Identifying the Appropriate Felling Direction » Wedges

Segments - Loggers must know if trees with back lean can be successfully felled using wedges. To calculate the effectiveness of a wedge on any tree we use the concept of segments. A segment is a square with sides that are equal to the distance measured on the stump of the tree, from the front of the hinge, to the back of the tree. This distance, measured in feet, forms the sides of the square for a segment in that tree. To calculate the total number of segments, divide the total height of the tree by the dimension of one segment. For example, a tree with a base of 1 foot that is 70 feet tall has 70 segments (70' divided by 1')

We know that lifting the bottom of a segment one inch moves the top of that same segment one inch over. Therefore, a tree with 70 segments will move 70 inches with one inch of lift at the stump.

Trees of the same height with narrower diameters will have more segments and therefore, can be wedged further that a larger diameter tree of the same height. For example, a tree with a 6 inch base that is 70 feet tall would have 140 segments (70' divided by 1/2') and a tree that is 1 1/2 feet in diameter and 70 feet tall would have 46 segments (70' divided by 1.5').

Trees Averaging 70' Tall
Tree Diameter   Approximate back lean that can be handled using a felling wedge
         
10"   63" or 5.25'
12"   52" or 4.33'
14"   45"  or 3.75'
16"   39" or 3.33'
18"   35" or 3'
20"   20" or 2.5'
Trees Averaging 50' Tall
Tree Diameter        
         
10"   45" or 3.75'
12"   36" or 3'
14"   32" or 2.66'
16"   28" or 2.5'
18"   25" or 2'
20"   22" or 1.75'

Rule of Thumb:

A simple precut rule-of-thumb method is to divide the height of the tree by the diameter breast high (DBH). For example, one foot DBH with a height of 70 feet has 70 segments.

Some lifting capacity of the felling wedge is lost because the wedge must first fill the thickness of the saw kerf before it can begin to lift the tree. The following chart takes this loss into account. Notice that smaller diameter trees can be wedged farther than larger diameter trees of the same height.

Lean Diagram

Turning the wedge sideways and moving it closer to the hinge will make the base of the tree smaller by moving the lifting point closer to the hinge. Therefore, it is easy to increase the number of segments in a tree. However, this also makes it harder to drive the wedge as there is more weight on it. Heavy trees may make it difficult to drive the wedge. Be careful not to place the wedge too close to the hinge as this may cause the hinge to lift and break. Please refer to the diagram below for further explanation.

Wedge Diagram

With this knowledge, a logger can make an estimation if a tree can be wedged over and will know that placing a wedge closer to the hinge will provide more lift.