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The Himalayas experienced long-term climate changes and recent extreme weather events that affected plant growth and the physiology of tree species at high-elevation sites. This study presents the first statistically robust δ 18 O TR chronologies for two native pine species, Pinus roxburghii, and Pinus wallichiana, in the lower Nepalese Himalaya. The isotope chronologies exhibited 0.88‰ differences in overall mean isotope values attributed to varying elevations (460-2000 m asl). Comparative analysis of climate response using data sets from different sources and resolutions revealed the superiority of the APHRODITE (Asian Precipitation - Highly-Resolved Observational Data Integration Towards Evaluation) data set calibrated for the South Asian Summer Monsoon (SASM)-dominated region. Both species exhibited negative correlations with monsoon precipitation and positive correlations with temperature. However, during the peak monsoon season (July-August), daily resolved climate data disentangled statistically insignificant relationships, and revealed that δ 18 O TR is influenced by atmospheric moisture. Both congeneric species showed a decoupling between the chronologies after 1995. However, no significant change in air moisture origin and monsoon regime between the study sites was observed, indicating a consistent dominant moisture source during different monsoon seasons. Besides, we also observed the decreased inter-series correlation of both δ 18 O TR chronologies after 1995, with P. wallichiana experiencing a steeper decrease than P. roxburghii. The weakening correlations between and within the chronologies coincided with a regional drought during 1993-1995 in both sites, highlighting the strong regulation of local climate on the impact of regional extreme climate events. Our findings emphasise the importance of employing climate data with optimal spatial and temporal resolution for improved δ 18 O TR -climate relationships at the intra-annual scale while considering the influence of site-specific local environmental conditions. Assessing climate data sets with station data is vital for accurately interpreting climate change's impact on forest response and long-term climate reconstructions., (© 2024. The Author(s).)

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., (© 2022. The Author(s).)

Key message: European hornbeam has a great potential for tree-ring based research when using a combination of conventional dendrochronological techniques and fluorescent microscopy. Arasbaran forests are among the most important ecological areas in Iran, but they have been studied less extensively in comparison to the famous Hyrcanian forests. For the first time, the potential of two dominant species in these forests, i.e. hornbeam (Carpinus betulus) and stinking juniper (Juniperus foetidissima) to study the climate-growth relations was evaluated using a dendroecological approach. Difficulties in distinguishing ring-width boundaries of hornbeam were overcome using fluorescence microscopy. The statistics used to evaluate the chronologies of both species confirmed their capability to study climate–growth relationships and their potential for developing regional climate reconstruction. Hornbeam and juniper showed similar climate-growth relationships. Across all sampling sites, the growth index displayed a positive correlation with precipitation and SPEI drought index, and a negative correlation with temperature. Precipitation in spring and early autumn played a significant role in stimulating the radial growth of the species. However, topography and microclimate could affect the relationship between growth and regional climate, as the highest elevation site receives abundant moisture input from frequent fog events. Our initial study highlights the potential of hornbeam as a widely spread but neglected species in the Northern Hemisphere for dendroecological studies. Furthermore, we conclude that despite some variance in the microclimate of different sites (ranging from cold, sub-humid to warm, semi-arid) within the Arasbaran region, trees of different species in the entire study area show a common response to climatic change, mainly affected by water availability. [ABSTRACT FROM AUTHOR]

We analyzed the tree-rings δ18O of Abies spectabilis (fir) growing at the subalpine treeline ecotone in the Magguchatti valley. The valley is located in the Indian summer monsoon (ISM) dominated region of western Himalaya and also receives snow precipitation derived by westerly disturbances (WDs) during the winter months. The 60 year developed (1960–2019 CE) tree-ring δ18O chronology revealed a strong positive correlation with the temperature of late winter and spring months (February to April). Strong negative correlations are also apparent for snowcover, soilmoisture, and relative humidity for the same spring season. Our findings partly contrast the significant correlation results of tree-ring δ18O with summer precipitation and drought indices recorded from other summer monsoon-dominated regions in the Himalayas. The spatial correlation analyses with sea surface temperatures (SSTs) and climate parameters showed subdued signals of tropical Pacific at the site, but with a shift to more moisture influx from the Arabian Sea during the last two decades. Moreover, a significant negative correlation with North Atlantic Oscillation further justifies the strongly captured spring temperature and snowcover signals and the weak effect of summer precipitation in fir trees. A temperature rising trend during the latter half of the 20th century and the elevation effect are taken as important factors controlling the moisture source at the treeline ecotone zones. [ABSTRACT FROM AUTHOR]

