Search

In recent decades, the Loess Plateau has experienced drying that has had a massive influence on society, ecosystems, and agriculture. However, the limited availability of observed climate data hampers the assessment of continuous drying. In this study, we present a robust tree-ring-width chronology of Chinese Pine with which we reconstructed the pre-monsoon self-calibration Palmer Drought Severity Index (scPDSI) for the last 246 years. The reconstruction is derived from cores sampled from two sites over the southeastern Loess Plateau, is reliable and stable, and explains 54.9% of the variance of observed scPDSI over the period 1957–2017. Our reconstruction reveals obvious annual and decadal variations, with an uneven temporal distribution of dry and wet years. Our reconstruction documents the ongoing drying in recent decades. The period from 2000 to 2018 was the driest over the last 246 years, as according to the 11-year moving average series, five of the top ten most severe droughts occurred during this period. Results of spatial correlation analysis and composite analysis suggest that the North Atlantic sea surface temperature may influence pre-monsoon drought variation over the southeastern Loess Plateau by influencing the westerly jet, the height field, and atmospheric vertical motion. [ABSTRACT FROM AUTHOR]

Urban forests, vital for providing ecosystem services in cities, face challenges from climatic factors, particularly in heterogeneous urban environments. Kyiv, one of Europe's largest and most populated cities, boasts a varied topography, with about 55 % of its area covered by forests, where Quercus robur predominates. In this study we investigate the sensitivity of Q. robur trees to climatic factors within Kyiv's urban forest, utilizing tree ring widths as a proxy. Employing dendrochronological approaches, we built nine site-mean ring-width chronologies and identified the growth pointer years and their frequency. Using moving windows in daily correlation analysis, we examined Q. robur response to climatic variations over the last 135 years. Additionally, linear mixed-effects models (LMMs) were applied to the site-specific characteristics such as slope steepness, altitude a.s.l., soil type, soil mechanical composition, soil pH, forest type and coefficient of soil saturated hydraulic conductivity, to identify which of them exert a significant influence on studied trees' sensitivity to precipitation and temperature. Our results showed that the frequency of negative or positive pointer years in Q. robur growth coincides with extremely dry or wet years. The precipitation amount falling from the dormant period to the early growing season emerges as the key factor for Q. robur trees' radial growth. The trees' sensitivity to this factor was found to be significantly influenced by the slope steepness. Our findings contribute valuable insights into the complex interplay between urban heterogeneity, climatic factors, and the climatic sensitivity of Q. robur in urban areas. This research contributes to a deeper understanding of urban forests' dynamics, proposing management strategies for slope stability, soil water retention, and natural tree regeneration. • Slope steepness drives Q. robur sensitivity to water deficit in urban forests. • Q. robur sensitivity to precipitation remains stable across sites and study period. • Q. robur shows unstable and inconsistent temperature sensitivity across sites. • Soil mechanical composition and stand age predict Q. robur growth. • Slope stabilization and water retention proposed to enhance forest resilience. [ABSTRACT FROM AUTHOR]

The radial growth pattern of alpine coniferous trees in the mid-high latitudes of the Northern Hemisphere has an unstable and inconsistent response to climate warming. Understanding the growth trends of trees in the past and future is crucial for forest cultivation against the background of climate change. Thus, we used traditional dendroclimatological methods to analyze the radial growth patterns and stability in response to climate change of the two dominant species on Guancen Mountain and concluded that: (1) the radial growth of Larix principis-rupprechtii was more sensitive than that of Picea meyeri to climatic factors; (2) before and after the abrupt temperature change, the major controlling climatic factors for the radial growth of the two dominant species were spring precipitation and mean temperature, respectively; (3) before the abrupt temperature change, the radial growth of L. principis-rupprechtii was affected by the mean temperature in autumn, while that of P. meyeri was restricted by the standardized precipitation evapotranspiration index in spring; after the abrupt temperature change, the major controlling climate factors of L. principis-rupprechtii and P. meyeri were winter drought and the combination of water and heat in summer, respectively; and (4) after the abrupt temperature change, the interannual basal area increments of the two species followed an upward trend, however, the radial growth rate of both species decreased after detrending, and the growth and development of both species were seriously stressed by drought. Under the background of climate warming, to explore the coping situation of different tree species in the same habitat, to provide theoretical and mechanism support for the future cultivation of forests according to local conditions, and to provide suggestions for the "greening" problem fundamentally. [ABSTRACT FROM AUTHOR]

The high northern latitudes offer an ideal environment to analyze tree growth responses to unprecedented recent warming. In this study, for the first time, we explore the dendroclimatological potential of latewood blue intensity (LWBI) and delta blue intensity (DBI) at two Siberian larch (Larix sibirica Ledeb.) sites in the upper treeline ecotone of the Ural Mountains, northern Russia. To assess the climate signals encoded in LWBI and DBI, as well as tree-ring width (TRW) and maximum latewood density (MXD), we correlated these parameter-specific chronologies against monthly temperature means, precipitation totals, and the SPEI index. LWBI and BDI exhibit robust and stable positive correlations with summer temperature, higher than TRW but slightly lower than MXD at both sites, with marginal negative effects from precipitation and strong negative correlations with SPEI. As direct surrogates for MXD, LWBI and DBI from larch trees offer reasonable alternatives as proxies for temperatures in northern latitudes. [ABSTRACT FROM AUTHOR]

Understanding the complex dynamics of past tree growth-climate interactions is essential for predicting forest ecosystem responses to current climate change. Here, we explore the climate drivers of long-term growth dynamics in 400-year-old Pinus ponderosa trees at Sunset Crater Volcano in northern Arizona, including recent responses to unprecedented warming. To evaluate multiple climate factors potentially limiting montane trees on porous lava at 2450 m elevation, we employed several tree-ring proxies, including total ring width (TRW), earlywood width (EWW), latewood width (LWW), earlywood minimum density (minD), and latewood maximum density (maxD). We used static and moving correlations to assess how variations in previous and current year temperatures, precipitation, Standardised Precipitation-Evapotranspiration Index (SPEI), El Niño 3.4, and Pacific Decadal Oscillation (PDO) indices impact overall growth and density and their seasonal pattern. Our analyses revealed a seasonal shift in climate drivers, from the positive influence of winter and spring precipitation on EWW and minD to the negative effect of high summer temperatures and drought on LWW and maxD. This supports the hypothesis that tree growth in semi-arid regions results from a complex interplay between soil water content and evaporative forcing. Diminished precipitation and increased temperatures reduced EWW (constituting ∼60 % of total TRW), notably in the years 1925–1950 and 1990–2010, while the most favorable periods for growth were during cooler, wetter years 1900–1925 and 1960–1980, resulting in large EWW with low minD. During the warmer and drier years of 1930–1960 and 1990–2016, warmer Pacific waters, indicated by positive PDO and El Niño 3.4 indices, promoted wider earlywood with larger lumen size and thus lower minD, likely due to increased moisture and reduced spring drought. There was no marked growth decline in the last three warmest decades due to relatively stable precipitation. However, since the 1980s, climate drivers have shifted from winter and spring to summer, possibly contributing to extremely low growth years and fire events in the region due to summer heatwaves and droughts. These findings contribute to a better understanding of the complex relationship between climate change and tree growth dynamics in vulnerable semi-arid mountain forests. • Pinus ponderosa trees from western USA are strongly affected by climate variations. • Both tree-ring width and density present a seasonal, temporal, and spatial sensitivity to climate. • Earlywood and latewood width and density present different climate relationships. • The tree-ring width and density relationships with climate are non-stable over time. • Pinus ponderosa present an intricate and complex growth and density responses to climate. [ABSTRACT FROM AUTHOR]

• TSCS is a novel definition of non-stationary climate-growth relationships. • High elevation spruce featured a declining summer temperature sensitivity. • Low elevation spruce is increasingly affected by water limitations. • Temporal shifts in spruce's climate sensitivity are modulated by the continentality. Across much of Europe, climate change has caused a major dieback of Norway spruce (Picea abies L.), an economically important tree species. However, the southeasternmost fringe of this tree species – the Eastern Carpathians – has not yet suffered large-scale dieback. Studying temporal shifts of climate sensitivity (TSCS) over time may elucidate the degree to which Norway spruce may be vulnerable to climate-change induced decline in upcoming decades. Under this framework, we analyzed a regional tree-ring network comprising >3000 trees, with the aim of quantifying TSCS since 1950. We mathematically defined TSCS as the slope parameter of the regression of climate sensitivity (the correlation coefficient) over time. Given the often-observed contrasting shift of climate sensitivity at low versus high elevations, we were particularly interested in studying potentially divergent TSCS along elevational and spatial gradients. Our analyses revealed several indications of TSCS for Norway spruce in the Eastern Carpathians. First, at high elevations (>1100 m a.s.l.), we found that the positive link between summer temperature and spruce growth decreased significantly over the study period. In turn, these trees, over time, featured an increasing positive relationship with late winter temperatures. At low elevations (<800 m a.s.l.), the signal of positive summer Standardised Precipitation-Evapotranspiration Index (SPEI) correlation became more frequent among sites towards 2021, while the strength of the positive winter SPEI correlation from the previous growing season weakened. Our results revealed that TSCS was driven significantly by an elevational climate gradient and a longitudinal continentality gradient. Overall, our findings indicate that Norway spruce is increasingly affected by water limitations under climate change at low elevations, highlighting a potentially rising risk of decline of this species in the Eastern Carpathians. [ABSTRACT FROM AUTHOR]

