Tree-ring Measurements Research Articles

Increasing Sensitivity of Tree Radial Growth to Precipitation

AbstractThe sensitivity of tree growth to precipitation regulates their responses to drought, and is a crucial metric for predicting ecosystem dynamics and vulnerability. Sensitivity may be changing with continuing climate change, yet a comprehensive assessment of its change is still lacking. We utilized tree ring measurements from 3,044 sites, climate data and CO2 concentrations obtained from monitoring stations, combined with dynamic global vegetation models to investigate spatiotemporal changes in the sensitivity over the past century. We observed an increasing sensitivity since around 1950. This increased sensitivity was particularly pronounced in arid biomes due to the combined effect of increased precipitation and elevated CO2. While elevated CO2 reduced the sensitivity of the humid regions, the intensified water pressure caused by decreased precipitation still increased the sensitivity. Our findings suggest an escalating vulnerability of tree growth to precipitation change, which may increase the risk of tree mortality under future intensified drought.

Dendrochronology with a medical X-ray photon counting computed tomography scanner

Dendrochronology traditionally involves invasive techniques that might harm cultural heritage artifacts. Non-invasive approaches using X-ray technology and computed tomography (CT) have emerged, but dedicated CT systems are limited in availability. This study explored the viability of using a recently developed photon counting medical CT scanner for growth ring analysis. Six wood samples from pine, oak and beech with varying growth rates were studied. Comparisons were made between traditional methods and CT scanning with measurements performed on the untreated surface, a prepared surface and on CT images. For samples with annual rings wider than 0.3–0.4 mm, CT scanning performed well, while samples with thinner rings or indistinct ring boundaries presented challenges. The combination of traditional tree-ring measurements and analyses of CT scanned images might be a superior study approach generating extra data and information.

A new method of high-resolution NPP estimation and its implementation in caragana shrublands on the Loess Plateau, China

ABSTRACT Accurate estimation for vegetation net primary production (NPP) at high resolution is essential for ecosystem management and at local to global scales. However, no reliable methods are available to achieve fine-resolution estimation. In this study, a new NPP estimation system was developed by integrating high spatial resolution remote sensing images, tree ring measurements, and process-based model CASA. The system was illustrated by estimating the historical NPP of caragana shrublands from 2011 to 2021 in Dingbian County, China. The results showed that: (1) by employing the biomass model and tree ring measurements, an NPP-crown width model was established to enable a large number of samples for calibrating the CASA model on high spatial resolution images without continuous field measurements. The calibrated parameters, including maximum NDVI, minimum NDVI, and maximum light use efficiency, were determined to be 0.415, 0.022 and 0.025, respectively; (2) according to the estimation by the calibrated CASA model, the NPP in Dingbian County revealed an increasing trend from 2011 to 2021, and the NPP in southern hilly and gully regions was significantly higher than the other regions; (3) among the different indices, max temperature of warmest month had a significant negative effect on the NPP of cagarana shrublands, whereas annual precipitation had a positive effect. In the northern and central regions, air temperature predominantly influenced NPP, while in the southern regions, both temperature and precipitation played a joint role. The implementation in this study illustrated that the NPP estimation system could provide reliable NPP with high resolution and efficient to monitor and detect dominant factors affecting NPP for ecosystem management.

A python package implementing Direct Reconstruction Technique (DIRECT) for dendroclimatological studies

The DIrect REConstruction Technique (DIRECT) is a dendroclimatological method that constructs a climatic response surface to account for changes of climatic response with tree age. This surface is then used as a transfer function for climatic reconstructions. Unlike widely-used standardization methods such as the traditional curve-fitting approach, the regional curve standardization, and their signal-free modifications that perform detrending explicitly, DIRECT accounts for age-size related trend in tree-ring measurements by construction of the response surface dependent on two variables: tree-ring parameter (width, blue intensity etc.) and cambial age. The method is capable of taking into account nonlinear climatic response of trees and differing response of younger and older trees. Here we describe an application of the newly developed open-source Python package that implements DIRECT (https://github.com/Gr1Lo/direct) to one real and one theoretical dataset. The package consists of functions for reading the initial data, constructing a response surface, and for reconstructing climate variables via this surface. The functions for visual assessment of the initial data and for the estimation and selection of parameters for constructing the response surface are also presented. Also here we provide a comparison of the DIRECT method with traditional standardization-reconstruction routines.

