Parresol and Vissage (1998) site index model for eastern white pine — si_parresolvissage1998 • CanadaForestAllometry

Implementation of the base-age invariant polymorphic site-index equations published by Parresol and Vissage (1998) for eastern white pine (PINU.STR).

Usage

si_parresolvissage1998(age, height = NULL, si = NULL, base_age = 50)

Arguments

age: Numeric vector. Breast-height age (years), with `age >= 10`.
height: Optional numeric vector. Dominant/codominant height (m). If provided, `si` is predicted.
si: Optional numeric vector. Site index (m) at `base_age` years breast-height age. If provided, `height` is predicted.
base_age: Positive numeric scalar. Site-index base age (years at breast height), with `base_age >= 10`. Defaults to `50`.

Value

A tibble with columns:

height: Predicted dominant/codominant height (m), returned when input `si` is provided.
si: Predicted site index (m), returned when input `height` is provided.

Details

Species coverage: PINU.STR.

Geographic use (Canada): the source data were adopted for the southern U.S. forest survey. In Canada, use is most defensible for eastern white pine in eastern regions, and should be treated cautiously outside that domain.

Age definition note: `age` is breast-height age (years).

Base-age note: the source paper derives a base-age invariant system. This implementation accepts any positive `base_age`; the default is 50 years at breast height.

Domain note: although the algebraic form can be evaluated below age 10, the source data and paper discussion indicate reliable behavior for ages 10 years and greater. This implementation therefore enforces `age >= 10` and `base_age >= 10`.

Provide exactly one of `height` or `si`:

If `height` is provided, the function predicts `si`.
If `si` is provided, the function predicts `height`.

Inputs/outputs are metric; the original equations are in imperial units, so the function converts internally.

Both directions are explicit closed forms from the source publication.

References

Parresol, B. R., & Vissage, J. S. (1998). White pine site index for the southern forest survey. U.S. Department of Agriculture, Forest Service, Southern Research Station, Research Paper SRS-10.

Examples

# Predict site index from age + height
si_parresolvissage1998(
  age = c(25, 50, 70),
  height = c(10, 18, 24)
)
#> # A tibble: 3 × 1
#>      si
#>   <dbl>
#> 1  22.2
#> 2  18  
#> 3  18.5

# Predict height from age + site index at a base age of 50 years
si_parresolvissage1998(
  age = c(25, 50, 70),
  si = c(12, 18, 24)
)
#> # A tibble: 3 × 1
#>   height
#>    <dbl>
#> 1   4.81
#> 2  18   
#> 3  30.7 

# Predict height using an alternative base age
si_parresolvissage1998(
  age = 35,
  si = 30 / 3.28084,
  base_age = 25
)
#> # A tibble: 1 × 1
#>   height
#>    <dbl>
#> 1   14.3