Investigtions into the Ecological Relationships of Ponderosa Pine in Southeast Arizona

TitleInvestigtions into the Ecological Relationships of Ponderosa Pine in Southeast Arizona
Publication TypeThesis
Year of Publication1963
AuthorsDodge, RA
AdvisorTurner, R
Academic DepartmentBotany
UniversityUniversity of Arizona

Studies to determine differences between Arizona and ponderosa pine have been carried on in the mountainous areas of southeast Arizona, utilizing plotless phytosociological techniques, morphological studies, and dendrometer investigations. Samples form northern Arizona and Sonora, Mexico, have been included for comparison. Ponderosa and Arizona pine are found in these regions from approximately 7000 to above 9000 feet elevation, associated with oaks in the lower portion of the elevational range and with other conifers in the upper part of the range. Comparison of needle number per fascicle indicated that three-needle ponderosa pine is found at the upper part of the elevational range, while the five-needle Arizona pine occupies habitats below ponderosa pine. Intergradation of the two taxa is indicated by a general increase from three to five needles per fascicle occurring with decreasing elevation; this relationship is more pronounced with decreasing latitude. The number of stomates per unit length of needle was found to increase slightly from north to south. Volume and length of pistillate cones were not useful criteria in separating taxa. Cone density, however, was found to increase with decreasing latitude, and little overlap was present in the two most distant stations. Cone-scale prickle curvature generally tended from an upward to downward pointing direction with decreasing latitude. Dendrometer studies among groups of trees classed as three-needle ponderosa pine, five-needle Arizona pine, and mixed needle hybrids indicated differences in time of radial expansion commencement. The trees classed as Arizona pine and hybrids between Arizona and ponderosa pine commenced radial expansion prior to ponderosa pine. No distinct differences were observed between the two taxa, and it is concluded that Arizona pine is a variety of ponderosa pine.