Sharma and Reid (2018) site index model for natural jack pine and black spruce — si

Implementation of the fixed-effects McDill-Amateis dynamic stand-height model published by Sharma and Reid (2018) for natural-origin jack pine (PINU.BAN) and black spruce (PICE.MAR) stands in northern Ontario.

Usage

si_sharmareid2018(age, height = NULL, si = NULL, species, base_age = 50)

Arguments

age: Numeric vector. Breast-height age (years), with `age > 0`.
height: Optional numeric vector. Stand 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.
species: Character vector of species codes (e.g., `"PINU.BAN"` or `"PICE.MAR"`).
base_age: Positive numeric scalar. Site-index base age (years at breast height). Defaults to `50`.

Value

A tibble with columns:

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

Details

Species coverage: PINU.BAN, PICE.MAR.

Geographic use: northern Ontario natural stands.

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

Height definition note: the source model uses stand height (top height) in metres measured from breast height.

Base-age note: the source paper recommends breast-height age 50 years as the operational base age for both species in Ontario. The underlying dynamic equation is base-age invariant, so any positive `base_age` can be supplied.

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

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

This implementation uses Equation 1 from Sharma and Reid (2018), i.e. the fixed-effects form without random effects or autocorrelation. The paper recommends this form when stand-level repeated measurements are unavailable.

References

Sharma, M., & Reid, D. E. B. (2018). Stand height/site index equations for jack pine and black spruce trees grown in natural stands. Forest Science, 64(1), 33-40. https://doi.org/10.5849/FS-2016-133

Examples

# Predict site index from age + height
si_sharmareid2018(
  age = c(40, 60),
  height = c(12, 15),
  species = c("PINU.BAN", "PICE.MAR")
)
#> # A tibble: 2 × 1
#>      si
#>   <dbl>
#> 1  13.9
#> 2  13.3

# Predict height from age + site index
si_sharmareid2018(
  age = c(40, 60),
  si = c(16, 14),
  species = c("PINU.BAN", "PICE.MAR")
)
#> # A tibble: 2 × 1
#>   height
#>    <dbl>
#> 1   14.1
#> 2   15.7