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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).)

A profound consideration of stable oxygen isotope source water origins is a precondition for an unambiguous palaeoenvironmental interpretation of terrestrial δ 18 O archives. To stress the influence of air mass origins on widely used δ 18 O tree-ring chronologies, we conducted correlation analyses between six annually resolved δ 18 O tree-ring cellulose ([Formula: see text]) chronologies and mean annual air package origins obtained from backward trajectory modeling. This novel approach has been tested for a transect at the southeastern Tibetan plateau (TP), where air masses with different isotopic composition overlap. Detailed examinations of daily precipitation amounts and monthly precipitation δ 18 O values ([Formula: see text]) were conducted with the ERA Interim and Laboratoire de Météorologie Dynamique General Circulation Model (LMDZiso) data, respectively. Particularly the southernmost study sites are influenced by a distinct amount effect. Here, air package origin [Formula: see text] relations are generally weaker in contrast to our northern located study sites. We found that tree-ring isotope signatures at dry sites with less rain days per year tend to be influenced stronger by air mass origin than tree-ring isotope values at semi-humid sites. That implies that the local hydroclimate history inferred from [Formula: see text] archives is better recorded at semi-humid sites.

We present a new teak (Tectona grandis L.f.) tree-ring stable oxygen isotope (δ18OTR) chronology from Mae Tuen (MT) site, Tak province, northwestern Thailand at inter-annual (167-year, A.D.1850–2016) and intra-annual (A.D.2006–2016) timescales. The inter-annual δ18OTR chronology showed a significant negative correlation (r = −0.678, p < 0.01) with the May–October amount of regional rainfall obtained from CRU TS4.03. We established a linear regression model that explained 46.0% of the actual rainfall variance and reconstructed monsoon season rainfall back to A.D.1850. The seasonal variations in moisture conditions were reflected in inter-annual δ18OTR variability. The rainfall amount and δ18O in precipitation (δ18Op) mainly controlled intra-annual variations in teak δ18OTR. These results show that the variation in Thai teak δ18OTR is dominated by rainfall, highlighting the strength of δ18OTR as a monsoon rainfall proxy. [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]

A 338-year oxygen isotope record from teak tree-ring cellulose collected from Mae Hong Son province in northwestern Thailand was presented. The tree-ring series preserves the isotopic signal of the regional wet season rainfall and relative humidity. Tree-ring δ18O correlates strongly with regional rainfall from May to October, showing coherent variations over large areas in Southeast Asia. We reconstructed the summer monsoon season (May to October) rainfall based on a linear regression model that explained 35.2% of the actual rainfall variance. Additionally, we found that in the 19th century, there was a remarkable drought during many years that corresponded to regional historic drought events. The signals of the June to September Indian summer monsoon (ISM) for the period between 1948 and 2009 were clearly found. Spatial correlations and spectral analyses revealed a strong impact of the El Niño-Southern Oscillation (ENSO) on tree-ring δ18O. However, ENSO influenced the tree-ring δ18O more strongly in the 1870–1906, 1907–1943, and 1944–1980 periods than in the 1981–2015 period, which corresponded to periods of weaker and stronger ISM intensity. [ABSTRACT FROM AUTHOR]

