Dealing with many scripted objects

I have a terrain with many cloned trees. I want them to change size based on main camera’s Y coordinates. If I put a script on tree clones which updates its size, I am afraid it would affect performance due to updates done every frame by lot of trees. Is there a way to make them all follow tree’s original prefabs scale? This way there would be one update operation.

You might want to have a look at this: