1. A method of operating a computer system to estimate the ages of trees shown in remotely sensed images, comprising: receiving a number of dated, remotely sensed images of an area of interest that include vegetation index (V.I.) values computed for a number of pixels; creating a composite image that stores the V.I. values computed for the pixel locations; analyzing the V.I. values stored in the composite image for the pixel locations for a V.I. value that correlates with a known age of a tree; and estimating the ages of the trees that correspond to the pixel locations based on the date of the remotely sensed image from which the V.I. value that correlates with the known age of a free was computed.