Sharma and Parton (2019) site index model for white pine plantations — si

Implementation of the non-climate-sensitive McDill-Amateis dynamic height equation fitted by Sharma and Parton (2019) for plantation-grown eastern white pine (PINU.STR) in Ontario.

Usage

si_sharmaparton2019(
  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: PINU.STR.

Geographic use: Ontario white pine plantations.

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

Height definition note: the source model uses heights above breast height (m), not total height. For consistency with other site-index functions in this package, this implementation 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 original source scale directly.

Base-age note: the underlying dynamic equation is base-age invariant. The source paper illustrates site-index curves using a base age of 25 years breast-height age. For consistency with other site-index functions in this package, this implementation instead defaults to a base age of 50 years breast-height age. 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`.

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. (2019). Modelling the effects of climate on site productivity of white pine plantations. Canadian Journal of Forest Research, 49, 1289-1297. https://doi.org/10.1139/cjfr-2019-0165

Examples

# Predict site index from age + height
si_sharmaparton2019(
  age = c(20, 25, 40),
  height = c(7, 9, 15)
)
#> # A tibble: 3 × 1
#>      si
#>   <dbl>
#> 1  13.3
#> 2  14.4
#> 3  16.6

# Predict height from age + site index (default base age 50)
si_sharmaparton2019(
  age = c(20, 25, 40),
  si = c(8, 10, 12)
)
#> # A tibble: 3 × 1
#>   height
#>    <dbl>
#> 1   4.58
#> 2   6.49
#> 3  11.1 

# Predict height using an alternative base age
si_sharmaparton2019(
  age = 35,
  si = 12,
  base_age = 25
)
#> # A tibble: 1 × 1
#>   height
#>    <dbl>
#> 1   17.4