It is published three times a year and has a circulation of 340,000.
The trust is a charitable coalition of the UK's 47 conservation trusts. Its magazine targets ABC1 families and older readers and follows the trust's work nationwide, as well as broader environmental issues.
Think's recently-established book publishing division already produces books for The Wildlife Trusts, including a guide to wildlife walks.
Ian McAuliffe, Think's publishing director, said: "Companies that have perhaps traditionally not been seen as environmentally friendly are increasingly using the magazine to get messages out about their green credentials. And members are very receptive to this kind of information because of the trust's endorsement."