Response of climate warming on tree-ring formation has attracted much attention during recent years. However, most studies are based on statistical analysis, lacking understanding of tree-physiological processes, especially in the mountainous regions of the Tibetan Plateau (TP). Herein, we firstly use an updated new version of the tree-ring process-based Vaganov-Shashkin model (VS-oscilloscope) to simulate tree-ring formation and its relationships with climate factors during the past six decades. Our analyses covered 341 sampled trees growing within elevations ranging from 2750 to 4575 m a.s.l. at five sampling sites across the TP. Simulated tree-ring width series are significantly ( p < 0.01) correlated with actual tree-ring width chronologies during their common interval periods. Starting dates of tree-ring formation are determined by temperature at all five sampling sites. After the initiation of tree stem cambial activity, soil moisture content has a significant effect on tree radial growth. Ending dates of cambial activity are driven by temperature over the whole study region. Simulated results indicate differences between wide and narrow tree-rings are mostly induced by soil moisture content, especially during the first half of the growing season, when effects from temperature variations are minor. Interestingly, we detected significantly ( p < 0.001) increased relative growth rates due to higher soil moisture content after the year 1985 at the five sampling sites. However, the variability of mean relative growth rates due to temperature is negligible before and after that. Based on the successful application of VS-oscilloscope modeling on the high-elevation tree stands on the TP, our study provides a new perspective on tree radial growth process and their varying relationships to climate factors during the past six decades. [ABSTRACT FROM AUTHOR]

Long-term instrumental records that provide estimates about the natural range of long-term climate fluctuation are lacking in Iran. Ring-width chronologies were developed from two oak sites in the central Zagros Mountains, dating back to 1705 A.D. Due to high correlations between the local site chronologies, a mean regional chronology ( RC) was calculated. Correlations with regionalized climate data showed significant negative correlations with maximum temperature in December of the previous year and February, May, June and August of the current year. However, May-June maximum temperatures of the current growing season showed the highest negative correlation coefficient with regional tree growth patterns. Based on this relationship, maximum temperature of May-June was reconstructed over the last 170 years (1840-2010). The average length of cold periods was shorter than that of warm periods. Further sampling may allow the analysis of long-term climatic trends in this region. [ABSTRACT FROM AUTHOR]

Monthly mean (TEM), maximum ( Tmax) and minimum ( Tmin) surface air temperatures at 119 meteorological stations on the Yunnan Plateau (YP, Southwest China) were analysed for temporal trends and spatial variation patterns during the period 1961-2004. Linear trend analyses revealed that annual temperature over the YP increased at a rate of 0.3 °C/decade during the period 1961-2004, while warming trend of 0.33 °C/decade and 0.26 °C/decade was observed for winter and summer temperatures, respectively. Warming trends of nighttime minimum temperature are more pronounced than those of daytime maximum temperature, especially during winter season. Consequently, a decreasing trend of diurnal temperature ranges (DTR = Tmax − Tmin) was observed. Five spatial patterns of temperature variability were objectively defined by rotated empirical orthogonal function (EOF) analysis, which are associated with distinct temporal temperature variations and geographical area over the YP. Annual temperature increases were found to be most pronounced in the southern and northwestern (high-elevation) parts of the YP, whereas the hot-dry valleys along the Yangtze and Red River basins experienced cooling during the past four decades. Copyright © 2010 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

