Calculates Basal Area
silv_basal_area.RdCalculates Basal Area in square meters.
Arguments
- diameter
Numeric vector of diameters or diameter classes
- ntrees
Numeric vector with number of trees of the diameter class per hectare. If `ntrees = NULL`, the function will assume that each diameter corresponds to only one tree. Therefore, basal area will be calculated for each individual tree
- units
The units of the diameter (one of `cm`, `mm`, or `m`)
Details
The function uses the next formula:
\(G = \frac{\pi}{40000} \cdot D^2\)
where G is the basal area in \(m^2\), and D is the diameter in the `units` specified in the function. It is recommended to use the squared mean diameter calculated with [silv_sqrmean_diameter]
Examples
## calculate G for inventory data grouped by plot_id and species
library(dplyr)
#>
#> Attaching package: ‘dplyr’
#> The following objects are masked from ‘package:stats’:
#>
#> filter, lag
#> The following objects are masked from ‘package:base’:
#>
#> intersect, setdiff, setequal, union
inventory_samples |>
mutate(dclass = silv_diametric_class(diameter)) |>
summarise(
height = mean(height, na.rm = TRUE),
ntrees = n(),
.by = c(plot_id, species, dclass)
) |>
mutate(
ntrees_ha = silv_ntrees_ha(ntrees, plot_size = 10),
dg = silv_sqrmean_diameter(dclass, ntrees_ha),
g = silv_basal_area(dclass, ntrees_ha),
.by = c(plot_id, species)
)
#> # A tibble: 57 × 8
#> plot_id species dclass height ntrees ntrees_ha dg g
#> <int> <int> <dbl> <dbl> <int> <dbl> <dbl> <dbl>
#> 1 7 27 50 18 3 95.5 57.9 18.8
#> 2 7 27 55 17.6 5 159. 57.9 37.8
#> 3 7 27 35 16.5 1 31.8 57.9 3.06
#> 4 7 27 45 14.6 2 63.7 57.9 10.1
#> 5 7 27 60 19.1 3 95.5 57.9 27
#> 6 7 27 25 12.9 1 31.8 57.9 1.56
#> 7 7 27 120 20.9 1 31.8 57.9 36
#> 8 8 83 20 5.10 3 95.5 15.1 3
#> 9 8 83 10 6.10 4 127. 15.1 1
#> 10 8 28 55 15.5 1 31.8 57.6 7.56
#> # ℹ 47 more rows
## calculate individual basal area
silv_basal_area(c(23, 11, 43.5, 94))
#> [1] 0.041547563 0.009503318 0.148616967 0.693977817