Pinus attenuata

Knobcone Pine

Pinaceae

The Basics

Taxonomy: Kingdom - Plantae (plants). Subkingdom - Tracheobionta (vascular plants). Superdivision - Spermatophyta (seed plants). Division - Coniferophyta (conifers). Class - Pinopsida. Order - Pinales. Family - Pinaceae (pine). Genus -Pinus L. Species - Pinus attenuata Lemmon

Ecology: The knobcone pine community occupies a transitional position between chaparral and woodland and higher elevation forests. Because of its patchy distribution, it is usually surrounded by other communities. At lower elevations, it is most often associated with chamise (Adenostoma fasciculatum)-manzanita (Arctostaphylos spp.) communities and various oak (Quercus spp.) woodlands. At higher elevations, it is associated with a variety of coniferous communities.

Identification

General: Knobcone pine is a rapidly growing, native tree from 20 to 40 feet (6-12 m) tall and 13.5 to 23 inches (34-58 cm) in d.b.h. [13,41]. The crown is dense and broad when young, becoming open when mature. Trees typically have multiple trunks with thin bark [36,42].

Roots: Excavation of knobcone pine roots in the Santa Ana Mountains showed that vertical roots grew to bedrock in the shallow soil. Average root depth was 10.4 inches (26.2 cm). Roots in less restrictive sites are reported as "wide and deep".

Cones: Female cones in groups of four or five, all firmly attached to stout branches in a tight whorl. The asymmetrical cones are arched in configuration, as are the individual ovuliferous scales. Cones remain closed and attached to the tree for life. The enclosed seeds are small and light, with thin seed coats and long seed wings.

Threats

Fire effects: Crown fire kills knobcone pine of all size classes and vaporizes the resin sealing their cones. The effect of surface fires on mature trees is undocumented. The thin bark, however, probably provides little protection from all but low-severity surface fire. Saplings are killed by surface fire. Fire is not a threat to young trees, however, since the preceding stand-replacing fire has removed most of the fuel load. Cones are extremely fire resistant and are seldom consumed by fire.

Reproduction

Regeneration Process: Knobcone pine reproduction is controlled exclusively by fire; trees occur in even-aged stands dating back to the last fire. Cones are sealed with a hard resin that requires high temperatures (average: 397 degrees Fahrenheit [203 deg C]) to liquefy, boil, and vaporize. Cone scales open gradually following heating. The first seeds fall within 1 to 12 hours after fire, when the ground has cooled.

Vegetative Production: Trees begin seed production between 10 and 12 years of age. Average production of trees over 20 years old is 176 cones per tree. Limited tests show seed viability does not decline with age. Seeds enclosed in cones for 27 and 60 years have proved viable. Following release, seeds require cold stratification for 60 days. Germinative capacity of seeds from mechanically opened cones has varied from 57 to 91 percent.

Species Distribution

Citation

Jepson Flora Project
Jepson FLora Project: Jepson Interchange for California Floristics. 2017. University of California.

USDA Plants Database
USDA, NRCS. 2017. The PLANTS Database. National Plant Data Team, Greensboro, NC 27401-4901 USA.
Distribution Map photo credit

USFS Plant Database
Habeck, R. J. 1992. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory.

Flora of North America
Flora of North America Editorial Committee, eds. 1993+. Flora of North America North of Mexico. 19+ vols. New York and Oxford.

Lady Bird Johnson Wildflower Center
Lady Bird Johnson Wildflower Center. 2017. Pinus attenuata [Online]. University of Texas at Austin.

Cal photos
Photo credit: 1995 Saint Mary's College of California, 2007 Dr. Mark S. Brunell.