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Tree-ring width chronologies of Pinus sibirica Du Tour from near the upper treeline in the Western Sayan, Southern Siberia are found to have an exceptional (below mean–3SD) multi-year drop near 1700 CE, highlighted by the seven narrowest-ring years in a 1524–2022 regional chronology occurring in the short span of one decade. Tree rings are sometimes applied to reconstruct seasonal air temperatures; therefore, it is important to identify other factors that may have contributed to the growth suppression. The spatiotemporal scope of the "nosedive" in tree growth is investigated with a large network of P. sibirica (14 sites) and Larix sibirica Ledeb. (61 sites) chronologies, as well as with existing climatic reconstructions, natural archives, documentary evidence (e.g., earthquake records), and climate maps based on 20th-century reanalysis data. We conclude that stress from low summer temperatures in the Little Ice Age was likely exacerbated by tree damage associated with weather extremes, including infamous Mongolian "dzuds", over 1695–1704. A tropical volcanic eruption in 1695 is proposed as the root cause of these disturbances through atmospheric circulation changes, possibly an amplified Scandinavia Northern Hemisphere teleconnection pattern. Conifer tree rings and forest productivity recorded this event across all of Altai–Sayan region. [ABSTRACT FROM AUTHOR]

Introduction: To investigate the differences in the response of radial growth of larch (Larix gmelinii) at varying altitude gradients to climatic factors, this study established tree-ring width chronologies of Larix gmelinii at altitudes of 900 m, 1,120 m and 1,300 m based dendroclimatology. Methods: We also employed R packages including "dplR," "static" and "moving" to determine the correlation between larch at different altitudes and climatic factors and to explore the sensitivity and stability between radial growth and the climate of larch at different altitudes in the northern part of the Greater Khingan Mountains Range in Northeast China. Results: The results revealed the radial growth of larch in high altitude areas to exhibit a downward trend due to climate warming, while the growth of trees in intermediate and low altitude areas showed an upward trend. The growth-- climate relationship exhibited a significant negative correlation between radial growth in low altitude larch (900 m) and temperatures in the current winter (February and March) and growing season (July, October of the current year, and October of the previous year) (p < 0.05). Moreover, high altitude larch (1,300 m) showed a significant negative correlation with temperature in January, March, and October of the current year (p < 0.05). However, in intermediate altitude areas (1,120 m), the radial growth of trees was significantly positively correlated with the temperature of the growing season (May, June and August). Precipitation in April was observed to promote the radial growth of low-altitude larch. Moving correlation analysis revealed that the inhibitory effect of low temperatures in winter and high temperatures in the growing season on the radial growth of larch at three altitudes gradually strengthened, transitioning from significant negative/positive correlations to significant positive/negative correlations along the altitudinal gradient. Discussion: Larch trees in high and low altitudes exhibited an increased sensitivity to winter and spring precipitation, while in the intermediate region, the inhibitory effect of growing season precipitation on larch radial growth continued to intensify. The results of the study have an important reference value for the indepth understanding of the growth dynamics of Larix gmelinii natural forests in the northern part of the Greater Khingan Mountains under climate change. [ABSTRACT FROM AUTHOR]

This study investigated the effects of climatic factors on radial growth of Picea schrenkiana var. tianschanica at various altitudes in Central Tianshan Mountains. Tree-ring core samples were collected at three altitudinal levels (1900, 2 200, 2 500 m) within the practice forest of Xinjiang Agricultural University. Dendrochronological techniques, including temperature, precipitation, the standardized precipitation evapotranspiration index, and the Palmer drought severity index, were employed to analyze meteorological data from 1955 to 2022. The results indicate that at low altitudes, tree-ring width is positively correlated with previous June and current June-August temperatures, previous August precipitation, and the current June-September Palmer drought severity index (P<0.05). At mid-altitudes, tree ring width was positively correlated with the previous June temperature, August precipitation, and previous June-August standardized precipitation evapotranspiration index (P<0.05). At high altitudes, tree-ring width was negatively correlated with the current January temperature and previous November to the current March standardized precipitation evapotranspi- ration index (P<0.05), but positively correlated with the current June-July precipitation (P<0.05). Therefore, in the forest, P. schrenkiana var. tianschanica growth is closely linked to the environmental moisture conditions, which vary with altitude. Precipi- tation is pivotal for radial growth of P. schrenkiana var. tianschanica at low altitudes, whereas temperature and precipitation jointly affected growth at mid-altitudes, with temperature exerting a greater impact than precipitation on radial growth at higher altitudes. [ABSTRACT FROM AUTHOR]

We investigated whether there are significant differences in the climatic response of resin-tapped and untapped maritime pine (Pinus pinaster Ait.) trees in four forest stands in the central mountains of Spain, where the species is of natural origin. The stands are located in different provenance regions, with the westernmost site located on the northern slopes of Sierra de Gredos and the easternmost in the transition to the middle Duero basin, with altitudes ranging from 900 to 1350 m a.s.l. Dominant trees were sampled and standard dendrochronological methods were used to compare tree growth of both types of trees at each site. Climate-tree growth relationships were assessed using bootstrap correlations and response functions between tree-ring growth indices and climate variables, for both partials and full local chronologies of each stand, selecting climatic data from the most complete and closest meteorological stations. Our results showed that the trees selected for resin extraction were older, on average, and when site characteristics were favorable enough for maritime pine growth and resin extraction, all trees were resin-tapped. Contrastingly, when site characteristics were unfavorable for resin extraction, only the largest and the best-developed trees were tapped. No major differences were found between the climatic responses of resin-tapped and untapped trees, and it was therefore possible to use all the available tree-ring width series per site, both resin-tapped and untapped trees, to identify the main climatic drivers of maritime pine growth in central Spain. In addition, we have expanded the chronologies network of Pinus pinaster in Spain in number and length. This work may provide valuable information to improve forest management strategies for sustainable resin production.

Tree-ring width chronologies of Pinus sibirica Du Tour from near the upper treeline in the Western Sayan, Southern Siberia are found to have an exceptional (below mean–3SD) multi-year drop near 1700 CE, highlighted by the seven narrowest-ring years in a 1524–2022 regional chronology occurring in the short span of one decade. Tree rings are sometimes applied to reconstruct seasonal air temperatures; therefore, it is important to identify other factors that may have contributed to the growth suppression. The spatiotemporal scope of the “nosedive” in tree growth is investigated with a large network of P. sibirica (14 sites) and Larix sibirica Ledeb. (61 sites) chronologies, as well as with existing climatic reconstructions, natural archives, documentary evidence (e.g., earthquake records), and climate maps based on 20th-century reanalysis data. We conclude that stress from low summer temperatures in the Little Ice Age was likely exacerbated by tree damage associated with weather extremes, including infamous Mongolian “dzuds”, over 1695–1704. A tropical volcanic eruption in 1695 is proposed as the root cause of these disturbances through atmospheric circulation changes, possibly an amplified Scandinavia Northern Hemisphere teleconnection pattern. Conifer tree rings and forest productivity recorded this event across all of Altai–Sayan region.

