ALBERT

Description: Previous studies have suggested that the Late Glacial period (LG; ∼14 600–11 700 cal BP) was characterised by abrupt and extreme climate variability over the European sector of the North Atlantic. The limited number of precisely dated, high-resolution proxy records, however, restricts our understanding of climate dynamics through the LG. Here, we present the first annually-resolved tree-cellulose stable oxygen and carbon isotope chronology (δ18Otree, δ13Ctree) covering the LG between ∼14 050 and 12 795 cal BP, generated from a Swiss pine trees (P. sylvestris; 27 trees, 1255 years). Comparisons of δ18Otree with regional lake and ice core δ18O records reveal that LG climatic changes over the North Atlantic (as recorded by Greenland Stadials and Inter-Stadials) were not all experienced to the same degree in the Swiss trees. Possible explanations include: (1) LG climate oscillations may be less extreme during the summer in Switzerland, (2) tree-ring δ18O may capture local precipitation and humidity changes and/or (3) decayed cellulose and various micro-site conditions may overprint large-scale temperature trends found in other δ18O records. Despite these challenges, our study emphasises the potential to investigate hydroclimate conditions using subfossil pine stable isotopes.

Description: Atmospheric CO2 (c(a)) rise changes the physiology and possibly growth of tropical trees, but these effects are likely modified by climate. Such c(a) x climate interactions importantly drive CO2 fertilization effects of tropical forests predicted by global vegetation models, but have not been tested empirically. Here we use tree-ring analyses to quantify how c(a) rise has shifted the sensitivity of tree stem growth to annual fluctuations in rainfall and temperature. We hypothesized that c(a) rise reduces drought sensitivity and increases temperature sensitivity of growth, by reducing transpiration and increasing leaf temperature. These responses were expected for cooler sites. At warmer sites, c(a) rise may cause leaf temperatures to frequently exceed the optimum for photosynthesis, and thus induce increased drought sensitivity and stronger negative effects of temperature. We tested these hypotheses using measurements of 5,318 annual rings from 129 trees of the widely distributed (sub-)tropical tree species, Toona ciliata. We studied growth responses during 1950-2014, a period during which c(a) rose by 28%. Tree-ring data were obtained from two cooler (mean annual temperature: 20.5-20.7 degrees C) and two warmer (23.5-24.8 degrees C) sites. We tested c(a) x climate interactions, using mixed-effect models of ring-width measurements. Our statistical models revealed several significant and robust c(a) x climate interactions. At cooler sites (and seasons), c(a) x climate interactions showed good agreement with hypothesized growth responses of reduced drought sensitivity and increased temperature sensitivity. At warmer sites, drought sensitivity increased with increasing c(a), as predicted, and hot years caused stronger growth reduction at high c(a). Overall, c(a) rise has significantly modified sensitivity of Toona stem growth to climatic variation, but these changes depended on mean climate. Our study suggests that effects of c(a) rise on tropical tree growth may be more complex and less stimulatory than commonly assumed and require a better representation in global vegetation models.

Description: 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 (urn:x-wiley:21698953:media:jgrg22058:jgrg22058-math-0003 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 urn:x-wiley:21698953:media:jgrg22058:jgrg22058-math-0004, 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.

Description: Dendroclimatic reconstructions, which are a well-known tool for extending records of climatic variability, have recently been expanded by using wood anatomical parameters. However, the relationships between wood cellular structures and large-scale climatic patterns, such as El Niño-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO), are still not completely understood, hindering the potential for wood anatomy as a paleoclimatic proxy. To better understand the teleconnection between regional and local climate processes in the western United States, our main objective was to assess the value of these emerging tree-ring parameters for reconstructing climate dynamics. Using Confocal Laser Scanning Microscopy, we measured cell lumen diameter and cell wall thickness (CWT) for the period 1966 to 2015 in five Douglas-firs [Pseudotsuga menziesii (Mirb.) Franco] from two sites in eastern Arizona (United States). Dendroclimatic analysis was performed using chronologies developed for 10 equally distributed sectors of the ring and daily climatic records to identify the strongest climatic signal for each sector. We found that lumen diameter in the first ring sector was sensitive to previous fall–winter temperature (September 25th to January 23rd), while a precipitation signal (October 27th to February 13th) persisted for the entire first half of the ring. The lack of synchronous patterns between trees for CWT prevented conducting meaningful climate-response analysis for that anatomical parameter. Time series of lumen diameter showed an anti-phase relationship with the Southern Oscillation Index (a proxy for ENSO) at 10 to 14year periodicity and particularly in 1980–2005, suggesting that chronologies of wood anatomical parameters respond to multidecadal variability of regional climatic modes. Our findings demonstrate the potential of cell structural characteristics of southwestern United States conifers for reconstructing past climatic variability, while also improving our understanding of how large-scale ocean–atmosphere interactions impact local hydroclimatic patterns.

