Take a look at this impressive animation created by Emecstudios. They have announced an upcoming Plants set of plugins designed for scattering objects over other objects or terrain. The Plants set includes WacoPlants, a plugin that offers animation features for all kinds of organical models (grass, flowers, plants and trees) with forces such as gravity and realistic wind. Also of note, they are working on other developments related to terrains, clouds, rivers, oceans and animals. Emecstudios released a Max to Terragen bridge plugin a while ago. More at Emecstudios.com.