Document: MIC-3-64-4

Return to Walhalla: 25 years of forest growth and its effects on Kaibab squirrels.

KEARSLEY, M.J.C.* ¹ and J.G.HALL ^2,3

Northern Arizona University, Flagstaff, AZ, 86011-5640, U.S.A. ¹
San Francisco State University, San Francisco, CA, 94132, U.S.A. ²
Grand Junction, CO, 81503, U.S.A. ³

Abstract:
Between 1961 and 1963, a series of 65 tenth-hectare plots were established on the Walhalla Plateau of Grand Canyon's North Rim. Baseline data were collected on stem density, size, crown density and crown vigor of all older (> 15 cm d.b.h.) Ponderosa pine trees when plots were established. After establishment, plots were visited annually during June until 1973 for the assessment of Kaibab squirrel phloem feeding activity, measured by the number of fallen terminal needle clusters in each plot. We returned to these plots in June of the past two summers to remeasure plot tree conditions and count fallen needle clusters to assess changes resulting from 25 years of forest growth and Park Service fire management practices. The tree data show significantly higher tree densities and total basal areas overall, although there was considerable variability in the changes in individual plots since establishment. The squirrel data indicate that feeding activity, at least on phloem tissues, was as low as it had been in any of the years of the original censuses. We attribute the reduction in squirrel phloem feeding to lower phloem palatability which results from canopy closure and inter-tree competition. Because of the high inter-annual variation seen in this system, we will need to revisit these plots for at least 5 years before we are completely confident in the results, but our preliminary analyses indicate the benefits of some thinning.

Keywords: succession, fire ecology, herbivory, Pinus ponderosa, Sciurus aberti kaibabensis, Grand Canyon

This abstract is being presented at: 3:30 PM in session:
ANIMAL ECOLOGY