I know that volunteering is not something that crosses the minds very often of people that are trying to get work in the natural resources, environmental science or biology fields but, sometimes you got to bite the bullet and do it.
It can be sometimes a very hard thing to do depending on your location and financial status and what opportunities you have available to you. I used to have a job that payed me very well, but it provided me nothing in the way of experience that I needed to advance my career. Not only was my job not helping me in the direction I wanted to go it was actually hindering me by denying me the time I needed to broaden my skill set.
So I made a hard choice and I resigned and moved across two states to end up in a area that provided a diversity of opportunities for work and volunteer opportunities.
Maybe you are luckier than me and you already live in a place with a plethora of opportunities and you can skip the hard decisions about moving or quitting a job. If that is the case you can get right to finding opportunities to expand your skills. There a a few ways you can find volunteer opportunities for what you are looking for, for example many government agencies have volunteer programs like VIP (Volunteer in Parks) or the Natural Resources Conservation Services Earth Team. But there also more informal ways you can find volunteer opportunities too, by going to local agencies both state and federal and simply asking about volunteer opportunities.
Also consider private organizations like the Sierra Club or The Nature Conservancy as they too may have offices in you area and a lot of the time they look for as many able bodied people they can get to complete projects.
Like finding a job finding a volunteer opportunity can be a job in itself, but it can provide invaluable experience to some one that is starting out or if you are considering a career move. For more links to volunteering opportunities check out the new Volunteering and Internships link page. The page is far from done and I always welcome new additions to it so let me know about and volunteering or internships that would be a good addition to the page.
Good Luck on your Job Hunt
Working for the Earth