Ongoing climate change and associated extreme events strongly impact the growth and vitality of forest ecosystems in Europe. Because of its' high drought sensitivity, European beech, which is considered as climax tree species in large parts of Central Europe, may specifically suffer. Hence, recent studies increasingly focus on the resistance and resilience of beech growth to climate change. Intra-specific variations in growth responses by comparing different beech provenances, however, received less attention, as did the question whether provenance selection can be used to mitigate potential future negative impacts of climate change. Therefore, we here investigated 24 provenances belonging to the International Beech Provenance Trial growing at three sites in Germany along a latitudinal gradient (study sites are referred to as 'North', 'Center', 'South'). Specifically, we compared tree-ring width (TRW), diameter breast height (DBH), climate-growth relationships, as well as drought resistance and resilience in the extreme years 2003 and 2018. Large differences in growth performance were observed between the three study sites. At site North, beech trees showed the highest DBH and TRW. Tree growth was predominantly driven by previous-year October and current-year winter temperature, whereas growth at sites Center and South was significantly impacted by summer SPEI and constrained by precipitation in late winter and early June, respectively. Overall, drought responses in 2003 were less variable than in 2018. We found increasing resistance and decreasing resilience from the wetter North to the drier South, but with minimal differences between the Center and the South. Whereas differences between study sites were large, provenance differentiation within sites was comparably low, substantiating that beech is a highly plastic tree species. Even though some provenances were found to perform slightly better or worse, differences were not statistically significant and show unclear patterns. Hence, we conclude that climate change will affect beech forests in Europe mainly depending upon site conditions, and that provenance selection may not ensure superior growth performance. [Display omitted] • Comparison of 24 beech provenances at 3 trial sites along an ecological gradient. • High within-provenance variance in growth, climate sensitivity and drought response. • Local site conditions mainly shape tree growth and climate sensitivity. • No evidence for provenance-specific drought responses. [ABSTRACT FROM AUTHOR]

More frequent and severe droughts have affected forest ecosystems throughout Europe in recent decades. In Central Europe, large-scale dieback of Norway spruce has, for example, been observed, whereas Norway spruce decline was so far less widespread in Eastern Europe. To assess the potential future impacts of drought on Norway spruce in the southeastern part of its natural distribution, studies on drought resilience are urgently needed. Here, we use a tree-ring network consisting of more than 3000 trees from 158 managed Norway spruce stands of different ages distributed along elevational gradients in the Eastern Carpathians to assess growth responses to drought. Specifically, we analyzed differences in resilience components (e.g., resistance, recovery, resilience, recovery period) with elevation and tree age, and used the 'line of full resilience' concept to comprehensively assess drought resilience. Our results show that Norway spruce at low elevations (<800 m) is characterized by the lowest resistance to drought, though has a high recovery, while at high elevations (>1400 m), a higher resistance is associated with a low recovery. In general, older trees were found to need more time to recover. Resilience decreases with a higher water deficit, suggesting that Norway spruce is at risk in the Carpathians with ongoing climate change, urging the need for adaptative forest management. • Spruce resilience was assessed using more than 3000 trees in the Carpathians. • Spruce suffers most from drought at low elevations, though it recovers quickly. • Older trees were found to need more time to recover. • Resilience decreases with a higher water deficit, suggesting that spruce is at risk. [ABSTRACT FROM AUTHOR]

In mountains, the reactions of trees to climatic fluctuations and changes depend on various factors, including ecological gradients and species. This study investigates the radial growth of Siberian stone pine (Pinus sibirica Du Tour), a widespread key conifer in the Siberian taiga, across its elevational range in the Western Sayan Mountains of Southern Siberia. Wood samples were gathered along three latitudinal-elevational transects spaced ca. 80–100 km apart from each other, spanning from west to east across the Western Sayan region. The midpoint of these transects coincided with a large reservoir on the Yenisei River. Each transect encompassed three distinct sites: the lower limit of species growth at 400–500 m a.s.l., a site located at 1700–2050 m a.s.l. near the upper forest line, and an intermediary site falling between these boundaries. A spectacular synchronicity was observed in TRW residual chronologies (R =0.56–0.78 over 1936–2010) and their climatic responses across all sites near the upper forest line and 200–300 m below it. In these areas, temperatures showed a predominantly positive impact from the previous July-August to the current August, except for the end of March–April. The negative influence of excess precipitation during these seasons decreased from west to east, whereas early spring precipitation exhibited a positive correlation with TRW. At the lower limit of growth, the TRW chronologies of species showed lower correlation values between each other (R =0.26–0.36). Here, the species exhibited a positive impact of annual precipitation and a negative influence of temperature, particularly in the previous August and current May-June, albeit of varying intensities. At the mid-montane site, located at 300–500 m above the lower limit of species growth, a mixed climatic influence was observed with a positive response to annual temperatures and June precipitation. Further, the pointer years of the maximum or minimum indexed TRW also occurred much more synchronously in highland forests. The observed shifts in climatic responses indicated that climate warming has advanced the onset of vegetation and delayed the dormancy in these regions. The majority of the Siberian stone pine stands under consideration showed a positive response to warming. Interestingly, an absence of steady growth decline, even in the foothills, indicated a non-climatic range border. The study approach allowed us to recognize with daily resolution annual and seasonal climatic variables impacting stone pine growth that can be probably reconstructed on a local (precipitation) or regional (temperature) scale. This study enhanced the understanding of climate–growth relationships in P. sibirica , offering insights into the species' resilience and vulnerability across ecological gradients in response to changing climatic conditions. • Pinus sibirica Du Tour growth in Western Sayan is more synchronized in highlands. • Heat impact is stable in highlands, but precipitation shows a longitudinal gradient. • Pinus sibirica growth and climatic signal are more diverse at lower elevations. • Climate warming lengthened vegetation period and increased impact of autumn rains. • Climate change in Western Sayan mostly benefited Pinus sibirica growth. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

China's north–south climatic transitional zone, the Qinling–Bashan Mountains (QBM), is sensitive to climate change. In this paper, we present a new tree-ring width chronology derived from a Pinus henryi Mast. from the southwestern part of the QBM and demonstrate that ring width was limited by the mean summer minimum temperature between 3 May and 20 July of the previous year (r = 0.68, p < 0.001). The start and end dates of this limiting period are close to the Beginning of Summer (5–7 May) and the Greater Heat (22–24 July), respectively, of the Chinese Twenty-four Solar Terms, which are important for plant growth. We reconstructed the minimum summer temperatures in the study area since 1879 AD and found four cold periods (1879–1891, 1926–1951, 1966–1980, and 1988–1999 AD) and three warm periods (1911–1916, 1956–1962, and 2004–2010 AD). This new reconstruction not only reveals strong local climate signals but was also able to capture large-scale temperature events. The results of multi-taper spectral analysis, cross wavelet transforms, wavelet coherence analysis, and spatial correlation analysis indicate that summer temperature variations in the QBM are associated with solar activity, the El Niño-southern oscillation (ENSO), the Pacific decadal oscillation (PDO), and the Atlantic multidecadal oscillation (AMO). Our Geodetector results indicate that the combined impact of these drivers on temperature variations is much stronger than that of each individual driver, and they especially emphasize the significant impact of the interaction between the PDO and AMO on temperature variability in the study area. [ABSTRACT FROM AUTHOR]

In order to further understand the past climate variation especially the history of drought and flood events in the East Asian summer monsoon (EASM) marginal area, precipitation from previous August to current July for the period of 1805–2014 AD was reconstructed from a ring-width chronology of Pinus tabulaeformis in Zhaogaoguan (ZGG), a site located in the EASM marginal area in northern China. The transfer function can explain 46.4% (adjusted to 45.4% for the loss of degrees of freedom) of the variance of the observed precipitation during the calibration period (1958–2014 AD). The reconstructed precipitation series revealed that the inter-annual variability was very prominent; 1843 and 1844 AD were the two wettest years, while 1931 and 1999 AD were the two driest years. We noticed that the droughts in 1900, 1906, 1931, 1955 and 1999 AD in the reconstruction series corresponded to the severe floods in the Yangtze River watershed in southern China during those same years. This phenomenon confirmed the typical climate pattern of northern droughts and southern floods in China. Moreover, the reconstructed precipitation series in ZGG showed synchronous variation patterns with the other tree-ring-based hydrological reconstructions in the marginal area of EASM on both inter-annual and inter-decadal scales, indicating the common precipitation variation characteristics of the EASM marginal area. [ABSTRACT FROM AUTHOR]

