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Poor drought tolerance of European beech trees raised concerns in Europe. We hypothesized that beech could show an opposite physiological response to the same level of climatic drought with change in edaphic drought. We performed a combined analysis of δ13C and δ18O in tree rings to reveal retrospective temporal physiological responses of trees to drought. The edaphic drought was assessed by quantifying the capacity of soil to store water in plots (classified as “dry” and “less-dry”) near the drought limit of the species in three near-natural oak-beech ecotones in Germany and Switzerland. Neighbourhood competition was quantified. A climatic drought index was calculated from meteorological records and related to the δ13C and δ18O values of the trees. Trees from dry plots showed a higher response to drought and climatic dependency than less-dry plots. Neighbourhood competetion increased δ18O values significantly. Dual isotope analysis shows a tendency of greater stomatal resistance in dry plots and higher stomatal conductance in less-dry plots. We conclude that beech trees belonging to the same population under changing soil water availability can show different physiological responses under climatic drought stress. Our finding indicates the high plasticity of the beech trees to survive drought stress with changing site conditions.

Large earthquakes can increase the amount of water feeding stream flows, raise groundwater levels, and thus grant plant roots more access to water in water‐limited environments. We examine growth and photosynthetic responses of Pine plantations to the Maule Mw 8.8 earthquake in headwater catchments of Chile's Coastal Range. We combine high‐resolution wood anatomic (lumen area) and biogeochemical (δ13C of wood cellulose) proxies of daily to weekly tree growth sampled from trees on floodplains and close to ridge lines. We find that, immediately after the earthquake, at least two out of six tree trees on valley floors had increased lumen area and decreased δ13C, while trees on hillslopes had a reverse trend. Our results indicate a control of soil water on this response, largely consistent with models that predict how enhanced postseismic vertical soil permeability causes groundwater levels to rise on valley floors, but fall along the ridges. Statistical analysis with boosted regression trees indicates that streamflow discharge gained predictive importance for photosynthetic activity on the ridges, but lost importance on the valley floor after the earthquake. We infer that earthquakes may stimulate ecohydrological conditions favoring tree growth over days to weeks by triggering stomatal opening. The weak and short‐lived signals that we identified, however, show that such responses are only valid under water‐limited, rather than energy‐limited tree, growth. Hence, dendrochronological studies targeted at annual resolution may overlook some earthquake effects on tree vitality., Plain Language Summary: Earthquakes deform and shake Earth's surface and the ground below. These changes may affect groundwater flow. Groundwater level may rise in the valley bottom and drop along higher elevated ridges. Trees depend on such groundwater resources, particularly in dry climates. Hence, we expect contrasting responses of trees after earthquakes: at higher elevations, access to groundwater may be impeded, but enabled in the valley bottoms. Thus, earthquake‐enhanced tree growth should be pronounced only on valley floors, with opposite responses happening along ridges. We test this hypothesis in pine forest plantations that were affected by the 2010 Maule earthquake, Chile. We find that tree growth increased following the earthquake because of enhanced photosynthesis on valley floors, but decreased on upper hillslopes due to increased water stress. Overall, these responses are small but measurable. Our study is the first to combine state‐of‐the‐art isotopic and wood anatomic proxies that we quantified at the cellular scale. Our results provide novel insights into the impacts of earthquakes on soil water and tree growth at an unprecedented daily to weekly resolution., Key Points: Earthquakes may stimulate tree growth by promoting photosynthesis. Direction of tree growth change depends on local topographic position. First dendroecohydrological study to explore earthquake‐water‐vegetation interactions at scale of cells., German Federal Ministry of Education and Research, NSF, BFA, Division of Grants and Agreements (DGA) http://dx.doi.org/10.13039/100005445