Abstract: High-resolution proxy data are still scarce in the southeastern Tibetan Plateau, which limit our understanding of climatic variability before instrumental records. In this study, we developed 595-year tree ring-width chronology from Larix speciosa near the timberlines of the Gaoligong Mountains, southeastern Tibetan Plateau. Ring-width site chronologies and a well-replicated regional chronology (RC) showed significant positive correlations with warm season temperatures from May to August. Using RC as predictor, we reconstructed mean May–August temperature for the study region that extends back to A.D. 1585. Cold conditions prevailed during the periods 1600s, 1620–30, 1640–50s, 1700s, 1730–40s, 1760s, 1810–20s, 1850s, 1900–10s and 1955–70. Warm episodes occurred during 1610s, 1660–1680s, 1710–20s, 1750s, 1780–90s, 1820–40, 1920–50 and 1980–present. Spatial correlations with gridded land surface temperatures revealed that our reconstruction represents regional temperature signal for the southern Tibetan Plateau. Comparison with other tree ring-based temperature reconstructions from surrounding areas implies a high degree of confidence for our reconstruction. [ABSTRACT FROM AUTHOR]

The article presents a study on the temperature history recorded by tree rings in the Tibetan Plateau (TP), China during 1612-1998. The study develops two ring-width index chronologies such as traditionally standardized chronology (TSC) and regional curve standardization (RCS) for detrending. The results show that low-frequency and high-frequency temperature variations are captured by RCS and TSC reconstructions, and the response patterns of RSC chronology to climate data are similar to the TSC.

Abstract: The climatological signal of δ 18O variations preserved in ice cores recovered from Puruogangri ice field in the central Tibetan Plateau (TP) was calibrated with regional meteorological data for the past 50 years. For the period AD 1860–2000, 5-yearly averaged ice core δ 18O and a summer temperature reconstruction derived from pollen data from the same ice core were compared. The statistical results provide compelling evidence that Puruogangri ice core δ 18O variations represent summer temperature changes for the central TP, and hence regional temperature history during the past 600 years was revealed. A comparison of Puruogangri ice core δ 18О with several other temperature reconstructions shows that broad-scale climate anomalies since the Little Ice Age occurred synchronously across the eastern and southern TP, and the Himalayas. Common cold periods were identified in the 15th century, 1625–1645 AD, 1660–1700 AD, 1725–1775 AD, 1795–1830 AD, 1850–1870 AD, 1890–1920 AD, 1940–1950 AD, and 1975–1985 AD. The period 1725–1775 AD was one of the most prolonged cool periods during the past 400 years and corresponded to maximum Little Ice Age glacier advance of monsoonal temperate glaciers of the TP. [Copyright &y& Elsevier]

Abstract: Variations in ring width and wood density of Picea brachytyla were used to develop high-resolution climate proxy data to extend the existing climate record in the central Hengduan Mountains, north-western Yunnan Province, China. Growth–climate response analyses showed that the total ring width (TRW) and maximum latewood density (MXD) in the sub-alpine zone are mainly influenced by summer temperature variability. Based on a MXD regional chronology derived from two high elevation sites, we developed a warm season (April–September) temperature reconstruction for the period A.D. 1750–2006. The climate/tree-growth model accounts for 41% of the instrumental temperature variance during the period 1958–2004. Warm summers occurred during 1750s, 1820–50s, 1880–1890s, 1930–1950s and 1990–present; while the periods of 1790–1810s, 1860–1870s, 1900–1920s, and 1960–1985 were relatively cold. Spatial climate correlation analyses with gridded land surface data revealed that our warm season temperature reconstruction contains a strong regional temperature signal for the Hengduan Mountain ranges. Our reconstruction successfully captured recent abrupt climatic changes and agreed in general with other tree ring-based temperature reconstructions from nearby regions on a decadal timescale. In addition, reconstructed summer temperature variations were consistent with recorded glacier fluctuations in the surrounding high mountains. [Copyright &y& Elsevier]

The article discusses a tree ring-based drought reconstruction in the central Hengduan Mountains in north-western Yunnan, China. The study involved developing four tree ring-width chronologies of three species. It was found that there are correlations existing among the chronologies, and that the first principal component makes up 60.5% of total variance in 1655-2005. Also, radial growth was observed to be affected by precipitation and relative humidity and Palmer drought severity index (PDSI), whereas tree growth is negatively affected by temperature in March.

