Forest ecosystems are increasingly vulnerable to climate change, particularly through rising temperatures and more frequent extreme droughts. Understanding how environmental heterogeneity shapes tree growth and drought responses is essential for predicting forest dynamics under these changing conditions.We investigated how fine-scale environmental heterogeneity, defined by micro-environmental (topo-edaphic) differences, modulates radial growth, climate sensitivity and drought resilience in Araucaria araucana, a keystone and endangered conifer native to Patagonian forests. We analyzed tree-ring series from 156 individuals across four forest stands in Argentina, spanning a broad regional mesic–xeric gradient and contrasting within-site environmental conditions. Growth sensitivity to drought was assessed using dendrochronological techniques, correlation analyses with atmospheric and soil moisture drought indices, and resistance and resilience metrics, the latter calculated using flexible, tree-specific recovery windows.Micro-environmental variability exerted a strong influence on growth patterns: within sites, trees in mesic units exhibited higher growth rates, while those in xeric units showed reduced radial growth. Growth–environment (climate and soil moisture) relationships varied across the regional gradient: in the wetter western range, growth was influenced by both atmospheric and edaphic conditions, while towards the drier eastern limit, atmospheric drivers predominated. Regardless of large-scale geographical distribution, trees in xeric micro-environments consistently showed greater sensitivity to climatic and soil moisture variability than their mesic counterparts.Drought responses reflected interacting effects operating across spatial scales. Micro‑environment determined baseline resistance and resilience, whereas the influence of climatic conditions before, during, and after drought events was contingent upon the macro‑regional context, as evidenced by the distinct response patterns of micro-environmental units located in the western (mesic) versus the eastern (xeric) regions. The flexible resilience index developed in this research proved more sensitive to inter-individual variation in post-drought recovery than traditional fixed-window metrics, suggesting its potential as a complementary metric in resilience studies.

Climate change threatens forest ecosystems by increasing frequency and intensity of extreme climatic events. In southern South America, extreme late-spring frost (LSF) episodes can cause severe leaf damage, leading to reduced tree growth and productivity and shortening the effective growing season. Nothofagus pumilio, a hardwood species Tierra del Fuego forests, is an ecologically important resource providing several ecosystemic services. We evaluated the growth resilience of 50 trees across three sites near treeline in Tierra del Fuego to examine LSF impact by quantifying individual resistance (immediate impact) and resilience (recovery capacity) in response to two distinct extreme frost episodes: a single-year (1979) and consecutive three-year event (2007-2009).The three-year LSF caused significantly greater reductions both in resistance and resilience compared to the single-year event. Statistical modelling revealed that tree resistance was negatively affected by higher frost-day frequency during each event relative to the preceding LSF period, while resilience was reduced by unfavorable (lower temperatures) post-event climatic conditions. Notably, fast pre-event growth rates increased tree vulnerability to the single-year frost event, while they had a weaker effect during the prolonged three-year episode, suggesting a stress threshold beyond which intrinsic growth strategy becomes less relevant. Our findings showed that N. pumilio has a limited capacity to tolerate and recover from multi-year frost stress, highlighting its vulnerability to consecutive extreme climate events. We conclude that conservation strategies for high altitude N. pumilio forests must account for the species’ differential sensitivity to frost event frequency under future climate scenarios.

