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In China, flash floods are one of the main natural disasters causing loss of life and damage to infrastructure. The threat of flash floods is exacerbated with climate change and increased human activities, such that the number of disasters has shown a clear upward trend in recent years. However, due to the scarcity of instrumental data or overly short timeseries, we are still lacking critical data to understand spatio-temporal patterns and driving factors of extreme flash floods. This missing knowledge is however crucial for a proper management of these hazards, especially in remote mountain environments. In forested catchments, dendrogeomorphology allows the reconstruction of past process activity based on growth disturbances (GDs) in trees that have been affected by past flash floods. Therefore, in our study, for the first time, we reconstruct past flash floods in the Qilian Mountains, northeast Tibetan Plateau, over past centuries. To this end, we sampled 99 Qinghai spruce (Picea crassifolia) trees affected by flash floods, with a total of 194 increment cores, and identified 302 GDs induced by past flash floods. These GDs have been caused by at least 21 flash floods that we are able to reconstruct over the last 170 years. The position of GDs within tree rings and the intra-seasonal dating of past events also allowed discussion of the likely synoptic situations that may have led to the triggering of flash floods in the past. Logistic regression analysis confirms that significant correlation exists between cumulative maximum 5-day August–September precipitation and reconstructed flash floods, which is corresponding to the majority of scars and related tangential rows of traumatic resin ducts (TRDs) found in the latewood portion of growth rings. These results support the idea that abundant precipitation occurring at the end of the summer season and early fall is the key factor driving flash floods in our study area. Our research not only fills the gaps regarding historical flash flood histories in the Qilian Mountains, but also provides a scientific basis for the region’s response to climate change and flood prevention and reduction., This work was supported by the National Natural Science Foundation of China [Grant No. 41977392], the National Key R&D Program of China [Grant No. 2019YFA0606602], the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDA20090000), and Qilian Mountain National Park Qinghai Province management bureau. Jiazhi Qie was financed by the China Scholarship Council

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Тhe results of identifying the causes of mass drying of pine trees in the Belarusian Polesje are presented. The object of the study is its modern generations on the former depleted sandy arable land and in natural conditions of growth. It is revealed that in the conditions of groundwater reduction after drainage reclamation in modern climatic conditions, the increase in the inflow of direct solar radiation in the 21st century was the limiting factor for the suppression of the stem productivity of pine, which led to the death of the stand.

Mining activity is often responsible for the drainage of acid or metal-enriched waters to fluvial systems. The release of metals is especially disturbing due to the toxicity and persistence of these products and their accumulation in the biosphere. Hence, a systematic detection and delimitation of highly polluted floodplains and linkages between pollution and high-flow stages would likely assist the improvement of land management and ease the design of mitigation or rehabilitation measures. Here we test how trees growing in different geomorphic positions along a fluvial system uptake metal during floods and how these uptakes can be documented “a posteriori”. To this end, we apply dendrogeochemical analyses to twenty Pinus pinaster Ait. trees growing on the banks of Odiel River (south-western Spain) as well as to five reference trees growing outside the river channel. In the field, trees were sampled with a large-diameter (1 cm) increment borer. In the lab, tree-ring series were dendrochronologically cross dated and separated into 5-yr blocks, so that wood blocks contained the dates of major floods. Then, Inductively Coupled Plasma Mass Spectrometry (ICPM) was employed to evaluate toxic metal concentrations in trees. Results point to clear correlations between the accumulation of toxic metals and the geomorphic position of trees within the fluvial network. We show that morphological units along a river exert control on toxic metal concentrations in trees, with uptake being much higher in trees located on meander cut banks than in trees growing on point-bar structures. Besides, we detect chemical signatures in trees located farthest away from the main river channel after the largest floods, but not in the aftermath of smaller events. We conclude that tree position is the single-most important determinant for metallic pollution in an environment controlled by fluvial processes, but also find that more studies are still needed to determine linkages with individual floods and interactions of metal uptake in roots via the water table in the river corridor.

Green alder (Alnus alnobetula), a tall multi-stemmed deciduous shrub, is widespread at high elevations in the Central European Alps. Its growth form frequently leads to asymmetric radial growth and anomalous growth ring patterns, making development of representative ring-width series a challenge. In order to assess the variability among radii of one shoot, among shoots belonging to one stock and among stocks, 60 stem discs were sampled at treeline on Mt. Patscherkofel (Tyrol, Austria). Annual increments were measured along 188 radii and analyzed in terms of their variability by applying dendrochronological techniques. Results revealed a high agreement in ring-width variation among radii of one shoot, among shoots of one stock and largely among stocks from different sites, confirming the pronounced limitation of radial stem growth by climate forcing at the alpine treeline. In contrast to this, a high variability in both absolute growth rates and long-term growth trends was found, which we attribute to different microsite conditions and disturbances. These factors also override climate control of radial growth under growth-limiting environmental conditions. Based on our findings we provide recommendations for the number of samples needed to carry out inter- and intra-annual studies of radial growth in this multi-stemmed clonal shrub.

In the context of global warming, climate change in river headwater regions and its drivers have attracted increasing attention. In this study, tree-ring width (TRW) chronology was constructed using tree-ring samples of fir (Abies faxoniana) in Dadu River Basin in the central part of the western Sichuan Plateau, China. Correlation analysis with climatic factors implies that the radial growth of trees in the region is mainly limited by temperature and has the highest correlation with the mean minimum temperature in summer (June and July) (R = 0.602, p < 0.001). On this basis, the TRW chronology was adopted to reconstruct variations in the mean minimum temperatures in summer from 1733 to 2010 in the upper reaches of Dadu River. The reconstruction equation was stable and reliable and offered a variance explanation rate of 36.2% in the observed period (1962~2010). In the past 278 years, the region experienced nine warm periods and ten cold periods. The warmest and coldest years occurred in 2010 and 1798, respectively, with values of 13.6 °C and 11.0 °C. The reconstruction was highly spatiotemporally representative and verified by temperatures reconstructed using other tree-ring data in surrounding areas. A significant warming trend was found in the last few decades. Moreover, the multi-taper method (MTM) analysis indicated significant periodic changes in quasi-2-year and 21–35-year periods, for which the El Niño Southern Oscillation (ENSO) and the Pacific decadal oscillation (PDO) could be the key controlling factors.

Introductory biology lessons around the world typically teach that plants absorb water through their roots, but, unfortunately, absorption of water through leaves and subsequent transport and use of this water for biomass formation remains a field limited mostly to specialists. Recent studies have identified foliar water uptake as a significant net water source for terrestrial plants. The growing interest in the development of a new model that includes both foliar water uptake (in liquid form) and root water uptake to explain hydrogen and oxygen isotope ratios in leaf water and tree rings demands a method for distinguishing between these two water sources. Therefore, in this study, I have devised a new labelling method that utilizes two different water sources, one enriched in deuterium (HDO + D2O; δD = 7.0 × 10 4‰, δ18O = 4.1‰) and one enriched in oxygen-18 (H218O; δD = −85‰, δ18O = 1.1 × 104‰), to simultaneously label both foliar-absorbed and root-absorbed water and quantify their relative contributions to plant biomass. Using this new method, I here present evidence that, in the case of well-watered Cryptomeria japonica D. Don, hydrogen and oxygen incorporated into new leaf cellulose in the rainy season derives mostly from foliar-absorbed water (69% from foliar-absorbed water and 31% from root-absorbed water), while that of new root cellulose derives mostly from root-absorbed water (20% from foliar-absorbed water and 80% from root-absorbed water), and new branch xylem is somewhere in between (55% from foliar-absorbed water and 45% from root-absorbed water). The dual-labelling method first implemented in this study enables separate and simultaneous labelling of foliar-absorbed and root-absorbed water and offers a new tool to study the uptake, transport and assimilation processes of these waters in terrestrial plants.

