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Sharma (2022) site index model for black spruce and trembling aspen

Source: R/si_sharma2022.R
si_sharma2022.Rd

Implementation of the fixed-effects component of the no-climate McDill-Amateis mixed-effects stand height model published by Sharma (2022) for black spruce (PICE.MAR) and trembling aspen (POPU.TRE) growing in natural-origin mixed stands in Ontario.

Usage

si_sharma2022(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., `"PICE.MAR"` or `"POPU.TRE"`).

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: PICE.MAR, POPU.TRE.

Geographic use: Ontario natural-origin mixed stands.

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

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

Base-age note: the paper defines site index as stand height at 50 years breast-height age. The underlying dynamic equation is base-age invariant, so any positive `base_age` can be supplied; 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 component of Sharma's no-climate mixed-effects model (Equation 2), with stand-level random effects set to zero.

References

Sharma, M. (2022). Climate effects on black spruce and trembling aspen productivity in natural origin mixed stands. Forests, 13(3), 430. https://doi.org/10.3390/f13030430

Examples

# Predict site index from age + height
si_sharma2022(
  age = c(40, 60),
  height = c(13, 18),
  species = c("PICE.MAR", "POPU.TRE")
)
#> # A tibble: 2 × 1
#>      si
#>   <dbl>
#> 1  15.6
#> 2  16.2

# Predict height from age + site index
si_sharma2022(
  age = c(40, 60),
  si = c(15, 18),
  species = c("PICE.MAR", "POPU.TRE")
)
#> # A tibble: 2 × 1
#>   height
#>    <dbl>
#> 1   12.5
#> 2   19.8