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Scott and Voorhis (1986) site index model

Source: R/si_scottvoorhis1986.R
si_scottvoorhis1986.Rd

Unified, vectorized implementation of the Scott and Voorhis (1986) polymorphic site-index equation for northeastern species.

Usage

si_scottvoorhis1986(
  age,
  height = NULL,
  si = NULL,
  species,
  convert_to_total_age = FALSE
)

Arguments

age

Numeric vector. Breast-height age (years).

height

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

si

Optional numeric vector. Site index (m, base age 50 years at breast height). If provided, `height` is predicted.

species

Character vector of species codes (e.g., `"ABIE.BAL"`).

convert_to_total_age

Logical scalar. If `TRUE`, converts breast-height age to total age internally using the Scott and Voorhis age-to-breast-height relation (source-consistent behavior). If `FALSE` (default), uses `age` directly in the height equation.

Value

A tibble with columns:

height

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

si

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

Details

Model scope (species coverage): this implementation includes parameter sets for 19 species: ABIE.BAL, PICE.GLA, PICE.MAR, PICE.RUB, PINU.BAN, PINU.ECH, PINU.RES, PINU.STR, PINU.TAE, PINU.VIR, THUJ.OCC, ACER.SAC, BETU.ALL, BETU.PAP, FRAX.AME, LIQU.STY, LIRI.TUL, POPU.GRA, QUER.ALB.

Geographic use (Canada): the model is intended for northeastern forest conditions. In Canada, it is most defensible for species/populations in eastern regions (notably Atlantic Canada and adjacent central Canada where these species occur). Use caution outside that domain.

Age definition note: `age` is breast-height age (years). The model internally computes age-to-breast-height and uses total age in the height equation.

Base-age note: site index in this model is referenced to base age 50 years, but the fitted equations were not constrained to pass exactly through SI at base age for every species.

Provide exactly one of `height` or `si`:

  • If `height` is provided, the function predicts `si`.

  • If `si` is provided, the function predicts `height`.

In this model, total age is the sum of breast-height age and age-to-breast-height. Age-to-breast-height is itself a function of site index, so predicting `si` from `height` is implicit and solved numerically with `stats::uniroot()`.

Inputs/outputs are metric; the original equations are in imperial units, so the function converts internally.

References

Scott, C. T., & Voorhis, N. G. (1986). Northeastern forest survey site index equations and site productivity classes. Northern Journal of Applied Forestry, 3(4), 144-148.

Examples

# Predict site index from age + height
si_scottvoorhis1986(
  age = c(25, 40, 60),
  height = c(8, 14, 20),
  species = c("ABIE.BAL", "PICE.MAR", "PINU.BAN")
)
#> # A tibble: 3 × 1
#>      si
#>   <dbl>
#> 1  22.7
#> 2  16.9
#> 3  18.2

# Predict height from age + site index
si_scottvoorhis1986(
  age = c(25, 40, 60),
  si = c(11, 13, 16),
  species = c("ABIE.BAL", "PICE.MAR", "PINU.BAN"),
  convert_to_total_age = TRUE
)
#> # A tibble: 3 × 1
#>   height
#>    <dbl>
#> 1   8.85
#> 2  12.1 
#> 3  18.3