At least part of that is the climate. A forest in a tropical zone is so efficient at processing nutrients that the soil beneath a forest is almost nutrient-free; the nutrients are always moving from plant to plant. If you take off the forest, what is left is not very hospitable and erodes easily.
Temperate forests accumulate humus; remove the trees and there are nutrients sitting there waiting to foster new growth.
I'd question that definition of "pristine". The old-growth temperate rainforests of the Olympic Peninsula in Washington, have only existed for about 10-12,000 years; that's about how long it's been since the entire area was covered by an ice sheet.
Here's an overview that has a timeline and some jumping off points if you're interested in learning more. What happened as the ice retreated varied by area and some of the valleys in particular have been studied to see what species arrived, in what order, and to investigate delays by some.
> In comparing the various palynological sources for Northwestern Washington and surrounding regions, it is clear that the vegetation history varies at least in its details from area to area. For example, Heusser (1978:1576) notes that treeless conditions persisted longer after glacial retreat in the Hoh Valley than in the northwestern corner of the Olympic Peninsula.
> ...the arrival of coniferous trees in this area was apparently delayed by aridity until sometime between 11,000 and 9,600 yr B.P.
This makes me want to see designated areas for old-growth forests to re-establish, and yet there’s almost no chance that the people living in those areas 2000 years from now will have continuously held the same values and kept the project going.
Plenty of people in California are doing this. Basically they buy a large amount of acreage up where nobody cares (mostly Mendocino county or Humboldt county, but sporadically throughout Sonoma County / Marin County/ rest of the Bay) then spend about a decade putting the land into a trust, and marking each separate trees to make sure people don’t poach them. The largest one is the ‘Save the Redwoods’ league, but I’ve spent many days hiking through redwood preserves just from some random person who died and made a land trust as their legacy.
People 2000 years from now will also be enamored with Redwoods (provided they still exist), they’ve been highly regarded for thousands of years already, and they will for thousands more.
The idea of using nuclear waste to protect pristine natural environments is a good one. It's the most effective one we have today. After a few generations I heard animals aren't affected anymore, it also depends on the kind of fallout.
Temperate forests accumulate humus; remove the trees and there are nutrients sitting there waiting to foster new growth.
(IANA forestry expert...)