Hey there OP-
First off, congrats on getting in and perusing a degree in Forestry. I'm a senior now about to graduate from UCD in Environmental Science and Management and Natural Resource Conservation. Here is my suggestion:
Go with the Pro. More space will be useful, and so will the CD drive. I imagine at some point you will probably be working with GIS and other modeling and data programs, and you'll likely want a computer that can handle putting windows on it too, while still truly being a Mac (that's what I did). I know a few people in my classes that have Airs. And while they are nice because of the weight, they find themselves still needing a little bit more. I take my computer to every single one of my classes to take notes and the weight really isn't a problem.
A few suggestions though as it seems from your posts you'll be using it in class like me:
get one of the plastic case things for it that kinda clip on... If that makes sense. That will save your computer from constantly placing it on desks and moving it around, especially on surfaces where other students seem to make a mess on with crumbs, tea, and other random shit.
Get a soft shell case (like Incase) for it as well for putting it in your backpack. That will protect if from the small bangs and when you are taking your bag on and off.
Get an external hard drive, no matter what computer you decided to get! I have seen computers die on campus, fall on the ground, etc. Even heard of one guy who got in a bike accident, the computer fell out of his backpack which was not in a case, it went rolling down the pavement and landed in a puddle. So it would suck balls to loose your crap like that. I back mine up every month or so but I really should do it more often. I do constantly back it up though when I'm writing 20 page research papers and stuff though.
regardless, get what you think will be best. I got my computer as a graduation present from high school to use in college, and I will get another in the spring when I graduate, kinda "This is the last shit we are paying for so make it count" deal from my parents.
I will be getting a 15" Pro with the 2.7GHz Processor (for map making and picture manipulation) 8 GB of memory for fastness, and the 750GB at 7200rpm hard drive for additional speed. In my eyes there's not much point to the retina display on such a large screen so I won't be getting that. I will however get the antiglare screen.
Hope this helps and let me know if you have any questions! Good luck to you in College!