Enter the DBH and the PRF into the calculator to determine the limiting distance for the tree line.

## Limiting Distance Formula

The following equation is used to calculate the Limiting Distance.

LD = DBH * PRF

• Where LD is the limiting distance (ft)
• DBH is the diameter at breast height of the tree (in)
• PRF is the plot radius factor (ft/in)

## What is a Limiting Distance?

Definition:

Limiting distance is the maximum distance between two points which can be bridged by a line of trees. The limiting distance depends on the species and size of tree, the spacing between trees and the height of the tree crowns.

Limiting distance is measured from center to center of tree trunks. Limiting distance is used for planning silvicultural systems and to determine the number of trees needed to be planted per hectare. A simple formula can be used to estimate limiting distance when tree crowns are high above ground level.

The formula is: D = 0.8 x H / S

where D is the limiting distance (m) H is the average height of tree tops (m) S is the average canopy cover (%). This value can be estimated by taking measurements of the trunk diameter at breast height and using a table to convert these values into an estimate of average canopy cover (see below). The limiting distance formula assumes that all trees are planted at breast height and that there are no gaps between planted trees.

For practical purposes, actual limiting distances will usually be less than half this calculated value because some treetops will be below ground level and some gaps will exist between individual trees.

## How to Calculate Limiting Distance?

Example Problem:

The following example outlines the steps and information needed to calculate Limiting Distance.

First, determine the diameter of the tree at breast height. In this example, the diameter of the tree at breast height is 12.5 inches.

Next, determine the PRF. The PRF for this example, the PRF is 2.5inches/ft.

Finally, calculate the limiting distance using the formula above:

LD = DBH * PRF

LD = 12.5*2.5

LD = 31.25 ft