Monty Pythons Meaning of Life - Suicidal Leaves (Is this what happened in my yard?)

The lawn was mowed for the last time this year on Friday.
On Saturday the yard was nice and clean,
Sunday, the yard was still beautifully void of tall grass and clutter,
Over night the temperature dropped dramatically,
I cam home from work to find the White Walnut (butternut) tree out front of the house has thrown up.

Was it a change in the temperature, 

or was it...

Mass Suicide?