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Prégent et al. (2010) site index model for white spruce plantations

Source: R/si_pregent2010.R
si_pregent2010.Rd

Implementation of the Chapman-Richards difference equation reported by Prégent et al. (2010) for white spruce plantations (PICE.GLA) in Quebec.

Usage

si_pregent2010(age, height = NULL, si = NULL, base_age = 25)

Arguments

age

Numeric vector. Plantation age (years), with `age > 0`. A warning is emitted when `age > 60`, because that exceeds the published range.

height

Optional numeric vector. Dominant height (m). If provided, `si` is predicted.

si

Optional numeric vector. Site index (m) at `base_age` years. If provided, `height` is predicted.

base_age

Positive numeric scalar. Site-index base age (years since planting). Defaults to `25`.

Value

A tibble with columns:

height

Predicted dominant height (m), returned when input `si` is provided.

si

Predicted site index (m), returned when input `height` is provided.

Details

Species coverage: PICE.GLA.

Geographic use: Quebec white spruce plantations.

Age definition note: `age` is plantation age (years since planting), not breast-height age.

Height definition note: the model uses dominant height (m) based on the mean height of the 100 tallest trees per hectare.

Base-age note: site index is dominant height at plantation age 25 years by default, matching the source study. The underlying difference equation is base-age invariant, so other positive `base_age` values can also be used. The package article plots this model with `base_age = 50` for visual comparison with other curves.

Domain note: the source tables and curves are presented for plantation ages up to 60 years. This implementation warns when `age > 60` and returns extrapolated values.

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 follow the source model scale directly.

References

Prégent, G., Picher, G., & Auger, I. (2010). Tarif de cubage, tables de rendement et modèles de croissance pour les plantations d'épinette blanche au Québec. Mémoire de recherche forestière no 160. Gouvernement du Québec, ministère des Ressources naturelles et de la Faune.

Examples

si_pregent2010(
  age = c(20, 30, 40),
  height = c(6, 10, 14)
)
#> # A tibble: 3 × 1
#>      si
#>   <dbl>
#> 1  7.87
#> 2  8.12
#> 3  8.42

si_pregent2010(
  age = c(20, 30, 40),
  si = c(8, 10, 12)
)
#> # A tibble: 3 × 1
#>   height
#>    <dbl>
#> 1   6.11
#> 2  12.2 
#> 3  18.7