A species-specific lookup table of estimated adjustment factors for crown width (CW) of saplings based on data from Bragg (2001).
Format
cw_sapling_adj
A data frame with 23 rows and 5 columns:
SPCDinteger, FIA tree species codeadj_1inchnumeric, CW adjustment factor at 1 in. DIA relative to 5 in. DIAadj_2inchnumeric, CW adjustment factor at 2 in. DIA relative to 5 in. DIAadj_3inchnumeric, CW adjustment factor at 3 in. DIA relative to 5 in. DIAadj_4inchnumeric, CW adjustment factor at 4 in. DIA relative to 5 in. DIA
Source
Toney et al. 2009. A stem-map model for predicting tree canopy cover of Forest Inventory and Analysis (FIA) plots. https://research.fs.usda.gov/treesearch/33381.
Details
FIA "saplings" are trees less than 5.0 in. (12.7 cm) diameter but greater than or equal to 1.0 in. (2.54 cm) diameter. In general, the data available to fit regression models predicting crown width (e.g., Bechtold 2003, 2004, see cw_coef) do not include trees with diameter less than 5.0 in. (12.7 cm). Extrapolating beyond the range of the model fitting data is undesirable, especially since a quadratic term is used in the regression equations for some species.
Adjustment is based on the proportion of crown width predicted for 5-in. (12.7 cm) diameter, at each 1-in. (2.54 cm) increment below that. Intermediate values are interpolated in the crown width prediction method. Mean adjustment factors are used if a species-specific adjustment is not available.
References
Bragg, D.C. 2001. A local basal area adjustment for crown width prediction. Northern Journal of Applied Forestry 18(1):22-28.
Examples
# Tsuga canadensis
cw_coef[cw_coef$SPCD == 261, ]
#> symbol SPCD common_name surrogate b0 b1 b2 reference
#> 154 TSCA 261 eastern hemlock <NA> 5.66 1.5 -0.02 Bechtold (2003)
cw_sapling_adj[cw_sapling_adj$SPCD == 261, ]
#> SPCD adj_1inch adj_2inch adj_3inch adj_4inch
#> 9 261 0.42 0.61 0.75 0.88