Development of Anatomical Tree-Ring Chonologies from Southern Arizona Conifers using Image Analysis

Climatic influences on the anatomical features of the last-formed latewood tracheids of southern Arizona conifers were examined using video image analysis. Video image analysis was shown to be a feasible method to obtain tracheid dimensions from tree rings. It also proved to be a precise method for measuring tree-ring density as a relative quantity (the lumen area percent, LUM%). Two cores from each of five ponderosa pines (Pinus ponderosa Laws.) were analyzed to obtain chronologies of radial and tangential diameter, lumen, cell wall and total areas, and LUM% in a range of 87-276 years. A fast and reliable sample preparation techniques using a sliding microtome was used to obtain microsections for the image analysis. Missing values for absent rings were estimated using stepwise regression with other non-missing series. Because no obvious biological trends were found for the mature periods, mean line fits were used for the standardization after removing the juvenile portions. Due to the large variabilities within and between trees, the anatomical chronologies possessed much weaker common signals than the ring-width or density chronologies. This indicated that a large number of cores per tree or trees per site should be taken to compensate for the biological heterogeneity in wood structure. The year-to-year variations in the anatomical chronologies were diverse, and autocorrelations were relatively high. Response function analyses revealed that most anatomical chronologies possessed a higher association with climatic variations than the ring-width or density chronologies. Reduced moisture stress during the early growing season, and high precipitation for the late growing season, induced high radial enlargement, consequently, greater tracheid area of the last-formed latewoods. The influence of climate on the tangential enlargement was inconsistent. Cell wall thickening was enhanced first by high precipitation for the prior growing season, then by low temperature for the growing season and by high October temperature. The effects of the cell enlargement were mixed with the effects of cell wall thickening in the lumen area % or maximum latewood density variation.