Fairytales, Sara Maitland thinks, arose from forests. Many of the stories gathered in the 19th century by the Brothers Grimm are set in woods and populated by forest dwellers, be they woodcutters, witches or wolves. Their history is intertwined and so, potentially, is their future. Both, Maitland argues, are under threat, jeopardised by our increasingly urban and technologically mediated lives.

In Gossip from the Forest she journeys, fairytale-like, deep into the woods, taking 12 walks in 12 British forests (one a month, over the course of a year). As she travels around the country, wandering the rides of the New Forest, hunting down relics of ancient woodland in Dulwich and meeting the last surviving Free Miners in the Forest of Dean, she muses on fairytales, using them as a way of understanding the mysterious space forests occupy within our psyches.

This is a bushy, sprawling book, as perhaps it should be. It roves busily back and forth through time, unpicking the complex history of British woodland from the Neolithic period to the present day. Maitland rejects the myth of an island covered in uninterrupted forest, revealing instead a history of exploitation, enclosure and artificial reconstruction. Likewise, she tracks "our robust and lovely fairy stories" through the centuries, observing how they shift emphasis in different eras, becoming increasingly pruned and pious.

Each walk closes with a retelling of a classic fairytale, often from an oblique angle. Rumpelstiltskin is told from the perspective of the angry little man who could spin straw into gold; Rapunzel by the witch. Hansel and Gretel explores the post-traumatic stress disorder aftermath of the siblings' nasty adventure, while Red Riding Hood places a lost child and a feral wolf into a modern Forestry Commission wood. Maitland's versions are earnest and endearing, a world away from Angela Carter's savage and anarchic marvels.

The earnestness derives from a strong sense of threat. Maitland is concerned that children no longer play in woods, particularly without adult supervision. They don't know the names of trees and leave blackberries rotting in the hedgerows. This state of estrangement from the wild is troubling both for conservation reasons (it's hard to preserve what one doesn't know), and also for human health (the average child, she states, has already lost an hour a day of outdoor play this century). What's more, a lack of free, wild play means children are missing out one of the essential lessons of the fairytale: that harm and danger can be survived and make a person more robust. "I seriously fear," she writes, "that we are failing to nourish the beautiful and precious quality of resilience in our children."

Considering how much attention is given to conservation, and to the lost art of dwelling more naturally in woods, it seems odd that there's no mention of the road protest movement of the 1990s, when hundreds of people moved into the forests, living in treehouses to try to prevent the destruction of ancient woodlands. One would have though that this quasi-medieval way of life would have appealed to Maitland, particularly since it drew explicitly on myths of forest outlaws she retells here.

Omissions aside, Maitland is a wonderfully enthusiastic guide to her twinned realms, writing gleefully of crystal brain fungi and "the strange smoky shimmer" of bluebells. Her relish is infectious, and I suspect as well as hope her 12 woods will see some new faces this year.

Olivia Laing is the author of To the River (Canongate £7.99)