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Tree -ring characteristics are studied within and among stems of four Pinus ponderosa Laws. located at several semiarid sites in northern Arizona. Analyses are made of changes associated with certain physiological, height, and age gradients within the tree. Rings are grouped into twenty or forty-year intervals, are classified in four different arrangements, and the characteristics for the intervals are averaged and plotted to represent the gradients within the tree stem. Tree-rings are widest near the base and central portions of the stem. Ring width decreases with increasing age of the cambium, with increasing height within the young stem, with decreasing terminal growth, and with increasing environmental stress. Double (false or intra-annual) rings occur most frequently in the wide rings near the base and in the younger portions of the stem, or in the upper stem and branches of older trees. The frequency of rings which are locally absent (partial rings) is inversely related to ring width, and directly related to the potentiality for water stress conditions in the site or within the tree. Correlations among the year-to-year ring-width patterns throughout the tree generally increase with increasing tree age and frequency of water stress. They are high within the lower and central bole portions of older trees, but in the upper stem, in lateral branches, and in trees on the most extreme sites correlations among ring-width patterns are somewhat lower. Relative variability in widths of adjacent rings increases with decreasing ring width, increasing age, increasing height in the stem, and increasing environmental stress. First order serial correlation is frequently highest in older trees on semiarid sites. Many of these changes in ring characteristics within the tree are attributed to specific gradients or changes in auxin, food, and water supplies. A wide sampling of annual rings from the base of many semiarid site trees appears more appropriate for evaluating past fluctuations in climatic factors than an intensive sampling of rings at several heights in only a few trees.

Data derived from specimens received from the Southern Sector, Navajo Land Claim, are presented. This Sector includes East Central Arizona and West Central New Mexico. Of the 797 specimens worked, 299 yielded dates.

The Wetherill Mesa Archeological Project devoted a portion of its funds and personnel to an attempt to reconstruct the past climate at Mesa Verde National Park. Data for this study were obtained from the thorough tree-ring dating of the archaeological excavations, from environmental measurement stations, and from measurements of tree growth. The results of the dendrochronological study on Wetherill Mesa include very long tree-ring chronologies; large clusters of dates from each site excavated on Wetherill Mesa; and a tentative climate reconstruction for Mesa Verde.

A long Douglas-fir tree-ring chronology was needed for use in a climatic interpretation of Mesa Verde. The archaeological portion of the chronology was derived from 21 archaeological specimens obtained from excavations on Wetherill Mesa and extended from A.D. 435 to 1276. The modern portion, extending to 1963, was derived from directional and non-directional cores from six very old living Douglas-fir trees. In addition, four directional cores from each of the six trees were used to compute tree-ring indices for the years 1860 to 1963, which have been used for an analysis of paleoclimate.

Contains: References, Indices for Four Directional Cores from SOT-1 to -6, Douglas-fir Indices for Climatic Analysis, Composite Species Indices for all Archaeological Specimens from Wetherill Mesa, Juniper Indices for Wetherill Mesa Archaeological Sites (A.D. 301-1274), Pinyon Pine Indices for Wetherill Mesa Archaeological Sites (A.D. 161-355; 486-1278), Douglas-fir Indices for Wetherill Mesa Archaeological Sites (A.D. 435-1276), Ponderosa Pine Indices for Wetherill Mesa Archaelogical Sites (A.D. 1060-1269) / The 1,916 wood and charcoal specimens obtained from five years of survey and excavations on Wetherill Mesa produced 501 tree-ring dates. The dated specimens filled a gap between A.D. 674 and 733, greatly lengthening the combined species' tree-ring series for Mesa Verde so that it now extends from A.D. 161 to 1280. In addition a very long tree-ring series was established for juniper, a tree rarely dated from Mesa Verde in the past.

Dendrochronological research in the Mexican state of Oaxaca in 1970 proved negative due to complacent ring series. It is suggested that this is caused by a flexible growing season triggered only by the onset of the rains. Pine and fir were sampled from eleven sites. No old age trees were located and crossdating could not be accomplished.

A method is presented for making probability statements about past climatic conditions for the state of Arizona given the corresponding relative width of tree rings. The probability statements about periods of extreme climate from 1650 to 1899 are based upon the joint occurrence of the state-wide average seasonal climate and ring widths during 1899-1957. The ring-width values used are index chronologies selected from four different areas within Arizona. Spatial homogeneity among the four chronologies is evaluated by using digital filtering and correlation techniques. The chronologies are then normalized, averaged to form a state-wide series, and the values of state-wide growth for each year placed into one of nine equally probable classes. Similarly, seasonal temperatures and seasonal precipitation are placed into three equally probable classes and the joint occurrences between temperature and precipitation become nine climatic classes. Contingency tables are used to establish the joint occurrence of the nine climatic classes and the nine ring-width classes. A number of 10 and 20 year intervals since 1650 are identified as periods of unusually high or low probability of occurrence of above or below normal precipitation for any season of the year. The period 1880-1889 is of special interest as it was a period when downcutting was initiated in many Arizona streams and is also one of the periods in which the probability for below normal seasonal precipitation was unusually high (p = 0.48).

In the last ten years tree-ring analysis in Europe and its application has been extended considerably. By varied methods, a number of chronologies have been established for conifers and deciduous trees from different climatic regions that partly reach back to periods before the birth of Christ. The focus of dendrochronological research is usually dating and climatological studies are carried on only sporadically.

A crossdating program for tree-ring research has been written to compare ring patterns of individual trees and composites. The program written in FORTRAN calculates the t value for correlation at every point of overlap of the two chronologies. The program is small enough to be used on a routine basis with a large number of trees. As the chronologies must be free from errors, the program is more suited to the study of oaks than coniferous trees.