International audience; Nearly 13,000 years ago, the warming trend into the Holocene was sharply interrupted by a reversal to near glacial conditions. Climatic causes and ecological consequences of the Younger Dryas (YD) have been extensively studied, however proxy archives from the Mediterranean basin capturing this period are scarce and do not provide annual resolution. Here, we report a hydroclimatic reconstruction from stable isotopes (δ 18 O, δ 13 C) in subfossil pines from southern France. Growing before and during the transition period into the YD (12 900-12 600 cal BP), the trees provide an annually resolved, continuous sequence of atmospheric change. Isotopic signature of tree sourcewater (δ 18 O sw) and estimates of relative air humidity were reconstructed as a proxy for variations in air mass origin and precipitation regime. We find a distinct increase in inter-annual variability of sourcewater isotopes (δ 18 O sw), with three major downturn phases of increasing magnitude beginning at 12 740 cal BP. The observed variation most likely results from an amplified intensity of North Atlantic (low δ 18 O sw) versus Mediterranean (high δ 18 O sw) precipitation. This marked pattern of climate variability is not seen in records from higher latitudes and is likely a consequence of atmospheric circulation oscillations at the margin of the southward moving polar front. During the abrupt and intense climate change from the Allerød warm phase to the YD cold reversal in the North Hemisphere (ca. 12 700-11 600 cal BP) 1,2 sea-ice production and drifting enhanced 3 , alpine glaciers advanced 4 , storm intensity strengthened 5 , and a reorganization of the atmosphere 6,7 may have occurred. Greenland ice core data (NGRIP) reveal temperature drops of 10-15 °C with simultaneous reductions in snow accumulation and amplifications in atmospheric dust within less than a decade 6,8. During the rapid cooling, lake sediment records across Europe signal intensified wind stress, aridity and detrital input, alongside drastic ecological changes 5,9,10. The results are spatially heterogeneous in terms of hydrological change, as other European lake records find more humid conditions and/or increased quantity and intensity of precipitation (associated with higher lake levels in certain cases) 11,12. Model simulations constrained by proxy data indicate no single factor could cause the observed YD cold reversal, but rather a complex combination of weakened Atlantic meridional overturning circulation (AMOC), altered atmospheric circulation patterns, and moderate negative radiative forcing as most plausible driving factors 13. Nevertheless, mechanisms of climate variability in the North Atlantic region remain under intense debate 8 , even for the most recent past 14 .

Observed recent and expected future increases in frequency and intensity of climatic extremes in central Europe may pose critical challenges for domestic tree species. Continuous dendrometer recordings provide a valuable source of information on tree stem radius variations, offering the possibility to study a tree's response to environmental influences at a high temporal resolution. In this study, we analyze stem radius variations (SRV) of three domestic tree species (beech, oak, and pine) from 2012 to 2014. We use the novel statistical approach of event coincidence analysis (ECA) to investigate the simultaneous occurrence of extreme daily weather conditions and extreme SRVs, where extremes are defined with respect to the common values at a given phase of the annual growth period. Besides defining extreme events based on individual meteorological variables, we additionally introduce conditional and joint ECA as new multivariate extensions of the original methodology and apply them for testing 105 different combinations of variables regarding their impact on SRV extremes. Our results reveal a strong susceptibility of all three species to the extremes of several meteorological variables. Yet, the inter-species differences regarding their response to the meteorological extremes are comparatively low. The obtained results provide a thorough extension of previous correlation-based studies by emphasizing on the timings of climatic extremes only. We suggest that the employed methodological approach should be further promoted in forest research regarding the investigation of tree responses to changing environmental conditions.

The dynamics of the Late Glacial have been demonstrated by numerous records from the Northern Hemisphere and far fewer from the Southern Hemisphere (SH). SH paleoclimate records reveal a general warming trend, interrupted by a deglaciation pause Antarctic Cold Reversal (ACR; ∼14,700–13,000 cal BP). Here, we present decadal tree‐ring stable isotope chronologies (δ18O, δ13C) from New Zealand (NZ) subfossil kauri trees (n = 6) covering the post‐ACR millennium from 13,020 to 11,850 cal BP. We find a distinct, simultaneous downturn (∼12,625–12,375 cal BP) in all tree‐ring proxies paralleling regional tree growth declines, suggesting a widespread climate deterioration. This downturn was characterized by sustained high precipitation, low temperatures, and high relative humidity in NZ with incoming weather fronts from the South Ocean. Despite these promising results, questions remain about what drove the Kauri Downturn and how the hydroclimatic conditions were altered during this time period.

Purification protocols to extract pollen from lake sediments contain chemicals that alter the carbon and oxygen pollen‐isotope values according to pollen characteristics and family affiliation. Modern (raw) pollen of broad‐leaved (Alnus glutinosa, Betula pendula, Carpinus betulus, Corylus avellana, Fagus sylvatica and Quercus robur) and coniferous tree species (Picea abies and Pinus sylvestris) were treated with potassium hydroxide (KOH), hydrofluoric acid (HF), sodium hypochlorite (NaClO) and sulphuric acid (H2SO4) to test the impact on δ13Cpollen and δ18Opollen and assess the applicability in purification protocols. Pollen of broad‐leaved and coniferous trees reacted differently to chemical exposure, but response patterns are generally alike. Alterations of δ13Cpollen values vary between + 1.0‰ (B. pendula, NaClO‐treatment) and −5.0‰ (P. sylvestris, H2SO4‐treatment). The δ13Cpollen values of raw and chemically treated samples seem to be related after treatments with KOH, NaClO and HF, whereas the application of H2SO4 led to inconsistent changes among species. The impact of chemicals on δ18Opollen are more diverse and offsets range between +1.1‰ (C. avellana, NaClO‐treatment) and −17.9‰ (P. sylvestris, H2SO4‐treatment). In general, the use of isotope‐altering chemicals in purification protocols should be brought to a minimum, but the application of KOH and NaClO seems mostly unproblematic before δ13Cpollen and δ18Opollen analysis., Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659