Nuts wrote:What turns them red? I spent three days based at Waldheim just looking for red one year with nothing like that.. yet some years they are more common. I never found any study specific to Fagus in a search..
There is a little bit about this on the Nothofagus gunnii page on the Parks site. Interestingly, as mentioned in that article, anthocyanins are present in many Eucalyptus and they cause the colouring in the bark of E.coccifera. They have even been proposed as a taxonomy aid in Eucalypts. It is thought they may act as a natural sun lotion. Carotenoids are present in most plants and have a role in photosynthesis. As SBS found, above, you just can't see them when there is a lot of chlorophyll about. To see lots of red or deep oranges you need bright days, because anthocyanin requires light. Duller days will mean yellow is more dominant. And of course, in some plants there is just not a lot of anthocyanin to begin with. When both the anthocyanin and carotenoids disintegrate the leaves will look brownish.
Now, just to find a way to put those explanations into 'quick answer' punter-friendly terms 
Cheers.. )
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