tree_pop: Objects of class tree_pop

In AWF-GAUG/fisim: Forest Inventory Simulator (fisim) is a package for simulating response and samplign designs common in forest inventories.

Description

The function tree_pop creates tree population objects holding data on individual trees forming a forest and a polygon that defines the border of the forest. The objects are used as an input for simulating forest inventories.

Usage

tree_pop(data, boundary)

Arguments

data	A data.table object that describes the individual trees in a forest. Each row represents a tree, while tree attributes are stored in columns. A minimum set of attributes with specific columns names is required; see Details section.
boundary	A SpatialPolygons object that defines the border of the forest.

Details

The following columns are needed as a minimum requirement in data:

• id_tree - integer values used to identify individual trees

• id_stem - integer values to identify individual stems. A tree can fork into multiple stems and stems are treated as individual record under certain circumstances (exact definitions depend on the particular surveys at which trees were measured). If a tree has two stems, for example, id_tree occurs twice for that tree, while id_stem is unique for each stem.

• x_tree The x-coordinates of the trees, defined at the stem center at a height of 1.3 meter above ground level. The data type is numeric (double) and the units are usually in meter.

• y_tree The y-coordinates of the trees, defined at the stem center at a height of 1.3 meter above ground level. The data type is numeric (double) and the units are usually in meter.

• is_dead A logical indicating whether the stem is dead (TRUE) or alive (FALSE).

• dbh The diameter of the stem, measured at a height of 1.3 meter above ground in cm (diameter at breast height, numeric).

During object initialization, three variables required for simulations will be added:

• ba The cross-section of the stems at a height of 1.3 meter above ground level calculated from the provided dbh values assuming a circular stem.

• n The number of stems; initialized with one for each entry. This is simply a helper variable for simualtions and estimation.

• f_edge Edge factor, used for edge correction of trees close to the forest border. Since such trees have a lower probability of being included into the sample due to the restriction of the sampling to the study area defined by boundary, edge correction must be performed to achieve unbiase estimation. The variable is initialized with one and will be modified during the simulation according to appropriate edge correction methods chosen by the user. After edge correction, some trees are counted twice to compensate for the lower inlcusion probabilities of border trees.

This minimum set of attributes is required for the estimation of stem counts, basal area (a measure for site occupation) and diameter distributions. Users may add additional variables like species, tree volume, aboveground biomass, etc. It will be possible to include such addtional variables in the simulation.

Value

An object of class tree_pop. A named list with the following two entries:

1. $data A data.table object as described above.

2. $boundary A SpatialPolygons object that defines the border of the forest.

AWF-GAUG/fisim documentation built on May 28, 2019, 11:02 a.m.