One of the best (if not the best) package for replacing the original vegetation, without spoiling the atmosphere of the game, most of the plants are similar to the original ones.
There are two versions in the archive: aero (high-resolution textures) and light (a more productive analogue, suitable for weak PCs).
Requires Mod Loader, ASI Loader.
Installation: drop the modloader folder into the root folder of the game.