Nations can, at the very least, do a couple of things to proactively protect their forests from dieback. Dieback in this context refers to the death of the trees in the forest due to things like pollution (typically heavy metal pollution) and acid rain.
Firstly, to protect their forests from dieback, nations can put in place stringent environment preservation legislation. That would be legislation to deal with things like how heavy metal pollutants should be handled as well as eradication of acid rain incidents. More important than just putting in place such legislation would be the strict enforcement, in order to ensure that the laws serve the intended purpose. That is, the purpose of keeping the trees in forests from suffering dieback. Agencies like the United Nations Environmental Programme can provide their expertise in the drafting of such laws.
Secondly, to protect their forests from dieback, nations can see to it that the areas adjacent to the forests are not heavily industrialized. The idea here would be to protect the forests against accidental dieback. This is after coming to appreciate that the legislative measures we recommended earlier on doesn’t always work: there are cases where the environment preservation legislation is adhered to to the letter, but where ‘accidental’ pollution still occurs. But if there are proper buffer zones between the industries and the forests, then we can be assured that even when such ‘accidental’ pollution occurs, the trees in the forests wouldn’t suffer dieback. This can work well with respect to preventing dieback from heavy metal pollutants. But it wouldn’t work well with respect to preventing dieback from acid rain: as acid rain can often end up coming down quite a huge distance from the place where the pollution causing it took place.