Hi There,
I live in SE Mass as well. I do not know of any jobs of this type, but planting natives, clearing out a stream of trash, etc. are great ways to give you the satisfaction of helping the local flora/fauna. You could check the county extension service, or UMass Dartmouth for jobs of this type. Jim Sears is the plant biology professor there.

Feel free to e-mail me. It seems there are several of us SE Mass folks on GW! Be sure to put Garden Web in the subject line.
Robin282mt@verizon.net
Robin

try the Student Conservation Association (SCA), which is not limited to students despite their name. they may have programs available in your area. i volunteered through them for two years and had a wonderful time.
check on univeristy web sites within their natural resource departments. there may be job boards which list jobs on research projects throughout the state and country.
and there are many many private organizations that deal with conservation land purchase (VERY IMPORTANT work), site remediation, etc. i'm sure you know this, but a peruse through a phone book or an web search and some phone calls could turn up an opportunity. my experience has been that people want to hire people who want to work, so initiative and enthusiasm (sane enthusiasm) can get you far.
good luck.

Great ideas. Thanks so much!