Paul R Sheppard
- Associate Professor, Dendrochronology
- Associate Professor, Public Health
- Associate Professor, School of Geography and Development
- Member of the Graduate Faculty
- Ph.D. Geosciences, Dendrochronology
- University of Arizona
- M.S. Natural Resources, Forest Science
- Cornell University
- B.S. Forest Management
- Humboldt State University, California
- A.S. General Education
- Long Beach City College
- Laboratory of Tree-Ring Research, University of Arizona (2007 - Ongoing)
- Laboratory of Tree-Ring Research, University of Arizona (2001 - 2007)
- Society of American Foresters, Fall 2018
Licensure & Certification
- Diploma Básico de Español, La Ministra de Educación y Cultura del Reino de España (1998)
Environmental History of the Southwest, Dendrochronology Workshop, Sense of Place
A Sense of PlaceGEOS 195D (Spring 2022)
Environ Hist SouthwestGEOS 220 (Fall 2021)
A Sense of PlaceGEOS 195D (Spring 2021)
Environ Hist SouthwestGEOS 220 (Fall 2020)
A Sense of PlaceGEOS 195D (Spring 2020)
Directed Rsrch In GeogGEOG 392A (Spring 2020)
Environ Hist SouthwestGEOS 220 (Fall 2019)
DendroecologyGEOS 497K (Summer I 2019)
DendroecologyGEOS 597K (Summer I 2019)
A Sense of PlaceGEOS 195D (Spring 2019)
Directed Rsrch In GeogGEOG 492A (Spring 2019)
Independent StudyGEOS 199 (Spring 2019)
Environ Hist SouthwestGEOS 220 (Fall 2018)
A Sense of PlaceGEOS 195D (Spring 2018)
DendochronologyANTH 597C (Spring 2018)
DendochronologyGEOS 597C (Spring 2018)
Environ Hist SouthwestGEOS 220 (Fall 2017)
DendroecologyGEOS 597K (Summer I 2017)
A Sense of PlaceGEOS 195D (Spring 2017)
DendochronologyGEOS 597C (Spring 2017)
DendrochronologyGEOS 497C (Spring 2017)
Environ Hist SouthwestGEOS 220 (Fall 2016)
A Sense of PlaceGEOS 195D (Spring 2016)
DendochronologyANTH 597C (Spring 2016)
DendochronologyGEOS 597C (Spring 2016)
DendochronologyWSM 597C (Spring 2016)
DendrochronologyGEOS 497C (Spring 2016)
- Brice, R., Guiterman, C., Sheppard, P. R., Woodhouse, C. A., & McClellan, C. (2020). Comparing tree-ring based reconstructions of snowpack variability at different scales. Climate Services.
- Hobson, C., Kulkarni, H., Johannesson, K., Bednar, A., Tappero, R., Mohajerin, T., Sheppard, P. R., Witten, M., Hettiarachchi, G., & Datta, S. (2020). Origin of tungsten and geochemical controls on its occurrence and mobilization in shallow sediments from Fallon, Nevada, USA. Chemosphere.
- Muñoz, A., & Sheppard, P. R. (2019). Multidecadal environmental pollution in a mega-industrial area in central Chile registered by tree rings.. Science of the Total Environment.
- Aguilera-Betti, I., Muñoz, A. A., Stahle, D., Figueroa, G., Duarte, F., González-Reyes, A., Christie, D., Lara, A., González, M. E., Sheppard, P. R., Sauchyn, D., Moreira-Muñoz, A., Toledo-Guerrero, I., Olea, M., Apaz, P., & Fernandez, A. (2017). The first millennium-age Araucaria araucana in Patagonia.. Tree-Ring Research, 73(1), 53–56.
- Bunn, A. G., Helfield, J. M., Gerdts, J. R., Gleaves, D. A., Drake, D. C., & Sheppard, P. R. (2017). A solvent-based extraction fails to remove mobile nitrogen from western redcedar (Thuja plicata).. Dendrochronologia, 44, 19–21.
- Muñoz, A. A., González-Reyes, A., Lara, A., Sauchyn, D., Christie, D., Puchi, P., Urrutia-Jalabert, R., Toledo-Guerrero, I., Aguilera-Betti, I., Mundo, I., Sheppard, P. R., Stahle, D., Villalba, R., Szejner, P., LeQuesne, C., & Vanstone, J. (2016). Streamflow variability in the Chilean Temperate-Mediterranean climate transition (35°S-42°S) during the last four hundred years inferred from tree-ring records.. Climate Dynamics, 47(12), 4051-4066.More infoMuñoz, A.A., A. González-Reyes, A. Lara, D. Sauchyn, D. Christie, P. Puchi, R. Villalba, I. Toledo, I. Aguilera-Betti, R. Urrutia, I. Mundo, P.R. Sheppard, D. Stahle, P. Szejner, C. LeQuesne, J. Vanstone.
- Bunn, A. G., Bunn, A. G., Helfield, J. M., Helfield, J. M., Gerdts, J. R., Gerdts, J. R., Gleaves, D. A., Gleaves, D. A., Drake, D. C., Drake, D. C., Sheppard, P. R., & Sheppard, P. R. (2017). A solvent-based extraction fails to remove mobile nitrogen from western redcedar (Thuja plicata).. Dendrochronologia, 44, 19–21.
- France, C. A., Sheppard, P. R., Cano, N., Little, N. C., & Speakman, R. J. (2014). Stable isotopic and chemical indicators of volcanic eruptions in tree rings from Parícutin, Mexico. Open Journal of Archaeometry, 2, 5261.More infoProceedings of the 38th International Symposium on Archaeometry, : R.H. Tykot (ed.), May 10th-14th 2010, Tampa, Florida.
- Sheppard, P. R., Lipson, R., Hansbrough, D., & Gilbert, J. (2013). Field trip pedagogy for teaching "sense of place" in middle school.. Science Scope, 36(7), 49–54.
- Fastje, C. D., Harper, K., Terry, C., Sheppard, P. R., & Witten, M. L. (2012). Exposure to sodium tungstate and Respiratory Syncytial Virus results in hematological/immunological disease in C57BL/6J mice. Chemico-Biological Interactions, 196(3), 89-95.More infoPMID: 21565177;Abstract: The etiology of childhood leukemia is not known. Strong evidence indicates that precursor B-cell Acute Lymphoblastic Leukemia (Pre-B ALL) is a genetic disease originating in utero. Environmental exposures in two concurrent, childhood leukemia clusters have been profiled and compared with geographically similar control communities. The unique exposures, shared in common by the leukemia clusters, have been modeled in C57BL/6 mice utilizing prenatal exposures. This previous investigation has suggested in utero exposure to sodium tungstate (Na 2WO 4) may result in hematological/ immunological disease through genes associated with viral defense. The working hypothesis is (1) in addition to spontaneously and/or chemically generated genetic lesions forming pre-leukemic clones, in utero exposure to Na 2WO 4 increases genetic susceptibility to viral influence(s); (2) postnatal exposure to a virus possessing the 1FXXKXFXXA/V 9 peptide motif will cause an unnatural immune response encouraging proliferation in the B-cell precursor compartment. This study reports the results of exposing C57BL/6J mice to Na 2WO 4 in utero via water (15 ppm, ad libetum) and inhalation (mean concentration PM 5 3.33 mg/m 3) and to Respiratory Syncytial Virus (RSV) within 2 weeks of weaning. Inoculation of C57BL/6J mice with RSV was associated with a neutrophil shift in 56% of 5-month old mice. When the RSV inoculation was combined with Na 2WO 4-exposure, significant splenomegaly resulted (p = 0.0406, 0.0184, 0.0108 for control, Na 2WO 4-only and RSV-only, respectively) in addition to other hematological pathologies which were not significant. Exposure to Na 2WO 4 and RSV resulted in hematological/immunological disease, the nature of which is currently inconclusive. Further research is needed to characterize this potential leukemia mouse model. © 2011 Elsevier Ireland Ltd. All rights reserved.
