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The tree rings' tale : understanding our changing climate
Science writer Fleck addresses one of the most important guiding principles for life in the arid West and one that scientists have long recognized: climate variability.
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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
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.
Journal Article
Differential response of radial growth and delta.sup.13C in Qinghai spruce to climate change on the southern and northern slopes of the Qilian Mountains in Northwest China
Tree radial growth can have significantly different responses to climate change depending on the environment. To elucidate the effects of climate on radial growth and stable carbon isotope ([delta].sup.13C) fractionation of Qinghai spruce (Picea crassifolia), a widely distributed native conifer in northwestern China in different environments, we developed chronologies for tree-ring widths and [delta].sup.13C in trees on the southern and northern slopes of the Qilian Mountains, and analysed the relationship between these tree-ring variables and major climatic factors. Tree-ring widths were strongly influenced by climatic factors early in the growing season, and the radial growth in trees on the northern slopes was more sensitive to climate than in trees on the southern. Tree-ring [delta].sup.13C was more sensitive to climate than radial growth. [delta].sup.13C fractionation was mainly influenced by summer temperature and precipitation early in the growing season. Stomatal conductance more strongly limited stable carbon isotope fractionation in tree rings than photosynthetic rate did. The response between tree rings and climate in mountains gradually weakened as climate warmed. Changes in radial growth and stable carbon isotope fractionation of P. crassifolia in response to climate in the Qilian Mountains may be further complicated by continued climate change.
Journal Article
Climate Response of a Dwarfed Population of Quercus marilandica in Central Illinois, United States
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 climategrowth 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.
Journal Article
Development and applications of accelerator mass spectrometry methods for measurement of .sup.14C, .sup.10Be and .sup.26Al in the CENTA laboratory
Terrestrial and extraterrestrial radioisotope research has been strongly dependent on the development of analytical methods which would enable to trace radioisotopes at low concentrations in subgram samples (e.g., in tree rings, ice cores, meteorites, etc.). Accelerator mass spectrometry (AMS) has become the most sensitive technique for ultralow-level analysis of long-lived radioisotopes, such as .sup.14C, .sup.10Be and .sup.26Al. We review developments and applications carried out in the CENTA laboratory, and describe a recently installed fully equipped AMS line, designed for analysis of long-lived radioisotopes from tritium to curium.
Journal Article
