Structure

forvol operates by interacting with the US Forest Service published volcfgrs_eqn_coefs.xlsx to calculate cubic foot tree volume.

To create a volume equation, two things are needed: an equation form that defines the relationship between the variables (dbh, ht, etc) and coefficients and the specific values of the coefficients themselves.

Rather than storing a large number of individual functions for each species within each geographic region, forvol "builds" the equations from your forest data dynamically by reading in equation forms and converting them into R functions. The coefficients are accessed from locally stored dataframes and combined with the equation form to produce the equation function. This allows for more flexibility and extensibility for the package.

forvol was built on the assumption that geographic region and species (along with aspects of the tree like diameter and height) are sufficient to define the default FIA equation to calculate tree volumes. As a result, the user must define the geographic region, and the data they provide must define the necessary variables to retrieve the correct equations.