Why does a lightsource postpone the time it takes for the leaves falling from a birch?

Question

It is autumn and the leaves have already left their trees on all birch and other trees that has leaves, except one. This birch has a spotlight pointed to the tree and it is on 24/7. I have recognized that this birch have lost almost no leaves. And if we take a closer look at this birch, the back side of the birch, which is faced away from the spotlight have lost a noticeable amount more leaves than the front side which is directly hit by the light from the spotlight. My conclusion is that having a lightsource pointing to a leafy tree will postpone the time from when it loses its leaves, relative to trees that does not have a lightsource pointerd at them. But I have no idea why this is happening. I do not know anything about trees, leaves, chloryphyll or the reason why trees drops their leaves in the autumn. If any one is a expert in this field and might know why this is happening, or just have a hypothesis of why this is happening please provide it since I find this really interesting and I can't find anything on Google about this phenomenon. You can make your anwer as complicated as you wish, I will understand it even if I might need to Google some of the things in the answer :). Thanks!

Answer 1

Not an expert but I believe trees can sense the length of day. When it shortens, and winter is approaching, a time not propitious for photosynthesis in deciduous trees, the trees drop their leaves. The spotlight is short circuiting this natural response by eliminating the input of shortening daylight hours.