The xylem of conifers can exhibit a certain degree of anatomical flexibility in response to drought, an adaptation that has contributed to their persistence in environments characterized by high climatic variability. In this context, the present study evaluates xylem anatomical variation in Austrocedrus chilensis in relation to water availability and climate variability in northwestern Argentine Patagonia. Specifically, we assessed how intertracheary pit traits-including pit density, pit membrane diameter, pit aperture diameter, and the hydraulic vulnerability index-differ between sites with contrasting environmental conditions (mesic and xeric) and how they respond to drought events over the period 1969-2019. Increment cores were extracted from mature trees at two sites, from which dendrochronological chronologies were developed and a detailed dendroanatomical analysis was performed. Using histological techniques and image analysis, >120,000 pits were quantified. Anatomical variables were compared between sites and among contrasting climatic periods, including years of moderate and severe drought defined using the Palmer Drought Severity Index (PDSI). Temporal trends and relationships with climatic variables, including temperature, precipitation, and the 3-month Standardized Precipitation Evapotranspiration Index (SPEI-3), were also evaluated. Trees growing at the xeric site exhibited higher pit density and smaller pit membrane diameter, whereas trees from the mesic site were characterized by larger and less dense pits. These anatomical configurations were associated with contrasting hydraulic strategies, with mesic populations showing traits consistent with higher hydraulic efficiency but also greater vulnerability to water stress, as reflected by higher values of the hydraulic vulnerability index. During drought events, these differences were generally maintained; however, trees from the mesic site showed greater anatomical sensitivity, particularly a reduction in pit aperture diameter under drought conditions. Overall, the results demonstrate that A. chilensis exhibits marked xylem anatomical differentiation in response to contrasting hydroclimatic conditions, reflecting coordinated structural adjustments of pit traits linked to the hydraulic safety-efficiency trade-off. These findings highlight the value of pit anatomical traits as functional indicators of forest responses to increasing drought stress under ongoing climate change.

The East Asian Monsoon Transition Zone is highly sensitive to hydroclimatic variability, making it essential to systematically investigate its hydrological dynamics from both historical and future perspectives. However, the scarcity of long-term hydrological observations hampers robust assessments of whether recent extreme events exceed the bounds of natural variability. Here, we reconstructed a 260-year streamflow record for a representative watershed in this transition zone using tree-ring chronologies. The reconstruction reveals that, relative to the East Asian Summer Monsoon, the regulatory influence of the upper-jet stream on regional streamflow variability has become increasingly prominent. To investigate the recent rise in extreme hydrological events, we integrate machine learning models with Shapley additive planation (SHAP)-based interpretability analysis. Results indicate that precipitation is the dominant control on runoff variability, while leaf area index and potential evapotranspiration emerge as particularly sensitive indicators of hydrological change. Furthermore, a comprehensive assessment combining the Budyko framework with CMIP6 multi-model ensemble projections suggests that future increases in runoff will be primarily governed by land surface processes, which account for approximately 59.5% of the total projected change. Overall, this study provides a long-term perspective and forward-looking assessment of hydrological evolution in the East Asian monsoon transition zone, offering critical insights into the mechanisms regulating regional water resources under ongoing climate change.

Although it is generally accepted today that climate and other environmental factors affected past human societies at different spatiotemporal scales, direct linkages are difficult to determine, and correlation should not be confused with causation. Here, we use a tree-ring width network of multimillennial chronologies from inner Eurasia to reconstruct annual changes in Net Primary Productivity (NPP) back to 200 BCE. Our findings reveal that episodes of reduced NPP around the 70s-100s, 360s-380s, and 470s-560s CE likely contributed to the westward and southward migration of nomadic people from their homelands in northwestern China and Mongolia. Although prolonged multidecadal periods of climate-induced low NPP served as tipping points for agricultural and pastoral subsistence systems, the inherent mobility of nomadic communities not only enabled them to adapt to adverse environmental conditions but also facilitated a widespread dispersal of ethnic groups.

Large-scale vegetation restoration on the Loess Plateau (LP) has significantly increased regional evapotranspiration (ET), raising concerns about water security. However, the net impact on meteorological drought, which balances moisture supply (ET) and atmospheric demand (PET), has remained poorly quantified. To address this, we employed a counterfactual modelling framework for 2001-2022, using the Standardized Evapotranspiration Deficit Index (SEDI) to compare a "Baseline" (actual greening) scenario against a "Fixed Vegetation" (no greening) scenario. A two-step attribution analysis was then used to quantify the contributions from vegetation structure, CO2 physiology, vegetation physiology, and climate drivers. Results show that vegetation restoration was the primary driver of the 23.2 mm decade-1 ET increase. Despite this, meteorological drought was substantially mitigated: the Baseline SEDI showed a wetting trend of 0.21 decade-1, nearly double the 0.11 decade-1 trend in the Fixed Vegetation scenario. This phenomenon can be explained by two mechanisms: (1) at the component level, vegetation's contribution to ET (17.83 mm decade-1) was almost twice its opposing contribution to PET (9.02 mm decade-1), leading to a net reduction in the atmospheric water deficit; and (2) at the driver level, the wetting trend in SEDI (0.21 decade-1) was mainly driven by favourable climate shifts (0.170 decade-1, 81.4% of the net trend) and reinforced by vegetation structural changes (0.104 decade-1, 49.5%), which together outweighed drying pressures from CO2 physiological (-26.3%) and vegetation physiological (-4.7%) effects. These findings demonstrate that human-led ecological restoration, while increasing total water consumption, has successfully alleviated atmospheric drought. This provides critical scientific evidence for the climate-resilience benefits of the 'Grain for Green' program and offers insights for sustainable water management in other water-limited regions.

