Not sure about environment art per se, but I think Michael Pavlovich's series (Intro to Zbrush - Part 1) on Youtube is best to get started with. He teaches all of what is required to sculpt a head. I think that should help you get started. Once you have those basics tackled, then you could look for specific project-based…
People use zB for a wide variety of purposes so pixologic have responded with tools to fit those needs. Having said that, you can also sculpt in Maya. I dont know what your requirements are but working strategically you might not need zB. You can also try both. Sculpt a tree in Maya and then try the same thing in a zB demo…