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Sharma et al. (2015) site index model for plantation-grown jack pine and black spruce

Source: R/si_sharma2015.R
si_sharma2015.Rd

Implementation of the non-climate-sensitive McDill-Amateis dynamic height equation reported by Sharma et al. (2015) for plantation-grown jack pine (PINU.BAN) and black spruce (PICE.MAR) in northern Ontario.

Usage

si_sharma2015(
  age,
  height = NULL,
  si = NULL,
  species,
  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.

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`.

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.BAN, PICE.MAR.

Geographic use: northern Ontario 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 source paper defines site index at a base age of 25 years breast-height age. The equation itself is a dynamic McDill-Amateis form written in terms of paired ages and heights, so this implementation treats `base_age` as user-configurable. For consistency with other site-index functions in this package, the default is 50 years breast-height age.

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 the fixed-effects no-climate form (Equation 1) that the paper recommends when climate variables are unavailable.

References

Sharma, M., Subedi, N., Ter-Mikaelian, M., & Parton, J. (2015). Modeling climatic effects on stand height/site index of plantation-grown jack pine and black spruce trees. Forest Science, 61(1), 25-34. https://doi.org/10.5849/forsci.13-190

Examples

# Predict site index from age + total height
si_sharma2015(
  age = c(20, 30),
  height = c(8, 12),
  species = c("PINU.BAN", "PICE.MAR")
)
#> # A tibble: 2 × 1
#>      si
#>   <dbl>
#> 1  14.3
#> 2  15.7

# Predict total height from age + site index
si_sharma2015(
  age = c(20, 30),
  si = c(9, 10),
  species = c("PINU.BAN", "PICE.MAR")
)
#> # A tibble: 2 × 1
#>   height
#>    <dbl>
#> 1   4.94
#> 2   7.58