I agree with Paul_B regarding the ranger role; expect to do a couple of years unpaid volunteering before you've a chance at a job with any of the big land-managing organisations, especially if you want to do practical habitat management work instead of education/engagement with the public. Have a look at the Countryside Jobs Service
http://www.countryside-jobs.com/Jobs/index.htm , if you haven't already, and you'll see the sort of thing that comes up. I left the military with chainsaw and brushcutter tickets and a diploma in Countryside Management and began as a volunteer with my local county park and the Wildlife Trust. That lead to a full-time volunteer placement with the Wildlife Trust that gained me a lot of good skills and experience and some useful contacts. That resulted in a paid summer job as a reserve warden, which was repeated the following year and ultimately lead to my current job with the Wildlife Trust. In between, I did some conservation work as a private contractor and applied for several jobs; I was amazed at how competitive that was: for one part-time, temporary job with the National Trust there were 40 applicants, most with good degrees and experience behind them!
A long story, but I'm trying to illustrate that you have got to be prepared to support yourself somehow for quite a while before you are likely to get paid employment, even with a few qualifications. Jobs are out there, not hugely well paid but rewarding in other ways.
You need to decide if you want it enough to put up with all that.