I hypothesize that the tree roughage helps keep parasites at bay in two ways: Firstly, tannin is an acid, which is used by plants themselves to keep insects etc at bay, and it may be adjusting the pH of the microbial digestion in order to be inhospitable to parasites. The older a plant is the more tannin it has collected over in its body. Secondly, cell walls are sharp. Tiny bacteria will have little trouble dodging around the sharp cell walls of older woody plants in a liquid filled sac. It's easy to move in all directions when you can swim. A larger parasite will quickly be lacerated by such sharp edges and succumb to it's wounds as it is jostled and squished against woody plants.
Mostly conjecture, but I believe that I am close to the mark.
Goat Guts!
I hypothesize that the tree roughage helps keep parasites at bay in two ways: Firstly, tannin is an acid, which is used by plants themselves to keep insects etc at bay, and it may be adjusting the pH of the microbial digestion in order to be inhospitable to parasites. The older a plant is the more tannin it has collected over in its body. Secondly, cell walls are sharp. Tiny bacteria will have little trouble dodging around the sharp cell walls of older woody plants in a liquid filled sac. It's easy to move in all directions when you can swim. A larger parasite will quickly be lacerated by such sharp edges and succumb to it's wounds as it is jostled and squished against woody plants.
Mostly conjecture, but I believe that I am close to the mark.