Malcolm K Hughes

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• Churakova, (., Fonti, M. V., Saurer, M., Guillet, S., Corona, C., Fonti, P., Myglan, V. S., Kirdyanov, A. V., Naumova, O. V., Ovchinnikov, D. V., Shashkin, A. V., Panyushkina, I. P., Buntgen, U., Hughes, M. K., Vaganov, E. A., Siegwolf, R., & Stoffel, M. (2019). Siberian tree-ring and stable isotope proxies as indicators of temperature and moisture changes after major stratospheric volcanic eruptions. CLIMATE OF THE PAST, 15(2), 685-700.
• Cook, E. R., Hughes, M. K., & Leavitt, S. W. (2019). In Memoriam Harold Clark Fritts 1928–2019. Tree-Ring Research, 75(2), 167-169. doi:http://dx.doi.org/10.3959/1536-1098-75.2.167
• Bunn, A. G., Salzer, M. W., Anchukaitis, K. J., Bruening, J. M., & Hughes, M. K. (2018). Spatiotemporal Variability in the Climate Growth Response of High Elevation Bristlecone Pine in the White Mountains of California. GEOPHYSICAL RESEARCH LETTERS, 45(24), 13312-13321.
• Panyushkina, I. P., Shishov, V. V., Grachev, A. M., Knorre, A. A., Kirdyanov, A., Leavitt, S. W., Vaganov, E. A., Chebykin, E. P., Zhuchenko, N. A., & Hughes, M. K. (2016). Trends In Elemental Concentrations of Tree Rings From the Siberian Arctic. Tree-Ring Research, 72(2), 67-77. doi:DOI 10.3959/1536-1098-72.02.67
• Churakova, O., Siegwolf, R. T., Bryukhanova, M., Boettger, T., Naurzbaev, M. M., Myglan, V. S., Ovchinnikov, D. V., Stoffel, M., Vaganov, E. A., & Hughes, M. K. (2015). Siberian trees, Eyewitnessess to the volcanic event of AD 536. Past Global Changes, 23, 64-65.
• Tolwinski-Ward, S. E., Tingley, M. P., Evans, M. N., Hughes, M. K., & Nychka, D. W. (2015). Probabilistic reconstructions of local temperature and soil moisture from tree-ring data with potentially time-varying climatic response. CLIMATE DYNAMICS, 44(3-4), 791-806.
• Churakova (Sidorova), O. V., Bryukhanova, M. V., Saurer, M., Boettger, T., Naurzbaev, M. M., Myglan, V. S., Vaganov, E. A., Hughes, M. K., & Siegwolf, R. T. (2014). A cluster of stratospheric volcanic eruptions in the AD 530s recorded in Siberian tree rings. GLOBAL AND PLANETARY CHANGE, 122, 140-150.
• Salzer, M. W., Bunn, A. G., Graham, N. E., & Hughes, M. K. (2014). Five millennia of paleotemperature from tree-rings in the Great Basin, USA. Climate Dynamics, 42(5-6), 1517-1526.
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  Abstract: The instrumental temperature record is of insufficient length to fully express the natural variability of past temperature. High elevation tree-ring widths from Great Basin bristlecone pine (Pinus longaeva) are a particularly useful proxy to infer temperatures prior to the instrumental record in that the tree-rings are annually dated and extend for millennia. From ring-width measurements integrated with past treeline elevation data we infer decadal- to millennial-scale temperature variability over the past 4,500 years for the Great Basin, USA. We find that twentieth century treeline advances are greater than in at least 4,000 years. There is also evidence for substantial volcanic forcing of climate in the preindustrial record and considerable covariation between high elevation tree-ring widths and temperature estimates from an atmosphere-ocean general circulation model over much of the last millennium. A long-term temperature decline of ~-1.1 °C since the mid-Holocene underlies substantial volcanic forcing of climate in the preindustrial record. © 2013 The Author(s).
• Salzer, M. W., Larson, E. R., Bunn, A. G., & Hughes, M. K. (2014). Changing climate response in near-treeline bristlecone pine with elevation and aspect. ENVIRONMENTAL RESEARCH LETTERS, 9(11).
• Salzer, M. W., Larson, E. R., Bunn, A. G., & Hughes, M. K. (2014). Climate Response in Near-Treeline Bristlecone Pine. Environmental Research Letters, 9(11), 114007. doi:https://doi.org/10.1088/1748-9326/9/11/114007
• Bunn, A. G., Hughes, M. K., Kirdyanov, A. V., Losleben, M., Shishov, V. V., Berner, L. T., Oltchev, A., & Vaganov, E. A. (2013). Comparing forest measurements from tree rings and a space-based index of vegetation activity in Siberia. Environmental Research Letters, 8(3).
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  Abstract: Different methods have been developed for measuring carbon stocks and fluxes in the northern high latitudes, ranging from intensively measured small plots to space-based methods that use reflectance data to drive production efficiency models. The field of dendroecology has used samples of tree growth from radial increments to quantify long-term variability in ecosystem productivity, but these have very limited spatial domains. Since the cambium material in tree cores is itself a product of photosynthesis in the canopy, it would be ideal to link these two approaches. We examine the associations between the normalized differenced vegetation index (NDVI) and tree growth using 19 pairs of tree-ring widths (TRW) and maximum latewood density (MXD) across much of Siberia. We find consistent correlations between NDVI and both measures of tree growth and no systematic difference between MXD and TRW. At the regional level we note strong correspondence between the first principal component of tree growth and NDVI for MXD and TRW in a temperature-limited bioregion, indicating that canopy reflectance and cambial production are broadly linked. Using a network of 21 TRW chronologies from south of Lake Baikal, we find a similarly strong regional correspondence with NDVI in a markedly drier region. We show that tree growth is dominated by variation at decadal and multidecadal time periods, which the satellite record is incapable of recording given its relatively short record. © 2013 IOP Publishing Ltd.
• Hughes, M. K. (2013). Growth response of the alpine shrub, Linanthus pungens, to snowpack and temperature at a rock glacier site in the eastern Sierra Nevada of California, USA. QUATERNARY INTERNATIONAL, 310, 20-33.
• Anchukaitis, K. J., Breitenmoser, P., Briffa, K. R., Buchwal, A., Büntgen, U., Cook, E. R., D'Arrigo, R. D., Esper, J., Evans, M. N., Frank, D., Grudd, H., Gunnarson, B. E., Hughes, M. K., Kirdyanov, A. V., Körner, C., Krusic, P. J., Luckman, B., Melvin, T. M., Salzer, M. W., , Shashkin, A. V., et al. (2012). Tree rings and volcanic cooling. Nature Geoscience, 5(12), 836-837.
• Arx, G. V., Archer, S. R., & Hughes, M. K. (2012). Long-term functional plasticity in plant hydraulic architecture in response to supplemental moisture. Annals of Botany, 109(6), 1091-1100.
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  PMID: 22396436;PMCID: PMC3336947;Abstract: Background and Aims: Plasticity in structural and functional traits related to water balance may determine plant performance and survival in ecosystems characterized by water limitation or high levels of rainfall variability, particularly in perennial herbaceous species with long generation cycles. This paper addresses whether and the extent to which several such seasonal to long-term traits respond to changes in moisture availability. Methods: Using a novel approach that integrates ecology, physiology and anatomy, a comparison was made of lifetime functional traits in the root xylem of a long-lived perennial herb (Potentilla diversifolia, Rosaceae) growing in dry habitats with those of nearby individuals growing where soil moisture had been supplemented for 14 years. Traditional parameters such as specific leaf area (SLA) and above-ground growth were also assessed. Key Results: Individuals from the site receiving supplemental moisture consistently showed significant responses in all considered traits related to water balance: SLA was greater by 24 ; roots developed 19 less starch storing tissue, an indicator for drought-stress tolerance; and vessel size distributions shifted towards wider elements that collectively conducted water 54 more efficiently - but only during the years for which moisture was supplemented. In contrast, above-ground growth parameters showed insignificant or inconsistent responses. Conclusions: The phenotypic changes documented represent consistent, dynamic responses to increased moisture availability that should increase plant competitive ability. The functional plasticity of xylem anatomy quantified in this study constitutes a mechanistic basis for anticipating the differential success of plant species in response to climate variability and change, particularly where water limitation occurs. © 2012 The Author.
• Bunn, A. G., Hughes, M. K., & Salzer, M. W. (2011). Topographically modified tree-ring chronologies as a potential means to improve paleoclimate inference: A letter. Climatic Change, 105(3-4), 627-634.
• Diaz, H. F., Trigo, R., Hughes, M. K., Mann, M. E., Xoplaki, E., & Barriopedro, D. (2011). Spatial and temporal characteristics of climate in medieval times revisited. Bulletin of the American Meteorological Society, 92(11), 1487-1500.
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  Abstract: Several spatial and temporal characteristics of climate in medieval times are presented. The recent symposium on the climate of the medieval period provided the evidences to support the several conclusions such as an abrupt rise in hemispheric and global temperature occurred in the twentieth century and continues through the first decade of the twenty-first century. Proxy records from mid and high latitudes of the Northern Hemisphere indicate that some 100-yr-long periods of the MCA might be as warm as much of the twentieth century in some regions. Paleodata from the Southern Hemisphere are generally too sparse to draw reliable conclusions about overall temperatures in medieval time. A recently published reconstruction of air temperature for southern South America indicates the presence of a prolonged period of elevated summer temperature occurring in the thirteenth and early fourteenth centuries.
• Tolwinski-Ward, S. E., Evans, M. N., Hughes, M. K., & Anchukaitis, K. J. (2011). An efficient forward model of the climate controls on interannual variation in tree-ring width. Climate Dynamics, 36(11-12), 2419-2439.
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  Abstract: We present a simple, efficient, process-based forward model of tree-ring growth, called Vaganov-Shashkin-Lite (VS-Lite), that requires as inputs only latitude and monthly temperature and precipitation. Simulations of six bristlecone pine ring-width chronologies demonstrate the interpretability of model output as an accurate representation of the climatic controls on growth. Ensemble simulations by VS-Lite of two networks of North American ring-width chronologies correlate with observations at higher significance levels on average than simulations formed by regression of ring width on the principal components of the same monthly climate data. VS-Lite retains more skill outside of calibration intervals than does the principal components regression approach. It captures the dominant low- and high-frequency spatiotemporal ring-width signals in the network with an inhomogeneous, multivariate relationship to climate. Because continuous meteorological data are most widely available at monthly temporal resolution, our model extends the set of sites at which forward-modeling studies are possible. Other potential uses of VS-Lite include generation of synthetic ring-width series for pseudo-proxy studies, as a data level model in data assimilation-based climate reconstructions, and for bias estimation in actual ring-width index series. © 2010 Springer-Verlag.
• Tolwinski-Ward, S. E., Evans, M. N., Hughes, M. K., & Anchukaitis, K. J. (2011). Erratum to: An efficient forward model of the climate controls on interannual variation in tree-ring width (Clim Dyn, 10.1007/s00382-010-0945-5). Climate Dynamics, 36(11-12), 2441-2445.
• Hughes, M. K., & Ammann, C. M. (2009). The future of the past-an earth system framework for high resolution paleoclimatology: Editorial essay. Climatic Change, 94(3-4), 247-259.
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  Abstract: High-resolution paleoclimatology is the study of climate variability and change on interannual to multi-century time scales. Its primary focus is the past few millennia, a period lacking major shifts in external climate forcing and earth system configuration. Large arrays of proxy climate records derived from natural archives have been used to reconstruct aspects of climate in recent centuries. The main approaches used have been empirical and statistical, albeit informed by prior knowledge both of the physics of the climate, and of the processes imprinting climate information in the natural archives. We propose a new direction, in which emerging tools are used to formalize the combination of process knowledge and proxy climate records to better illuminate past climate variability on these time scales of great relevance to human concerns. © 2009 Springer Science+Business Media B.V.
• Mann, M. E., Bradley, R. S., & Hughes, M. K. (2009). Reply to McIntyre and McKitrick: Proxy-based temperature reconstructions are robust. Proceedings of the National Academy of Sciences of the United States of America, 106(6), E11.
• Mann, M. E., Zhang, Z., Hughes, M. K., Bradley, R. S., Miller, S. K., Rutherford, S., & Ni, F. (2009). Proxy-based reconstructions of hemispheric and global surface temperature variations over the past two millennia. PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 105(36), 13252-13257.
• Mann, M. E., Zhang, Z., Rutherford, S., Bradley, R. S., Hughes, M. K., Shindell, D., Ammann, C., Faluvegi, G., & Fenbiao, N. i. (2009). Global signatures and dynamical origins of the little ice age and medieval climate anomaly. Science, 326(5957), 1256-1260.
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  PMID: 19965474;Abstract: Global temperatures are known to have varied over the past 1500 years, but the spatial patterns have remained poorly defined. We used a global climate proxy network to reconstruct surface temperature patterns over this interval. The Medieval period is found to display warmth that matches or exceeds that of the past decade in some regions, but which falls well below recent levels globally. This period is marked by a tendency for La Niña-like conditions in the tropical Pacific. The coldest temperatures of the Little Ice Age are observed over the interval 1400 to 1700 CE., with greatest cooling over the extratropical Northern Hemisphere continents. The patterns of temperature change imply dynamical responses of climate to natural radiative forcing changes involving El Niño and the North Atlantic Oscillation-Arctic Oscillation. Copyright 2009 by the American Association for the Advancement of Science; all rights reserved.
• Salzer, M. W., Hughes, M. K., Bunn, A. G., & Kipfmueller, K. F. (2009). Recent unprecedented tree-ring growth in bristlecone pine at the highest elevations and possible causes. Proceedings of the National Academy of Sciences of the United States of America, 106(48), 20348-20353.
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  PMID: 19918054;PMCID: PMC2777957;Abstract: Great Basin bristlecone pine (Pinus longaeva) at 3 sites in western North America near the upper elevation limit of tree growth showed ring growth in the second half of the 20th century that was greater than during any other 50-year period in the last 3,700 years. The accelerated growth is suggestive of an environmental change unprecedented in millennia. The high growth is not overestimated because of standardization techniques, and it is unlikely that it is a result of a change in tree growth form or that it is predominantly caused by CO2 fertilization. The growth surge has occurred only in a limited elevational band within ≈150 m of upper treeline, regardless of treeline elevation. Both an independent proxy record of temperature and high-elevation meteorological temperature data are positively and significantly correlated with upper-treeline ring width both before and during the high-growth interval. Increasing temperature at high elevations is likely a prominent factor in the modern unprecedented level of growth for Pinus longaeva at these sites.
• Hughes, M. K., & Diaz, H. F. (2008). Climate variability and change in the drylands of Western North America. Global and Planetary Change, 64(3-4), 111-118.
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  Abstract: We argue that it is important to expand the consideration of climate in the context of provision of ecosystem services in drylands. In addition to climate change, it is necessary to include climate variability on timescales relevant to human and ecological considerations, namely interannual to decadal and multidecadal. The period of global instrumental record (about a century and a half long at the very most) is neither an adequate nor an unbiased sample of the range and character of natural climate variability that might be expected with the climate system configured as it is now. We base this on evidence from W. N. America, where there has recently been a major multi-year drought, of a scale and intensity that has occurred several times in the last 2000 years, and on attempts to provide explanations of these phenomena based on physical climatology. Ensembles of runs of forced climate system models suggest the next 50 years will bring much more extensive and intense drought in the continental interior of North America. The trajectory followed by the supply of ecosystem services will be contingent not only on the genotypes available and the antecedent soil, economic and social conditions but also on climate variability and change. The critical features of climate on which patterns of plant growth and water supply depend may vary sharply during and between human generations, resulting in very different experiences and hence, expectations. © 2008 Elsevier B.V. All rights reserved.
• Mann, M. E., Zhang, Z., Hughes, M. K., Bradley, R. S., Miller, S. K., Rutherford, S., & Fenbiao, N. i. (2008). Proxy-based reconstructions of hemispheric and global surface temperature variations over the past two millennia. Proceedings of the National Academy of Sciences of the United States of America, 105(36), 13252-13257.
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  PMID: 18765811;PMCID: PMC2527990;Abstract: Following the suggestions of a recent National Research Council report [NRC (National Research Council) (2006) Surface Temperature Reconstructions for the Last 2,000 Years (Natl Acad Press, Washington, DC).], we reconstruct surface temperature at hemispheric and global scale for much of the last 2,000 years using a greatly expanded set of proxy data for decadal-to-centennial climate changes, recently updated instrumental data, and complementary methods that have been thoroughly tested and validated with model simulation experiments. Our results extend previous conclusions that recent Northern Hemisphere surface temperature increases are likely anomalous in a long-term context. Recent warmth appears anomalous for at least the past 1,300 years whether or not tree-ring data are used. If tree-ring data are used, the conclusion can be extended to at least the past 1,700 years, but with additional strong caveats. The reconstructed amplitude of change over past centuries is greater than hitherto reported, with somewhat greater Medieval warmth in the Northern Hemisphere, albeit still not reaching recent levels. © 2008 by The National Academy of Sciences of the USA.
• Mann, M. E., Zhang, Z., Rutherford, S., Bradley, R. S., Hughes, M. K., Shindell, D., Ammann, C., Faluvegi, G., & Ni, F. (2008). Global Signatures and Dynamical Origins of the Little Ice Age and Medieval Climate Anomaly. SCIENCE, 326(5957), 1256-1260.
• Graham, N. E., & Hughes, M. K. (2007). Reconstructing the Mediaeval low stands of Mono Lake, Sierra Nevada, California, USA. Holocene, 17(8), 1197-1210.
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  Abstract: Palaeosimulations of Mono Lake covering the past 2 kyr have been conducted using a water balance model forced with tree-ring derived inflow estimates. The results show two low stands, during the ninth to tenth and twelfth to thirteenth centuries, that agree well in timing and magnitude with those described by Stine (1987, 1990, 1994) on the basis of geomorphic evidence and relict trees and shrubs exposed on Mono Lake's artificially exposed shorelands. The lake simulation provides independent corroboration of the timing and magnitude of Stine's drought-induced low stands and supports the accuracy of tree-ring-derived estimates of Mediaeval precipitation and runoff reductions in the central Sierra Nevada. Specifically, we estimate that during the two Mediaeval droughts, centennial average precipitation and river runoff in the central Sierra Nevada reached as low as 75% of the twentieth century values, with multidecade averages as low as 60-65%. In both magnitude and duration, these droughts far exceed anything experienced in the region during modern times. An analysis of the spatial patterns of reconstructed drought indices shows that the particular 'two drought' Mono Lake low stand signal was focused over central and southern California, indicating the dominant role of boreal winter precipitation deficits. In this respect, the 'Great Sierra Nevada droughts' were somewhat distinct from the more general Great Basin/far western Plains pattern of Mediaeval aridity over the western USA. © 2007 SAGE Publications.
• Graham, N. E., Hughes, M. K., Ammann, C. M., Cobb, K. M., Hoerling, M. P., Kennett, D. J., Kennett, J. P., Rein, B., Stott, L., Wigand, P. E., & Taiyi, X. u. (2007). Tropical Pacific - Mid-latitude teleconnections in medieval times. Climatic Change, 83(1-2), 241-285.
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  Abstract: Terrestrial and marine late Holocene proxy records from the western and central US suggest that climate between approximately 500 and 1350 A.D. was marked by generally arid conditions with episodes of severe centennial-scale drought, elevated incidence of wild fire, cool sea surface temperatures (SSTs) along the California coast, and dune mobilization in the western plains. This Medieval Climate Anomaly (MCA) was followed by wetter conditions and warming coastal SSTs during the transition into the "Little Ice Age" (LIA). Proxy records from the tropical Pacific Ocean show contemporaneous changes indicating cool central and eastern tropical Pacific SSTs during the MCA, with warmer than modern temperatures in the western equatorial Pacific. This pattern of mid-latitude and tropical climate conditions is consistent with the hypothesis that the dry MCA in the western US resulted (at least in part) from tropically forced changes in winter NH circulation patterns like those associated with modern La Niña episodes. We examine this hypothesis, and present other analyses showing that the imprint of MCA climate change appears in proxy records from widely distributed regions around the planet, and in many cases is consistent with a cool medieval tropical Pacific. One example, explored with numerical model results, is the suggestion of increased westerlies and warmer winter temperatures over northern Europe during medieval times. An analog technique for the combined use of proxy records and model results, Proxy Surrogate Reconstruction (PSR), is introduced. © 2007 Springer Science+Business Media, B.V.
• Kirdyanov, A. V., Vaganov, E. A., & Hughes, M. K. (2007). Separating the climatic signal from tree-ring width and maximum latewood density records. Trees - Structure and Function, 21(1), 37-44.
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  Abstract: We propose a technique for separating the climatic signal which is contained in two tree-ring parameters widely used in dendroclimatology. The method is based on the removal of the relationship between tree-ring width (TRW) and maximum latewood density (MXD) observed for narrow tree rings from high latitudes. The new technique is tested on data from three larch stands located along the northern timberline in Eurasia. Correlations were calculated between the temperatures of pentads (five consecutive days), TRW chronologies and MXD chronologies calculated according to the standard and proposed methods. The analysis confirms the great importance of summer temperature for tree radial growth and tree-ring formation. TRW is positively correlated with the temperature of four to eight pentads (depending on the region) at the beginning of the growth season, but MXD as obtained by the standard technique is correlated with temperature over a much longer period. For maximum density series from which the relationship between MXD and TRW has been removed (MXD′), there is a clear correlation with temperatures in the second part of the growing season. These results are consistent with the known dynamics of tree-ring growth in high latitudes and mechanisms of tree-ring formation. © 2006 Springer-Verlag.
• Meko, D. M., Woodhouse, C. A., Baisan, C. A., Knight, T., Lucas, J. J., Hughes, M. K., & Salzer, M. W. (2007). Medieval drought in the upper Colorado River Basin. Geophysical Research Letters, 34(10).
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  Abstract: New tree-ring records of ring-width from remnant preserved wood are analyzed to extend the record of reconstructed annual flows of the Colorado River at Lee Ferry into the Medieval Climate Anomaly, when epic droughts are hypothesized from other paleoclimatic evidence to have affected various parts of western North America. The most extreme low-frequency feature of the new reconstruction, covering A.D. 762-2005, is a hydrologic drought in the mid-1100s. The drought is characterized by a decrease of more than 15% in mean annual flow averaged over 25 years, and by the absence of high annual flows over a longer period of about six decades. The drought is consistent in timing with dry conditions inferred from tree-ring data in the Great Basin and Colorado Plateau, but regional differences in intensity emphasize the importance of basin-specific paleoclimatic data in quantifying likely effects of drought on water supply. Copyright 2007 by the American Geophysical Union.
• Salzer, M. W., & Hughes, M. K. (2007). Bristlecone pine tree rings and volcanic eruptions over the last 5000 yr. Quaternary Research, 67(1), 57-68.
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  Abstract: Many years of low growth identified in a western USA regional chronology of upper forest border bristlecone pine (Pinus longaeva and Pinus aristata) over the last 5000 yr coincide with known large explosive volcanic eruptions and/or ice core signals of past eruptions. Over the last millennium the agreement between the tree-ring data and volcano/ice-core data is high: years of ring-width minima can be matched with known volcanic eruptions or ice-core volcanic signals in 86% of cases. In previous millennia, while there is substantial concurrence, the agreement decreases with increasing antiquity. Many of the bristlecone pine ring-width minima occurred at the same time as ring-width minima in high latitude trees from northwestern Siberia and/or northern Finland over the past 4000-5000 yr, suggesting climatically-effective events of at least hemispheric scale. In contrast with the ice-core records, the agreement between widely separated tree-ring records does not decrease with increasing antiquity. These data suggest specific intervals when the climate system was or was not particularly sensitive enough to volcanic forcing to affect the trees, and they augment the ice core record in a number of ways: by providing confirmation from an alternative proxy record for volcanic signals, by suggesting alternative dates for eruptions, and by adding to the list of years when volcanic events of global significance were likely, including the mid-2nd-millennium BC eruption of Thera. © 2006 University of Washington.
• Sidorova, O. V., Vaganov, E. A., Naurzbaev, M. M., Shishov, V. V., & Hughes, M. K. (2007). Regional features of the radial growth of larch in north central Siberia according to millennial tree-ring chronologies. Russian Journal of Ecology, 38(2), 90-93.
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  Abstract: A 1138-year tree-ring chronology has been constructed for the region of the Bol'shoi Avam River (the Putoran Plateau). Its comparison with millennial chronologies for the Taimyr Peninsula and Mangazeya has shown that all these chronologies are fairly synchronous with respect to both high-frequency (annual) and low-frequency (long-term) components, although each has its specific regional features. The results of dendroclimatic analysis provide evidence for the prevailing influence of air temperature in July (compared to that in June) on the radial growth of larch in the middle reaches of the Bol'shoi Avam. Consistent long-term changes in radial tree increment (and in summer air temperature) in a large sector of the Subarctic over the past 1000 years have been revealed. © 2007 Pleiades Publishing, Ltd.
• Touchan, R., Akkemik, Ü., Hughes, M. K., & Erkan, N. (2007). May-June precipitation reconstruction of southwestern Anatolia, Turkey during the last 900 years from tree rings. Quaternary Research, 68(2), 196-202.
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  Abstract: A May-June precipitation reconstruction (AD 1097-2000) has been developed for southwestern Anatolia in Turkey, the longest reported to date in this region. The reconstruction was derived from a regional Juniperus excelsa chronology that was built from material sampled at four sites in the Antalya and Mersin Districts. The regional tree-ring chronology accounts for 51% of the variance of instrumentally observed May-June precipitation. The years AD 1518 to 1587 are the most humid period in the reconstruction, coinciding with a major shift in European climate. The driest 70-year period in the reconstruction is AD 1195 to 1264. The period AD 1591-1660 represents the third driest and was characterized by instability climatically, politically, and socially in Anatolia. © 2007 Elsevier Inc. All rights reserved.
• Anchukaitis, K. J., Evans, M. N., Kaplan, A., Vaganov, E. A., Hughes, M. K., Grissino-Mayer, H., & Cane, M. A. (2006). Forward modeling of regional scale tree-ring patterns in the southeastern United States and the recent influence of summer drought. Geophysical Research Letters, 33(4).
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  Abstract: We use a mechanistic model of tree-ring formation to simulate regional patterns of climate-tree growth relationships in the southeastern United States. Modeled chronologies are consistent with actual tree-ring data, demonstrating that our simulations have skill in reproducing broad-scale patterns of the proxy's response to climate variability. The model predicts that a decrease in summer precipitation, associated with a weakening Bermuda High, has become an additional control on tree ring growth during recent decades. A nonlinear response of tree growth to climate variability has implications for the calibration of tree-ring records for paleoclimate reconstructions and the prediction of ecosystem responses to climate change. Copyright 2006 by the American Geophysical Union.
• Bradley, R. S., Hughes, M. K., & Mann, M. E. (2006). Authors were clear about hockey-stick uncertainties [2]. Nature, 442(7103), 627-.
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  PMID: 16900179;
• Evans, M. N., Reichert, B. K., Kaplan, A., Anchukaitis, K. J., Vaganov, E. A., Hughes, M. K., & Cane, M. A. (2006). A forward modeling approach to paleoclimatic interpretation of tree-ring data. Journal of Geophysical Research G: Biogeosciences, 111(3).
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  Abstract: We investigate the interpretation of tree-ring data using the Vaganov-Shashkin forward model of tree-ring formation. This model is derived from principles of conifer wood growth, and explicitly incorporates a nonlinear daily timescale model of the multivariate environmental controls on tree-ring growth. The model results are shown to be robust with respect to primary moisture and temperature parameter choices. When applied to the simulation of tree-ring widths from North America and Russia from the Mann et al. (1998) and Vaganov et al. (2006) data sets, the forward model produces skill on annual and decadal timescales which is about the same as that achieved using classical dendrochronological statistical modeling techniques. The forward model achieves this without site-by-site tuning as is performed in statistical modeling. The results support the interpretation of this broad-scale network of tree-ring width chronologies primarily as climate proxies for use in statistical paleoclimatic field reconstructions, and point to further applications in climate science. Copyright 2006 by the American Geophysical Union.
• Malamud-Roam, F. P., Ingram, B. L., Hughes, M., & Florsheim, J. L. (2006). Holocene paleoclimate records from a large California estuarine system and its watershed region: linking watershed climate and bay conditions. Quaternary Science Reviews, 25(13-14), 1570-1598.
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  Abstract: The San Francisco Bay-Delta system includes a watershed that covers a large area of California and provides water to two-thirds of the State's population. Climate over the estuary and its watershed in the dry summer months is controlled by the subtropical high which dominates and deflects storms from California. The subtropical high weakens and migrates south as the Aleutian Low strengthens, bringing wet winter storms to the region. Paleoclimatic records from the Bay and its greater watershed, spanning the Holocene, are reviewed here in order to better understand natural variations of precipitation and runoff and the linkages between those variations and the salinity and ecosystems of the estuary. To better understand regional-scale climate patterns, paleoclimate records from coastal California and the Great Basin are also considered. Large fluctuations in climate have occurred during the period of interest, and there is generally good agreement between the paleoclimate records from different regions. Early Holocene climate throughout California was marked by rising temperatures and reduced moisture as seen in fire records from the watershed. This warmth and aridity peaked about 5000-7000 years ago and was followed by a cooling trend, with variable moisture conditions. The Estuary formed relatively rapidly in response to a high rate of sea level rise that dominated the Holocene until about 6000 years ago, and the subsequent reduced rate of inundation allowed vast tidal marshes to form along the edges of the estuary, which have since been recording changes in environmental conditions. The impacts of changing regional climate patterns are experienced in the San Francisco Bay-Delta system, as altered fresh water flows result in altered estuary salinity. For example, approximately 3800 cal yr B.P., records from throughout the state indicate a cool, moist period, and Bay salinity was reduced; this period was followed by a general drying trend throughout California over the last two millennia, punctuated by decades to centuries-long droughts and brief, extremely wet events. In particular, during the period ca. 1000-800 cal yr B.P. (A.D. 950-1150) conditions seem to have been unusually dry in many parts of the watershed, reducing the fresh water flows to the estuary, and shifting tidal marsh plant assemblages toward less diverse, but more salt-tolerant plants. In contrast, the Little Ice Age (ca. 550-200 cal yr B.P.) brought unusually cool and wet conditions to much of the watershed, and lowered salinity in the Bay. Many reconstructions suggest that notably stable conditions have prevailed over the instrumental period, i.e., after ca. A.D. 1850, even including the severe, short-term anomalies experienced during this period. Interdecadal variability is common in many of the records, with timescales of ca. 55, 70, 90, 100, 150, and 200 years. © 2006 Elsevier Ltd. All rights reserved.
• Mann, M. E., & Hughes, M. K. (2006). A not-so-abrupt departure [5]. Science, 312(5773), 528-529.
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  PMID: 16645077;
• Garfin, G. M., Hughes, M. K., Liu, Y. u., Burns, J. M., Touchan, R., Leavitt, S. W., & Zhisheng, A. (2005). Exploratory temperature and precipitation reconstructions from the Qinling Mountains, North-Central China. Tree-Ring Research, 61(2), 59-72.
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  Abstract: February-April (FMA) temperature at Foping (1879-1989) and July-August (JA) precipitation at Xian (1895-1988) have been reconstructed using total ring width (TRW) and maximum latewood density (MXD) from trees in the Qinling Mountains, at the northern limit of the East Asian monsoon, in central China. The Xian JA precipitation reconstruction, albeit short, represents the first well-replicated, crossdated dendroclimatic reconstruction of summer monsoon precipitation for this region. Reconstructed Xian precipitation shows significant positive relationships with historical evidence from the region. The key feature of the precipitation reconstruction is prolonged summer drought during the late 1920s and early 1930s. The Foping reconstruction displays warmer-than-average FMA temperatures during this time period. These exploratory reconstructions, along with a previous reconstruction from Huashan, demonstrate the complexity of attempting dendroclimatic reconstructions from this region. Our results indicate that further attempts to locate long-lived conifers from here can result in an extended well-calibrated and verified reconstruction of summer monsoon precipitation. Copyright © 2005 by the Tree-Ring Society.
• Liu, Y., Cai, Q., Shi, J., Hughes, M. K., Kutzbach, J. E., Liu, Z., Fenbiao, N. i., & Zhisheng, A. n. (2005). Seasonal precipitation in the south-central Helan Mountain region, China, reconstructed from tree-ring width for the past 224 years. Canadian Journal of Forest Research, 35(10), 2403-2412.
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  Abstract: Chinese pine (Pinus tabulaeformis Carr.) trees from the Helan Mountain range in central China have been used to reconstruct total January-July precipitation from AD 1775 to 1998. For the calibration period R 2adj = 0.52. Narrow rings are associated with below-average precipitation from March through August. Wide rings are produced in years when the East Asian summer monsoon front arrives early. We use local historical writings over the last 300 years about extreme climatic conditions between spring and early summer to verify the extreme years. Most of the extreme dry years could be identified in local historical documents. Another East Asian summer monsoon front related precipitation reconstruction from northern Helan Mountain is also used to verify this reconstruction. They are well correlated from year to year, with a correlation coefficient of 0.52 (N = 218), and the wet or dry extreme events are well matched in many cases. This comparison could indicate a spatial and temporal connection of spring to early summer climatic conditions for the southern to northern portion of the Helan Mountain region. The sustained wet period before the 20th century lasts from the 1850s to the 1890s, and the longest dry period before the 20th century is in the 1830s and 1840s, largely coinciding with a spring-summer drought in Kashmir. Overall, multiyear fluctuations, such as the spectacular large-scale drought of the late 1920s and droughts in the 1830s-1840s and the 1970s, are well captured in this reconstruction, but only the 1970s drought is in the instrumental period. The reconstruction shows increasing variance from the 18th to the late 20th century. © 2005 NRC.
• Rutherford, S., Mann, M. E., Osborn, T. J., Bradley, R. S., Briffa, K. R., Hughes, M. K., & Jones, P. D. (2005). Proxy-based Northern Hemisphere surface temperature reconstructions: Sensitivity to method, predictor network, target season, and target domain. Journal of Climate, 18(13), 2308-2329.