Anthropogenic climate change affects regional hydrological cycles and poses significant challenges to the sustainable supply of freshwater. The Central China water tower (CCWT) is the key source region feeding the Yangtze and Yellow Rivers, and its runoff is indispensable for the surrounding mega-city clusters. Here we present a reconstruction of CCWT runoff depth (RD) back to 1595 CE, based on a new dendrochronological network including 100 tree-ring sampling sites and an ensemble averaging approach that combines multiple regression models. Comparison of this reconstruction with similar records from six water tower regions along the Pacific Rim (Mongolian Plateau, Tibetan Plateau TP, Great Dividing Range, Southern and Northern Rocky Mountains, Andes Mountains) revealed that the CCWT provide the most stable water supply, while the TP to be most susceptible to extreme runoff events. Twenty-first century projections indicate generally increasing runoff across most Pacific Rim water towers, whereas the Northern Rocky Mountains are projected to decline substantially. We attribute the differences in runoff variability and projected trends across Pacific Rim water towers to their distinct geographies and synoptic climatic conditions. The long-term runoff reconstructions and projected changes highlighted in this study provide insights for adaptive management strategies in China and all other regions relying on supply from mountain water towers.

Understanding the long-term variability of forest productivity is crucial in the context of climate change. While remote sensing data provide valuable information on vegetation dynamics, their temporal coverage is often limited. Tree-ring width, however, serves as a reliable proxy for reconstructing past forest productivity and extending NDVI records. In this study, we reconstructed the Normalized Difference Vegetation Index (NDVI) for Austrocedrus chilensis forests in northwestern Argentine Patagonia using multi-centennial tree-ring chronologies. A total of 162 wood samples from living trees and 65 from dead trees were used to develop the regional chronology, which exhibited a significant and positive correlation with NDVI from January to March over the period 1981-2019. Based on this relationship, a linear regression model was applied to reconstruct NDVI for these months extending back to 1405. The reconstruction explained 44% of the total NDVI variance and showed significant positive associations with the Standardized Precipitation Evaporation Index (SPEI), the Palmer Drought Severity Index (PDSI), and the Southern Annular Mode (SAM). Long-term cycles in vegetation productivity were detected, potentially linked to solar activity and other low-frequency climate forcings. The results indicate secular changes in forest productivity dynamics, reflecting the influence of ongoing climate change. By providing a multi-century perspective on NDVI variability, this reconstruction offers critical insights into past forest dynamics and establishes a robust baseline for understanding contemporary ecosystem functioning. Moreover, these findings provide a valuable framework for predictive modeling of future productivity responses under changing climatic conditions.