In conifers, xylogenesis produces during a growing season a very characteristic tree-ring structure: large thin-walled earlywood cells followed by narrow thick-walled latewood cells. Although many factors influence the dynamics of differentiation and the final dimensions of xylem cells, the associated patterns of variation remain very stable from one year to the next. While radial growth is characterised by an S-shaped curve, the widths of xylem differentiation zones exhibit characteristic skewed bell-shaped curves. These elements suggest a strong internal control of xylogenesis. It has long been hypothesised that much of this regulation relies on a morphogenetic gradient of auxin. However, recent modelling works have shown that while this hypothesis could account for the dynamics of stem radial growth and the zonation of the developing xylem, it failed to reproduce the characteristic tree-ring structure. Here we investigated the hypothesis of a regulation by a crosstalk between auxin and a second biochemical signal, using dynamical modelling. We found that, in conifers, such a crosstalk is sufficient to simulate the characteristic features of wood formation dynamics, as well as the resulting tree-ring structure. In this model, auxin controls cell enlargement rates while another signal (e.g., cytokinin, TDIF) drives cell division and auxin polar transport.HighlightA dynamical model proves that two interacting signals (auxin, plus a cytokinin or the TDIF peptide) can drive wood formation dynamics and tree-ring structure development in conifers.

International audience; The Milo River in Guinea is one of the tributaries of Upper Niger. Its basin has a semi-arid climate with alternating dry and wet seasons in a biogeographic context of savannah. The West African monsoon brings rain between June and September with a long dry period affecting river levels and vegetation. The rainfall and flow of the Milo River have declined of about 20 % since the 1970s. Trees that concentrate mainly along river margins are likely to be affected by this change in climate and water resource. Little data is available on the age, growth rate and origin of water used by riparian trees in Guinea. These data are nevertheless essential for measuring the impact of environmental changes on the functioning and sustainability of riparian forests. A dendrochronological and dendroisotopic study was carried out on trees bordering the Milo River in order to test the effectiveness of these techniques for obtaining such data. A difficulty with the use of dendrochronology in tropical environments is that few species form annual rings. Of thirteen tree species studied half form more or less distinct ring boundaries but three species showed clearly visible ring boundaries. These species are Pericopsis laxiflora, Tamarindus indica and Tectona grandis. This study shows that it is possible to estimate the age (15 to 102 years) and radial growth rates (0.26 to 1.39 cm/year) for species with discernible rings. However, the poor anatomical definition of ring boundaries on most of the other species, especially towards the pith, highlights all the difficulty of conducting a long-term, robust, dendroclimatic study in the semi-arid African context. A dendroisotopic test analysis (delta 13C, delta 18O) on a single tree of Pericopsis laxiflora, Tamarindus indica and Tectona grandis shows that this riparian species is able to regulate its water acquisition during hydrological variations. This is marked by a physical trace in the rings related to the use of the more perennial alluvial water during the dry period.; La rivière Milo, en Guinée, est l'un des affluents du haut-Niger. Son bassin connaît un climat de type semi-aride à saisons contrastées dans un contexte biogéographique de savane. La mousson d'Afrique de l'Ouest apporte ses pluies entre juin et septembre ; d'octobre à mai, une longue période sèche affecte le niveau des rivières et la végétation. Depuis les années 1970, la pluviométrie et le débit de la rivière Milo subissent une baisse d'environ 20 %. La végétation arborée, qui se concentre principalement le long du cours d'eau, est susceptible d'être touchée par cette évolution du climat et de la ressource en eau. Peu de données sont disponibles concernant l'âge, la vitesse de croissance et l'origine de l'eau utilisée par les arbres riverains du Milo. Ces données sont pourtant indispensables pour estimer l'impact des changements environnementaux sur le fonctionnement et la pérennité de la ripisylve. Une étude dendrochronologique et dendro-isotopique exploratoire a été réalisée sur des arbres riverains du Milo afin de tester ces techniques dans l'acquisition de telles données. Une difficulté liée à l'utilisation de la dendrochronologie en milieu tropical vient du fait que peu d'espèces ligneuses forment des cernes annuels. Sur treize espèces d'arbres étudiées, près de la moitié ont des limites de cernes peu distinctes, mais trois espèces ont des limites de cernes bien visibles. Il s'agit de Pericopsis laxiflora, Tamarindus indica et Tectona grandis. Cette étude montre qu'il est possible d'estimer l'âge (15 à 102 ans) et la vitesse de croissance radiale (0,26 à 1,39 cm/an) pour les espèces présentant des cernes discernables. Toutefois la mauvaise définition anatomique des limites de cernes sur la plupart des autres espèces, notamment vers le cœur, compromet la réalisation d'une étude dendroclimatique robuste en contexte semi-aride africain. Un essai d'analyse dendro-isotopique (delta13C, delta18O) réalisé sur un individu de Pericopsis laxiflora, de Tamarindus indica et de Tectona grandis montre comment l'arbre riverain peut réguler sa consommation hydrique en fonction des conditions hydriques locales et faire appel à l'eau de la nappe alluviale pendant la période sèche.

The Rhododendron spp. (R. yedoense and R. mucronulatum) at high elevations of Mt. Halla in Jeju Island are the dominant species in the shrubland. Despite the recent damage to their growth due to climate change and the spread of Sasa spp., these species have not yet been studied systematically in Korea. Therefore, the current study aimed to verify the effect of abiotic factors, e.g., temperature and precipitation, and the spread of Sasa spp. as a neighbor species on their growth based on ring-width measurement data. In addition, the death years were dated using the cross-dating method developed in dendrochronology by comparing the individual ring-width time series from dead Rhododendron spp. with the corresponding chronology established using living trees. For the study, disk samples were obtained from 11 and 10 living R. yedoense and R. mucronulatum, respectively, to establish tree-ring time series. To investigate the death years, six disk samples were also collected from each shrub species. The relatively high occurrence of missing or discontinuous rings is a characteristic of shrubs, which makes tree-ring analysis difficult. Through cross-dating, it was verified that the R. mucronulatum and R. yedoense have 4.3% and 5.3% missing and/or discontinuous rings (the total number of missing and/or discontinuous rings/the total number of tree rings), respectively. All dead shrubs were successfully dated based on synchronization of the individual time series with the corresponding chronologies established using the cross-dated time series; nine shrubs died in the 2010s and the other two shrubs in 1996 and 2001, respectively. Most deaths occurred when Sasa quelpaertensis dominantly occupied the study sites. From the analysis of the relationships between the residual chronologies and the bioclimate predictors (BioClim), only R. mucronulatum showed reliable correlations with the Bio5 (maximum temperature of the warmest month) as +0.28 (p < 0.05) and the Bio18 (precipitation of warmest quarter) as −0.33 (p < 0.05). This result means that summer temperature is a limiting factor for the growth of R. mucronulatum. Through this study, it was verified that Rhododendron spp. at high elevations in Korea can be used for research using tree rings.

Along with tree ring width, carbon isotopes are also good proxies for climate change. Water use efficiency (WUE) can be calculated more quickly and accurately based on carbon isotopes. In this study, according to the principle of dendroclimatology, the sequence of δ13C and WUE of tree rings of Picea meyeri are built. Pearson correlation analysis and multiple regression analysis are used to explore the response of carbon stable isotopes of Picea meyeri to climate change, which revealed the relationship between δ13C of Picea meyeri and climatic factors. Based on δ13C, we calculated the WUE of Picea meyeri and analyzed its response to climate change. The main conclusions are as follows: (1) The δ13C of Picea meyeri decreases year-by-year from 1957 to 2020, in the range from −23.89‰~−21.67‰, and the average value is −22.67‰. The water use efficiency of Picea meyeri increases in the range from 17.26~61.31, with an average of 39.45. (2) The δ13C of Picea meyeri is negatively correlated with temperature, which has the highest correlation with the temperature of the growing season (c5–c9), and its coefficient is higher than that of the mean temperature of each month. (3) There is a significant positive correlation between WUE sequence and temperature. Meanwhile, due to the effect of precipitation and temperature, the Picea meyeri is subject to drought stress to some extent. Above all, temperature is the main climatic factor affecting the δ13C and WUE of Picea meyeri on Luya mountain.

Bosten Lake Basin not only is a major source of drinking water for the residents of the surrounding area, but also maintains the ecological balance of the region. However, with the influence of climate change and human activities, the water level of Bosten Lake fluctuates sharply and has a great impact on the surrounding ecological environment. Therefore, the study of its historical water flow changes as a reference has become a focus of research. In this study, the radial growth of Schrenk spruces (Picea schrenkiana Fisch. et Mey.) significantly correlated with the tributary streamflow coming from the mountainous region near Bosten Lake Basin. On the basis of this good coherence, the tree-ring chronologies were used to reconstruct the streamflow for Huangshuigou River from the previous August to the present July (r = 0.766, p < 0.0001, n = 50). The reconstructed streamflow series matched observations well, explaining 63.3% of the variation in the observed streamflow of 1956–2005. Then, the sum of the streamflow reconstruction of Huangshuigou River and another two tree-ring-based streamflow reconstructions (Kaidu River and Qingshui River) was used to represent the hydrological variation of the upper catchment of Bosten Lake Basin, and the reconstruction sequence was 306 years. The 10.7, 5.5, and 2.1 year cycles of the power spectrum and wavelet analysis revealed that the runoff series reconstructed from tree-ring hydrometeorology was related to solar activity. Some dry and wet years in the reconstructed streamflow series of the upper catchment of Bosten Lake Basin corresponded to the historical record. During the wet years, the Indian Ocean was probably the main source of precipitation.

We compared climate–growth relationships (1956–2013) of two natural pedunculate oak (Quercus robur L.) stands with different water-holding capacities growing at the species distribution limit of the Mediterranean Region in NW Iberia. For this, tree-ring chronologies of earlywood vessel size (separating the first row from the other vessels) and latewood width were obtained. Earlywood traits were coupled to conditions during dormancy, whereby an elevated winter temperature appears to induce a high consumption of carbohydrates, resulting in smaller vessels. This effect was reinforced by waterlogging at the wettest site, whose correlation to winter precipitation was strongly negative. Soil water regimes caused differences between vessel rows, since all earlywood vessels were controlled by winter conditions at the wettest site, but only the first row at the driest one; radial increment was related to water availability during the previous rather than the current season. This confirms our initial hypothesis that oak trees near their southern distribution boundary adopt a conservative strategy, prioritizing reserve storage under limiting conditions during the growing period. We believe that wood formation is highly dependent on the balance between the previous accumulation of carbohydrates and their consumption to maintain both respiration during dormancy and early spring growth.

In the context of forecasted climate change scenarios, the growth of forest tree species at their distribution margin is crucial to adapt current forest management strategies. Analyses of beech (Fagus sylvatica L.) growth have shown high plasticity, but easternmost beech populations have been rarely studied. To describe the response of the marginal beech population to the climate in the far east sites of its distribution, we first compiled new tree ring width chronologies. Then we analyzed climate–growth relationships for three marginal beech populations in the Republic of Moldova. We observed a relatively high growth rate in the marginal populations compared to core distribution sites. Our analyses further revealed a distinct and significant response of beech growth to all climatic variables, assessing for the first time the relationship between growth and vapor pressure deficit (VPD) which described how plant growth responds to drought. These results highlight that accumulated water deficit is an essential limiting factor of beech growth in this region. In conclusion, beech growth in the easternmost marginal population is drought-limited, and the sensitivity to VPD will need to be considered in future studies to update the forest management of other economic and ecologically important species.

The tree-ring width index (RWI) and satellite-derived vegetation indices, such as the Normalized Difference Vegetation Index (NDVI), are used as long-term indicators of the past forest carbon uptake. However, fundamental questions remain with respect to what is represented by the RWI and NDVI at the ecosystem level. To address this question, we compared tree-ring parameters (RWI and the carbon isotope ratio: delta C-13) and NDVI products with forest ecosystem CO2 fluxes estimated using the eddy covariance method, at a larch forest in eastern Siberia. The RWI and tree-ring delta C-13 correlated well with the ecosystem gross primary production (GPP), and their temporal stabilities were high during 2004-2014. However, the NDVI products did not show any temporally stable relationship with the GPP. This could be ascribed to significant changes in the understory vegetation in this forest, i.e., from dense cowberry to shrubs and moisture-tolerant grasses, because of an excessively moist environment during 2007-2008. Changes in the understory vegetation could be reflected by the NDVI products but not by the GPP. Our results indicate that it is more feasible to study forest carbon uptake using tree-ring parameters than using satellite-derived vegetation indices in such larch-dominated forest ecosystems in eastern Siberia.

Mass movements in China typically encompass landslides, rockfalls, and debris flows, and these processes affect almost 70% of all mountain areas of China. An improved understanding of geomorphic process dynamics and their drivers and process histories are important prerequisites for a proper assessment and a sustainable management of mountain hazards. Tree rings have on varied occasions proven to be a reliable tool for the acquisition of data on past mountain hazards. Here we present the first reconstruction of past landslide activity on a slope in the Qilian Mountains, northeast Tibetan Plateau, China. To this end, a total of 543 Qilian juniper (Sabina przewalskii Kom.) samples were selected from 239 trees growing on or next to a complex landslide body, with the aim to reconstruct past landslide histories at the site. The dataset of disturbed trees was complemented with 174 increment cores from 84 reference Qilian juniper trees growing on three adjacent, yet undisturbed sites. Based on the dating of the samples and the interpretation of growth disturbances (GD) in the tree-ring series of affected trees, we provide the first reconstruction of past landslides as retrieved from a dendrogeomorphic record covering more than a millennium (956–2011 CE). Results show that the first detectable GD occurred as early as in 1042 CE, followed by seven major landslide reccurrences in 1703, 1816, 1848, 1863, 1913, 1970, and 1982. Comparison between our landslide record and a dendroclimatic precipitation reconstruction points to the crucial role of major, longer-term wet precipitation anomalies on landslide occurrence.

This work was funded by the US National Science Foundation (NSF) Grants AGS 1159430, AGS 1502186, AGS 1502150, PLR 15-04134, PIRE 1743738, AGS-15-167 and PLR16-03473. In north-western North America, the so-called divergence problem (DP) is expressed in tree ring width (RW) as an unstable temperature signal in recent decades. Maximum latewood density (MXD), from the same region, shows minimal evidence of DP. While MXD is a superior proxy for summer temperatures, there are very few long MXD records from North America. Latewood blue intensity (LWB) measures similar wood properties as MXD, expresses a similar climate response, is much cheaper to generate and thereby could provide the means to profoundly expand the extant network of temperature sensitive tree-ring (TR) chronologies in North America. In this study, LWB is measured from 17 white spruce sites (Picea glauca) in south-western Yukon to test whether LWB is immune to the temporal calibration instabilities observed in RW. A number of detrending methodologies are examined. The strongest calibration results for both RW and LWB are consistently returned using age-dependent spline (ADS) detrending within the signal-free (SF) framework. RW data calibrate best with June–July maximum temperatures (Tmax), explaining up to 28% variance, but all models fail validation and residual analysis. In comparison, LWB calibrates strongly (explaining 43–51% of May–August Tmax) and validates well. The reconstruction extends to 1337 CE, but uncertainties increase substantially before the early 17th century because of low replication. RW-, MXD- and LWB-based summer temperature reconstructions from the Gulf of Alaska, the Wrangell Mountains and Northern Alaska display good agreement at multi-decadal and higher frequencies, but the Yukon LWB reconstruction appears potentially limited in its expression of centennial-scale variation. While LWB improves dendroclimatic calibration, future work must focus on suitably preserved sub-fossil material to increase replication prior to 1650 CE. Postprint

Isotopes in tropical trees rings can improve our understanding of tree responses to climate. We assessed how climate and growing conditions affect tree-ring oxygen and carbon isotopes (δ18OTR and δ13CTR) in four Amazon trees. We analysed within-ring isotope variation for two terra firme (non-flooded) and two floodplain trees growing at sites with varying seasonality. We find distinct intra-annual patterns of δ18OTR and δ13CTR driven mostly by seasonal variation in weather and source water δ18O. Seasonal variation in isotopes was lowest for the tree growing under the wettest conditions. Tree ring cellulose isotope models based on existing theory reproduced well observed within-ring variation with possible contributions of both stomatal and mesophyll conductance to variation in δ13CTR. Climate analysis reveal that terra firme δ18OTR signals were related to basin-wide precipitation, indicating a source water δ18O influence, while floodplain trees recorded leaf enrichment effects related to local climate. Thus, intrinsically different processes (source water vs leaf enrichment) affect δ18OTR in the two different species analysed. These differences are likely a result of both species-specific traits and of the contrasting growing conditions in the floodplains and terra firme environments. Simultaneous analysis of δ13CTR and δ18OTR supports this interpretation as it shows strongly similar intra-annual patterns for both isotopes in the floodplain trees arising from a common control by leaf stomatal conductance, while terra firme trees showed less covariation between the two isotopes. Our results are interesting from a plant physiological perspective and have implications for climate reconstructions as trees record intrinsically different processes. © The Author(s) 2019.