- Pleil, J. D., Sobus, J. R., Sheppard, P. R., Ridenour, G., & Witten, M. L. (2012). Strategies for evaluating the environment-public health interaction of long-term latency disease: The quandary of the inconclusive case-control study. Chemico-Biological Interactions, 196(3), 68-78.More infoPMID: 21382361;Abstract: Environmental links to disease are difficult to uncover because environmental exposures are variable in time and space, contaminants occur in complex mixtures, and many diseases have a long time delay between exposure and onset. Furthermore, individuals in a population have different activity patterns (e.g., hobbies, jobs, and interests), and different genetic susceptibilities to disease. As such, there are many potential confounding factors to obscure the reasons that one individual gets sick and another remains healthy. An important method for deducing environmental associations with disease outbreak is the retrospective case-control study wherein the affected and control subject cohorts are studied to see what is different about their previous exposure history. Despite success with infectious diseases (e.g., food poisoning, and flu), case-control studies of cancer clusters rarely have an unambiguous outcome. This is attributed to the complexity of disease progression and the long-term latency between exposure and disease onset. In this article, we consider strategies for investigating cancer clusters and make some observations for improving statistical power through broader non-parametric approaches wherein sub-populations (i.e., whole towns), rather than individuals, are treated as the cases and controls, and the associated cancer rates are treated as the dependent variable. We subsequently present some ecological data for tungsten and cobalt from studies by University of Arizona researchers who document elevated levels of tungsten and cobalt in Fallon, NV. These results serve as candidates for future hybrid ecologic case-control investigations of childhood leukemia clusters. © 2011 Elsevier Ireland Ltd. All rights reserved.
- Sheppard, P. R., Bierman, B. J., Rhodes, K., Ridenour, G., & Witten, M. L. (2012). Comparison of size and geography of airborne tungsten particles in Fallon, Nevada, and sweet home, Oregon, with implications for public health. Journal of Environmental and Public Health, 2012.More infoPMID: 22523506;PMCID: PMC3317226;Abstract: To improve understanding of possible connections between airborne tungsten and public health, size and geography of airborne tungsten particles collected in Fallon, Nevada, and Sweet Home, Oregon, were compared. Both towns have industrial tungsten facilities, but only Fallon has experienced a cluster of childhood leukemia. Fallon and Sweet Home are similar to one another by their particles of airborne tungsten being generally small in size. Meteorologically, much, if not most, of residential Fallon is downwind of its hard metal facility for at least some fraction of time at the annual scale, whereas little of residential Sweet Home is downwind of its tungsten facility. Geographically, most Fallon residents potentially spend time daily within an environment containing elevated levels of airborne tungsten. In contrast, few Sweet Home residents potentially spend time daily within an airborne environment with elevated levels of airborne tungsten. Although it cannot be concluded from environmental data alone that elevated airborne tungsten causes childhood leukemia, the lack of excessive cancer in Sweet Home cannot logically be used to dismiss the possibility of airborne tungsten as a factor in the cluster of childhood leukemia in Fallon. Detailed modeling of all variables affecting airborne loadings of heavy metals would be needed to legitimately compare human exposures to airborne tungsten in Fallon and Sweet Home. © Copyright 2012 Paul R. Sheppard et al.
- Sheppard, P. R., Helsel, D. R., Speakman, R. J., Ridenour, G., & Witten, M. L. (2012). Additional analysis of dendrochemical data of Fallon, Nevada. Chemico-Biological Interactions, 196(3), 96-101.More infoPMID: 22227064;Abstract: Previously reported dendrochemical data showed temporal variability in concentration of tungsten (W) and cobalt (Co) in tree rings of Fallon, Nevada, US. Criticism of this work questioned the use of the Mann-Whitney test for determining change in element concentrations. Here, we demonstrate that Mann-Whitney is appropriate for comparing background element concentrations to possibly elevated concentrations in environmental media. Given that Mann-Whitney tests for differences in shapes of distributions, inter-tree variability (e.g., "coefficient of median variation") was calculated for each measured element across trees within subsites and time periods. For W and Co, the metals of highest interest in Fallon, inter-tree variability was always higher within versus outside of Fallon. For calibration purposes, this entire analysis was repeated at a different town, Sweet Home, Oregon, which has a known tungsten-powder facility, and inter-tree variability of W in tree rings confirmed the establishment date of that facility. Mann-Whitney testing of simulated data also confirmed its appropriateness for analysis of data affected by point-source contamination. This research adds important new dimensions to dendrochemistry of point-source contamination by adding analysis of inter-tree variability to analysis of central tendency. Fallon remains distinctive by a temporal increase in W beginning by the mid 1990s and by elevated Co since at least the early 1990s, as well as by high inter-tree variability for W and Co relative to comparison towns. © 2011 Elsevier Ireland Ltd. All rights reserved.
- Witten, M. L., Sheppard, P. R., & Witten, B. L. (2012). Tungsten toxicity. Chemico-Biological Interactions, 196(3), 87-88.More infoPMID: 22182474;Abstract: There is emerging evidence that tungsten has toxic health effects. We summarize the recent tungsten toxicity research in this short review. Tungsten is widely used in many commercial and military applications because it has the second highest melting temperature of any element. Consequently, it is important to elucidate the potential health effects of tungsten. © 2011 Elsevier Ireland Ltd. All rights reserved.
- Drake, D. C., Sheppard, P. J., & Naiman, R. J. (2011). Relationships between salmon abundance and tree-ring δ 15N: Three objective tests. Canadian Journal of Forest Research, 41(12), 2423-2432.More infoAbstract: Quantification of a relationship between salmon escapement in rivers and riparian tree-ring δ 15N could allow reconstruction of prehistorical salmon abundance. Unfortunately, attempts to quantify this link have met with little success. We examined the feasibility of the approach using natural abundance of δ 15N in riparian tree rings formed before and after extirpation of salmon and 15N tracer studies in a river and riparian soils. We concluded that (i) extractable (sap) N must be removed for interpretation of tree-ring δ 15N because it contains up to 78% of the N in wood, is mobile, and differs from structural N in isotopic composition, (ii) no significant change in structural tree-ring δ 15N was associated with salmon extirpation in a natural system, (iii) 500‰ 15NH 4+ added to a stream was detected in riparian tree rings spanning at least 8 years, demonstrating interring movement of N that confounds detection of an annual signal, and (iv) addition of 28 000‰ 15NH 4+ to riparian soils at a rate equaling 7.25 kg salmon·50 m -2 resulted in maximum tree-ring δ 15N of ~100‰-600‰. Thus, the calculated maximum signal possible from salmon was 0.08‰-0.43‰, which is within the range of natural variation. Evidence suggested that neither total nor structural tree-ring δ 15N was useful for reconstructing salmon abundance.