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  Abstract: Results are presented from a set of experiments designed to investigate factors that may influence proxy-based reconstructions of large-scale temperature patterns in past centuries. The factors investigated include 1) the method used to assimilate proxy data into a climate reconstruction, 2) the proxy data network used, 3) the target season, and 4) the spatial domain of the reconstruction. Estimates of hemispheric-mean temperature are formed through spatial averaging of reconstructed temperature patterns that are based on either the local calibration of proxy and instrumental data or a more elaborate multivariate climate field reconstruction approach. The experiments compare results based on the global multiproxy dataset used by Mann and coworkers, with results obtained using the extratropical Northern Hemisphere (NH) maximum latewood tree-ring density set used by Briffa and coworkers. Mean temperature reconstructions are compared for the full NH (Tropics and extratropics, land and ocean) and extratropical continents only, with varying target seasons (cold-season half year, warm-season half year, and annual mean). The comparisons demonstrate dependence of reconstructions on seasonal, spatial, and methodological considerations, emphasizing the primary importance of the target region and seasonal window of the reconstruction. The comparisons support the generally robust nature of several previously published estimates of NH mean temperature changes in past centuries and suggest that further improvements in reconstructive skill are most likely to arise from an emphasis on the quality, rather than quantity, of available proxy data. © 2005 American Meteorological Society.
• Touchan, R., Funkhouser, G., Hughes, M. K., & Erkan, N. (2005). Standardized precipitation index reconstructed from Turkish tree-ring widths. Climatic Change, 72(3), 339-353.
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  Abstract: May-July Standardized Precipitation Index (SPI) for the land area of most of Turkey and some adjoining regions are reconstructed from tree rings for the period 1251-1998. The reconstruction was developed from principal components analysis (PCA) of four Juniperus excelsa chronologies from southwestern and south-central Turkey and is based on reliable and replicable statistical relationships between climate and tree ring growth. The SPI reconstruction shows climate variability on both interannual and interdecadal time scales. The longest period of consecutive drought years in the reconstruction (SPI threshold ≤-1) is 2 yr. These occur in 1607-1608, 1675-1676, and 1907-1908. There are five wet events (SPI threshold ≥+1) of two consecutive years each (1330-1331, 1428-1429, 1503-1504, 1629-1630, and 1913-1914). A 5-yr moving average of the reconstructed SPI shows that two sustained drought periods occurred from the mid to late 1300s and the early to mid 1900s. Both episodes are characterized by low variability. © Springer 2005.
• Touchan, R., Xoplaki, E., Funkhouser, G., Luterbacher, J., Hughes, M. K., Erkan, N., Akkemik, Ü., & Stephan, J. (2005). Reconstructions of spring/summer precipitation for the Eastern Mediterranean from tree-ring widths and its connection to large-scale atmospheric circulation. Climate Dynamics, 25(1), 75-98.
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  Abstract: This study represents the first large-scale systematic dendroclimatic sampling focused on developing chronologies from different species in the eastern Mediterranean region. Six reconstructions were developed from chronologies ranging in length from 115 years to 600 years. The first reconstruction (1885-2000) was derived from principal components (PCs) of 36 combined chronologies. The remaining five, 1800-2000, 1700-2000, 1600-2000, 1500-2000 and 1400-2000 were developed from PCs of 32, 18, 14, 9, and 7 chronologies, respectively. Calibration and verification statistics for the period 1931-2000 show good levels of skill for all reconstructions. The longest period of consecutive dry years, defined as those with less than 90% of the mean of the observed May-August precipitation, was 5 years (1591-1595) and occurred only once during the last 600 years. The longest reconstructed wet period was 5 years (1601-1605 and 1751-1755). No long term trends were found in May-August precipitation during the last few centuries. Regression maps are used to identify the influence of large-scale atmospheric circulation on regional precipitation. In general, tree-ring indices are influenced by May-August precipitation, which is driven by anomalous below (above) normal pressure at all atmospheric levels and by convection (subsidence) and small pressure gradients at sea level. These atmospheric conditions also control the anomaly surface air temperature distribution which indicates below (above) normal values in the southern regions and warmer (cooler) conditions north of around 40°N. A compositing technique is used to extract information on large-scale climate signals from extreme wet and dry summers for the second half of the twentieth century and an independent reconstruction over the last 237 years. Similar main modes of atmospheric patterns and surface air temperature distribution related to extreme dry and wet summers were identified both for the most recent 50 years and the last 237 years. Except for the last few decades, running correlation analyses between the major European-scale circulation patterns and eastern Mediteranean spring/summer precipitation over the last 237 years are non-stationary and insignificant, suggesting that local and/or sub-regional geographic factors and processes are important influences on tree-ring variability over the last few centuries. © Springer-Verlag 2005.
• Comrie, A. C., Lemos, M. C., Hughes, M., & Overpeck, J. (2004). Climate science and services: Some lessons from climas. Bulletin of the American Meteorological Society, 4981-4990.
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  Abstract: The integration of basic climate science and stakeholder interests was carried out by Climate Assessment for the Southwest (CLIMAS) by adopting an iterative model of regional assessment research. The data could be used by all stakeholders to improve their stock situation. CLIMAS integrates the basic climate science and the interests of the stakeholders by making the stakeholders involve and interact in regional assessment research. Its work also involves close interaction with doctors and public health officials to study the environmental factors which affect the climate sensitive diseases. The research results provides evidences in diversified fields of ecology, socioeconomics, and cultural fields.
• Hughes, M. K., Swetnam, T. W., & F.Diaz, H. (2004). Tree rings and climate: Sharpening the focus. Eos, 85(32), 303-.
• Mann, M. E., Bradley, R. S., & Hughes, M. A. (2004). Erratum: Global-scale temperature patterns and climate forcing over the past six centuries (Nature (1998) 392 (779-787)). Nature, 430(6995), 105-.
• Naurzbaev, M. M., Hughes, M. K., & Vaganov, E. A. (2004). Tree-ring growth curves as sources of climatic information. Quaternary Research, 62(2), 126-133.
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  Abstract: Regional growth curves (RGCs) have been recently used to provide a new basis for removing nonclimatic trend from tree-ring data. Here we propose a different use for RGCs and explore their properties along two transects, one meridional and the other elevational. RGCs consisting of mean ring width plotted against cambial age were developed for larch samples from 34 sites along a meridional transect (55-72°N) in central Siberia, and for 24 sites on an elevational gradient (1120 and 2350 m a.s.l.) in Tuva and neighboring Mongolia at approximately 51°N. There are systematic gradients of the parameters of the RGCs, such as I 0 -maximum tree-ring width near pith, and I min , the asymptotic value of tree-ring width in old trees. They are smaller at higher latitude and elevation. Annual mean temperature and mean May-September temperature are highly correlated with latitude here, and hence RGC parameters are correlated with these climatic variables. Correlations with precipitation are more complex, and contradictory between meridional and elevational transects. The presence of a similar gradient in the elevational transect is consistent with temperature being the causal factor for both gradients, rather than, for example, latitude-dependent patterns of seasonal photoperiod change. Taking ring measurements from collections of relict and subfossil wood, the RGC-latitude and RGC-temperature relationships are used to estimate paleo-temperatures on centennial time scales. These estimates are consistent with earlier "traditional" dendroclimatic approaches, and with independent information on the northern extent of forest growth in the early mid-Holocene. It may be possible to use this same approach to make estimates of century-scale paleo-temperatures in other regions where abundant relict wood is present. © University of Washington. All rights reserved.
• Vaganov, E. A., Hughes, M. K., Silkin, P. P., & Nesvetailo, V. D. (2004). The Tunguska event in 1908: Evidence from tree-ring anatomy. Astrobiology, 4(3), 391-399.
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  PMID: 15383242;Abstract: We analyzed tree rings in wood samples collected from some of the few surviving trees found close to the epicenter (within 4-5 km) of the Tunguska event that occurred on the last day of June 1908. Tree-ring growth shows a depression starting in the year after the event and continuing during a 4-5-year period. The most remarkable traces of the event were found in the rings' anatomical structure: (1) formation of "light" rings and a reduction of maximum density in 1908; (2) non-thickened tracheids (the cells that make up most of the wood volume) in the transition and latewood zones (the middle and last-formed parts of the ring, respectively); and (3) deformed tracheids, which are located on the 1908 annual ring outer boundary. In the majority of samples, normal earlywood and latewood tracheids were formed in all annual rings after 1908. The observed anomalies in wood anatomy suggest two main impacts of the Tunguska event on surviving trees - (1) defoliation and (2) direct mechanical stress on active xylem tissue. The mechanical stress needed to fell trees is less than the stress needed to cause the deformation of differentiating tracheids observed in trees close to the epicenter. In order to resolve this apparent contradiction, work is suggested on possible topographic modification of the overpressure experienced by these trees, as is an experimental test of the effects of such, stresses on precisely analogous growing trees. © Mary Ann Liebert, Inc.
• Bradley, R. S., Hughes, M. K., & Diaz, H. F. (2003). Climate in Medieval Time. Science, 302(5644), 404-405.
• Dong, J., Kaufmann, R. K., Myneni, R. B., Tucker, C. J., Kauppi, P. E., Liski, J., Buermann, W., Alexeyev, V., & Hughes, M. K. (2003). Remote sensing estimates of boreal and temperate forest woody biomass: Carbon pools, sources, and sinks. Remote Sensing of Environment, 84(3), 393-410.
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  Abstract: The relation between satellite measurements of the normalized difference vegetation index (NDVI), cumulated over the growing season, and inventory estimates of forest woody biomass carbon is estimated statistically with data from 167 provinces and states in six countries (Canada, Finland, Norway, Russia and the USA for a single time period and Sweden for two periods). Statistical tests indicate that the regression model can be used to represent the relation between forest biomass and NDVI across spatial, temporal and ecological scales for relatively long time scales. For the 1.42 billion ha of boreal and temperate forests in the Northern Hemisphere, the woody biomass carbon pools and sinks are estimated at a relatively high spatial resolution (8 x 8 km). We estimate the carbon pool to be 61 ± 20 gigatons (109) carbon (Gt C) during the late 1990s and the biomass sink to be 0.68 ± 0.34 Gt C/year between the 1982 and 1999. The geographic detail of carbon sinks provided here can contribute to a potential monitoring program for greenhouse gas emission reduction commitments under the Kyoto Protocol. © 2002 Elsevier Science Inc. All rights reserved.
• Hughes, M. K., & Funkhouser, G. (2003). Frequency-dependent climate signal in upper and lower forest border tree rings in the mountains of the Great Basin. Climatic Change, 59(1-2), 233-244.
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  Abstract: We examine the relationships, over the past millennium, between tree-ring chronologies from long-lived pines at their upper and lower limits in four mountain ranges in and near to the semi-arid Great Basin. We confirm LaMarche's (1974a) finding, based on a single mountain range in this same region, and a much shorter period of comparison, that climate responses are frequency dependent. In particular, upper and lower forest border chronologies in each mountain range are strongly coherent at decadal periods and less, with particular strength in the 3-7 year band. This variability is significantly correlated with precipitation. Conversely, we find no significant correlation between the low frequency fluctuations (60 years and longer) of upper and lower forest border chronologies. There are, however, significant correlations between the low-frequency components of the upper forest border chronologies in the different ranges, consistent with their containing a growing season temperature signal on decadal time scales. The four upper forest border chronologies all show an anomalous increase in growth since the late 19th century, and an apparent change in climate control of ring growth.
