[thedoc (OP)]

Eduardo Cervantes  asked the Naked Scientists:
   
It is autumn here in the Shenandoah Valley and the leaves are rapidly
changing to brilliant colors.

I have been cutting branches off small maple trees to feed my rabbit.
Mimi loves to eat the leaves and bark. Before you ask if my rabbit
barks, no I mean she eats the bark.

I noticed that the new leaves are growing back (almost full sized
already) and are colored beautifully bright green as if it is spring.
It's curious to me that the tree does this. I wonder why?

What do you think?

[CliffordK]

I have noticed that most trees will replace lost leaves most of the summer, at least as long as the plant gets adequate water & nutrients.  And, of course, the new leaves would look like spring leaves.  Obviously trees need to cope with damage from animals, insects, wind, etc.

There was a discussion earlier about why fresh leaves (or needles) are often lighter in color than older leaves.  My conclusion was that the young leaves may initially benefit from less solar absorption, perhaps being more heat sensitive.

I don't think I've seen new growth as much in the fall, although some trees will drop their leaves earlier than others. 

We have had a couple of heavy frosts, and my Fig leaves have all slumped off in a pile.  Most of the cherries have lost their leaves, but some of the apples still have leaves, and presumably continue to photo-synthesize, as we still get quite a bit of sunshine, even in the late fall.