Multiple layers of vegetation make up a buffer.

The different layers of leaves both hold rain (up to 1/2 inch of rain can be held on the tree leaves) and slow its descent. Rain falling gently will erode the ground less or not at all.

The ground vegetation slows the runoff on the ground, encourages it to be absorbed into the soil, and catches and holds sediments that may be in the runoff.

The duff, or decomposing organic matter, is an essential component of a buffer. Its spongy and absorbant characteristics allow for absorption of runoff from uphill land uses.

The lack of a duff layer is the reason why lawns do not provide the runoff treatment of a buffer, as lawns tend to be hard packed and offer little absorption. A lawn, even under trees, also does not provide most of the habitat values and benefits of a buffer.