ForestElementsR (version 2.0.1)

v_gri: Calculate Tree Volumes With the GRI Volume Equations franz_gri_methods_1973ForestElementsR

Description

Merchantable standing tree volumes over bark calculated with the GRI volume equations developed by Friedrich Franz in 1971. These volume equations are standard in the German Federal State of Bavaria

Usage

v_gri(species_id, dbh_cm, height_m)

Value

A vector of merchantable standing tree wood volumes over bark in m³. "Merchantable" means only wood with a minimum diameter of 7 cm over bark is taken into account. Therefore, for small trees without any merchandable wood, the function will return 0 m³.

Arguments

species_id

Vector of species id's following the tum_wwk_short species coding. Ideally, these species_id's are provided as an fe_species_tum_wwk_short or an fe_species_bavrn_state_short object. If they are provided as another fe_species object, v_gri will make an attempt to convert them into fe_species_tum_wwk_short. The exception is the coding fe_species_bavrn_state which will be converted into fe_species_bavrn_state_short. If all conversion attempts fail, the function will terminate with an error. The species id's can also be provided as numeric values (double or integer) or character. These will be internally converted to fe_species_tum_wwk_short. If this fails (i.e. the user provided species codes are not defined in the tum_wwk_short coding), an error is thrown and the function terminates.

dbh_cm

Vector of tree dbh values in cm (dbh = stem diameter at breast height, i.e. 1.3 m)

height_m

Vector of tree height values in m

Details

The abbreviation GRI stands for the German word "Großrauminventur" (large area inventory). This forest inventory was conducted in 1971 by Friedrich Franz and his team of the Chair for Forest Growth and Yield Science at the Munich Ludwig-Maximilians-University franz_gri_methods_1973ForestElementsR. The inventory covered the whole federal state of Bavaria (~ 70,600 km²). The volume equations implemented in this function were calibrated with the data of several ten thousands of trees which were felled for that purpose during the inventory. The volume equations are available for exactly the species (groups) defined in the coding tum_wwk_short. If they are called with another species coding supported by the package ForestElementsR, v_gri will attempt to convert them accordingly.

References

Examples

# Find out the species codes that work with v_gri
fe_species_get_coding_table("tum_wwk_short") |>
  dplyr::select(-genus, -species_no) |>
  dplyr::distinct()

# Merchantable volume of a European beech with dbh = 30 cm,
# and height = 29 m
v_gri("5", 30, 29)
v_gri(5, 30, 29)
v_gri(as_fe_species_tum_wwk_short(5), 30, 29)

# Several trees (three species, three sizes)
species_id <- fe_species_tum_wwk_short(c(1, 1, 1, 3, 3, 3, 5, 5, 5))
dbh_cm <- c(12, 30, 55, 12, 30, 55, 12, 30, 55)
height_m <- c(14, 33, 39, 14, 33, 39, 14, 33, 39)
v_gri(species_id, dbh_cm, height_m)

# The same, but the species id's are now originally defined in the
# coding of the 2012 German national forest inventory
species_id <- fe_species_ger_nfi_2012(
  c(10, 10, 10, 20, 20, 20, 100, 100, 100)
)
v_gri(species_id, dbh_cm, height_m)