Abstract: We developed five tree ring-width chronologies from one fir (Abies georgei) and four spruce (Picea brachytyla) stands near the upper treeline in the central Hengduan Mountain, northwestern Yunnan, China. Similar growth patterns and significant correlations are embodied among the five chronologies. A principal component analysis for the four spruce chronologies indicated that the first component accounts for 54.8% of the total variance over the period 1750–2003. Climate–growth response analysis revealed that radial growth is mainly controlled by temperature variations, especially in the winter season. The first principal component of the spruce chronology network accounts for 43% of the annual mean temperature (from previous October until September) variance during the common period 1959–2003. By using a linear regression approach, we reconstructed annual mean temperature for the past 250 years. The reconstruction shows that the central Hengduan Mountain experienced some cool episodes during the 1810s, 1860s, and during 1960–1980. Warm intervals occurred during the 1780s, 1850s, 1940–1960 and in the past two decades. These general patterns are in general accordance with other records from nearby regions. [Copyright &y& Elsevier]

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

The Himalayan region has already witnessed profound climate changes detectable in the cryosphere and the hydrological cycle, already resulting in drastic socio-economic impacts. We developed a 619-yea-long tree-ring-width chronology from the central Nepal Himalaya, spanning the period 1399–2017 CE. However, due to low replication of the early part of the chronology, only the section after 1600 CE was used for climate reconstruction. Proxy climate relationships indicate that temperature conditions during spring (March–May) are the main forcing factor for tree growth of Tsuga dumosa at the study site. We developed a robust climate reconstruction model and reconstructed spring temperatures for the period 1600–2017 CE. Our reconstruction showed cooler conditions during 1658–1681 CE, 1705–1722 CE, 1753–1773 CE, 1796–1874 CE, 1900–1936 CE, and 1973 CE. Periods with comparably warmer conditions occurred in 1600–1625 CE, 1633–1657 CE, 1682–1704 CE, 1740–1752 CE, 1779–1795 CE, 1936–1945 CE, 1956–1972 CE, and at the beginning of the 21st century. Tropical volcanic eruptions showed only a sporadic impact on the reconstructed temperature. Also, no consistent temperature trend was evident since 1600 CE. Our temperature reconstruction showed positive teleconnections with March–May averaged gridded temperature data for far west Nepal and adjacent areas in Northwest India and on the Southwest Tibetan plateau. We found spectral periodicities of 2.75–4 and 40–65 years frequencies in our temperature reconstruction, indicating that past climate variability in central Nepal might have been influenced by large-scale climate modes, like the Atlantic Multi-decadal Oscillation, the North Atlantic Oscillation, and the El Niño-Southern Oscillation. [ABSTRACT FROM AUTHOR]

The potential of shrub-ring oxygen isotopes (SRO) as a paleoclimatic proxy is not well demonstrated. In this study we explored the climate signals embedded in an SRO chronology from Saga, on the northern slope of the central Himalayas by correlation analysis with climate variables and comparison with tree-ring and/or ice-core δ18O records. The Saga SRO had significant and positive correlations with May–July temperatures in both local (r = 0.43) and moisture source areas (r = 0.49) during the period 1955–2015 (CE), while no significant correlations were found with hydroclimatic variables. It is also in good agreement with two tree-ring δ18O series from the southern slope of the central Himalayas, the source of moisture to the site. The temperature signals are further verified by an ice core δ18O record from the Tanggula Mountains on the central Tibetan Plateau. However, it shows little similarity with the nearest Himalayan ice core δ18O record from Dasuopu, demonstrating temperature signals of different seasons. This study suggests that SRO could be used as an acceptable climate proxy, like tree-ring and ice-core δ18O, to broaden the spatial extent of the paleoclimatic records network. However, we should be cautious when combining different proxies with climate signals of different seasons in paleoclimate studies. • A high-elevation shrub-ring δ18O (SRO) chronology was developed. • The SRO captures summer temperature of both local and moisture source areas. • The SRO is comparable with δ18O of tree rings and ice cores. • SRO is a promising high-resolution proxy for paleoclimatology. [ABSTRACT FROM AUTHOR]