• Kirdyanov, A., Hughes, M., Vaganov, E., Schweingruber, F., & Silkin, P. (2003). The importance of early summer temperature and date of snow melt for tree growth in the Siberian Subarctic. Trees - Structure and Function, 17(1), 61-69.
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  Abstract: Wood material for at least 12 larch trees at six sites [Larix sibirica Ldb, Larix gmelinii (Rupr.) Rupr, Larix cajanderi Mayr] near the northern timberline in Siberia was analyzed to investigate influence of climatic factor changes on tree-ring growth at high latitudes. Tree-ring cell size, maximum latewood density and ring width measured by means of image analysis and X-ray radiodensitometry and calculated latewood cell-wall thickness were used. Correlation analysis of tree-ring structure parameter chronologies with temperatures averaged over periods of 5 days (pentad) shows that early summer temperature (mean for 5-6 pentads, depending on the region, starting from the middle of June) and date of snow melt are the most important factors that define seasonal growth and tree-ring structure. Analysis of instrumental climatic data indicates that a positive trend of early summer temperature was combined with winter precipitation (October-April) increase and this combination leads to later snow melt. Based of the results of tree-ring growth modelling, it was shown that later snow melt (hence, delayed initiation of cambial activity and, as a result, decrease of wood production) explains the changes in the relationship between tree ring width and summer temperature dynamics observed after the 1960s for a large area of the Siberian Subarctic. The understanding of the role of winter precipitation in controlling ring growth, through its effect on the timing of cambial activation, suggests the possibility of using ring structure parameters to create reconstructions of past winter precipitation variations.
• Mann, M. E., Rutherford, S., Bradley, R. S., Hughes, M. K., & Keimig, F. T. (2003). Optimal surface temperature reconstructions using terrestrial borehole data. Journal of Geophysical Research D: Atmospheres, 108(7), ACL 1-1 ACL 1-11.
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  Abstract: We derive an optimal Northern Hemisphere mean surface temperature reconstruction from terrestrial borehole temperature profiles spanning the past five centuries. The pattern of borehole ground surface temperature (GST) reconstructions displays prominent discrepancies with instrumental surface air temperature (SAT) estimates during the 20th century, suggesting the presence of a considerable amount of noise and/or bias in any underlying spatial SAT signal. The vast majority of variance in the borehole dataset is efficiently retained by its two leading eigenvectors. A sizable share of the variance in the first eigenvector appears to be associated with non-SAT related bias in the borehole data. A weak but detectable SAT signal appears to be described by a combination of the first two eigenvectors. Exploiting this eigendecomposition, application of optimal signal estimation methods yields a hemispheric borehole SAT reconstruction that is largely consistent with instrumental data available in past centuries, and is indistinguishable in it smajor features from several published long-term temperature estimates based on both climate proxy data and model simulations.
• Mann, M., Amman, C., Bradley, R., Briffa, K., Jones, P., Osborn, T., Crowley, T., Hughes, M., Oppenheimer, M., Overpeck, J., Rutherford, S., Trenberth, K., & Wlgley, T. (2003). On past temperatures and anomalous late-20th century warmth. Eos, 84(27), 256-.
• Mann, M., Ammann, C., Bradley, R., Briffa, K., Jones, P., Osborn, T., Crowley, T., Hughes, M., Oppenheimer, M., Overpeck, J., Rutherford, S., Trenberth, K., & Wigley, T. (2003). Response. Eos, 84(44), 473-474.
• Panyushkina, I. P., Hughes, M. K., Vaganov, E. A., & Munro, M. A. (2003). Summer temperature in northeastern Siberia since 1642 reconstructed from tracheid dimensions and cell numbers of Larix cajanderi. Canadian Journal of Forest Research, 33(10), 1905-1914.
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  Abstract: We reconstructed air temperature for two periods in the growth season from cell dimension and cell number variability in cross-dated tree rings of Larix cajanderi Mayr. from northeastern Siberia. Thirteen tree-ring chronologies based on cell size, cell wall thickness, and cell number were developed for AD 1642-1993. No clear evidence was found of an age-related trend in cell dimensions in the sampled materials, but cell numbers were correlated with cambial age. The chronologies contain strong temperature signals associated with the timing of xylem growth. We obtained reliable reconstructions of mean June temperature from the total cell number and July-September temperature from the cell wall thickness of latewood. June temperature and July-September temperature covaried for most of the period from AD 1642 to AD 1978. After that time, June temperature became cooler relative to July-September temperature. This difference caused disproportional changes in earlywood tracheids because of the late start of growth and cool conditions in June followed by warming during the rest of the season. The identification of this unusual recent change has shown that intraseasonal resolution may be achieved by cell dimension and cell number chronologies.
• Touchan, R., Garfin, G. M., Meko, D. M., Funkhouser, G., Erkan, N., Hughes, M. K., & Wallin, B. S. (2003). Preliminary reconstructions of spring precipitation in Southwestern Turkey from tree-ring width. International Journal of Climatology, 23(2), 157-171.
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  Abstract: Two reconstructions of spring (May-June) precipitation have been developed for southwestern Turkey. The first reconstruction (1776-1998) was developed from principal components of nine chronologies of Cedrus libani, Juniperus excelsa, Pinus brutia, and Pinus nigra. The second reconstruction (1339-1998) was derived from principal components of three J. excelsa chronologies. Calibration and verification statistics of both reconstructions indicate reasonably accurate reconstruction of spring precipitation for southwestern Turkey, and show clear evidence of multi-year to decadal variations in spring precipitation. The longest period of reconstructed spring drought, defined as consecutive years with less than 80% of normal May-June precipitation, was 4 years (1476-79). Only one drought event of this duration has occurred during the last six centuries. Monte Carlo analysis indicates a less than 33% probability that southwestern Turkey has experienced spring drought longer than 5 years in the past 660 years. Apart from the 1476-79 extended dry period, spring droughts of 3 years in length have only occurred from 1700 to the present. The longest reconstructed wet period, defined as consecutive years with more than 120% of normal May-June precipitation, was 4 years (1532-35). The absence of extended spring drought during the 16th and 17th centuries and the occurrence of extended wet spring periods during these centuries suggest a possible regime shift in climate. Preliminary analysis of links between large-scale climatic variation and these climate reconstructions shows that there is a relationship between extremes in spring precipitation and anomalous atmospheric circulation in the region. © 2003 Royal Meteorological Society.
• Fenbiao, N. i., Cavazos, T., Hughes, M. K., Comrie, A. C., & Funkhouser, G. (2002). Cool-season precipitation in the southwestern USA since AD 1000: Comparison of linear and nonlinear techniques for reconstruction. International Journal of Climatology, 22(13), 1645-1662.
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  Abstract: A 1000 year reconstruction of cool-season (November-April) precipitation was developed for each climate division in Arizona and New Mexico from a network of 19 tree-ring chronologies in the southwestern USA. Linear regression (LR) and artificial neural network (NN) models were used to identify the cool-season precipitation signal in tree rings. Using 1931-88 records, the stepwise LR model was cross-validated with a leave-one-out procedure and the NN was validated with a bootstrap technique. The final models were also independently validated using the 1896-1930 precipitation data. In most of the climate divisions, both techniques can successfully reconstruct dry and normal years, and the NN seems to capture large precipitation events and more variability better than the LR. In the 1000 year reconstructions the NN also produces more distinctive wet events and more variability, whereas the LR produces more distinctive dry events. The 1000 year reconstructed precipitation from the two models shows several sustained dry and wet periods comparable to the 1950s drought (e.g. 16th century mega drought) and to the post-1976 wet period (e.g. 1330s, 1610s). The impact of extreme periods on the environment may be stronger during sudden reversals from dry to wet, which were not uncommon throughout the millennium, such as the 1610s wet interval that followed the 16th century mega drought. The instrumental records suggest that strong dry to wet precipitation reversals in the past 1000 years might be linked to strong shifts from cold to warm El Niño-southern oscillation events and from a negative to positive Pacific decadal oscillation. © 2002 Royal Meteorological Society.
• Hughes, M. K. (2002). Dendrochronology in climatology - The state of the art. Dendrochronologia, 20(1-2), 95-116.
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  Abstract: The current state of dendrochronology's contributions to climatology is surveyed, with an emphasis on the extent to which its actual and potential strengths are being used, and its weaknesses recognized and surmounted. After the growth in climatologists' interest in the potential of dendrochronology to contribute to their field is described, a brief account is given of the development of dendroclimatology over the past quarter-century. The strengths and weaknesses of tree rings as natural archives of climate variability are discussed. The greatest strengths are: the capability to date tree rings to the calendar year with a very high degree of confidence; the existence of large geographic-scale patterns of common year-to-year tree-ring variability; the development of very extensive, shared networks of tree-ring chronologies meeting common standards; the surprising effectiveness of very simple linear models of tree-ring/climate relationships; and the growing understanding of the mechanisms leading to variability in tree-ring features. The greatest weaknesses are that: tree-ring chronologies only capture a fraction of climate variability; their response may be limited to specific seasonal "windows"; some do not respond directly to a single monthly or even seasonal climate variable; they may not record the climate variables of interest to climatologists; their use to reconstruct past climate is based on the assumption that the same factors, acting in the same way, controlled the formation of tree rings in the past as in the twentieth century; and, the techniques used to remove non-climatic variability, such as that caused by tree age/size trend and interactions with neighbors, limit the faithful representation of climate variations on centennial and longer time scales in many cases. The manner in which these strengths have been used, and these weaknesses addressed, is discussed. The overall assessment is that the state of the art of dendrochronology in climatology is vibrant, with much robust debate and innovative work. © Urban & Fischer Verlag.
• Mann, M. E., & Hughes, M. K. (2002). Tree-ring chronotogies and climate variability [2]. Science, 296(5569), 848-849.
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  PMID: 11989486;
• Sheppard, P. R., Comrie, A. C., Packin, G. D., Angersbach, K., & Hughes, M. K. (2002). The climate of the US Southwest. Climate Research, 21(3), 219-238.
