The crown displays the leaves to allow capture of radiant energy for photosynthesis. Thus, measurement of the tree crown is often made to assist in the quantification and understanding of the growth of the tree. The biomass of the crown and the quantity and quality of the branch material however is also of direct interest to ecological studies and research into the effects of trees on pollution. The crown also has great visual impact. This impact is important in urban forests because it will affect the perceived beauty of a tree.
Tree crowns are highly variable.
Their general shape varies from relatively dense conoids for young and healthy trees of an excurrent habit to wide open hemispherical shapes for older trees of a deliquescent habit. The parameters selected for measurement will depend on the selected tree and the reason for measurement. The width of a crown can be measured by projecting the edges of the crown to the ground and measuring the length along one axis from edge to edge through the crown centre. Unless the crown has a regular shape, the width measured will depend on the axis selected for measurement. If the crown is highly irregular, the projected points from a number of crown edges should be plotted on scaled graph paper.