Abstract The alpine tree line is generally assumed to be controlled by low temperatures, and thus to be experiencing an upward shift under global warming. As global temperatures rise, tree growth at the tree line could either increase if temperature is the limiting factor or decrease if a warming-induced loss of moisture limits growth. Here, we use dendrochronological techniques to understand the abiotic drivers of the Northern Hemisphere's highest tree line ecotones on the southern Tibetan Plateau (TP). Ring-width measurements from three juniper sites between 4680 and 4900 m asl were significantly and negatively correlated with May-June-July evapotranspiration (ET 0), and positively correlated with relative humidity and other moisture-related meteorological variables. At the same time, ring widths were negatively correlated with temperature means and sunshine rates. Our results highlight the common sensitivity of tree growth to moisture variations despite the differential growth trends occurring since 1850 (end of the Industrial Revolution) at the three tree line ecotones. These findings indicate that low temperatures may not be the sole driving force behind tree growth and the range dynamics of alpine tree lines. Tree lines in the dry parts of the TP and possibly also beyond are likely to retreat rather than to advance in a warmer world due to water limitations. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Foggy days decreased a 62% in the last 40 years in a Mediterranean mountain range. • Radial growth of evergreen and deciduous species is positively affected by summer fog. • Summer fog dampened the negative effect of warm temperatures on growth. • Deciduous trees presented negative growth trends in sites exposed to sea breezes. • Evergreen species may outcompete deciduous ones under a warmer, less foggy climate. Abstract The performance and persistence of rear-edge tree populations are relevant issues for conserving biodiversity because these stands harbor high intraspecific biodiversity and play a key role during periods of climate change. The occurrence of these populations is associated with the influence of heterogeneous topography, creating suitable refugia with regionally rare environmental conditions. Climate is changing at a global-scale, but little is known about the long-term impact on local climatic singularities and the associated taxa. We analyzed tree-ring growth chronologies of the two species (Fagus sylvatica and Quercus ilex) forming the evergreen-deciduous forest ecotone, constitutive of the rear-edge of F. sylvatica distribution. The study area is a coastal range with frequent fog immersion, which has been hypothesized to favor the persistence of F. sylvatica in Mediterranean peninsulas. We analyzed the long-term effect of fog on tree growth along a topographical gradient and the sensitivity of growth to rainfall and temperature. The annual number of foggy days has decreased by 62% over the last four decades, concomitant with increasing temperatures. Fog frequency was a relevant factor determining tree growth; fog during summer had positive effects on F. sylvatica growth mainly through a temperature buffering effect. The positive effect of fog on the growth of Q. ilex , however, was likely caused by a collinearity with rainfall. Q. ilex growth was less sensitive to climate than F. sylvatica , but growth of both species was enhanced by a positive early-summer water balance. Our results indicate that a decrease in fog frequency and an increase in temperature may generally benefit Q. ilex in this forest ecotone. Although future changes in rainfall and temperature matter most for the fate of rear-edge tree populations, local climatic singularities such as fog should also be considered. Those can have complementary effects that can swing the balance in ecotones and rear-edge tree populations such as those studied here. [ABSTRACT FROM AUTHOR]

The Sikkim region of the Himalayas is among one of the most highly sensitive hotspots to climate change due to its fragile mountainous environment and rapidly growing population, which exert significant impacts on regional ecosystem factors, including biodiversity and hydrology. Limited observational data coverage in space and time for the high-altitude mountainous region impedes our understanding of climate change and its impact on the environment. In this paper, we develop a 437-year tree-ring width index chronology of Tsuga dumosa (D.Don) Eichler in northern Sikkim as a climate proxy. The substantial dendroclimatic potential of this proxy is evidenced in various statistics computed from the tree-ring chronology. An analysis of the tree-ring chronology indicates a strong negative relationship between late-summer mean temperatures (July–August–September; JAS) and tree growth. This relationship enables us to reconstruct the JAS mean temperature over northern Sikkim since 1705 C.E. The 304-year (1705–2008 C.E.) reconstructed temperature series shows similar warm and cool epochs, which have been observed in many other temperature reconstructions in the region and other proxy records of glacial fluctuations. An overall steady decreasing trend in the regional surface temperature is observed since 1705 C.E., while an increasing trend with intermittent, short and cool epochs are noticed from 1850 C.E. to the present. Prior to the observational period (before 1901 C.E.), cold conditions (X̄ - 1σ) prevailed during 1816–1819, 1831–1837, 1856–1859, and 1884–1887 C.E, with extremely cold conditions (X̄ - 2σ) occurring in 1816, 1817, 1832, 1833, 1857, 1877, 1884, and 1885 C.E; Warm conditions (X̄ + 1σ) prevailed during 1713–1735 and 1823–1827 C.E, with extremely warm (X̄ + 2σ) conditions occurring in 1724, 1823, 1824, and 1825 C.E. Global teleconnections of the reconstructed temperature variations indicate the important roles of the Pacific Decadal Oscillation (PDO), El Niño Southern Oscillation (ENSO), and volcanic eruptions as drivers of temperature variations in the Sikkim region of the Himalayas. [ABSTRACT FROM AUTHOR]

Tree-ring width chronologies from the upper timberline are an important material to reconstruct past temperature variability on the northeastern Tibetan Plateau (NTP). However, precipitation signals are often encoded in the upper timberline chronologies, which complicate the temperature reconstructions and should be removed properly. Here, we propose to use the chronologies from the middle to lower forest zones to remove the precipitation signals encoded in the upper timberline chronologies on the NTP, as tree growth at the two elevation zones records similar precipitation signals but has different temperature responses. We compiled a dataset of 13 Qilian juniper ( Sabina przewalskii Kom.) tree-ring width chronologies, and employed two independent methods to develop millennial (AD 1000–2000) temperature reconstructions on the NTP. The two reconstructions are very consistent with each other over the past millennium, with a correlation of 0.97, and account for more than 50% of the observed temperature variance during 1958–2000. Both reconstructions contain little precipitation signals, suggesting that we have extracted purer temperature information than before. Our reconstructions show similar warm-cold patterns to the temperature records from the surrounding areas, indicating that they are capable of representing large-scale temperature variability during the past millennium. Comparison of our reconstructions with five millennial Northern Hemisphere (NH) temperature series indicates that temperature changes on the NTP are generally distinct from the NH temperature patterns except for the long-term trend during the past millennium, suggesting specific characteristics of regional temperature variability. The distinct variations may be related to the influence of local precipitation, which generally has inverse variations with the temperature on multi-decadal timescales. Our results also show that temperature variability on the NTP has a strong linkage with the strength of the Indian summer monsoon (ISM), with the warm and cool phases of NTP temperature associated with strong and weak ISM, respectively. [ABSTRACT FROM AUTHOR]

Over the past two decades, the dendroclimate community has produced various annually resolved, warm season temperature reconstructions for the extratropical Northern Hemisphere. Here we compare these tree-ring based reconstructions back to 831 CE and present a set of basic metrics to provide guidance for non-specialists on their interpretation and use. We specifically draw attention to (i) the imbalance between (numerous) short and (few) long site chronologies incorporated into the hemispheric means, (ii) the beneficial effects of including maximum latewood density chronologies in the recently published reconstructions, (iii) a decrease in reconstruction covariance prior to 1400 CE, and (iv) the varying amplitudes and trends of reconstructed temperatures over the past 1100 years. Whereas the reconstructions agree on several important features, such as warmth during medieval times and cooler temperatures in the 17th and 19th centuries, they still exhibit substantial differences during 13th and 14th centuries. We caution users who might consider combining the reconstructions through simple averaging that all reconstructions share some of the same underlying tree-ring data, and provide four recommendations to guide future efforts to better understand past millennium temperature variability. [ABSTRACT FROM AUTHOR]

Sunshine is as essential as temperature and precipitation for tree growth, but sunshine duration reconstructions based on tree rings have not yet been conducted in China. In this study, we presented a 497-year sunshine duration reconstruction for the southeastern Tibetan Plateau using a width chronology of Abies forrestii from the central Hengduan Mountains. The reconstruction accounted for 53.5% of the variance in the observed sunshine during the period of 1961–2013 based on a stable and reliable linear regression. This reconstructed sunshine duration contained six sunny periods (1630–1656, 1665–1697, 1731–1781, 1793–1836, 1862–1895 and 1910–1992) and seven cloudy periods (1522–1629, 1657–1664, 1698–1730, 1782–1792, 1837–1861, 1896–1909 and 1993–2008) at a low-frequency scale. There was an increasing trend from the 16th century to the late 18th and early 19th centuries and a decreasing trend from the mid-19th to the early 21st centuries. Sunshine displayed inverse patterns to the local Palmer drought severity index on a multidecadal scale, indicating that this region likely experienced droughts under more sunshine conditions. The decrease in sunshine particularly in recent decades was mainly due to increasing atmospheric anthropogenic aerosols. In terms of the interannual variations in sunshine, weak sunshine years matched well with years of major volcanic eruptions. The significant cycles of the 2- to 7-year, 20.0-year and 35.2-year durations as well as the 60.2-year and 78.7-year durations related to the El-Niño Southern Oscillation, the Pacific Decadal Oscillation and the Atlantic Multidecadal Oscillation suggested that the variation in sunshine duration in the southeastern Tibetan Plateau was possibly affected by large-scale ocean-atmosphere circulations. [ABSTRACT FROM AUTHOR]

