Populus tremuloides or quaking aspen is the natural weed of the boreal forest. I spent a few weeks once doing regeneration surveys for the forest industry in Alberta. These were aspen forests that had been cut down and just allowed to regrow naturally. Of thousands of plots only one I ever did there failed. For a number of years an animal(moose?) had been biting off the shoots of the branches at just under the height required by the forestry department.
As for the length of time a seed can rest before it grows into a tree I don't know. I can say that pine acorns will open after the heat of a fire releasing the seeds. I remember walking into burnt area a number of years ago where a fire had traveled quickly through. I don't think there was anywhere where you could step in the entire forest without stepping on a little pine.
I do know that a properly stored batch of spruce seeds can last through a foresters career. In the wild here natural spruce is a sign of an older forest. After a fire pine or aspen will be the first species to come back depending on what was previously there. From what I've seen the second stage in an aspen forest is a slow encroachment of spruce or tamarack from an existing source after the aspen is well on its way to maturity if the land is suitable.