Question

how does a tree respond to stimuli

Answer 1

usually for organism to repsond to any stimuli must be a living organism
Yes they do respond to stimulation - by sun light - they respond the same as flowers do by bending and shifting their leaves toward the sun. The amount of movement is somewhat less noticable than the bending of a flower but it is there. If a tree is planted in a location where the sunlight only reaches it from one area, it will grow towards that area to recieve the maximum amount of light that it can get. This is called phototropism