Whether the tree growth–climate relationship is consistent in subtropical China has not yet been reported. To fill this gap, we chose Pinus taiwanensis which grow on Lushan Mountain in a subtropical region of China as the target tree species, established a standard tree-ring width chronology, and conducted a moving correlation analysis with climatic factors. The results showed that the relationship between radial growth of P. taiwanensis and climate changed significantly during 1980–1990. From 1955 to 1985, tree rings were negatively affected mainly by precipitation in September of the current growing season. From 1990 to 2014, however, a significant negative correlation appeared between tree rings and sunshine duration from March to April in the growing season. Our results suggest the need to pay attention to this growth–climate inconsistency when conducting dendroclimatology studies in subtropical China. However, the causes of the inconsistency still require further confirmation.

Producción Científica, Wood microdensitometry provides an integrated measurement of inter and intra-annual changes in wood anatomy and lignification. Although it can be acquired through a wide array of techniques, X-ray-based techniques are still the standard. Conversion of a grayscale X-ray image to density and annual ring boundaries delimitation is performed through image analysis software. Proprietary software has dominated these applications, albeit Free Open Source Software (FOSS) has been developed recently. We present ρ-MtreeRing, a user-friendly FOSS that streamlines the entire microdensitometry analysis process through a graphical user interface based on Shiny R Software without any programming knowledge. We compared the results of this program with the most widely used commercial software (WinDendro), showing the validity of the results. ρ-MtreeRing can be personalized and developed by the microdensitometry research community., Junta de Castilla y León (VA171P20), Ministerio de Ciencia e Innovación y Ministerio de Universidades grant number CGL2017-87309-P (MGH PRE2018-084106) and project PROWARM (PID2020-118444GA-I00), Universidad Politécnica de Madrid (through Project RP200060107), Centro de Recursos Hídricos para la Agricultura y la Minería (ANID/FONDAP/15130015)

Significance Forests remove about 30% of anthropogenic CO2 emissions through photosynthesis and return almost 40% of incident precipitation back to the atmosphere via transpiration. The trade-off between photosynthesis and transpiration through stomata, the water-use efficiency (WUE), is an important driver of plant evolution and ecosystem functioning, and has profound effects on climate. Using stable carbon and oxygen isotope ratios in tree rings, we found that WUE has increased by a magnitude consistent with estimates from atmospheric measurements and model predictions. Enhanced photosynthesis was widespread, while reductions in stomatal conductance were modest and restricted to moisture-limited forests. This result points to smaller reductions in transpiration in response to increasing atmospheric CO2, with important implications for forest–climate interactions, which remain to be explored., Multiple lines of evidence suggest that plant water-use efficiency (WUE)—the ratio of carbon assimilation to water loss—has increased in recent decades. Although rising atmospheric CO2 has been proposed as the principal cause, the underlying physiological mechanisms are still being debated, and implications for the global water cycle remain uncertain. Here, we addressed this gap using 30-y tree ring records of carbon and oxygen isotope measurements and basal area increment from 12 species in 8 North American mature temperate forests. Our goal was to separate the contributions of enhanced photosynthesis and reduced stomatal conductance to WUE trends and to assess consistency between multiple commonly used methods for estimating WUE. Our results show that tree ring-derived estimates of increases in WUE are consistent with estimates from atmospheric measurements and predictions based on an optimal balancing of carbon gains and water costs, but are lower than those based on ecosystem-scale flux observations. Although both physiological mechanisms contributed to rising WUE, enhanced photosynthesis was widespread, while reductions in stomatal conductance were modest and restricted to species that experienced moisture limitations. This finding challenges the hypothesis that rising WUE in forests is primarily the result of widespread, CO2-induced reductions in stomatal conductance.

Tree-ring with series of Pinus sylvestris L. have been studied in relation to local climate. Ten chronologies have been established, six of them are located in the Prepyrenees, two in the Montseny mountains and two in Prades. Tree-ring width series and climate relationships have been studied by means of multiple regression after extracting principal components. The results showed that there is a strong influence of water deficits during current season growth in the region, but differences occur among chronologie. The inertia of the growth response to external stimuli is showed by those significative coefficients for some months prior to current growth. The results are discussed by means of the ecophysiological facts of this species and its adaptative strategy as a pioneer species considered. En el presente trabajo se ha llevado a cabo un estudio de las limitaciones climaticas del crecimiento secundario de Pinus sylvestris L. en tres zonas de Catalunya. Para ello se han establecido 10 cronologias en otras tantas localidades, de las que 6 corresponden al Prepirineo, 2 al Montseny y 2 a Prades. La metodologia utilizada para poner de manifiesto las relaciones clima-crecimiento ha sido el análisis de regresión múltiple en componentes principales, obteniéndose así las funciones respuesta. Los resultados confirmaron la hipotesis de que esta especie, incluso en la zona del Prepirineo, se ve influenciada por el estrés hídrico durante la estación de crecimiento y aunque existe una respuesta similar en las tres zonas de estudio, también se producen diferencias. El efecto de inercia o el retardo con que las especies responden a los estímulos climaticos se ha puesto de manifiesto al presentar, alguno de 10s factores climaticos, coeficientes significativos en periodos anteriores a la estación actual de crecimiento. Los resultados son comentados desde la ecofisiologia de esta especie, comparándolos con los obtenidos por otros autores en el norte de su distribución geográfica. Finalmente se hace referencia a la estrategia adaptativa de P. sylvestris, considerada una especie pionera.

The monitoring of the spatial and temporal dynamics of vegetation productivity is important in the context of carbon sequestration by terrestrial ecosystems from the atmosphere. The accessibility of the full archive of medium-resolution earth observation data for multiple decades dramatically improved the potential of remote sensing to support global climate change and terrestrial carbon cycle studies. We investigated a dense time series of multi-sensor Landsat Normalized Difference Vegetation Index (NDVI) data at the southern fringe of the boreal forests in the Mongolian forest-steppe with regard to the ability to capture the annual variability in radial stemwood increment and thus forest productivity. Forest productivity was assessed from dendrochronological series of Siberian larch (Larix sibirica) from 15 plots in forest patches of different ages and stand sizes. The results revealed a strong correlation between the maximum growing season NDVI of forest sites and tree ring width over an observation period of 20 years. This relationship was independent of the forest stand size and of the landscape’s forest-to-grassland ratio. We conclude from the consistent findings of our case study that the maximum growing season NDVI can be used for retrospective modelling of forest productivity over larger areas. The usefulness of grassland NDVI as a proxy for forest NDVI to monitor forest productivity in semi-arid areas could only partially be confirmed. Spatial and temporal inconsistencies between forest and grassland NDVI are a consequence of different physiological and ecological vegetation properties. Due to coarse spatial resolution of available satellite data, previous studies were not able to account for small-scaled land-cover patches like fragmented forest in the forest-steppe. Landsat satellite-time series were able to separate those effects and thus may contribute to a better understanding of the impact of global climate change on natural ecosystems.

The worldwide increase in urban and industrial areas represents a challenge for urban green management, pollutant mitigation and environmental monitoring. We propose an analysis approach for the spatial and spatial-temporal distribution of pollutants in the environment through dendrochemistry techniques, in order to gauge the value of this discipline in urban ecosystem. The proposed analysis models can be useful to evaluate significant changes in space and time related to economic activities and to describe the “impacts” of adopted strategies, as demonstrated in the case study of the opening or closure of factories, and therefore to describe the cause-effect relation connected with human activities. Trees represent a key factor for urban planning, providing a wide variety of ecosystem services including in-depth environmental monitoring, which is one of the main elements to be included in a high quality urban design. The proposed approach aims at suggesting the dendrochemistry as a novel and feasible tool definable as a cost-saving ecosystem service in the urban context.

