Radial distribution of .sup.239,240Pu and .sup.90Sr originating from atmospheric nuclear tests in tree rings and trunk bark at heights of 1.3, 10, 18 and 22 m above ground was studied. .sup.239,240Pu ...activity concentrations in air dried tree ring samples (each containing 10 annual rings) at all heights were under detection limit of the used method. .sup.90Sr activity concentrations in tree ring samples ranged from 0.54 to 2.81 Bq kg.sup.-1. .sup.239,240Pu and .sup.90Sr were present in the trunk bark. The paper presents data for .sup.239,240Pu and .sup.90Sr aggregated transfer factors to tree trunk.
Nitrogen deposition in the northeastern US changed N availability in the latter part of the twentieth century, with potential legacy effects. However, long-term N cycle measurements are scarce. N ...isotopes in tree rings have been used as an indicator of N availability through time, but there is little verification of whether species differ in the strength of this signal. Using long-term records at the Fernow Experimental Forest in West Virginia, we examined the relationship between soil conditions, including net nitrification rates, and wood delta.sup.15N in 2014, and tested the strength of correlation between tree ring delta.sup.15N of four species and stream water NO.sub.3.sup.- loss from 1971 to 2000. Higher soil NO.sub.3.sup.- was weakly associated with higher wood delta.sup.15N across species, and higher soil net nitrification rates were associated with higher delta.sup.15N for Quercus rubra only. The delta.sup.15N of Liriodendron tulipifera and Q. rubra, but neither Fagus grandifolia nor Prunus serotina, was correlated with stream water NO.sub.3.sup.-. L. tulipifera tree ring delta.sup.15N had a stronger association with stream water NO.sub.3.sup.- than Q. rubra. Overall, we found only limited evidence of a relationship between soil N cycling and tree ring delta.sup.15N, with a strong correlation between the wood delta.sup.15N and NO.sub.3.sup.- leaching loss through time for one of four species. Tree species differ in their ability to preserve legacies of N cycling in tree ring delta.sup.15N, and given the weak relationships between contemporary wood delta.sup.15N and soil N cycle measurements, caution is warranted when using wood delta.sup.15N to infer changes in the N cycle.
Quercus marilandica is distributed widely across the eastern United States, but dwarfed specimens (<3.4 m in height) are found where tree growth is limited by nutrient-poor soils. Few studies have ...explored the tree rings of Q. marilandica, with no research examining tree rings of any dwarfed species of tree in the U.S. In this report, we examine the climate-growth response of dwarfed Q. marilandica sampled on a sandstone bluff in central Illinois. This is one of the first attempts at identifying the climate-growth response of Q. marilandica and any dwarfed tree species in the U.S. Ring widths positively correlated with the standardized precipitation evapotranspiration index, and dew point, and negatively correlated with summer maximum temperature and vapor pressure deficit. The results of a moving-window analysis suggest that the influence of climate variability has become more important to radial growth in the past thirty-plus years. Our results indicate that dwarfed Q. marilandica are sensitive to hot, dry summers, making future projections of increased temperatures and drought a concern. Our findings suggest that future conditions could increase the vulnerability of dwarfed populations of trees.
