Flowering and Fruiting
Pinyon is considered monoecious, the male and female strobili being borne on the same tree (67). However, dioecy has been observed under certain environmental conditions associated with moisture stress and insect damage (23,74). Although ovulate cones require most of three growing seasons to mature, the stages of growth vary with elevation, weather, and individual trees. In general, winter buds containing the strobili primordia begin to form in August, and by October of the first year are fully formed. Bud growth the following year is resumed near the first of May for staminate cones, and about mid-May for ovulate cones. By mid-June, staminate cones are mature, and ovulate cones become visible and receptive to pollen. Pollination is completed by the end of June when cone scales close, and a period of rapid growth of cones and seed commences, terminating at the end of August. During the third year, conelets start growth about the first of May, and fertilization occurs in early July. Shortly thereafter, cones and seeds reach full size, and seed coats darken and harden. Seeds mature early in September, and cone opening begins during mid-month and extends for about a 50-day period.
Burns, Russell M., and Barbara H. Honkala, technical coordinators. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods. Agriculture Handbook 654 (Supersedes Agriculture Handbook 271,Silvics of Forest Trees of the United States, 1965). U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 pp.