Growth responses to climate warming and their physiological mechanisms differ between mature and young larch trees in a boreal permafrost region

The effects of tree age-related intrinsic water-use efficiency (iWUE) under climate change such as warming and rising atmospheric CO2 concentrations (Ca) on tree growth are still poorly understood. We measured tree-ring δ13C, δ18O, tree-ring width, and their relationships with climate variables, calculated iWUE for relatively young (90 ± 5 yr) and mature (230 ± 40 yr) Larix dahurica trees in a boreal permafrost region in northeastern China. The period of tree-ring measurements covering 70 years includes a pre-warming period (1951–1984; base period) and a warm period (1985–2018; warm period). The growth rate of both mature and young trees did not change with time over the base period, while the mature trees but not the young ones significantly increased the growth rate with time over the warm period. The iWUE of mature trees consistently increased from 1951 to 2018, whereas that of the young trees increased only with time during the warm period from 1985 to 2018. The tree-ring δ13C and δ18O were not correlated for both young and mature trees over both base and warm periods, except for a significantly positive correlation between tree-ring δ13C and δ18O for mature trees during the warm period. We found that mature trees were more sensitive to Ca than young trees. Our results suggest that mature trees have a more ‘conservative’ (low stomatal conductance (gs), constant assimilation rate (A)) water use strategy than young trees (constant gs, high A) in the permafrost regions in a warming world.

Covariation between oxygen and hydrogen stable isotopes declines along the path from xylem water to wood cellulose across an aridity gradient.

Oxygen and hydrogen isotopes of cellulose in plant biology are commonly used to infer environmental conditions, often from time series measurements of tree rings. However, the covariation (or the lack thereof) between δ18 O and δ2 H in plant cellulose is still poorly understood. We compared plant water, and leaf and branch cellulose from dominant tree species across an aridity gradient in Northern Australia, to examine how δ18 O and δ2 H relate to each other and to mean annual precipitation (MAP). We identified a decline in covariation from xylem to leaf water, and onwards from leaf to branch wood cellulose. Covariation in leaf water isotopic enrichment (Δ) was partially preserved in leaf cellulose but not branch wood cellulose. Furthermore, whilst δ2 H was well-correlated between leaf and branch, there was an offset in δ18 O between organs that increased with decreasing MAP. Our findings strongly suggest that postphotosynthetic isotope exchange with water is more apparent for oxygen isotopes, whereas variable kinetic and nonequilibrium isotope effects add complexity to interpreting metabolic-induced δ2 H patterns. Varying oxygen isotope exchange in wood and leaf cellulose must be accounted for when δ18 O is used to reconstruct climatic scenarios. Conversely, comparing δ2 H and δ18 O patterns may reveal environmentally induced shifts in metabolism.

Non-destructive Dendrochronology: The Effect of Conservation Agents on Tree-ring Measurements in Archaeological Oak with Micro-computed Tomography

ABSTRACT The effect of different conservation methods on non-destructive dendrochronology with micro-computed tomography (μCT) of waterlogged archaeological wood (WAW) was assessed. To this end, oak samples were conserved with alcohol-ether-resin, Kauramin 800®, lactitol/trehalose, saccharose, silicone oil and different polyethylene glycol (PEG) treatments with subsequent freeze-drying. Tree-ring measurements were compared with respect to the number of rings and the mean ring width using (a) an analog linear measuring table and (b) the digital μCT. Overall, the measurements in the μCT data agreed very well with the corresponding microscopic measurements. It was possible in all cases to recognize the rings in the samples with μCT. A dendrochronological cross dating with regional absolutely dated oak ring width chronologies was successful. However, the varying influence of conservation agents on the quality of the μCT data were also evident. To quantify this influence, the contrast in the μCT data were calculated using gray-scale profiles. An influence on the contrast in the μCT data were detectable for all conservation agents. The contrast is especially reduced due to conservation methods using lactitol/trehalose, PEG, saccharose and silicone oil. Overall, the experiments confirm, though, that μCT is a powerful and accurate tool for dendrochronology of conserved archaeological oak objects.