- Grissino-Mayer, H. D., Sheppard, P. R., Cleaveland, M. K., Cherubini, P., Ratcliff, P., & Topham, J. (2010). Adverse implications of misdating in dendrochronology: Addressing the re-dating of the "Messiah" violin. Dendrochronologia, 28(3), 124-132.More infoAbstract: A recent report by Mondino and Avalle (2009) was widely distributed that demonstrated a re-dating of the famous "Messiah" violin, a violin attributed to Antonio Stradivari with a label date of 1716. An outermost ring date of 1844 is instead suggested rather than dates in the 1680s reported in previous studies. Mondino and Avalle suggest that this outermost ring date supports the attribution of the violin to Jean-Baptiste Vuillaume, a prolific French instrument maker who was well known for his copies of famous instruments. The statistical techniques and exercises used by Mondino and Avalle, however, are problematic and do not support this revised outermost date for the "Messiah" violin. Raw measurement data with original trends are used in their statistical crossdating, properties previously shown to hinder precise crossdating. They then substantiate their re-dating with polynomial trend curves, which has ever been accepted practice in dendrochronology. Furthermore, the authors use re-scaled correlation coefficients and t-values which artificially inflate the strength of the relationship between tree-ring series that are being statistically crossdated. Using the exact same tree-ring data, but using accepted techniques in statistical crossdating (e.g., the removal of all low-frequency trends and autocorrelation), we could not verify the revised dating of the "Messiah" violin. We urge caution for those who intend to use the SynchroSearch software, book, and lesson plans developed and distributed by Mondino and Avalle. This study illustrates the adverse effects possible in dendrochronology when investigators do not adhere to accepted and time-tested techniques, and are not versed in the extensive literature that highlights issues commonly encountered in statistical crossdating. © 2010 Elsevier GmbH.
- Sheppard, P. R. (2010). Dendroclimatology: Extracting climate from trees. Wiley Interdisciplinary Reviews: Climate Change, 1(3), 343-352.More infoAbstract: The scientific discipline called dendrochronology is the study of tree rings and of environmental conditions and events of the past that tree growth can reflect. The beginning of scientific study of tree rings is generally ascribed to an astronomer named Andrew Ellicott Douglass, who in the early 1900s noticed not only variation in tree-ring width but also that this variability was similar between multiple trees. Dendrochronology subsequently expanded worldwide, and now over 3000 of the 12,000+ publications on dendrochronology can be classified as dendroclimatology. As a subfield of tree-ring analysis, dendroclimatology estimates climate back in time beyond the start of recorded meteorological measurements.Dendroclimatology starts with site and tree selection and continues with dating, measuring, data quality control, and chronology construction. Tree rings are associated with climate using statistical models that are then evaluated for their full length to reconstruct climate of the past. Most commonly, either precipitation or temperature is reconstructed, and reconstructions are then analyzed for frequency of extreme years, changes in mean conditions, ranges of long-term variability, and changes in interannual variability. For example, from reconstructions of Northern Hemisphere temperature based on tree rings and other natural archives of climate collected from multiple sites, it appears that current temperature (since ad 1850) exceeds the range of variability reconstructed for ad 1000-1850. Uncertainties in dendroclimatology exist, including a relatively recent issue called divergence, but dendroclimatology has played, and continues to play, a substantial role in interdisciplinary research on climate change. © 2010 John Wiley & Sons, Ltd.
- Sheppard, P. R., Donaldson, B. A., & Huckleberry, G. (2010). Quantitative assessment of a field-based course on integrative geology, ecology and cultural history. International Research in Geographical and Environmental Education, 19(4), 295-313.More infoAbstract: A field-based course at the University of Arizona called Sense of Place (SOP) covers the geology, ecology and cultural history of the Tucson area. SOP was quantitatively assessed for pedagogical effectiveness. Students of the Spring 2008 course were given pre- and post-course word association surveys in order to assess awareness and comprehension of the geology, ecology and cultural history of the Tucson area. Students who had previously taken SOP (2005-2007) and students who had never taken SOP also completed the survey. The survey consisted of 12 stimulus terms, all of which represent concepts integral to an understanding of environmental geography of the Tucson area. The students wrote words that they associate with each stimulus term. Differences between the pre- and post-course responses showed clear improvement in awareness and comprehension of the geology, ecology and cultural history of the Tucson area. Results from students who took SOP in past years indicate that long-term retention of course content is good. The word association technique proved to be effective for collecting data and evaluating the course. The field trips of SOP are described in the Appendix, which also contains the word association survey used in this research. © 2010 Taylor & Francis.
- Fastje, C. D., Kim, L. e., Sun, N. N., Wong, S. S., Sheppard, P. R., & Witten, M. L. (2009). Prenatal exposure of mice to tungstate is associated with decreased transcriptome-expression of the putative tumor suppressor gene, DMBT1: Implications for childhood leukemia. Land Contamination and Reclamation, 17(1), 169-178.More infoAbstract: Background. Two concurrent, childhood leukemia clusters have been identified in the southwestern United States at Fallon, Nevada, and Sierra Vista, Arizona. Additionally, Fallon, Nevada has also experienced concurrent contamination by atmospheric tungsten particles. The etiology of leukemia is not known. Hypothesized risk factors for leukemia are environmental exposure, genetic predisposition, and viral infection. Additionally, strong evidence supports a prenatal origin. Our objective is to generate testable hypotheses towards elucidating the probable, multi-factorial etiology of leukemia by identifying the exposures unique to Fallon, Nevada, and held in common with Sierra Vista, Arizona, then exposing C57BL/6 mice, while In utero, to these chemicals to ascertain their leukemogenic potential. Utilizing advances in medical geology to analyze tree rings, surface dust, lichens and atmospheric particulate matter, we have identified tungsten and arsenic as potentially relevant to leukemogenesis. Methods. We utilized microarray (Affymetrix 430A 2.0 mouse) and real-time RTPCR of Dmbt1 transcriptome-expression in spleen tissue collected from four-week-old C57BL/6 mouse pups (N = 6-8/group/gender) exposed, while In utero, to tungstate, arsenite, tungstate/arsenite and longitudinal controls at 20% of the normalized exposure a human mother would receive during gestation at mean environmental concentrations. Results. Prenatal exposure to tungstate is associated with a 37 + 1.2-fold (p = 0.012) decrease in DMBT1 transcriptome-expression in mice expressing DMBT1 at high levels. Additionally, prenatal exposure to tungstate/arsenite significantly altered a cytokine-cytokine receptor interaction pathway associated with lymphocyte activation and a network associated with hematological/immunological disease. Conclusion. Because DMBT1 protein products are known to aggregate viruses and possibly regulate immune response, additional research is warranted to determine the potential that prenatal exposure to tungstate or tungstate/ arsenite has to increase susceptibility to viruses and to induce leukemogenesis. © 2009 C.D. Fastje, K. Le, N.N. Sun, S.S. Wong, P.R. Sheppard and M.L. Witten.
- Sheppard, P. R., Hallman, C. L., Rldenour, G., & Witten, M. L. (2009). Spatial patterns of tungsten and cobalt on leaf surfaces of trees in Fallon, Nevada. Land Contamination and Reclamation, 17(1), 31-41.More infoAbstract: Spatial patterns of airborne tungsten and cobalt are described from leaf-surface chemistry of trees in Fallon, Nevada, where a cluster of childhood leukemia has been ongoing since 1997. In earlier research, airborne tungsten and cobalt have been shown to be elevated in total suspended particulates, surface dust, and lichens from Fallon. To update data on the spatial patterns of airborne tungsten and cobalt in Fallon, leaves were collected in October 2007 from trees growing throughout Fallon. Collected leaves were measured for metals accumulated onto their surfaces. On Fallon leaf surfaces, tungsten and cobalt show maxima of 17 ppm and 6 ppm, respectively, near the center of town, north of Highway 50 and west of Highway 95. These two peaks overlap spatially, and given the dense and widespread pattern of collection, the source area of these two airborne metals can be pinpointed to the vicinity of a hard-metal industry located north of Highway 50 and west of Highway 95. Fallon is distinctive in west central Nevada for its elevated airborne tungsten and cobalt particulates, and given its cluster of childhood leukemia cases, it stands to reason that additional biomedical research is in order to test directly the leukogenicity of combined airborne tungsten and cobalt particulates. © 2009 Paul R. Sheppard, Christine L. Hallman, Gary Ridenour and Mark L. Witten.