Background and Aims Annually resolved biological climate proxies beyond the altitudinal and latitudinal distribution limit of trees are rare. In such regions, several studies have demonstrated that annual growth rings of dwarf shrubs are suitable proxies for palaeoclimatic investigations. In High Asia, the pioneer work of Liang et al. (Liang E, Lu X, Ren P, Li X, Zhu L, Eckstein D, 2012. Annual increments of juniper dwarf shrubs above the tree line on the central Tibetan Plateau: a useful climatic proxy. Annals of Botany 109 : 721–728) confirmed the suitability of shrub growth-ring chronologies for palaeoclimatic research. This study presents the first sensitivity study of an annually resolved δ18O time series inferred from Wilson juniper (Juniperus pingii var. wilsonii) from the northern shoreline of lake Nam Co (Tibetan Plateau). Methods Based on five individual dwarf shrub discs, a statistically reliable δ18O chronology covering the period 1957–2009 was achieved (expressed population signal = 0.80). Spearman's correlation analysis between the δ18O chronology and climate variables from different sources was applied. In a first step, the suitability of various climate data was evaluated. Key Results Examinations of climate–proxy relationships revealed significant negative correlations between the δ18O shrub chronology and summer season moisture variability of the previous and current year. In particular, relative humidity of the previous and current vegetation period significantly determined the proxy variability (ρ = −0.48, P < 0.01). Furthermore, the δ18O variability of the developed shrub chronology significantly coincided with a nearby tree-ring δ18O chronology of the same genus (r = 0.62, P < 0.01). Conclusions The δ18O shrub chronology reliably recorded humidity variations in the Nam Co region. The chronology was significantly correlated with a nearby moisture-sensitive tree-ring δ18O chronology, indicating a common climate signal in the two chronologies. This climate signal was likely determined by moisture variations of the Asian summer monsoon. Local climate effects were superimposed on the supra-regional climate signature of the monsoon circulation. Opposing δ18O values between the two chronologies were interpreted as plant-physiological differences during isotopic fractionation processes. [ABSTRACT FROM AUTHOR]

We developed a stable oxygen isotope chronology of tree-ring alpha cellulose (δ18O TR) from archaeological teak (Tectona grandis L.f.) samples from Mae Hong Son (MHS) province, northwestern Thailand. The samples were collected from ancient coffins belonging to the log coffin culture excavated at the Ban Rai rock shelter (BR). The chronology spans a period of 283 years in the late Holocene (AD14–296). The oxygen isotopic composition of BR δ18O TR ranged from 21.15‰ to 26.31‰. Since δ18O TR variations in Thailand teak can be used as indicators for precipitation amount during the rainy summer monsoon season, our chronology can be used as a proxy for regional late Holocene hydroclimate variability. This is confirmed by a significant positive correlation of our BR δ18O TR record with a stalagmite δ18O record from Klang cave, southern Thailand (r = 0.303, p < 0.01). In addition, a REDFIT spectral analysis revealed the existence of multidecadal (26.9-year) and interannual (5.6, 3.4 and 2.8-year) cycles, which may potentially be the fingerprints of climate forcing mechanisms impacting Thailand monsoon precipitation, such as the Pacific Decadal Oscillation (PDO) and the El Niño-Southern Oscillation (ENSO). [ABSTRACT FROM AUTHOR]

Key message: Intra-annual oxygen isotope patterns of tree-ring cellulose fromPinus nigrasubsp.laricioandPinus pinasteralong an elevation gradient can be divided into four distinct patterns ((1) high values in the beginning of the tree ring, declining trend afterwards; (2) low values in the beginning, increasing trend afterwards; (3) high values in the middle of the tree ring; (4) declining trend over the whole tree ring). These patterns reflect the dependency on local site conditions and different water sources. Context: Intra-annual oxygen isotope chronologies from tree-ring cellulose can serve as a proxy for past climate conditions at inter- or even intra-seasonal resolution. Aims: We explore the potential of these chronologies from pine trees (Pinus nigra J.F. Arn subsp. laricio (Poiret) Maire var Corsicana Hyl. and Pinus pinaster Aiton) growing on the Mediterranean island of Corsica, France, along an elevation gradient ranging from sea level to 1600 m asl. Methods: We developed high-resolution intra-annual oxygen isotope chronologies from tree-ring cellulose of eight trees from five sites along the elevation gradient. The analysis period covers the decade 2007–2016 for seven trees and the period 1987–2016 for one tree, respectively. Results: The chronologies show a high variability between trees, sites, and years. We identified four different intra-annual oxygen isotope patterns which reflect the dependency of tree growth on different water sources (precipitation during the growing season vs. deeper soil water reservoirs) and climate conditions during the growth season. Trees at coastal sites have access to groundwater, while trees growing in high elevations mostly depend on precipitation during the growth season as water source. Conclusion: The different patterns can be attributed to the use of different water sources. The intra-annual chronology covering 30 years indicates an increasing frequency of dry-warm summers after 2007. [ABSTRACT FROM AUTHOR]