Background and objectives: The Hyrcanian forests in northern Iran exhibit diverse rainfall and air temperature patterns. Altitude above sea level is a crucial topographical factor that influences plant growth and development, prompting trees to adopt different morphological, anatomical, and physiological strategies for survival and growth at varying elevations. This study aims to understand the impact of altitude on radial growth and tree-ring width by examining the rate of radial growth of Oriental beech (Fagus orientalis Lipsky) across different age classes in three altitude zones: low, middle, and high altitudes of the Hyrcanian forests in Kordkuy and Asalem habitats. Methodology: t three selected sites, located at approximately 700, 1400, and 2000 meters above sea level, tree-ring cores were extracted from 62 beech trees using an increment borer. Following core extraction, the holes on the trees were completely sealed with grafting wax. The surface of each core was prepared using a sequence of 100-, 400-, and 1000-grit sandpaper. Tree-ring widths (TRWs) were measured using LINTAB 5 and TSAP software. Measurements were taken from one side of the core and then from the other side. The obtained TRW series were analyzed using statistical parameters such as sign test, correlation coefficient, and Student's t-test. After cross-dating, average TRW chronologies were prepared for each tree. This method was then used to match the trees within each site. TRW chronologies for each site were verified using statistical methods. A one-way analysis of variance (ANOVA) test was performed to compare TRW chronologies. Meteorological data such as rainfall and temperature were obtained from the nearest weather stations. Meteorological data for Kordkuy and Asalem were obtained from the Gorgan and Astara meteorological stations, respectively. Results: The findings demonstrated that the elevation gradient had a significant impact on the radial growth of beech trees. TRW in the examined habitats is influenced by elevation above sea level in trees aged 50 to 150 years. The average radial growth of these trees in the middle elevations of Asalem and the lower elevations of Kordkuy is substantially higher than in other altitude areas. The mean growth of trees aged 100-150 years in the middle elevations of Asalem was the highest, amounting to 3.98 mm. Statistical analysis revealed a significant difference between the TRW of trees aged 100-150 years in the highland of Kordkuy with a mean annual growth of 1.94 mm and the lowerland of Kordkuy with a mean annual growth of 2.97 mm. During this age period, no significant difference was observed between trees from the upperland of Kordkuy and the moderate altitudes of Kordkuy, but there was a statistical difference between trees from moderate altitudes and the lowerland. A comparison of trees aged 200-250 years revealed a statistically significant difference between Kordkuy and Asalem moderate altitudes. The mean radial growth of trees aged 300-350 years in the upperland and moderate altitudes of Asalem is 1.25 and 1.32 mm, respectively. Statistical analysis demonstrated that there is no statistically significant difference between the mean radial growth of trees aged 300-350 years in the upper and middle altitudes of Asalem and the lowerlands of Kordkuy. Conclusion: This study demonstrated that radial growth and tree-ring width of beech trees exhibited notable variations along an east-west transect across the Hyrcanian forests. The observed variations in beech radial growth and tree-ring sensitivity along the elevational gradient highlight the ability of beech trees to develop adaptive functional traits in response to environmental changes. [ABSTRACT FROM AUTHOR]

As a feature of global warming, climate change has been a severe issue in the 21st century. A more comprehensive reconstruction is necessary in the climate assessment process, considering the heterogeneity of climate change scenarios across various meteorological elements and seasons. To better comprehend the change in minimum temperature in winter in the Jinsha River Basin (China), we built a standard tree-ring chronology from Picea likiangensis var. balfouri and reconstructed the regional mean minimum temperature of the winter half-years from 1606 to 2016. This reconstruction provides a comprehensive overview of the changes in winter temperature over multiple centuries. During the last 411 years, the regional climate has undergone seven warm periods and six cold periods. The reconstructed temperature sensitively captures the climate warming that emerged at the end of the 20th century. Surprisingly, during 1650–1750, the lowest winter temperature within the research area was about 0.44 °C higher than that in the 20th century, which differs significantly from the concept of the "cooler" Little Ice Age during this period. This result is validated by the temperature results reconstructed from other tree-ring data from nearby areas, confirming the credibility of the reconstruction. The Ensemble Empirical Mode Decomposition method (EEMD) was adopted to decompose the reconstructed sequence into oscillations of different frequency domains. The decomposition results indicate that the temperature variations in this region exhibit significant periodic changes with quasi-3a, quasi-7a, 15.5-16.8a, 29.4-32.9a, and quasi-82a cycles. Factors like El Niño–Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and solar activity, along with Atlantic Multidecadal Oscillation (AMO), may be important driving forces. To reconstruct this climate, this study integrates the results of three machine learning algorithms and traditional linear regression methods. This novel reconstruction method can provide valuable insights for related research endeavors. Furthermore, other global climate change scenarios can be explored through additional proxy reconstructions. [ABSTRACT FROM AUTHOR]

The climate in the source region of the Yangtze River, Yellow River, and Mekong River is of great research interest because of its sensitivity to global change and its importance in regulating water resources to densely populated and vast areas downstream. A five-century long record of spring (May–June) for the Palmer Drought Severity Index (PDSI) was reconstructed for this region using tree-ring width chronologies of Qilian juniper (Juniperus przewalskii Kom.) from five high-elevation sites. The reconstruction explained 46% variance in the PDSI during the instrumental period 1955–2005. The reconstructed PDSI showed that the occurrence of dry extremes became frequent during the last century relative to the previous four centuries. The standard deviation of the reconstructed PDSI in the 100-year window showed that the recent century held apparent high values of standard deviation in the long-term context. Sustained droughts occurred in periods 1582–1631, 1737–1757, 1772–1791, 1869–1891, 1916–1939, and 1952–1982, whereas relatively wet intervals were observed in 1505–1527, 1543–1564, 1712–1736, 1792–1816, 1852–1868, 1892–1915, and 1983–2008. Notably, in the context of the past five centuries, the study region showed an increased inter-annual variability in the recent century, suggesting an intensified hydroclimatic activity possibly associated with global warming. Moreover, through diagnostic analysis of atmospheric circulation, we found that the negative phase East Asian–Pacific teleconnection pattern may be likely to trigger drought in the study region. [ABSTRACT FROM AUTHOR]

[Objective] Tamarix spp. is a typical species in the arid desert ecosystem, which is important to study the response of Tamarix spp. to groundwater for its protection. [Methods] Based on the data of groundwater depth in the Daliyaboyi oasis at the hinterland of the Taklimakan Desert, this study analyzed the variation of tree-ring width of Tamarix spp. and discussed the relationship between tree-ring width and groundwater depth. [Results] The groundwater depth of the first sample site was increased year by year, ranging from 1.2-2.6 m. Tree-ring width of T . spp. was increased significantly from 2001 to 2020 with a range of 0.98-5.80 mm at the first sample site, and the interannual difference of tree-ring width was significant. The range of the groundwater depth of the second sample site was 2.7-4.5 m, which was increased first and then decreased with time. The tree-ring width of T . spp. at the second sample site changed as a sine function from 1977 to 2020, ranging from 1.46 mm to 4.41 mm, with no significant interannual difference. The standard chronological amplitude of T . spp. was ranging from 0.502 to 1.641 at the first sample site, which was larger than the second site that was ranging from 0.577 to 1.331. [Conclusion] A moderate increase in groundwater depth was beneficial to T . spp. growth at the first sample site, supported by the increase of tree-ring width. There was no significant correlation between treering width and groundwater depth at the second sample site. These results are helpful to understand the radial growth of T . spp. with the changes in groundwater depth.

The long-term effects of climate change and climate extremes have been associated with changes in tree growth and forest productivity worldwide, and dendrochronological analyses are important tools that can be used to investigate the influence of climatic forces on tree growth at a particular site. In this study, a 180-year tree ring width chronology (spanning from 1843 to 2022) of living pine trees (Pinus latteri) in Tak province, northwestern Thailand, was developed. The analysis of the climate–tree growth relationship indicated the influences of the annual total rainfall (r = 0.60, p < 0.001) and annual averaged relative humidity (r = 0.47, p < 0.001) on tree growth in this area. Anomalously high (for example, in 1853, 1984, 2011, and 2018) and low growths (for example, in 1954, 1983, 1992, and 1996) were found. Growth anomalies in the Thai pine in this study were related to changes in abnormal and extreme rainfall (r = 0.94, p < 0.001) and the El Niño Southern Oscillation (ENSO). Our results confirm that rainfall and relative humidity are the main climatic factors regulating the radial growth of Thai pine. This finding could be an important contribution to further research on the effects of climate change and extreme weather events on the vulnerability of tropical and subtropical trees in this region. [ABSTRACT FROM AUTHOR]

Extreme droughts are anticipated to have detrimental impacts on forest ecosystems, especially in water-limited regions, due to the influence of climate change. However, considerable uncertainty remains regarding the patterns in species-specific responses to extreme droughts. Here, we conducted a study integrating dendrochronology and remote sensing methods to investigate the mosaic-distributed maple-oak (native) natural forests and poplar plantations (introduced) in the Horqin Sandy Land, Northeast China. We assessed the impacts of extreme droughts on tree performances by measuring interannual variations in radial growth and vegetation index. The results showed that precipitation and self-calibrated palmer drought severity index (scPDSI) are the major factors influencing tree-ring width index (RWI) and normalized difference vegetation index (NDVI). The severe droughts between 2000 and 2004 resulted in reduced RWI in the three studied tree species as well as led to NDVI reductions in both the maple-oak natural forests and the poplar plantations. The RWI reached the nadir during the 2000-2004 severe droughts and remained at low levels two years after the severe drought, creating a legacy effect. In contrast to the lack of significant correlation between RWI and scPDSI, NDVI exhibited a significant positive correlation with scPDSI indicating the greater sensitivity of canopy performance to droughts than radial growth. Furthermore, interspecific differences in RWI and NDVI responses were observed, with the fast-growing poplar species experiencing a more significant RWI decrease and more negative NDVI anomaly during severe droughts than native species, highlighting the species-specific trade-offs between drought resilience and growth rate. This study emphasizes the importance of combining tree-level radial growth with landscape-scale canopy remote sensing to understand forest resilience and response. Our study improves our understanding of forest responses to extreme drought and highlights species differences in climate responses, offering crucial insights for optimizing species selection in sustainable afforestation and forest management in water-limited regions under the influence of climate change. [ABSTRACT FROM AUTHOR]

