Ours is a rainforest nation. Up and down the drenched western seaboard of England, Wales and Scotland, ‘temperate rainforest’ once carpeted our hills and valleys. According to Guy Shrubsole, it should – and could – do so again.

Temperate rainforest is characterised by extreme wetness and, as a result of this wetness, rich populations of epiphytes, such as mosses, liverworts, lungworts, lichens, ferns and other organisms that grow not in the soil but on the trunks and branches of trees. Shrubsole makes his soggy way from Cornwall to Argyll through ancient rainforests, marvelling at the growths that sprout and ooze from twisted trunks of oak and hazel. He’s no expert and learns as he goes along. His enthusiasm is catching (at least at first): you can’t read without wanting to have a wander yourself through these dripping microclimatic wonderlands, among trees ‘heavily garlanded with beardy lichens’, the ‘spreading filigree of liverworts’ and the ‘translucent fronds’ of polypody ferns. He meets mycologists and bryologists down damp ravines and up storm-lashed fellsides.

These forests are, it’s made clear, rare and fragile living communities. This is why The Lost Rainforests of Britain is not just a book but a campaign too. Shrubsole, in seeking to persuade lawmakers to do more to support our remaining rainforests, draws interesting parallels with the Amazon-focused ‘save the rainforest’ campaigns of the past. ‘Rainforests aren’t just someone else’s problem,’ he writes, ‘they’re right here on our doorsteps. And we shouldn’t simply seek to save them, but to restore them.’ So in what should be at heart a slow-moving book – it’s mostly about moss, lichens and rain – the author has to work to a demanding agenda. Over 250 pages, Shrubsole has first to tell us that British rainforests exist, explain how they work and why they’re important, and then fast-talk us into joining his campaign to restore them.

The proposed means of restoration is, in a sense, simple: rewilding. This is the idea – popularised by books like George Monbiot’s Feral and Isabella Tree’s Wilding – that nature, broadly speaking, functions best when left to its own devices, that human interventions ought to be redundant in conservation and that, once wild places are restored to pre-human conditions, they should be left in a state of self-governance. Shrubsole is four-square behind these principles; indeed there’s a certain right-side-of-history self-confidence to his rewilding prescriptions that verges on complacency.

Rainforests, we’re told, will in time restore themselves, if left alone by us and – crucially – by our sheep (Shrubsole more than once likens the advance of naturally reseeding forest to the march of Birnam Wood on Dunsinane in Macbeth, seeming to miss the point of that episode). For this to happen effectively at the present time, however, it isn’t enough for us to simply step away: ‘that would mean walking away from the mess left by previous generations. For rewilding to work, it still requires people to step in at the start of the restoration process, to try to correct the errors humans made’. Rewilding sounds like quite heavy work – literally as well as philosophically. Eye-poppingly momentous interventions, such as the introduction of bison (to create ‘dynamic new patterns of disturbance’) and wolves, are waved through with cheerful breeziness. Animals in general are discussed primarily as landscape engineers (‘tools like exclosure fences … make it easier to control grazing levels and vary it over time and by location – you can decide if a wood needs to be given a break, or could cope with a little grazing’). One might sometimes think, why not just use human engineers? And indeed, that’s not off the table either: an army of volunteers will be needed to rip out invasive rhododendron, grub up conifer plantations and keep holly under control. When exactly do such interventions become redundant? It will probably become obvious nearer the time.

Shrubsole is upbeat, too, about the role of farmers in these rewilded, rewooded landscapes, making the very fair point that only land of thin, hardscrabble agricultural potential is in the rewilders’ sights. His vision of an alternative future for these marginal farmers, however, is one of subsidies and diversified income streams (which, it turns out, means yoga studios and ‘forest bathing’). In general, here, the pursuit of profit in natural resources is regarded as plunder. Shrubsole reports that a mid-20th-century forester, in a book chapter headed ‘What Foresters On Private Estates Are Trying To Do’, wrote that fundamentally the aim ‘is to make money in a useful industry’. We are expected to clutch our pearls in horror.

But there is no denying the history of greed, folly and misguided priorities – a history as long as our species has lived on these islands – that has brought our rainforests to their current predicament, and no doubt that Shrubsole’s intent and ambition are to be applauded. The writing here is mostly workmanlike (maps are always to be ‘pored over’) and stitched together with the well-worn thread of, in the words of the critic Ben Thompson, the ‘Bogus Quest Narrative’ (‘I had to know more’; ‘I felt like I’d hit a dead end’), but Shrubsole covers a lot of ground and writes intelligently on temperate rainforests in Tolkien, Wordsworth and the Mabinogion.

Even if you don’t find yourself supporting Shrubsole’s restoration agenda, it’s hard to read The Lost Rainforests of Britain and not conclude that something substantial must be done, and quickly. If not rewilding, then what?