Yes, that's a good possiblity on the stress..
Heat, or lack of water..
The tree does that on purpose to conserve
having to feed so many leaves, so it will, in a sense "shut down" certain leaves..

Also, the change in evening temps can do it..
And the change in the sun's position in the sky,
is also a trigger for the plant/tree/leaves to do that..

And believe it or not, every tree is different..
You can have two trees, side by side, and both can have different reactions...
***I know this, because we have two very big mature maples just to the back of our back door.
Side by side, one goes into dormancy before the other and that same one buds open before the other one too..
Side by side, same growing conditions, but they do different things...

There's also another post here some one asked, about it too, and I put a post there about some technical stuff too.. about photosnythesis.
I think it was under SnazziT..
I'll check..

* * * *
Weezie

Don't forget to be kind to strangers. For some who have
done this have entertained angels without realizing it.
- Bible - Hebrews 13:2





http://photobucket.com/albums/y250/weezie13/