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Key message: Resin production and growth in Pinus pinaster and Pinus pinea show a trade-off under varying environmental conditions, impacting future resin yields under climate change. Resin production in pines constitutes an important defense mechanism against biotic and abiotic factors, and it is also an important forestry product. In Portugal, resin is mainly extracted from Pinus pinaster and to a lesser extent from Pinus pinea, the two most widespread pine species in the country. The resin tapping season coincides with the growing season, from spring to autumn. Thus, growth and resin production may compete for carbon, although their response to environmental conditions can differ. This study investigates how the daily growth and biweekly resin production of P. pinaster and P. pinea in a mixed stand respond to environment over the 2021 growing season. During the resin tapping period, growth of both species showed a positive correlation with temperature, soil moisture, air relative humidity and radiation. Resin yield of both species showed a positive relation with soil temperature, and a negative relation with growth, suggesting a trade-off between growth and resin yield. Our results indicate that both growth and resin yield increase with temperature, with growth being more sensitive to soil moisture and relative humidity. Under a scenario of rising temperatures and precipitation reduction, both functions (growth and resin yield) are expected to be affected positively. However, resin production depends on carbon assimilation and allocation, both of which are reduced or altered during periods of extreme drought. This can lead to increasing competition for carbon allocation between growth, storage and resin yield, making resin yield responses to climate change scenarios uncertain. [ABSTRACT FROM AUTHOR]

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]

Increases in temperatures and atmospheric CO2 concentration influence the growth performance of trees worldwide. The direction and intensity of tree growth and physiological responses to changing climate do, however, vary according to environmental conditions. Here we present complex, long-term, tree-physiological responses to unprecedented temperature increase in East Asia. For this purpose, we studied radial growth and isotopic (δ13C and δ18O) variations using tree-ring data for the past 100 yr of dominant Quercus mongolica trees from the cool-temperate forests from Hallasan, South Korea. Overall, we found that tree stem basal area increment, intercellular CO2 concentration and intrinsic water-use efficiency significantly increased over the last century. We observed, however, short-term variability in the trends of these variables among four periods identified by change point analysis. In comparison, δ18O did not show significant changes over time, suggesting no major hydrological changes in this precipitation-rich area. The strength and direction of growth–climate relationships also varied during the past 100 yr. Basal area increment (BAI) did not show significant relationships with the climate over the 1924–1949 and 1975–1999 periods. However, over 1950–1974, BAI was negatively affected by both temperature and precipitation, while after 2000, a temperature stimulus was observed. Finally, over the past two decades, the increase in Q. mongolica tree growth accelerated and was associated with high spring–summer temperatures and atmospheric CO2 concentrations and decreasing intrinsic water-use efficiency, δ18O and vapour pressure deficit, suggesting that the photosynthetic rate continued increasing under no water limitations. Our results indicate that the performance of dominant trees of one of the most widely distributed species in East Asia has benefited from recent global changes, mainly over the past two decades. Such findings are essential for projections of forest dynamics and carbon sequestration under climate change. [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]

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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.

Global warming may lead to increased tree growth but also reduced tree performance due to increased moisture stress. Under what conditions these conflicting responses occur remains uncertain, especially when growth is controlled by different climatic factors throughout the year. Here, we investigate the growth response of Tsuga dumosa, a Himalayan endemic tree species, to global climate change in unique old-growth forests that persist at around 3000 m elevation near Kanchenjunga, Nepal. Specifically, we are examining various growth parameters, including earlywood, adjusted latewood, maximum latewood density, and total basal area increment, to determine how different climatic factors influence growth dynamics during the year. First, we found that the response to climate change varied by season. Climate warming had contrasting effects on different components of tree growth. Higher temperatures during previous October and previous December and warming-induced moisture stress in April reduce earlywood and total annual increment. On the other hand, higher rainfall during June and July limits total tree ring width and adjusted latewood width, respectively. Second, warming is changing the sensitivity of tree growth to various climatic factors. Growth in the past two decades became more dependent on autumn conditions than on spring and summer conditions. Warming alleviates the cold limitation during the cool monsoon summer but reinforces the water deficit during autumn, winter, and pre-monsoon dry spring. Third, analysis of basal area increments, an indicator of aboveground biomass production, showed that accelerated warming in summer contributes to increased annual productivity. However, the growth reduction observed during warming spring and autumn months counteracts this effect. In conclusion, this study highlights the contrasting responses of Tsuga dumosa to climate warming in Himalayan montane forests. While accelerated warming makes the trees less sensitive to summer temperature limitations, warm autumns, dry springs, and less snowy winters become the main limiting factors for their growth. Understanding these complex and contrasting responses, as well as the sensitivity of different growth parameters, is essential for predicting the long-term impacts of climate change on mountain ecosystems. [ABSTRACT FROM AUTHOR]

