Unified, vectorized implementation of the Carmean and Hahn (1981) site-index equations for Lake States balsam fir and white spruce.
Arguments
- age
Numeric vector. Total 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 total age). If provided, `height` is predicted.
- species
Character vector of species codes (e.g., `"ABIE.BAL"`).
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 2 species: ABIE.BAL, PICE.GLA.
Geographic use: this model was fit to revised Lake States harmonized curves and should be used with caution outside that domain.
Age definition note: `age` is total age (years), not breast-height age.
Base-age note: site index in this model is total height at 50 years total age.
Provide exactly one of `height` or `si`:
If `height` is provided, the function predicts `si`.
If `si` is provided, the function predicts `height`.
Inputs/outputs are metric; the original equations are in imperial units, so the function converts internally.
References
Carmean, W. H., & Hahn, J. T. (1981). Revised site index curves for balsam fir and white spruce in the Lake States. U.S. Department of Agriculture, Forest Service, North Central Forest Experiment Station.
Examples
# Predict site index from age + height
si_carmeanhahn1981(
age = c(30, 50, 70),
height = c(8, 15, 22),
species = c("ABIE.BAL", "ABIE.BAL", "PICE.GLA")
)
#> # A tibble: 3 × 1
#> si
#> <dbl>
#> 1 12.8
#> 2 15.0
#> 3 16.4
# Predict height from age + site index
si_carmeanhahn1981(
age = c(30, 50, 70),
si = c(12, 16, 20),
species = c("ABIE.BAL", "ABIE.BAL", "PICE.GLA")
)
#> # A tibble: 3 × 1
#> height
#> <dbl>
#> 1 7.46
#> 2 16.0
#> 3 26.0