The demand for large-scale and long-term information on tree growth is increasing rapidly as environmental change research strives to quantify and forecast the impacts of continued warming on forest ...ecosystems. This demand, combined with the now quasi-global availability of tree-ring observations, has inspired researchers to compile large tree-ring networks to address continental or even global-scale research questions. However, these emergent spatial objectives contrast with paleo-oriented research ideas that have guided the development of many existing records. A series of challenges related to how, where, and when samples have been collected is complicating the transition of tree rings from a local to a global resource on the question of tree growth. Herein, we review possibilities to scale tree-ring data (A) from the sample to the whole tree, (B) from the tree to the site, and (C) from the site to larger spatial domains. Representative tree-ring sampling supported by creative statistical approaches is thereby key to robustly capture the heterogeneity of climate-growth responses across forested landscapes. We highlight the benefits of combining the temporal information embedded in tree rings with the spatial information offered by forest inventories and earth observations to quantify tree growth and its drivers. In addition, we show how the continued development of mechanistic tree-ring models can help address some of the non-linearities and feedbacks that complicate making inference from tree-ring data. By embracing scaling issues, the discipline of dendrochronology will greatly increase its contributions to assessing climate impacts on forests and support the development of adaptation strategies.
•Scaling issues complicate the growing use of tree rings in large-spatial analyses.•New tree-ring networks should represent and quantify forest growth across scales.•Forest plot and remote sensing data help account for non-climatic drivers of growth.•Hind- and forecasting tree growth requires broadly applicable mechanistic models.•Dendrochronology needs new quality criteria for the collection and scaling of data.
The imaging of wood samples using X-rays for the study of dendrochronology and densitometry is predominantly conducted through analog films subsequently digitized or, in more advanced instances, with ...expensive flat-panel systems characterized by resolutions on the order of tenths of microns. For this reason, this work proposes as an alternative the utilization of Commercial-Off-The-Shelf (COTS) complementary metal–oxide–semiconductor (CMOS) image sensors as affordable direct detectors for the acquisition of 10.2 μm resolution radiographic images, which represents sufficient resolution to observe the small structures formed by wood cells called tracheids. The raw images are subsequently processed to mitigate the impact of non-uniformities inherent in pixel response, including the total dose effects, and artifacts present in the image generated by irregularities and defects in the materials utilized to support the wood samples. Moreover, an exhaustive study of the sensor response over different x-ray tube voltage was performed, comparing the results obtained with a simple calculation model and finding a negligible contribution of the photons above the 20 keV. The model was developed based on diverse analyses of geometry and composition of the sensor, such as Focus Ion Beam, Scanning Electron Microscopy, and Time-of-Flight Secondary Ion Mass Spectrometry, and takes into account the X-ray beam attenuations and the photon interaction with the sensor. Finally, this model enables the estimation of the transmission based on the density and thickness of the wood samples.
•Applications of COTS CMOS image sensor as direct X-ray detectors•10 μm resolution radiographic images for wood dendrochronology and densitometry•Model developed to contrast results and simplify current wood densitometric methods
Though tree-ring chronologies are annually resolved, their dating has never been independently validated at the global scale. Moreover, it is unknown if atmospheric radiocarbon enrichment events of ...cosmogenic origin leave spatiotemporally consistent fingerprints. Here we measure the
C content in 484 individual tree rings formed in the periods 770-780 and 990-1000 CE. Distinct
C excursions starting in the boreal summer of 774 and the boreal spring of 993 ensure the precise dating of 44 tree-ring records from five continents. We also identify a meridional decline of 11-year mean atmospheric radiocarbon concentrations across both hemispheres. Corroborated by historical eye-witness accounts of red auroras, our results suggest a global exposure to strong solar proton radiation. To improve understanding of the return frequency and intensity of past cosmic events, which is particularly important for assessing the potential threat of space weather on our society, further annually resolved
C measurements are needed.
Determination of long-term tropical cyclone (TC) variability is of enormous importance to society; however, changes in TC activity are poorly understood owing to discrepancies among various datasets ...and limited span of instrumental records. While the increasing intensity and frequency of TCs have been previously documented on a long-term scale using various proxy records, determination of their poleward migration has been based mostly on short-term instrumental data. Here we present a unique treering–based approach for determination of long-term variability in TC activity via forest disturbance rates in northeast Asia (33–45°N). Our results indicate significant long-term changes in TC activity, with increased rates of disturbances in the northern latitudes over the past century. The disturbance frequency was stable over time in the southern latitudes, however. Our findings of increasing disturbance frequency in the areas formerly situated at the edge of TC activity provide evidence supporting the broad relevance of poleward migration of TCs. Our results significantly enhance our understanding of the effects of climate change on TCs and emphasize the need for determination of long-term variation of past TC activity to improve future TC projections.
Treeline shift and tree growth often respond to climatic changes and it is critical to identify and quantify their dynamics. Some regions are particularly sensitive to climate change and the Altai ...Mountains, located in Central and East Asia, are showing unequivocal signs. The mean annual temperature in the area has increased by 1.3-1.7 °C in the last century. As this mountain range has ancient and protected forests on alpine slopes, we focus on determining the treeline structure and dynamics. We integrated in situ fine-scale allometric data with analyses from dendrochronological samples, high-resolution 3D drone photos and new satellite images to study the dynamics and underlying causal mechanisms of any treeline movement and growth changes in a remote preserved forest at the Aktru Research Station in the Altai Mountain. We show that temperature increase has a negative effect on mountain tree growth. In contrast, only younger trees grow at higher altitudes and we document a relatively fast upward shift of the treeline. During the last 52 years, treeline moved about 150 m upward and the rate of movement accelerated until recently. Before the 1950s, it never shifted over 2150-2200 m a.s.l. We suggest that a continuous upward expansion of the treeline would be at the expense of meadow and shrub species and radically change this high-mountain ecosystem with its endemic flora. This documented treeline shift represents clear evidence of the increased velocity of climate change during the last century.