Considerable progress has been made in dendroclimatological research in China during the period 2000–2017, including a significant increase in the spatial coverage of tree-ring chronologies developed for paleoclimatic research. New tree-ring sampling sites have been established across the Tibetan Plateau, as well as the northeastern and sub-tropical eastern parts of China. Most of the studies use coniferous trees, although different plant functional types (e.g., broadleaf species and shrubs) have also been increasingly investigated. Tree-ring chronologies longer than 600 years, however, are mostly found on the Tibetan Plateau, with the longest one extending back to 2637 BCE (before Common Era). Most tree-ring records in the eastern parts of China are <400 years long. Tree-ring width is the most commonly studied parameter, although stable isotope ratios and wood density data have also been obtained for specific sites. Stable oxygen isotope data frequently shares a common hydroclimate signal, whereas the climate or environmental signals remain inconsistent for the few available stable carbon isotope records. In general, tree-ring width-based temperature reconstructions originate from higher elevation sites (i.e., treeline) compared to hydroclimate reconstructions. Precipitation or drought reconstructions are mainly obtained from regions with an annual precipitation of <800 mm. Most of the tree-ring reconstructions are based on individual site or local-scale chronologies, although a limited number of regional-scale and field reconstructions have been produced. The most prominent identified characteristics of the recent advances in dendroclimatological research for China have manifested in aspects such as an expanded network of sampling sites, improved climate reconstruction methodology, and improved uncertainty estimations in the latter. Furthermore, the traditional statistical-based tree growth–climate relationships have been supplemented by monitoring and modeling approaches. Based on the progress from 2000 to 2017, and on the research potential of the country in this field, we expect additional widening of the dendroclimatological investigations in China during the coming years. [ABSTRACT FROM AUTHOR]

For the mechanistic understanding of hydroclimate variability, stable oxygen isotopic ratios (δ 18 O) of tree-ring α-cellulose can play a key role in paleoclimatic research. On the north-east Tibetan Plateau (TP), a region particularly sensitive to climate change, there exists a distinct lack of δ 18 O research in tree-ring archives. The few currently existing tree-ring δ 18 O chronologies were obtained by pooling the wood material from the same year from different trees prior to preparation and analysis. Although this method is time and cost efficient, it might impede the analysis of changes within the internal variability of oxygen isotope signals and a deeper understanding of the resulting climate reconstruction. We selected five Qilian juniper ( Sabina przewalskii Kom .) trees covering the period 1951–2011 on the north-east TP to investigate the climate signals contained in stable oxygen isotopic composition records obtained using single tree analysis. Although the inter-series correlation between the five individual δ 18 O series indicates a highly significant relationship (mean r = 0.59, n = 59, p = 0.01), the five individual δ 18 O series show significantly differently mean values. We found significant negative correlations between drought/hydroclimatically triggered climate parameters (PDSI, precipitation) and each of the individual δ 18 O series. Spatial correlation maps indicate negative correlation of tree-ring δ 18 O and Indian Ocean sea surface temperatures, and inverse correlation patters of moisture conditions on the northern and southern TP. Our results provide a reference for future research on stable oxygen isotope/climate signals in the species S. przewalskii Kom .. [ABSTRACT FROM AUTHOR]