Non-destructive dendrochronology with X-ray computed tomography: The influence of different conservation methods for waterlogged archaeological wood

In this study, the influence of different conservation methods for waterlogged archaeological wood (WAW) on non-destructive dendrochronological dating by micro-computed tomography (µCT) was evaluated. For this purpose, samples of different wood species were conserved using the following methods: alcohol-ether-resin, Kauramin 800®, lactitol/trehalose, saccharose, silicone oil and different polyethylene glycol (PEG) treatments with subsequent freeze-drying. The tree ring measurements of all samples in the digital µCT data were compared with the measurements on an analog linear measuring table in terms of the total number of rings per sample and the mean ring width. The year-to-year ring width measurements in the µCT data agreed very well overall with the corresponding microscopic measurements. It was possible to detect the rings in the samples with µCT in all cases. A dendrochronological cross dating with regional absolutely dated ring width chronologies was successful in two cases. However, the different influence of the conservation agents on the quality of the µCT data was clearly visible. In order to assess this influence, the contrast in the µCT data was determined using grey-scale profiles. A decrease in contrast in the µCT data was detectable for all conservation agents. A particular strong influence is observed for the conservation methods using silicone oil, lactitol/trehalose, PEG and saccharose. Overall, the study performed confirms that µCT is a powerful and accurate method for non-destructive dendrochronology of conserved archaeological objects.

The Longevity of Fruit Trees in Basilicata (Southern Italy): Implications for Agricultural Biodiversity Conservation

In the Mediterranean basin, agriculture and other forms of human land use have shaped the environment since ancient times. Intensive and extensive agricultural systems managed with a few cultured plant populations of improved varieties are a widespread reality in many Mediterranean countries. Despite this, historical cultural landscapes still exist in interior and less intensively managed rural areas. There, ancient fruit tree varieties have survived modern cultivation systems, preserving a unique genetic heritage. In this study, we mapped and characterized 106 living fruit trees of ancient varieties in the Basilicata region of southern Italy. Tree ages were determined through tree ring measurements and radiocarbon analyses. We uncovered some of the oldest scientifically dated fruit trees in the world. The oldest fruit species were olive (max age 680 ± 57 years), mulberry (647 ± 66 years), chestnut (636 ± 66 years), and pear (467 ± 89 years). These patriarchs hold a unique genetic resource; their preservation and genetic maintenance through agamic propagation are now promoted by the Lucan Agency for the Development and Innovation in Agriculture (ALSIA). Each tree also represents a hub for biodiversity conservation in agrarian ecosystems: their large architecture and time persistence guarantee ecological niches and micro-habitats suitable for flora and fauna species of conservation significance.

Using 14C of tree rings to study CO2 emissions from fossil sources at the sampling point of the Meteorological Tower in Beijing

Atmospheric fossil fuel CO2 information is an important reference for local government to formulate energy-saving and emission reduction in Beijing. We present a reconstruction of the fossil fuel CO2 mole fraction from 2007 to 2014 near the Beijing meteorological tower using AMS to measure 14C of cedar tree rings. The results show that the mole fraction of fossil fuel CO2 at the sampling point first decreased from 22.3 ± 0.7 ppm (2007) to 21.0 ± 0.9 ppm (2008), then increased to 22.5 ± 0.9 ppm (2010), and finally decreased to 18.7 ± 0.7 ppm (2014). This trend correlates (r = 0.958, p < 0.01) well with one third (May-August) of fossil source consumption of secondary industry in Beijing during 2007–2014. It is attributed to environmental policy programs and control measures at local scope in Beijing during 2007–2014. This study suggests that 14C measurements of tree rings by AMS provide an effective method to evaluate the effect of the environmental policies.