Fertilisation is often used to increase plant productivity in agriculture but has also been used in forestry. In our study, Scots pine forest growing in a nitrogen-poor environment was fertilised with NPK post-production wastewater from a potato starch factory. Our research aimed to investigate the dependence of tree growth on different NPK concentrations. Cell characteristics such as cell wall thickness (CWT), lumen diameter (LD) and tree-ring features such as ring width (RW), total number of cells in annual growth (nTotal), earlywood (EW) and latewood (LW) were investigated. Twenty-six years of regular fertilisation of the forest with different doses of wastewater rich in NPK elements have affected the anatomical structure of Scots pine trees. It is presumed that the reduction in CWT and LD on the fertilised site was due to deficiencies in plant water conductivity, which may have occurred due to physiological drought. The influence of nitrogen on unfertilised site from the wastewater area could contribute to the CWT thickening. The results confirm that the use of NPK in excessive doses is detrimental to trees' conductive system.

Warming and persistent droughts may exacerbate drought stress in water-scarce areas, thereby negatively affecting tree growth. When riparian plants in arid regions experience severe drought stress, they sacrifice non-dominant branches with less competitive sap flow to improve the sap flow of dominant branches and thus ensure strong plant growth. Populus euphratica is one of the most dominant tree species in the riparian forest ecosystems of inland river basins in arid zones and is a reliable indicator of ecological change because of its diversity in growth and environment. To understand the adaptability of P. euphratica to the environment, the relationship between radial growth and meteorological factors, the growth decline and resistance of different heights and components of P. euphratica, as well as the resilience and resilience after recession were investigated. The results indicated that tree-ring width decreased gradually with increasing height and branching class of P. euphratica. Growth decreased at the bottom of the stem earlier than at the middle and top. Temperature, precipitation, and the Palmer drought index contributed to the growth at the bottom of P. euphratica, while precipitation contributed to growth at the top. The decline in the P. euphratica growth change rate was highly synchronized across heights and parts, with relatively high declines at the bottom and top. There were no significant differences in the recovery values for different heights and parts of P. euphratica, but the resistance, resilience, and relative resilience for the bottom and top were significantly lower than those for the other components, indicating vulnerability in the bottom and top of P. euphratica to drought. The relative resilience gradually decreased with the increase in branching class, and that of the secondary lateral branches at different heights was the lowest. In conclusion, the sensitivity of the top and lateral branches of P. euphratica to drought would cause the phenomenon of "breaking its arm" under drought disturbance in the future. [ABSTRACT FROM AUTHOR]

Although the hawthorn is not a forest-forming species, and it has no high economic significance, it is a very valuable component of forests, mid-field woodlots or roadside avenues. The literature, however, lacks information on the growth rate, growth phases, or growth–climate–habitat relationship for trees of this genus. This work aimed to establish the rate of growth of Craraegus monogyna and C. xmedia Bechst growing in various parts of Poland, in various habitats; analyze the growth–climate relationship; and distinguish dendrochronological regions for these species. Samples were taken using a Pressler borer from nine populations growing in different parts of Poland, from a total of 192 trees (359 samples). The tree-ring width was measured down to 0.01 mm. The average tree-ring width in the studied hawthorn populations ranged from 1.42 to 3.25 mm/year. Using well-established cross-dating methods, nine local chronologies were compiled with tree ages between 45 and 72 years. Dendroclimatic analyses (pointer year analysis, correlation and response function analysis) were performed for a 33-year period from 1988 to 2020, for which all local chronologies displayed EPS > 0.85. The tree-ring width in the hawthorn populations depended mostly on temperature and rainfall through the May–August period. High rainfall and the lack of heat waves through these months cause an increase in cambial activity and the formation of wide tree rings. Conversely, rainfall shortages through this period, in conjunction with high air temperatures, caused growth depressions. Cluster analysis enabled the identification of two dendrochronological regions among the hawthorn in Poland: a western and eastern region, and a single site (CI), whose separation was most likely caused by contrasting habitat and genetic conditions. The obtained results highlight the need for further study of these species in Poland and other countries. [ABSTRACT FROM AUTHOR]

The dependence of the width of annual rings of woody plants on the characteristics of the snow cover is analyzed in various natural zones of the West Siberian Plain and adjacent mountainous areas: the maximum depth and water reserve for the entire winter period and for individual months, the dates of disappearing, establishment, and duration of the occurrence of a stable snow cover. It has been shown that the role of the depth and water content of snow cover for the radial growth of trees is differentiated by geographical location. On the plain, it intensifies in the forest-tundra and dry steppe. The response of radial growth to snow cover in the upper and lower parts of the forest belt is often the opposite. Dates of establishment of stable snow cover are more important for tree growth compared to dates of disappearance. Dates of disappearance of stable snow cover are more significant in the southern regions than in the northern ones. The value of the duration of the period with stable snow cover for tree growth is higher in the southern regions. [ABSTRACT FROM AUTHOR]

Norway spruce (Picea abies (L.) Karst.) is a significant conifer tree species in Europe that holds significant economic and ecological value. However, it remains one of the most sensitive to climate change. This study describes the climate–growth relationship, focusing on dendroecology in hilly spruce forests (319–425 m a.s.l.) located in Bohemia, the Czech Republic, during 1950–2018. The results confirmed that the highest radial increment was obtained in locations with higher precipitation (Kostelec), while the lowest growth was observed in locations with lower precipitation (Karlstejn). Tree-ring growth shows very low increments for the years 1964 and 1976 for all plots, and the years with the least growth were confirmed by the negative pointer year analysis. This study confirmed precipitation as the main factor that affects the growth of spruce at lower altitudes. The radial growth for all study sites shows a statistically significant positive correlation with precipitation during the growing season, while no statistically significant values between radial growth and temperature were obtained. This study demonstrates that Norway spruce is affected more by precipitation than temperature, and the results indicate that this conifer is seriously affected by the lack of precipitation at lower altitudes in the Czech Republic, where the species is not native. [ABSTRACT FROM AUTHOR]

Fifteen years after a murder and an act of cannibalism, the police in Szczecin have conducted an investigation, in which neither the time of the murder, nor the victim identity were known, no body was found, and the defendants have not confessed. Due to the circumstantial nature of the investigation and the trial, a number of analyses were performed, and expert opinions were requested as part of the inquiry. A dendrochronological study of a birch tree growing on the shore of Lake Żabie was one of the analyses lending credibility to the testimony of one of the defendants and pointing to the murder site. The aim of this study was to determine the age and size of the birch tree in the 1998–2002 period, and to determine whether the tree was a distinctive feature of the landscape through the period in question. Field work was performed in April 2019, under the supervision of the police. The birch tree was measured and samples collected using a Pressler borer. The measurements and observations revealed that the birch tree, due to its size, and the absence of other trees of this species in this segment of the lake shore, may have been a characteristic landscape element in the late 1990s and early 2000s. According to the police officer and the prosecutor in charge of the case, the results of the dendrological analysis have lent a strong credibility to the testimony of one of the defendants and other findings of the investigation. [ABSTRACT FROM AUTHOR]

In forests, the growth and productivity of individual trees and stands as a whole are regulated by stand density among other factors, because access to vital resources is limited by competition between trees. On 18 experimental plots of Scots pine (Pinus sylvestris L.) planted with a density of 500–128,000 trees/ha in the south taiga (Middle Siberia), interactions between stand density, tree- and stand-scale productivity, and tree-ring parameters were investigated. Tree-scale productivity variables, tree-ring width, and latewood width had stable negative allometric relationships with stand density (R2 > 0.75), except for tree height (insignificant for inventory surveys at ages of 20 and 25 years; R2 > 0.4 at the age of 35 years), while positive allometry was registered for stand productivity variables (R2 > 0.7) and the all-time average latewood ratio (R2 = 0.5 with planting density). Tree-ring parameters aside from the age trends correlate (p < 0.05) between the plots and demonstrate common responses to moderate moisture deficit. Although, its seasonality apparently depends on the resource base and intensity changes with stand density. February–June precipitation is more important for pine growth in dense stands, July–August conditions affect the latewood ratio stronger in sparse stands, and medium-density stands are more resistant to winter frosts. [ABSTRACT FROM AUTHOR]

