abstract: Livestock-grazing, in particular cattle grazing, is a common use of public and private lands in western North America. As a result, the effects of grazing on both plants and animals are widely studied. Few studies, however, look directly at the long-term effects that cattle grazing may have on a particular species. The goal of this experiment was to continue research begun in 1988, to determine if the effects of cattle grazing are still seen in the age structure of two populations of saguaros (Carnegiea gigantea [Engelm.] Britton & Rose) at Saguaro National Park - Rincon Mountain District (SNP-RMD). The null hypothesis stated that enough time has elapsed since the cessation of grazing, and there is no difference in the age distribution of the saguaros of the two populations. The study area was comprised of a former fence line where grazing ceased on the western side of the fence in 1958 and the eastern side in 1978. Belt transects were laid on each side of the fence line and height was measured for each saguaro encountered in a transect. Approximate age of the individual was then calculated using an age-height correlation for SNP-RMD. Individuals were then placed into age classes of 10 year increments and a Log-Likelihood test was performed. The resulting calculated P value of 0.12 meant the null hypothesis was not rejected and there was no statistical difference between the age structure of the two populations. After 34 and 54 years rest from grazing, the negative effects of cattle grazing on the retention and recruitment of saguaro seedlings have ended, and replenishment of the populations is now dependent upon factors such as temperature and precipitation. Other factors such as climate change, increasing fire frequency, encroachment by invasive species, and poaching are sources of concern and increased mortality for these and other saguaros. / Dissertation/Thesis / M.S. Applied Biological Sciences 2013

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The role of high infrared (IR) reflectance in the temperature regulation of a single species of cactus, Cereus giganteus (saguaro cactus), was investigated. Two independent methods were used to determine the effect of high near-IR reflectance on C. giganteus stem temperatures. The first method was to measure the surface temperature of two individual plants of comparable size and health, one of which was partially shaded by a canopy of loose sun-screening material. The second method involved the numerical solution on a computer of the energy balance, or heat transfer, equation for C. giganteus. High reflectance at near-IR wavelengths was found to decrease the peak surface temperature reached by C. giganteus by 3.2 to 3.3°C. This figure is valid for the fairly mild environmental conditions encountered in the Sonoran Desert at an altitude of 940 m during late September and early October.

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3 pp. / Problems and pests of cacti, agave, and yuccas / Barrel cactus and Saguaro (Carnegiea gigantea) are easily transplanted. Procedures for safely and succesfully moving these plants are discussed in this bulletin.

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