e-on software made for years programs to create 3d plants, terrains, environments.
Another company that gets purchased but luckily they decide to give for free their product and is a great program to make all sort of 3d environments, plants, terrain, etc. and export to your favorite 3D engine like Unreal or Unity.
Here we have 2 programs with libraries to download, Vue itself as the main program, and Plant Factory to make all your forests and trees for your project. You can download from their main website (HERE)
Also there is plenty tutorials in their YouTube account to learn it.
If you are into 3D architecture, animation or game developing this tools are fantastic and now they are free.
Also comes with a huge library of plants, trees, flowers to add to your projects.