The original data, also supplied in the package, are measures of stem diameter and height at various locations on the bole of 39 sweetgum trees from Texas, USA.
data(sweetgum)A data frame with 39 tree-level observations on the following 8 variables.
plotIdentifies the plot in which the tree was felled.
treeA factor that identifies the tree.
dbh.inThe tree diameter (in.) at 1.37 m (4'6'')
stump.ht.ftThe height of the stump after felling (ft).
height.ftThe height of the tree (ft).
height.mThe height of the tree (m).
dbh.cmThe tree diameter (cm.) at 1.37 m (4'6'')
vol.m3The estimated biological volume of the stem (cubic meters).
The height measure is of the standing tree, so it includes the stump height. The volume was computed by fitting a spline to the height and diameter measures, and integrating the solid that corresponds to the profile of the spline. See Section 2.4.2 of Robinson and Hamann (2010) for more details.
Robinson, A.P., and J.D. Hamann. 2010. Forest Analytics with R: an Introduction. Springer.