Allowing the forest to face an eruption, uninhibited, is probably what will keep it old. Most of these truly old ecosystems have developed with natural disasters common to the area in mind. Trees have to function on a centuries long timeline.

If you RTFA, they said that old growth forests managed to recover from the eruption.

That would be selfish and terrible. The most productive farming in the USA is largely because of previous volcanic eruptions. Similarly the water cycle, subduction, earthquakes, floods, fires, and carbon cycle are what keeps soil healthy and allows for nutritious food.

If you remove all that you end up with MUCH more energy intensive agriculture and an economic incentive to cheap out.