Existing streamflow reconstructions based on tree-ring analysis mostly rely on species from upland, mainly montane areas, while lowland species (generally plain) areas are rarely used. This limits the understanding of streamflow change history in the lowlands, which is an important basis for water resource management. This study focused on Populus euphratica stands located along the main stream, eastern and western tributaries in the lower reaches of the Heihe River basin (HRb), in arid northwestern China. We investigated how streamflow regulation interferes with riparian trees in lowlands when they used for streamflow reconstruction. Tree-ring width chronologies were developed and analyzed in conjunction with meteorological and hydrologic observation data. The results show streamflow regulation leads in sharp fluctuations in the streamflow allocation between the eastern tributaries and western tributaries. This resulted in instability of the correlation between streamflow at the two tributaries and at the Zhengyixia hydrologic station, with corresponding fluctuations in radial growth of poplar trees on the banks of the two tributaries and at the station. Streamflow regulation altered the natural patterns of seasonal streamflow below the station, changing the time window of poplar response. This study provides useful insight into tree-ring width based streamflow reconstruction in the lowlands. [ABSTRACT FROM AUTHOR]

Tree-ring width (RW), density, elemental composition, and stable carbon and oxygen isotope (δ13C, δ18O) are widely used as proxies to assess climate change, ecology, and environmental pollution; however, a specific pretreatment has been needed for each proxy. Here, we developed a method by which each proxy can be measured in the same sample. First, the sample is polished for ring width measurement. After obtaining the ring width data, the sample is cut to form a 1-mm-thick wood plate. The sample is then mounted in a vertical sample holder, and gradually scanned by an X-ray beam. Simultaneously, the count rates of the fluorescent photons of elements (for chemical characterization) and a radiographic grayscale image (for wood density) are obtained, i.e. the density and the element content are obtained. Then, cellulose is isolated from the 1-mm wood plate by removal of lignin, and hemicellulose. After producing this cellulose plate, cellulose subsamples are separated by knife under the microscope for inter-annual and intra-annual stable carbon and oxygen isotope (δ13C, δ18O) analysis. Based on this method, RW, density, elemental composition, δ13C, and δ18O can be measured from the same sample, which reduces sample amount and treatment time, and is helpful for multi-proxy comparison and combination research. [ABSTRACT FROM AUTHOR]

Changes in annual radial growth is an important indication of climate change. Dendroclimatology studies in northern China have focused on linear statistical analysis, but lacking studies based on the process of ring formation to clarify the radial growth of trees. Tree-ring width standard chronology (STD) was established using samples of Larix principis-rupprechtii collected at 2303 m altitude on Luya Mountain. Using the Vaganov-Shashkin (VS) model to simulate growth and development, the internal physiological mechanism of radial growth is identified. It was concluded that: (1) the growing season of L. principis-rupprechtii was May to September; (2) soil moisture was a significant factor in the early and late growing seasons, and temperature was the dominant factor in its main growth period; and (3) formation of narrow ring widths was closely related to drought stress, the development of wide ring widths will be restricted by increasing future temperatures. The VS model is applicable for radial growth simulation of subalpine coniferous forests and for guiding the cultivation of local tree species in the future. [ABSTRACT FROM AUTHOR]

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]