- Sheppard, P. R., Ort, M. H., Anderson, K. C., Clynne, M. A., & May, E. M. (2009). Multiple dendrochronological responses to the eruption of Cinder Cone, Lassen Volcanic National Park, California. Dendrochronologia, 27(3), 213-221.More infoAbstract: Two dendrochronological properties - ring width and ring chemistry - were investigated in trees near Cinder Cone in Lassen Volcanic National Park, northeastern California, for the purpose of re-evaluating the date of its eruption. Cinder Cone is thought to have erupted in AD 1666 based on ring-width evidence, but interpreting ring-width changes alone is not straightforward because many forest disturbances can cause changes in ring width. Old Jeffrey pines growing in Cinder Cone tephra and elsewhere for control comparison were sampled. Trees growing in tephra show synchronous ring-width changes at AD 1666, but this ring-width signal could be considered ambiguous for dating the eruption because changes in ring width can be caused by other events. Trees growing in tephra also show changes in ring phosphorus, sulfur, and sodium during the late 1660s, but inter-tree variability in dendrochemical signals makes dating the eruption from ring chemistry alone difficult. The combination of dendrochemistry and ring-width signals improves confidence in dating the eruption of Cinder Cone over the analysis of just one ring-growth property. These results are similar to another case study using dendrochronology of ring width and ring chemistry at Parícutin, Michoacán, Mexico, a cinder cone that erupted beginning in 1943. In both cases, combining analysis with ring width and ring chemistry improved confidence in the dendro-dating of the eruptions. © 2009 Elsevier GmbH. All rights reserved.
- Gates, J. B., Edmunds, W. M., Jinzhu, M. a., & Sheppard, P. R. (2008). A 700-year history of groundwater recharge in the drylands of NW China. Holocene, 18(7), 1045-1054.More infoAbstract: A 700-year semi-quantitative history of diffuse groundwater recharge in the Badain Jaran Desert (Inner Mongolia) is proposed on the basis of solute data from multiple unsaturated zone groundwater profiles using mass balance of chloride to establish recharge rates and profile chronologies. Four relatively humid (1330-1430, 1500-1620, 1700-1780 and 1950-1990) and three relatively arid phases (1430-1500, 1620-1700 and 1900-1950) are discernable across the profiles. The recharge history broadly reflects multidecadal to centurial timescale precipitation changes in the northern Tibetan Plateau and suggests that variations in East Asian Summer Monsoon intensity affect desert recharge rates. Uncertainties in the records owing to assumptions about the Cl inputs are examined by comparing deterministic and stochastic Cl input scenarios. Such records are valuable for assessing spatial aspects of climate changes in the region, as well as for informing sustainable water resource management strategies for northwestern China's drylands. © 2008 SAGE Publications.
- Sheppard, P. R., Hallman, C. L., & Towner, R. H. (2008). Environmental history of the southwest as a general science education course. Journal of Geoscience Education, 56(3), 212-219.More infoAbstract: Environmental History of the Southwest is a general science education course at the University of Arizona with an emphasis on human-environment interaction of the past and an objective of preparing non-science majors to understand and critically evaluate contemporary environmental issues. The American Southwest is well suited for such a course, as it is rich in many data sets of paleoenvironmental reconstruction techniques and has been inhabited by humans for thousands of years. Lectures are grouped into three parts. Part 1, Background, covers geology and climatology, paleoenvironmental techniques, and ecosystems. Part 2, Past Environments and Societies, covers environmental changes since the late Pleistocene and human response to and interaction with those changes. Part 3, Modern Environmental Issues, covers contemporary environmental issues as well as past analogs of these issues for comparison. Lecture topics are interconnected with one another, making for a comprehensive study of environmental history. Several elements of science are revealed and discussed, improving general science literacy among the students, who are mostly non-science majors. Other regions of North America have had long-term human habitation and are also rich in multiple data sets of paleoenvironmental indicators, so nearly all of the continental U.S. and Canada is suitable for a course on environmental history and human-environment interaction.
- Sheppard, P. R., Ort, M. H., Anderson, K. C., Elson, M. D., Vázquez-Selem, L., Clemens, A. W., Little, N. C., & Speakman, R. J. (2008). Multiple dendrochronological signals indicate the eruption of Parícutin volcano, Michoacán, Mexico. Tree-Ring Research, 64(2), 97-108.More infoAbstract: The eruption of Parícutin (1943-1952), a cinder cone volcano in Michoacán, Mexico, caused dendrochronological and dendrochemical responses that might be useful as general dating tools for eruptions. For the eruption period, pines near Parícutin have slightly suppressed ring widths plus high inter-annual variability of width. Wood anatomy changes include traumatic resin ducts and thin bands of false latewood. Dendrochemistry of tree rings shows little temporal variation in most elements, but beginning in 1943 sulfur content increased in rings of four trees and phosphorus content increased in rings of two trees. Hypotheses for increased S and P include new availability of pre-existing soil S and P and/or new input of S and P from the tephra itself. Pines at Parícutin also show suppressed ring widths for five years beginning in 1970, and had the eruption date not been known, the most likely conclusion from ring-width data alone would have been an eruption from 1970 to 1974. However, the 1970s suppression was in response to defoliation by a pine sawfly outbreak, not an eruption. For dendrochronological dating of cinder-cone eruptions, a combination of multiple characteristics (width, chemistry, and anatomy) would be more reliable than depending on any one characteristic alone. Copyright © 2008 by The Tree-Ring Society.
- Sheppard, P. R., Speakman, R. J., Ridenour, G., & Witten, M. L. (2008). Tungsten and cobalt: Sheppard et al. Respond. Environmental Health Perspectives, 116(5), A197.
- Sheppard, P. R., & Wiedenhoeft, A. (2007). An advancement in removing extraneous color from wood for low-magnification reflected-light image analysis of conifer tree rings. Wood and Fiber Science, 39(1), 173-183.More infoAbstract: This paper describes the removal of extraneous color from increment cores of conifers prior to reflected-light image analysis of tree rings. Ponderosa pine in central New Mexico was chosen for study. Peroxide bleaching was used as a pretreatment to remove extraneous color and still yield usable wood for image analysis. The cores were bleached in 3% peroxide raised to pH 12 and heated to 60° C, and then they were soaked in 95% ethanol and rinsed in water. The cores were dried slowly to avoid checking or cracking. This treatment removed heartwood color while leaving the wood reasonably sound. Wood reflectance and latewood width were measured using reflected-light image analysis. For dendroclimatic modeling, best-subsets regression was used to determine the strongest predictive model, which was May-September rainfall using latewood reflectance and latewood width. The ability to dendroclimatically model and reconstruct summer precipitation is contingent on having latewood reflectance (density) measurements, and reconstructing summer precipitation in the Southwest will enhance paleoclimatology of the region. Image analysis with reflected white light is thus closer to being more widely applicable in dendrochronology. © 2007 by the Society of Wood Science and Technology.
- Sheppard, P. R., Speakman, R. J., Farris, C., & Witten, M. L. (2007). Multiple environmental monitoring techniques for assessing spatial patterns of airborne tungsten. Environmental Science and Technology, 41(2), 406-410.More infoPMID: 17310699;Abstract: This paper describes the application of the chemistry of total suspended participates, lichens/mosses, and surface dust for assessing spatial patterns of airborne tungsten and other metals. These techniques were used recently in Fallon, NV, where distinctive spatial patterns of airborne tungsten were demonstrated. However, doubt has been raised about the extent of airborne tungsten in Fallon. Therefore, these techniques were tested specifically for W in another town that has a small industry known to emit tungsten particles. Airborne particulates were collected in Sweet Home, OR, as well as in nearby comparison towns to provide baseline data. Lichens/mosses were collected in Sweet Home near the known source of W as well as outside of Sweet Home. Surface dust was collected throughout Sweet Home to map concentrations of metals. All three of these environmental monitoring techniques confirm that W is elevated right near the known source of airborne W in Sweet Home but no where else in Sweet Home. This test should allay doubts about the multiple findings of elevated airborne W in Fallon, NV, and this should also instill confidence in these techniques generally for assessing W and other metals in urban environments. © 2007 American Chemical Society.
- Sheppard, P. R., Speakman, R. J., Ridenour, G., & Witten, M. L. (2007). Temporal variability of tungsten and cobalt in Fallon, Nevada. Environmental Health Perspectives, 115(5), 715-719.More infoPMID: 17520058;PMCID: PMC1867993;Abstract: Background: Since 1997, Fallon, Nevada, has experienced a cluster of childhood leukemia that has been declared "one of the most unique clusters of childhood cancer ever reported." Multiple environmental studies have shown airborne tungsten and cobalt to be elevated within Fallon, but the question remains: Have these metals changed through time in correspondence with the onset of the leukemia cluster? Methods: We used dendrochemistry, the study of element concentrations through time in tree rings, in Fallon to assess temporal variability of airborne tungsten and cobalt since the late 1980s. The techniques used in Fallon were also tested in a different town (Sweet Home, OR) that has airborne tungsten from a known source. Results: The Sweet Home test case confirms the accuracy of dendrochemistry for showing temporal variability of environmental tungsten. Given that dendrochemistry works for tungsten, tree-ring chemistry shows that tungsten increased in Fallon relative to nearby comparison towns beginning by the mid-1990s, slightly before the onset of the cluster, and cobalt has been high throughout the last - 15 years. Other metals do not show trends through time in Fallon. Discussion: Results in Fallon suggest a temporal correspondence between the onset of excessive childhood leukemia and elevated levels of tungsten and cobalt. Although environmental data alone cannot directly link childhood leukemia with exposure to metals, research by others has shown that combined exposure to tungsten and cobalt can be carcinogenic to humans. Conclusion: Continued biomedical research is warranted to directly test for linkage between childhood leukemia and tungsten and cobalt.
- Sheppard, P. R., Speakman, R. J., Ridenour, G., & Witten, M. L. (2007). Using lichen chemistry to assess airborne tungsten and cobalt in Fallon, Nevada. Environmental Monitoring and Assessment, 130(1-3), 511-518.More infoPMID: 17131081;Abstract: This paper describes the use of lichen chemistry to assess airborne tungsten and cobalt in Fallon, Nevada, where a cluster of childhood leukemia has been on going since 1997. Lichens and their rock substrates were collected from Rattlesnake Hill within Fallon as well as from four different rock outcrops located north, east, south, and west of Fallon and at least 20 km away from the town center. In the lichens themselves, W and Co are significantly higher within Fallon than in the combined control site outside of Fallon. In the rock substrates of the lichens, no differences exist in W and Co. The W and Co differences in lichens cannot be attributed to substrate geochemistry. Fallon is distinctive in west central Nevada for high airborne W and Co, and given its cluster of childhood leukemia, it stands to reason that additional biomedical research is in order to test directly the leukogenicity of combined airborne W and Co. © Springer Science+Business Media B.V. 2006.
- Sheppard, P. R., Speakman, R. J., Ridenour, G., Glascock, M. D., Farris, C., & Witten, M. L. (2007). Spatial patterns of tungsten and cobalt in surface dust of Fallon, Nevada. Environmental Geochemistry and Health, 29(5), 405-412.More infoPMID: 17345005;Abstract: Spatial patterns of tungsten and cobalt are described for surface dust of Fallon, Nevada, where a cluster of childhood leukemia has been ongoing since 1997. In earlier research, airborne tungsten and cobalt was shown to be elevated in total suspended particulates in Fallon. To fine-tune the spatial patterns of tungsten and cobalt deposition in Fallon, surface dust was collected in a grid pattern within as well as outside of Fallon to establish background concentrations of metals. In surface dust, tungsten and cobalt show sharp peaks (934 ppm and 98 ppm, respectively) within Fallon just north of highway 50 and west of highway 95. These two peaks overlap spatially, and given the grid pattern used for collecting surface dust, the source area of these two airborne metals can be pinpointed to the vicinity of hard-metal industry located north of highway 50 and west of highway 95. Fallon is distinctive in west central Nevada because of high airborne tungsten and cobalt particulates, and given its cluster of childhood leukemia, it stands to reason that additional biomedical research is in order to test directly the leukogenicity of combined airborne tungsten and cobalt particulates. © Springer Science+Business Media B.V. 2007.
- Sheppard, P. R., Toepfer, P., Schumacher, E., Rhodes, K., Ridenour, G., & Witten, M. L. (2007). Morphological and chemical characteristics of airborne tungsten particles of Fallon, Nevada. Microscopy and Microanalysis, 13(4), 296-303.More infoPMID: 17637079;Abstract: Morphological and chemical characteristics were determined for airborne tungsten particles in Fallon, Nevada, a town that is distinguishable environmentally by elevated airborne tungsten and cobalt. From samples of airborne dust collected previously at six different places in Fallon, tungsten-rich dust particles were isolated and analyzed with automated electron microprobe and wavelength-dispersive spectrometry. Representative W particles were further analyzed using transmission electron microscopy. Morphologically, Fallon W particles are angular and small, with minimum and maximum sizes of ≤1 μm and 5.9 μm in diameter, respectively. The number and size of tungsten-rich particles decrease in Fallon with distance from a hard-metal facility located near the center of town. Chemically, Fallon airborne W particles include mixtures of tungsten with cobalt plus other metals such as chromium, iron, and copper. No W-rich particles were identifiable as CaWO 4 (scheelite) or MnWO4 (huebnerite). From d-spacings, Fallon particles are most consistent with identification as tungsten carbide. Based on these multiple lines of evidence, airborne W particles in Fallon are anthropogenic in origin, not natural. The hard-metal facility in Fallon processes finely powdered W and W-Co, and further investigation using tracer particles is recommended to definitively identify the source of Fallon's airborne tungsten. © MICROSCOPY SOCIETY OF AMERICA 2007.
- Seiler, R. L., Sheppard, P. R., Speakman, R. J., Ridenour, G., & Witten, M. L. (2006). Comment on "Elevated tungsten and cobalt in airborne particulates in Fallon, Nevada: Possible implications for the childhood leukemia cluster" by P.R. Sheppard, G. Ridenour, R.J. Speakman and M.L. Witten. Applied Geochemistry, 21(4), 713-723.
- Sheppard, P. R., & Singavarapu, S. Y. (2006). Solving the "magnification irony" in microscope-based reflected light image analysis of conifer tree rings. Journal of Imaging Science and Technology, 50(3), 304-308.More infoAbstract: This paper describes a technique for allowing the magnification of a microscope to be changed and still obtain quantitative reflectance values for low-magnification reflected light image analysis of conifer tree rings. A remotely controllable digital camera is used to capture images, and a multireflectance gray standard is used to calibrate the luminance response of the camera across a range of reflectances. The imaging system was tested by measuring two conifer rings of differing widths and densities at several different levels of magnification. Upon adjusting the camera and converting gray values to true reflectances, the earlywood maximum and late-wood minimum reflectances of each ring were essentially identical across all magnification settings. Total ring widths were also equal across all magnification settings. The "magnification irony" is solved for microscope-based reflected light image analysis of conifer tree rings, and reflected light image analysis of conifer tree rings should become more prominent in future dendrochronological investigations. © 2006 Society for Imaging Science and Technology.
