International Tree-Ring Data Bank Research Articles

Validation of global precipitation time series products against tree ring records and remotely sensed vegetation greenness.

Global interpolated climate products are widely used in ecological research to investigate biosphere-climate interactions and to track ecological response to climate variability and climate change. In turn, biological data could also be used for an independent validation of one aspect of climate data quality. All else being equal, more variance explained in biological data identifies the better climate data product. Here, we compare seven global precipitation time series products, including gauge-based datasets (CRU-TS, UDEL-TS, GPCC), re-analysis products (ERA5, CHELSA), a satellite-based dataset (PERSIANN) and a multi-source product that draws on gauge, re-analysis, and satellite data (MSWEP). We focus on precipitation variables, because they are more difficult to interpolate than temperature, and show larger divergence among gridded data products. Our validation is based on 20 years of remotely sensed vegetation greenness (MODIS-EVI) and 120 years of tree ring records from the International Tree Ring Data Bank (ITRDB). The results for the 20-year EVI based validation shows that all gauge and re-analysis data products performed similarly, but were outperformed by the multi-source MSWEP product, especially in regions with low weather station coverage, such as Africa. For analyzing long 120-year time-series, UDEL-TS showed superior performance prior to the 1940s, with especially large margins for northern Asia and the Himalayas region. For other regions, CRU-TS and GPCC could be recommended. We provide maps that can guide the best regional choice of climate product for research involving time series of biological response to historic climate variability and climate change.

The International Tree-Ring Data Bank at Fifty: Status of Stewardship for Future Scientific Discovery

The International Tree-Ring Data Bank at Fifty: Status of Stewardship for Future Scientific Discovery

Trends in Atmospheric CO2 Fertilization Effects with Stand Age Based on Tree Rings

The increase in global carbon emissions has intensified the effects of CO2 fertilization on the carbon cycle. CO2 fertilization is shaped by several factors, including the physiological differences among trees of varied forest ages and types, as well as the influence of different climatic conditions. It is essential to investigate the differences in CO2 fertilization effects across diverse climate zones and delve into the association between these effects and forest age and type. Such exploration will deepen our knowledge of forest responses to environmental changes. This study used annual ring width data from the International Tree-Ring Data Bank, employing the generalized additive mixed models and the Random Forest model to discern the pattern of the CO2 fertilization effect concerning forest age in the Northern Hemisphere. This study also explored the variations in the effect of CO2 fertilization across unique climate zones and the disparities among various forest types within the same climatic zone. The results indicated a link between forest age and the CO2 fertilization effect: it tends to increase in sapling forests and middle-aged forests and diminish in mature forests. Warmer, drier environments had a more marked effect of increased CO2 on tree fertilization. Additionally, coniferous forests demonstrated a more substantial CO2 fertilization effect than broadleaf forests, and deciduous needle-leaf forests surpassed evergreen needle-leaf forests in this regard. This research is pivotal in understanding the shifting patterns of CO2 fertilization effects and how forests respond to atmospheric changes.

Ecosystems dynamics and environmental management: An NDVI reconstruction model for El Alto-Ancasti mountain range (Catamarca, Argentina) from 442 AD through 1980 AD

Vegetation dynamics play a crucial role in understanding the complex interactions between climate variability, ecosystem changes and human land use. In this study, we use the Hindcasting Ecosystems Model (HEMO) to reconstruct the paleo Normalized Difference Vegetation Index (paleo-NDVI), which provides valuable insights into the historical vegetation patterns. Our research focuses on the El Alto Ancasti mountain range, a region characterized by its rich environmental diversity, and archaeological evidence of pre-Hispanic agricultural village landscapes, showcasing the knowledge and management of diverse environments and their fluctuations.To reconstruct the paleo-NDVI, we employed a Neuronal Network trained with two datasets. First, we utilized NDVI data extracted from AVHRR/NOAA satellite images spanning from 1982 to 2015, representing 8 km pixels from the Global Inventory Modeling and Mapping Studies. Second, we incorporated growth ring chronologies from Northwest Argentina sourced from the International Tree Ring Data Bank, enabling the calibration of the NDVI-ring relationship. This methodology allowed us to reconstruct the paleo-NDVI back to 442 AD and to calculate anomalies.Our analysis revealed significant negative anomalies around 600 AD, coinciding with previous research conducted in the nearby Ambato valley. These anomalies may be attributed to the eruption of Tres Cruces volcano in Catamarca during that period. Additionally, extensive positive anomalies emerged from 1600 AD onwards, which align with anomalies detected in earlier studies. The eruption of Huaynaputina volcano in southern Peru in 1600 AD is a possible factor contributing to these positive anomalies.Ongoing investigations focusing on the paleoenvironment and human occupations in the El Alto-Ancasti area aim to provide further insights into how these detected changes could have influenced environmental management decisions. By integrating multidisciplinary approaches, we can better comprehend the complex relationship between vegetation dynamics, climatic events and human activities, ultimately enhancing our understanding of past environmental transformations and their implications for sustainable management strategies.