Ongoing climate warming has been demonstrated to impact the cryosphere in the Indian Himalayas, with substantial consequences for the risk of disasters, human well-being, and terrestrial ecosystems. ...Here, we present evidence that the warming observed in recent decades has been accompanied by increased snow avalanche frequency in the Western Indian Himalayas. Using dendrogeomorphic techniques, we reconstruct the longest time series (150 y) of the occurrence and runout distances of snow avalanches that is currently available for the Himalayas. We apply a generalized linear autoregressive moving average model to demonstrate linkages between climate warming and the observed increase in the incidence of snow avalanches. Warming air temperatures in winter and early spring have indeed favored the wetting of snow and the formation of wet snow avalanches, which are now able to reach down to subalpine slopes, where they have high potential to cause damage. These findings contradict the intuitive notion that warming results in less snow, and thus lower avalanche activity, and have major implications for the Western Himalayan region, an area where human pressure is constantly increasing. Specifically, increasing traffic on a steadily expanding road network is calling for an immediate design of risk mitigation strategies and disaster risk policies to enhance climate change adaption in the wider study region.
Widespread tree growth decline and absence of acorn production are observed in formerly coppiced Quercus pyrenaica stands. Attempts to convert oak coppices into high forests by thinning have failed ...to date, possibly due to the massive root system developed by trees after centuries of coppicing. We tested root trenching and stem girdling as silvicultural treatments to mitigate this hypothetical root-to-shoot imbalance and enhance the physiological performance of multi-stemmed clonal trees. We expected that severing the roots within a clone by trenching would reduce root respiratory carbon losses. Alternatively, stem girdling would increase carbon availability above the girdled zone, whilst the communal root system is maintained by non-girdled stems. After clonal structure delineation in a one-hectare experimental plot, root trenching and stem girdling were applied to stems belonging to different clones. Twig hydraulic traits, leaf water potential, non-structural carbohydrates (NSC) concentration in twigs, stems and roots, stem xylem CO2 as an indicator of root respiration, stem growth, and acorn production were discretely monitored up to 12 years after treatment application for comparison with control stems. Stem girdling led to short-term enhancements in NSC pools above the girdled zone. However, hydraulic dysfunction symptoms and canopy dieback were observed four years after girdling, eventually causing mortality. Root trenching initially increased root respiration and reduced stem growth without an apparent decline in the hydraulic function and NSC pools above-ground. Ten years after trenching, stem NSC increased while stem growth limitations diminished. Although not statistically significant, slight enhancements in acorn production were observed 6 and 12 years after trenching. We discourage stem girdling as a silvicultural practice to mitigate a root-to-shoot imbalance in abandoned oak coppices, as long-term detrimental effects outweighed potential benefits. Root trenching enhanced tree NSC above ground. However, such improvement may not offset the potential costs of root trenching.
•Trenching and girdling may help to mitigate the root-to-shoot imbalance in coppices.•Stem girdling is discouraged due to long-term detrimental effects.•Root trenching enhanced the availability of carbohydrates aboveground.
The chemical analysis of tree rings has attracted the interest of researchers in the past five decades in view of the possibility of exploiting this biological indicator as a widely available, ...high-resolution environmental archive. Information regarding the surrounding environment can be derived either by directly measuring environmental variables (nutrient availability, presence of pollutants, etc.) or by exploiting proxies (e.g. paleoclimatic and paleoenvironmental reconstructions). This review systematically covers the topic and provides a critical view on the reliability of dendrochemical information. First, we introduce the determinable chemical species, such as major elements, trace metals, isotopic ratios, and organic compounds, together with a brief description of their uptake mechanisms and functions in trees. Subsequently, we present the possibilities offered by analytical techniques in the field of tree ring analysis, focusing on direct methods and recent developments. The latter strongly improved the details of the accessible information, enabling the investigation of complex phenomena associated with plant life and encouraging the direct analysis of new analytes, particularly minor organic compounds. With regard to their applications, dendrochemical proxies have been used to trace several processes, such as environmental contamination, paleoclimate reconstruction, global environmental changes, tree physiology, extreme events, ecological trends, and dendroprovenance. Several case studies are discussed for each proposed application, with special emphasis on the reliability of tracing each process.
Starting from the reviewed literature data, the second part of the paper is devoted to the critical assessment of the reliability of tree ring proxies. We provide an overview of the current knowledge, discuss the limitations of the inferences that may be drawn from the dendrochemical data, and provide recommendations for the best practices to be used for their validation. Finally, we present the future perspectives related to the advancements in analytical instrumentation and further extension of application fields.
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•Dendrochemical proxies used to trace natural and human-induced processes are critically reviewed.•Direct methods for tree ring analysis and the commonly determined analytes are presented.•The reliability of dendrochemical proxies for different environmental applications is discussed.•Criteria to define reliable dendrochemical proxies are proposed.
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