Climate warming, rising atmospheric CO.sub.2 concentration (C.sub.a), and nitrogen (N) availability are exerting profound impacts on global forest ecosystems, particularly in high-altitude mountains. ...This study investigated the tree-growth dynamics of timberline Larix chinensis in the Taibai Mountain, central China, and explored its ecophysiological responses to environmental stresses by combining tree growth and stable isotopes. The results showed that the growth rate of L. chinensis has significantly increased since the 1960s, and that tree growth in this timberline was particularly sensitive to temperature in spring. Moreover, the continuously rising intrinsic water-use efficiency (iWUE), linked to higher C.sub.a and warmer environment, promoted the growth of L. chinensis. Before the 1960s, tree-ring deltasup.15N gradually increased, then shifted to an insignificant decline with the acceleration of tree growth, and broke the preexisting carbon-nitrogen balance. Meanwhile, climate warming and increased iWUE have replaced N as the principal drivers of tree growth since the 1960s. It is believed that L. chinensis may gradually suffer a decline in N availability as it continues to grow rapidly. The insightful understanding of the biochemical mechanisms of plant responses to growth-related environmental conditions will improve our ability to predict the evolution of high-elevation mountain ecosystems in the future. Keywords tree rings, stable isotopes, alpine forest, climate warming, CO.sub.2 fertilization, Taibai Mountain
Iceland, located in the climatologically sensitive subarctic zone, is one of the key areas for studying climate change and the current Arctic warming. Poor and rich heathland covers approximately 30% ...of Iceland, with heath vegetation being the area’s most important vegetation type. Prostrate and erect dwarf shrub and shrub species are the primary sources of dendrochronological information on the changes and characteristics of Iceland’s climate. Here, we investigate the dendrochronological potential of seven common Icelandic heathland species (Dryas octopetala, Calluna vulgaris, Salix arctica, Salix herbacea, Empetrum nigrum, Juniperus communis nana, and Betula nana) and explore the impact of climate conditions on their growth, particularly with regard to extreme meteorological events. We conducted comparative analyses among species and observed their climatic responses in a climatically, morphologically, and geologically homogeneous setting in north-eastern Iceland. After sampling, measurements, and cross-dating, we constructed local chronologies for the seven species. Of approximately 200 samples, only 113 were included in the final shrub chronologies. All chronologies covered at least 50 years, with few of them exceeding 100 years. Dendroclimatological analysis indicated that above-average temperatures in June and summer positively influence the growth of D. octopetala (June–September), J. communis (July–August), B. nana (July–August), C. vulgaris (June–August), and S. arctica (August–September). The opposite is observed for S. herbacea and E. nigrum. Climate–growth correlations indicate that the growth of these species is negatively correlated with temperature and positively correlated with winter and summer precipitation. Furthermore, among the long-lived woody species growing in Iceland, seven common species were used to assess the impact of extreme meteorological conditions on their growth. The most pronounced extreme year in the wood anatomy of Icelandic shrubs was 1979, depicted as very narrow or missing rings and as the blue ring in J. communis.
The analysis of climate variability and development of reconstructions based on tree-ring records in tropical forests have been increasing in recent decades. In the Amazon region, ring width and ...stable isotope long-term chronologies have been used for climatic studies, however little is known about the potential of wood traits such as density and chemical concentrations. In this study, we used well-dated rings of Cedrela fissilis Vell. from the drought-prone southern Amazon basin to assess the potential of using inter-annual variations of annually-resolved ring width, wood density, stable oxygen isotope (δ18OTR) measured in tree-ring cellulose and concentration of Sulfur (STR) and Calcium (CaTR) in xylem cells to study climate variability. During wet years, Cedrela fissilis produced wider and denser rings with higher CaTR and lower STR, as well as depleted δ18OTR values. During dry years, a wider range of responses was observed in growth, density and STR, while lower CaTR and enriched δ18OTR values were found. The annual centennial chronologies spanning from 1835 to 2018 showed good calibration skills for reconstructing local precipitation, evapotranspiration (P-PET), Amazon-wide rainfall, as well as climate modes related to sea surface temperature (SST) anomalies such as El Niño South Oscillation (ENSO), Tropical Northern Atlantic (TNA), and the Western Hemisphere Warm Pool (WHWP) oscillations. CaTR explained 42 % of the variance of local precipitation (1975–2018), RW explained 30 % of the P-PET variance (1975–2018), while δ18OTR explained 60 % and 57 % of the variance of Amazon rainfall (1960–2018) and El Niño 3.4 (1920–2018), respectively. Our results show that a multi-proxy tropical tree-ring approach can be used for high-reliable reconstructions of climate variability over Amazon basin at inter-annual and multidecadal time scales.
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•Long-term radial growth, density, inorganic chemistry and stable isotope series were developed.•Chronologies extend back to 1835 CE local and regional climate variability.•Tree-ring width, density and Ca and S concentration records mainly express local climate variability.•The δ18O record mostly reflects Amazon precipitation and sea surface temperature anomalies.
Tree‐ring records provide global high‐resolution information on tree‐species responses to global change, forest carbon and water dynamics, and past climate variability and extremes. The underlying ...assumption is a stationary (time‐stable), quasi‐linear relationship between tree growth and environment, which however conflicts with basic ecological and evolutionary theory. Indeed, our global assessment of the relevant tree‐ring literature demonstrates non‐stationarity in the majority of tested cases, not limited to specific proxies, environmental parameters, regions or species. Non‐stationarity likely represents the general nature of the relationship between tree‐growth proxies and environment. Studies assuming stationarity however score two times more citations influencing other fields of science and the science–policy interface. To reconcile ecological reality with the application of tree‐ring proxies for climate or environmental estimates, we provide a clarification of the stationarity concept, propose a simple confidence framework for the re‐evaluation of existing studies and recommend the use of a new statistical tool to detect non‐stationarity in tree‐ring proxies. Our contribution is meant to stimulate and facilitate discussion in light of our results to help increase confidence in tree‐ring‐based climate and environmental estimates for science, the public and policymakers.