- Sheppard, P. R., Ridenour, G., Speakman, R. J., & Witten, M. L. (2006). Elevated tungsten and cobalt in airborne particulates in Fallon, Nevada: Possible implications for the childhood leukemia cluster. Applied Geochemistry, 21(1), 152-165.More infoAbstract: Trace metal content was measured in airborne particulates in five towns located in west central Nevada with an emphasis on Fallon, where 16 cases of childhood leukemia were diagnosed recently. Airborne dust samples were collected using portable, high-volume particulate air samplers, and each filter was chemically analyzed by acid-dissolution, inductively coupled plasma mass spectroscopy. Tungsten was the most notable metal in Fallon dust, with cobalt of secondary but still important interest. Tungsten and cobalt were elevated in Fallon relative to comparison towns of west central Nevada, and within Fallon they co-varied closely temporally and spatially. These results were obtained and confirmed in two different collections during two different seasons of the year and using entirely different hardware and different types of filters. By weight of multiple lines of evidence, the source of tungsten and cobalt in airborne particulates in Fallon is probably not natural, but rather a hard-metal facility located in Fallon should tentatively be considered a candidate source of the airborne exposure of these metals within Fallon. Neither tungsten nor cobalt has yet to be definitively associated with childhood leukemia, but cobalt and tungsten carbide together are probably carcinogenic to humans. We concur with calls by others for more research in Fallon, and we recommend that cobalt be added into the toxicological studies, especially as an interactive factor with tungsten. © 2005 Elsevier Ltd. All rights reserved.
- Sheppard, P. R., Speakman, R. J., Ridenour, G., & Witten, M. L. (2006). Reply to comment on "Elevated tungsten and cobalt in airborne particulates in Fallon, Nevada: Possible implications for the childhood leukemia cluster", by Blasland, Bouck & Lee, Inc.. Applied Geochemistry, 21(6), 1083-1088.More infoAbstract: Several criticisms of Sheppard et al. (2006a) are raised in this comment. One, airborne W and Co loadings are expressed as mass of element per volume of air rather than mass of element per mass of dust and therefore cannot be reasonably interpreted. Two, inter-seasonal patterns of airborne W and Co in Fallon seem inconsistent. Three, the role of wind direction on airborne W and Co in Fallon is not clear. Four, elevated levels of airborne W and Co in Fallon do not approach threshold limits of exposure established for workplaces. Five, children of Fallon do not necessarily live near the hard-metal facility in Fallon and therefore are not exposed to elevated airborne W and Co. Six, research on total suspended particulates of Fallon was not warranted because airborne W in Fallon had been studied already. The authors respond to these criticisms as well as to additional points made in this comment. © 2006 Elsevier Ltd. All rights reserved.
- Sheppard, P. (2005). The Italian Mezzogiorno. Geography Review, 19(1), 14-16.More infoAbstract: This short article presents a case study in regional development on the periphery of the EU. It is relevant to the study of Europe, regional planning and migration.
- Sheppard, P. R., & Witten, M. L. (2005). Laser trimming tree-ring cores for dendrochemistry of metals. Tree-Ring Research, 61(2), 87-92.More infoAbstract: This article discusses the application of laser to trim the outer surface from tree-ring increment cores in preparation for dendrochemistry of certain metals. A source of contamination specific to dendrochemistry of metals is metal constituents, such as iron, tungsten, chromium, nickel, and cobalt, coming off tools used to collect and process cores and adhering to the sample surface. One method to eliminate this contamination is to trim off the outer surface of cores using laser. To test this application of laser, three tree-ring increment cores were collected from each of three trees. For each tree, one core was trimmed using a CO2 laser, one core was trimmed using a stainless steel razor blade, and one core was left untrimmed. The resultant cores were measured for metals using acid dissolution inductively coupled plasma mass spectroscopy. Trimmed cores had on average one-third the content of iron, tungsten, and chromium than that of untrimmed cores. Laser-trimmed cores had less of these metals than razor-trimmed cores. Razor-trimmed cores also had measurable nickel, but laser-trimmed cores had no nickel. Laser trimming is an ideal solution to potential contamination of cores with metals from increment borers without imparting other contamination from tools such as razor blades. Copyright © 2005 by the Tree-Ring Society.
- Sheppard, P. R., May, E. M., Ort, M. H., Anderson, K. C., & Elson, M. D. (2005). Dendrochronological responses to the 24 October 1992 tornado at Sunset Crater, northern Arizona. Canadian Journal of Forest Research, 35(12), 2911-2919.More infoAbstract: This paper documents tree-ring responses to a historic tornado and reevaluates prehistoric tree-ring changes seen in archaeological wood of Wupatki Ruin used to date the 11th-century eruption of Sunset Crater. The historic tornado occurred at Sunset Crater, northern Arizona, on 24 October 1992, and trees within areas damaged by the tornado survived the event and continue living today. The objectives of this research were to document their ring-growth changes and to consider the possibility of tornadoes as a candidate disturbance for the prehistoric ring-growth changes of Wupatki. About half of the trees sampled within areas damaged by the tornado show one or more dendrochronological responses to that event, including ring-width release, reaction wood, ring-width suppression, and (or) reduced latewood. Tornado damage is not a likely candidate for having caused the abrupt ring-width changes at AD 1064-1065 seen at Wupatki. However, five living ponderosa pines (Pinus ponderosa Dougl. ex P. & C. Laws.) at Sunset Crater experienced abrupt and severe suppressions in ring growth beginning decades ago and continuing today. No single disturbance seems obvious for causing these growth suppressions, but further research is merited to find the cause of these modern suppressions to propose a new candidate explanation for the AD 1064 suppression. © 2005 NRC.
- Grissino-Mayer, H. D., Sheppard, P. R., & Cleaveland, M. K. (2004). A dendroarchaeological re-examination of the "Messiah" violin and other instruments attributed to Antonio Stradivari. Journal of Archaeological Science, 31(2), 167-174.More infoAbstract: The "Messiah" violin is considered by many to be the finest work by Antonio Stradivari and one of the most valuable musical instruments in existence. Questions were recently raised concerning its authenticity on stylistic and historical grounds, especially in light of conflicting sets of tree-ring dates for the spruce top of the violin. To resolve this controversy, we analysed the tree rings on the "Messiah" and those found on five other instruments constructed in the same general period, dating these against a regional chronology that integrated 16 alpine tree-ring chronologies from five countries. We conclusively dated both the "Archinto" (1526-1686) and "Kux"/"Castelbarco" (1558-1684) violas against the regional chronology. We could not directly date the "Messiah" against the regional master chronology, but found that its tree rings dated well against both the "Archinto" and "Kux"/"Castelbarco" violas. Our results strongly suggest that the tree rings of the "Messiah" violin date between 1577-1687, dates that support the attribution to Antonio Stradivari and the label date of 1716. We hypothesize the wood used to make the "Messiah" came from a low-elevation tree growing distant from the high alpine areas, whereas the wood used to make the two violas likely came from an intermediate, mid-elevation location. © 2003 Elsevier Ltd. All rights reserved.
