Trees

In this document:
Tree life history stages
Tree life history stage transitioning - growth and death
Tree organization
Tree population initial conditions - densities and maps
Tree parameters

The basic unit of data in the model is the tree. Each tree is a discrete individual with a location in space and attributes which describe its size and shape. More information about how tree size is measured and how different aspects of tree shape are calculated can be found in the Allometry topic. In addition, a tree may carry data added to it by Behaviors to help simulate different processes.

Tree life history stages

Tree life history stage (also referred to as tree type), along with species, is the basic way to classify trees. When you set up behaviors for a run, you tell each behavior which trees to act on by species and type. There is support for seven tree life history stages in the model:

Tree life history stage transitioning - growth and death

Trees transition between life history stages as they grow. When a seedling reaches the maximum height set for its species, it becomes a sapling. The diam10 value is converted to a DBH value, which is then used to calculate the rest of the sapling's new dimensions. Since height is re-calculated with a different equation and input parameters, there may be a discontinuity in height values right around the seedling/sapling transition point. If a species uses different allometric relationships for its saplings and adults, another discontinuity may occur at the time of this transition as well. For more on the allometric relationships and how they are calculated, see the Allometry topic. (The automatic updating of these allometric relationships during the growth phase can be overridden. For more, see the Growth behaviors topic.)

Death also produces tree life history stage transitions. Behaviors can request to a tree population that a tree be killed. How the tree population responds to this request depends on the type of tree, the reason for death, and the type of run. The reasons why a tree is killed are natural causes, harvest, insects, fire, and disease (there may not be behaviors set up to create tree death for all of these reasons). Check the documentation for your chosen disturbance behaviors and mortality behaviors for more information on which codes will apply to your run.

There are life history stages for dead trees, but a run may not be set up to handle them. The tree population takes this into account. It examines the run to see if any behaviors directly deal with stumps and snags. If either is the case, the run is classified as "stump aware" and/or "snag aware".

Here's what happens to a tree to be killed in different situations:

You can include information on dead trees in output files. For the purposes of output, dead trees are those which have been removed from memory and are no longer interacting with the model in any way. In this case, a snag is considered alive, although a tree that produced a snag will show up in output mortality records in the timestep in which it died to become a snag. Then the snag would show up again when it was finally removed from the model.

Tree organization

Trees are organized by location and size in what is called the tree population. The tree population indexes trees into 8 m by 8 m areas, lined up by height. The population acts as a librarian for behaviors that wish to find certain sets of trees upon which to act.

Tree population initial conditions - densities and maps

When setting up a simulation, a key part is to define the initial tree population. There are two ways to add trees at the beginning of the run, and they can be used together or separately. The first is to ask the model to create trees for you by describing a particular pattern of densities by species and size range (size class). You define size classes in the Tree setup window, and enter densities in the Parameters window. The second way is to directly list a particular set of trees in a tree map within the parameter file.

Tree maps are lists of particular trees. You can add one or more maps to your parameter file. The maps can come from detailed output files from other runs, or you can make your own tab-delimited tree maps. The preferred method of incorporating a tree map to a run is to add it directly into a parameter file. However, if the number of trees is very large, it may make the XML file too big to read. In this case, a text tree file's filename can be added to the parameter file instead and SORTIE can read the trees directly from the file.

Tree parameters

In addition to the values listed in the parameter window, the tree population also keeps the list of species and size classes. These can be edited in the Tree setup window.


Last updated: 07-Apr-2011 11:35 AM