Does anyone know a program specialized in park / environmental design ?
I'm not aware of any. I think that many CAD applications support that sort of option, but none of them are specialized for what you ask for. ArchiCAD would be the closest that comes to my mind, but I might be wrong.
ArchiCAD seems to be ok.Thanks Robert.
I am glad it helped. Several years ago, I downloaded ArchiCAD for evaluation of CAD package by mistake (not knowing what I really need or want) and it came back to me now that it's probably a fine (specialized) CAD package for what you might need.