In this study, we made use of a regional oak tree-ring network from six stands that cover the northern Moldavian Plateau (eastern Europe) to analyze how different tree ring parameters (i.e., early wood tree-ring width, late wood tree-ring width, and total tree-ring width) of Quercus sp. are influenced by the occurrence of extreme climatic events (e.g., long-lasting drought events). In order to explore the influence of extreme hydroclimatic events on tree ring width, we have selected each of the six most extreme positive and negative years of tree growth and addressed the seasonal cycle of tree growth in comparison with the main climatic parameters, then evaluated both the current and lagged consequences of extreme hydroclimatic events on tree ring width and the capacity of trees to recover. Our results indicate that the variability of oak tree ring width from the Moldavian Plateau is mainly influenced by the availability of water resources, and that an important limiting growth factor for Quercus sp. is the occurrence of long-lasting drought events, e.g., at least two years in a row with severe drought conditions. [ABSTRACT FROM AUTHOR]

In the last decade, coniferous stands outside their natural range in Romania have experienced declines in both their health and growth and, in tandem with global climate trends, these forests are becoming even more threatened. We studied the relationship between tree growth and defoliation as an indicator of tree health. The data came from black pine stands monitored from 2012 to 2021 in the Postăvarul Massif in the Romanian Carpathians. Analyses were carried out on 508 individual trees based on their defoliation and radial growth data and also at the stand level. The results revealed an increase in the percentage of tree defoliation from 17% to 38% during the studied decade, along with 13.5% tree mortality. Over the decade, radial growth showed a negative trend, driven significantly by defoliation. The biometric parameters of the trees did not influence their percentage of defoliation. In contrast, spring/summer droughts associated with high temperatures affect the health and growth of trees. Models generated from the temperature–defoliation–radial-growth relationship estimated a significant continuous reduction in the radial growth of the trees of 0.5%–0.6% for each 1% increase in defoliation. Under the site conditions of the investigated stands, an increase in basal area and stocking degree significantly increased stand defoliation. This was further accentuated when the pine stand included an understory of young trees. As a rule, in the interest of production, stands are kept dense to fully exploit the site, but thinning may become necessary to protect these stands and ensure their survival as the climate changes. [ABSTRACT FROM AUTHOR]

Simple Summary: In the dry and hot climates of Central Asia, forested areas are small and vulnerable to climate change. Therefore, it is important to understand the reactions of tree growth to climatic factors there. We studied several habitats of Scots pine, Schrenk spruce, and Zeravschan juniper near the semiarid limits of the respective forest types across Kazakhstan, the largest country in Central Asia. Standardized chronologies of tree-ring width were obtained for each site from wood samples, and then compared among themselves with a series for temperature and precipitation. Large distances and differences between species and habitats limited similarity in the dynamics of conifer growth. However, a common pattern was found in their reactions to climate. Maximal temperatures of the current and previous growing seasons were found to be crucial factors limiting the growth of all considered forest stands. Reactions to the precipitation and drought index are positive, but their strength depends on the species and aridity of a particular habitat. Temporal intervals of climatic impact on tree growth also vary across the country. The forests of Central Asia are biodiversity hotspots at risk from rapid climate change, but they are understudied in terms of the climate–growth relationships of trees. This classical dendroclimatic case study was performed for six conifer forest stands near their semiarid boundaries across Kazakhstan: (1–3) Pinus sylvestris L., temperate forest steppes; (4–5) Picea schrenkiana Fisch. & C.A. Mey, foothills, the Western Tien Shan, southeast; (6) Juniperus seravschanica Kom., montane zone, the Western Tien Shan, southern subtropics. Due to large distances, correlations between local tree-ring width (TRW) chronologies are significant only within species (pine, 0.19–0.50; spruce, 0.55). The most stable climatic response is negative correlations of TRW with maximum temperatures of the previous (from −0.37 to −0.50) and current (from −0.17 to −0.44) growing season. The strength of the positive response to annual precipitation (0.10–0.48) and Standardized Precipitation Evapotranspiration Index (0.15–0.49) depends on local aridity. The timeframe of climatic responses shifts to earlier months north-to-south. For years with maximum and minimum TRW, differences in seasonal maximal temperatures (by ~1–3 °C) and precipitation (by ~12–83%) were also found. Heat stress being the primary factor limiting conifer growth across Kazakhstan, we suggest experiments there on heat protection measures in plantations and for urban trees, alongside broadening the coverage of the dendroclimatic net with accents on the impact of habitat conditions and climate-induced long-term growth dynamics. [ABSTRACT FROM AUTHOR]

Iberian populations of Scots pine (Pinus sylvestris L.) have been declining since the late-glacial period; among those that remain, relict stands have great biological and ecological value. This paper investigates the effects of a 2009 fire on tree growth in one of these small populations in the Sierra de Gredos (Spain) by examining the responses recorded in the tree-ring width series of the surviving trees. The current status and distribution of these surviving trees reveal the severity of the fire; indeed most show scars or other evidence of fire damage. Dendroecological analysis revealed narrower tree rings, indicating negative pointer years for the year of the fire and the following year. A very significant reduction in growth was recorded for the years after the fire, both in terms of tree-ring width and basal area increment; incomplete and even absent rings were also recorded. No relationship was seen between these effects and climatic events. The dates and geographical extension of former possible disturbances were also investigated, using the data from these same trees plus information collected from others in the region. The vulnerability of these populations to past fires was evident. Lastly, given the problems affecting the regeneration of these relict populations, it is strongly suggested to urgently include all these populations in conservation and environmental management programs.

Tree growth at alpine regions is sensitive to climate change. However, there is still uncertainty about the spatial and temporal stability of tree growth in response to warming. Herein, through collecting 302 cores from 162 conifer trees at 4 sites of paired timberline and subalpine forests on the southeastern Tibetan Plateau, we analyzed the spatial and temporal pattern of radial growth in response to warming. Response analysis result of standard and first-order difference chronology showed that the variation of radial growth was mainly affected by summer temperature in the Sergyemla Mountains (SGM), Baima Snow Mountains (BSM), and Meri Snow Mountains (MSM), by winter temperature and early summer drought stress at Chagyab (CY). The radial growth in timberline forests is more sensitive to temperature than those in subalpine forests. Growth-temperature sensitivity generally decreased during the past 60 years. The analysis of the Standardized Precipitation Evapotranspiration Index (SPEI) indicated that the drought stress was one of the main reasons for the variation of temperature insensitivity, suggesting that the moisture condition may play an increasingly important role on tree growth in warming future.

Whether and how the timing of extreme events affects the direction and magnitude of legacy effects on tree growth is poorly understood. In this study, we use a global database of Ring-Width Index (RWI) from 2,500 sites to examine the impact and legacy effects (the departure of observed RWI from expected RWI) of extreme drought events during 1948-2008, with a particular focus on the influence of drought timing. We assessed the recovery of stem radial growth in the years following severe drought events with separate groupings designed to characterize the timing of the drought. We found that legacies from extreme droughts during the dry season (DS droughts) lasted longer and had larger impacts in each of the 3 years post drought than those from extreme droughts during the wet season (WS droughts). At the global scale, the average integrated legacy from DS droughts (0.18) was about nine times that from WS droughts (0.02). Site-level comparisons also suggest stronger negative impacts or weaker positive impacts of DS droughts on tree growth than WS droughts. Our results, therefore, highlight that the timing of drought is a crucial factor determining drought impacts on tree recovery. Further increases in baseline aridity could therefore exacerbate the impact of punctuated droughts on terrestrial ecosystems.

Dendroclimatology offers the unique opportunity to reconstruct past climate at annual resolution and wood from historical buildings can be used to extend such information back in time up to several millennia. However, the varying and often unclear origin of timbers affects the climate sensitivity of individual tree‐ring samples. Here, we compare tree‐ring width and density of 143 living larch (Larix decidua Mill.) trees at seven sites along an elevational transect from 1400 to 2200 m asl and 99 historical tree‐ring series to parametrize state‐of‐the‐art classification models for the European Alps. To achieve geographical provenance of the historical series, nine different supervised machine learning algorithms are trained and tested in their capability to solve our classification problem. Based on this assessment, we consider a tree‐ring density‐based and a tree‐ring width‐based dataset for model building. For each of these datasets, a general not species‐related model and a larch‐specific model including the cyclic larch budmoth influence are built. From the nine tested machine learning algorithms, Extreme Gradient Boosting showed the best performance. The density‐based models outperform the ring‐width models with the larch‐specific density model reaching the highest skill (f1 score = 0.8). The performance metrics reveal that the larch‐specific density model also performs best within individual sites and particularly in sites above 2000 m asl, which show the highest temperature sensitivities. The application of the specific density model for larch allows the historical series to be assigned with high confidence to a particular elevation within the valley. The procedure can be applied to other provenance studies using multiple tree growth characteristics. The novel approach of building machine learning models based on tree‐ring density features allows to omit a common period between reference and historical data for finding the provenance of relict wood and will therefore help to improve millennium‐length climate reconstructions. [ABSTRACT FROM AUTHOR]

Global warming is causing some regions to experience frequent and severe drought, with important impacts on montane forest vegetation. In this study, the Qilian Mountains is on the northeastern margin of the Tibetan Plateau which was divided into three study areas, the eastern (HaXi), middle (XiShui) and western (QiFeng) parts. This work focused on interannual trend comparison of tree-ring width (TRW) and enhanced vegetation index (EVI), their relationship characterization from 2000 to 2020, and spatial and temporal pattern portrayal of response to climate factors. The results showed that: (1) the overall interannual variation of TRW and EVI showed a stable increasing trend, and the trend of TRW and EVI gradually became consistent with the increase in drought stress (from the eastern region to the western region and from high elevation to low elevation) (p < 0.01); (2) a significant positive relation was observed between TRW and EVI at the same sampling sites, and the synchrony of the positive correlation gradually increased with the increase of drought stress (p < 0.01); and (3) compared to TRW, EVI is significantly more sensitive with climatic variations, and the dominant climate factors affecting both TRW and EVI dynamics are gradually identical with the increase of drought stress. [ABSTRACT FROM AUTHOR]

The impact of lag effects produced by disturbances on primary production has been a major concern among ecologists during the last decade. Sudden and extreme climatic events are imposing drastic reductions in radial growth of trees as evidenced in tree-rings series Dendrochronological samples are obtained at tree level but analyzed at an aggregated scale (i.e., mean chronologies), although aggregating tree-ring chronology on a regional scale may reduce the possibility of studying the variability of individual tree response to drought, by amplifying the average population response. Here, we conducted experimental research in which 370 trees of 5 species were analyzed to assess the potential statistical and scaling issues that may occur when using regressionbased methods to analyze ecosystem responses to disturbances. Drought legacy effects were quantified using individual and aggregated scales. Then, lag effects were validated using confidence and prediction intervals to identify values falling outside the certainty of the climate-growth model Individual scale legacy effects contrasted with confidence intervals were commonly distributed across species but were scarce when compared with prediction intervals. The analysis of aggregated scale legacies detected significant growth reductions when validated using prediction intervals; however, individual scale legacy lag effects were not detected. This finding directly contrasts the results obtained when using an aggregated scale. Our results provide empirical evidence on how aggregating ecological data to infer processes that emerge from an individual scale can lead to distorted conclusions. We therefore encourage the use of individual based statistical and ecological procedures to analyze tree rings as a means of further understanding the ecosystem responses to disturbances. [ABSTRACT FROM AUTHOR]

The impact of lag effects produced by disturbances on primary production has been a major concern among ecologists during the last decade. Sudden and extreme climatic events are imposing drastic reductions in radial growth of trees as evidenced in tree-rings series Dendrochronological samples are obtained at tree level but analyzed at an aggregated scale (i.e., mean chronologies), although aggregating tree-ring chronology on a regional scale may reduce the possibility of studying the variability of individual tree response to drought, by amplifying the average population response. Here, we conducted experimental research in which 370 trees of 5 species were analyzed to assess the potential statistical and scaling issues that may occur when using regression-based methods to analyze ecosystem responses to disturbances. Drought legacy effects were quantified using individual and aggregated scales. Then, lag effects were validated using confidence and prediction intervals to identify values falling outside the certainty of the climate-growth model Individual scale legacy effects contrasted with confidence intervals were commonly distributed across species but were scarce when compared with prediction intervals. The analysis of aggregated scale legacies detected significant growth reductions when validated using prediction intervals; however, individual scale legacy lag effects were not detected. This finding directly contrasts the results obtained when using an aggregated scale. Our results provide empirical evidence on how aggregating ecological data to infer processes that emerge from an individual scale can lead to distorted conclusions. We therefore encourage the use of individual based statistical and ecological procedures to analyze tree rings as a means of further understanding the ecosystem responses to disturbances.

Radial growth is influenced by the local environment, regional climate, and tree species. Assessing the influence of these variables on radial growth can help to reveal the relationships between tree growth and the environment. Here, we used standard dendrochronological approach to explore the response of radial growth to climate factors. We reported ring-width (TRW) residual chronologies from five sites along a longitudinal gradient in the Hexi area, arid northwestern China, based on a total of 249 Qinghai spruce (Picea crassifolia) ring-width records. We found that Qinghai spruce in the west of the Hexi area is more sensitive to climate change than in the east, and that drought condition in the previous growing season and the early growing season (March to June) limits spruce growth. Comparison between the regional standard chronologies of Qinghai spruce and Qilian juniper (Juniperus przewalskii) in the Hexi area during 1813-2001 showed that both chronologies were more consistent in the high-frequency domain than in the low-frequency domain. The findings emphasize the impacts of local environment, regional climate and tree species on radial growth, suggesting that accounting for these variables could improve large-scale and multi-species dendrochronological studies. [ABSTRACT FROM AUTHOR]

Abrupt changes in temperature have especially strong impacts on fragile ecosystems located in semi-arid regions. In this study, we analyzed tree-ring widths (TRW) of Mediterranean cypress (Cupressus sempervirens var. horizontalis) in the Zagros Mountains, Iran. Furthermore, we separately measured earlywood width (EWW) and latewood width (LWW) of Persian oak (Quercus brantii Lindl.) to examine if intra-annual resolution of tree-ring parameters of Q. brantii tree rings can be used as high-resolution paleoclimate proxies. Climate-growth relationships revealed that mean monthly maximum temperatures (Tmax) are a dominant factor determining radial tree growth and negatively affect both oak and cypress in the Zagros Mountains. Accordingly, we reconstructed two different seasonal windows of past Tmax variability, namely, January–March and June–August over the periods 1860–2015 and 1560–2015, respectively. Regime shift detection identified twelve warm and nine cold significant regime shifts in our summer Tmax reconstructions. The longest hot summer period occurred in the twentieth century, and two warm regime shifts occurred in 1999 and 2008. The highest values of the warm summer regime shift index occurred in 2008, which coincided with fungal pathogen attacks and insect outbreak of the oak leaf roller moth (Tortrix viridana L.) in the Zagros oak woodlands. Interestingly, we found common warm and cold periods in historic climate variability between the summer and winter Tmax reconstructions. Warm and cold regime shifts occurred simultaneously from 1955 to 2015, and significant regional warm summer and winter regime shifts have occurred between 2008 and 2015. The winter and summer Tmax reconstructions show high spatial correlations with large areas in West Asia, North Africa, and the eastern Mediterranean region. Our results strengthen initial studies on past climate variability in Iran and contribute to an enhanced understanding of past temperature variability in West Asia. [ABSTRACT FROM AUTHOR]

Siberian stone pine (Pinus sibirica Du Tour) is one of the keystone conifers in Siberian taiga, but its radial growth is complacent and thus rarely investigated. We studied its growth in subalpine stands near the upper timberline along the Western Sayan Mountains, Southern Siberia, because climatic responses of trees growing on the boundaries of species distribution help us better understand their performance and prospects under climate change. We performed dendroclimatic analysis for six tree-ring width chronologies with significant between-site correlations at distances up to 270 km (r = 0.57–0.84, p < 0.05). We used ERA-20C (European Reanalysis of the Twentieth Century) daily climatic series to reveal weak but spatially coherent responses of tree growth to temperature and precipitation. Temperature stably stimulated growth during the period from the previous July–August to current August, except for an adverse effect in April. Precipitation suppressed growth during periods from the previous July–September to December (with reaction gradually strengthening) and from the current April to August (weakening), while the snowfall impact in January–March was neutral or positive. Weather extremes probably caused formation of wide tree rings in 1968 and 2002, but narrow rings in 1938, 1947, 1967, 1988, and 1997. A subtle increase in the climatic sensitivity of mature trees was observed for all significant seasonal climatic variables except for the temperature in the previous October–January. The current winter warming trend is supposedly advantageous for young pine trees based on their climatic response and observed elevational advance. [ABSTRACT FROM AUTHOR]