A tree-ring width (TRW) chronology was developed from Larix chinensis Beissn at the divide sampling site in the mid-Qinling Mountains, central China. The relationships between tree radial growth and climate factors on several timescales (Daily, Pentad, Dekad and Month) were studied. Compared to precipitation, temperature shown stronger impacts on Larix chinensis Beissn on each timescales. Particularly, pentad was a more suitable scale for tree growth-climate response analysis. Significantly positive correlation was found between tree-ring index and the mean minimum temperature from May to July, i.e. 28 to 42 pentads (r = 0.625, p < 0.001). Based on this relationship, the May to July mean minimum temperature was reconstructed in the last 194 years, with an explained variance of 39.1% for the calibration period from 1957 to 2007. The results of leave-one-out tests showed that the reconstruction mode was stable and reliable. This minimum temperature reconstruction revealed that cold spans mainly occurred in 1816–1831, 1840–1852, 1879–1888 and 1976–1984, while warm spans prevailed in 1863–1878, 1889–1897, 1916–1932 and 2000–2007. Comparisons with other surrounding temperature series from tree rings, our reconstruction could provide a good regional representation of temperature change in the mid-Qinling Mountains. The reconstructed minimum temperature series was further verified by dryness-wetness index (DWI) sequence based on Chinese historical literature. Significant quasi-periodic signals at 32.2a, 20.5a, 8.9–13.1a and 2-8a suggested that temperature variability in the study area may associate with the El Niño-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO). [ABSTRACT FROM AUTHOR]

Pinus plantation forestry in South America has expanded quickly and assumed a significant portion of land use, including in urban arborization. This invasive alien genus changes the plant community, resulting in a loss of biodiversity, and environmental issues that require public policy actions. Here, we applied dendrochronology to assess ecological growth dynamics and micro and macro scale climate effects on an abandoned Pinus elliottii trees in urban forest fragments, and provide insights into the management for public policies. We constructed a robust 41-year (1978 – 2019) chronology that showed r = 0.63, r bar = 0.47, and EPS = 0.92 with an average annual growth rate of 7.10 mm/year. Modeling tree growth of diameter, height and volume of P. elliottii based on tree-ring analysis, we assessed the average diameter without bark (42.37 cm) and height (19 m). The growth rates in the early years evidence pioneer behavior, representing rapid sexual maturity. The volume growth model indicates an average individual volume of 1.23 m³ , with maximum productivity at 16 years when the current annual volume increment peaks. This age corresponds to a diameter of 32 cm, which would be an appropriate minimum logging diameter to wood destined for a sawmill. Volumetric increment rates highlight the potential trade-in forestry sector and application in public policies that aim to control and manage P. elliotti. We evidence significant climatic signals, but with moderate influence on the variability of growth. For the local climatic variables, there was a positive influence of warm and humid summer and late spring, during the previous and current growth seasons. Furthermore, considering global climatic factors, there was only a positive influence of the Annual Southern Oscillation Index for June, representing a positive correlation for dry and cold early winter, influenced by La Niña events. This work provides an understanding of the biological growth of P. elliotti in urban forest fragments and opens a perspective to assist public policies in managing the invasion of Pinus spp. linked to the forest trade. [ABSTRACT FROM AUTHOR]

Knowledge of drought variability and their possible mechanisms during the past hundred years is still limited in the mountainous region of south-central Tibetan Plateau (TP). In this study, a long-term tree-ring width chronology dating back to 1190 CE was combined using 328 increment cores from the Nagqu region. Based on the relationships between this tree-ring width chronology and climate data, we reconstructed May–June self-calibrated Palmer Drought Severity Index (scPDSI) for the past 821 years (1190–2010 CE). Additional comparisons with other available precipitation or drought reconstructions were conducted. We further investigated the influence of the South Asian summer monsoon (SASM) on the drought variability in our study region. Results indicated that our tree-ring width chronology contained stable drought signal in the early summer season (May–June). During the past 821 years, the longest dry and wet periods lasted for 116 and 90 years, respectively, based on a 21-year Fast Fourier transform filter. Specifically, longer than ten years’ dry periods prevailed during 1211–1245 CE, 1280–1358, 1421–1471, 1500–1571, 1580–1598, 1650–1691, 1782–1807 and 1867–1982; while wet intervals occurred in 1190–1210 CE, 1246–1279, 1359–1420, 1472–1499, 1599–1649, 1692–1781, 1808–1866 and 1983–2010. Generally consistent dry and wet intervals across the southern TP were found by comparisons with other available datasets during their common periods. Interestingly, we detected an unstable influence of the SASM on the May–June drought variability in our study region, at least for the past three and a half centuries. This study therefore gives a new perspective of drought variability as well as their relationships with the SASM over a long-term period on the south-central TP. [ABSTRACT FROM AUTHOR]

Age, genetics and social status of trees affect their sensitivity to environmental factors, and information about such effects is needed for comprehensive assessment of growth potential. Climatic sensitivity of radial increment (i.e., tree-ring width) of introduced European beech ( Fagus sylvatica L.) of different generations and social status, growing in its northeasternmost stands in Europe, was studied by dendroclimatological methods. At present, the studied stands occur outside of the natural distribution area of the species, providing opportunity to study adaptability and potential growth of beech in novel environments under changing climate. The sensitivity of radial growth to climatic factors was modulated by the generation and social status (size) of trees. The first generation trees, which were propagated from the material transferred from the northern Germany, were highly sensitive to climatic factors and showed wide spectrum of responses. The dominant trees were particularly sensitive to June precipitation, indicating sensitivity to water deficit in summer. The suppressed trees were mainly sensitive to temperature in the dormant period. Tree-ring width of the second generation trees, which were propagated from the first generation stands, was mainly affected by water deficit in summer, yet the local factors, modulated the mechanisms of response. In one stand, tree-ring width was affected by conditions during the formation of tree-ring, indicating direct influence of weather conditions on xylogenesis. In the other stand, tree-ring width was correlated to weather conditions in the preceding year, suggesting influence via carbohydrate reserves. The effect of social status on climatic sensitivity in the second generation stands was considerably weaker, likely due to the natural and anthropogenic selection of the material best adapted for local conditions. The effect of climatic factors on radial growth of beech has shifted during the 20th century. The effect of autumn temperature has weakened, likely due to warming; the effect of factors related to water deficit in summer has intensified that could be related to both, changes in climate and ageing. The observed climate-growth relationships suggested that conditions in winter have become suitable for beech, yet careful selection of sites/regions with appropriate hydrological conditions appear necessary to counteract the increasing effect of water deficit, hence to ensure productivity of future beech sites in Latvia. [ABSTRACT FROM AUTHOR]

We present the longest high-elevation tree-ring width dataset in the Mediterranean reaching back to the 6th century CE. The network includes 101 living and 92 relict Pinus heldreichii Christ trees from four differently exposed sites in the 2100–2200 m a.s.l. elevation range of Mt. Smolikas in the Pindus Mountains in Greece. Though the sites were all sampled within a distance of <1 km, inter-site correlations are surprisingly low (r 1550–2014 = 0.65–0.87), indicating site exposure might affect tree-ring formation. We here explore the consequence of exposure differences on the climate signals in an eastern Mediterranean treeline ecotone. Temporally stable growth/climate relationships reveal similar seasonal patterns among the four sites, but differences in signal strength. P. heldreichii growth at Mt. Smolikas is significantly controlled by temperature in April (r 1951–2014 = 0.33–0.50) and precipitation in June-July (r 1951–2014 = 0.23–0.42), which emphasizes the overall importance of an early growth onset and subsequent moisture conditions. The association between stem growth and April climate is strongest in the South-facing stand, supporting the significance of higher insolation rates at this thermally privileged site. Strongest summer precipitation signals are found in the NE-facing stand, where trees seem to benefit least from an early growth onset and where reduced meltwater supply may enhance the dependency on early summer precipitation. The significance of spring temperature on tree growth in all four sites constrains the emergence of a distinct summer precipitation signal in the Mt. Smolikas high elevation ecotone. Exploration of the site-specific influences on a new millennium-long tree-ring width dataset is an important step towards an improved understanding of long-term climate variability in the Eastern Mediterranean. Site-related differences in climate sensitivity in the high-elevation tree-ring network at Mt. Smolikas indicate that both temperature and precipitation during different seasons could potentially be reconstructed if distinct site exposures (S versus NE) are considered. [ABSTRACT FROM AUTHOR]