Combining conventional tree-ring measurements with wood anatomy and strontium isotope analyses enables dendroprovenancing at the local scale

Dendroprovenancing provides critical information regarding the origin of wood, allowing further insights into economic exploitation strategies and source regions of timber products. Traditionally, dendroprovenancing relies on pattern-matching of tree rings, but its spatial resolution is limited by the geographical coverage of species-specific chronologies available for crossdating and, in the case of short-distance trades, by scarce environmental variability. Here, we present an approach to provenance timber with high spatial resolution from forested areas that have been exploited intensively throughout history, with the aim to understand the sustainability of the various woodland management practices used to supply timber products. To this end, we combined tree-ring width (TRW), wood anatomical and geochemical analyses in addition to multivariate statistical validation procedures to trace the origin of living oak trees (Quercus robur) sampled in four stands located within a 30-km radius around the city of Limoges (Haute-Vienne, France). We demonstrate that TRW and wood anatomical variables (and in particular cell density) robustly discriminate the eastern from the western site, while failing to trace the origin of trees from the northern and southern sites. Here, strontium isotopic ratios (87Sr/86Sr) and Ca concentrations identify clusters of trees which could not be identified with TRW or wood anatomy. Ultimately, our study demonstrates that the coupling of wood anatomy with geochemical signatures allows to correctly pinpoint the origin of trees. Given the small geographic scale of our study and the limited differences in elevation and climate between study sites, our results are particularly promising for future dendroprovenancing studies. We thus conclude that the combination of multiple approaches will not only increase the accuracy of dendroprovenancing studies at local scales, but could also be implemented at much larger scales to identify trends in historic timber supply throughout Europe.

Growth response of four dominant conifer species in moist temperate region of Pakistan (Ayubia National Park)

Dendrochronological potential of conifers from Ayubia National Park, Pakistan was determined. A total of four conifer species (Abies pindrow (Royle ex D. Don), Cedrus deodara (Roxb. ex D. Don), Pinus wallichiana A.B. Jacks. and Taxus baccata L.) were studied from different elevations. Comparative analysis of DBH-growth rate and DBH-age were performed among the species with maximum age showed by A. pindrow of 456 years with 0.01 cm/year growth rate. P. wallichiana was found to be fast growing with 0.05 cm/year growth among other species while C. deodara trees were having the strongest correlation between their age and DBH values (R2= 0.9225). Quality of cross dating and accuracy of tree ring measurements was checked by COFECHA. Mean sensitivity of all species ranges from 0.265 to 0.328 with auto-correlations range from 0.562 to 0.712 which specified the dendrochronological significance of these conifers. ARSTAN program was used for autoregressive modeling to remove any possible variance other than climatic disturbance and to standardize the tree ring chronologies. Tree-ring variations were evident among all the cores possessing distinct wide and narrow fluctuations of ring growth with A. pindrow (Avg. mean ring width = 1.46 mm) and T. baccata (Avg. mean ring width = 1.80 mm). All the conifer species showed good climatic signals in their tree ring measurements and are valuable for the dendroclimatic growth response investigations.

From lakes to ratios: 14C measurement process of the Finnish tree-ring research consortium

Annual and sub-annual tree-ring 14C measurements allow the study of past natural phenomena such as rapid 14C increases and solar behavior. In addition, they provide precise calibration data sets that help in improving the dating accuracy of past natural and cultural events. However, for the data to be comparable, it is important that laboratories describe the whole process from sample retrieval to eventual results. In this paper, we describe the full 14C measurement procedure adopted in the Finnish tree-ring consortium, including sample collection and preparation, dendrochronology, chemical pretreatment, combustion and graphitization, Accelerator Mass Spectrometry (AMS) measurements and data processing. In addition, we report the 14C background components for our traditional Closed-Tube Combustion (CTC) and Elemental Analyzer (EA) based processes, both yielding to high-quality data. Furthermore, we study the mass-dependence effects of tree-ring measurements and find them to be practically insignificant for ages up to several millennia but growing in significance when approaching the 14C limit.

Early–latewood carbon isotope enhances the understanding of the relationship between tree biomass growth and forest-level carbon fluxes