We present a new multi-parameter dataset from Corsican black pine growing on the island of Corsica in the Western Mediterranean basin covering the period AD 1410–2008. Wood parameters measured include tree-ring width, latewood width, earlywood width, cell lumen area, cell width, cell wall thickness, modelled wood density, as well as stable carbon and oxygen isotopes. We evaluated the relationships between different parameters and determined the value of the dataset for climate reconstructions. Correlation analyses revealed that carbon isotope ratios are influenced by cell parameters determining cell size, whereas oxygen isotope ratios are influenced by cell parameters determining the amount of transportable water in the xylem. A summer (June to August) precipitation reconstruction dating back to AD 1185 was established based on tree-ring width. No long-term trends or pronounced periods with extreme high/low precipitation are recorded in our reconstruction, indicating relatively stable moisture conditions over the entire time period. By comparing the precipitation reconstruction with a summer temperature reconstruction derived from the carbon isotope chronologies, we identified summers with extreme climate conditions, i.e. warm-dry, warm-wet, cold-dry and cold-wet. Extreme climate conditions during summer months were found to influence cell parameter characteristics. Cold-wet summers promote the production of broad latewood composed of wide and thin-walled tracheids, while warm-wet summers promote the production of latewood with small thick-walled cells. The presented dataset emphasizes the potential of multi-parameter wood analysis from one tree species over long time scales. [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]

Abstract Oxygen isotope ratios (δ 18 O) are the most commonly used parameters recorded in paleoclimate archives since they link different natural archives via the water cycle. Tree-ring δ 18 O (δ 18 O TR) has been widely used for hydroclimate reconstructions in the Himalaya. However, few of them record temperature signals, which are dominant in Himalaya ice-core δ 18 O. We hypothesize that the "precipitation amount effect" due to the South Asian Summer Monsoon (SASM) may overprint temperature signals in δ 18 O TR series. The purpose of this study is to investigate whether temperature signals could be found in the δ 18 O TR in locations where the influence of SASM is weak. We developed a 105-yr δ 18 O TR chronology from the northern slope of the western Himalaya which greatly blocks the SASM. Our δ 18 O TR clearly shows stronger correlations with temperature (dominant winter and weak summer) than summer precipitation signals. It also agrees well with summer soil moisture δ 18 O simulated by the global isotope model LMDZ4 (r = 0.72, 1979–2010). In LMDZ4, low winter temperature was found to increase winter snowfall and subsequent snow melt, and thus to increase the contribution of winter snowfall to soil moisture in summer at the expense of summer precipitation. Since winter snowfall is more depleted than summer precipitation, this leads to lower summer soil moisture δ 18 O. The temperature signals found in our δ 18 O TR series are consistent with those found in the Dasuopu ice-core δ 18 O. This implies that δ 18 O TR series from the southwest Tibetan Plateau (TP), with a weak monsoon, hold great potential to capture temperature signals. Climate interpretations of δ 18 O proxies in the Himalaya largely depend on the influence of seasonal water from the dominant atmosphere circulation systems of the westerlies or monsoon. The δ 18 O proxies from the monsoon-affected region have a higher potential for the reconstruction of boreal summer hydroclimate, whereas δ 18 O proxies from westerly-affected sites have a higher potential for temperature reconstructions. Highlights • A tree-ring δ 18 O record was developed from the northern slope of the Himalayas. • The δ 18 O TR recorded dominant winter and weak summer temperature signals. • No summer monsoon precipitation signals were found. • Winter temperature signals were mainly transferred into δ 18 O TR through snowmelt. [ABSTRACT FROM AUTHOR]

• A new method that isolates the RH signal from tree-ring δ18O is proposed. • Reconstructed millennium RH revealed cycles of ∼ 35, ∼85, 130–160 and ∼ 200 years. • Local RH may decrease in the future with continuous global warming. As one of the driest regions in the Asia, the ecological conditions in Northwest China are very fragile. Although relative humidity (RH) plays a vital role in the environment, the lack of long-term RH records hinders the development of reliable scenarios for future extreme environmental conditions in this region. We developed a new method for quantitative regional RH reconstruction; in this method, the signals of precipitation oxygen isotope ratios (δ18O) and temperature in the tree-ring δ18O series are removed to extract the RH signal from the tree-ring δ18O records to the greatest extent. We then combined published millennium tree-ring δ18O, ice core δ18O, and paleo-temperature data to reconstruct a new millennium-long RH record around Delingha, Qinghai, China, on the edge of the northeastern Tibetan Plateau (TP). The reconstructed RH was closely related to both temperature and rainfall, and revealed cycles of approximately 35, 85, 130–160 and 200 years, which are associated with solar insolation variations, Pacific decadal oscillation, and the Atlantic multidecadal variability. With continuous global warming, RH may decrease as the contribution of the temperature increase becomes larger than that of the precipitation over the northeastern TP. This study provides a basis for a new method of RH reconstruction based on different paleoclimate archives. [ABSTRACT FROM AUTHOR]

