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Prégent et al. (2016) site index model for Norway spruce plantations

Source: R/si_pregent2016.R
si_pregent2016.Rd

Implementation of the Schumacher difference equation reported by Prégent et al. (2016) for Norway spruce plantations (PICE.ABI) in Quebec.

Usage

si_pregent2016(age, height = NULL, si = NULL, base_age = 25)

Arguments

age

Numeric vector. Plantation age (years), with `age > 0`. A warning is emitted when `age > 70`, 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.ABI.

Geographic use: Quebec Norway 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 70 years. This implementation warns when `age > 70` 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., Auger, I., & others. (2016). Tarif de cubage, tables de rendement et modèles de croissance pour les plantations d'épinette de Norvège au Québec. Mémoire de recherche forestière no 176. Gouvernement du Québec.

Examples

si_pregent2016(
  age = c(20, 30, 40),
  height = c(6, 10, 14)
)
#> # A tibble: 3 × 1
#>      si
#>   <dbl>
#> 1  8.10
#> 2  7.98
#> 3  8.14

si_pregent2016(
  age = c(20, 30, 40),
  si = c(8, 10, 12)
)
#> # A tibble: 3 × 1
#>   height
#>    <dbl>
#> 1   5.92
#> 2  12.3 
#> 3  19.2