Resin is a renewable forest resource that can increase the economic value of some forests in rural areas. Resin production is associated with climatic conditions. However, its impact on trees' growth remains unclear. Here, we studied radial growth in six Portuguese Pinus pinaster forests that had been resin tapped for 5–7 years along a latitudinal and climatic gradient to understand whether resin tapping affects tree growth, and how it is affected by climate, stand and tree traits. Tree-ring width (TRW) on tapped and untapped trunk sides was compared before and during the tapping period. Tree-ring width decreased in the three youngest populations (< 30 years), with no changes in older populations (> 40 years), while TRW increased after resin harvesting began in the oldest stand (> 55 years). Annual resin-tapping impact (RTI), calculated as the ratio between TRW during tapping years and the 5-year average TRW before tapping, was below and above 1 in the younger and older stands, respectively. Among stand characteristics and across sites, RTI was negatively correlated with tree competition and positively correlated with TRW, cambial age, and tree height. Climatic conditions had a minor role on tree growth response to resin tapping. Our main conclusion is that the effect of resin extraction on growth is age-dependent. Our results encourage the co-production of resin and wood on maritime pine stands over 40 years old where resin extraction impact on growth is negligible. [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.

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

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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]

Oxygen (δ 18 O) and hydrogen (δ 2 H) stable isotope ratios are tightly coupled in precipitation and, albeit damped, in leaf water, but are often decoupled in tree-ring cellulose. The environmental and physiological conditions in which this decoupling occurs are not yet well understood. We investigated the relationships between δ 18 O and δ 2 H and tree-ring width (TRW), tree crown volume, tree age and climate in silver fir and Douglas-fir and found substantial differences between δ 18 O and δ 2 H. Overall, δ 18 O-δ 2 H correlations were weak to absent but became significantly negative under high summer vapour pressure deficit (VPD). δ 18 O and δ 2 H had positive and negative nonlinear relationships with TRW, respectively, with clear relationships at the site and tree levels for silver fir and, to a lesser extent, for Douglas-fir. Age trends for silver fir were weakly negative in δ 18 O but positive in δ 2 H. Tree crown volume and δ 18 O or δ 2 H had no significant relationships. Most strikingly, δ 18 O strongly depended on spring climate (precipitation and VPD), whereas δ 2 H depended on summer climate (temperature and VPD) for both species. Our study shows that the δ 18 O-δ 2 H decoupling in tree-ring cellulose in two temperate conifer species could be highlighted by their contrasting relationships to climate and tree intrinsic variables (TRW, age)., (© 2024 The Author(s). Plant, Cell & Environment published by John Wiley & Sons Ltd.)

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.

Global change, characterized by elevated atmospheric CO2 concentrations and warming, is profoundly affecting terrestrial forests. However, whether the increasing atmospheric CO2 concentration has a fertilizer effect on tree growth and whether intrinsic water use efficiency (iWUE) promotes tree growth in semi‐arid regions is not entirely clear. In this study, we evaluated the relationships between tree‐ring widths, δ13C values and iWUE of Qinghai Spruce (Picea crassifolia Kom.) in the eastern Qilian Mountains, northwestern China. We found that the iWUE is significantly consistent with the δ13C of rings in the high‐frequency signal, and the relationship between iWUE and tree‐ring width is unstable. The first‐order difference correlation analysis with meteorological data showed that both the iWUE and tree‐ring width were drought‐limited. The radial growth was mainly regulated by water availability in current April and July, while annual variation of iWUE was primarily controlled by that in current July. In the early stage of trees growth, there was a positive relationship between iWUE and radial growth due to the CO2 fertilization. During the 1970s–2000s, the effect of water availability in July on radial growth increases because of the decreased precipitation in July. This has decreased stomatal conductance, intercellular CO2 concentration, carbon uptake and growth, contributing to the negatively significant correlation between tree‐ring widths and iWUE (p <.05). Since the year of 2010, the relationship between the radial growth and iWUE shifted because of the increased precipitation in July. This study provided new insights for whether increased water‐use efficiency enhances tree growth under semixeric conditions. [ABSTRACT FROM AUTHOR]

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]