Summary for correlations of tree-ring cellulose oxygen isotopes from the western Kunlun Mountains with climates for the raw data (left) and 5-year high-frequency data (right). The key finding is that δ18O TRC is indicative of atmospheric aridity (VPD) at high-frequency interannual variations (right, 5-year high-frequency data), while such indicative ability disappears for longer timescales (Left, Raw data). [Display omitted] • A δ18O TRC record from 1951 to 2015 for the western Kunlun Mountains was generated. • δ18O TRC indicate May to August VPD variability at timescales <5 years. • Frequency-dependency can highly influence the climatic interpretation of δ18O TRC. As an important indicator of atmospheric aridity, the vapor pressure deficit (VPD) is being paid increasing attention in global change researches during recent decades. However, available proxy data with the capability to represent VPD is still scarce in the globe. Herein we demonstrated a "hidden" frequency-dependent indication of tree-ring cellulose oxygen isotope (δ18O TRC) to atmospheric aridity in the western Kunlun Mountains, Central Asia. In applying correlation and partial correlation analysis, frequency-dependent climatic drivers triggering the δ18O TRC values were detected. For the raw data with inter-decadal variability, δ18O TRC variations mainly indicated May–August precipitation (Local: r = –0.59, p < 0.001; Moisture source: r = –0.53, p < 0.001), evapotranspiration (ET) (Local: r = –0.57, p < 0.001; Moisture source: r = –0.51, p < 0.001). After a 5-year high-pass filter, the δ18O TRC series revealed highly significant correlation with May–August VPD (Local: r = 0.82, p < 0.001; Moisture source: r = 0.80, p < 0.001). The partial correlation further confirmed the strong linkages with high-frequency VPD when the impact of any additional eco-climatological variable (precipitation, temperature, ET, soil moisture 0–40 cm) was excluded. In contrast, if the effect of May–August VPD was excluded, relationships between δ18O TRC and other variables turned insignificant. Collectively, it was concluded that δ18O TRC from the western Kunlun Mountains may indicate VPD at timescales < 5 years. Our results suggest that frequency-dependent climatic significances should be considered when interpreting multi-process determined δ18O TRC as a climate-proxy. [ABSTRACT FROM AUTHOR]

Schematic diagram for frequency-dependent climatic signals in tree-ring latewood δ18O and its indication to water source of tree growth. [Display omitted] • A tree-ring latewood δ18O series was developed for the Karakoram. • Winter temperature/summer precipitation trigger its different frequency domains. • Usage of winter precipitation by trees lasts until the end of the growing season. Identifying the influence of seasonal source water on tree growth is essential to understand the effect of climate change on forest dynamics. However, due to the lack of available long-term monitoring studies, little is known on how long moisture originating from winter precipitation influences tree growth in the following growing season. Herein, we developed a tree-ring latewood oxygen isotope (δ18O LW) chronology from the Karakoram (1955–2013) in northern Pakistan. We investigated whether winter climate signals are incorporated in the δ18O LW and how long winter precipitation through soil moisture contributed to tree growth during the growing season. Significant correlations were found between δ18O LW with both, winter to spring (January–May) temperature (r = 0.43, p < 0.05) and summer (July–August) precipitation (Local: r = −0.38, p < 0.05; Moisture source region: r = −0.44, p < 0.05). As shown by the cross-spectrum and commonality analysis, the climate signals in the δ18O LW are frequency-dependent. Winter temperature signals stored in the δ18O LW variations dominate at low frequencies more than 7 years (59% variance explained), while the summer precipitation signals dominate variations with higher frequencies shorter than 7 years (47% variance explained). Further analysis using reanalysis data shows that the growing season soil moisture at root depth (10–40 cm) is more strongly related to winter precipitation than to summer rainfall. Winter precipitation formed as ground snow provides root-zone soil moisture and tree growth via snowmelt during the growing season. Our study highlights that winter precipitation is the dominant water source contributing to Karakoram tree growth until the late growing season. Given the possibility of a decrease in winter precipitation under climate change in the Karakoram region, local forest is potentially threatened by the declining water supply during the growing season. [ABSTRACT FROM AUTHOR]

