Well, of course, there is the satisfaction of really making a difference. You will be part of an innovative conservation project that is restoring the Cascades from the damage that has been done to it.
But as well:
* you get several hours of exercise in a varied and attractive environment. Much more fun than running on a treadmill at the gym, or walking the same old circuit near home.
* the hours you spend to keep fit aren't 'dead time'. You will achieve something worthwhile while you are doing it.
* you will make friends with a great group of people
* you can involve yourself in some really interesting events eg bird captures and releases, ecological studies.
* You will discover hidden places in the bush that are otherwise never visited - groves of kauri, giant podocarps (rimu and rata), waterfalls, streams.