The Kashmir region in the western Himalayas is located in a transition zone between areas dominated by the South Asian Summer Monsoon (SASM) and the North Atlantic Oscillation (NAO). Currently being primarily influenced by westerly disturbances (WDs), the area is important to decipher teleconnections between these two important circulation systems for the assessment of past climate variability. We evaluated climate-growth relationships of Abies pindrow (Royle ex D. Don) and reconstructed April to June (AMJ) self-calibrated Palmer drought severity index (scPDSI) for the south Kashmir region during the period 1643–2016 CE. Our reconstructed scPDSI revealed a long wet phase during 1650–1816 CE, indicating the impact of the Little Ice Age (LIA) over the region, followed by prominent drier post-LIA episodes. The mid 18th century (1730–1760 CE) was the wettest period in the past four centuries, whereas the period 1817 to 1865 CE marked the driest phase. These phases are consistent with other precipitation reconstructions from the WD-dominated western and Trans-Himalayan regions, but inconsistant with summer precipitation reconstructions from the SASM-dominated Himalayan regions. A significant positive correlation between our scPDSI reconstruction and the North Atlantic Oscillation (NAO) for the wet phase of the LIA suggests that the NAO remained dominant in modulating the winter and spring precipitation at the study region. During the 19th and 20th centuries, scPDSI was either weakly or negatively correlated with the NAO index, indicating the influence of other atmospheric circulation systems in driving the spring/summer precipitation in the study area. This study, augmented with other moisture records, contributes to analyze the temporal and spatial extent of moisture variability in a regional perspective. • Abies at westerly dominated Kashmir Himalaya are sensitive to spring moisture. • A 373-yrs of drought reconstruction revealed moist Little Ice Age and dry post-LIA. • Radiative forcings due to volcanic eruption affected the annual growth of Abies. • North Atlantic Oscillations influence winter/spring precipitation at study region. • Strong teleconnection with NINO 3.4 in last four decades due to ocean warming. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new annual runoff was reconstructed since 1672 in Moqu river based on tree ring. • Moqu river was undergoing the most protracted low flow period over the past 348 years. • Runoff reconstruction shows close linkages with climate pattern and Indian summer monsoon. The runoff of Moqu river in Zoige, one of most important water conservation ecological function areas in the upper reaches of the Yellow River, located in the north-east of the Tibetan Plateau, is highly sensitive to climate change. However, the current understanding of the long-term changes in the hydrology of this rives is still fragmentary. In this study, we created a regional tree-ring width chronology from two sample sites in Moqu River Basin and analysed the relationships between tree-ring width, climate, and runoff. We found significant positive correlations between tree-ring width and runoff in multiple months, the highest correlation coefficient occurred with annual runoff from previous July to current June (r = 0.617, 1981–2013). Based on this highly significant (p < 0.01) relationship, we reconstructed runoff variations of Moqu River for the period 1672 to 2019. The reconstructed runoff showed unusual prolonged and frequent low flow periods in recent decades. We found that the continuous low precipitation and the high temperature in the context of global warming are the main reasons for the abnormal runoff in recent decades. We assume that a weakening of the Indian summer monsoon (ISM) circulation system may be the key large-scale factor that caused the unusually prolonged low flow. With global warming, the weakening of ISM intensity leads to reduced water vapor transport from the tropical Indian Ocean to High Asia, resulting in less precipitation and low runoff events in Zoige. Our reconstruction improves the understanding of regional runoff variability over multiple timescales, and also provides a scientific basis for the protection, development, and utilization of water resources related to ongoing global warming. [ABSTRACT FROM AUTHOR]

Tree growth varies closely with high–frequency climate variability. Since the 1930s detrending climate data prior to comparing them with tree growth data has been shown to better capture tree growth sensitivity to climate. However, in a context of increasingly pronounced trends in climate, this practice remains surprisingly rare in dendroecology. In a review of Dendrochronologia over the 2018–2021 period, we found that less than 20 % of dendroecological studies detrended climate data prior to climate-growth analyses. With an illustrative study, we want to remind the dendroecology community that such a procedure is still, if not more than ever, rational and relevant. We investigated the effects of detrending climate data on climate–growth relationships across North America over the 1951–2000 period. We used a network of 2536 tree individual ring-width series from the Canadian and Western US forest inventories. We compared correlations between tree growth and seasonal climate data (Tmin, Tmax, Prec) both raw and detrended. Detrending approaches included a linear regression, 30-yr and 100-yr cubic smoothing splines. Our results indicate that on average the detrending of climate data increased climate–growth correlations. In addition, we observed that strong trends in climate data translated to higher variability in inferred correlations based on raw vs. detrended climate data. We provide further evidence that our results hold true for the entire spectrum of dendroecological studies using either mean site chronologies and correlations coefficients, or individual tree time series within a mixed-effects model framework where regression coefficients are used more commonly. We show that even without a change in correlation, regression coefficients can change a lot and we tend to underestimate the true climate impact on growth in case of climate variables containing trends. This study demonstrates that treating climate and tree-ring time series "like-for-like" is a necessary procedure to reduce false negatives and positives in dendroecological studies. Concluding, we recommend using the same detrending for climate and tree growth data when tree-ring time series are detrended with splines or similar frequency-based filters. • Climate data are rarely detrended prior to dendroecological analyses. • We remind the community of the relevance of detrending climate data in dendro-ecological studies. • Detrending climate data on average strengthened climate–growth correlations. • The stronger the climate trend the stronger the possible correlation change. • Even with no correlation change, regression coefficients can vary substantially. [ABSTRACT FROM AUTHOR]

This study concerns dendrochronology and dendroclimatology of yew growing in Poland. The yew (Taxus baccata L.), a long-lived, slow-growing tree, is regarded as a species threatened with extinction. The eastern boundary of its range transects Poland. The analyses were performed on 34 yew populations which are protected as parts of nature reserves, as nature monuments, or which are planned to be protected. Samples were collected using Pressler borer from a total of 774 trees yielding 1307 profiles. Classical dating techniques (including cross-dating method) were subsequently used to reconstruct 34 local chronologies. Average tree-ring width was 0.84 mm and ranged from 0.27 to 1.47 mm. For most stands, the age of the yew trees is overestimated. The studied populations most frequently are 100–200 years old, and the oldest yew trees in Poland are growing in the KS population (age estimated at 500–600 years). Average tree-ring width was found to be strongly dependent on the chronology length/tree age. The 674 pointer years calculated for the local chronologies served as a basis for determining pointer years for the entire study area. Negative years include: 1862, 1865, 1917, 1927, 1940, 1947, 1956, 1963, 1969, 1976, 1979, 1993, 1996, and 2003. Positive years are: 1884, 1914, 1916, 1965, 1977, 1988, 1997, and 2007. Analysis of weather conditions in those years demonstrated a strong relationship between tree-ring width and air temperature in winter, pre-spring, and early spring. Higher-than-average temperatures during those seasons correlate positively with yew tree-ring width. Response function analysis performed for local and regional chronologies point to a dominant role of air temperature in December of the year preceding growth and in January, February, and March of the current year (linear relationships). June precipitation is an additional factor affecting tree-ring width in some areas of northern and northwestern Poland: the higher the precipitation, the wider the tree-rings. The results obtained, particularly those concerning growth-climate relationships and dendroclimatic regionalisation, can be used in the on-going programme of yew restitution in Poland. • Yew trees growing in Poland, on most stands, are less than 200 years old, but their age is often overestimated. The oldest yew population in Poland is 500–600 years old. • The yew is a slow-growing species – average tree-ring width is only 0.84 mm. • Tree-ring width in yew trees depends on winter and early spring air temperature (cold winters and late onset of spring cause a decrease in tree-ring width). [ABSTRACT FROM AUTHOR]

