Yes, over hundreds of years. I have a few acres of land and there's several trees on ~.5 acres. There's some young trees in the ground spreading from the origin

Yes, over hundreds of years. I have a few acres of land and there's several trees on ~.5 acres. There's some young trees in the ground spreading from the original half acre that got there naturally. They're a good 4-5 feet from the original tree. It'll take a while to get the rest forested if I wait, though squirrels and birds moving seeds could help. Part of it is that trees can make the area better for other trees; the conifers stop grass from growing under them, which is good since the grass can be as tall as I am and block out light.