Although air pollution decreased in some cities that shifted from an industrial to a service-based economy, and vehicular emission regulation became more restrictive, it is still a major risk factor for mortality worldwide. In central São Paulo, Brazil, air quality monitoring stations and tree-ring analyses revealed a decreasing trend in the concentrations of particulate matter and metals. Such trends, however, may not be observed in industrial districts located in the urban periphery, where the usual mobile sources may be combined with local stationary sources. To evaluate environmental pollution in an industrial district in southeastern São Paulo, we assessed its spatial variability, by measuring magnetic properties and concentrations of Al, Ba, Ca, Cl, Cu, Fe, K, Mg, Mn, P, S, Sr, Zn in the bark of 62 trees, and its temporal trends, by measuring Cd, Cu, Ni, Pb, V, Zn in tree rings of three trees. Source apportionment analysis based on tree barks revealed two clusters with high concentrations of metals, one related to vehicular and industrial emissions (Al, Ba, Cu, Fe, Zn) in the east side of the industrial cluster, and the other related to soil resuspension (Cu, Zn, Mn) in its west side. These patterns are also supported by the magnetic properties of bark associated with iron oxides and titanium-iron alloy concentrations. Dendrochemical analyses revealed that only the concentrations of Pb consistently decreased over the last four decades. The concentrations of Cd, Cu, Ni, V, and Zn did not significantly decrease over time, in contrast with their negative trends previously reported in central São Paulo. This combined biomonitoring approach revealed spatial clusters of metal concentration in the vicinity of this industrial cluster and showed that the local population has not benefited from the decreasing polluting metal concentrations in the last decades CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP Fechado

A tree-ring width chronology was developed from the Chinese pine (Pinus tabuliformis) in northern North China. To acquire a long-term perspective on the history of droughts in this region, the Standardized Precipitation Evapotranspiration Index (SPEI) from August of the previous year to February of the current year was reconstructed for the period of 1903–2012 AD. The reconstruction explained 46.6% of the instrumental records over the calibration period of 1952–2012. Five dry periods (1916–1927, 1962–1973, 1978–1991, 1994–1999 and 2002–2005) and three wet periods (1908–1915, 1928–1961 and 1974–1977) were found in the reconstructed period, and most of the dry years (periods) in the reconstruction were supported by historical records. Comparisons between the reconstruction and other nearby dryness/wetness indices and precipitation reconstructions demonstrated a good repeatability and high reliability in our reconstruction. Spatial correlation implied that the reconstruction could represent regional hydroclimatic characteristics on a larger regional scale. Significant periodicities and correlations were observed between the reconstructed data and the quasi-biennial oscillation (QBO), El Niño–Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO), which suggested that the hydroclimatic variation in northern North China may be closely connected to remote oceans. The significant and high correlation between the reconstructed series and sea surface temperatures (SSTs) in the eastern equatorial and Southeast Pacific Ocean indicated that ENSO may be the main factor influencing the regional climate.

Substantial amounts of annual radiocarbon (14C) data have recently been produced with the purpose of increasing the time resolution of 14C records used for constructing the calibration curve and for studying the occurrence of abrupt cosmic-ray events. In this study, we investigate if it is possible to resolve sub-annual scale changes in the atmospheric 14C content by measuring radiocarbon in early-wood and late-wood fractions from Danish oak. The tree-ring samples span the period 1954–1970 CE, hereby covering the peak of the bomb pulse. A least squares test comparing the atmospheric 14C content and the new sub-annual 14C record from Danish tree rings reveals that by measuring early-wood and late-wood fractions, it may be possible to resolve sub-annual variations in past atmospheric 14C levels.

Projected changes in drought occurrence in the Mediterranean region are raising concerns about the adaptive capability of rainfed crops, such as grapevine, to in- creasing aridity. Cultivation management, especially the techniques in uencing the hydraulic pathway, can play a role in plant adaptation to drought for the con- sequent changes in wood anatomical functional traits. The aim of this study was to assess the effect of grafting on wood anatomy in tree-ring series of Vitis vini- fera L. ‘Piedirosso’ grapevine cultivated in a volcanic area in Southern Italy. Tree- ring anatomy was analysed in vines grown on their own roots or grafted onto 420A rootstock. results showed that grafted vines had a higher occurrence of wood traits linked with safety of water transport if compared with non-grafted vines. Grafting induced the formation of tree rings with higher incidence of latewood also characterised by narrower and more frequent vessels if compared with non-grafted vines. This study suggested a different regulation of water ow in the grafted and non-grafted vines. Such ndings support the analysis of wood anatomy as a tool to drive decisions linked with plant cultivation management. In this speci c case, our results encourage to further explore the change from a traditional cultivation with own-rooted grapevines towards grafted models inducing better xylem adaptation to increasing drought. Projected changes in drought occurrence in the Mediterranean region are raising concerns about the adaptive capability of rainfed crops, such as grapevine, to in-creasing aridity. Cultivation management, especially the techniques influencing the hydraulic pathway, can play a role in plant adaptation to drought for the con-sequent changes in wood anatomical functional traits. The aim of this study was to assess the effect of grafting on wood anatomy in tree-ring series of Vitis vinifera L. Piedirosso' grapevine cultivated in a volcanic area in Southern Italy. Tree-ring anatomy was analysed in vines grown on their own roots or grafted onto 420A rootstock. Results showed that grafted vines had a higher occurrence of wood traits linked with safety of water transport if compared with non-grafted vines. Grafting induced the formation of tree rings with higher incidence of latewood also characterised by narrower and more frequent vessels if compared with non-grafted vines. This study suggested a different regulation of water flow in the grafted and non-grafted vines. Such findings support the analysis of wood anatomy as a tool to drive decisions linked with plant cultivation management. In this specific case, our results encourage to further explore the change from a traditional cultivation with own-rooted grapevines towards grafted models inducing better xylem adaptation to increasing drought.

BACKGROUND AND AIMS: Mediterranean trees have patterns of cambial activity with one or more pauses per year, leading to intra-annual density fluctuations (IADFs) in tree rings. We analysed xylogenesis (January 2015–January 2016) in Pinus pinea L. and Arbutus unedo L., co-occurring at a site on Mt. Vesuvius (southern Italy), to identify the cambial productivity and timing of IADF formation. METHODS: Dendrochronological methods and quantitative wood anatomy were applied and enabled IADF identification and classification. KEY RESULTS: We showed that cambium in P. pinea was productive throughout the calendar year. From January to March 2015, post-cambial (enlarging) earlywood-like tracheids were observed, which were similar to transition tracheids. The beginning of the tree ring was therefore not marked by a sharp boundary between latewood of the previous year and the new xylem produced. True earlywood tracheids were formed in April. L-IADFs were formed in autumn, with earlywood-like cells in latewood. In A. unedo, a double pause in cell production was observed, in summer and winter, leading to L-IADFs in autumn as well. Moreover, the formation of more than one IADF was observed in A. unedo. CONCLUSIONS: Despite having completely different wood formation models and different life strategies, the production of earlywood, latewood and IADF cells was strongly controlled by climatic factors in the two species. Such cambial production patterns need to be taken into account in dendroecological studies to interpret climatic signals in wood from Mediterranean trees.

Concerning the ecological and economical importance of the Pearl River basin, short-term climate changes have been widely studied by using the instrumental records in the basin, but there is still a lack of long-term climatic reconstructions that can be used to evaluate the centennial scale climate anomalies. Here, we present a 237-year tree-ring width chronology from Tsuga longibracteata in the north-central Pearl River basin, with reliable coverage from 1824 to 2016. Based on the significant relationship between tree growth and mean temperature from the previous March to the previous October, we reconstructed the previous growing season (pMar-pOct) temperatures for the past 193 years, with an explained variance of 43.3% during 1958–2016. The reconstruction reveals three major warm (1857–1890, 1964–1976, and 1992–2016) and cold (1824–1856, 1891–1963, and 1977–1991) periods during 1824–2016. Comparison with other temperature sensitive proxy records from nearby regions suggests that our reconstruction is representative of large-scale temperature variations. Significant correlations of tree growth with the sea surface temperatures (SSTs) in the western Pacific Ocean, northern Indian Ocean, and Atlantic Ocean suggest that SST variability in these domains may have strongly influenced the growing season temperature change in the Pearl River basin.

