Tree and Stand Simulator - Features/Functions

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Tree and Stand Simulator
Features/Functions

Overview

TASS is a biologically oriented spatially explicit individual tree model.

It was designed to produce potential growth and yield tables for even-aged managed stands. It is calibrated for four coastal and four interior species in British Columbia.

It generates the yield table database for TIPSY and is also the growth and yield model within SYLVER.

It incorporates a number of sub-models such as:

ROTSIM Mitchell and Bloomberg, 1986; Bloomberg, 1990) a laminated root-rot model,
SWAT (Alfaro, 1996) a spruce weevil attack model, White Pine Weevil Modelling - Canadian Forest Service, and
TRAYCI (Brunner, 1998) a light interception model.

Link to Future Development

How TASS Works

Growth Relationships

The processes that drive the development of individual trees in TASS include:

height growth (i.e., it uses the Ministry recommended site index or height-age curves),
branch extension,
accumulation of foliage and crown expansion of competing trees,
production and distribution of bole increment,
suppression of height growth, and
mortality.

The model grows trees and simulates crown competition in a three-dimensional growing space simulated within a computer. The crowns of individual trees add a shell of foliage each year and either expand or contract asymmetrically in response to:

internal growth processes (e.g., height growth),
physical restrictions imposed by the crowns of competitors,
environmental factors (e.g., site quality, defoliation, pest damage),
cultural practices (e.g., thinning, pruning, fertilization), and
genetic variation among trees.

The volume increment produced by the foliage is distributed over the bole annually, and is accumulated to provide tree and stand statistics.

tass.gif (22907 bytes)
Figure 1

Figure 1 illustrates the development of a 10 by 12 m plot from age 0 to 45, including a thinning at age 37 years. The growth of every branch in each tree shown in these physical models is simulated by the computer and identified on the crown maps used to construct these miniature models.

More information about TASS development can be found in the publications by Mitchell (1969), Mitchell (1975), Mitchell and Cameron (1985) and Mitchell (1986).

Link to System Requirements

Link to Getting Software

Database

TASS is calibrated to conform with data from research trials and remeasured plots located in managed and unmanaged stands. Most of the biological growth relationships in TASS are derived from detailed stem analysis of tree boles, branches and foliage. A total of 11 989 permanent plots (i.e. comprised of 43 799 plot measurements) established for local species growing within British Columbia, Alberta, the Pacific Northwest region of the United States, Europe and New Zealand have been consistently summarized and classified by species and treatments including control, thinned and fertilized (Goudie, 1998). The number of plots and measurements from untreated natural stands and plantations is listed in Table 1.

Coastal

Interior

Species

Number of Plots

Number of Plot Measurements

Species

Number of Plots

Number of Plot Measurements

Douglas-fir

885

4539

Lodgepole pine

2160

5351

Western hemlock

1115

4396

White spruce

456

1286

Sitka spruce

173

643

Douglas-fir

348

764

Western redcedar

38

163

Western hemlock

5

10

Total

2211

9795

Total

2969

7411

Table 1. Permanent Sample Plots Description

The Stand Modelling staff, from the BC MOF, Research Branch, test and evaluate TASS on a regular basis using existing and new data. In a recent paper, Jim Goudie (1998) compared model output with plot data from thinned stands to identify potential biases in the predictions.

Model Components (Interface)

Input

TASS is not interactive. It operates via instructions given in an ASCII input file. The commands are designed to be fairly self-explanatory, and easy to construct by hand or by a specialized editor. New commands are added as needed, and old commands are sometimes modified to make them more flexible.

TASS input parameters are:

species and stand origin (i.e., single species of natural or planted origin);
initial number of trees per hectare;
spatial tree distribution or optional tree map list (e.g., uniform, clump or any distribution defined by tree coordinates);
site index or a combination of height and age;
volume merchantability limits (e.g., minimum diameter at breast height outside bark, top diameter inside bark, and stump height);
operational adjustment factors;
plot dimensions in metres;
silvicultural treatment specifications (e.g., pre-commercial and commercial thinning, pruning and fertilization); and
output table specifications (i.e., height or age steps and end point of the simulation and steps).

TASS Input file example

Output

Some examples of yield tables, output images and information produced are presented below.

Standard yield summary: includes the following variables:

stand age;
stand site height;
stand crown cover percent;
stand basal area;
total and merchantable stand volume per hectare;
total and merchantable stand mean annual volume increment per hectare; and
average tree statistics.

Standard run example

Stand table: displays the number of trees by diameter class (variable) for each stand age requested.

Stock table: displays merchantable volume in by diameter class (variable) for each stand age requested.

Mortality summary table: displays a stand table of the number of trees that die due to non-competitive juvenile mortality, and due to suppression between age steps by 10-cm diameter size classes.

Mortality summary example

Height profile table: shows the interception of tree crowns at given heights. Includes number of trees, basal area, percent crown cover, and percent crown interception.

Height profile example

Standard TIPSY yield table and extended output table: standard TIPSY-style yield table includes merchantable volume by several diameter limits, and crop/prime tree statistics. Extended output table shows mean DBH, stem count, and basal area by the same DBH limits.

Standard TIPSY yield table examples

Extended output table example

Dead tree list table: displays a list of all trees that have died to a specified point in time. Includes year of death, cause of death, and current status (standing/fallen).

Dead tree list example

Live tree list table: displays a list of all live trees, showing all common variables. Optionally, upper stem diameters can also be given.

Live tree list example

Coarse woody debris table: displays a list of all trees that have died and fallen between age steps. Includes mean age, DBH, length, volume and breakdown of quantity by size classes.

Coarse woody debris example

Customized yield tables: TASS custom report command lets you choose from dozens of stand-level statistics, and format them in any length and number of decimal places. Even DBH and height classes can be specified, for stand and stock tables.

Custom stand report example

Standard SYLVER files: are special format files for passing on to other programs within SYLVER. The TTF file contains overall plot info, including a record of treatments and the final harvest. The TAS file contains a detailed list of stem information for all harvested trees. These files can then be passed to bucking, sawing, grading, and financial analysis programs.

SYLVER file example (TTF)

Graphic output examples:

2D Image (crown map). While TASS runs, it can generate images of the current state of the simulated stand, showing summary statistics, and an overhead view of crown expansion.