Extreme climatic events in the Amazon region open questions about how the interactions between exogenous and endogenous variables occur in the wood formation of widely distributed tree species such as Cedrela fissilis Vell. In this study, eleven mature-phase trees from a C. fissilis population growing on a non-flooded forest in the southern Amazon basin were selected to determine the interaction between climatic (precipitation, temperature, and moisture indicators: precipitation minus potential evapotranspiration - P-PET and standardized precipitation evapotranspiration index - SPEI), chemical (xylem concentrations of Al, P, S, Ca, K, Mn, Fe, Sr and their meaningful molar ratios) and anatomical (proportion of vessels - PV, fibres - PF, and parenchyma - PP) predictors to explain the variability of ring width (RW) and wood densities (average - RD, minimum - MND, and maximum - MXD). Decision tree regression was applied for understand this interaction in three datasets, values of narrow or less dense, complacent, and wide or dense rings. Narrow or wider rings vary manly associated to hydraulic tissues (PV) and SPEI. Less dense and complacent (in density values) rings vary manly associated to structural tissues (PF) and elements involved in soil-root interactions (Al) and resistance to water stress (Ca/Mn). Less dense MND vary associated to storage and transportation tissues (PP) and elements involved in soil-root interactions (Al and Mn), whereas dense MXD vary associated to structural (PF) and hydraulic (PV) tissues, precipitation and elements related to cambial activity (Ca and K/Ca). In the context of an increase in the frequency and intensity of droughts in the region, the formation of narrower and less dense rings in C. fissilis is expected. In this sense, our results suggest that higher values, which ensure the functionality of these variables under these extreme conditions, are associated with a higher proportion of structural tissues to the detriment of hydraulic ones, in addition to higher K, Mn, and Al storage in the xylem, which mediate cambial activity based on cell expansion, reduced vulnerability to water stress, and healthier root system conditions, respectively. Altogether, this study offers clues to understand variables combination associated with wood formation in the face of extreme water-availability stress that can lead hydraulic failure, carbon starvation, increasing vulnerability, and even specie's dieback.

Understanding height growth dynamics of mature forests under changing climatic conditions is crucial for sustainable management and predicting future productivity. This study aimed to analyse the apical growth dynamics of dominant, mature Nothofagus pumilio trees in Tierra del Fuego, Argentina, over the 1970-2020 period, and to determine the effects of climate variability, including resilience thresholds. Apical growth was reconstructed from 48 felled trees across three different stands (S1, S2, S3), by performing stem analysis. Net Current Annual Increment (NCAI), inter-annual Site Index variation (Delta SI60), and 5-year Periodic Annual Increment (PAI(5)) were derived. These were then related to temperature and precipitation records using Pettitt's test for change-point detection, correlation, and linear regression models. Results revealed significant initial differences in site quality (S1>S2>S3). A consistent regional warming trend was observed, with a significant shift towards warmer conditions, while annual precipitation lacked a significant long-term trend. The NCAI in the two higher-quality stands showed significant declines (S1 K = 566, p < 0.001; S2 = 549, p < 0.001) after identified change points: a 43.6 % reduction in S1 after 1994 and a 55.8 % reduction in S2 after 2005. Delta SI60 showed a significant negative relationship with temperature in S1 and S2 suggesting that warming conditions tend to reduce inferred site quality. Critical temperature thresholds for N. pumilio height growth were identified within a range of approximately 5.73-5.93 degrees C. Beyond this range, warmer temperatures were associated with significant declines in PAI(5) (R-2 up to 69 % in S1), indicating a physiological optimum has been surpassed. We conclude that rising temperatures since the early 1990s have negatively impacted height growth dynamics in the most productive mature N. pumilio stands once critical thermal thresholds were exceeded. This growth reduction highlights a vulnerability to continued warming, potentially compromising long-term sustainability and productivity.

