latewood density (MXD) series, with a focus on European larch. By contrast, only a very limited number of dendroclimatic studies exists for long-lived, multi-centennial Pinus cembra, despite the widespread occurrence of the species at treeline sites across the European Alps. This lack of reconstructions can be ascribed to the difficulties encountered in past studies in extracting a robust climate signal from TRW and MXD chronologies. In this study, we tested various wood anatomical parameters from P. cembra as proxies for the reconstruction of past air temperatures. To this end, we measured anatomical cell parameters and TRW of old-growth trees from the God da Tamangur forest stand, known for being the highest pure, and continuous P. cembra forest in Europe. We demonstrate that several wood anatomical parameters allow robust reconstruction of past temperature variability at annual to multidecadal timescales. Best results are obtained with maximum latewood radial cell wall thickness (CWTrad) measured at 40 μm radial band width. Over the 1920–2017 period, the CWTrad chronology explains 62 % and >80 % of interannual and decadal variability of air temperatures during a time window corresponding roughly with the growing season. These values exceed those found in past work on P. cembra and even exceed the values reported for MXD chronologies built with L. decidua and hitherto considered the gold standard for dendroclimatic reconstructions in the European Alps. The wood anatomical analysis of P. cembra records therefore unveils a dormant potential and opens new avenues for a species that has been considered unsuitable for climate reconstructions so far.

Responses to Climate Change of Maximum Latewood Density from Larix speciosa Cheng et Law and Abies delavayi Franch. in the Northwest of Yunnan Province, China

Tree-ring density has been used for climate-response analysis and climate reconstruction for many species. However, our knowledge of wood density for the responses of different species to climate remains very limited and inconclusive. To determine the relationship between maximum latewood density (MXD) and climate for deciduous and evergreen coniferous species, MXD chronologies were developed from Larix speciosa Cheng et Law and Abies delavayi Franch. growing at 3200–3300 m a.s.l. in Gongshan county, northwestern Yunnan, in China. Significant positive correlations with late summer mean temperature were found for the MXD chronologies of both species. However, the highest correlation occurred in August–September for L. speciosa (r = 0.551, p < 0.01) and in September–October for A. delavayi (r = 0.575, p < 0.01), which may be associated with the physiological habits of trees. Linear model can describe relationships between late-summer temperature and MXD index for L. speciosa (MXD = 0.0506T8–9 − 0.0509, R2 = 30.3%) and A. delavay (MXD = 0.0317T9–10 + 0.4066, R2 = 33.0%). The composite chronology from the two species can reveal a late summer temperature (August−October) signal with the explained variance 32.2% for its response model. However, in dry areas and or at high altitudes close to upper tree line, the responses of wood densities to climate require further investigation for deciduous and evergreen coniferous species.

Variability of the Early Summer Temperature in the Southeastern Tibetan Plateau in Recent Centuries and the Linkage to the Indian Ocean Basin Mode

Abstract Although many temperature time-series reconstructions, constructed on the basis of tree-ring widths, with lengths of centuries to millennia have been published for many parts of the southeastern Tibetan Plateau (SETP), field reconstruction has been unaddressed to date. Here, we present a tree-ring network comprising 53 chronologies (one δ13C chronology, one regional maximum latewood density chronology, and 51 width chronologies). Using the modified point-by-point reconstruction method, a temperature field consisting of data from 28 meteorological stations in the SETP over the past 200–500 y (the common period was from 1730 to 1998; the longest single period was from 1480 to 2002) was reconstructed. Principal component analysis and rotated principal component analysis results indicated that the reconstructed temperature field may be representative of spatial distribution characteristics. The temperature changes in the SETP were similar. The correlation coefficients between the reconstructed regional average temperature and each observed series were 0.44–0.83 (86% were greater than 0.6, and all the significance tests reported a level of 0.01). Temperature changes were mainly synchronous with those in the middle and low latitudes of the Northern Hemisphere. We then explored the influence of possible climatic forcing and found that the Indian Ocean Basin mode may be a principal factor controlling the interannual variations in the STEP summer temperatures.