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  Abstract: This paper summarizes the current state of knowledge of the climate of southwest USA (the 'Southwest'). Low annual precipitation, clear skies, and year-round warm climate over much of the Southwest are due in large part to a quasi-permanent subtropical high-pressure ridge over the region. However, the Southwest is located between the mid-latitude and subtropical atmospheric circulation regimes, and this positioning relative to shifts in these regimes is the fundamental reason for the region's climatic variability. Furthermore, the Southwest's complex topography and its geographical proximity to the Pacific Ocean, the Gulf of California, and the Gulf of Mexico also contribute to this region's high climatic variability. El Niño, which is an increase in sea-surface temperature of the eastern equatorial Pacific Ocean with an associated shift of the active center of atmospheric convection from the western to the central equatorial Pacific, has a well-developed teleconnection with the Southwest, usually resulting in wet winters. La Niña, the opposite oceanic case of El Niño usually results in dry winters for the Southwest. Another important oceanic influence on winter climate of the Southwest is a feature called the Pacific Decadal Oscillation (PDO), which has been defined as temporal variation in sea-surface temperatures for most of the Northern Pacific Ocean. The effects of ENSO and PDO can amplify each other, resulting in increased annual variability in precipitation over the Southwest. The major feature that sets the climate of the Southwest apart from the rest of the United States is the North American monsoon, which in the US is most noticeable in Arizona and New Mexico. Up to 50% of the annual rainfall of Arizona and New Mexico occurs as monsoonal storms from July through September. Instrumental measurement of temperature and precipitation in the Southwest dates back to the middle to late 1800s. From that record, average annual rainfall of Arizona is 322 mm (12.7″), while that of New Mexico is 340 mm (13.4″), and mean annual temperature of New Mexico is cooler (12°C [53°F] than Arizona (17°C [62°F]). As instrumental meteorological records extend back only about 100 to 120 yr throughout the Southwest, they are of limited utility for studying climate phenomena of long time frames. Hence, there is a need to extend the measured meteorological record further back in time using so-called 'natural archive' paleoclimate records. Tree-ring data, which provide annual resolution, range throughout the Southwest, extend back in time for up to 1000 yr or more in various forests of the Southwest, and integrate well the influences of both temperature and precipitation, are useful for this assessment of climate of the Southwest. Tree growth of mid-elevation forests typically responds to moisture availability during the growing season, and a commonly used climate variable in paleo-precipitation studies is the Palmer Drought Severity Index (PDSI), which is a single variable derived from variation in precipitation and temperature. June-August PDSI strongly represents precipitation and, to a lesser extent, temperature of the year prior to the growing season (prior September through current August). The maximum intra-ring density of higher elevation trees can yield a useful record of summer temperature variation. The combined paleo-modern climate record has at least 3 occurences of multi-decadal variation (50 to 80 yr) of alternating dry (below average PDSI) to wet (above average PDSI). The amplitude of this variation has increased since the 1700s. The most obvious feature of the temperature record is its current increase to an extent unprecedented in the last 400 yr. Because this warming trend is outside the variation of the natural archives, it is possible that anthropogenic impacts, such as increased atmospheric concentrations of greenhouse trace gases, are playing a role in climate of the Southwest. Accordingly, this pattern merits further research in search of its cause or combination of causes.
• Shishov, V. V., Vaganov, E. A., Hughes, M. K., & Korets, M. A. (2002). The spatial variability of tree-ring growth in Siberian region during the last century. Doklady Akademii Nauk, 387(5), 690-694.
• Shishov, V. V., Vaganov, E. A., Hughes, M. K., & Koretz, M. A. (2002). Spatial variations in the annual tree-ring growth in Siberia in the past century. Doklady Earth Sciences, 387(9), 1088-1091.
• Alverson, K., Bradley, R., Briffa, K., Cole, J., Hughes, M., Larocque, I., Pedersen, T., Thompson, L., & Tudhope, S. (2001). A global paleoclimate observing system [2]. Science, 293(5527), 47-48.
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  PMID: 11444288;
• Bradley, R. S., Briffa, K. R., Crowley, T. J., Hughes, M. K., Jones, P. D., & Mann, M. E. (2001). The scope of medieval warming [5]. Science, 292(5524), 2011-2012.
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  PMID: 11411490;
• Meko, D. M., Therrell, M. D., Baisan, C. H., & Hughes, M. K. (2001). Sacramento river flow reconstructed to A.D. 869 from tree rings. Journal of the American Water Resources Association, 37(4), 1029-1038.
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  Abstract: A time series of annual flow of the Sacramento River, California, is reconstructed to A.D. 869 from tree rings for a long-term perspective on hydrologic drought. Reconstructions derived by principal components regression of flow on time-varying subsets of tree-ring chronologies account for 64 to 81 percent of the flow variance in the 1906 to 1977 calibration period. A Monte Carlo analysis of reconstructed n-year running means indicates that the gaged record contains examples of drought extremes for averaging periods of perhaps = 6 to 10 years, but not for longer and shorter averaging periods. For example, the estimated probability approaches 1.0 that the flow in A.D. 1580 was lower than the lowest single-year gaged flow. The tree-ring record also suggests that persistently high or low flows over 50-year periods characterize some parts of the long-term flow history. The results should contribute to sensible water resources planning for the Sacramento Basin and to the methodology of incorporating tree-ring data in the assessment of the probability of hydrologic drought.
• Myneni, R. B., Dong, J., Tucker, C. J., Kaufmann, R. K., Kauppi, P. E., Liski, J., Zhou, L., Alexeyev, V., & Hughes, M. K. (2001). A large carbon sink in the woody biomass of northern forests. Proceedings of the National Academy of Sciences of the United States of America, 98(26), 14784-14789.
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  PMID: 11742094;PMCID: PMC64936;Abstract: The terrestrial carbon sink, as of yet unidentified, represents 15-30% of annual global emissions of carbon from fossil fuels and industrial activities. Some of the missing carbon is sequestered in vegetation biomass and, under the Kyoto Protocol of the United Nations Framework Convention on Climate Change, industrialized nations can use certain forest biomass sinks to meet their greenhouse gas emissions reduction commitments. Therefore, we analyzed 19 years of data from remote-sensing spacecraft and forest inventories to identify the size and location of such sinks. The results, which cover the years 1981-1999, reveal a picture of biomass carbon gains in Eurasian boreal and North American temperate forests and losses in some Canadian boreal forests. For the 1.42 billion hectares of Northern forests, roughly above the 30th parallel, we estimate the biomass sink to be 0.68 ± 0.34 billion tons carbon per year, of which nearly 70% is in Eurasia, in proportion to its forest area and in disproportion to its biomass carbon pool. The relatively high spatial resolution of these estimates permits direct validation with ground data and contributes to a monitoring program of forest biomass sinks under the Kyoto protocol.
• Conner, W. S., Schowengerdt, R. A., Munro, M., & Hughes, M. K. (2000). Engineering design of an image acquisition and analysis system for dendrochronology. Optical Engineering, 39(2), 453-463.
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  Abstract: The design and implementation of a computer-vision-based analysis system for dendrochronology are described. The primary issues covered are automatic focus detection, illumination distortion, spatial and radiometric registration of a sequence of images into a single mosaic, and edge detection and linking. These issues are not unique to the application, but are likely of interest to anyone developing automated image analysis systems. A modification of the Canny edge detection algorithm that adapts to the variable characteristics of tree-ring images is also described.
• Biondi, F., Perkins, D. L., Cayan, D. R., & Hughes, M. K. (1999). July temperature during the second millennium reconstructed from Idaho tree rings. Geophysical Research Letters, 26(10), 1445-1448.
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  Abstract: An 858-year proxy record of July temperature for east-central Idaho shows multi-decadal periods of extreme cooling centered around AD 1300, 1340, 1460, and after AD 1600. These cold intervals are interrupted by prolonged warm spells in the early 1400s, late 1500s, and in the 1930s. The spatial signature of the paleoclimate record is centered on the north-central Rockies and central Great Plains, and expands over North America following a wave-like pattern. Neither instrumental nor proxy data in Idaho northeast valleys show unusual warming during the twentieth century. Climate episodes over the last three centuries are in broad agreement with the Greenland borehole temperature history. Low-frequency patterns are consistent with other northern hemisphere tree-ring records for the late Holocene, and provide a chronology of warm and cold intervals during the Little Ice Age. Copyright 1999 by the American Geophysical Union.
• Hughes, M. K., Vaganov, E. A., Shiyatov, S., Touchan, R., & Funkhouser, G. (1999). Twentieth-century summer warmth in northern Yakutia in a 600-year context. Holocene, 9(5), 629-634.
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  Abstract: We report unusual twentieth-century early-summer warmth recorded by larch tree-rings at the northern tree-line in far northeastern Eurasia (Yakutia). The tree-ring series are strongly replicated and well suited to the detection of fluctuations on interannual to century timescales. They are strongly correlated with local instrumental temperature data. Mean early-summer temperature in the twentieth century significantly exceeds that of any period of the same length since AD 1400. A century-scale trend, which commences in the mid-nineteenth century, is superimposed on interannual and decadal fluctuations, for example a marked cooling since 1978. While many of the 20 coolest early summers in the reconstruction occur within a few years after major explosive volcanic eruptions from low-latitude volcanoes, several of the 20 warmest early summers followed major explosive eruptions from high-latitude volcanoes.
• Mann, M. E., Bradley, R. S., & Hughes, M. K. (1999). Northern hemisphere temperatures during the past millennium: Inferences, uncertainties, and limitations. Geophysical Research Letters, 26(6), 759-762.
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  Abstract: Building on recent studies, we attempt hemispheric temperature reconstructions with proxy data networks for the past millennium. We focus not just on the reconstructions, but the uncertainties therein, and important caveats. Though expanded uncertainties prevent decisive conclusions for the period prior to AD 1400, our results suggest that the latter 20th century is anomalous in the context of at least the past millennium. The 1990s was the warmest decade, and 1998 the warmest year, at moderately high levels of confidence. The 20th century warming counters a millennial-scale cooling trend which is consistent with long-term astronomical forcing.
• Touchan, R., & Hughes, M. K. (1999). Dendrochronology in Jordan. Journal of Arid Environments, 42(4), 291-303.
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  Abstract: Dendrochronology is a valuable tool for the study of past climate and increases our knowledge of climate variability beyond the short period covered by instrumental data. Two annual tree-ring width chronologies were developed for northern Jordan (Pinus halepensis and Quercus aegilops), one chronology for Carmel Mountain, Israel (Pinus halepensis), and one chronology for southern Jordan (Juniperus phoenicia). The results of our study show that the northern site chronologies are significantly correlated, but the northern and southern sites are not. A relatively high correlation was shown between October-April precipitation and a Pinus halepensis chronology, and between October-May precipitation and Quercus aegilops, both in the north. October-May precipitation was reconstructed for the time span AD 1600 to 1995 from the Juniperus phoenicia tree-ring chronology. The longest reconstructed drought, defined as consecutive years below a threshold of 80% of the 1946-1995 mean observed October-May precipitation, was 4 years, compared with 3 years for the 1946-95 instrumental data.
• Touchan, R., Meko, D., & Hughes, M. K. (1999). A 396-year reconstruction of precipitation in southern Jordan. Journal of the American Water Resources Association, 35(1), 49-59.
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  Abstract: Water resources are the lifeblood of the Near East region. Careful planning and management of water resources in dry land regions requires information on the likelihood of extreme events, especially prolonged drought. It is essential to understand the variability of climate on time scales of decades to centuries to assign reasonable probabilities to such events. Tree-ring analysis is one way to increase our knowledge of the climate variability beyond the short period covered by the instrumental data. In this paper, we reconstruct October-May precipitation from a Juniperus phoenicia tree-ring chronology in southern Jordan to gain a long-term (A.D. 1600-1995) perspective on runs of dry years and on time series fluctuations in precipitation averaged over several years. The reconstruction equation derived by regression of log-transformed precipitation on tree-ring indices explains 44 percent of the variance of observed precipitation. The longest reconstructed drought, as defined by consecutive years below a threshold of 217.4 mm, was four years, compared with three years for the 1946-95 instrumental data. A Monte Carlo analysis designed to account for uncertainty in the reconstruction indicates a lower than 50 percent chance that the region has experienced drought longer than five years in the past 400 years.
• Vaganov, E. A., Hughes, M. K., Kirdyanov, A. V., Schweingruber, F. H., & Silkin, P. P. (1999). Influence of snowfall and melt timing on tree growth in subarctic Eurasia. Nature, 400(6740), 149-151.
