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Winter snow plays a crucial role in regulating tree growth during the subsequent growing season in regions suffering seasonal or even annual drought stress, but the mechanisms of the potential compensation effect of winter snow on subsequent growing-season tree growth are not well understood. In this study, we establish tree-ring chronologies of six larch forest stands along a marked drought gradient across Northeast China. We identify the spatial pattern in the compensation effects of winter snow on subsequent growing-season tree radial growth and uncover a potentially enhanced compensation effect in drier climates. Our results indicate that in snow-rich sites, winter snow tends to exert a significantly positive effect on tree growth during the growing season, whereas this growth compensation effect is reduced in drier sites. More importantly, our findings identify a much higher compensation effect of winter snow on growing-season larch growth in drier years (24.4–48.0%) than in wetter years (6.1–8.1%) at snow-rich sites. Given the projected increase in both severity and duration of droughts in temperate regions, the potential compensation effect of winter snow could play a crucial role in mediating the adaptation ability of boreal/hemi-boreal forest ecosystems in response to a warmer and drier future climate in these regions.

Increasing summer droughts represent a major threat for the vitality and productivity of forests in the temperate zone. European beech, the most important tree species of Central Europe’s natural forest vegetation, is known to suffer from increased drought intensity at its southern distribution limits, but it is not well known how this species is affected in the center of its distribution range in a suboceanic climate. We compared tree-ring chronologies and the climate sensitivity of growth (MS) in 11 mature beech stands along a precipitation gradient (855–576 mm y⁻¹) on two soil types with contrasting water storage capacity (WSC) in northwest Germany to test the hypotheses that recent warming is impairing beech growth also in the center of its distribution below a certain precipitation limit, and stands with low soil WSC are more susceptible. We found a threshold of about 350 mm of mean growing season precipitation below which basal area increment (BAI) showed a consistent decline since the 1970s. The frequency of negative pointer years and MS were highest in low-precipitation stands on sandy soil, but both parameters have increased during the last decades also in the moister stands. The factor with largest impact on BAI was precipitation in June, in combination with high mid-summer temperatures. Contrary to our hypothesis, the edaphic effect on growth dynamics was surprisingly small. We conclude that global warming-related growth decline is affecting European beech even in the center of its distribution below a hydrological threshold that is mainly determined by mid-summer rainfall.

The dendrochronological potential of Juniperus foetidissima, growing in central Anatolia, was assessed. Raw, standard, and residual tree-ring chronologies were prepared for J. foetidissima trees in the Eskişehir region using classical dendrochronological methods for the period between 1875 and 2014. All the chronologies were statistically relevant, and the running correlation, expressed population signal, and mean sensitivity values in the residual tree-ring chronology were within the given limits. Therefore, the residual tree-ring chronologies were used to assess the climate-growth relationship. The relationships between tree-ring width growth and climate variables (mean temperature, monthly sum of precipitation) were investigated using response function analysis (moving windows correlations) in the R platform. Positive or negative relations were found between the residual tree-ring widths and the monthly precipitation and mean temperature, but with low coefficient values. The tree-ring width growth showed a significantly negative response to precipitation in August of the current year for the period in 1977-2001 and 1978-2002 and significantly positive to temperature in June of the current year for the period in 1971-1995, 1972-1996, and 1993-1996. In conclusion, despite some problems with cross-dating, J. foetidissima can generally be used for dendrochronological research and is suitable for developing long-term chronologies.

A 105-year chronology (AD 1917–2021) was developed from mountain birch (Betula pubescens Ehrh.) from beyond the coniferous treeline on the Kola Peninsula in Northwestern Russia (68.86 N, 34.69 E). A total of 22 trees were cored, including the oldest living mountain birch of 105 years old. The highest correlations occurred for the May temperature (r = 0.39, p < 0.01) and July sunshine duration (r = −0.39, p < 0.05). The increase in radial growth in May seemed to be caused by snowmelt giving rise to soil temperature, which can lead to a resumption in radial growth after winter dormancy. The negative correlation with the July sunshine duration seemed to be connected to changes in the spectral composition of solar radiation in the red to far-red ratio in the end of the polar day in July. The application of wavelet coherency revealed a significant (>95%) connection between the radial growth of B. pubescens, and solar activity in frequency bands encompassed the main solar cycles: 5.5 years (the second harmonic of the Schwabe cycle), 11 years (the Schwabe cycle) and 22 years (the Hale cycle). The results show that the northernmost birch trees in Europe are suited for tree-ring research. This allows us to expand the area of dendrochronological research further beyond the conifer treeline above the Polar Circle.

Extreme weather variability has long posed difficulties for food, energy, and water systems in the Western US and is only projected to become more variable in a changing climate. The key to understanding weather in the West lies in understanding variability of large-scale weather regimes that dictate regional weather patterns. In this study, we propose a novel, multi-objective optimization and regression-based framework that reconstructs the annual frequency of regional weather regimes based on a gridded, tree-ring based reconstruction of cold season precipitation. The approach optimally smooths and selects the tree-ring based information used in the weather regime reconstruction to enhance out of sample performance and minimize model complexity. Multiple objectives are considered within the optimization to balance the preservation of low and high frequency modes of variability in the multivariate weather regime dynamics. We reconstruct weather regime frequencies back to 1400 CE and show that the reconstructed weather regimes are consistent with previously identified megadroughts and pluvials. Further, the reconstructed weather regimes exhibit significant variability in the 3–15-year frequency band and extend far beyond the bounds of the instrumental period. Overall, the weather regime reconstructions developed here provide important insight into the extent of natural atmospheric variability that can influence Western US weather.