After a decades-long increasing trend, the recent results of the National Forest Inventory (NFI) reported a decline of forest growth in North Finland. The aim of this study was to assess climatic and reproduction influences behind the growth decline. We used tree-ring data that had been collected by NFI using systematic sampling. The tree-ring width series were detrended using the regional curve standardisation (RCS) removing age-related trends. The resulting tree-ring indices of Scots pine (Pinus sylvestris L.) showed decadal variations with low increment in the 1990s, and high increment in the 1980s and the early years of the current century. Thereafter, a prolonged growth reduction for pine started both on the mineral soil sites and peatlands. The tree-ring indices of Norway spruce (Picea abies (L.) Karst.) had less pronounced decadal variations and no trend-like reduction over the last 15 years. High spring and summer temperatures were found to enhance radial growth, but high winter temperatures were related to low growth for pine and spruce in the following summer. Temperature variation, accompanied by variables indicating years of drought and intensive flowering, accounted for 34% annual growth variance of pine and 21–44% for spruce. Thus, the results imply that climatic factors may have to some extent contributed to the recent growth reduction of pine. Due to its ecological and economic consequences growth decline needs to be further monitored and investigated. Moreover, analyses of stand and age structure, potentially affecting the growth decline, were beyond the scope of this paper, but also warrant further investigation.

One of the most important proxy archives for past climate variation is tree rings. Tree-ring parameters offer valuable knowledge regarding how trees respond and adapt to environmental changes. Trees encode all environmental changes in different tree-ring parameters. In this study, we analyzed how air temperature is encoded in different Norway spruce tree-ring proxies along an altitude gradient in an intramountain valley of the Carpathians. The study area, in the Gheorgheni region, Romania (Eastern Carpathians), has a mountain climate with a frequent temperature inversion in winter. The climate–growth relationship was analyzed for two contrasting altitudes: low elevation, i.e., below 1000 m a.s.l., and high elevation, i.e., above 1500 m a.s.l. Two local weather stations, one in the valley and the other on the upper part of the mountains, provide daily temperatures (Joseni—750 m a.s.l. and Bucin—1282 m a.s.l.). The bootstrap Pearson correlation between cumulative daily temperature data and three tree-ring proxies (tree-ring width—TRW, basal area increment—BAI, and blue intensity—BI) was computed for each series. The results show that elevation modulates the climate response pattern in the case of BI, and remains relatively similar for TRW and BAI. The winter temperature's positive influence on spruce growth was observed in both TRW and BAI chronologies. Additionally, the BAI chronology highlights a positive relationship with summer temperature. The highest correlation coefficient (r = 0.551, p < 0.05, n = 41) was recorded between BI residual chronology from high elevation series and summer/autumn temperature from the upper-part weather station for a cumulative period of 59 days (the second half of August to the beginning of October). Our results show that, for this intramountain valley of the Eastern Carpathians, different tree-ring proxies capture different climate signals. [ABSTRACT FROM AUTHOR]

Background and Aims Tree growth in plateau forests is critically limited by harsh climatic conditions. Many mathematical statistical methods have been used to identify the relationships between tree growth and climatic factors, but there is still uncertainty regarding the relative importance of these factors across different regions. We tested major climatic limits at 30 sites to provide insights into the main climatic limits for juniper trees (Juniperus tibetica Kom.) across the southern Tibetan Plateau. Methods We analysed the linear and non-linear relationships between tree growth and climatic factors using Pearson correlation statistics and a process-based forward Vaganov–Shashkin-Lite (VS-Lite) model, respectively. These relationships were used to identify the strength of the influence of different climatic factors throughout the species' growing season and to identify the main climatic factors limiting tree growth. Key Results Growth of juniper trees began in April and ended in October in the study area. The radial growth of juniper trees was limited by soil moisture throughout the summer (June–August) of the current year at 24 sampling sites and was limited by temperature at the other six sites on the southern Tibetan Plateau. Conclusions Soil moisture limited juniper growth at the majority of sites. Temperature in the current summer limited the growth of juniper trees at a few sampling sites in the western part of the study area. Local climate conditions may contribute to different limiting factors in the growth response of trees on the southern Tibetan Plateau. These findings may contribute to our understanding of divergent forest dynamics and to sustainable forest management under future climate scenarios. [ABSTRACT FROM AUTHOR]

Simple Summary: This paper analyzed the different relationships between earlywood and latewood as well as total tree-ring growth and the climate factors and reconstructed 106 years of May–June mean temperature (TMJ) in the Tongbai Mountains based on the earlywood width chronology of Pinus taiwanensis Hayata. It also analyzed the linkages to the Indian and Pacific Oceans. This paper found that earlywood width chronology has better response to the climate factors than latewood width and total tree-ring width. This study also found that the main limiting factors that restrained radial growth of Pinus taiwanensis Hayata in the Tongbai Mountains were May–June mean temperature and mean maximum temperature. The reconstructed TMJ series have a better reliability and are significantly negatively correlated with sea surface temperature (SST) over the tropical Western Pacific Ocean and Indian Ocean and are significantly positively correlated with SST over the subtropical Pacific Ocean. Finally, the periodic fluctuations of TMJ in the Tongbai Mountains might be related to the quasi-biennial interannual oscillation of SST over the Indo-Pacific equatorial region (QBO). The results of this study are significant for further understanding and exploring forest growth and climate change in the climatic transition zone. The Tongbai Mountains are an ecologically sensitive region to climate change, where there lies a climatic transitional zone from a subtropical to a warm–temperate monsoon climate. The northern boundary of Pinus taiwanensis Hayata is here; thus, climate information is well recorded in its tree rings. Based on developed earlywood width (EWW), latewood width (LWW) and total ring width (RW) chronologies (time period: 1887–2014 year) of Pinus taiwanensis Hayata in the Tongbai Mountains in central China, this paper analyzed characteristics of these chronologies and correlations between these chronologies and climate factors. The correlation results showed that earlywood width chronology contains more climate information than latewood width chronology and total ring width chronology, and mean temperature and mean maximum temperature in May–June were the main limiting factors for radial growth of Pinus taiwanensis Hayata. The highest significant value in all correlation analyses is −0.669 (p < 0.05) between earlywood width chronology and May–June mean temperature (TMJ) in the pre-mutation period (1958–2005) based on mutating in 2006. Thus, this paper reconstructed May–June mean temperature using earlywood width chronology from 1901 to 2005 (reliable period of earlywood width chronology is 1901–2014). The reconstructed May–June mean temperature experienced eight warmer periods and eight colder periods and also showed 2–3a cycle change over the past 105 years. The spatial correlation showed that the reconstructed series was representative of the May–June mean temperature variation in central and eastern China and significant positive/negative correlation with the sea surface temperature (SST) of the subtropical Pacific Ocean and the tropical Western Pacific Ocean and Indian Ocean from the previous October to the current June. This also indicated that May–June mean temperature periodic fluctuations might be related to the quasi-biennial oscillation (QBO) in the tropical Western Pacific Ocean and Indian Ocean. The results of this study have extended and supplemented the meteorological records of the Tongbai Mountains and have a guiding significance for forest tending and management in this area. [ABSTRACT FROM AUTHOR]

There is a tendency of warming and wetting in northwestern China in recent decades. However, less is known about whether or not tree growth shows an increasing trend. In this study, we developed three tree-ring width chronologies of Picea schrenkiana in the northern Tianshan Mountains to assess changes in the radial growth of P. schrenkiana and to discuss the stability of the relationships between tree growth and climate. Three chronologies all showed that the tree-ring index has declined significantly since the 1960s. At two western sites, the growth of P. schrenkiana was negatively affected by the summer temperature of the previous year. At the eastern site, early summer temperature-induced drought of the current year was the key factor affecting tree growth. The result of moving-window correlations was consistent with correlation analyses. Spatial correlation analyses revealed that variations in tree-ring width could respond to a wide range of temperature changes in northwestern China, especially in the past half century. We expect that climate warming hinders the radial growth of P. schrenkiana in the northern Tianshan Mountains. Our study also helps to clarify the characteristics of tree growth in northwestern China under the influence of westerlies. [ABSTRACT FROM AUTHOR]

