Does the government sometimes do good things? Maybe, just don't ask why.
From the US Forest Service's site:
The Forest Vegetation Simulator (FVS) is a forest growth simulation model. It simulates forest vegetation change in response to natural succession, disturbances, and management. It recognizes all major tree species and can simulate nearly any type of management or disturbance at any time during the simulation. Outputs include tree volumes, biomass, density, canopy cover, harvest yields, fire effects, and much, much more.
It's a downloadable suite of software complete with its own tutorial, and you can sign up for instructor-led trainings. The software and tutorial are free as far as I can tell, I don't know about the instructor trainings.
Though I'm sure the USFS designed it with the intent of helping timber companies shuck the forests more efficiently (the only robust modeling so far is for Western states, shocking), it doubtless can be coopted by permaculturists. After all, we all did pay for it whether we wanted to or not, not having been asked either...might as well put it to some use.