The temperature sensitivity along elevational gradients is more stable in maximum latewood density than tree-ring width

Tree ring-based temperature reconstructions are preferably derived from maximum latewood density (MXD) compared to tree-ring width (TRW). Although temperature signals in MXD are less dependent on site ecology, systematic analyses of the effects of elevation and slope aspect on ring formation are still lacking. Here, we assess the climate sensitivity of MXD and TRW chronologies from six larch (Larix decidua Mill.) sites across the Simplon valley in the southwestern Swiss Alps, representing elevations from 1400 to 2150 m asl on both north- and south-facing slopes. We find decreasing temperature signals with decreasing elevation in MXD and TRW, though correlation coefficients are generally higher for MXD and on the warmer and dryer south exposed slopes. While the greatest temperature signals are found for MJJA at highest elevations with r = 0.71 for MXD and r = 0.57 for TRW (both p < 0.05 and for the 1928–2009 common period), MXD still correlates significantly positive at the lowest elevation site that is ~750 m below the treeline. Our findings indicate the suitability of MXD over TRW for temperature reconstructions when using historical wood sources of unknown origin.

Reduced Temperature Sensitivity of Maximum Latewood Density Formation in High-Elevation Corsican Pines under Recent Warming

Maximum latewood density (MXD) measurements from long-lived Black pines (Pinus nigra spp. laricio) growing at the upper treeline in Corsica are one of the few archives to reconstruct southern European summer temperatures at annual resolution back into medieval times. Here, we present a compilation of five MXD chronologies from Corsican pines that contain high-to-low frequency variability between 1168 and 2016 CE and correlate significantly (p &lt; 0.01) with the instrumental April–July and September–October mean temperatures from 1901 to 1980 CE (r = 0.52−0.64). The growth–climate correlations, however, dropped to −0.13 to 0.02 afterward, and scaling the MXD data resulted in a divergence of &gt;1.5 °C between the colder reconstructed and warmer measured temperatures in the early-21st century. Our findings suggest a warming-induced shift from initially temperature-controlled to drought-prone MXD formation, and therefore question the suitability of using Corsican pine MXD data for climate reconstruction.

Reconstructing Summer Precipitation with MXD Data from Pinus sylvestris Growing in the Stockholm Archipelago

Maximum latewood density (MXD) chronologies have been widely used to reconstruct summer temperature variations. Precipitation signals inferred from MXD data are, however, rather scarce. In this study, we assess the potential of using MXD data derived from Scots pine (Pinus sylvestris L.) growing in the Stockholm archipelago (Sweden) to reconstruct past precipitation variability. In this area, slow-growing pine trees emerge on flat plateaus of bedrock outcrops with thin or absent soil layers and are, therefore, sensitive to moisture variability. A 268-year-long MXD chronology was produced, and climate–growth relationships show a significant and robust correlation with May–July precipitation (PMJJr = 0.64, p &lt; 0.01). The MXD based May–July precipitation reconstruction covers the period 1750–2018 CE and explains 41% of the variance (r2) of the observed precipitation (1985–2018). The reconstruction suggests that the region has experienced more pluvial phases than drought conditions since the 1750s. The latter half of the 18th century was the wettest and the first half of the 19th century the driest. Climate analysis of “light rings” (LR), latewood layers of extreme low-density cells, finds their occurrence often coincides with significantly dry (&lt;41 mm precipitation) and warmer (1–2 °C above average temperature), May–July conditions. Our analysis suggests that these extremes may be triggered by the summer North Atlantic Oscillation (SNAO).

Maximum July–September temperatures derived from tree‐ring densities on the western Loess Plateau, China

AbstractTree‐ring densitometric studies conducted in semi‐arid regions are exceedingly rare. In this study, we evaluate a new maximum latewood density chronology from a collection of Picea purpurea trees growing in semi‐arid northwestern China for climatic reconstruction purposes. We find statistically significant correlations between annual maximum density variations and July–September maximum temperatures over the 1957–2014 calibration period. Using a linear model to transfer the density variations to temperature estimates, we then reconstruct maximum summer temperatures from 1840 to 2014. Statistical analyses and verification tests demonstrate that the resulting transfer function is both reliable and stable. The reconstructed temperature series shows strong inter‐annual and decadal variability. Several extremely cool and warm years are apparent on an inter‐annual scale, while three extended cool periods and a warm period are observed on a decadal scale. In addition, the reconstructed temperature series exhibits a pattern synchronous with that of the Indian monsoon index, as well as a moderate relationship to volcanic eruptions. This densitometric study reveals typical climatic variation characteristics and provides useful data for deepening our understanding of climate history in the semi‐arid regions of China.

