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Variations in Climate Since 1602 as Reconstructed from Tree Rings
- Harold C. Fritts, G. Robert Lofgren, Geoffrey A. Gordon
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- Journal:
- Quaternary Research / Volume 12 / Issue 1 / July 1979
- Published online by Cambridge University Press:
- 20 January 2017, pp. 18-46
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Spatial anomalies of tree-ring chronologies can provide information on high-frequency spatial anomalies in paleoclimate representing droughts, colder-than-normal intervals, and other synoptic-scale features. Examples are presented in which 65 tree-ring chronologies are calibrated with spatial anomalies in North American meteorological records of seasonal temperature and precipitation, and with sea-level pressure over the North American and North Pacific sectors. Multivariate transfer functions are obtained that scale and convert the past spatial variations in the tree-ring record into estimates of past variations in the meteorological record. Objective verifications of the reconstructions are obtained using independent meteorological observations for time periods other than those used in the calibration. Historical information or other proxy data from the 19th century are also used for verifying the decadal (or longer) and regional reconstructions and for identifying strengths and weaknesses of the various sources of information. The reconstructed winter and summer temperatures for the United States and southwestern Canada and winter precipitation for the Columbia Basin and California during the 17th through 19th centuries were found to differ from the 20th century means with large-scale variations evident. Extreme winters similar to 1976–77 are also identified and found to be more frequent in the past, especially in the 17th century. The climatic reconstructions in this time domain are dominated by high-frequency, synoptic-scale fluctuations that can be interpreted as cyclonic-scale changes in atmospheric circulation. Such reconstructions may be useful for testing various climatic models and estimates developed primarily from 20th-century meteorological data against the longer estimated record for the 17th through 19th centuries.
Dendroclimatology and Dendroecology
- Harold C. Fritts
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- Journal:
- Quaternary Research / Volume 1 / Issue 4 / December 1971
- Published online by Cambridge University Press:
- 20 January 2017, pp. 419-449
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Dendrochronology is the science of dating annual growth layers (rings) in woody plants. Two related subdisciplines are dendroclimatology and dendroecology. The former uses the information in dated rings to study problems of present and past climates, while the latter deals with changes in the local environment rather than regional climate.
Successful applications of dendroclimatology and dendroecology depend upon careful stratification. Ring-width samples are selected from trees on limiting sites, where widths of growth layers vary greatly from one year to the next (sensitivity) and autocorrelation of the widths is not high. Rings also must be cross-dated and sufficiently replicated to provide precise dating. This selection and dating assures that the climatic information common to all trees, which is analogous to the “signal”, is large and properly placed in time. The random error or nonclimatic variations in growth, among trees, is analogous to “noise” and is reduced when ring-width indices are averaged for many trees.
Some basic facts about the growth are presented along with a discussion of important physiological processes operating throughout the roots, stems, and leaves. Certain gradients associated with tree height, cambial age, and physiological activity control the size of the growth layers as they vary throughout the tree. These biological gradients interact with environmental variables and complicate the task of modeling the relationships linking growth with environment.
Biological models are described for the relationships between variations in ring widths from conifers on arid sites, and variations in temperature and precpitation. These climatic factors may influence the tree at any time in the year. Conditions preceding the growing season sometimes have a greater influence on ring width than conditions during the growing season, and the relative effects of these factors on growth vary with latitude, altitude, and differences in factors of the site. The effects of some climatic factors on growth are negligible during certain times of the year, but important at other times. Climatic factors are sometimes directly related to growth and at other times are inversely related to growth. Statistical methods are described for ascertaining these differences in the climatic response of trees from different sites.
A practical example is given of a tree-ring study and the mechanics are described for stratification and selection of tree-ring materials, for laboratory preparation, for cross-dating, and for computer processing. Several methods for calibration of the ring-width data with climatic variation are described. The most recent is multivariate analysis, which allows simultaneous calibration of a variety of tree-ring data representing different sites with a number of variables of climate.
Several examples of applications of tree-ring analysis to problems of environment and climate are described. One is a specification from tree rings of anomalies in atmosphere circulation for a portion of the Northern Hemisphere since 1700 A.D. Another example treats and specifies past conditions in terms of conditional probabilities. Other methods of comparing present climate with past climate are described along with new developments in reconstructing past hydrologic conditions from tree rings.
Tree-ring studies will be applied in the future to problems of temperate and mesic environments, and to problems of physiological, genetic, and anatomical variations within and among trees. New developments in the use of X-ray techniques will facilitate the measurement and study of cell size and cell density. Tree rings are an important source of information on productivity and dry-matter accumulation at various sites. Some tree-ring studies will deal with environmental pollution. Statistical developments will improve estimation of certain past anomalies in weather factors and the reconstructtion of atmosphere circulation associated with climate variability and change. Such information should improve chances for measuring and assessing the possibility of inadvertent modification of climate by man.
The Biological Model for Paleoclimatic Interpretation of Mesa Verde Tree-Ring Series1
- Harold C. Fritts, David G. Smith, Marvin A. Stokes
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- Journal:
- Memoirs of the Society for American Archaeology / Volume 19 / October 1965
- Published online by Cambridge University Press:
- 27 June 2018, pp. 101-121
- Print publication:
- October 1965
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Ring-width chronologies in Douglas-fir, pinyon pine, and Utah juniper show some distinctly different characteristics and exhibit highly predictable relationships with variations in climate. Narrow rings in Douglas-fir are largely the result of low precipitation and high temperatures of the previous June, low precipitation during August through February, low precipitation and low temperatures during March through May, and low precipitation and high temperatures of the current June. Narrow rings in pinyon pine are largely a function of low precipitation from October through May, but high July temperatures near the end of the growing season may also exert an influence. Narrow rings in Utah juniper are the result of low precipitation and high temperatures during the previous October through November, low precipitation during December through February, and low precipitation and high temperatures during March through May. A biological model for these relationships is proposed. The tree-ring chronology from A.D. 1273 through 1285 exhibits a clearly defined drought which exceeds in length and intensity any dry period occurring since A.D. 1673. A comparison of the chronologies from species which are influenced differently by summer precipitation indicates that during this period both summers and winters must have been dry. However, the A.D. 1273-1285 drought at Mesa Verde was surpassed by six other droughts of greater intensity during the period A.D. 500–1300. The A.D. 1273–1285 drought may be only one of several factors in a chain of events which led to the decline of prehistoric population in the Mesa Verde.