How Does the Bristlecone Pine Disperse?

Bristlecone Pine Characteristics

• Named for the claw-like bristle tips on each scale of the immature pine cone, the tree has a needle arrangement on the branches that resembles a foxtail or a bottle brush. Cones are purple when young, turning brown in two years at maturity. Female cones produce winged seeds built for wind dispersal. Old trees have great character, with fissured trunks and irregularly shaped branches. Trees put on a thin new layer of light-colored growth just beneath the bark each year, followed by a period of darker-colored slow growth in winter. The growth cycles create annual tree rings, useful in dating the age of a tree. Some bristlecone pines in California's White Mountains are over 4,000 years old and still growing.

Kinds of Bristlecones

• The most famous of the bristlecone pines is the Great Basin bristlecone pine (Pinus longaeva), because of the importance of its tree ring data in recalibrating archaeological radiocarbon dating. Thanks to the measurement of bristlecone pine wood through its long history of 10,000 years of growing in the same areas, archaeologists could reinterpret readings from around the world. Other bristlecone pines are the Rocky Mountain bristlecone (Pinus aristata) and the Sierra foxtail pine (Pinus balfouriana). Bristlecone pines grow in U.S. Department of Agriculture plant hardiness zones 4 through 8, depending on the species. Seed dispersion depends on the elevation, with birds aiding in dispersion at higher elevations.

Seed Production

• Bristlecone pines have separate male and female cones on the same tree. The pollen produced by the male cones is carried by the wind to the ovules of the female cones, which become pollinated and set seeds. The tree continue to produce seeds over its lifetime, although seed production declines with age. The seeds are pale brown with red mottling and are about 1/3 inch long with a wing almost 1/2 inch wide. Bristlecone pine grows at lower elevations as well, but it grows faster, has a single straight trunk, and grows larger. Low-elevation bristlecone pines have seeds dispersed primarily by the wind carrying the winged seeds to a new location.

Clark's Nutcracker

• Ronald Lanner from Utah State University studied the life cycle of Great Basin bristlecone pines in the White Mountains in 1988, discovering that the main seed dispersal was due to the activity of Clark's nutcracker, a gray-and-black bird related to crows that inhabits western mountains. (see Reference 8) The birds extract the seeds from opened female cones, tuck them into a pocket under their tongue and cache one to three seeds at a time in holes dug with their beaks for later retrieval. At high elevations, bristlecone pines grow in clumps of several individual trees because of nutcracker caching, compared to the single-trunked wind-dispersed trees of lower elevations.