Actually, over the course of a year, a managed forest produces more surface water than old growth. Maybe lower in summer but more runoff. The true "old growth" forests tended to be open with space between trees and very few branches until way up. So, a fire on the ground would not damage the trees and would not get into the crown.

As Rivrguy alluded to, a tree farm is not a forest; it is a crop. 40-60 year old pecker-poles are rather easy to torch from the ground up into the crown. Fire used to occur regularly on grasslands and forests; we prevent them for economic reasons and build up fuels. We also have situations now where it is hotter, drier, more destructive insects, and it all folds into a real disaster waiting to happen.

Years ago I was having a conversation with a Oly NP bio and he said that the tree-ring record showed that the OP burned about once every thousand years or so. Looking at the climate record since the last glaciation, there have drier and hotter periods than we have now. This is just the beginning..........