Here are some of my concepts. I've gone for something that's fairly clean and simple, yet striking. Creating an icon that works well within the logo or as a stand alone element, one that can be used for things like favicons or watermarks.
With #1 and #2, my idea / thinking was based on that ... Your brief mentioned that there is "a lot of hands on work", so I thought leaves turning into hands represented that. Also the fact that its looping into each one represents a "group" whether the entire lot or the individual groups responsible for a particular nature reserve.
The logos are 100% vector so will scale well to any size, and works well in full colour, B&W and on coloured backgrounds if needed. I've also used the current colours and fonts.
It would be my pleasure to work up any variations so please do say. I look forward to your comments or thoughts.