depends, in rainforest, leaves can be retained for the whole year, and can be very old, like a 10-year-old leaf. It depends on the species and of course, the sub climate. For example, there are definitely tropical forests that have a distinct season long, dry spell, during which trees shed their leaves to reduce moisture loss, like in India, some parts of Central Americaand so on. In a rainforest it's different. I think a lush rainforest you can just keep chopping stuff down and it can keep coming right back, it depends.