Argentine Patagonia, recognised as the southernmost wine-producing region in the world, frequently experiences moderate to strong winds. Wind is a key environmental factor that affects plant growth, development, and fruit yield. This study investigates how two contrasting wind conditions (exposed and sheltered) influence the xylem structure of Vitis vinifera L. cultivars Malbec (Mb) and Cabernet-Sauvignon (CS) throughout the lifespan of the vines (2011–2021). We hypothesised that wind exposure modulates xylem structure and hydraulic performance differently depending on the cultivar, based on differences in phenotypic plasticity. During the 2021 dormant season, wood cores were extracted from the main trunk of vines growing under wind exposure and sheltered sectors of the vineyard plot. The differential wind conditions were given by a poplar windbreak. The analysis focused on the response to wind intensity through different anatomical variables, including basal area increment (BAI), cumulative BAI, vessel lumen fraction (F), and vessel area relative to ring area. Climatic data were integrated to explore correlations with xylem modifications. Results showed that CS vines under wind sheltered conditions had significantly greater mean vessel area, indicating enhanced growth and potential hydraulic efficiency, whereas CS vines under wind exposure exhibited vessels with smaller diameter and higher vessel density, maintaining F values while reducing wood productivity. This pattern suggests a structural trade-off between anatomical traits such as vessel size and vessel density, which are typically associated with hydraulic efficiency and resistance to cavitation, rather than a direct assessment of hydraulic safety margin. Results also showed that Mb vines had no significant differences in radial growth but increased vessel size and F under wind conditions, reflecting a more stable and plastic hydraulic strategy. The correlations with seasonal climatic variables revealed a spatial dichotomy: while wind exposure directly shaped anatomy in wind-exposed vines (reducing vessel size, increasing density), temperature was the dominant driver influencing xylem traits in sheltered conditions. These findings provide new evidence of cultivar-specific xylem responses to wind and highlight the importance of considering the phenotypic plasticity in vineyard management. Tailored strategies may enhance vine performance and resilience in windy environments.

Increasing climatic pressures on global forest ecosystems highlight the urgent need to quantify their responses to climate change. This study integrates tree-ring chronologies, Normalized Difference Vegetation Index (NDVI), and climate reanalysis data to investigate vegetation-climate interactions and the role of ocean-atmosphere circulation in mid-latitude Pacific regions. We developed new chronologies for Pinus tabuliformis in northern China and Araucaria araucana in northern Patagonia Argentina, revealing distinct response mechanisms under global warming. Recently, both regions have exhibited rapid tree radial growth, although the growth of A. araucana in northern Patagonia Argentina remains comparatively weaker. P. tabuliformis growth is closely aligned with monsoon precipitation and maintains significant correlations with local NDVI; likewise, A. araucana growth also responds high sensitively to local moisture variability and exhibits stronger coupling with NDVI over the northern Patagonian Plateau during the summer months. Favorable thermal conditions combined with adequate precipitation or snowmelt during spring and summer driver tree growth in both regions. Over the past century, evolving teleconnection patterns suggest that the El Nino-Southern Oscillation (ENSO) has had a diminishing negative impact on P. tabuliformis growth while exerting an increasingly persistent and intensifying positive influence on A. araucana. The Arctic Oscillation (AO) and Southern Annular Mode (SAM) also exhibit significant temporal variations in their impacts across both regions. The findings suggest that the observed forest resilience in northern China and Patagonia represents a crucial ecological positive feedback mechanism, particularly for developing climate adaptation strategies against intensifying heatwaves and drought events.

Large tropical tree samples are driving new research in dendrochronology. The development of imaging tools for these substantial samples represents a significant challenge. Specifically, tree-ring measurements are strongly associated with images acquired through scanning, with an A3 large-format scanner being the preferred choice for these sizable samples. However, the literature lacks information about image distortions resulting from this approach. To address this gap, we developed a system comprising a table, a mobile scanner lift, and a fixed sample-support unit. This system ensures the production of aligned composite images of wooden disc samples and safeguards the scanning equipment from damage. To test its efficiency, we evaluated distortions in the measurements of treering widths across various digitized images at nine different heights, ranging from 2 to 10 mm. Remarkably, we observed no distortions in the growth ring measurements at any assessed height. Furthermore, the images of samples positioned 2 mm and 3 mm away from the scanner glass were clear, allowing precise measurements of small growth rings between 0.1 and 0.5 mm in size. Our equipment offers flexibility of use with other models and sizes, including A4 scanners. It can digitize wooden discs with diameters ranging from 60 to 200 cm.

