initial stand ages

[rswaty]

Can someone explain how VDDT assigns initial stand age? When setting up a model run, the user assigns each class a proportion of the landscape. Do all cells in that class start out as the youngest age for the class, or are the ages assigned based on some general distribution function? This assumes that the initial age of stands influences the final proportions of each class on the landscape given a specific number of time steps (with the earliest timesteps being the most heavily influenced by the initial age distribution).

For an ongoing project, we lack stand age data for our otherwise classified landscape. We were considering using the age distribution generated by VDDT after a run of several hundred years to obtain an age distribution for each BPS. Since we have updated the VDDT model of each BPS to simulate current conditions the age distribution after this model run should replicate current conditions with some accuracy. Is this strategy reasonable?

Thanks,
Randy

[leonardo-frid]

In assigning initial conditions (Run | Settings | Initial Conditions), the user is given the option of selecting an age range for each record by selecting the Ages checkbox. The default age range is the same as the age range that spans the class as defined in the Deterministic Transitions. For each cell beggining in the class, VDDT then assigns an age randomly from a uniform distribution spanning the age range defined in the Initial Conditions screen. It is very likeley that the way that ages are initialized will influence the final conditions, particularly if run times are short.

Your idea of using final age conditions to initialize ages for a new run makes sense. One question that you will need to resolve is: how long is it appropriate to run your VDDT models before extracting the age distribution? If your models represent current conditions which have only been present for 100 years, you may want to start with reference conditions then run your current conditions model from this starting point for 100 years to get the age distribution for your current conditions.

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