Abstract: Digital photos can be used conveniently for measuring the width of tree ring, but geometric rectification is required because of image distortion. This paper introduced a new and easy-to-use method for the correction, which is called segmental rectification. By dividing a section into segments with certain intervals, the pixel resolution is determined for each segment, which is then used to calculate the tree ring width in corresponding segment. The basic process is: 1) divide the section into segments with 1 cm or smaller intervals, 2) calculate the resolution after counting the number of pixels in each segment, and 3) measure the tree ring width in pixels before converting to length unit based on segment-specific resolution. With common image processing software, the approach is simple and practical, and high accuracy can be secured.

Key words: Moss, Shanghai, Niche breadth, Niche overlaps