Deciduous trees lose their leaves in the Fall... everybody knows this. Leaves begin to change into beautiful colors and then almost as quickly as they change they begin to drop or "Fall" as it were.
But did you know that it isn't the colder temperatures or wind that triggers this event?
It's because of a hormone produced by the tree, the production of which is triggered by...
Around this time of year in the Northern Hemisphere, as the days grow shorter and colder, those changes trigger a hormone in leaf-dropping trees that sends a chemical message to every leaf that tells it that it's time to go. The tree is programmed by millions of years of evolution to make sure this happens.
If this process were not to occur and the weather were to warm up, the leaves may begin to start the process of photosynthesis and start taking up water and creating food... and that's not a good thing. Once the freeze comes back the leaf will die and permanently seal off the food source for the tree, thus killing the tree.
So there you have it... Light or the lack thereof causes the leaves to drop. Hopefully you found this information as interesting as I did when I first learned this fun fact.