Woody biomass in tropical trees contributes significantly to global carbon stocks; however, these stocks are increasingly affected by climate and land-use changes. Understanding the growth mechanisms driving woody biomass production is essential for assessing the short- and long-term contributions to carbon stocks and dynamics in tropical forests. Trees accumulate biomass by increasing their size (wood volume) and/or tissue density (wood density). However, estimates of tree biomass production are often based solely on size increment through measurements of stem diameter growth, overlooking the potential spatial and temporal variation in wood density within trees. Tree-ring analysis can be applied to reconstruct past tree volume-growth and wood-density variations, allowing the quantification of their relative contributions when reconstructing past woody biomass production. Here, we studied trees of the widespread Neotropical genus Cedrela along an environmental (climate and soil) gradient to address two key questions: (1) How does temporal variation in tree diameter growth and wood density affect biomass production? (2) To what extent do these relationships vary along the environmental gradient? We examined both long-term (ontogenetic) and short-term (annual) variations in diameter growth and wood density, covering eighteen sites in the Amazon rainforest, Atlantic Forest, Cerrado savanna and Caatinga dry forest. We found that diameter growth and wood density drive short- and long-term biomass production dynamics. Interestingly, diameter growth patterns predominantly explained short-term variability in biomass production at all sites, whereas wood density explained ontogenetic biomass patterns mainly at humid sites. These results highlight the importance of accounting for both short- and long-term variation, including climatic and ontogenetic drivers, to increase the accuracy of biomass estimations in tropical trees, particularly in humid forest ecosystems such as the Amazon. Synthesis. Diameter growth is an important and good indicator of forest carbon production. However, size-related changes in wood density, which are usually neglected, are critical for accurate short- and long-term carbon assessments, especially in tropical humid sites. A biomassa lenhosa das & aacute;rvores tropicais contribui de forma significativa para os estoques globais de carbono. No entanto, esses estoques est & atilde;o cada vez mais amea & ccedil;ados por mudan & ccedil;as clim & aacute;ticas e de uso do solo. Compreender os mecanismos de crescimento que regulam a produ & ccedil;& atilde;o de biomassa & eacute; essencial para avaliar as contribui & ccedil;& otilde;es de curto e longo prazo para os estoques e a din & acirc;mica do carbono em florestas tropicais. & Aacute;rvores acumulam biomassa, aumentando seu tamanho (volume de madeira) e/ou a densidade dos tecidos (densidade da madeira). Contudo, as estimativas de produ & ccedil;& atilde;o de biomassa costumam basear-se apenas no incremento em di & acirc;metro, desconsiderando varia & ccedil;& otilde;es espaciais e temporais da densidade da madeira. A an & aacute;lise de an & eacute;is de crescimento permite reconstruir o crescimento em volume e as varia & ccedil;& otilde;es de densidade da madeira, quantificando sua contribui & ccedil;& atilde;o relativa & agrave; produ & ccedil;& atilde;o hist & oacute;rica de biomassa lenhosa. Neste estudo, analisamos & aacute;rvores do g & ecirc;nero Cedrela ao longo de um gradiente ambiental (clima e solo) para responder a duas perguntas: (1) Como a varia & ccedil;& atilde;o temporal no crescimento em di & acirc;metro e na densidade da madeira afeta a produ & ccedil;& atilde;o de biomassa? (2) At & eacute; que ponto essas rela & ccedil;& otilde;es variam ao longo do gradiente ambiental? Avaliamos tanto varia & ccedil;& otilde;es ontogen & eacute;ticas (de longo prazo) quanto anuais (de curto prazo) em 18 popula & ccedil;& otilde;es distribu & iacute;das ao longo da Amaz & ocirc;nia, Mata Atl & acirc;ntica, Cerrado e Caatinga. Observamos que o crescimento em di & acirc;metro e a densidade da madeira impulsionam a din & acirc;mica da produ & ccedil;& atilde;o de biomassa em diferentes escalas temporais. Curiosamente, os padr & otilde;es de crescimento em di & acirc;metro explicaram predominantemente a variabilidade de curto prazo da produ & ccedil;& atilde;o de biomassa em todos os s & iacute;tios, enquanto a densidade da madeira explicou os padr & otilde;es ontogen & eacute;ticos de biomassa principalmente em & aacute;reas & uacute;midas. Esses resultados destacam a import & acirc;ncia de considerar varia & ccedil;& otilde;es de curto e longo prazo, incluindo fatores clim & aacute;ticos e ontogen & eacute;ticos, a fim de aumentar a precis & atilde;o das estimativas de biomassa em & aacute;rvores tropicais, especialmente em ecossistemas & uacute;midos como a Amaz & ocirc;nia. S & iacute;ntese: O crescimento em di & acirc;metro & eacute; um indicador importante da produ & ccedil;& atilde;o de carbono florestal. No entanto, altera & ccedil;& otilde;es ontogen & eacute;ticas na densidade da madeira, frequentemente negligenciadas, s & atilde;o cruciais para avalia & ccedil;& otilde;es precisas de estoques de carbono em diferentes escalas temporais, sobretudo em florestas tropicais & uacute;midas.

