Decomposition
If you look around you, you may see a number of leaves, sticks, and trees on the ground. While they may no longer be living, they are all providing valuable nutrients to the other plants around them.
Bacteria, worms, insects, and other animals help the decomposing which breaks down the plants and releases important nutrients and minerals back into the soil. New plants can use these nutrients to grow.
Due to this importnat circle of life, collecting firewood is prohibited in state parks.