Tree‐ring‐width chronology of Betula ermanii was developed at the timberline (2,400 m a.s.l.) on Mount Norikura in central Japan, and climatic factors affecting the tree‐ring width of B. ermanii were examined. Three monthly climatic data (mean temperature, insolation duration, and sum of precipitation) were used for the analysis. The tree‐ring width of B. ermanii was negatively correlated with the December and January temperatures and with the January precipitation prior to the growth. However, why high temperatures and heavy snow in winter had negative effects on the growth of B. ermanii is unknown. The tree‐ring width was positively correlated with summer temperatures during June–August of the current year. The tree‐ring width was also positively correlated with the insolation duration in July of the current year. In contrast, the tree‐ring width was negatively correlated with summer precipitation during July–September of the current year. However, these negative correlations of summer precipitation do not seem to be independent of temperature and insolation duration, i.e., substantial precipitation reduces the insolation duration and temperature. Therefore, it is suggested that significant insolation duration and high temperature due to less precipitation in summer of the current year increase the radial growth of B. ermanii at the timberline. The results were also compared with those of our previous study conducted at the lower altitudinal limit of B. ermanii (approximately 1,600 m a.s.l.) on Mount Norikura. This study suggests that the climatic factors that increase the radial growth of B. ermanii differ between its upper and lower altitudinal limits.

The sun’s activity role in climate change has become a topic of debate. According to data from the IPCC, the global average temperature has shown an increasing trend since 1850, with an average increase of 0.06 °C/decade. Our analysis of summer temperature records from five weather stations in northern Fennoscandia (65°–70.4° N) revealed an increasing trend, with a range of 0.09 °C/decade to 0.15 °C/decade. However, due to the short duration of instrumental records, it is not possible to accurately assess and predict climate changes on centennial and millennial timescales. In this study, we used the Finnish super-long (~7600 years) tree-ring chronology to create a climate prediction for the 21st century. We applied a method that combines a long short-term memory (LSTM) neural network with the continuous wavelet transform and wavelet filtering in order to make climate change predictions. This approach revealed a significant decrease in tree-ring growth over the near term (2063–2073). The predicted decrease in tree-ring growth (and regional temperature) is thought to be a result of a new grand solar minimum, which may lead to Little Ice Age-like climatic conditions. This result is significant for understanding current climate processes and assessing potential environmental and socio-economic risks on a global and regional level, including in the area of the Arctic shipping routes.

Very few annually resolved millennial-length temperature reconstructions exist for the Southern Hemisphere. Here we present four 979-year reconstructions for southeastern Australia for the austral summer months of December-February. Two of the reconstructions are based on the Australian Water Availability Project dataset and two on the Berkeley Earth Surface Temperature dataset. For each climate data set, one reconstruction is based solely on Lagarostrobos franklinii (restricted reconstructions) while the other is based on multiple Tasmanian conifer species (unrestricted reconstructions). Each reconstruction calibrates ~50−60% of the variance in the temperature datasets depending on the number of tree-ring records available for the reconstruction. We found little difference in the temporal variability of the reconstructions, although extremes are amplified in the restricted reconstructions relative to the unrestricted reconstructions. The reconstructions highlight the occurrence of numerous individual years, especially in the 15th−17th Centuries, for which temperatures were comparable with those of the late 20th Century. The 1950−1999 period, however, stands out as the warmest 50-year period on average for the past 979 years, with a sustained shift away from relatively low mean temperatures, the length of which is unique in the 979-year record. The reconstructions are strongly and positively related to temperatures across the southeast of the Australian continent, negatively related to temperatures in the north and northeast of the continent, and uncorrelated with temperatures in the west. The lack of a strong relationship with temperatures across the continent highlights the necessity of a sub-regional focus for Australasian temperature reconstructions.

Rainfall and river levels in the Amazon are associated with significant precipitation anomalies of opposite sign in temperate North and South America, which is the dominant mode of precipitation variability in the Americas that often arises during extremes of the El Niño/Southern Oscillation (ENSO). This co-variability of precipitation extremes across the Americas is imprinted on tree growth and is detected when new tree-ring chronologies from the eastern equatorial Amazon are compared with hundreds of moisture-sensitive tree-ring chronologies in mid-latitude North and South America from 1759 to 2016. Pan-American co-variability exists even though the seasonality of precipitation and tree growth only partially overlaps between the Amazon and mid-latitudes because ENSO forcing of climate can persist for multiple seasons and can orchestrate a coherent response, even where the growing seasons are not fully synchronized. The tree-ring data indicate that the El Niño influence on inter-hemispheric precipitation and tree growth extremes has been strong and stable over the past 258-years, but the La Niña influence has been subject to large multi-decadal changes. These changes have implications for the dynamics and forecasting of hydroclimatic variability over the Americas and are supported by analyses of the available instrumental data and selected climate model simulations.

This paper describes variability in trends of annual tree growth at several locations in the high latitudes of Eurasia, providing a wide regional comparison over a 2000-year period. The study focuses on the nature of local and widespread tree-growth responses to recent warming seen in instrumental observations, available in northern regions for periods ranging from decades to a century. Instrumental temperature data demonstrate differences in seasonal scale of Eurasian warming and the complexity and spatial diversity of tree-growing-season trends in recent decades. A set of long tree-ring chronologies provides empirical evidence of association between inter-annual tree growth and local, primarily summer, temperature variability at each location. These data show no evidence of a recent breakdown in this association as has been found at other high-latitude Northern Hemisphere locations. Using Kendall's concordance, we quantify the time-dependent relationship between growth trends of the long chronologies as a group. This provides strong evidence that the extent of recent widespread warming across northwest Eurasia, with respect to 100- to 200-year trends, is unprecedented in the last 2000 years. An equivalent analysis of simulated temperatures using the HadCM3 model fails to show a similar increase in concordance expected as a consequence of anthropogenic forcing.