Wildfires are one of the most important environmental factors controlling forest ecosystem physiology and the carbon balance in the permafrost zone of North Siberia. We investigated tree-ring width (TRW) and stable isotope chronologies in tree-ring cellulose (δ13CCell, δ18OCell) of Larix Gmelinii (Rupr.) Rupr. from a wet (WS) and a dry (DS) site. These sites are characterized by different fire histories (fire in 1852 at the wet and 1896 at the dry sites, respectively). TRW and δ18OCell are identified to be the most sensitive parameters in the changing tree growth conditions after fire. The differences in the soil seasonal thermal regime of sites after fires are shown in the relationship between the studied parameters. The δ13CCell values in tree rings from the two sites are positively correlated independently of the fire impact. This fact indicates that δ13CCell chronologies might be more adequate for climatic reconstruction in the region due to the climate signal consistency. Relationships of δ18OCell values between the two sites are still significantly positive 60 years after the fire impact. Dendroclimatic analysis indicates significant changes in tree-ring growth and isotopic ratio responses to climate due to the increased demand of water for trees during the post-fire period (deeper seasonal subsidence of permafrost). [ABSTRACT FROM AUTHOR]

Coastal dunes near the Baltic Sea are often stabilized by Scots pine forests and are characterized by a mild climate. These ecosystems are affected by water shortages and might be influenced by climate extremes. Considering future climate change, utilizing tree rings could help assess the role of climate extremes on coastal forest growth. We used superposed epoch analysis to study Scots pine responses to droughts and cold winters, with focus on frequency, timing, and duration. We measured ring widths (RW) and latewood blue intensity (LBI) on samples extracted from trees growing at dune ridge and bottom microsites at the south Baltic Sea. At the regional scale, we observed some similarities in tree responses to both extremes between RW and LBI within the same microsite type and region. At the local scale, RW and LBI were more frequently influenced by cold winters than droughts. RW and LBI from dune ridges were more frequently influenced by droughts than RW and LBI from dune bottoms. LBI from both microsites was more often influenced by droughts than RW. RW and LBI from both microsites were similarly often influenced by cold winters. At both scales, the response time of RW and LBI after droughts predominantly lagged by one year, while cold winters were recorded in the same year. The typical duration of growth reductions after both extremes was one year for both RW and LBI. Our study indicates that Scots pine from the Baltic Sea region is sensitive to climate extremes, especially cold winters. [ABSTRACT FROM AUTHOR]

This study focuses on analyzing the growth rate and growth–climate relationship in Scots pine (Pinus sylvestris L.) growing on coastal dunes of different ages on the Southern Baltic coast. Podzols have developed on these dunes. Depending on dune age, however, podzols are characterized by a different degree of development and richness, which represents the main factor differentiating the studied habitats: the oldest brown dunes (BD), younger yellow dunes (YD), and the youngest white dunes (WD). Samples were taken from 68 trees using Pressler borers. Using classic cross-dating methods, local chronologies were compiled that served as the basis for further analyses. Basic analyses of soil properties were also performed. Trees growing on brown dunes display the widest tree-rings and the highest rate of cumulative radial growth. Both rates are the lowest for trees growing on white dunes (WD). The dominant meteorological factor shaping tree-ring widths is late winter/early spring air temperature (February/March). However, in poorer habitats with inferior soil air–water conditions, rainfall sums and rainfall distribution through the year become progressively more significant factors. On white dunes (WD), the strongest growth–climate correlations are obtained for summer precipitation. These results identify habitat richness as the main factor shaping growth dynamics in Scots pines growing on dunes. Due to the protective function of the studied tree stands (coast protection), and in light of the rising sea levels and increasing storm intensities, further studies are required, aiming at understanding all interrelationships occurring in these valuable ecosystems. [ABSTRACT FROM AUTHOR]

Larix chinensis Beissn., as a native, dominant and climate-sensitive coniferous species at Mount Taibai timberline, Qinling mountains, is rarely disturbed by anthropogenic activities; thus, it is an ideal proxy for the investigation of climate change or vegetation evolution. In this study, we applied dendrochronological methods to the L. chinensis tree-ring series from Mt. Taibai and investigated the relationships between tree-ring widths and NDVI/climate factors using Pearson correlation analysis. On the basis of the remarkable positive correlations (r = 0.726, p < 0.01, n = 23) between local July normalized difference vegetation indices (NDVI) and tree-ring width indices, the regional 146-year annual maximum vegetation density was reconstructed using a regression model. The reconstructed NDVI series tracked the observed data well, as the trans-function accounted for 52.8% of observed NDVI variance during AD 1991–2013. After applying an 11-year moving average, five dense vegetation coverage periods and six sparse vegetation coverage periods were clearly presented. At a decadal scale, this reconstruction was reasonably and negatively correlated with a nearby historical-record-based dryness/wetness index (DWI), precisely verifying that local vegetation cover was principally controlled by hydrothermal variations. Spectral analysis unveiled the existence of 2–3-year, 2–4-year, 5–7-year and 7–11-year cycles, which may potentially reflect the connection between local NDVI evolution and larger-scale circulations, such as the El Niño–Southern Oscillation (ENSO) and solar activity. This study is of great significance for providing a long-term perspective on the dynamics of vegetation cover in the Qinling mountains, and could help to guide expectations of future forest variations. [ABSTRACT FROM AUTHOR]

Climatic change will affect elevational vegetation distribution because vegetation distribution is related to thermal conditions. However, how elevational species distributions are determined by biotic and abiotic factors is not clear. The long‐term plot census along an elevational gradient is indispensable to clarify mechanisms of elevational distribution of tree species. Two congeneric conifers, the less shade‐tolerant Abies veitchii and shade‐tolerant A. mariesii, dominate at low and high elevations, respectively, in the subalpine zone in Japan. This study investigated the population dynamics of the two species at three elevations (low, middle, high) for 13 years to examine why the two species dominated the different elevations from the viewpoints of competition and disturbance. This study showed that growth and survival rates were not highest at the most dominant elevations for each species. At the high elevation where A. mariesii dominated and small disturbances frequently occurred, the recruitment rate of A. mariesii was highest among the three elevations and that of A. veitchii was largely decreased by tree competition. However, A. veitchii was dominant earlier than A. mariesii at the low elevation after large disturbances by the high growth rate of individual trees. Therefore, A. mariesii was superior to A. veitchii at the high elevation because of its high recruitment rate and large reduction of recruitment of A. veitchii due to competition, while A. veitchii was superior to A. mariesii at the low elevation after large disturbances because of higher growth rate than A. mariesii. It is suggested that the elevational distributions of the two species were determined by elevational changes in population dynamics in relation to competition and disturbance. Long‐term observational studies of forest dynamics among various elevations are indispensable to predict the effects of climatic change on vegetation distribution. [ABSTRACT FROM AUTHOR]

Local adaptation and plasticity of growth play important roles in the adaptability of trees to changing conditions. Under accelerating climatic changes, the adaptive capacity of metapopulations can be exceeded, implying a necessity for assisted gene flow to sustain the productivity of forests. Such management is knowledge intensive, and information on the responsiveness of metapopulations (provenances) across the climatic gradient can aid more comprehensive projections of their performance. The plasticity of growth responses to weather conditions of five provenances of Scots pine with differing field performance across the climatic gradient of the south-eastern Baltic Sea region was assessed using dendrochronological methods and generalized additive models. Weather conditions related to water availability in summer, as well as during dormancy, were the main regional drivers of an increment in the provenances. The provenances differed by the plasticity of responses according to field performance, indicating adaptation in terms of growth sensitivity and uneven adaptability. The weather–growth responses of the top-performing provenances to summer weather were more plastic, providing advantages under a changing climate. Accordingly, regional sensitivity and plasticity of growth responses could be used for the screening of genotypes best suited for the projected climates. In addition, the estimated growth responses encourage supplementation of the local breeding populations with the top-performing provenances originating from sites with the projected climates. [ABSTRACT FROM AUTHOR]