This paper presents an analysis of the radial growth, tree dimensions, and allometry of three phenological pedunculate oak (Quercus robur L., QURO) varieties (early (E-QURO), typical (T-QURO), and late (L-QURO)), from a common garden experiment. We focused on the resistance and resilience of each variety to drought events, which occurred in 2012 and 2017, as well as their recovery potential during juvenile and mature growth phases, with the goal of clarifying how QURO drought sensitivity is influenced by tree phenology and growth stage. Our results indicate that E-QURO is more drought resistant, while T-QURO and L-QURO exhibit greater recovery potential after a drought event. Hence, typical and late QURO varieties are better prepared to withstand climate change. We also noted differences in the physical dimensions and the allometry of the studied QURO varieties. On average, 21-year-old QURO specimens from the analyzed stand are 9.35 m tall, have a crown width (CW) of 8.05 m, and a diameter at breast height (DBH) of 23.71 cm. Although T-QURO varieties had the greatest DBH and CW, they were shorter than E- and L-QURO, which are similar in height. T-QURO is also shorter relative to DBH, while L-QURO has a wider crown relative to tree height (TH). Intra-variety variations are higher than variations among half-sib (open-pollinated) families of each variety. Moreover, the adopted regression model provided a better fit to the CW/DBH ratio than to TH/DBH and CW/TH.

Temperature plays a key role in phenology and growth of dominant tree species and hence in the structure and function of coniferous forests in cold temperate zones. We used a dendrochronological method to determine the critical temperatures of Pinus sylvestris var. mongolica (Mongolian pine) radial growth and the xylem growing season. Results showed that Mongolian pine radial growth is sensitive to daily mean temperatures of 4.0–5.5 °C in early spring, 14.0 °C in summer and 2.0–2.5 °C in autumn. A temperature of 4 °C might be the initial temperature required for sap flow, photosynthesis and tree germination in this area in early spring, and 5.5 °C is the most critical temperature for earlywood onset growth. The advance and extension of temperature 14.0 °C in summer can exacerbate water stress for trees and inhibit earlywood growth under the condition of insufficient precipitation. In autumn, 2.0–2.5 °C may be the minimum temperature for the xylem growth. These critical temperatures are important in predicting the changes in the phenology of cambial activity and the growth of conifers in cold temperate regions under a scenario of a warming climate. We defined the mean xylem growing season of pines in this region as 151 days from early May to early October. With the increase in temperatures during 1972–2015, the start date of the xylem growing season advanced by 0.24 days/year, the duration of the xylem growing season increased by 0.27 days/year and the basal area increment of Mongolian pine increased significantly (P

Site properties have received limited attention in analyzing the weather-growth relationship of trees. We analyzed the annual growth variation of Scots pine on two extreme sites in southern Finland: a dry hill top site and a moist patch of mineral soil surrounded by a large peatland. The effects of daily precipitation and temperature were related to growth variation using correlation analyses. In addition, the common signal and the difference of ring-width indices from the dry and moist sites were studied via principal component analysis and related to the daily weather measurements. All possible time intervals longer than 14 days from current year April 1st to August 31st were tested. We also modeled daily photosynthetic production of Scots pine using two parameter sets, one describing limited stomatal closure and the other one easily triggered stomatal closure. Growth variation at the dry site was linked with variation of precipitation during early and middle parts of growing season, while growth at moist site was correlated with temperature during the middle part of growing season. Daily photosynthetic production, modeled with parameters describing mostly open stomata produced a rather strong negative correlation with ring-width indices from the dry site, possibly indicating that the parametrization overestimated growth during dry years. Other than that, the modeled photosynthetic production was relatively weakly correlated with the ring-width indices. Evidently, the mechanisms controlling Scots pine growth at drought-sensitive sites in southern Finland are complex. Overall, the results indicate that site properties, especially water retention capacity, need to be considered in dendroecological research.

The ratio of leaf internal (ci ) to ambient (ca ) partial pressure of CO2 , defined here as χ, is an index of adjustments in both leaf stomatal conductance and photosynthetic rate to environmental conditions. Measurements and proxies of this ratio can be used to constrain vegetation model uncertainties for predicting terrestrial carbon uptake and water use. We test a theory based on the least-cost optimality hypothesis for modelling historical changes in χ over the 1951-2014 period, across different tree species and environmental conditions, as reconstructed from stable carbon isotopic measurements across a global network of 103 absolutely dated tree-ring chronologies. The theory predicts optimal χ as a function of air temperature, vapour pressure deficit, ca and atmospheric pressure. The theoretical model predicts 39% of the variance in χ values across sites and years, but underestimates the intersite variability in the reconstructed χ trends, resulting in only 8% of the variance in χ trends across years explained by the model. Overall, our results support theoretical predictions that variations in χ are tightly regulated by the four environmental drivers. They also suggest that explicitly accounting for the effects of plant-available soil water and other site-specific characteristics might improve the predictions.

The effect of fire severity on Pinus pinaster growth and ecophysiological responses was evaluated in four burned sites of Vesuvio National Park, Southern Italy. After the wildfire of 2017, when over 1300 hectares of vegetation, mainly P. pinaster woods, were destroyed, four sites were selected according to the different degree of fire severity and a multidisciplinary approach based on tree rings, stable isotopes and percentage of crown scorched or consumed was applied. All the sampled trees in the burned sites showed a decrease in tree growth in 2017, in particular in the latewood at high-severity site. The dendrochronology analyses showed that several individuals experienced and endured higher fire severity in the past compared to 2017 fire. Further delta C-13 and delta O-18 underlined the ecophysiological responses and recovery mechanisms of P. pinaster, suggesting a drastic reduction of photosynthetic and stomata activity in the year of the fire. Our findings demonstrated that P. pinaster growth reduction is strictly linked to the percentage of crown scorch and that even trees with high level of crown scorched could survive. In all the burned sites the high temperatures and the time of exposure to the flames were not sufficient to determine the death of the cambium and all the trees were able to complete the 2017 seasonal wood formation. This data can contribute to define guidelines to managers making post-fire silvicultural operations in pine forest stands in the Mediterranean Basin.

The stability and balance of forest ecosystems have been seriously affected by climate change. Herein, we use dendrochronological methods to investigate the radial growth and climate response of pioneer tree species in the southern margin of cold temperate coniferous forest based on Populus davidiana growing on the Greater Hinggan Mountains in northeastern China. Correlations of P. davidiana growth with temperature and precipitation in a year (October–September) were rhythmically opposed: while temperatures in previous October–June (winter and spring) and in May–September (growing season) respectively inhibited and promoted radial growth on P. davidiana (p < 0.01), precipitation in the same periods respectively promoted and inhibited of growth (p < 0.01). High temperature or less rain/snow in winter and early spring, and low temperature or excess rainfall in summer, are inconducive to P. davidiana growth and vice versa (p < 0.01). In addition, in March–April, when air temperature was above 0 °C and ground temperature below 0 °C, physiological drought caused significant growth inhibition in P. davidiana (p < 0.05). In general, temperatures play a driving and controlling role in the synergistic effect of temperature and precipitation on P. davidiana growth. Under current conditions of available water supply, changes of temperature, especially warming, are beneficial to the growth of P. davidiana in the study area. The current climate conditions promote the growth of P. davidiana, the pioneer species, compared with the growth inhibition of Larix gmelinii, the dominant species. Thus, the structure and function of boreal forest might be changed under global warming by irreversible alterations in the growth and composition of coniferous and broadleaf tree species in the forest.

The N-Ohkawa landslide, and the southern section of the Ohkawa landslide, occurred during the snow-melt seasons of 1999 and 2006, respectively, in the Shirakami Mountains, Japan. This paper examines the response of trees in the Shirakami Mountains to landslides, and also investigates the spatio-temporal occurrence patterns of landslide events in the area. Dendrogeomorphological analysis was used to identify growth suppression and growth increase (GD) markers in tilted deciduous broadleaved trees and also to reveal the timing of the establishment of shade-intolerant tree species. Analysis of the GD markers detected in tree-ring width series revealed confirmatory evidence of landslide events that occurred in 1999 and 2006 and were observed by eyewitnesses, as well as signals from eight additional (previously unrecorded) landslide events during 1986–2005. Furthermore, shade-intolerant species were found to have become established on the N-Ohkawa and southern Ohkawa landslides, but with a lag of up to seven years following the landslide events causing the canopy opening.

Short-term climate change in South China has been extensively studied based on meteorological or hydrological records. However, tree ring-based long-term climate change research is rare, especially in the Pearl River basin, owing to the difficulty in finding old-aged trees. Here, we present a 200-year tree ring width chronology of Pinus kwangtungensis in the east Pearl River basin with reliable coverage from 1894 to 2014. Based on the significant climate&ndash, growth relationship between tree growth and annual self-calibrating Palmer drought severity index (scPDSI) from previous May to current April, the pMay&ndash, cApr scPDSI was reconstructed for the period 1894&ndash, 2014. The reconstruction reveals four dry periods during 1899&ndash, 1924, 1962&ndash, 1974, 1988&ndash, 1994, and 2003&ndash, 2014, and four wet periods during 1894&ndash, 1898, 1925&ndash, 1961, 1975&ndash, 1987, and 1995&ndash, 2002. Significant spatial correlations between the reconstructed scPDSI and the Climatic Research Unit (CRU) gridded scPDSI indicate that our reconstruction can effectively represent regional moisture variability in the Pearl River basin. Spatial correlations with global sea surface temperatures (SSTs) show that our reconstruction is negatively correlated with northern and western Pacific SSTs while positively correlated with eastern Pacific SSTs, suggesting that SST variability in these domains strongly affects moisture change in the Pearl River basin.

International audience; Understanding how climate and soil hydrology control tree growth is critical to predict the response of Siberian ecosystems to climate change. The general aim of this study was to (i) characterize the soil water budget and identify the factors controlling aspen (Populus tremula L.) radial growth in south-western Siberia, and (ii) assess its potential response to future climate change. Along a gradient of climate and soil hydrological conditions, soil water budgets were reconstructed by modeling at four sites, and dendrochronological analyses were performed. Aspen growth potential was simulated in response to different climate change scenarios represented by shifts in soil water budgets. Simulated soil water budgets varied with climate variables, specifically increased temperature and drier summer combined with varying winter precipitation occurring as snowfall.. We show that plant-available soil water and drainage gradually increased while stress decreased from the warmest and driest (south, forest-steppe zone) site to the coldest and wettest (north, southern taiga zone) site. Aspen radial growth was mainly limited by summer temperature in the north and by summer water deficit in the south. Surprisingly, we did not find clear evidence of snow level impact on radial growth, either positively in the south (water supply and protection against soil freezing) or negatively in the north (water-logging and drainage). In the context of climate change, water stress intensity could increase dramatically in the south inhibiting aspen growth; in those places summer soil water content depends on the refilling that occurs at snow-melt and increasing winter precipitation could alleviate stress levels. Conversely, in the north, aspen growth may mostly benefit from rising temperature.

[EN] Flash floods represent one of the most common natural hazards in mountain catchments, and are frequent in Mediterranean environments. As a result of the widespread lack of reliable data on past events, the understanding of their spatio-temporal occurrence and their climatic triggers remains rather limited. Here, we present a dendrogeomorphic reconstruction of past flash flood activity in the Arroyo de los Puentes stream (Sierra de Guadarrama, Spanish Central System). We analyze a total of 287 increment cores from 178 disturbed Scots pine trees (Pinus sylvestris L.) which yielded indications on 212 growth disturbances related to past flash flood impact. In combination with local archives, meteorological data, annual forest management records and highly-resolved terrestrial data (i.e., LiDAR data and aerial imagery), the dendrogeomorphic time series allowed dating 25 flash floods over the last three centuries, with a major event leaving an intense geomorphic footprint throughout the catchment in 1936. The analysis of meteorological records suggests that the rainfall thresholds of flash floods vary with the seasonality of events. Dated flash floods in the 20th century were primarily related with synoptic troughs owing to the arrival of air masses from north and west on the Iberian Peninsula during negative indices of the North Atlantic Oscillation. The results of this study contribute considerably to a better understanding of hazards related with hydrogeomorphic processes in central Spain in general and in the Sierra de Guadarrama National Park in particular., This study has been partially funded by the projects IDEA-GesPPNN-163/2010 (OAPN - Organismo Autonomo de Parques Nacionales, Ministerio de Agricultura, Alimentacion y Medio Ambiente) and CGL2010-19274 (projects MAS Dendro-Avenidas) of the Spanish Ministry of Economy and Competitiveness. The authors sincerely acknowledge Marco Borga and other anonymous reviewer. Special recognition must be given to CENEAM, Montes de Valsain, OAPN and JCyL for providing information for this study. Specifically, they want to thank Javier Dones (Director of Montes de Valsain), Ramzi Touchan and Dave Meko for their support during the study, as well as Andres Diez and Gerardo Benito and all participants of the Tree-ring summer school carried out in 2012 in Valsain (Touchan et al., 2013). R. Sanchez-Salguero thanks the financial support from University of Cordoba-Campus de Excelencia Internacional-ceiA3.

GRYC, V., VAVRCIK, H., GOMOLA, S.: The variability of selected properties of beech (Fagus sylvatica L.). Acta univ. agric. et silvic. Mendel. Brun., 2007, LV, No. 4, pp. 29–36 Variability of ring width, wood density and swelling in beech from two different areas was analysed. The variability of each property was described along the stem radius. The analysis proved that the ring width decreased in direction from the pith to the outer part of the stem (cambium). Statistically signifi cant difference of mean ring width between locality 1 and 2 was not found. Density and volumetric swelling of wood were statistically signifi cantly different between localities. Results showed that the density and volumetric swelling decreased from pith to cambium. Statistically signifi cant dependency between density and volumetric swelling of wood was proved. The average wood density of beech was 752 kg·m –3 at 12% moisture content. beech wood, tree ring, density, structure of wood Dřevo je významnou obnovitelnou surovinou, na niž je vedle lesnictvi a dřevařstvi zavisla řada dalsich průmyslových odvětvi. Na rozdil od ostatnich průmyslových materialů ma tu výhodu, že je surovinou obnovitelnou. Je nutne mit na paměti, že dřevo je přirodnim materialem, který ma na rozdil od větsiny ostatnich materialů velmi variabilni strukturu a vlastnosti. Struktura dřeva a nasledne vlastnosti jsou urcovany v průběhu růstu stromu (Gryc a Horacek, 2004). Buk lesni (Fagus sylvatica L.) patři k nejvýznamnějsi listnate hospodařske dřevině nejen v Ceske republice, ale i v ostatnich statech středni Evropy. Plosne zastoupeni v roce 2005 bylo 6,6 % z celkove plochy ceských a moravských lesů (Zprava o stavu lesa a lesniho hospodařstvi Ceske republiky, 2005). Za zakladni ukazatel kvality dřeva lze považovat hustotu dřeva, ktera významným způsobem ovlivňuje větsinu jeho fyzikalnich a mechanických vlastnosti. Průměrna hustota dřeva se v připadě buku pohybuje kolem 720 kg·m –3 při vlhkosti 12 % (Trendelenburg

Research Highlights: We applied neighborhood and dendro-ecological methods in a stand with a 33-year record of forest dynamics, finding that growth will decrease for several species under predicted climate trends. Background and Objectives: Conventional tree-ring analysis removes the influence of competition and size on growth, precluding assessment of the relative influence of these factors. An old-growth eastern hemlock forest in east&ndash, central New York was mapped in 1978 and was measured at eight-year intervals since then. Our objective was to use these data to examine the influence of climate, neighborhood, and tree size on radial growth. Materials and Methods: We evaluated an array of climatic indices to find which ones had the strongest influence on radial growth from increment cores of eastern hemlock (Tsuga canadensis L.), yellow birch (Betula alleghaniensis Britton), and sugar maple (Acer saccharum Marsh.). We used the strongest climatic indices in combination with neighborhood and target-tree size information to create growth models for the three tree species. Results: Size accounted for 2% to 21% of observed growth, the shade-tolerant sugar maple and eastern hemlock grew fastest when large, but the mid-tolerant yellow birch grew fastest when small. Competition accounted for 9% to 21% of growth, conifers had a weaker competitive effect than deciduous trees, and eastern hemlock was less sensitive to competition than sugar maple and yellow birch. Climate accounted for only 2% of growth variation, eastern hemlock showed a positive response to warming climate trends, but yellow birch and sugar maple showed negative responses. Conclusions: Predicted climate trends are likely to result in decreased growth of sugar maple and yellow birch, and the sensitivity of these species to competition suggests the effect will be exacerbated when they grow in crowded conditions.

