Sharma and Parton (2018) site index model for white spruce plantations — si_sharmaparton2018a • CanadaForestAllometry

Implementation of the non-climate-sensitive McDill-Amateis dynamic height equation reported by Sharma and Parton (2018) for plantation-grown white spruce (PICE.GLA) in Ontario.

Usage

si_sharmaparton2018a(
  age,
  height = NULL,
  si = NULL,
  base_age = 50,
  total_height = TRUE
)

Arguments

age: Numeric vector. Breast-height age (years), with `age > 0`.
height: Optional numeric vector. Stand height (m). If `total_height = TRUE` (default), this is total height; otherwise it is height above breast height. If provided, `si` is predicted.
si: Optional numeric vector. Site index (m above breast height) 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). Defaults to `50`.
total_height: Logical scalar. If `TRUE` (default), interpret input `height` as total height and return predicted `height` as total height. If `FALSE`, use the source-paper scale of height above breast height.

Value

A tibble with columns:

height: Predicted stand height (m), returned when input `si` is provided. This is total height when `total_height = TRUE`, otherwise height above breast height.
si: Predicted site index (m above breast height), returned when input `height` is provided.

Details

Species coverage: PICE.GLA.

Geographic use: Ontario white spruce plantations.

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

Height definition note: this implementation assumes the source model uses heights above breast height (m), not total height. For consistency with other site-index functions in this package, it defaults to using total height in the public API (`total_height = TRUE`) and converts internally by subtracting or adding 1.3 m as needed. Set `total_height = FALSE` to work on the source scale directly.

Base-age note: the underlying dynamic equation is written in a base-age invariant paired-age form. For consistency with other site-index functions in this package, this implementation defaults to a base age of 50 years breast-height age, while still allowing users to supply any positive `base_age`.

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

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

Inputs and outputs are metric and match the source model scale.

Both directions are explicit closed forms derived from the same dynamic equation.

References

Sharma, M., & Parton, J. (2018). Analyzing and modelling effects of climate on site productivity of white spruce plantations. The Forestry Chronicle, 94, 173-182.

Examples

# Predict site index from age + height
si_sharmaparton2018a(
  age = c(20, 30, 40),
  height = c(6, 9, 12)
)
#> # A tibble: 3 × 1
#>      si
#>   <dbl>
#> 1  12.2
#> 2  12.7
#> 3  13.2

# Predict height from age + site index
si_sharmaparton2018a(
  age = c(20, 30, 40),
  si = c(8, 10, 12)
)
#> # A tibble: 3 × 1
#>   height
#>    <dbl>
#> 1   4.18
#> 2   7.17
#> 3  11.0