The Asian Summer Monsoon (ASM) is a crucial driver of precipitation, sustaining ecological balance and socioeconomic development in North China. However, the extent to which climate change has influenced this monsoonal system, leading to detectable and attributable modifications in precipitation regimes, remains unclear. Here, we present a robust annual precipitation reconstruction spanning 1770-2020, using delta 18O from tree ring cellulose and a simple linear regression model in the North China Monsoon Marginal Region (NCMMR). Reconstructed precipitation and independent hydroclimatic records reveal a pronounced drying trend across the NCMMR since the 1950s. Multiple linear regression modelling, water vapor transport analyses using ensemble means from the Community Earth System Model-Last Millennium Ensemble, and correlation analysis indicate that precipitation variability in the NCMMR is modulated by the Indian Ocean Dipole, El Nino-Southern Oscillation, Atlantic Multidecadal Oscillation, and Interdecadal Pacific Oscillation. Nevertheless, fingerprint analysis suggests that the observed precipitation decline since the 1950s is strongly associated with greenhouse gas concentrations, albeit partially offset by the effects of anthropogenic aerosol emissions and internal variability. The impact of greenhouse gas forcing on precipitation variability is expected to intensify in the coming decades.

The Brujas cave is located in the eastern flank of the subtropical Andes, in the boundary between two major components of the climate system that drives precipitation variability over the South America: The South American monsoon system (SAMS) domain and the Southern hemisphere westerlies (SHW). As a result, the long-term hydroclimate variability in this region can be complex. Paleorecords from lake sediments and ice cores surrounding the area show meridional fluctuations of either the SAMS or the SHW, yet without long and high-resolution records, this area remains poorly constrained.The deglacial and Holocene are interesting periods in this regard, providing valuable information about the atmospheric circulation in the western sector of SAMS in response to millennial-scale events of the last glacial. Moreover, changing climate forcings associated with ice volume and greenhouse gases can impact hydroclimate at these latitudes by reorganizing atmospheric circulation during the onset of the interglacial boundary conditions. For instance, the expansion of the Hadley cell under current global warming severely affects the regional hydroclimate of the mid-latitudes. Yet, our knowledge of this region is limited compared to what we know about the core SAMS region or the SHW in southernmost South America. New records from this transitional zone can provide clarity on the extent of variability in space and intensity of the SAMS and the SHW, serving as useful benchmarks to assess the performance of climate models in such a sensitive zone, right in interphase between two systems.Here we present preliminary results from a stalagmite record (15,000 to 3,000 years) from Las Brujas cave, on the northern edge of the SHW domain. The westerlies transport moisture from the Pacific Ocean to the continent, where the Andes barrier induces orographic convection so that intense precipitation falls on the uphill side of the cordillera, over the Chilean Andes. The limited moisture that crosses the Andes and reaches the downslope area, produces precipitation over Las Brujas cave site during the cold months (April-September). Immediately north of Las Brujas cave, precipitation is concentrated in the warm season, produced by the South American low-level jet (SALLJ), a main component of the SAMS that transports moisture from the Amazon to northwestern Argentina. Given the proximity of both systems to our cave, precipitation contribution of either source is likely to have occurred in the past. Our multiproxy record can potentially show periods of rainfall dominated by the SAMS or the westerlies and the relationship unveil local temperature variations. We find evidence of a slight trend from dryer to wetter conditions from the mid-Holocene onwards and a large shift from dry to wet from the deglacial to the early Holocene.

