Intense sun, extremely arid conditions, high winds and winter exposure wear away at the exposed bark of a bristlecone pine, leaving striations along its exterior.  A small amount of living bark is all that is necessary to sustain a mature bristlecone pine tree into extreme old age.  Patriarch Grove, Ancient Bristlecone Pine Forest. White Mountains, Inyo National Forest, California, USA, Pinus longaeva, natural history stock photograph, photo id 17483