Comparing the impact of live-tree versus historic-timber data on palaeoenvironmental inferences in tree-ring science, eastern North America

Dendroarchaeological data from historic structures and artefacts have the potential to extend tree-ring chronologies spatially and temporally, especially where old-growth forests have been extensively modified or harvested. While these data may contribute to an improved understanding of past climate and ecology, critical differences in the properties of live-tree and historic-timber data might affect results and interpretations of large-scale studies, such as those relying on large datasets from public databases like the International Tree-Ring Data Bank (ITRDB). The objective of this work was to compare summary measures of live-tree versus historic-timber datasets likely to affect outcomes and inferences of typical paleoenvironmental applications. We used 99 live-tree (LT) and 41 historic-timber (HT) datasets collected in the Appalachian region of the eastern United States and compared common analytical measures for understanding past climate and ecology, including temporal coverage, species composition, recruitment patterns, segment length, series coherence/mean interseries correlation (as Rbar), expressed population signal (EPS), subsample signal strength (SSS) and response to drought and extreme climate events. We found that tree-ring data from historic timbers record some ecological events similarly to live trees and are sensitive to some climate conditions, with important caveats related to the influence of site and tree selection on analytical measures. In some cases, these caveats can be overcome through improved collection of metadata and additional analyses. In all cases, potential differences in LT and HT data should be considered by those who perform large-scale analyses using public tree ring databases, especially as more scientists contribute historic-timber datasets.

Quantitative analysis of multiple forest disturbances and their compound influences on tree growth in the western U.S.

As the frequencies of extreme weather increase, forest ecosystems experience stronger influences from various disturbances. Previous research focuses on single disturbances or qualitative analysis of overlaid effects from two disturbances. Studies rarely explored the interactions between three or more disturbances, especially mechanisms behind the multiple disturbances. Our study covered four states (Idaho, Montana, Wyoming, and Utah) in the U.S. which shared similar climate patterns and vegetation distributions. We collected 241 chronologies from the International Tree-Ring Data Bank (ITRDB) and our own field expeditions. We assigned each tree ring to eight possible disturbance combinations. From the correlations between tree indices and climate (monthly temperature and total precipitation), the radial growth of tree rings showed a significant positive correlation with summer precipitation and a negative correlation with summer temperature. With three-factor ANOVA and one-way ANOVA, we ranked the impacts of each disturbance and combination of disturbances on tree growth based on tree-ring index; control (1.038) > insect (1.029) > fire (1.008) > fire & insect (0.963) > drought & insect (0.918) > drought (0.890) > drought, fire & insect (0.803) > drought & fire (0.784). We found that in most cases, the combined impact from two disturbances was larger than the impacts from single disturbances with the inclusion-exclusion principle. This research quantitatively revealed the interactions between disturbances and evaluated the effects from a combination of multiple disturbances.

Maximum tree lifespans derived from public-domain dendrochronological data.

The public-domain International Tree-Ring Data Bank (ITRDB) is an under-utilized dataset to improve existing estimates of global tree longevity. We used the longest continuous ring-width series of existing ITRDB collections as an index of maximum tree age for that species and site. Using a total of 3,689 collections, we obtained longevity estimates for 237 unique tree species, 157 conifers and 80 angiosperms, distributed all over the world. More than half of the species (167) were represented by no more than 10 collections, and a similar number of species (144) reached longevity greater than 300 years. Maximum tree ages exceeded 1,000 years for several species (22), all of them conifers, whereas angiosperm longevity peaked around 500 years. Given the current emphasis on identifying human-induced impacts on global systems, detailed analyses of ITRDB holdings provide one of the most reliable sources of information for tree longevity as an ecological trait.