Rivers originating from the Andes Mountains are vital water sources for agricultural and societal needs in South America, yet are increasingly threatened by climate change. Here we reconstruct streamflow of the Negro River (Rió Negro) in northern Patagonia over the past 827 years using tree-ring records from the south-central Andes foothills. This reconstruction reveals an unprecedented decline in river flow in recent decades. Moisture from the El Niño–Southern Oscillation and the Southern Annular Mode provides a key water source, but temperature rise has increased atmospheric moisture demand and reduced availability. Antarctic amplification has further disrupted circulation patterns and accelerated warming, intensifying regional aridity. Since the 20th century, the Negro River has experienced a sustained flow reduction of approximately 10

Background: Annual seed production is key to understand natural forest dynamics and to apply sustainable forest management. This process is subjected to variations according to annual and seasonal climatic conditions, locally affected by El Niño-Southern Oscillation (ENSO) and the Southern Annular Mode (SAM) seasonality. Recognising how these variables affect the dynamics of harvested forests is useful for developing forest management strategies. Therefore, the objective of this study was to analyse annual seed production (SP) in Nothofagus pumilio (Poepp. & Endl.) Krasser stands harvested under variable retention and unmanaged primary forests in Tierra del Fuego, Argentina, related to the occurrence of climatic events over a 17-year period (2006-2022). Methods: Seed production (million ha-1 year-1) was annually measured in three managed stands with different retention levels (AR: aggregates; DRI: dispersed with aggregate protection; DR: dispersed without aggregate protection) and three primary forests (PF) stands as control sites (4 treatments x 3 areas x 6 replicates x 17 years). Values of occurrences of climatic events (positive or negative values of ENSO and SAM) were related to monthly temperature and rainfall. ANOVAs, correlation analyses and statistical modelling were performed to predict SP based on climatic variables and forest treatments. Results: Seed production varied over years and among forest treatments depending on annual climate variations, with annual averages for the studied period of: 9.35 million ha-1 year-1 for PF, 7.16 million ha-1 year-1 for AR, 2.25 million ha-1 year-1 for DRI and 1.08 million ha-1 year-1 for DR. ENSO+ and SAM+ acted as a trigger of high SP, associated to higher temperatures and dry conditions, mainly during spring and summer. The models predicted SP explaining 73-85% of its variability, considering minimum and maximum temperatures and ENSO mean values as better predictors. Conclusions: Findings presented in this study have important implications for forest management as a tool for understanding forest dynamics related to seeding, a key factor for forest regeneration in a context of high climate variability. However, within a context of climate change with extreme events, there is a need for long-term monitoring of seeding processes in Nothofagus forests.

The reproduction of many long-lived plants is highly variable and synchronized, known as masting. Masting is a key driver of plant regeneration dynamics and has cascading effects on food webs and carbon and nutrient fluxes through ecosystems. Masting patterns can respond to changes in climate, but natural long-term variability in masting behavior (i.e., baseline variability) is poorly understood. Here we use tree-rings to create a four-century reconstruction of annual cone production to uncover centennial-scale evolution in masting of Araucaria araucana, a dioecious masting species in South America. Over the last four decades, direct observations of annual cone production in this species revealed remarkable range-wide synchrony of masting. Our tree-ring-based reconstruction places this in a long-term context, revealing that intense regional masting is not a consistent feature of A. araucana reproduction. For extensive periods over the last four centuries, masting has been a site-specific phenomenon, with variability in cone production that was not regionally synchronized. Comparison with regional climate reconstructions indicates that regional synchrony of masting varies with regional temperature trends, including during recent decades. During warmer periods, synchrony is enhanced, and during cooler periods, regional synchrony breaks down. These dynamics have implications for understanding the reproduction of this iconic and endangered tree species and provide evidence of long-term linkages between climate change and masting behavior. Our study demonstrates the potential for novel tree-ring-based reconstructions of masting to reveal crucial insights into baseline variability and the response of masting to climate change.