Knobcone pines (Pinus attenuata) are rather short-lived with a life-span averaging about 60 years. A small tree, this native species varies in form and size depending whether it grows in an exposed or sheltered area. In extremely poor sites it can be shrubby. Shade intolerant, knobcone pines can be found in widely scattered localities below 6,200 feet in the coast ranges between Western Oregon and Baja California. Their habitat is shallow, rocky, infertile soils, especially serpentine soils.
The slender trunk is generally forked in older trees creating a sparse crown with an irregular, open, branching pattern. Mature knobcone pine bark is a dull greyish-brown and may be tinged with purple. Shallow furrows are separated by large, loose, scaly ridges.
Knobcone pine needles (leaves) are a pale green and occur in bundles of three with a persistent sheath. The needles often have a slight twist. They remain on the tree about four or five years.
The pollen cones are conical, orange-brown and occur in tight clusters. Seed cones are asymmetrical, elongated and recurved. Buff in color, knobcone pine seed cones are set in whorls of 3 to 5 (or more) along the trunk and main branches. Persistent, the seed cones may remain on the tree for 15 to 25 years or more. The cones stay on the tree so long they are often embedded within the growing wood of the trunk – “the tree that swallows itself”. The scales have prickles and are massive on the upper side, particularly near the base where they look “knobby”. The scales are thick and flat elsewhere on the cone. Knobcone pines mature at an early age with small trees barely eight feet tall bearing seed cones.
Knobcone pine seed cones are serotinous, that is, they require fire to crack the resin seal and allow the scales to open. (Occasionally the cones will open during successive days of extreme heat in the summer.) The blackish seeds have wings, a high rate of germination and remain viable no matter how old they are, readily sprouting after a forest fire. Because of this fire requirement for seed release, knobcone pines are considered “fire forest trees”. (I should do a post on fire forest trees soon.)
Knobcone pine wood is light, soft, coarse-grained and brittle with no commercial value except as firewood.
Another common name for P attenuata is narrowcone pine. Pinus tuberculata is a synonym.
These knobcone pines were photographed along the Babyfoot Lake Trail in Rogue River -Siskiyou National Forest, Josephine County OR. The site, as seen in the pictures, is recovering from the massive Biscuit Fire in 2002.