Growth plasticity of conifers did not avoid declining resilience to soil and atmospheric droughts during the 20th century

BackgroundPlasticity in response to environmental drivers can help trees cope with droughts. However, our understanding of the importance of plasticity and physiological adjustments in trees under global change is limited. MethodsWe used the International Tree-Ring Data Bank (ITRDB) to examine 20th century growth responses in conifer trees during (resistance) and following (resilience) years of severe soil and atmospheric droughts occurring in isolation or as compound events. Growth resilience indices were calculated using observed growth divided by expected growth to avoid spurious correlations, in which the expected values were obtained by the autoregressive moving average (ARIMA) model. We used high atmospheric vapour pressure deficit (VPD) to select years of atmospheric drought and low annual values of the Standardized Precipitation-Evapotranspiration Index (SPEI) to select years with soil drought. We acquired the sensitivities (i.e., the slopes of the relationships) by fitting the resilience indices as a function of environmental drivers, and assessed how these sensitivities changed over time for different types of drought events using linear mixed models. We also checked whether plasticity in growth responses was sufficient to prevent long-term trends of growth reductions during or after severe droughts. We acknowledge that by focusing on the response of surviving trees from the ITRDB we are potentially biasing our results towards higher resilience, as stand level responses (e.g., mortality) may result in lowered competition after the disturbance event. ResultsSensitivities of resilience to VPD and SPEI changed throughout the 20th century, with the directions of these changes often reversing in the second half of the century. For the 1961–2010 period, changing sensitivities had positive effects on resilience, especially following years of high-VPD and compound events, avoiding growth losses that would have occurred if sensitivities had remained constant. Despite sensitivity changes, resilience was still lower at the end of the 20th century compared to the beginning of the century. ConclusionsFuture adjustments to low-SPEI and high-VPD events are likely to continue to compensate for the trends in climate only partially, leading to further generalized reductions in tree growth of conifers. An improved understanding of these plastic adjustments and their limits, as well as potential compensatory processes at the stand level, is needed to project forest responses to climate change.

Legacy effects in radial tree growth are rarely significant after accounting for biological memory

Abstract Drought legacies in radial tree growth are an important feature of variability in biomass accumulation and are widely used to characterize forest resilience to climate change. Defined as a deviation from normal growth, the statistical significance of legacy effects depends on the definition of “normal”—expected growth under average conditions—which has not received sufficient scrutiny. We re‐examined legacy effect analyses using the International Tree‐Ring Data Bank (ITRDB) and then produced synthetic tree‐ring data to disentangle four key variables influencing the magnitude of legacy effects. We hypothesized that legacy effects (i) are mainly influenced by the auto‐correlation of the radial growth time series (phi), (ii) depend on climate‐growth cross‐correlation (rho), (iii) are directly proportional to the inherent variability of the growth time series (standard deviation, SD), and (iv) scale with the chosen extreme event threshold. Using a data simulation approach, we were able to reproduce observed lag patterns, demonstrating that legacy effects are a direct outcome of ubiquitous biological memory. We found that stronger legacy effects for conifers compared to angiosperms is a consequence of their higher auto‐correlation, and that the detectability of legacy effects following rare drought events at individual sites is compromised by strong background stochasticity. Synthesis. We propose two pathways forward to improve the assessment and interpretation of legacy effects: First, we highlight the need to account for auto‐correlated residuals of climate‐growth regression models a posteriori, thereby retrospectively adjusting expectations for “normal” growth variability. Alternatively, we recommend including lagged climate variables in regression models a priori. By doing so, the magnitude of detected legacy effects is greatly reduced and biological memory is directly attributed to antecedent climatic drivers. We argue that future analyses should focus on understanding the functional reasons for how and why key statistical parameters describing this biological memory differ across species and sites. These two pathways should also stimulate improved process‐based representation of vegetation carbon dynamics in mechanistic models.

