[QUOTE=unit23;478401]
Does this mean i could add my own tree meshes?
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I’ll try to explain it on an example: Trees are generated using random trunk sections, plants are generated using specified meshes for leaves/blossoms/etc. You can always add your own meshes - if you want to create a plant with a butterfly sitting on top 
then you just import your butterfly mesh, add it into plant generator as a plant element. For trees, there are trunk sections with hollows and bulges that appear randomly. If you want to have a trunk secion with a see-through hole, you can add a mesh like this into the generator and it will appear randomly when generating a tree.
Same for materials, if you have some special leaf texture, you can add it and tree will generate using it. You can also add any tileable texture as a bark material. So e.g. if you want a tree with tileable kittens texture on trunk (because why not ), just add it as a material and specify to use this material when generating a tree. Bark materials also have separate moss textures that appear always on top of surface - you can add a snow texture instead of one of moss textures and then you have a tree covered in snow… And so on.