"Leaves" is the plural of "leaf," and it also means "goes away."  Even if the leaves fall from trees, they may still leave behind something. There are many leaves on campus. Through experiments, we are able to extend the life of fallen leaves and make them useful after their life has "gone away."
One way to use fallen leaves is to make them into tiles to lay on the uneven pavements on campus, which will be an effective use of campus resources. Another way is to make them into transplant pots to replace plastic pots. This way the plants, along with pots, can be planted directly into the ground. The pots will eventually decompose underground.