Trees can gain in height with or without thickening the trunk or stem. For this reason, standard measures of diameter or circumference of the main stem of trees have been developed so that these can be added to enhance detailed plant specifications.
Root Collar Diameter
The Root Collar Diameter is defined as ‘‘the diameter of the main stem measured at or within a specified distance from the root collar.’’ The root collar is between the base of the aerial part of the plant and the top of the root system. The collar is generally a lighter colour than the stem.
The Root Collar Diameter may be specified for Seedlings (especially Cell grown trees), and cuttings and transplants, particularly where these are used as rootstocks.
For Cell grown trees, minimum Root Collar Diameters vary from 4 to 8 mm for Broadleaf trees and 4 to 8 mm for Conifers, depending on overall height and size of cell.
For Seedlings, Cuttings and Transplants, Root Collar Diameters will be minimum of 3mm and be graded in one or two bands, increasing with height and must be typical of the species e.g. 3/4, 4/6, 6/8, 8/10 or 10/12.
The girth of a tree is ‘‘the circumference of the stem measured at 1 metre above ground level.’’ Usually this measure applies to standard trees, but girth grades can be given for large feathered trees.
|Girth in cm||Form||Tag Colour|
For trees above 50 cm girth, the measure increases in 10 cm steps, 50-60, 60-70, etc.
The colours indicate the European colour system for marking trees.
Girth for Feathered trees
When the girth size is greater than 6 cm it should be specified as for clear stem standard trees, e.g. 6-8, 10-12, etc.
Multi Stemmed trees
For these trees, the number of stems required must be specified and the height of the tree.
Due to the many stems of bushy trees, these trees should only be specified by height.