A ring-width series was developed from Dahurian larch (Larix gmelinii) in the northeastern forest area of Inner Mongolia, China. By analyzing the relationships between tree-ring data and climate records, an August–September mean maximum temperature (T89) series during 1845 and 2012 was reconstructed based on a simple linear regression equation. This reconstructed series explained 40.9% variance of the observed temperature from 1959 to 2012. The reconstructed T89 series was consistent with the historical disaster events caused by extreme climate (e.g., flood, frost disaster, and cold damage). Besides, the temperature comparisons showed that the year in which the warm months (April–September) in northeast China began to warm up has latitude differences. It started with a gradual delay from north to south, starting 1980 in the south region, after 1950 AD in the central region and after 1940 in the north region. Our study can enrich high-resolution temperature series in Northeast China and help clarify the characteristic of recent warming in northeast China. [ABSTRACT FROM AUTHOR]

Climate change, namely increased warming coupled with a rise in extreme events (e.g., droughts, storms, heatwaves), is negatively affecting forest ecosystems worldwide. In these ecosystems, growth dynamics and biomass accumulation are driven mainly by environmental constraints, inter-tree competition, and disturbance regimes. Usually, climate–growth relationships are assessed by linear correlation due to the simplicity and straightforwardness of modeling. However, applying this method may bias results, since the ecological and physiological responses of trees to environmental factors are non-linear, and usually bell-shaped. In the Eastern Carpathian, Norway spruce is at the southeasternmost edge of its natural occurrence; this region is thus potentially vulnerable to climate change. A non-linear assessment of climate–growth relationships using machine-learning techniques for Norway spruce in this area had not been conducted prior to this study. To address this knowledge gap, we analyzed a large tree-ring network from 158 stands, with over 3000 trees of varying age distributed along an elevational gradient. Our results showed that non-linearity in the growth-climate response of spruce was season-specific: temperatures from the previous autumn and current growing season, along with water availability during winter, induced a bell-shaped response. Moreover, we found that at low elevations, spruce growth was mainly limited by water availability in the growing season, while winter temperatures are likely to have had a slight influence along the entire elevational gradient. Furthermore, at elevations lower than 1400 m, spruce trees were also found to be sensitive to previous autumn water availability. Overall, our results shed new light on the response of Norway spruce to climate in the Carpathians, which may aid in management decisions. • Physiological tree responses to climate factors are non-linear, usually bell-shaped. • At low elevations, spruce growth is strongly limited by water availability. • Younger trees are more drought-sensitive compared to older trees. • Non-linearity in the growth response of spruce is season-specific. [ABSTRACT FROM AUTHOR]

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

With ongoing climate change, episodes of severe flooding are predicted to become more frequent despite a general trend towards increasing summer drought. We investigated how wood growth of adult trees of two species characteristic of floodplain forests in Central Germany (Fraxinus excelsior L., Quercus robur L.) and two less-typical species (Acer pseudoplatanus L., Carpinus betulus L.) responded to both maximum stream water level and climate, with a special focus on the effects of the extraordinary flood of the Saale River in June 2013 and the extreme drought in summer 1976. Tree-ring widths were measured on wood cores, and standardized ARSTAN tree-ring chronologies were produced. Using variance partitioning as well as linear mixed-effects models, we compared the effects of monthly values for maximum water level, temperature and precipitation sum on tree-ring width. Further, we calculated resistance, resilience and recovery of the tree species to the extreme events of flooding in 2013 and drought in 1976. Wood growth of all species studied, and particularly of F. excelsior, responded positively to the extraordinary flooding in June 2013. However, in the best models for the characteristic floodplain forest species (F. excelsior and Q. robur), mainly precipitation (F. excelsior) or a combination of precipitation and wood growth of the previous year (Q. robur) acted as drivers of wood growth of the current year. In contrast, growth of the less habitat-specific species (A. pseudoplatanus) mainly showed a significant response to the combination of temperature and wood growth of the previous year. C. betulus was the only species studied that benefited from the extreme drought in 1976. However, two years afterwards, only the wood growth of A. pseudoplatanus was still reduced, while F. excelsior and Q. robur fully recovered. In comparison to other regions in Central Europe, the moderate flood regime of the Saale River seems to have the potential to mitigate effects of summer drought in this region, which is one of the driest in Germany. Thus, increased flooding frequency might, to some degree, reduce drought effects brought about by climate change as well.

Abstract Background Climate-induced challenge remains a growing concern in the dry tropics, threatening carbon sink potential of tropical dry forests. Hence, understanding their responses to the changing climate is of high priority to facilitate sustainable management of the remnant dry forests. In this study, we examined the long-term climate-growth relations of main tree species in the remnant dry Afromontane forests in northern Ethiopia. The aim of this study was to assess the dendrochronological potential of selected dry Afromontane tree species and to study the influence of climatic variables (temperature and rainfall) on radial growth. It was hypothesized that there are potential tree species with discernible annual growth rings owing to the uni-modality of rainfall in the region. Ring width measurements were based on increment core samples and stem discs collected from a total of 106 trees belonging to three tree species (Juniperus procera, Olea europaea subsp. cuspidate and Podocarpus falcatus). The collected samples were prepared, crossdated, and analyzed using standard dendrochronological methods. The formation of annual growth rings of the study species was verified based on successful crossdatability and by correlating tree-ring widths with rainfall. Results The results showed that all the sampled tree species form distinct growth boundaries though differences in the distinctiveness were observed among the species. Positive and significant correlations were found between the tree-ring widths and rainfall, implying that rainfall plays a vital role in determining tree growth in the region. The study confirmed the formation of annual growth rings through successful crossdating, thus highlighted the potential applicability of dendroclimatic studies in the region. Conclusions Overall, the results proved the strong linkage between tree-ring chronologies and climate variability in the study region, which further strengthens the potential of dendrochronological studies developing in Ethiopia, and also has great implications for further paleo-climatic reconstructions and in the restoration of degraded lands. Further knowledge on the growth characteristics of tree species from the region is required to improve the network of tree-ring data and quality of the chronology so as to successfully reconstruct historic environmental changes.

The radial growth of coniferous trees in the mid–high latitudes of the Northern Hemisphere has an unstable response to climate warming. We analyzed the differences in the radial growth patterns of the two dominant species (Larix principis-rupprechtii Mayr and Picea meyeri Rehd. et Wils.) on Guancen Mountain, north-central China, and the differences in the stability of their radial growth in response to climate change. Pearson correlation and sliding analysis were performed to study the correlations and dynamic relationships between radial growth and climatic factors. The main results are as follows: (1) the standard chronologies of L. principis-rupprechtii and P. meyeri contained rich climate information, and the radial growth of L. principis-rupprechtii was more sensitive to climatic factors than that of P. meyeri; (2) on a long-term scale, changes in the radial growth of L. principis-rupprechtii and P. meyeri in response to the monthly mean temperature and standardized precipitation evapotranspiration index (SPEI) were unstable; (3) after the abrupt temperature change, the interannual basal area increments (BAIs) of the two dominant species followed an upward trend, and the radial growth rate of L. principis-rupprechtii was much greater than that of P. meyeri. The results of this paper can help to understand the response of the radial growth of coniferous forests in north-central China to future climate change, and provide a basis for future forest cultivation in the middle and high latitudes of the northern hemisphere.

This study addressed the effects of climate drivers on the tree-ring width (TRW) parameters (total ring width (TR), earlywood width (EW) and latewood width (LW)) and the total ring δ13C series of different wood components (whole wood, α-cellulose and holocelluose) from Masson pine in subtropical China. Pairwise correlation coefficients between three ring width parameters were statistically significant. EW and LW did not reveal much stronger climate sensitivity rather than TR. This indicated that the use of intra-annual ring width has little benefit in extracting more climate information. The mean δ13C series of the three components of the total ring had the strongest climate response to the July–September relative humidity (r = −0.792 (whole wood), −0.758 (holocellulose) and −0.769 (α-cellulose)). There are no significant differences in the dendroclimatic relationships of the δ13C series of different wood components. Through both stationary temporal and spatial-statistical perspectives, the moisture drivers (summer/autumn) had a significant impact on three ring width parameters and three components of Masson pine. Overall, the radial growth and the δ13C series showed different responses to the same climate drivers during the same period. Moreover, the R-squared values of the strongest climate-proxy correlation coefficients were smaller than 50% for TRW. Consequently, the δ13C series of Masson pine may be a more representative climate proxy than TRW parameters for dendroclimatology in subtropical China.