Eddy covariance (EC) and biometric (based on tree diameter and tree ring measurements) methods are used extensively to estimate annual variability in forest productivity. Many previous studies obtained inconsistent findings between net ecosystem productivity (NEP) based on EC (NEPEC) and tree biomass growth based on biometric methods, partly because of delayed responses in trees due to temporary non-structural carbohydrate (NSC) storage. Direct measurement of the amount of NSCs stored in trees is challenging; however, using carbon (C) isotope ratios in different tree components is considered an indirect and effective alternative approach for assessing NSC dynamics. We measured stable C isotope ratios in earlywood (EW) and latewood (LW) of rings of 70 trees (categorized as 4–10, 10–20, and > 20 cm diameter at breast height [DBH]) to test relationships between trunk-growth NEPEC time series and annual tree biomass growth (based on tree ring width) in a young mixed forest in northern China over 13 years. Our results revealed a strong correlation (r = 0.691) between trunk-growth NEPEC (March–August in a calendar year) and tree biomass growth. The change in correlation between current-year EW δ13C and LW δ13C of the previous year observed in trees with 10–20 cm DBH, which accounted for 51.8% of the total tree biomass growth, was consistent with the synchronicity of trunk-growth NEPEC and tree biomass growth. Colder early growing seasons, which significantly increase the reliance of early-season structural growth on stored labile C accumulated in the previous year, may lead to postponed tree biomass growth responses related to NEPEC. In conclusion, this approach, investigating C isotope analysis in EW and LW, helps elucidate the relationships between tree biomass growth and stand-level C fluxes in forest sites.

Combining Conventional Tree-Ring Measurements with Wood Anatomy and Strontium Isotope Analyses Enables Dendroprovenancing at the Local Scale

Combining Conventional Tree-Ring Measurements with Wood Anatomy and Strontium Isotope Analyses Enables Dendroprovenancing at the Local Scale

Temporal connections between long-term Landsat time-series and tree-rings in an urban–rural temperate forest

Time-series of satellite-derived vegetation proxies and tree-rings widths (TRW) are similar, providing temporal records of forest productivity change from different perspectives and processes. Previous research on this relationship has focused on temperature or moisture limited coniferous forests, using lower spatial resolution (e.g., 8000 m) satellites and normalized difference vegetation index (NDVI) to test relationships over 15–30 years. There is an opportunity to leverage recent advances in building Landsat (30 m) time-series to expand comparisons into new forest types (e.g., coniferous vs. deciduous), areas (e.g., fragmented forests) and over longer periods (e.g., nearly 50 years). However, a better understanding of factors that influence relationship strength is required. We compared tree-ring measurements, converted to a ring width index (RWI), and Landsat tasseled cap angle (TCA) derived canopy cover (CC) from 1972 to 2018 across 16 deciduous, mixed, and coniferous stands in southern Ontario, Canada. For all chronologies, overall relationship strength was assessed with correlation approaches (RWI-CC, both vs. climate), and shorter-term increase-decline trends were compared with segmented regression. There were significant forest type differences, with coniferous chronologies correlating stronger with CC than deciduous. Deciduous chronologies and CC had opposite connections with summer temperature, with climate warming increasing CC and coniferous RWI but not deciduous RWI from 1980 to 2010. More recent decline at most sites appears related to a major ice storm, but multiple factors may be coexisting. We tested the utility of tree-rings for validating nearly 50 years of Landsat-observed change in urban–rural temperate forests, identifying useful connections at coniferous sites. However, there are limitations to comparing long-term Landsat time-series (based on yearly summer data) with annual tree-ring growth.

EVOLUTION OF RADIOCARBON CALIBRATION

ABSTRACTIn the late 1950s it was recognized that levels of atmospheric radiocarbon (14C) had not been constant over time. Since then, researchers have sought to document those changes, initially through measurements of known age tree rings and more recently using other archives to create curves to correct or calibrate radiocarbon ages to calendar ages. This paper highlights some, but by no means all, of the efforts to create and extend radiocarbon calibration curves.

Comparing automatically generated and manually measured tree-ring transects of growth trends with Hawaiian sandalwood as an example species

