* Trees always make energy. They use sunlight to convert carbon dioxide and water into sugars (food) through photosynthesis. This happens whether their leaves are green, yellow, orange, or brown.

* Yellow leaves are dying. The chlorophyll (green pigment) that makes photosynthesis possible breaks down in the fall. This reveals other pigments like carotenoids (yellow and orange) that were there all along.

* Dying leaves are less efficient. As the leaves age and chlorophyll declines, they become less efficient at photosynthesis.

So, while trees with yellow leaves still make some energy, they are not as efficient at it as when their leaves are green.

Let me know if you have other questions!