Eco-Physiological Response of Conifers from High-Latitude and -Altitude Eurasian Regions to Stratospheric Volcanic Eruptions

Stratospheric volcanic eruptions have had significant impacts on the radiation budget, atmospheric and surface temperatures, precipitation and regional weather patterns, resulting in global climatic changes. The changes associated with such eruptions most commonly result in cooling during several years after events. This study aimed to reveal eco-physiological response of larch trees from northeastern Yakutia (YAK), eastern Taimyr (TAY) and Altai (ALT) regions to climatic anomalies after major volcanic eruptions CE 535, 540, 1257, 1641, 1815 and 1991 using new multiple tree-ring parameters: tree-ring width (TRW), maximum latewood density (MXD), cell wall thicknesses (CWT), δ13C and δ18O in tree-ring cellulose. This investigation showed that TRW, CWT, MXD and δ18O chronologies recorded temperature signal, while information about precipitation and vapor pressure deficit was captured by δ13C chronologies. Sunshine duration was well recorded in δ18O from YAK and ALT. Tree-ring parameters recorded cold, wet and cloudy summer anomalies during the 6th and 13th centuries. However, significant summer anomalies after Tambora (1815) and Pinatubo (1991) eruptions were not captured by any tree-ring parameters

Climate sensitivity of high- and low-elevation Larix decidua MXD chronologies from the Tatra Mountains

Maximum latewood density (MXD) measurements from high-elevation/-latitude sites are an important proxy for summer temperature reconstructions. Here, we present 201 MXD series from living larch (Larix decidua Mill.) trees that were growing at around 850 and 1450 m a.s.l. in the Slovakian Tatra Mountains, together with 56 MXD series from historical timbers of the same species and region. We explore the climate signal at the high- and low-elevation sites and assess the effects of varying temperature and precipitation regimes on MXD formation. Ranging from spring temperature to summer precipitation, the elevation-specific climate sensitivity suggests that the MXD measurements from living and relict sources should not be merged for paleoclimatic studies. This finding emphasizes the challenge of attributing a predominant climate factor that controls wood formation across a wide range of historical constructions. A better understanding of the ‘true’ climate signal requires more samples during the period of overlap between the living and historical trees.

Seasonal and synoptic climatic drivers of tree growth in the Bighorn Mountains, WY, USA (1654–1983 CE)

In the United States’ (US) Northern Rockies, synoptic pressure systems and atmospheric circulation drive interannual variation in seasonal temperature and precipitation. The radial growth of high-elevation trees in this semi-arid region captures this temperature and precipitation variability and provides long time series to contextualize instrumental-era variability in synoptic-scale climate patterns. Such variability in climate patterns can trigger extreme climate events, such as droughts, floods, and forest fires, which have a damaging impact on human and natural systems. We developed 11 tree-ring width (TRW) chronologies from multiple species and sites to investigate the seasonal climatic drivers of tree growth in the Bighorn Mountains, WY. A principal component analysis of the chronologies identified 54% of shared common variance (1894–2014). Tree growth (expressed by PC1) was driven by multiple seasonal climate variables: previous October and current July temperatures, as well as previous December and current April precipitation, had a positive influence on growth, whereas growth was limited by July precipitation. These seasonal growth-climate relationships corresponded to circulation patterns at higher atmospheric levels over the Bighorn Mountains. Tree growth was enhanced when the winter jet stream was in a northward position, which led to warmer winters, and when the spring jet stream was further south, which led to wetter springs. The second principal component, explaining 19% of the variance, clustered sites by elevation and was strongly related to summer temperature. We leverage this summer temperature signal in our TRW chronologies by combining it with an existing maximum latewood density (MXD) chronology in a nested approach. This allowed us to reconstruct Bighorn Mountains summer (June, July, and August) temperature (BMST) back to 1654, thus extending the instrumental temperature record by 250 years. Our BMST reconstruction explains 39–53% of the variance in regional summer temperature variability. The 1830s were the relatively coolest decade and the 1930s were the warmest decade over the reconstructed period (1654–1983 CE) – which excludes the most recent 3 decades. Our results contextualize recent drivers and trends of climate variability in the US Northern Rockies, which contributes to the information that managers of human and natural systems need in order to prepare for potential future variability.