Dating Coastal Archaeological Wood From Pingusugruk (15th–17th CE), Northern Alaska:

Abstract Along the coasts of northern Alaska, in a treeless tundra environment, the primary wood resource for coastal populations is driftwood, a seasonal and exogenous resource carried by the major rivers of western North America. The potential of Alaskan coastal archaeological wood for tree-ring research was first assessed in the 1940s by archaeologist and tree-ring research pioneer J. L. Giddings. Despite his success, the difficulties of dendrochronological studies on driftwood and the development of radiocarbon dating during the 1950s resulted in the near-abandonment of dendrochronology to precisely date archaeological sites and build long sequences using archaeological wood in Alaska. In this study, we explored the possibilities and limitations of standard ring-width dendrochronological methods for dating Alaskan coastal archaeological wood. We focus on the site of Pingusugruk, a late Thule site (15th–17th CE) located at Point Franklin, northern Alaska. The preliminary results have been obtained from the standard dendrochronological analyses of 40 timber cross-sections from two semi-subterranean houses at Pingusugruk. We cross-correlated individual ring-width series and built floating chronologies between houses before cross-dating them with existing regional 1000-year-long master chronologies from the Kobuk and Mackenzie rivers (available on the International Tree-Ring Databank, ITRDB). Additional work on various dendro-archaeological collections using an interdisciplinary approach (geochemical analyses of oxygen isotopes and radiocarbon dating) will help develop and expand regional tree-ring chronologies and climatic tree-ring sequences in Alaska.

Evaluating alternative study designs for optimal sampling of species' climatic niches

Ecologists have traditionally studied intraspecific variation by sampling species across their geographic ranges. However, whether this classic approach produces samples that accurately represent species' climatic niches is largely unknown. Alternative niche‐based study designs using species' climatic niches to inform sampling locations should more efficiently and completely capture the breadth of the niche, but the magnitude of this difference and how it may vary is unclear. Here we use conifers as a model system to explore these issues and reach specific recommendations for future sampling designs. Using an independent data set of high‐quality species' occurrences, we first show that recent publications examining variation across geographic space do a poor job of capturing the full breadth of species' niches, such that on average, only 22% of species' niche space was sampled. This was also true of a large compiled database, the International Tree‐Ring Data Bank (ITRDB), which yielded average niche coverage of only 45%. Finally, we simulated common sampling designs (i.e. random points, grids and transects) in both geographic and niche‐based sampling frameworks. Using two sampling metrics, niche coverage and niche undersampling, we measured how completely and evenly these simulated studies characterized the niches of 64 North American conifers. Niche‐based sampling better represented species' niches than geographic sampling, with the magnitude of this difference depending on study design and sample size. Niche‐based gridded study designs achieved the most complete sampling at all but the smallest sample sizes, covering ~15–25% more of a species' niche than similar designs implemented geographically. With fewer than 10 samples, however, all study designs performed poorly, and niche‐based transects achieved slightly higher niche coverage. Consequently, when more than a handful of samples are collected, we recommend that studies seeking to characterize variation across a species' niche consider using a gridded study design implemented in a niche‐based sampling framework.

Degree of connectivity in reconstructed precipitation dynamics and extremes for semiarid regions across South Siberia

Tree rings from forest-steppes of temperate continental Asia are useful proxies for the moisture regime reconstructions, encompassing environmental variations such as warming climate, changing frequency and intensity of droughts. Heterogeneity of precipitation leaves open the question of the probability of spatially large-scale droughts in this macro-region. Theoretically, such events could be driven by global tele-connections and/or common astronomic cycles. We have attempted the precipitation reconstructions of two distant (~1000 km) intermountain valleys in South Siberia, based on the tree ring width of Pinus sylvestris L. To enhance the quality of the precipitation reconstruction models, networks of existing tree-ring data were expanded and daily precision of instrumental precipitation series was implemented for calibration. Within-region (150–200 km) common signal between local chronologies r = 0.37–0.90 (p < 0.05) allowed obtaining regional ones, registering precipitation up to annual temporal scale. High correlations of both regional chronologies with annual precipitation were found for period from previous July 22 to current July 21 (r = 0.71–0.72). These precipitation series were further reconstructed. Reconstruction models explaining 50–52% of variation were developed for the years 1753–2015 and 1798–2015. Although both valleys do not record many concurrent extreme precipitation events, some common and opposite extremes have been revealed. For both regions, an 11-year and 26–29-year cycles were commonly observed. These were probably associated with the solar activity and Pacific Decadal Oscillation (PDO). However, phase shifts of these cycles were recorded between the regions and with PDO. Stronger impact of oceanic air masses was observed in the eastern one of the two considered territories. Whereas higher significance of frequencies associated with astronomic cycles (solar and lunar-nodal) was found in the western one. Data availabilityTemperature and precipitation series of climatic stations were obtained from the website of All-Russia Research Institute of Hydrometeorological Information, World Data Centre (RIHMI-WDC, http://meteo.ru/data). Other climatic time series and solar activity series were obtained from the website of The Royal Netherlands Meteorological Institute (KNMI) Climate Explorer (https://climexp.knmi.nl). Used in the study tree-ring width measurements will be submitted to the International Tree-Ring Data Bank (ITRDB; https://www.ncei.noaa.gov/products/paleoclimatology/tree-ring) upon publication of the manuscript and with reference to it.