The mountain forest steppe and taiga in northern Mongolia have experienced a forest decline in area and quality since the end of the last century. Changes in land use, climate, fire frequency and pest occurrence are considered to be the main drivers of this vegetation shift and desertification. Because this region is the source for major rivers, is home to a unique flora and fauna and represents an important source of timber for Mongolia, the ability of different tree species to respond to these changes and regenerate is of increasing interest. Our contribution focuses on the climate-growth relationship of old and young birch trees from two valleys in the Mongolian province of Selenge Aimag. The research site Bugant, located in the Western Khentey Mountains, was the most important logging centre in Mongolia during socialist times. Today, the vegetation is dominated by succession forests of light taiga. The research site Altansumber, on the border of the Sant and Khushat soum, is dominated by light taiga and mountain forest steppe. Traditional nomads who depend on these forests for different reasons inhabit this area. Wood cores were sampled and chronologies of young and old birch trees at Bugant and Altansumber were created. Climate data were obtained from the Eroo station, which is known in the region for its long and reliable climate record. We analysed the climate-growth relationships of the chronologies from 1962 to 2009. At both sites and in both age classes, correlations with temperature were predominantly negative, particularly in April (Bugant, south- and east-facing slopes) and May (Altansumber, north-facing slopes). Precipitation of the late summer of the previous year (August/September) positively correlated with the growth of birch at Altansumber. We assume that the significant negative correlation between winter precipitation (December/January) and the growth of old birches at both sites is due to positive effects of snow cover on the survival rate of herbivorous insect populations. Our results indicate that during the early vegetation period, younger birch trees are more dependent on water availability than older ones. Negative pointer years were characterized by below-average precipitation during the current summer period and above-average spring temperatures. For the old trees, positive pointer years were characterized by above-average summer precipitation. We conclude that water availability is the most crucial factor for the growth of white birch in northern Mongolia. [ABSTRACT FROM AUTHOR]

Millennial long tree-ring records are crucial for better understanding temperature and hydroclimatic variability over the globe. Juniper is one of particularly long-lived species, which can provide more than a thousand-year record, especially in Central Asia. However, there is a lack of dendrochronological series from the Pamir Mountains. Here we report the first 1010-year (AD 1005–2014) juniper tree-ring chronology from the mountain ranges of north-western Tajikistan, the western Pamir-Alay. We present the potential of Juniperus semiglobosa and Juniperus seravshanica in developing millennia-long records. We sampled three study sites at the elevations from 2200 to 3500 m. In general, the climate-growth analyses show that radial growth of the Himalayan pencil juniper is positively correlated with the winter precipitation and spring temperature. At some sites tree rings were also positively correlated with summer temperature. Our findings demonstrate the importance of developing the tree-ring data network for the Pamir-Alay and its potential for reconstruction of hydroclimatic variability over the last thousand years in this region. [ABSTRACT FROM AUTHOR]

Knowledge about tree age is critical to forestry, nature conservation and ecological studies. Direct age determination of large diameter trees through increment cores is complicated by various obstacles, primarily because of rot and insufficient borer length. Here, we aim to (1) test the accuracy of various methods (tree-ring width, basal area increment, age-size relationship) for tree age estimation, (2) select the most accurate approach and (3) enable age estimation of large individuals of Quercus robur . This was done through increment cores collected in an alluvial forest in the Czech Republic. We achieved 75 age estimates for each tree, including our novel approach, which reduces the effect of decreasing tree-ring width and increasing basal area increment during tree life. The extrapolation of mean ring width to missing radius generally overestimates the number of missing rings (by up to 27.5% of actual age) and the level of overestimation increases with decreasing partial core length, while the application of basal area increment largely underestimates the age estimation (by up to 20.5%). Thus, to eliminate the over- and underestimation caused by natural tree ring width decrease and basal area increase during the tree senescence and increasing size, we averaged the number of estimated rings by these two methods. This technique obtained the most reliable age estimates, with an error up to 3.5%. Thus it is suggested here that this technique provides a relatively accurate age estimate for trees where it is impossible to directly determine the age; at least for light-demanding species. Moreover, the proposed technique does not require complicated analysis and is not time consuming. However, future research should test the applicability of this technique for tree species with various ecological strategies, i.e. shade-tolerant species. Finally, we estimate that the age of large oaks in our study area does not exceed 400 years. Due to such fast growth, it is possible to keep the continuity of these keystone structures in a given landscape and thus preserve the associated biodiversity. [ABSTRACT FROM AUTHOR]

Tree rings reveal climatic variations through years, but also the effect of solar activity in influencing the climate on a large scale. In order to investigate the role of solar cycles on climatic variability and to analyse their influences on tree growth, we focused on tree-ring chronologies of Araucaria angustifolia and Araucaria araucana in four study areas: Irati and Curitiba in Brazil, Caviahue in Chile, and Tolhuaca in Argentina. We obtained an average tree-ring chronology of 218, 117, 439, and 849 years for these areas, respectively. Particularly, the older chronologies also included the period of the Maunder and Dalton minima. To identify periodicities and trends observable in tree growth, the time series were analysed using spectral, wavelet and cross-wavelet techniques. Analysis based on the Multitaper method of annual growth rates identified 2 cycles with periodicities of 11 (Schwebe cycle) and 5.5 years (second harmonic of Schwebe cycle). In the Chilean and Argentinian sites, significant agreement between the time series of tree rings and the 11-year solar cycle was found during the periods of maximum solar activity. Results also showed oscillation with periods of 2–7 years, probably induced by local environmental variations, and possibly also related to the El-Niño events. Moreover, the Morlet complex wavelet analysis was applied to study the most relevant variability factors affecting tree-ring time series. Finally, we applied the cross-wavelet spectral analysis to evaluate the time lags between tree-ring and sunspot-number time series, as well as for the interaction between tree rings, the Southern Oscillation Index (SOI) and temperature and precipitation. Trees sampled in Chile and Argentina showed more evident responses of fluctuations in tree-ring time series to the variations of short and long periodicities in comparison with the Brazilian ones. These results provided new evidence on the solar activity-climate pattern-tree ring connections over centuries. [ABSTRACT FROM AUTHOR]

Tree-ring research in the Altai-Sayan Mountains so far only considered a limited number of well-replicated site chronologies. The dendroecological and palaeoclimatological potential and limitations of large parts of south-central Russia therefore remain rather unexplored. Here, we present a newly updated network of 13 larch ( Larix sibirica Ldb.) tree-ring width (TRW) chronologies from mid to higher elevations along a nearly 1000 km west-to-east transect across the greater Altai-Sayan region. All data were sampled between 2009 and 2014. The corresponding site chronologies cover periods from 440 to 860 years. The highest TRW agreement is found between chronologies ≥2200 m asl, whereas the material from lower elevations reveals overall less synchronized interannual to longer-term growth variability. While fluctuations in average June–July temperature predominantly contribute to the growth at higher elevations, arid air masses from Mongolia mainly affect TRW formation at lower elevations. Our results are indicative for the dendroclimatological potential of the Altai-Sayan Mountains, where both, variation in summer temperature and hydroclimate can be robustly reconstructed back in time. These findings are valid for a huge region in central Asia where reliable meteorological observations are spatially scarce and temporally restricted to the second half of the 20th century. The development of new high-resolution climate reconstruction over several centuries to millennia will further appear beneficial for timely endeavors at the interface of archaeology, climatology and history. [ABSTRACT FROM AUTHOR]

It is generally assumed in dendroecological studies that annual tree-ring growth is adequately determined by a linear function of local or regional precipitation and temperature with a set of coefficients that are temporally invariant. However, various researchers have maintained that tree-ring records are the result of multivariate, often nonlinear biological and physical processes. To describe critical processes linking climate variables with tree-ring formation, the process-based tree-ring Vaganov–Shashkin model (VS-model) was successfully used. However, the VS-model is a complex tool requiring a considerable number of model parameters that should be re-estimated for each forest stand. Here we present a new visual approach of process-based tree-ring model parameterization (the so-called VS-oscilloscope) which allows the simulation of tree-ring growth and can be easily used by researchers and students. The VS-oscilloscope was tested on tree-ring data for two species ( Larix gmelinii and Picea obovata ) growing in the permafrost zone of Central Siberia. The parameterization of the VS-model provided highly significant positive correlations ( p < 0.0001) between simulated growth curves and original tree-ring chronologies for the period 1950–2009. The model outputs have shown differences in seasonal tree-ring growth between species that were well supported by the field observations. To better understand seasonal tree-ring growth and to verify the VS-model findings, a multi-year natural field study is needed, including seasonal observation of the thermo-hydrological regime of the soil, duration and rate of tracheid development, as well as measurements of their anatomical features. [ABSTRACT FROM AUTHOR]

Age-related alternation in the sensitivity of tree-ring width (TRW) to climate variability has been reported for different forest species and environments. The resulting growth-climate response patterns are, however, often inconsistent and similar assessments using maximum latewood density (MXD) are still missing. Here, we analyze climate signal age effects (CSAE, age-related changes in the climate sensitivity of tree growth) in a newly aggregated network of 692 Pinus sylvestris L. TRW and MXD series from northern Fennoscandia. Although summer temperature sensitivity of TRW ( r All = 0.48) ranges below that of MXD ( r All = 0.76), it declines for both parameters as cambial age increases. Assessment of CSAE for individual series further reveals decreasing correlation values as a function of time. This declining signal strength remains temporally robust and negative for MXD, while age-related trends in TRW exhibit resilient meanderings of positive and negative trends. Although CSAE are significant and temporally variable in both tree-ring parameters, MXD is more suitable for the development of climate reconstructions. Our results indicate that sampling of young and old trees, and testing for CSAE, should become routine for TRW and MXD data prior to any paleoclimatic endeavor. [ABSTRACT FROM AUTHOR]