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  Abstract: The causes of a reduced sensitivity of high-latitude tree growth to variations in summer temperature for recent decades, compared to earlier this century, are unknown. This sensitivity change is problematic, in that relationships between tree-ring properties and temperature are widely used for reconstructing past climate. Here we report an analysis of tree-ring and climate data from the forest-tundra zone, in combination with a mechanistic- model of tree-ring growth, to argue that an increasing trend of winter precipitation over the past century in many subarctic regions led to delayed snow melt in these permafrost environments. As a result, the initiation of cambial activity (necessary for the formation of wood cells) has been delayed relative to the pre-1960 period in the Siberian subarctic. Since the early 1960s, less of the growth season has been during what had previously been the period of maximal growth sensitivity to temperature. This shift results not only in slower growth, but also in a reduced correlation between growth and temperature. Our results suggest that changes in winter precipitation should be considered in seeking explanations for observer changes in the timing of the 'spring greening' of high-latitude forests, and should be taken into account in the study of the role of the Siberian subarctic forest in the global carbon cycle.
• Conner, W., Schowengerdt, R. A., Munro, M., & Hughes, M. K. (1998). Design of a computer vision based tree ring dating system. Proceedings of the IEEE Southwest Symposium on Image Analysis and Interpretation, 256-261.
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  Abstract: The purpose of this paper is to describe the design and implementation of a computer vision based analysis system for dendrochronology. The issues involved in the detection and analysis of tree rings are not unique to the application, but are likely of interest to anyone developing automated image analysis systems.
• Damon, P. E., Eastoe, C. J., Hughes, M. K., Kalin, R. M., Long, A., & Peristykh, A. N. (1998). Secular variation of Δ¹⁴C during the medieval solar maximum: A progress report. Radiocarbon, 40(1), 343-350.
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  Abstract: The Earth is within the Contemporaneous Solar Maximum (CSM), analogous to the Medieval Solar Maximum (MSM). If this analogy is valid, solar activity will continue to increase well into the 21st century. We have completed 75 single-ring and 10 double-ring measurements from AD 1065 to AD 1150 to obtain information about solar activity during this postulated analog to solar activity during the MSM. Δ14C decreases steadily during the period AD 1065 to AD 1150 but with cyclical oscillations around the decreasing trend. These oscillations can be successfully modeled by four cycles. These four frequencies are 1/52 yr-1, 1/22 yr-1, 1/11 yr-1, and 1/5.5 yr, i.e., the 4th harmonic of the Suess cycle, the Hale and Schwabe cycles and the 2nd harmonic of the Schwabe cycle.
• Mann, M. E., Bradley, R. S., & Hughes, M. K. (1998). Global-scale temperature patterns and climate forcing over the past six centuries. Nature, 392(6678), 779-787.
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  Abstract: Spatially resolved global reconstructions of annual surface temperature patterns over the past six centuries are based on the multivariate calibration of widely distributed high-resolution proxy climate indicators. Time-dependent correlations of the reconstructions with time-series records representing changes in greenhouse-gas concentrations, solar irradiance, and volcanic aerosols suggest that each of these factors has contributed to the climate variability of the past 400 years, with greenhouse gases emerging as the dominant forcing during the twentieth century. Northern Hemisphere mean annual temperatures for three of the past eight years are warmer than any other year since (at least) AD 1400.
• Mann, M. E., Bradley, R. S., Hughes, M. K., & Jones, P. D. (1998). Global temperature patterns [3]. Science, 280(5372), 2029-2030.
• Biondi, F., Lange, C. B., Hughes, M. K., & Berger, W. H. (1997). Inter-decadal signals during the last millennium (AD 1117-1992) in the varve record of Santa Barbara basin, California. Geophysical Research Letters, 24(2), 193-196.
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  Abstract: Annual varve thickness (AD 1117-1992) from Santa Barbara basin has been decomposed into orthogonal components using singular spectrum analysis (SSA) to identify and retrieve inter-decadal oscillations. After removing all variability with periods greater than 150 years, leading SSA eigenfunctions (EOFs) identify four oscillatory pairs with periods of ∼100, ∼58, ∼25, and ∼12 years respectively. Based on 2500 simulated series and on two-sided confidence intervals, EOFs 1-7 are significant at the 99% level and EOFs 8-9 are significant at the 90% level. Oscillatory signals retrieved from the marine varves show an abrupt change in frequency and amplitude near AD 1600. The largest contribution to this environmental shift is given by the interdecadal components, especially the ∼25 and the ∼12-year oscillation. The near-AD 1600 change may be related to multi-annual events reported in the stratigraphy of the nearby Santa Monica Basin and in dendrochronological records of the American Southwest.
• Hughes, M. K., & Diaz, H. F. (1994). Was there a 'medieval warm period', and if so, where and when?. Climatic Change, 26(2-3), 109-142.
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  Abstract: It has frequently been suggested that the period encompassing the ninth to the fourteenth centuries A.D. experienced a climate warmer than that prevailing around the turn of the twentieth century. This epoch has become known as the Medieval Warm Period, since it coincides with the Middle Ages in Europe. In this review a number of lines of evidence are considered, (including climatesensitive tree rings, documentary sources, and montane glaciers) in order to evaluate whether it is reasonable to conclude that climate in medieval times was, indeed, warmer than the climate of more recent times. Our review indicates that for some areas of the globe (for example, Scandinavia, China, the Sierra Nevada in California, the Canadian Rockies and Tasmania), temperatures, particularly in summer, appear to have been higher during some parts of this period than those that were to prevail until the most recent decades of the twentieth century. These warmer regional episodes were not strongly synchronous. Evidence from other regions (for example, the Southeast United States, southern Europe along the Mediterranean, and parts of South America) indicates that the climate during that time was little different to that of later times, or that warming, if it occurred, was recorded at a later time than has been assumed. Taken together, the available evidence does not support a global Medieval Warm Period, although more support for such a phenomenon could be drawn from high-elevation records than from low-elevation records. The available data exhibit significant decadal to century scale variability throughout the last millennium. A comparison of 30-year averages for various climate indices places recent decades in a longer term perspective. © 1994 Kluwer Academic Publishers.
• Hughes, M. K., Xiangding, W., Xuemei, S., & Garfin, G. M. (1994). A Preliminary Reconstruction of Rainfall in North-Central China since A.D. 1600 from Tree-Ring Density and Width. Quaternary Research, 42(1), 88-99.
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  Abstract: May-June (MJ) and April-July (AJ) precipitation at Huashan in north-central China has been reconstructed for the period A.D. 1600 to 1988 using tree-ring density and width from Pinus armandii. MJ precipitation (based on ring width and maximum latewood density) calibrated and cross-validated against local instrumental data more strongly than AJ precipitation (based only on ring width). A major drought was reconstructed for the mid- and late 1920s, confirmed by local documentary sources. This drought (culminating in 1929) was the most severe of the 389-yr period for MJ and second most severe for AJ, after an event ending in 1683. Neither reconstruction shows much spectral power at frequencies lower than 1 in 10 yr, but both show concentrations of power between 2.1 and 2.7 yr and 3.5 to 9 yr. There are significant correlations between the two reconstructions and a regional dryness/wetness index (DW) based on documentary sources, particularly at high frequencies. These correlations are focused in the 7.6- to 7.3-, 3.8- to 3.6-, and 2.5-yr periods. Using singular spectrum analysis, quasiperiodic behavior with a period close to 7.2 yr was identified in the MJ precipitation reconstruction and in the DW index based on documents.
• Meko, D., Cook, E. R., Stahle, D. W., Stockton, C. W., & Hughes, M. K. (1993). Spatial patterns of tree-growth anomalies in the United States and southeastern Canada. Journal of Climate, 6(9), 1773-1786.
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  Abstract: A network of 248 tree-ring chronologies in the conterminous United States is assembled and analyzed by rotated principal components analysis (RPCA) to delineate "regions' of common tree-growth variation during the period 1705-1979. Principal component drought information is evaluated by comparing PC scores and primary pattern coefficients with Palmer Drought Severity Index (PDSI) data from instrumental records. High PC pattern coefficients group geographically into regions coinciding roughly with nine drought regions delineated by RPCA of PDSI by other researchers. The drought signal as measured by the correlation between tree-ring PC scores and July PDSI, 1929-79, is strongest in the South and the interior West (r>0.7), and weakest in the Northeast and Pacific Northwest (r
• Hughes, M. K., & Brown, P. M. (1992). Drought frequency in central California since 101 B.C. recorded in giant sequoia tree rings. Climate Dynamics, 6(3-4), 161-167.
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  Abstract: Well replicated tree-ring width index chronologies have been developed for giant sequoia at three sites in the Sierra Nevada, California. Extreme low-growth events in these chronologies correspond with regional drought events in the twentieth century in the San Joaquin drainage, in which the giant sequoia sites are located. This relationship is based upon comparison of tree-ring indices with August Palmer Drought Severity Indices for California Climate Division 5. Ring-width indices in the lowest decile from each site were compared. The frequency of low-growth events which occurred at all three sites in the same year is reconstructed from 101 B.C. to A.D. 1988. The inferred frequency of severe drought events changes through time, sometimes suddenly. The period from roughly 1850 to 1950 had one of the lowest frequencies of drought of any one hundred year period in the 2089 year record. The twentieth century so far has had a below-average frequency of extreme droughts. © 1992 Springer-Verlag.
• Kelly, P. M., Munro, M. A., Hughes, M. K., & Goodess, C. M. (1989). Climate and signature years in west European oaks. Nature, 340(6228), 57-60.
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  Abstract: It has been shown that in certain 'signature' years tree-ring chronologies from living oaks throughout much of western Europe exhibit the same characteristic of either increasing or decreasing growth1. Remarkably, these chronologies, many of which are the product of the recent extension of the European tree-ring network2-4, are distributed over a latitude span of ∼10°and a longitude span of 20°. This phenomenon means that archaeological series from more distant areas can be compared, increasing the likelihood that gaps in regional dating chronologies can be bridged5,6. The question arises as to what circumstances could induce trees over such a large area to behave in unison so frequently. We have examined climate departures from modern signature years to determine whether or not there is a typical climate pattern associated with years of large-scale growth increase or decrease. We find that particular climatic conditions affecting the area from which the tree-ring chronologies are drawn can account for the signature years and suggest that this relationship may enable archaeological chronologies to be used in climate reconstruction. © 1989 Nature Publishing Group.
• Briffa, K. R., Jones, P. D., Pilcher, J. R., & Hughes, M. K. (1988). Reconstructing summer temperatures in northern Fennoscandinavia back to AD 1700 using tree-ring data from Scots pine. Arctic & Alpine Research, 20(4), 385-394.
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  Abstract: Estimates of mean July-August temperatures for northern Fennoscandinavia are made back to 1700 using ring width and maximum latewood density chronologies of Pinus sylvestris L. (Scots pine) as predictors. Several prediction models are used and the best results are achieved with a simple two-variable model where climate in year t is estimated as a function of tree growth in years t and t + 1 at each site. The best reconstruction equation accounts for 56% of the temperature variance over a 74yr fitting period and 45% of the variance over a 39yr independent verification period. Relatively short-period variability (periods
• Hughes, M. K. (1988). Ice-layer dating of eruption at Santorini. Nature, 335(6187), 211-212.
• Hughes, M. K., Schweingruber, F. H., Cartwright, D., & Kelly, P. M. (1984). July-August temperature at Edinburgh between 1721 and 1975 from tree-ring density and width data. Nature, 308(5957), 341-344.
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  Abstract: The use of wood density measurements in dendroclimatology is a relatively recent development1. There have been few attempts to use these data in climate reconstruction or to test the result rigorously. We now report on the reconstruction of July-August surface air temperature for Edinburgh, Scotland, for the period AD 1721-1975 using maximum latewood density and ring-width data from pine trees in the Scottish Highlands. In a series of tests, it is shown that the relationship between the climate and tree-ring variables is statistically significant and stable with time, confirming the power of dendroclimatic reconstruction even in a moist region such as the British Isles. © 1984 Nature Publishing Group.
