Estimating Pinyon Cone Production in New Mexico and Western Oklahoma

Abstract

Seeds of pinyon (Pinus edulis) provide food for several birds, mammals (including humans), and some insects that depend entirely upon them (Little 1943, Frischknecht 1975, Vander Wall and Balda 1977). Because seed production by pinyon is important for the fauna associated with pinyon communities, quantitative predictions of annual production, average production, and yearly variation of pinyon seed crops are valuable to natural-resource managers. The variability of cone production results in population changes among dependent animals, which in turn affect the plants themselves. For example, the pifion jay (Gymnorhinus cyanocephalus) normally breeds in spring, but if immature pinyon cones are abundant in late summer, autumnal breeding also occurs (Ligon 1974). If pinyons produce 2 large cone crops consecutively, the latter crop is devastated by host-specific cone insects (Forcella 1978, 1980). Erratic cone crops appear to provide evolutionary advantage for the species. I present a simple and efficient method to quantitatively evaluate past cone crops estimate the immediately forthcoming cone crop(s), and predict average crops (10-year mean).