Вплив змін клімату на насадження сосни звичайної: стан, проблеми, виклики

It is proved that since the beginning of the XIX century. the degradation of pine stands is enormous on all continents. In Ukraine, according to the Ministry of Environmental Protection and Natural Resources of Ukraine, the average annual temperature since the beginning of the 20th century has increased by more than 2 °C, including 1.2 °C over the past 30 years. In recent years, the number of days with maximum summer temperatures above 35 °C and 40 °C has almost doubled in extreme weather. In most of the territory of Ukraine, there is already a tendency towards an increase in drought, increased fire hazard, recurrence of years during which plantations will experience water stress, damage by pests, as well as degradation of forest ecosystems as a whole as a result of an increase in forest areas. number and duration of hot periods. It was found that dendrochronological methods are used to study the relationship between climate change and pine radial increment. The main methods for studying radial increment are taking cores at a height of 1.3 meters from two opposite radii in order to prevent the influence of random factors on radial increment. The annual ring width is determined using dendrochronological instruments with automatic data recording. The data on the values of annual rings are processed according to the programs of the International Tree Ring Data Bank (ITRDB). To synchronize the series with the establishment of the calendar year for the formation of each annual increment, the specialized COFECHA program is used. It has been established that the growth of scots pine is limited by the humidification of the climate and the presence of sufficient moisture in the soil, however, in the presence of extreme temperatures, the negative tendency towards drying out of plantations persists.

Using the International Tree-Ring Data Bank (ITRDB) records as century-long benchmarks for global land-surface models

Abstract. The search for a long-term benchmark for land-surface models (LSMs) has brought tree-ring data to the attention of the land-surface modelling community, as tree-ring data have recorded growth well before human-induced environmental changes became important. We propose and evaluate an improved conceptual framework of when and how tree-ring data may, despite their sampling biases, be used as century-long hindcasting targets for evaluating LSMs. Four complementary benchmarks – size-related diameter growth, diameter increment of mature trees, diameter increment of young trees, and the response of tree growth to extreme events – were simulated using the ORCHIDEE version r5698 LSM and were verified against observations from 11 sites in the independent, unbiased European biomass network datasets. The potential for big-tree selection bias in the International Tree-Ring Data Bank (ITRDB) was investigated by subsampling the 11 sites from European biomass network. We find that in about 95 % of the test cases, using ITRDB data would result in the same conclusions as using the European biomass network when the LSM is benchmarked against the annual radial growth during extreme climate years. The ITRDB data can be used with 70 % confidence when benchmarked against the annual radial growth of mature trees or the size-related trend in annual radial growth. Care should be taken when using the ITRDB data to benchmark the annual radial growth of young trees, as only 50 % of the test cases were consistent with the results from the European biomass network. The proposed maximum tree diameter and annual growth increment benchmarks may enable the use of ITRDB data for large-scale validation of the LSM-simulated response of forest ecosystems to the transition from pre-industrial to present-day environmental conditions over the past century. The results also suggest ways in which tree-ring width observations may be collected and/or reprocessed to provide long-term validation tests for land-surface models.

