And to add a bit to how physicists simulate stuff. They build a model. Make it as simple as possible, while still approximating the natural phenomena under investigation. So the mean free path model would have a lot of parameters as the parent commenter noted (collisional cross-section, tree density, trunk diameter, etc.).
And it's also important to keep in mind that there are theory builders in physics (theorists), "applied physicists" (phenomenologists, who try to use the fancy theories, match it with real data) and derive future predictions (like climatologists, cosmologists doing large scale universe evolution simulation from the big bang, and so on), the experiment designers, who basically try to weed out the useless models/theories through very targeted experiments.
All of these are about the same natural world, but different aspects, different levels of details, different concerns. (Eg. experimental physicists place enormous care on quantifying the systemic and particular uncertainties of the experiment, whereas theoretical physicists instead focus on the fundamental workings of the theory - they test it through computation. All of those are math, math, math, just different.)
And to add a bit to how physicists simulate stuff. They build a model. Make it as simple as possible, while still approximating the natural phenomena under investigation. So the mean free path model would have a lot of parameters as the parent commenter noted (collisional cross-section, tree density, trunk diameter, etc.).
And it's also important to keep in mind that there are theory builders in physics (theorists), "applied physicists" (phenomenologists, who try to use the fancy theories, match it with real data) and derive future predictions (like climatologists, cosmologists doing large scale universe evolution simulation from the big bang, and so on), the experiment designers, who basically try to weed out the useless models/theories through very targeted experiments.
All of these are about the same natural world, but different aspects, different levels of details, different concerns. (Eg. experimental physicists place enormous care on quantifying the systemic and particular uncertainties of the experiment, whereas theoretical physicists instead focus on the fundamental workings of the theory - they test it through computation. All of those are math, math, math, just different.)