kozak_vol {timbeR}

Estimate the total or partial volume of the tree, based on a fitted Kozak (2004) taper function.

Description

Estimates the total or partial volume of the tree from the diameter at breast height, total height, initial section height, final section height and coefficients of the Kozak (2004) taper equation.

Usage

kozak_vol(dbh, h, coef, p, hi, h0)

Arguments

dbh

tree diameter at breast height, in centimeters.

h

total tree height, in meters.

coef

numerical vector containing eight coefficients of the Kozak taper equation.

p

numerical value representing the first inflection point calculated in the segmented model of Max and Burkhart (1976).

hi

final height of the tree section whose volume will be calculated, in meters. Default is the total tree height (h).

h0

initial height of the tree section whose volume will be calculated, in meters. Default is 0 (ground height).

Details

the Kozak (2004) variable-form taper function is represented mathematically by the following expression

di ~ b0*(dbh^b1)(h^b2)((1-(hi/h)^(1/4))/(1-(p^(1/3))))^(b3*(hi/h)^4+b4*(1/exp(dbh/h))+b5*((1-(hi/h)^(1/4))/(1-(p^(1/3))))^0.1+b6*(1/dbh)+b7*(h^(1-(hi/h)^(1/3)))+b8*((1-(hi/h)^(1/4))/(1-(p^(1/3)))))

Value

a numeric value indicating the total or partial volume of the tree.

Examples

library(dplyr)
library(minpack.lm)
library(timbeR)

tree_scaling <- tree_scaling %>%
mutate(did = di/dbh,
       hih = hi/h)

kozak <- nlsLM(di ~ taper_kozak(dbh, h, hih, b0, b1, b2, b3, b4, b5, b6, b7, b8, p),
               start=list(b0=1.00,b1=.97,b2=.03,b3=.49,b4=-
                            0.87,b5=0.50,b6=3.88,b7=0.03,b8=-0.19, p = .1),
               data = tree_scaling,
               control = nls.lm.control(maxiter = 1000, maxfev = 2000)
)

coef_kozak <- coef(kozak)[-10]
p_kozak <- coef(kozak)[10]

h <- 20
dbh <- 25
di <- 5

kozak_vol(dbh, h, coef_kozak, p_kozak)

hi = 15
h0 = .2

kozak_vol(dbh, h, coef_kozak, p_kozak, hi, h0)