A couple of years ago, a botanist emailed Cory some nifty insights into why some leaves on a vine maple turn red and others yellow, and still others a mix of both. Go read that again first, then come back here, because it provides some good background information. Since then, it seems, scientists have been able to add to our understanding of leafy color change--particularly when it comes to answering the broader question of why some tree species tend toward yellow and why others tend toward red.
One thing I'm curious about, after reading this, does Europe really have less red leaves in Autumn than the U.S.? I'd never heard that before...
Image copyright John Bennett and licensed for reuse under this Creative Commons Licence
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Didn't follow link so if this is covered already, sorry.
I read something those yellowy european autumns: Apparently an ice age came between the dominance of the red trees and the yellow trees. In North America and Japan, the dominant mountain ranges run North South, so when the ice advanced, the trees retreated South. In Europe the red trees ran against the East West mountain ranges and died out. When the yellow tree lineage emerged they dominated and filled in all the red trees' previous niches.
Bingo! That's exactly what the article is talking about. Fascinating stuff.
Cool! Now what makes leaves fall?
gravity
I live in the north-west of ireland and the leaves are about 75 percent red/orange on the street outside my house..
Why leaves fall is interesting. They fall at just the right time, and fruits do just the same thing. The implications for worldwide crop success are enormous, of course. Gravity... that only explains why leaves and fruits fall *down*.