- Grissino-Mayer, H. D., Sheppard, P. R., & Cleaveland, M. K. (2004). A dendroarchaeological re-examination of the "Messiah" violin and other instruments attributed to Antonio Stradivari. Journal of Archaeological Science, 31(8), 167-174.More infoAbstract: The "Messiah" violin is considered by many to be the finest work by Antonio Stradivari and one of the most valuable musical instruments in existence. Questions were recently raised concerning its authenticity on stylistic and historical grounds, especially in light of conflicting sets of tree-ring dates for the spruce top of the violin. To resolve this controversy, we analysed the tree rings on the "Messiah" and those found on five other instruments constructed in the same general period, dating these against a regional chronology that integrated 16 alpine tree-ring chronologies from five countries. We conclusively dated both the "Archinto" (1526-1686) and "Kux"/ "Castelbarco" (1558-1684) violas against the regional chronology. We could not directly date the "Messiah" against the regional master chronology, but found that its tree rings dated well against both the "Archinto" and "Kux"/ "Castelbarco" violas. Our results strongly suggest that the tree rings of the "Messiah" violin date between 1577-1687, dates that support the attribution to Antonio Stradivari and the label date of 1716. We hypothesize the wood used to make the "Messiah" came from a low-elevation tree growing distant from the high alpine areas, whereas the wood used to make the two violas likely came from an intermediate, mid-elevation location. © 2003 Elsevier Ltd. All rights reserved.
- Sheppard, P. R., Tarasov, P. E., Graumlich, L. J., Heussner, K. -., Wagner, M., Österle, H., & Thompson, L. G. (2004). Annual precipitation since 515 BC reconstructed from living and fossil juniper growth of northeastern Qinghai Province, China. Climate Dynamics, 23(7-8), 869-881.More infoAbstract: Annual precipitation for the last 2,500 years was reconstructed for northeastern Qinghai from living and archaeological juniper trees. A dominant feature of the precipitation of this area is a high degree of variability in mean rainfall at annual, decadal, and centennial scales, with many wet and dry periods that are corroborated by other paleoclimatic indicators. Reconstructed values of annual precipitation vary mostly from 100 to 300 mm and thus are no different from the modern instrumental record in Dulan. However, relatively dry years with below-average precipitation occurred more frequently in the past than in the present. Periods of relatively dry years occurred during 74-25 BC, AD 51-375, 426-500, 526-575, 626-700, 1100-1225, 1251-1325, 1451-1525, 1651-1750 and 1801-1825. Periods with a relatively wet climate occurred during AD 3760-425, 576-625, 951-1050, 1351-1375, 1551-1600 and the present. This variability is probably related to latitudinal positions of winter frontal storms. Another key feature of precipitation in this area is an apparently direct relationship between interannual variability in rainfall with temperature, whereby increased warming in the future might lead to increased flooding and droughts. Such increased climatic variability might then impact human societies of the area, much as the climate has done for the past 2,500 years. © Springer-Verlag 2004.
- Sun, N. N., Fastje, C. D., Wong, S. S., Sheppard, P. R., Macdonald, S. J., Ridenour, G., Hyde, J. D., & Witten, M. L. (2003). Dose-dependent transcriptome changes by metal ores on a human acute lymphoblastic leukemia cell line. Toxicology and Industrial Health, 19(7-10), 157-163.More infoPMID: 15747776;Abstract: The increased morbidity of childhood leukemia in Fallon, Nevada and Sierra Vista, Arizona has prompted great health concern. The main characteristic that these two towns share is the environmental pollution attributed to metal ore from abandoned mining operations. Consequently, we have investigated the transcriptome effects of metal ores from these endemic areas using a human T-cell acute lymphoblastic leukemia cell line (T-ALL). Metal ore from Fallon significantly increased cell growth after 24, 48 and 72 h of incubation at 1.5 μg/mL concentration, as measured by trypan-blue. Sierra Vista ore significantly increased cell growth with 0.15 and 1.5 μg/mL following 72 h of incubation. From human cDNA microarray, results indicate that in total, eight genes, mostly metallothionein (MT) genes, were up-regulated and 10 genes were down-regulated following treatment of the T-ALL cells with 0.15 and 1.5 μg/mL of metal ores at 72 h, in comparison with untreated cells. Twenty-eight metals of both ores were quantified and their presence may be associated with the cell growth rate and dose-dependent activation of transcriptomes in immature T-cells.
- Grissino-Mayer, H. D., Cleaveland, M. K., & Sheppard, P. R. (2002). Mastering the rings. Strad, 113(1344), 408-455.
- Sheppard, P. R., & Thompson, T. L. (2000). Effect of extraction pretreatment on radial variation of nitrogen concentration in tree rings. Journal of Environmental Quality, 29(6), 2037-2042.More infoAbstract: When other nutrients are not limiting, increased nitrogen availability from atmospheric deposition can lead to increased plant growth. In this study, different wood extraction pretreatments to remove mobile N and/or other extraneous compounds to better assess N concentrations in tree rings were tested and compared. The study was conducted using two stands of trees in southern Arizona, consisting of Douglas-fir and ponderosa pine. Three cores were collected from each sampled tree. One was used as a control; one was extracted for 4 h in a 50:50 mixture of toluene and ethanol, then for 4 h in ethanol, and then for 1 h in distilled water; and the third was extracted with the same solvents, but each was used for 24 h. Results showed that extraction of wood significantly reduced radial variation of N concentration, eliminating most of the variation in N concentration attributed to the heartwood-sapwood boundary or to the most-recently formed rings. Results from the extended extraction regime were similar to those generated by shorter-duration extraction.
- Sheppard, P. R. (1999). Overcoming extraneous wood color variation during low-magnification reflected-light image analysis of conifer tree rings. Wood and Fiber Science, 31(2), 106-115.More infoAbstract: The objective of this study was to test ways of overcoming extraneous wood color variation during low-magnification reflected-light image analysis of conifer tree rings and thereby improve the applicability of reflected-light image analysis in dendrochronology. Increment cores from ponderosa pines exhibiting strong heartwood discoloration were examined using image analysis. The research design included three sample preparation treatments (CONTROL, EXTRACT, or BLEACH) crossed with two dendrochronology treatments (STANDARD or RESIDUAL) crossed with two data treatments (SPLIT at the heartwood-sapwood boundary or left at FULL length) to remove the effects of the extraneous color variation. Using a combination of two ring-brightness variables and total ring width, the climate-ring growth model of the EXTRACT-RESIDUAL-FULL was strongest and explained 31.2% of variation in July-October precipitation of southeastern Arizona. Organic extraction (EXTRACT) was helpful in this study but did not fully remove heartwood discoloration. Weak bleaching (BLEACH) removed extraneous color, including heartwood discoloration, but it also removed the ring-brightness signal related to climate. Removing autocorrelation from brightness variables (RESIDUAL) overcame the problem of extraneous color but also possibly removed environmentally relevant information. Keeping brightness series at full length (FULL) worked satisfactorily. Hopefully, future research can successfully isolate some other bleaching, extraction, and/or staining treatment that removes only extraneous color variation from the wood while retaining environmentally relevant color variation so that low-magnification reflected-light image analysis can be widely applicable in dendrochronological studies of conifers.
- Kang, X., Graumlich, L. J., & Sheppard, P. (1997). A 1 835 a tree-ring chronology and its preliminary analyses in Dulan region, Qinghai. Chinese Science Bulletin, 42(13), 1122-1124.
- Sheppard, P. R., Graumlich, L. J., & Conkey, L. E. (1996). Reflected-light image analysis of conifer tree rings for reconstructing climate. Holocene, 6(1), 62-68.More infoAbstract: We use reflected-light image analysis to measure brightness of conifer rings, and we use brightness as an alternative to density for reconstructing climate. Using densitometry and image analysis, we measured cores from red spruce (Picea rubens Sarg.) growing at Elephant Mountain, Maine, and then compared statistical characteristics of density and brightness and climate-tree growth models using density or brightness. Auto-correlational and cross-correlational statistics of density and brightness do not differ substantially, and late wood density and brightness both correlate with April-May average temperature, which both tree-ring variables reconstruct equally well. April-May temperature was highly variable during most of the nineteenth century and was below average during the AD 1830s, 1870s and late 1880s. When done carefully, reflected-light image analysis can substitute for X-ray densitometry for measuring tree rings to reconstruct climate of the latest Holocene.
