Pines

The bristlecone pine (Pinus aristata) is an important species to scientists because it lives so long, and has tree rings can provide important clues about the climate of previous eras. This species grows in the arid mountainous regions of California, Nevada, Utah, and Colorado at an elevation of about 9,840 ft (3,000 m). Bristlecone pine grows very slowly, but can live for several thousand years. The oldest known specimen is nearly 5,000 years old. Bristle-cone pines have been intensively studied by dendrochronologists, scientists who examine and interpret tree rings.

The tree rings of bristlecone pines and other trees appear as concentric rings, and are visible in a cross-section of a trunk or in a core sample. A new growth ring typically forms each year, as the tree trunk expands. Growth rings are relatively wide in years favorable for growth, and narrow in unfavorable years. Bristlecone pines grow so slowly that there can be more than a hundred rings in the space of only a few centimeters, so their tree rings must be examined with a microscope. The width and other features of these growth rings provide valuable clues to archaeologists about the prevailing local climate during the period when ancient native American cultures inhabited the western United States.