What makes pecans all fall off the tree while still green ?

Answers:
The green you see is the outside covering of the pecan. Under that is the real shell. The green covering is bitter so some animals will not eat it. Drying the pecans makes the nut 'ripe' as you've seen it in stores, but it is ready to reproduce as soon as it drops from the tree.
When the green part opens, the pecan is ready to grow. Winter temperatures keep most bugs away from pecans ( & keep most pecans from germinating too early) but squirrells know how to remove the green casing and the the nutshell, so many pecans don't turn into trees. Squirrells also bury many nuts, then some of those germinate in spring.
The ones that do germinate without help from squirrells are usually buried under a mound of leaves, twigs & other things and lying in a slight depression so plenty of water will help them germinate.

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