Here are the main things I learned, without citations at the moment:
- Fall foliage isn't a natural consequence of the changing weather for leaves. Instead, the plant has to actively catalyze (i.e. destroy) its chlorophyll.
- Why do trees do this? This is a subject of debate and research. I saw an article that said it had something to do with co-evolution with animals... I really don't know.
- A scientist on twitter told me that trees are hyper sensitive to temperature and conditions, so maybe different trees start their fall foliagein different ways, depending on very very local conditions.
Still, I haven't been able to find anything about what I was initially curious about: where does fall foliage start on a tree? The top, the sides, in bunches or randomly distributed across a tree? I still don't know the answer to this.