Rating Winter Crown Density of Deciduous Trees: A Photographic Procedure

Abstract

A study was undertaken to develop inexpensive yet accurate procedures for rating trees in terms of winter crown density, which correlates closely with amount of blocked solar radiation. Such procedures provide a basis for identifying better trees for energy-conserving planting. Leafless crowns of 69 trees of three species were photographed. The proportion of each crown image consisting of tree parts was then determined by dot-grid procedures. Crown density was least for the Kentucky coffeetree (Gymnocladus dioica), greatest for Modesto ash trees (Fraxinus velutina ‘Modesto’), and intermediate for London plane trees (Platanus x acerifolia). Crown density increased with tree size, and the pattern of this increase differed among species. The azimuth at which trees were photographed did not affect density estimates. The elevation angle at which photos were taken did affect density estimates, but regression procedures permit estimates based on a convenient elevation angle to be adjusted to correspond with estimates based on photos taken at the elevation best expressing the sun's average angle above the horizon during the dates and hours of interest. Photographic and dot-count procedures are rapid, require no specialized equipment, and are well suited to ranking species and cultivars by the density of their winter crowns.