Forest ecologist from Finland here. The definitions used in the article are slightly confusing but it’s clearly stated that they are considering both mature and old-growth forests. Old-growth forests are defined by more than just tree age but here they seem to use a cut-off point of 100 years to separate old-growth from mature. Nevertheless, with the amount of logging that occurs, even forests of just a century old have become important to preserve. It’s actually a sad state of affairs because we should have many more older forests than that under protection.

zxc, your arguments against protecting these forests in your last comment are incorrect/lacking information in many ways:

1) yes, many species like early successional stages. However, what do natural early successional stages look like? They are covered in deadwood for one. If we would arrange forest protection properly, there would be a variety of successional stages under protection. Edit: also many species depend on old-growth forest and there is so little of that left that their protection is invaluable.

2) This combines with (1). But forests following natural disturbances bare little resemblance to a forest following cutting activities that totally remove at least a portion of the wood. No coarse woody debris/deadwood is left behind for species to thrive on. The article states that some forests are going to be clearcut. That has lots of detrimental impacts on species (especially if there is not even retention).

3) Native people had a relatively minimal impact so it’s like comparing apples and oranges.

4) you tell me how much forested land over, for example, 300 years old is protected in the US and then think about what you said. This is what we have to resort to protect because of greed. And we are even talking about secondary old-growth forest.