Post‐industrial late summer warming recorded in tree‐ring density in the eastern Tibetan Plateau

AbstractTree‐ring density has been suggested to be a useful proxy for revealing long‐term late summer or growing season temperature variability on the Tibetan Plateau (TP). However, the current chronology length of tree‐ring density records on the TP is obviously shorter than both tree‐ring width and tree‐ring isotope records. This phenomenon implies the possibility of extending the current tree‐ring density record into earlier times and provides us with an opportunity to evaluate recent warming on a longer time scale. In this study, we present a 640‐year tree‐ring maximum latewood density (MXD) chronology of Balfour spruce back to 1,375 CE in the eastern TP. This tree‐ring MXD chronology is longer than the previous ones on the TP. Growth‐climate relationship analysis shows that the established MXD chronology correlates significantly and positively with August–September mean temperatures recorded at the nearest meteorological station over the common period of 1954–2014 (r = 0.66, effective degree of freedom [edf] = 62.7, p &lt; 0.0001). Based on the growth‐climate response relationship, the August–September mean temperature was reconstructed from 1,625 to 2,014, which is the reliable period of the MXD chronology, with the expressed population signal (EPS) greater than 0.85. The reconstructed August–September temperatures show an increasing trend since the late 19th century, and this reconstruction suggests that the last 10‐, 30‐, 50‐ and 100‐year periods all appear to be the warmest over the past 390 years. Together with preciously published temperature reconstructions based on tree‐ring MXD near our study area, the results of this study demonstrate that the southeastern TP has experienced post‐industrial warming since the late 19th century.

Were medieval warm-season temperatures in Jämtland, central Scandinavian Mountains, lower than previously estimated?

Today few high-quality tree-ring based temperature reconstructions extending over the past millennium exist, and those have, in general, low replication in their early parts. Here we present a new and updated maximum latewood density (MXD) chronology extending over the last 1200 years, built from local Scots pine wood sources (living trees, drywood preserved the ground, and subfossil wood extracted from lakes) all collected within 20 km in the Scandinavian Mountains in Jämtland. The MXD data was used to reconstruct April-September mean temperatures, where 60% of the variance in observed temperatures could be explained. The reconstruction exhibited distinct multidecadal variability, with the coldest periods centred on ca. 900, 1450, 1600 and 1900 CE, and the warmest periods on ca. 1160, 1250, 1500, 1660 CE. The last part of the 20th – early part of 21st century was the warmest period throughout the whole record, and the reconstruction suggests that, on average, the Medieval Climate Anomaly (MCA, 950–1250 CE) was only slightly warmer than the Little Ice Age (LIA, 1450–1900 CE). In fact, compared to earlier reconstructions from the region, the new reconstruction suggested lower MCA warm-season temperatures. However, despite sufficient replication during that period, high inhomogeneity among the MXD series makes this period slightly uncertain. The unique drywood on which the chronology was built, displayed a distinct regeneration pattern, where changes in Scots pine establishment was interpreted as responses to changes in forest fire activity and climate throughout the past millennium.

Different climate response of three tree ring proxies of Pinus sylvestris from the Eastern Carpathians, Romania

The aim of this study was to compare the climatic responses of three tree rings proxies: tree ring width (TRW), maximum latewood density (MXD), and blue intensity (BI). For this study, 20 cores of Pinus sylvestris covering the period 1886–2015 were extracted from living non-damaged trees from the Eastern Carpathian Mountains (Romania). Each chronology was compared to monthly and daily climate data. All tree ring proxies had a stronger correlation with the daily climate data compared to monthly data. The highest correlation coefficient was obtained between the MXD chronology and daily maximum temperature over the period beginning with the end of July and ending in the middle of September (r = 0.64). The optimal intervals for the temperature signature were 01 Aug – 24 Sept for the MXD chronology, 05 Aug – 25 Aug for the BI chronology, and both 16 Nov of the previous year – 16 March of the current year and 15 Apr – 05 May for the TRW chronology. The results from our study indicate that MXD can be used as a proxy indicator for summer maximum temperature, while TRW can be used as a proxy indicator for just March maximum temperature. The weak and unstable relationship between BI and maximum temperature indicates that BI is not a good proxy indicator for climate reconstructions over the analysed region.