Event Establish (Simulate Trees Tab)
Establishes a tree list using parameters entered by user or chosen from standard lookup tables.
The tree list in a stand is initialized by the execution of the Establish event of each crop plan. The Establish event (simulate tree tab) has a table of user-determined parameters for simulating cohorts of trees. Each line of the table specifies one cohort in the tree list. Cohorts can differ in species, age, site and the associated average tree sizes. The user can enter these parameters directly or use the optional table lookup for different combinations of species, age (1.3 m height), and site.
When the desired settings are obtained, click the "OK" button to place the settings into the Crop Plan.
The following picture of the Establish event with simulation of trees dialog window is followed by explanatory text.
Tree List Parameter Lookup:
- Species. The species code appearing in the drop-down box will be determined by the Variant setting. They will only include only the primary MGM species (spruce, pine, aspen, and black spruce).
- Site Tool is included to provide some additional information on height of trees at different ages.
- Age (BH). Average age at 1.3 m height for the trees.
Tree list Parameter Definitions
Spp Species codes: Regional codes are used
bhAge Average number of years (age) since tree reached 1.3 m height
Site Site index, stand height at 50 years using definition for site curves source selected in Options event
Tpha Density, number trees per hectare; Den may be lower than the nominal value (e.g. "Planting shock" loss could lower the established density below the nominal planting density
Av D Average tree diameter at 1.3 m height
sd D Standard deviation of diameters, usually 50-100% of AvD
Av H Average total tree height
sd H Standard deviation of heights, usually 40-60% of AvH
Correl Correlation between heights and diameters, default is 0.95
Buttons associated with the table permit addition, deletion, replacement and rearrangement of cohort rows. The user may override the table-lookup values by editing the lookup entry values before adding a new cohort row. Intermediate values may be entered and looked up in the tables by supplying the first three parameters (Species, Age and Site) and pressing the "Lookup" button. Parameter combinations outside the table-lookup range result in a warning message.
Note that entries on the 'New/Modified entry' row must be added or replaced before clicking the OK button.
Variation is as important as the mean when establishing a stand. Low variation leads to trees of very similar size and form. This in turn can prevent the mortality functions for behaving well. Stands with greater variability allow the mortality functions to better identify trees that will have lower survival rates. Empirical data is very helpful in determining what level of variation is appropriate. Also note that establishing a stand at very young ages (< 5 years old at 1.3 m height) leads to reduced variation. Current growth functions do not allow for the differentiation of trees that leads to increasing variation.
The stand establishment settings provided as input have a MAJOR impact on the simulation of stand growth. The analyst must always be watchful that the input settings are appropriate and reasonable for the stand conditions that are to be simulated.