Tree‐ring records provide global high‐resolution information on tree‐species responses to global change, forest carbon and water dynamics, and past climate variability and extremes. The underlying assumption is a stationary (time‐stable), quasi‐linear relationship between tree growth and environment. Our results show that this assumption might be too simplistic. Non‐stationarity between tree growth and climatic or environmental drivers is evident at global scale.
•We investigated stand and tree features on spruce response to climate.•Age, competition, disturbance, elevation interact to modify growth–climate response.•Tree growth was mainly temperature-driven ...but water availability was also important.•Old trees and low-elevation dense stands are vulnerable to drought.
Stands and trees may exhibit different climate–growth responses compared to neighbouring forests and individuals. The study of these differences is crucial to understanding the effects of climate change on the growth and vulnerability of forests and trees. In this research we analyse the growth responsiveness of primary Norway spruce forests to climate as a function of different stand (elevation, aspect, slope, crowding, historic disturbance regime) and tree (age, tree-to-tree competition) features in the Romanian Carpathians. Climate–growth relationships were analysed using Pearson correlation coefficients between ring-width indices (RWIs) and climate variables. The influence of stand and tree characteristics on the RWI responses to climate were investigated using linear mixed-effects models. Elevation greatly modulated the climate–growth associations and it frequently interacted with competition intensity or tree age to differentially influence growth responsiveness to climate. Old trees were more sensitive to climate than young trees, but while old tree’s response to climate highly depended on elevation (e.g. positive influence of summer temperature on old trees’ RWIs at high elevations, but negative effect at low elevations), differences of the young trees’ response across the elevation gradient were less evident. The severity of the past disturbance also modified the climate–growth associations because of contrasting canopy structures. Our results suggest that although an increase in temperature might enhance growth at high elevations, it may also induce growth declines due to drought stress at lower elevations, particularly for old trees or trees growing under high levels of competition, which may increase their vulnerability to disturbances.
Tree‐ring records of preinstrumental hydroclimate, which contribute needed context for understanding recent drought and flood events, typically provide one value per year that represents the entire ...year or one particular season. This may introduce a seasonal bias to the records or omit seasonally variable moisture. Here, I use tree‐ring records to reconstruct precipitation and runoff in 28 U.S. West Coast watersheds for running 1, 3, 6, and 12‐month intervals. When compared on a yearly basis, the Monthly and Four‐Season models have higher overall skill and better extreme capture in most basins than the Cool‐Warm and Annual models. The Monthly and Four‐Season versions also decrease model error in years with more intense precipitation and retain more variability in the preinstrumental period. Improved capture of year‐round moisture can provide a more complete representation of the preinstrumental past and strengthen capacity to study shorter‐duration and season‐specific events like atmospheric rivers.
Plain Language Summary
Records from long‐lived trees help us learn what the Earth's climate was like before we had thermometers and rain gauges. These records are useful for understanding how and why our current climate is different than it was in the past, information that can help us plan for the future. Most tree‐ring records provide one value per year, which might miss precipitation that falls outside the season that most influences tree growth or that does not arrive in the same months each year. In this study, I used tree‐ring widths to produce records of precipitation and runoff in watersheds along the U.S. West Coast over 1, 3, 6, and 12‐month time periods for the past 200 years. I compared all four versions on a yearly basis and found that the 1 and 3‐month versions replicated the instrumental data more closely than the 6 and 12‐month records and more accurately identified the very wet and very dry years in most watersheds. This research will help us learn more about past climate patterns by better describing the entire year and by increasing our ability to study a particular season of interest.
Key Points
New annual, seasonal, and monthly precipitation and runoff reconstructions provide year‐round moisture records along the U.S. West Coast
Monthly and Four‐Season reconstructions increase model skill, extreme capture, and variability retained in most watersheds
Higher temporal resolution can help characterize shorter‐duration, season‐specific events like atmospheric rivers in the paleoclimate past
![Assessing tree ring [delta]...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0029-8549/small "Assessing tree ring [delta].sup.15N of four temperate deciduous species as an indicator of N availability using independent long-term records at the Fernow Experimental Forest, WV")
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