For my vietnamese insects if any old leaves fall to the ground I just leave it there, otherwise I just clean the old sticks out and replace them with fresh stuff whether it's oak and whatever. The interesting thing I have noticed about vietnamese insects is the adults eat dried up leaves, as long as they get misted regularly while they wait for fresh stuff they do fine. The babies won't do that. But I don't remove the old leaves for a completely different reason. I have realized when I remove the stick insect eggs from the enclosure they do much more worse for me then when they are just inside the cage and naturally incubating in the leaf litter and getting misted every now and then when I mist the adults. I have had much fewer successful hatches from when I remove them and try the usual incubation method for the eggs and a lot of the time the babies have issues with their legs after hatching. When they do it naturally in the big stick enclosure they have fewer hatching issues and less injuries.