Volume of wood in hardwood trees

Use this diagram to illustrate the estimate of the 3rd regn model parameter — the error standard deviation:

Drag the line to make the residual sum of squares small.

Click Least squares to dispay the best estimate of σ.

The value of a hardwood tree depends on the volume of timber that can be harvested from it. However the volume of timber cannot be measured easily before a tree is cut down, so forestry managers must estimate it from other measurements that are easier to make. A common measurement is the diameter of the tree at breast height, 4.5 feet above ground level.

Data were obtained from 31 black cherry trees that were harvested in the Allegheny National Forest in Pennsylvania. The volume of timber (cubic feet) is plotted against the area at breast height (square inches, determined from the diameter).