This paper presents a method for animating and rendering an interactive natural scenery in real-time. It improves the prairie model of [11] by enabling the on-the-fly generation of blades of grass, at three different levels of detail, from user-specified density maps. A new animation function, the tread on grass, is defined to allow virtual objects or characters to crush the grass. The resulting grass model is incorporated into a more complex natural scene with the adjunction of trees that respond to the same wind. Results are illustrated by the real-time animation of autonomous virtual humans interacting with this natural scenery.