Miyawaki forest at Kasuga Shrine in Japan

Dear Readers, in my British Wildlife magazine this month Peter Thomas describes the rise of the microforest – 6 have been planted in the Lichfield area alone, and 21 are planned in Middlesborough. These are forests, sometimes only a few metres square, which are planted extremely densely, which encourages competition and results in rapid growth and, over time, the development of a dense and biodiverse understorey.

The method was developed by Japanese botanist Akira Miyawaki (1928 -2021)who was especially interested in the reforestation of degraded land. Firstly, the soil in the area to be reforested is improved with whatever organic matter is available, from coffee grounds to old woolly jumpers to manure to waste vegetable matter. The method also recognises the importance of mycorrhizal fungi, which are added to the substrate. Then, native trees and shrubs are planted as densely as possible – typically between two and seven trees per square metre (even more densely in tropical regions), echoing what would happen in nature when a clearing appears due to a tree dying, or on the edge of a woodland. Thomas lists the species planted in a three year-old forest in Oxfordshire as being Goat Willow, Field Maple, Silver Birch, Dogwood, Guelder-rose and Hazel, with some Elder and Apple trees. The downside is that survival rates for individual trees are very low (possibly as low as 15%), but the thinking is that within a decade the forest will be up to 30 times denser than a conventional mixed-species plantation.

During his lifetime, Miyawaki was involved in the planting of almost 1300 mini forests across Japan and neighbouring countries, but his method has been taken up all over the world – in the UK, Earthwatch Europe plans to develop five hundred urban ‘mini-forests’. The method is especially suited to degraded environments, and so a ‘pocket forest’ can easily spring up where a house has been demolished, or where there is a small area of unused ground. You can see an interactive map of the tiny forests planted by Earthwatch so far here. Sadly none in London (yet) so I shall have to make a special pilgrimage to check one out (though I do note that London Borough of Barnet, my local council, is one of the sponsors, so maybe one will arrive soon).

Witney Tiny Forest 17 months after it was planted (Photo by Whitney Tree Keepers from https://earthwatch.org.uk/component/k2/witney-tiny-forest)

Of course, there are also criticisms of the Miyawaki method. The first one that springs to my mind is the sheer waste of seedlings – why plant so many if so few of them will thrive? However, the whole point of the method is that the sheer competition means that trees will grow quickly, sequestering carbon as they go. In a ‘real’ forest, only a tiny proportion of the trees will ever grow to adulthood, so perhaps my dislike of ‘waste’ is clouding my judgement here.

Further criticisms seem to be based on implementations where the basic premise of only using native trees has been ignored – species that have no natural predators or competitors will often outrace native trees that are already an integral part of an ecosystem. An interesting article about the use of Miyawaki forests in Chennai points out that the city has mainly slow-growing palm trees and mangroves rather than dense deciduous forests, and points out that the native wildlife is attuned to Chennai’s natural habitats.

Another criticism is that the cost of a Miyawaki microforest can be high, what with the soil preparation and the number of viable young seedlings that are required.

There is a sense that lots of people have jumped on the Miyawaki bandwagon – as in all fields, there are ‘flavours of the month’ in conservation, and in many ways this looks like a no-brainer – tiny, fast-growing forests in environments that would otherwise be concrete wastelands. In the right place, with the right plants, Miyawaki forests seem to be oases of peace and biodiversity. However, there is also a real need to protect the native forests and street trees that we have in urban areas and beyond – a forest that has grown up over generations will have a range of interactions with its local ecosystem that a microforest won’t achieve for many years, and as I mentioned in my ‘Tree of the Year’ post last week, a single mature elm tree can form a habitat for a rare butterfly all on its own. However, there is evidence that the microforests, because they’re young, will attract a different range of insects and birds to the established forests, thus increasing biodiversity overall. There is no single answer to the problems that we face – climate change, biodiversity loss and pollution – but I applaud any attempts to restore nature and mitigate global heating. It will be interesting to see how the Miyawaki forests thrive in the UK. I look forward to reporting back in a decade or so.

If you have Miyawaki/miniforests in your area, do let me know how they’re doing, and all opinions welcomed, as usual!