• Fritts, H. C., Hughes, M. K., & Milsom, S. J. (1982). The climate-growth response.. Climate from tree rings, 33-38.
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  Abstract: Properly selected, adequately replicated and appropriately standardised tree-ring chronologies will correlate with macroclimatic factors that vary in kind from month to month and from one season to the next. This causes the coefficients for monthly temperature and precipitation to vary within and among response function results. Some of this variation is due to statistical uncertainty, but the remainder can be attributed to differences in physiological responses. -L.F.Musk
• Graybill, D. A., Hughes, M. K., Aniol, R. W., & Schmidt, B. (1982). Chronology development and analysis.. Climate from tree rings, 21-31.
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  Abstract: Presents a summary of basic analytical strategies for tree-ring chronology building. Emphasis is upon the procedures of their implementation with a series of recently revised computer programs. -L.F.Musk
• Hughes, M. K., Kelly, P. M., Pilcher, J. R., & Lamarche Jr, V. C. (1982). Climate from tree rings.. Climate from tree rings..
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  Abstract: Annual rings formed in the wood of many trees are well established as records of past environments. This volume is based largely on the proceedings of the second international workshop on global dendroclimatology, Norwich, July 1980. Detailed descriptions and evaluations of current field, laboratory, and statistical methods are given. The availability of dendroclimatic data is reviewed in depth, region by region and the prospects for future developments are assessed. Papers are abstracted separately.- L.F.Musk
• Sizhong, Z., Xiangding, W., Zhenyao, L., & Hughes, M. K. (1982). Asia.. Climate from tree rings, 155-158.
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  Abstract: Dendroclimatic work began in Japan in 1920 and in China in the 1930s. As the largest landmass in the N Hemisphere, Asia is of great significance to the development of a hemispheric tree-ring data base. Discusses the limited studies that have been performed; the main problems for the future would appear to be the calibration and verification of reconstructions, since the areas without historical records are those often most remote from weather stations.-L.F.Musk
• Hughes, M. K., Milsom, S. J., & Leggett, P. A. (1981). Sapwood estimates in the interpretation of tree-ring dates. Journal of Archaeological Science, 8(4), 381-390.
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  Abstract: Many timber finds lack some or all of the outer, sapwood rings formed in the years just before felling. In order to estimate felling date once the outermost remaining ring has been dated, it is necessary to estimate the number of sapwood rings originally present. Methods doing this for oak are reviewed in the light of an intensive study of living trees at one site and an extensive study of 175 samples from living trees in North Wales and northwest England. Some methods reported in the literature are found to be invalid. A method reported by Hollstein (1965) is most reliable, with modifications for known variations in sapwood number with position in the tree. At present the best available estimate is that a value of 30 sapwood rings be used (95% confidence limits: 19-50). © 1981.
• Hughes, M. K., Kelly, P. M., Pilcher, J., & Lamarche Jr, V. C. (1980). Report and Recommendations (2nd International Workshop on Global Dendroclimatology).. Report and Recommendations (2nd International Workshop on Global Dendroclimatology)..
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  Abstract: The aims of the Workshop were: to review basic concepts and techniques; to consider what kinds of information available from tree rings would be of value to scientists; to evaluate the contribution of tree-ring data to palaeoclimatic studies; to exchange information on analytical techniques and results; to review the existing tree-ring collections; and to prepare a review of the current status of dendroclimatology. Recommendations on these are included. -L.F.Musk
• Hughes, M. K., Lepp, N. W., & Phipps, D. A. (1980). Aerial Heavy Metal Pollution and Terrestrial Ecosystems. Advances in Ecological Research, 11(C), 217-327.
• Hughes, M. K., Gray, B., Pilcher, J., Baillie, M., & Leggett, P. (1979). Climatic signals in tree-ring chronologies for British oaks (reply). Nature, 278(5701), 283-.
• Hughes, M. K., Leggett, P., Gray, B., Pilcher, J., & Baillie, M. (1978). Climatic signals in British Isles tree-ring chronologies. Nature, 272(5654), 605-606.
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  Abstract: INTERPRETATION of proxy records of past environmental conditions derived from dated geological or biological materials is of great importance for the extension of the climatic record1,2. Precisely dated, replicated tree-ring series have been particularly useful as they provide records (usually ring-widths) dated to the individual year, for hundreds or thousands of years. Each such series, or chronology, is derived from a particular known location. Thus a network of such chronologies may be developed for a particular region and used as a proxy record of spatial and temporal climatic variations. This has been achieved in North America by Fritts et al.3,4, using principally chronologies from semi-arid areas or from near altitudinal or polar tree-lines. We report evidence here that tree-ring chronologies from sites in the British Isles will provide suitable proxy records for the reconstruction of historical temporal and spatial variation of climate. © 1978 Nature Publishing Group.
• Hughes, M. K. (1975). Ground vegetation net production in a Danish beech wood. Oecologia, 18(3), 251-258.
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  Abstract: Biocontent of the above and below-ground parts of ground vegetation in a Danish beech forest was between 1685 and 3025 Kj/m2 (94.57 to 169.43g/m2). Net production as the difference between overall maximum and overall minimum biocontent was 1340 Kj/m2/yr (74.86g/m2/yr); as the sum of differences between species maximum and minimum 1832 Kj/m2/yr (111.49g/m2/yr); and as the sum of calculated losses to litter and biomass change 2759 Kj/m2/yr (160.05g/m2/yr). The data indicate that an estimate based on above ground parts alone would be one-third of those presented. Ground vegetation was a major contributor to litter production. © 1975 Springer-Verlag.

Presentations

• Graham, N., Salzer, M. W., Hughes, M. K., & Verschuren, D. (2017, Spring). Dust-lake-climate interactions and the “4.2 kyr event”.. European Geoscience Union. Vienna, Austria: European Geoscience Union.
• Bunn, A. G., Tran, T. J., Brauning, J. M., Salzer, M. W., Weiss, S. B., & Hughes, M. K. (2016, Fall). Identifying Threshold Temperatures Associated with Bristlecone Pine Growth Signals in the Great Basin, USA.. American Geophysical Union. San Francisco, CA.
• Bunn, A. G., Tran, T., Bruening, J., Salzer, M. W., Weiss, S. W., & Hughes, M. K. (2016, MArch). Niche spaces in the growth of high elevation Bristlecone Pine in the Great Basin, U.S.A.. Ameridendro. Mendoza, Argentina: Tree-Ring Society.
• Hughes, M. K., Piermattei, A., Salzer, M. W., & Gaertner, H. (2016, March). Incomplete lignification in tracheids of bristlecone pine from near upper tree limit in California and Nevada, USA.. Ameridendro. Mendoza, Argentina: Tree-Ring Society.
• Hughes, M. K. (2015, May). Life at the limit - high elevation tree-ring growth and climate in the Great Basin, USA. Departmental seminar. Durham, England: Dept. of Biological and Biomedical Sciences, Durham University.
• Bunn, A., Salzer, M., Larson, E., Weiss, S., & Hughes, M. K. (2014, December). The Role of Topoclimate in Explaining Abrupt Growth Thresholds of Bristlecone Pine in the White Mountains of California, USA.. Fall Meeting, AGU. San Francisco, CA.
• Evans, M. N., Tolwinski-Ward, S., Anchukaitis, K. J., Duke, G., & Hughes, M. K. (2014, January). Applications of proxy system modeling in dendroclimatology. World Dendro 2014. Melbourne, Australia.
• Hughes, M. K., & Salzer, M. (2014, January). Current status of the Methuselah Walk bristlecone pine chronology for radiocarbon calibration.. World Dendro 2014. Melbourne, Australia.
• Hughes, M. K., Salzer, M., Bunn, A., & Larson, E. (2014, January). Spatiotemporal variations in tree-ring/climate links in millennia-long bristlecone pine chronologies.. World Dendro 2014. Melbourne, Australia.
• Panyushkina, I. P., authors, F. o., Leavitt, S. W., & Hughes, M. K. (2014, January). Tree-ring evidence of wood property changes caused by modern acidification of arctic soils.. World Dendro 2014. Melbourne, Australia.
• Hughes, M. K. (2013, October). Life at the limit – high elevation tree-ring growth and climate in the Great Basin, USA.. Seminar: Climate Change IGERT, University of Washington, Seattle. Seattle, Washington.
• Hughes, M. K. (2013, October). Life at the limit – high elevation tree-ring growth and climate in the Great Basin, USA. Departmental Seminar, Biology Department, University of Quebec at Chicoutimi, Canada. Chicoutimi, Quebec, Canada.
• Hughes, M. K. (2013, October). What can we learn from the ‘Hockey Stick Episode’?. Seminar Oceans and Policy Program, Department of Oceanography, University of Washington, Seattle,. Seattle, Washington.
• Hughes, M. K., Salzer, M., & Bunn, A. (2013, May). Mixed signals, mixed messages and lessons from bristlecone pine.. Second American Dendrochronology Conference, May 13-17, 2013, Tucson, AZ. Tucson, AZ.
• Anchukaitis, K. J., authors, T. o., & Hughes, M. K. (2012, December). The dendroclimatology of Common Era volcanic eruptions.. AGU Fall Meeting. San Francisco, CA.
• Bunn, A., Salzer, M., Weiss, S., & Hughes, M. K. (2012, December). Quantifying Climate Thresholds for Bristlecone Pine Using Landscape Heterogeneity to Improve Climate Reconstructions from Tree Rings.. AGU Fall Meeting. San Francisco, CA.
• Hughes, M. K. (2012, May). Keynote lecture: Reframing dendroclimatology. TRACE (Tree Rings in Archeology, Climatology and Ecology) Conference. Potsdam, Germany: Association of Tree-RIng Research.
• Hughes, M. K. (2012, May). Life at the limit - high elevation tree-ring growth and climate in the Great Basin, USA. Institute Colloquium. Nuremberg, Germany: Physical Geography Institute, Friedrich-Alexander University Erlangen-Nurembergg.
• Hughes, M. K., & authors, Hughes lead, S. o. (2012, December). Comparing NDVI and observed stem growth and wood density in forests of Northern Eurasia. AGU Fall Meeting. San Francisco, CA.

Poster Presentations

• Hughes, M. K., Piermattei, A., Siekacz, L., Conciatori, F., Bunn, A., Tardif, J., Pearson, C. L., & Salzer, M. (2019, July). Blue-stained rings in ancient bristlecone pine as a volcanic proxy. INQUA 2019. Dublin, Ireland: INQUA.
• Monson, R. K., Szejner, P., Belmecheri, S., Morino, K., Wright, w., Babst, F., Hughes, M. K., Leavitt, S. W., Trouet, V. M., & Ehleringer, J. (2017, August). Reconstructing drought legacies in the North American Monsoon climate system using tree ring stable isotopes. ESA meeting. Portland, OR.
• Hughes, M. K., Morino, K., & Brown, P. M. (2016, Spring). Cambial phenology, xylogenesis and tree-ring anatomy in pines in semi-arid southern Arizona. Ameridendro. Mendoza, Argentina: Tree-Ring Society.
• Salzer, M., Bunn, A., Graham, N., & Hughes, M. K. (2012, December). Paleotemperature from high elevation tree-ring width and treeline change over 4,500 years in the Great Basin, USA. AGU Fall Meeting. San Francisco, CA.