If you were to draw a square around each tree, the sides of each square would also be 5 meters (see diagram). The area occupied by each tree is therefore 5 m X 5 m (or 52) sq. m = 25 sq. m. This gives you the number of square meters per tree. We want to calculate density, which is the number of trees per square meter. Density is therefore the inverse. Density = 1/(distance between trees)2.
In nature, organisms are seldom distributed in such a regular pattern. The distance between each tree in a forest, for example varies. The formula for density calculations given above can still be used if we use the average (mean) distance between each tree.
To calculate the density of all species, it is necessary to sum the point-to-organism distances for all species and calculate a mean. The square of this number is equal to the mean area occupied per organism.
Mean area per organism = mean point-to-plant distance2
Density is equal to the inverse of the area per organism as shown below.