Sounds like an exam question?

And, maybe just because I am from the States, what is a greenfield?

Hi tugbrethil, greenfield means a piece of land that has not previously been built on, as opposed to a brownfield site, which means land that has been built on previously.
In the uk we try to keep as much "greenfield" or what we call "greenbelt" as we possibly can, and try to utilise as much "brownfield" as we can, as we have an ever decreasing amount of countryside to work with.
hope this explains for you, regards Derek

Are you actually faced with a site that you yourself want to level or are you talking generalities?

Hmm, Derek, it sounds, then like clearing and levelling isn't something you want to do to an area like that. Too many of our wild lands here in Arizona had chains dragged across them in the 1970's in the name of "watershed improvement". Translate: the cattle barons wanted less brush and more grass. What they got was more gullies and weeds! : /

You can always spot an essay topic - the question would need an essay for a proper answer.

Password, please don't rely on others to do your research and writing. When you are out in the real world, you will need to actually understand the whys and wherefors of this material, so you can adapt the methods to local conditions, not just spout rote answers. You owe it to yourself and the people affected by your work to put the time and mental effort into actually learning the course material, along with the critical thinking involved.
There, that's my quarterly essay against academic and intellectual laziness! ; )

I know the previous comments are from over 10 years ago, but I feel that Tugbrethils comments are too harsh.

Whether this is a school essay question or not, it takes nothing to share knowledge or at least point people in the right direction to obtain the correct knowledge. There's nothing lazy about seeking knowledge and answers. Even if you do not wish to hand them the answer you can still educate them and provide context or background for their answer, perhaps a few links or names of books to point them in the right direction.

I am currently studying horticulture myself and there is a severe lack of accessible recourses out there especially for a specific question such as this. Even the all-knowing google throws up a myriad of irrelevant websites when trying to find answers to some horticultural and landscaping questions.

I don't have the answer myself to this question other than greenfield sites are undeveloped "natural" areas so steps should be taken to limit the impact that you have on environment - whether that be the vehicles needed to move the vegetation, or any herbicides used to clear areas. Aside from that, dig through relevant landscaping books and ask in forums where hopefully you'll get more "help" than Tugbrethil could offer.