Aspen usually matures at around 50 years of age, and regenerates best under full sunlight conditions.  As a result, the proper management technique is to clearcut the stand.  After the harvest, aspen responds buy sending up thousands of stump sprouts and root suckers per acre.  Over time, they get bigger and begin to out compete one another.  Eventually, the strongest and most vigorous become the new forest.  Often times, spruce, pine, and oak are left uncut for aesthetics and as a seed source for these species.