An important question for our understanding of Roman history is how the Empire's economy was structured, and how long-distance trading within and between its provinces was organised and achieved. Moreover, it is still unclear whether large construction timbers, for use in Italy, came from the widespread temperate forests north of the Alps and were then transported to the sparsely-wooded Mediterranean region in the south. Here, we present dendrochronological results from the archaeological excavation of an expensively decorated portico in the centre of Rome. The oak trees (Quercus sp.), providing twenty-four well-preserved planks in waterlogged ground, had been felled between 40 and 60 CE in the Jura Mountains of north-eastern France. It is most likely that the wood was transported to the Eternal City on the Sao ^ne and Rho ^ne rivers and then across the Mediterranean Sea. This rare dendrochronological evidence from the capital of the Roman Empire gives fresh impetus to the ongoing debate on the likelihood of transporting timber over long distances within and between Roman provinces. This study reconstructs the administrative and logistic efforts required to transport high-quality construction timber from central Europe to Rome. It also highlights an advanced network of trade, and emphasises the enormous value of oak wood in Roman times

Tree-ring fire scars, tree ages, historical photographs, and historical surveys indicate that, for centuries, fire played different ecological roles across gradients of elevation, forest, and fire regimes in the Taos Valley Watersheds. Historical fire regimes collapsed across the three watersheds by 1899, leaving all sites without fire for at least 119 years. Historical photographs and quaking aspen (Populus tremuloides Michx.) ages indicate that a high-severity fire historically burned at multiple high-elevation subalpine plots in today&rsquo, s Village of Taos Ski Valley, with large high-severity patches (&gt, 640 ha). Low-severity, frequent (9&ndash, 29-year median interval) surface fires burned on the south aspects in nearby lower elevation dry conifer forests in all watersheds. Fires were associated with drought during the fire year. Widespread fires commonly burned synchronously in multiple watersheds during more severe drought years, preceded by wet years, including fire in all three watersheds in 1664, 1715, and 1842. In contrast, recent local &ldquo, large&rdquo, wildfires have only burned within single watersheds and may not be considered large in a historical context. Management to promote repeated low-severity fires and the associated open stand structures is within the historical range of variability in the dry conifer forests of these watersheds. In the high-elevation, subalpine forests, different management approaches are needed, which balance ecological and socioeconomic values while providing public safety.

Dendroclimatology and dendroecology have entered mainstream dendrochronology research in subtropical and tropical areas. Our study focused on the use of the chronology series of Masson pine (Pinus massoniana Lamb.), the most widely distributed tree species in the subtropical wet monsoon climate regions in China, to understand the tree growth response to ecological and hydroclimatic variability. The boosted regression trees (BRT) model, a nonlinear machine learning method, was used to explore the complex relationship between tree-ring growth and climate factors on a larger spatial scale. The common pattern of an asymptotic growth response to the climate indicated that the climate-growth relationship may be linear until a certain threshold. Once beyond this threshold, tree growth will be insensitive to some climate factors, after which a nonlinear relationship may occur. Spring and autumn climate factors are important controls of tree growth in most study areas. General circulation model (GCM) projections of future climates suggest that warming climates, especially temperatures in excess of those of the optimum growth threshold (as estimated by BRT), will be particularly threatening to the adaptation of Masson pine.

Forests around the world are subject to risk of high rates of tree growth decline and increased tree mortality from combinations of climate warming and drought, notably in semi-arid settings. Here, we assess how climate warming has affected tree growth in one of the world's most extensive zones of semi-arid forests, in Inner Asia, a region where lack of data limits our understanding of how climate change may impact forests. We show that pervasive tree growth declines since 1994 in Inner Asia have been confined to semi-arid forests, where growing season water stress has been rising due to warming-induced increases in atmospheric moisture demand. A causal link between increasing drought and declining growth at semi-arid sites is corroborated by correlation analyses comparing annual climate data to records of tree-ring widths. These ring-width records tend to be substantially more sensitive to drought variability at semi-arid sites than at semi-humid sites. Fire occurrence and insect/pathogen attacks have increased in tandem with the most recent (2007-2009) documented episode of tree mortality. If warming in Inner Asia continues, further increases in forest stress and tree mortality could be expected, potentially driving the eventual regional loss of current semi-arid forests.

Plasticity of xylem architecture can be a species specific strategy to reduce vulnerability to climate change. To study how the evergreen shrub Erica arborea regulates its xylem at different time scales as a response to climatic variability, we compared time series of annual xylem traits such as ring-width (growth), vessel size (hydraulic diameter and mean vessel area), vessel density, and potential conductivity (Kh) at two sites characterized by contrasting Mediterranean climates in Italy and Spain. Shrubs regulated their xylem in response to major differences in climate by modifying mostly their growth and vessel density. The different adjustment of xylem observed at the two sites was partly explained by the nonlinear nature of the relationship between the studied traits and temperature. Xylem development was mostly limited by low winter temperature at the cold and moist site, where plants produced more vessels per unit area of xylem and reduced growth in comparison with the warm and dry site. The responses of vessel size and density to climate were opposite. Vessel size and Kh were similar at the two sites and exhibited less sensitivity to climate than vessel density and growth. Humid conditions in spring increased growth and vessel size but decreased vessel density at the cold site, whereas the effect on xylem adjustment of high temperatures during the vegetation period was generally contrary to that of high moisture availability. These results likely express within species adaptations of the hydraulic function and the safety-efficiency trade-off in response to climate. A decline in growth in response to a recent decrease in precipitation at the dry site could be interpreted as a first sign of vulnerability to increasing drought severity. Similar to other species, climate change may have contrasting effects for E. arborea at its cold and dry distributional limits.

Terrestrial ecosystem plays a critical role in the global carbon cycle and climate system. Therefore, it is important to accurately quantify the carbon dynamics of terrestrial ecosystem under future climatic change condition. This dissertation evaluates the regional carbon dynamics by using upscaling approach, mechanistically-based biogeochemistry models and in situ and remotely sensed data. The upscaling studies based on FLUXNET network has provided us the spatial and temporal pattern of the carbon fluxes but it fails to consider the atmospheric CO2 effect given its important physiological role in carbon assimilation. In the second chapter, we consider the effect of atmospheric CO2 using an artificial neural network (ANN) approach to upscale the AmeriFlux tower of net ecosystem exchange (NEE) and the derived gross primary productivity (GPP) to the conterminous United States. We found that atmospheric CO 2effect on GPP/NEE exhibited a great spatial and seasonal variability. Further analysis suggested that air temperature played an important role in determining the atmospheric CO2 effects on carbon fluxes. In addition, the simulation that did not consider atmospheric CO2 failed to detect ecosystem responses to droughts in part of the US in 2006. The study suggested that the spatially and temporally varied atmospheric CO2 concentrations should be factored into carbon quantification when scaling eddy flux data to a region. The process-based ecosystem models are useful tools to predicting future change in the terrestrial ecosystem. However, they suffer the great uncertainty induced by model structure and parameters. The carbon isotope (13C) discrimination by terrestrial plants, involves the biophysical and biogeochemistry processes and exhibits seasonal and spatial variations, which may provide additional constraints on model parameters. In the third chapter, we found that using foliar 13C composition data, model parameters were constrained to a relatively narrow space and the site-level model simulations were slightly better than that without the foliar 13C constraint. The model extrapolations with three stomatal schemes all showed that the estimation uncertainties of regional carbon fluxes were reduced by about 40%. In addition, tree ring data have great potentials in addressing the forest response to climatic changes compared with mechanistic model simulations, eddy flux measurement and manipulative experiments. In the fourth chapter, we collected the tree ring isotopic carbon data at 12 boreal forest sites to develop a linear regression model, and the model was extrapolated to the whole boreal region to obtain the water use efficiency (WUE) and GPP spatial and temporal variation from 1948 to 2010. Our results demonstrated that most of boreal regions except parts of Alaska showed a significant increasing WUE trend during the study period and the increasing magnitude was much higher than estimations from other land surface models. Our predicted GPP by the WUE definition algorithm was comparable with site observation, while for the revised light use efficiency algorithm, GPP estimation was higher than site observation as well as land surface model estimates. In addition, the increasing GPP trends estimated by two algorithms were similar with land surface model simulations.