- Sheppard, P. R., & White, L. O. (1995). Tree-ring responses to the 1978 earthquake at Stephens Pass, northeastern California. Geology, 23(2), 109-112.More infoAbstract: The 1978 earthquake at Stephens Pass, dropped a series of grabens that average 4.5 m in width, extend up to 1 m in depth, and are found intermittently along a 2-km-long rupture zone. The formation of this graben series killed or otherwise affected many trees growing in or immediately adjacent to the rupture zone. Nine trees responded to the 1978 earthquake with anomalously narrow ring widths, beginning in 1979 and continuing for several years. One tree responded with anomalously wide latewood relative to total ring width. This study serves as a specific calibration example for dendrochronologically studying prehistoric earthquakes. -from Authors
- Sheppard, P. R., & Jacoby, G. C. (1989). Application of tree-ring analysis to paleoseismology: two case studies. Geology, 17(3), 226-229.More infoAbstract: Knowledge of earthquake probabilities is essential for planning earthquake hazard mitigation, and valid estimation of future probabilities requires precise information on past earthquake occurrences. Previous studies documented effects of earthquakes on trees and how these effects are recorded by tree rings. Tree-ring analysis can be combined with other disciplines to date and delineate earthquake-induced disturbance. Two case studies show the impact of the 1964 Alaska earthquake on shoreline trees and how a previously unknown southern San Andreas fault earthquake was recorded in tree rings. -Authors
- Jacoby Jr., G. C., Sheppard, P. R., & Sieh, K. E. (1988). Irregular recurrence of large earthquakes along the San Andreas fault: Evidence from trees. Science, 241(4862), 196-199.More infoAbstract: Old trees growing along the San Andreas fault near Wrightwood, California, record in their annual ring-width patterns the effects of a major earthquake in the fall or winter of 1812 to 1813. Paleoseismic data and historical information indicate that this event was the "San Juan Capistrano" earthquake of 8 December 1812, with a magnitude of 7.5. The discovery that at least 12 kilometers of the Mojave segment of the San Andreas fault ruptured in 1812, only 44 years before the great January 1857 rupture, demonstrates that intervals between large earthquakes on this part of the fault are highly variable. This variability increases the uncertainty of forecasting destructive earthquakes on the basis of past behavior and accentuates the need for a more fundamental knowledge of San Andreas fault dynamics.
- Sheppard, P. R., Means, J. E., & Lassoie, J. P. (1988). Cross-dating cores as a nondestructive method for dating living, scarred trees. Forest Science, 34(3), 781-789.More infoAbstract: Twenty-one of 37 sampled trees were successfully dated and had identical core and wedge dates. -from Authors
- Sheppard, P. R., & Lassoie, J. P. (1986). A nondestructive method for dating living, fire-scarred trees in wilderness areas.. Proc. national wilderness research conference, Fort Collins, 1985, 35-38.More infoAbstract: The method of coring through the scar to the pith and then cross-dating the prescar growth is adequate for dating single-scarred trees, but not for multiple-scarred trees, as shown for lodgepole pine Pinus contorta. -from Authors
- Sheppard, P. R. (2018, July). Red Cones of the John Muir Trail: An Ideal field site for dendro reconstruction of Sierra snowpack. California Extreme Precipitation Symposium. Davis, CA: California Department of Water Resources.
- Sheppard, P. R. (2017, October). Advances in dendrochemistry in Chile: Issues of cities, industries and volcanoes.. EuroDendro 2017. Tartu, Estonia: EuroDendro.
- Sheppard, P. R. (2015, Spring). Dendrochemistry: It's Not As Easy As It Looks (And It Doesn't Look Easy). TRACE 2015. Sevilla, Spain: Association for Tree-Ring Research.More infoKeynote presentation at TRACE 2015, Sevilla, Spain, in English.
- Sheppard, P. R. (2015, Spring). Dendroquimica: Teoria y Applicaciones. Open presentation to ENPRESA, a commercial firm in Chile. Santiago, Chile.More infoIn conjunction with Dr. Ariel Muñoz, Valparaíso, Chile, I gave a 1-hour presentation on theory and applications of dendrochemistry to a commercial firm that has provided Ariel with funding. This presentation was entirely in Spanish.
- Sheppard, P. R. (2015, Spring). Grandes Logros de Dendrocronologia. Geografia, Universidad de Valparaiso, Chile. Valparaiso, Chile: Geografia, Universidad de Valparaiso.More infoOpen lecture in Geography, University of Valparaiso, Chile, entirely in Spanish.
- Sheppard, P. R. (2015, Summer). Measurements of nitrogen concentration and d15N in wood samples.. Advances in Stable Isotope Techniques and Analysis (ASITA) 2015. Ottawa, Canada: ISOGEOCHEM.More infoTwo presentations (one oral and one poster) on measuring nitrogen content and isotopes in tree rings.
- Sheppard, P. R. (2015, Summer). Pretreatment of wood prior to measurement of tree rings for nitrogen content and isotopes.. Advances in Stable Isotope Techniques and Analysis (ASITA) 2015. Ottawa, Canada: ISOGEOCHEM.More infoTwo presentations (one oral and one poster) on measuring nitrogen content and isotopes in tree rings.
- Hobson, C., Bednar, A., Tappero, R., Mohajerin, T. J., Sheppard, P. R., & Witten, M. L. (2014, NA). Factors influencing tungsten mobility in soils from Fallon, Nevada. Goldschmidt Conference. Sacramento, CA: Goldschmidt Geochemistry.More infoGoldschmidt Conference, Sacramento, June, 2014.
- Sheppard, P. R. (2014, January). Applications of Dendrochemistry (in Spanish). Workshop on Dendrochronology. Universidad Austral, Valdivia, Chile: Laboratory of Tree-Ring Research.
- Sheppard, P. R. (2014, January). Dendrochemistry in Chile (in Spanish). Workshop on Dendrochronology. Universidad Austral, Valdivia, Chile: Laboratory of Tree-Ring Research.
- Sheppard, P. R. (2014, June). Dendrochemistry: Applications and Measurement Issues. Stanford SLAC. Stanford, CA: Synchrotron Linear Accelerator Center.
- Sheppard, P. R. (2014, NA). Problems with measuring nitrogen in wood samples. Advances in Stable Isotope Techniques and Analysis (ASITA). Davis, Ca: ASITA.More infoInvited presentation and discussion.
- Bristilo, L., Christie, D., Alvarez, C., Muñoz, A., Lara, A., & Sheppard, P. R. (2018, September). Árboles milenarios, testigos vivos de erupciones volcánicas: registro eruptivo del volcán Calbuco durante los últimos 500 años mediante dendroquímica en Fitzroya cupressoides. XV Congreso Geológico Chileno. ???: ???.
- Sheppard, P. R., Friedt, A., Neathamer, M., & Bashir, F. (2016, April). Dendrochronology of Culturally Modified Trees, Philmont Scout Ranch, NM. 2016 Southwest Section SAF Spring Meeting. Las Cruces, New Mexico: Society of American Foresters.
- Sheppard, P. R., Friedt, A., Neathamer, M., & Bashir, F. (2016, March). Dendrochronology of Culturally Modified Trees, Philmont Scout Ranch, NM. 3rd AmeriDendro Conference. Mendoza, Argentina: Tree-Ring Society.
- Sheppard, P. R., & Falk, D. A. (2013, May). Conference Field Trip: The Santa Catalina ecological gradient. AmeriDendro: Second American Dendrochronology Conference.