Grown using the Miyawaki method, fast-growing miniature forests in the middle of cities can bring surprisingly big benefits for people and the environment.

"It's like going on a bear hunt!"

Not quite, perhaps, but these kids are definitely excited. They are on a visit to a miniscule patch of forest in the grounds of Queen Margaret University on the outskirts of Edinburgh, Scotland, and are about to head out armed with a bucket of water, a jug and a stopwatch.

They are measuring how fast patches of soil inside and outside the forest absorb water, so we leave the small circular howff (a traditionally-built shelter with a wildflower roof) in the middle of the vegetation. The child in charge of the stopwatch does a couple of test runs and the pouring begins.

"I want you to decide when it's all gone," says Elly Kinross, the woodland and greenspace officer at Edinburgh and Lothians Greenspace Trust who is running this session for the kids. "The grass can be wet, but basically the water needs to be gone… Yeh I think that's gone. OK, good, give it a stop."

This class of eight- and nine-year-olds is spending the day in a tiny forest (known, in Scotland, as a wee forest): small tennis court-sized patches of land, usually in urban areas, rigorously prepared and planted with the makings of a fast-growing, dense native forest.

These petite patches of greenery have been springing up across the world for decades now. Japan has planted thousands; India, where the tiny forest concept was developed, hundreds. The Netherlands is a hotspot for them too, and they are also now beginning to spring up across the US. But it is the UK that has most recently seen an enormous push towards these miniature urban forests, with hundreds planted since 2020.

As I visit the site alongside these schoolchildren on a beautifully sunny spring day, I'm also on a kind of hunt. I'm trying to work out how big the benefits of foresting such tiny areas really are. As it turns out, I've stumbled onto a thorny, decades-long debate.

In many countries, including my home country of Scotland, there is now a huge effort to try to reforest large areas of land. This tends to concentrate on large, unbroken patches of land, and with good reason: such forests are critical for protecting wildlife and human health and have enormous benefits for carbon storage and water cycling.

But while smaller patches of forest have historically been somewhat dismissed as useful nature reserves, they do have benefits. One big plus is that they are easier to fit into an urban area – and thus be nearer to where most people live. And emerging evidence is showing we might have underestimated their benefits for nature too.

At around 200 sq m (2,200 sq ft), though, tiny forests are seriously small even compared to many urban forests. They involve around 600 trees being densely planted all at the same time in a heavily prepared soil. Ross Woodside, head of operations at Edinburgh and Lothians Greenspace Trust, the local delivery partner for this wee forest, points out to me some of the 18 different species planted here, from broom bushes to wild cherry and oak trees. As he does so, I wonder, how small a forest is too small?

This wee forest was planted just three years ago, so it's got a long way to go before its Scots pines and hazel trees become what looks like a forest. For now, though, butterflies and bees skit around the yellow gorse bushes and tree saplings.

This wee Scottish forest is grown according to the Miyawaki method to grow them. Developed by Japanese botanist and ecologist Akira Miyawaki in the 1970s, it's a way of speedily restoring native woodland on areas of degraded land. It's a key aspect of what makes these areas "tiny forests", not just small patches of trees.

The method involves randomly planting a mix of native species in a soil intensively restored with organic nutrients. All layers of a forest are planted together, with species based on an established native woodland nearby. In Scotland, for example, this might mean planting a canopy layer of tall oak and Scots Pine, a sub-canopy of smaller trees like silver birch and rowan and a scrub layer of broom and blackthorn all at once. The densely planted young trees fight for sunlight and grow faster. The result, its proponents say, is a mature, native forest in 10 years rather than 100.

Widespread in Japan, Miyawaki's restoration methods have spread across the world, from the Amazon to India. It has its

© BBC