A sample of 66 grand fir (Abies grandis) trees was selected from national forests around northern and central Idaho. The trees were selected to be dominant in their environment, with no visible evidence of crown damage, forks, broken tops, etc. For each tree the habitat type and the national forest from which it came were recorded. We have data from nine national forests and six different habitat types.
data(treeg)A data frame with 542 observations on the following 6 variables.
Tree number.
National forest number.
Habitat code (see Details).
Bole diameter at 1.37 m, in inches
Tree height, in feet.
Age at which measurement was taken.
For each tree the height, diameter and age were measured (age is measured using tree rings), then the tree was split lengthways, which allows you to determine the height and diameter of the tree at any age. In this instance height and diameter were recorded for the age the tree was felled and then at ten year periods going back in time. The diameter of the tree was measured at a height of 1.37 m (4'6''), which is called breast height in forestry. The height refers to the height of the main trunk only.
The habitats corresponding to codes 1 through 5 are: Ts/Pach; Ts/Op; Th/Pach; AG/Pach and PA/Pach. These codes refer to the climax tree species, which is the most shade-tolerant species that can grow on the site, and the dominant understorey plant, respectively. Ts refers to Thuja plicata and Tsuga heterophylla, Th refers to just Thuja plicata, AG is Abies grandis, PA is Picea engelmanii and Abies lasiocarpa, Pach is Pachistima myrsinites, and Op is the nasty Oplopanaz horridurn. Grand fir is considered a major climax species for AG/Pach, a major seral species for Th/Pach and PA/Pach, and a minor seral species for Ts/Pach and Ts/Op. Loosely speaking, a community is seral if there is evidence that at least some of the species are temporary, and climax if the community is self-regenerating (Daubenmire, 1952).
R. Daubenmire, 1952. Forest Vegetation of Northern Idaho and Adjacent Washington, and Its Bearing on Concepts of Vegetation Classification, Ecological Monographs 22, 301--330.
A. R. Stage, 1963. A mathematical approach to polymorphic site index curves for grand fir. Forest Science 9, 167--180.