REFINEMENT OF CONIFER GROWTH MODELS BASED ON TREE-RING CHRONOLOGIES OF THE NORTH OF WESTERN SIBERIA

The subject of this research is conifer growth model based on time-series of annual rings width. The article addresses processing of data and model update in respect of forest dendrology. The purpose of study is to update the conifer growth model due to expansion of time-series of tree-rings width in regards to conifer forests in Western Siberia. The method represents expansion of time-series due to the fact that some growth phases had not been taken into account. When measurements were taken at the height of 1.3 meters, the following phases were not considered: seedling, juvenile, immature and beginning of virginile phase. The authors carried out examination of a number of scans and core samples, as well as time-series received by other scientists and which are contained in the International Tree-Ring Data Bank. Based on the results of field studies, the authors recommend to add some zeroes to the beginning of time-series within the range of 10-15 years for pine-trees in the south of Western Siberia, depending on growth conditions; the range of 15-30 years in the north for larch-trees and pine-trees depending on soil and climate conditions and latitude. The sequence of data pre-processing operations for time-series, received by means of core sampling, is as follows: averaging out of radius gain in 2 (3) mutually perpendicular directions for one specimen, graphing of radius gain curve, adding to the beginning of time-series, its normalization, approximation by specified growth function. It is possible to build area growth function for the scans. For averaging out a group of model trees, the sequence of operations is as follows: synchronization of time-series by cross-correlation method, approximation by specified growth function. Methods and results of studies can be applied in forest sectors and oil and gas industries for monitoring of forest health conditions. The proposed method of curve growth model update will allow to define more precisely time intervals for efficient forest exploitation as well as to reconstruct digital models of conifer populations in the north of Western Siberia.

Sampling density and date along with species selection influence spatial representation of tree-ring reconstructions

Abstract. Our understanding of the natural variability of hydroclimate before the instrumental period (ca. 1900 CE in the United States) is largely dependent on tree-ring-based reconstructions. Large-scale soil moisture reconstructions from a network of tree-ring chronologies have greatly improved our understanding of the spatial and temporal variability in hydroclimate conditions, particularly extremes of both drought and pluvial (wet) events. However, certain regions within these large-scale network reconstructions in the US are modeled by few tree-ring chronologies. Further, many of the chronologies currently publicly available on the International Tree-Ring Data Bank (ITRDB) were collected in the 1980s and 1990s, and thus our understanding of the sensitivity of radial growth to soil moisture in the US is based on a period that experienced multiple extremely severe droughts and neglects the impacts of recent, rapid global change. In this study, we expanded the tree-ring network of the Ohio River valley in the US, a region with sparse coverage. We used a total of 72 chronologies across 15 species to examine how increasing the density of the tree-ring network influences the representation of reconstructing the Palmer Meteorological Drought Index (PMDI). Further, we tested how the sampling date and therefore the calibration period influenced the reconstruction models by creating reconstructions that ended in the year 1980 and compared them to reconstructions ending in 2010 from the same chronologies. We found that increasing the density of the tree-ring network resulted in reconstructed values that better matched the spatial variability of instrumentally recorded droughts and, to a lesser extent, pluvials. By extending the calibration period to 2010 compared to 1980, the sensitivity of tree rings to PMDI decreased in the southern portion of our region where severe drought conditions have been absent over recent decades. We emphasize the need of building a high-density tree-ring network to better represent the spatial variability of past droughts and pluvials. Further, chronologies on the ITRDB need updating regularly to better understand how the sensitivity of tree rings to climate may vary through time.

Growth-climate relationship of Pinus wallichiana in three different parts of the Himalayas

We have used six tree-ring width chronologies of Pinus wallichiana from the Himalayan region, which are available in the International Tree-Ring Data Bank (ITRDB), to determine their growth trends through time and the growth-climate relationship. Each of the chronologies downloaded from the ITRDB was detrended using an Age-dependent Cubic Smoothing Spline with a 20-year starting spline stiffness in the RCSigfree Software Program. We broke the six chronologies into three regions based on natural breaks between the sample sites. Altogether, three composite chronologies were made, one each from Bhutan, Nepal, and Pakistan. The average value for common periods was taken from each of those two chronologies to make a composite chronology. Across the three regions, the growth was lowest in the 1810s and has increased since 1980s. The growth showed a significant positive response to the winter temperature (November-February) in the eastern Himalayas in Bhutan. The chronology from Nepal showed that the growth of this species had a significant positive response to the self-calibrated Palmer Drought Severity Index of the previous year’s December and the current year’s January and March. In the western Himalayas of Pakistan, the growth of the same species is positively correlated to the annual self-calibrated Palmer Drought Severity Index. Winter temperature limits the growth of this species in the eastern Himalayas where there is enough moisture whereas the growth of this species is primarily limited by moisture in the western Himalayas

