Tree-Ring Characteristics Along a Vegetation Gradient in Northern Arizona

Fritts, Harold; Smith, David; Cardis, John; Budelsky, Carl

Tree-ring samples of Pseudotsuga menziesii (Mirb.) Franco, Pinus ponderosa Laws., and Pinus Edulis Engelm. for 1860 through 1962 were obtained from sites along a vegetational gradient, ranging from forest interior sites to semiarid lower forest border sites. Samples were analyzed using a stratified nested plot design. Near the lower forest border tree rings are narrowest, the variability in the relative ring-width response from year to year is greatest, and the variance in common or the correlation between radii and between trees is highest. This variability is more highly related to climatic fluctuations than the variability in forest interior trees and may be attributed to longer and more frequent periods during which waterstress is limiting to physiological processes in the trees. Hence, at the arid forest border tree-ring chronologies contain the most consistent, but variable, growth responses and provide the best record of climatic flucuations. Chronologies from the forest border trees exhibit very few partial growth layers. Crossdating between both types of sites and among many individuals of different species makes absolute dating not only possible but exceedingly reliable. Such tree-ring analysis may have considerable application to the evaluation of ecological forest gradients.

Tree-Ring Characteristics Along a Vegetation Gradient in Northern Arizona

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