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Sharma (2021) site index model for jack pine and black spruce in mixed natural stands

Source: R/si_sharma2021.R
si_sharma2021.Rd

Implementation of the fixed-effects non-climate McDill-Amateis dynamic height equation reported by Sharma (2021) for jack pine (PINU.BAN) and black spruce (PICE.MAR) growing in natural-origin mixed stands in Ontario.

Usage

si_sharma2021(
  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 natural-origin mixed stands.

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 source scale directly.

Base-age note: site index is defined at 50 years breast-height age. The underlying dynamic equation is written in paired-age form, so this implementation allows any positive `base_age`; the default remains `50` to match the source definition.

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 8) with stand-level random effects omitted.

References

Sharma, M. (2021). Climate effects on jack pine and black spruce productivity in natural origin mixed stands and site index conversion equations. Trees, Forests and People, 5, 100089. https://doi.org/10.1016/j.tfp.2021.100089

Examples

# Predict site index from age + height
si_sharma2021(
  age = c(60, 80),
  height = c(16, 18),
  species = c("PINU.BAN", "PICE.MAR")
)
#> # A tibble: 2 × 1
#>      si
#>   <dbl>
#> 1  13.3
#> 2  12.6

# Predict height from age + site index
si_sharma2021(
  age = c(60, 80),
  si = c(14, 13),
  species = c("PINU.BAN", "PICE.MAR")
)
#> # A tibble: 2 × 1
#>   height
#>    <dbl>
#> 1   16.7
#> 2   18.4