Tree-ring measurements are a primary quantitative tool used in numerous scientific disciplines. Some species, however, exhibit morphological complexities leading to significant uncertainty in these measurements. Hawaiian Sandalwood (Santalum paniculatum) stems, for example, often develop asymmetric growth features that hinder tree-ring measurements. These features include faint-ring boundaries and wedging rings which disappear in portions of the cross-section. In this work we a use a novel two-dimensional transect methodology and our own open-source software, svg-dendro, to analyze particularly difficult cross-sections. Our method accomplishes this by first tracing all rings by hand and automatically generating a user-specified number of transects. On average, these traced measurements had more sensitivity to tree-ring variability without losing important equivalencies with the traditional binocular stereomicroscope technique (e.g., radii, skewness) as indicated by greater mean variance for ring number, mean tree-ring width, and standard deviation. All S. paniculatum samples had ring wedging, where certain sides of the stem had many locally absent tree rings but to different intensities. The new technique allows us to analyze the shift from complete rings with little to no wedging to rings with more wedging starting between the 19th and 40th ring, where deep stem lobes begin forming. The new method also reveals the difficulty in measuring these trees, as the wedging creates multiple lobes with different visible ring counts. This research suggests that this two-dimensional methodology would be best applied to non-circular trees with fewer incomplete rings, supporting the importance of species and population selection. Overall, we have developed an efficient and flexible means to measure otherwise unmeasurable growth features in tree samples through representing tree-ring boundaries as curves and developing software to sort and map transects.

A Tree Ring Measurement Method Based on Error Correction in Digital Image of Stem Analysis Disk

Stem analysis is an essential aspect in forestry investigation and forest management, as it is a primary method to study the growth law of trees. Stem analysis requires measuring the width and number of tree rings to ensure the accurate measurement, expand applicable tree species, and reduce operation cost. This study explores the use of Open Source Computer Vision Library (Open CV) to measure the ring radius of analytic wood disk digital images, and establish a regression equation of ring radius based on image geometric distortion correction. Here, a digital camera was used to photograph the stem disks’ tree rings to obtain digital images. The images were preprocessed with Open CV to measure the disk’s annual ring radius. The error correction model based on the least-square polynomial fitting method was established for digital image geometric distortion correction. Finally, a regression equation for tree ring radius based on the error correction model was established. Through the above steps, click the intersection point between the radius line and each ring to get the pixel distance from the ring to the pith, then the size of ring radius can be calculated by the regression equation of ring radius. The study’s method was used to measure the digital image of the Chinese fir stem disk and compare it with the actual value. The results showed that the maximum error of this method was 0.15 cm, the average error was 0.04 cm, and the average detection accuracy reached 99.34%, which met the requirements for measuring the tree ring radius by stem disk analysis. This method is simple, accurate, and suitable for coniferous and broad-leaved species, which allows researchers to analyze tree ring radius measurement, and is of great significance for analyzing the tree growth process.

A national tree-ring data repository for Canadian forests (CFS-TRenD): structure, synthesis, and applications

Understanding the magnitude and cause of variation in tree growth and forest productivity is central to sustainable forest management. Measurements of annual growth rings allow assessments of individual-tree, tree population, and forest ecosystem vulnerabilities to drought stress or other changing forest disturbance regimes (insects, diseases, fire), which can be used to identify areas at greatest risk of forest losses. Given a heightened demand for tree-ring data, we consolidated and synthesized tree-ring studies and datasets gathered over the past 30 years in Canada by scientists with the Canadian Forest Service and research partners. We incorporated these datasets into a data repository that currently contains tree-ring measurements from 40 206 tree samples from 4594 sites and 62 tree species from all Canadian provinces and territories. Through our synthesis, we demonstrate the value of such large ensembles of tree-ring data for identifying patterns in tree growth over large spatial scales by mapping pan-Canadian drought sensitivity. Overall, we found high coherence in the samples analyzed; low coherence was generally limited to data-poor regions and species. Drought sensitivity was widespread across species and regions: 34% of sampled trees displayed a significant positive relationship between annual growth increment and summer soil moisture index. Dependence upon water availability in species Picea mariana (Mill.) BSP, Pinus banksiana Lamb., Pinus contorta Douglas ex Loudon, and Pseudotsuga menziesii (Mirb.) Franco was more strongly expressed in the warmest regions of the species’ range; for species Picea glauca (Moench) Voss and Populus tremuloides Michx., drought sensitivity was stronger in the driest regions. This unprecedented consolidation and synthesis of tree-ring data will enable new research initiatives (e.g., meta-analyses) aimed at improved understanding of the drivers, patterns, and implications of changes in tree growth, as well as facilitating new research collaborations in earth and environmental sciences. Among other things, there is a need for expanding the spatial distribution of sites across Canada’s northern regions, increasing the number of samples collected from older stands and angiosperm species, and integrating datasets from studies that evaluate the effects of silvicultural experiments, including provenance and progeny trials, on tree growth.