Description: Plant transpiration links physiological responses of vegetation to water supply and demand with hydrological, energy, and carbon budgets at the land–atmosphere interface. However, despite being the main land evaporative flux at the global scale, transpiration and its response to environmental drivers are currently not well constrained by observations. Here we introduce the first global compilation of whole-plant transpiration data from sap flow measurements (SAPFLUXNET, https://sapfluxnet.creaf.cat/, last access: 8 June 2021). We harmonized and quality-controlled individual datasets supplied by contributors worldwide in a semi-automatic data workflow implemented in the R programming language. Datasets include sub-daily time series of sap flow and hydrometeorological drivers for one or more growing seasons, as well as metadata on the stand characteristics, plant attributes, and technical details of the measurements. SAPFLUXNET contains 202 globally distributed datasets with sap flow time series for 2714 plants, mostly trees, of 174 species. SAPFLUXNET has a broad bioclimatic coverage, with woodland/shrubland and temperate forest biomes especially well represented (80 % of the datasets). The measurements cover a wide variety of stand structural characteristics and plant sizes. The datasets encompass the period between 1995 and 2018, with 50 % of the datasets being at least 3 years long. Accompanying radiation and vapour pressure deficit data are available for most of the datasets, while on-site soil water content is available for 56 % of the datasets. Many datasets contain data for species that make up 90 % or more of the total stand basal area, allowing the estimation of stand transpiration in diverse ecological settings. SAPFLUXNET adds to existing plant trait datasets, ecosystem flux networks, and remote sensing products to help increase our understanding of plant water use, plant responses to drought, and ecohydrological processes. SAPFLUXNET version 0.1.5 is freely available from the Zenodo repository (https://doi.org/10.5281/zenodo.3971689; Poyatos et al., 2020a). The “sapfluxnetr” R package – designed to access, visualize, and process SAPFLUXNET data – is available from CRAN.

Description: Knowledge of historic changes in vegetation, relief, and soil is key in understanding how the uplands in central Europe have changed during the last millennium, being an essential requirement for measures on forest conversion and nature conservation in that area. Evidence of forest‐clearing horizons from the medieval period could be systematically documented at four low‐ to mid‐altitudinal sites (360–640 meters above mean sea level) in the Harz (Harz Mountains), Erzgebirge (Ore Mountains), and Českomoravská vrchovina (Bohemian‐Moravian Highlands). Subfossil trees with traces of human cutmarks and burning were recovered from buried wet‐organic soils (paleosols) within a context of mining and settlement archaeology, applying a multiproxy‐approach by using data from archaeology, paleobotany, geochronology, dendrochronology, and pedology. Tree stumps and trunks, as well as small‐scale wood remains represent an in situ record of local conifer stands (spruce, fir, and pine). Some deciduous tree taxa also occur. Dating of the tree remains yielded ages from the 10th/11th to the 13th/14th centuries A.D. After deforestation, the tree remains were buried by technogenic and alluvial–colluvial deposits. The reconstructed conifer‐dominated woodlands on wet soils mirror the local vegetation structure immediately before the medieval deforestation. As such wet sites are common in the uplands, conifers were significantly present in the natural vegetation even at mid and lower altitudes.

Description: We investigate the climate signature of δ18O tree-ring records from sites distributed all over Europe covering the last 400 years. An empirical orthogonal function (EOF) analysis reveals two distinct modes of variability on the basis of the existing δ18O tree-ring records. The first mode is associated with anomaly patterns projecting onto the El Niño–Southern Oscillation (ENSO) and reflects a multi-seasonal climatic signal. The ENSO link is pronounced for the last 130 years, but it is found to be weak over the period from 1600 to 1850, suggesting that the relationship between ENSO and the European climate may not be stable over time. The second mode of δ18O variability, which captures a north–south dipole in the European δ18O tree-ring records, is related to a regional summer atmospheric circulation pattern, revealing a pronounced centre over the North Sea. Locally, the δ18O anomalies associated with this mode show the same (opposite) sign with temperature (precipitation). Based on the oxygen isotopic signature derived from tree rings, we argue that the prevailing large-scale atmospheric circulation patterns and the related teleconnections can be analysed beyond instrumental records.