ForestElementsR (version 2.0.1)

d_q: Quadratic Mean Diameter

Description

Function for calculating the quadratic mean of a vector. The typical application in forestry is to calculate the quadratic mean diameter.

Usage

d_q(d, n_rep = 1)

Value

the quadratic mean of d

Arguments

d

vector of (stem diameter at breast height) values to calculate the quadratic mean of

n_rep

vector of representation numbers (typically the number of trees per ha corresponding to the diameter at the same position), will be used as individual weights for each diameter. If n_rep has length 1, it will be recycled to the length of d. Otherwise, if the length of n_rep does not correspond to the length of d, the function will terminate with an error.

See Also

Other stand diameters: d_100(), d_dom_weise()

Examples

# Evaluate a sample of equally weighted tree diameters
d_cm <- c(12, 13, 25, 27, 28, 26, 26.1, 32, 35, 31, 42)
d_q(d_cm) # quadratic mean diameter
mean(d_cm) # the arithmetic mean is not the same!

# Assume, the same sample comes from an angle count sample, where each
# tree represents a basal area of 4 m²/ha
n_rep_ha <- 4 / ((d_cm / 100)^2 * pi / 4) # representation number of each tree
d_q(d_cm, n_rep_ha)


# Typical application to a set of single tree data grouped by survey
# time and species
library(dplyr)
oldopt <- options(fe_spec_lang = "eng") # display colloquial species names
# extract the tree data to allow insights into the mechanics
trees <- mm_forest_1_fe_stand_spatial$trees |> filter(!removal)
trees |>
  group_by(species_id, time_yr) |>
  summarise(
    n_ha   = round(sum(n_rep_ha)),
    d_q_cm = d_q(dbh_cm, n_rep_ha)
  ) |>
  print(n = Inf)
options(oldopt) # set species name display to previous value