Tree-ring based climate reconstructions have been critical for understanding past variability and recent trends in climate worldwide, but they are scarce in Australia. This is particularly the case for temperature: only one tree-ring width based temperature reconstruction – based on Huon Pine trees from Mt Read, Tasmania – exists for Australia. Here, we investigate whether additional tree-ring parameters derived from Athrotaxis cupressoides trees growing in the same region have potential to provide robust proxy records of past temperature variability. We measured wood properties, including tree-ring width (TRW), mean density, mean cell wall thickness (CWT), and tracheid radial diameter (TRD) of annual growth rings in Athrotaxis cupressoides , a long-lived, high-elevation conifer in central Tasmania, Australia. Mean density and CWT were strongly and negatively correlated with summer temperatures. In contrast, the summer temperature signal in TRW was weakly positive. The strongest climate signal in any of the tree-ring parameters was maximum temperature in January (mid-summer; JanT max ) and we chose this as the target climate variable for reconstruction. The model that explained most of the variance in JanT max was based on TRW and mean density as predictors. TRW and mean density provided complementary proxies with mean density showing greater high-frequency (inter-annual to multi-year) variability and TRW showing more low-frequency (decadal to centennial-scale) variability. The final reconstruction model is robust, explaining 55% of the variance in JanT max , and was used to reconstruct JanT max for the last five centuries (1530–2010 C.E.). The reconstruction suggests that the most recent 60 years have been warmer than average in the context of the last ca. 500 years. This unusually warm period is likely linked to a coincident increase in the intensity of the subtropical ridge and dominance of the positive phase of the Southern Annular Mode in summer, which weaken the influence of the band of prevailing westerly winds and storms on Tasmanian climate. Our findings indicate that wood properties, such as mean density, are likely to provide significant contributions toward the development of robust climate reconstructions in the Southern Hemisphere and thus toward an improved understanding of past climate in Australasia. [ABSTRACT FROM AUTHOR]

Changing climate is expected to cause range shifts and reduced growth in Norway spruce ( Picea abies (L.) Karst). In order to mitigate these changes, genetic variation between populations can be utilized in selecting alternative tree origins that are better suited to the new conditions. The aim of this study was to examine the intraspecific differences in the climatic drivers of radial growth in Norway spruce. We used tree-ring data from seven Norway spruce provenance experiments in Finland, located in different climatic conditions and including a large variety of provenances. The annual ring-width indices were studied with hierarchical clustering, correlation analysis with climate variables, pointer year analysis and linear models to identify the provenance differences in growth variation and its climatic control, and compare them on a latitudinal gradient. The cluster analysis revealed patterns of provenance differences in growth variation: north European and central European provenances were grouped in separate clusters within sites, although with some exceptions. Largest provenance differences in climate-growth responses were found in relation to winter and spring temperatures. In the southern provenances warm winters were typically associated with faster growth whereas for the northern provenances the correlations varied from non-significant to negative. In addition, the pointer year analysis showed negative growth anomalies only in the southern provenances for years with exceptionally cold winters. These patterns may reflect the physiological differences between the provenances relating to, for example, cold tolerance and the timing of spring phenology. As the climate warming in Europe is predicted to be strongest during the winter months, acknowledging the intraspecific growth responses to climate in Norway spruce becomes increasingly important. [ABSTRACT FROM AUTHOR]

Drought is a key factor affecting forest ecosystem processes at different spatio-temporal scales. For accurately modeling tree functioning – and thus for producing reliable simulations of forest dynamics – the consideration of the variability in the timing and extent of drought effects on tree growth is essential, particularly in strongly seasonal climates such as in the Mediterranean area. Yet, most dynamic vegetation models (DVMs) do not include this intra-annual variability of drought effects on tree growth. We present a novel approach for linking tree-ring data to drought simulations in DVMs. A modified forward model of tree-ring width (VS-Lite) was used to estimate seasonal- and site-specific growth responses to drought of Scots pine ( Pinus sylvestris L.), which were subsequently implemented in the DVM ForClim. Ring-width data from sixteen sites along a moisture gradient from Central Spain to the Swiss Alps, including the dry inner Alpine valleys, were used to calibrate the forward ring-width model, and inventory data from managed Scots pine stands were used to evaluate ForClim performance. The modified VS-Lite accurately estimated the year-to-year variability in ring-width indices and produced realistic intra-annual growth responses to soil drought, showing a stronger relationship between growth and drought in spring than in the other seasons and thus capturing the strategy of Scots pine to cope with drought. The ForClim version including seasonal variability in growth responses to drought showed improved predictions of stand basal area and stem number, indicating the need to consider intra-annual differences in climate–growth relationships in DVMs when simulating forest dynamics. Forward modeling of ring-width growth may be a powerful tool to calibrate growth functions in DVMs that aim to simulate forest properties in across multiple environments at large spatial scales. [ABSTRACT FROM AUTHOR]

Searching for a robust tree-ring parameter useful for paleoclimatic purposes is one of the most demanding topics in the modern paleoscience. Since Blue Intensity has already expressed itself in different geographical locations all over the world as a possible replacement for maximum density, close attention is paid to investigate features of the inferred signal. The Solovki Islands is a unique location in Northern Russia where two important factors that make this territory attractive for developing a long tree-ring chronology have been met: modern long-living trees and building activities using old trees that were started by monks in the middle of the 16th century. The main goal of the research is to develop pine and spruce chronologies based on tree-ring width (TRW) and delta Blue Intensity (dBI) and to assess the ability of these parameters to be used as climate predictors. As a result, 14 conifer chronologies from 7 sites (4 for pine and 3 for spruce) were developed. The composite pine and spruce chronologies span a period of 474 and 378 years each. Cross-correlation of dBI-based chronologies of both conifers is high (r = up to 0.71 while for TRW-based chronologies it is lower on average (−0.18 to 0.63). Intra-species correlation of TRW chronologies in some cases achieved even negative values (r = −0.18. Discrepancies found between TRW chronologies of pine and spruce could be explained by differences in climatic signals. Response function analysis with monthly temperatures revealed that growth of pine depends on the previous August, while spruce has a temporally stable and strong relation to June temperatures. Compared to TRW, dBI-based chronologies have a high correlation with summer temperatures (r = 0.64 and 0.66 for spruce and pine, respectively). Presented research points out the importance of the response function analysis suggesting that depending on goals of the study several tree-ring parameters could be used, e.g., tree-ring width of spruce responses to June temperatures, while dBI to the whole summer. [ABSTRACT FROM AUTHOR]

A regional chronology (RC) based on tree-ring-width data at two sites was developed for the southern Hulun Buir Sandy Land, a marginal area of the eastern Mongolian Plateau, China. This chronology significantly and positively correlated with the relative humidity from the previous December to September, except in May. The highest correlation of the RC with the mean June–August relative humidity suggested that the growth of Pinus sylvestris var. mongolica strongly reflects seasonal moisture conditions. Consequently, the variation in the mean June–August relative humidity was reconstructed for the reliable time period of 1835–2013; 41.6% of the variance occurred during the calibration period of 1953–2012. Similar patterns of drought and pluvial fluctuations were found in other tree-ring-based moisture reconstructions. Our reconstruction implied that the characteristics of regional hydroclimatic variations, such as the drought and low humidity of the late 1990s to 2000s, were not unusual from the long-term perspective, as suggested by the hydrological records obtained from tree-ring material. Spectrum analyses results and significant spatial correlations of our relative humidity reconstruction with the sea surface temperature (SST) in the eastern equatorial Pacific Ocean and tropical Indian Ocean implied close linkages between moisture in the eastern Mongolian Plateau and remote oceans. When the SST related to the El Niño–Southern Oscillation was high (low), the intensity of the Indian summer monsoon at the northern extremities weakened (strengthened). Thus, moisture decreased (i.e., the relative humidity was low) in North China and in our study area. The low land-sea thermal contrast between Asia and the Indian Ocean due to the enhanced SSTs in the tropical Indian Ocean also influenced the strength of the moisture transfer via the Indian summer monsoon, thereby reducing the moisture variations in the eastern Mongolian Plateau. [ABSTRACT FROM AUTHOR]