Tree-Ring Reconstructions of Streamflow for the Tennessee Valley

This study reports the preliminary results from a statistical screening of tree-ring width records from the International Tree-Ring Data Bank (ITRDB), to evaluate the strength of the hydrological signal, in dendrochronological records from the Tennessee Valley. We used United States Geological Survey (USGS) streamflow data from 11 gages, within the Tennessee Valley, and regional tree-ring chronologies, to analyze the dendroclimatic potential of the region, and create seasonal flow reconstructions. Prescreening methods included correlation, date, and temporal stability analysis of predictors to ensure practical and reliable reconstructions. Seasonal correlation analysis revealed that large numbers of regional tree-ring chronologies were significantly correlated (p ≤ 0.05) with the May–June–July streamflow. Stepwise linear regression was used to create the May–June–July streamflow reconstructions. Ten of the 12 streamflow stations were considered statistically skillful (R2 ≥ 0.40). Skillful reconstructions ranged from 208 to 301 years in length, and were statistically validated using leave-one-out cross validation, the sign test, and a comparison of the distribution of low flow years. The long-term streamflow variability was analyzed for the Nolichucky, Nantahala, Emory, and South Fork (SF) Holston stations. The reconstructions revealed that while most of the Western United States (U.S.). was experiencing some of its highest flow years during the early 1900s, the Tennessee Valley region was experiencing a very low flow. Results revealed the potential benefit of using tree-ring chronologies to reconstruct hydrological variables in the Southeastern U.S., by demonstrating the ability of proxy-based reconstructions to provide useful data beyond the instrumental record.

Additions to the Last Millennium Reanalysis Multi-Proxy Database

Progress in paleoclimatology increasingly occurs via data syntheses. We describe additions to a collection prepared for use in paleoclimate state estimation, specifically the Last Millennium Reanalysis (LMR). The 2290 additional series include 2152 tree ring chronologies and 138 other series. They supplement the collection used previously and together form a database titled LMRdb 1.0.0. The additional data draws from lake core, ice core, coral, speleothem, and tree ring archives, using published data primarily from the NOAA Paleoclimatology archive and a set of tree ring width chronologies standardized from raw International Tree Ring Data Bank ring width series. In contrast to many previous paleo compilations, the data were not selected (screened) on the basis of their environmental correlation, multi-century length, or other attributes. The inclusion of proxies sensitive to moisture and other environmental variables expands their use in data assimilation. A preliminary calibration using linear regression with mean annual temperature reveals characteristics of the proxy series and their relationship to temperature, as well as the noise and error characteristics of the records. The additional records are structured as individual files in the NOAA Paleoclimatology format and archived at NOAA Paleoclimatology (Anderson et al. 2018) and will continue to be improved and expanded as part of the LMR Project. The additions represent a four-fold increase in the number of records available for assimilation, provide expanded geographic coverage, and add additional proxy variables. Applications include data assimilation, proxy system model development, and paleoclimate reconstruction using climate field reconstruction and other methods.

Reconstruction of annual runoff since CE 1557 using tree-ring chronologies in the upper Lancang-Mekong River basin

In this study, with the use of a multiple linear regression approach, the tree-ring chronologies of eight sampling sites in the upper Lancang-Mekong River Basin were developed to provide a 449-year (CE 1557–2005) reconstruction of the annual runoff, thus placing recent changes in annual runoff into a long-term context. These eight tree-ring chronologies have recently been archived in publicly available databases through the International Tree-Ring Data Bank. Reconstruction results showed a good correlation coefficient of 0.662 (n = 39, p-value < 0.01) between the reconstructed and the observed annual runoff. The adjusted coefficient (R2) for the degrees of freedom is 42.3%, which meets the precision requirements of reconstruction. The reconstructed runoff displays a trend toward more moist conditions: there were 37 extremely wet years and 23 extremely dry years, exceeding the mean ±1 standard deviation, during the past 449 years. Empirical mode decomposition (EMD) was used to fully analyze and understand the multi-scale variation of the reconstructed runoff. Six intrinsic mode function (IMF) components with different scales were obtained and the sum of all components can be reverted to the original variable sequence. The first and second IMF mainly reflect the change characteristics of the interannual scale of reconstructed sequence. Both are likely controlled by the Quasi-Biennial Oscillation (QBO) and the El Niño-Southern Oscillation (ENSO), respectively. The third IMF showed a 10–13 year scale fluctuation, which is very similar to the solar activity of an 11-year cycle. The fourth and fifth IMF mainly represents multidecadal and centennial oscillations, and they have shown coherent variations with predecessors’ reconstructed May-September precipitations in the same time domain. The lowest frequency component (the residue IMF) represents the trend term of the original signal.