If you look closely, you will notice different extents of marcescence among Beech trees. Some keep their copper cover, others discard it to the forest floor. Why?
Young saplings often cling to their finery. They are at a different stage of development, a kind of sylvan puberty, which the Queens of the Forest have long since passed. Growth brings hormonal change, and not always in the same way or at the same pace. We see the same effect induced by the pruning of garden hedges, an enforced rejuvenification.
Exposure may also play a part. The youngsters are more sheltered, less tested by wind and weather.
And then there is individuality. Natural variation, subtle stimuli, things that remain outside our ken and beyond tidy explanation.
The Beech is a curious creature. Thankfully, we have thousands to observe, admire, and quietly wonder at in our Forest.