Understanding the interactions between the East Asian summer monsoon and Indian summer monsoon is a challenging task because of the insufficient proxy records. In this study, we reconstructed a 225-year precipitation record by combining ring widths of Pinus tabulaeformis and stable oxygen isotope ratios of Larix principis-rupprechtii using a multi-proxy dendroclimatology approach in the North China. The reconstructed record explained 51.9% of the variance in the observed precipitation during 1955–2003. The precipitation series could indicate the intensity of the East Asian summer monsoon. A spatial field analysis indicated that the series was strongly correlated with the reconstructed records of the surrounding area and a large part of the Indian subcontinent. The reconstructed records were significantly and positively correlated with All Indian Precipitation records ( r = 0.32, n = 132, p < 0.001) and with a proxy of the Indian summer monsoon. These findings suggest that a persistent teleconnection exists between the reconstructed record and the Indian summer monsoon records from the past 225 years. The observed interannual synchronisation potentially resulted from the transport of partial water vapour from the Indian summer monsoon area to NC; however, this synchronisation could not be attributed to the El Nino-South Oscillation (ENSO). When considering an interdecadal time scale, the synchronisation with the North Atlantic Oscillation (NAO) has varied since 1779, implying that the NAO may serve as an additional atmospheric pattern that affects this teleconnection. [ABSTRACT FROM AUTHOR]

Global warming is most pronounced in high-latitude regions by altering habitat conditions and affecting permafrost degradation, which may significantly influence tree productivity and vegetation changes. In this study, by applying a “space-for-time” approach, we selected three plots of Larix gmelinii forest from a continuous permafrost zone in Siberia with different thermo-hydrological soil regimes and ground cover vegetation with the objective of assessing how tree growth and productivity will change under different stages of permafrost degradation. A tree-ring multi-proxy characterization of mature trees was used to identify shift in ecophysiological responses related to the modified plant-soil system. Variability of tree-ring width (1975–2009), stable isotope ratios (oxygen and carbon, 2000–2009) and xylem structural characteristics (2000–2009) under climatic conditions of particular years indicated that an increased depth of the soil active layer will initially lead to increase of tree productivity. However, due to an expected water use increase through transpiration, the system might progressively shift from a temperature to a moisture-limited environment. [ABSTRACT FROM AUTHOR]

• Vaganov–Shashkin lite was integrated with stochastic antecedent modeling. • Tree-ring width data of 109 conifers in temperate China were analyzed. • Tree-ring width series were clustered into warm-dry, cold-dry, and cold-wet. • Current and antecedent climatic drivers of tree-ring width series were quantified. • Our model improves the simulated results of tree-ring growth in diverse forests. Process modeling of tree growth responses to climate can improve our understanding of the functioning of tree growth under climate change, but these models do not consider so-called memory effects. Further, memory effects are unstudied in temperate forests of China, which is showing high vulnerability to climate warming. Here, we integrate a process-based Vaganov–Shashkin–Lite (VS-Lite) model of tree ring formation with the stochastic antecedent modeling (SAM) approach, to quantify the current and antecedent climatic drivers of the tree-ring width chronologies of 109 conifers in temperate China. Based on climate-response patterns, tree-ring width series were clustered into "warm-dry," "cold-dry," and "cold-wet." The VS-Lite results indicated growth in the "warm-dry" and "cold-dry" sites were primarily constrained by current soil moisture, while growth in the "cold-wet" sites was mainly constrained by cotemporaneous temperature. Compared to VS-Lite alone, we found significant improvements in model fit for the SAM framework in all forest types. Notably, antecedent drivers explained 14%, 11%, and 21% of the growth variations in "warm-dry," "cold-dry," and "cold-wet" sites, respectively, challenging the assertion that long memory is only important in dry forests. Commonality analysis revealed that growth in "cold-dry" and "cold-wet" sites was determined by antecedent climate while growth in the "cold-dry" and "warm-dry" clusters were determined by the endogenous (autoregressive) memory. In "warm-dry" and "cold-wet" sites, growth was significantly affected by antecedent temperature in opposite directions, whereas in the "cold-dry" sites it was affected by antecedent soil moisture conditions and soil moisture-temperature interactions. Our combined process-empirical model demonstrates that memory is prevalent across temperate forests in China and also improves representation of tree growth in diverse forests under novel climate conditions of the future. [Display omitted] [ABSTRACT FROM AUTHOR]

In this study we used 14 spruce tree-ring width local chronologies from sites that are located in different landscape conditions. The climatic response function for the entire period (116 years) shows that all local chronologies without exception have a positive relationship with June temperature (from 0.196 to 0.408) despite quite different local environmental conditions. This finding allowed us to combine all tree-ring width local chronologies into a composite spruce chronology covering the period of 1676–2016 CE with EPS exceeding the 0.85 threshold. The composite chronology was scaled against June air temperatures (CRU TS 4.01) in order to reconstruct it. Monthly air temperature records from the Arkhangelsk weather station were used as an additional source to validate tree-ring based June temperature reconstruction. It is quite remarkable that our reconstruction matches the Archangelsk records not only in the 20th-early 21st centuries but also in the 19th century, confirming the reliability of the reconstruction over more than two centuries. We also used daily records from the nearest Kem'-Port station to identify a more precise target-window. Current research shows that the spruce response to daily temperature is not limited by June, but also extends up to almost half of July. The warmest reconstructed year occurred in 1856 as confirmed by the data published in the local chronicle. The cooling recorded in the historical evidences (describing extremely severe ice conditions in the Arctic seas during the Great Northern Expedition (1733–1743)) was not corroborated by our reconstruction. In the study, we discuss the reasons of the discrepancies found between Solovki June temperature reconstructions and other data such as different seasonality of the compared records, real local climate warming in Solovki, the applied standardization technique, and low of chronologies' replication. The most reliable part of the reconstruction part lasting from the early 19th to the early 21st centuries is also discussed in terms of its properties like wavelength analyses, and the assessment of influence of volcanic eruptions. [ABSTRACT FROM AUTHOR]

Silver birch (Betula pendula Roth.) is a widespread species with a high potential for aiding sustainability and multifunctionality of European forests, as evidenced in Finland and the Baltics. However, under increasing relevance of climate change for tree growth, the meteorological sensitivity of the species is largely unknown, presuming it to be weather tolerant (low sensitivity). Considering local adaptations of populations of widespread species, climatic changes are subjecting trees to extreme conditions, thus testing their adaptability. Accordingly, information on the plasticity (variability) of responses across a gradient of meteorological conditions is crucial for reliable predictions of tree growth. Tree-ring width network was established to assess the plasticity of growth responses of silver birch to meteorological conditions across the eastern Baltic climatic gradient. Time series analysis in combination with generalized additive modelling were applied to assess responses of birch from 21 naturally regenerated conventionally managed stands scattered from southern Finland to northern Germany. Despite the presumed tolerance, explicit meteorological sensitivity of silver birch was estimated. A gradient of local linear weather-growth relationships was estimated, as growth limitation shifted from temperature during the dormancy to water availability during vegetation period in southern Finland and northern Germany, respectively. However, these relationships were nonstationary, as the effect of summer water shortage was intensifying and sensitivity to it has likely been subjected to local adaptation. The regional generalization revealed presence of stationary, yet nonlinear and plastic growth responses, implying disproportional effects of climatic changes. Such responses also explained the nonstationarities, as the local climates shifted along the regional gradient. At the regional scale, summer water shortage was the main driver of increment, while winter conditions had a secondary role; temperature of the preceding vegetation season also had an effect on increment. Accordingly, increased variability of increment of silver birch is expected under changing climate; still, sensitivity and plasticity of increment can be considered as an adaptation to shifting environments. • Regional weather drivers of radial increment of silver birch were assessed. • Responses of increment to meteorological conditions were non-linear and complex. • Moisture availability was a stronger driver of increment than temperature. • Weather sensitivity of silver birch was comparable with that of Norway spruce. • Weather sensitivity of silver birch was higher than that of Scots pine. [ABSTRACT FROM AUTHOR]

Riparian forests in natural desert oases are extremely vulnerable to water shortages; of late these shortages have been associated with climate change and with increased human-led water allocation. This study covers a hundred-year history (1876–2017) of riparian forest growth at the Ejina Oasis, which is located in the lower reaches of the Heihe River basin of northwestern China. We collected tree cores from Populus euphratica , which is the major tree species found in the Ejina riparian forests. These samples allowed us to chart variations in riparian forest growth and to examine correlations between tree growth and local precipitation, temperature, drought indices, groundwater depth, and runoff volume from the middle reaches of the river. We found that groundwater depth (groundwater being mainly recharged by runoff) is the major factor limiting tree-stem radial growth. We compared runoff reconstruction series from upper reaches and P. euphratica radial growth in the lower reaches. We found a period of greatly decreased growth (1942–1951); which seems to have been due to human water diversion. We note that mountain runoff increased after 2000, but that riparian forest growth didn't increase in tandem; the water that would otherwise have supported the forests had been diverted. Our study provides a warning for future water resource planning and suggests the desirability of policies that will balance the needs of natural ecosystems (riparian forests) with the requirements of artificial ecosystems (croplands). [Display omitted] • Riparian tree radial growth variations were studied at the Ejina Oasis. • The main limit to radial growth is runoff-recharged groundwater depth. • Recently, mountain runoff increase rate is higher than riparian tree radial growth. • Our study provides a warning for future water resource planning. [ABSTRACT FROM AUTHOR]