I did similar last winter, but with a brush saw on slightly bigger trees - total of ~2 acres in a couple different areas. Wound up getting probably 75% stump sprouts in terms of regrowth on aspen (not sure if we are talking about the same tree - everyone calls all types of aspens poplars up here).
Not sure how well they will burn in the spring unless you are able to pile it up. The trees I knocked down had a lot of moisture - they were growing leaves while lying on the ground for at least two months after things started greening up. I really underestimated how much work it would be to clean up; because I did it on snowshoes with a brush saw a lot of my stumps were 12-18" high.... made it so I couldn't choke a bunch of them together and yank out with my tractor without just getting hung up, so I wound up having to go back through the criss-crossed debris that was 2-3' stacked on top of eachother and chainsawing stuff into shorter lengths so it would lay on the ground and deer could walk through. This winter when I do more I am going to knock down the shrubs/small trees with my brush saw, and then use my chainsaw on the bigger stuff as it falls to avoid handling everything twice once the snow falls.
Attached pictures showing stump sprouts starting, what the area looked like in spring after I started cleaning it up, and then what it looked like early August. Had a pretty bad drought over the summer, but by September most of the regrowth was 3-4' tall.