We present the first annually resolved and statistically reliable tree-ring δ18O (δ18O T) chronologies for the three South Asian tropical moist forest tree species (Chukrasia tabularis A. Juss., Toona ciliata M. Roem., and Lagerstroemia speciosa Roxb.) which differ in their shade tolerance and resistance to water stress. We found significantly higher mean δ18O T values in light-demanding T. ciliata than in intermediate shade tolerant C. tabularis and shade tolerant L. speciosa (p < 0.001). δ18O T in C. tabularis was mainly influenced by pre-monsoon vapor pressure deficit (VPD; r = −0.54, p < 0.01) and post monsoon maximum temperature (T max) (r = 0.52, p < 0.01). δ18O T in T. ciliata was strongly negatively correlated with a dry season drought index PDSI (r = −0.65, p < 0.001) and VPD (r = −0.58, p < 0.001). Pre-monsoon T max was strongly positively linked with δ18O T in L. speciosa (r = 0.65, p < 0.001), indicating that climatic influences on δ18O T are species-specific and vary among tree functional types. Although there was a week correlation between local precipitation and δ18O T in our studied species, we found a strong correlation between δ18O T and precipitation at a larger spatial scale. Linear mixed effect models revealed that multiple factors improved model performance only in C. tabularis , yielding the best model, which combined VPD and T max. The top models in T. ciliata and L. speciosa included only the single factors PDSI and T max , highlighting that the way C. tabularis interacts with climate is more complex when compared with other two species. Our analyses suggest that stable oxygen isotope composition in tree rings of South Asian tropical moist forest trees are a suitable proxy of local and regional climate variability and are an important tool for understanding the physiological mechanisms associated with the global hydrological cycle. Unlabelled Image • Tree-ring δ18O chronologies are developed for three species varying among tree functional types. • The main forcing factor driving inter-annual δ18O T variability is related to variations in hydroclimate. • δ18O T captured local and regional climate variability. • The mean δ18O T values may vary among the studied tree species. • δ18O T help understand how different tree functional types respond to changes in the hydrological cycle. [ABSTRACT FROM AUTHOR]

Water availability is the most important factor for the vitality of forest ecosystems, especially in dry environments. The Mediterranean region is one of the hotspots of future climate change; therefore, data on the water cycle are urgently needed. We measured oxygen isotope compositions in creek water, precipitation, stem water, needle water, and tree-ring cellulose over one growing season to establish the relationship between isotope compositions in different compartments along a fractionation pathway. We analyzed plant material from pine trees (Pinus nigra J.F. Arn subsp. laricio (Poiret) Maire var. Corsicana Hyl. and Pinus pinaster Aiton) at five locations along an elevation gradient from sea level to 1600 m asl. We traced back the oxygen isotope composition from source to sink in tree-ring cellulose in order to identify the water sources used by the trees, and to quantify the extent of isotope fractionation processes. Our results showed that the trees used different water sources over the course of the growing season, ranging from winter snow meltwater to summer precipitation at higher sites and deep soil water reservoirs at coastal sites. Needle water enrichment was higher at higher elevation sites than at coastal locations, highlighting the importance of site-specific climate conditions on the isotopic composition values in tree material. Water availability seems to be most restricted at the highest site, making these trees most vulnerable to climate change. • Oxygen isotope compositions are used to identify water sources used by pine trees. • Water availability differs along the elevation gradient on Corsica. • Trees at coastal locations have access to deeper soil water reservoirs. • Trees in mountain areas depend on summer precipitation as water source. [ABSTRACT FROM AUTHOR]