Estimating ages of giant sequoias

When a tree's bole diameter exceeds 2 m, it is often impractical or impossible to determine its age directly and nondestructively, such as by counting or cross-dating rings on increment cores that sample the entire bole radius. We used ring measurements from complete stump cross sections of giant sequoia (Sequoiadendrongiganteum (Lindley) Buchholz) to develop a new method for estimating ages, which models age as a power function of bole radius. The value of the function's exponent varies from tree to tree and is most strongly related to the reciprocal of a tree's growth rate, as determined from increment cores that sample only the outer portion of the bole. For sequoia stumps up to 3200 years old and 6.5 m in diameter, our age estimates were within 10% of actual age 62% of the time, and within 25% of actual age 98% of the time, even when increment cores had sampled less than 20% of bole radius. This is a substantial improvement over previously published methods that estimate tree age from diameter alone, by assuming that basal area increment is constant through time, or by linear extrapolation of growth rates from the innermost portion of an increment core. The latter three methods are shown to be special cases of our more general approach.