Miyawaki Forest – Do Mini-Forests Really Work?

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Robert Pavlis

Miyawaki mini-forests are becoming more popular and even my own town has put one in. Is this another environmental fad or does this type of reforestation really work? Let’s have a look at the process and the science to see if the Miyawaki method is a better way to build forests.

Dark forest with the name Miyawaki Mini-forest
Miyawaki Mini-Forest, source: reNature

What is a Miyawaki Forest?

These forests are created by following a special method developed in the early 1970s by the late Japanese forest ecologist Akira Miyawaki. The planting method results in fast growth, limited maintenance and a significant increase in biodiversity. It is a good way to rehabilitate unused urban land that has been degraded. It’s proponents claim that it results in a better forest ecosystem than other ways of creating a forest and the method is becoming popular on a global basis. Urban Forests, a proponent of the method, claim that “over 2000 forests have been successfully created using this method“.

The claims for these forests include:

  • They grow 10 times faster
  • They’re 20 times more diverse
  • Plant density is 30 times higher

Trees, in temperate regions, normally grow at between 6″ and 12″. If they grew 10 times faster they would grow between 5 and 10 feet per year. That does not happens, so clearly the first claim is wrong. Even Akira Miyawaki disputes the claim by writing “In about three years the trees grow 6 to 9 ft high (2 – 3 ft/yr). The trees in these forests do grow faster than in other reforestation methods, but at a rate more like 3 times faster, not 10.

Diversity depends on what is planted. You can plant a diverse collection of native plants without following the Miyawaki method and still attain a high level of diversity. The claim of 20 times more diverse is quite ridiculous. As the forests mature and the trees become larger, they produce a lot of shade due to the close planting. The groundcovers and understory plants die out, except at the  edges of the forest. So as the forest matures, the initial planted diversity drops significantly.

Compost Science for Gardeners by Robert Pavlis

Is the plant density 30 times higher? It is unlikely, but it is more dense than most other plantings in the first couple of years. Over time, the density starts approaching the density of a normal forest.

Some of the claims for these mini-forests are clearly overstated.

The Miyawaki Method

left panel with several shovels in flat ground, right panel, dated 4 years later showing shrubs and small trees
Before and after shots of a 3 year old mini-forest, source: Urban Forests

Akira Miyawaki was studying forests in urban areas of Japan and noticed a lot of unused land. Unfortunately, the area of each parcel of land was small and the soil was generally in poor condition so he developed a system for remediating the soil and forming a rapidly growing forest. This method with some modifications has been adopted in many countries and follows these basic steps.

Select a Site

A site is selected so that it will not be modified by human activity for a long time. It therefore needs to be excess land that is not currently being used.

Determine a List of Native Species

An important step in this method is the selection of native species. The idea is to use plants that grow at various heights. It includes groundcovers, understory plants, shorter woody plants and finally the taller trees. They are all planted together to form a complex ecosystem with lots of variation. They are also selected to be compatible with one another. This diversity of plants attracts a wider range of other organisms, such as birds, animals and insects.

There is also interest in following the concepts of Potential Natural Vegetation (PNV), which tries to match plants to the long term potential of the land.

Improve the Soil

Many reforestation projects use the existing soil, but the Miyawaki method includes a soil remediation process where large amounts of organic matter are added to the soil. This allows the plants to get established with minimum casualties and flourish. The organic matter also jumpstarts the soil ecosystem and it holds more moisture for the plants.

Plant Saplings

As is common with most reforestation projects, the method starts with smaller sapling. Such plants are less expensive but more importantly, they establish much better than larger trees.

Mulch Well

Mulch is a critical step. It holds moisture and reduces the amount of maintenance required.

Manage for a Few Years

Most of the reports about establishing min-forests say that maintenance needs to be carried out for about 3 years. This includes watering and weed control. After that the forest can be left on its own.

Benefits of Forests and Mini-Forests

If you read through the claimed benefits of mini-forests you soon realize that they apply to both regular forests and mini-forests. For example, the following are commonly listed benefits.

  • Remove carbon from the air and store it in soil.
  • Increase the level of organic matter in soil.
  • Build a better soil ecosystem.
  • Increase the biodiversity of plants, animals, birds and insects.
  • Reduce air temperatures at ground level.
  • Generate oxygen and improve air quality
  • Purify ground water.
  • Reduce erosion.
  • Lesson impact of floods and storms.
  • Rapid Growth.

With the exception of the last item, rapid growth, all of these things are true for mini-forests as well as other forests.

Reforestation can be done in a number of ways. A lot of this is done with monocrop plants where a large area of land is covered with a single species of tree and over time a forest develops. This type of forest provides some of the above benefits but it doesn’t increase biodiversity as much as a Miyawaki Forest.

Other reforestation methods include a more diverse planting and these will provide most of the benefits described above but it might take longer to achieve them.

What Makes Miyawaki Forests Unique?

Other reforestation techniques can and do use native species. They can and do amend soil. So what is unique about this method? It is the close planting. No other reforestation method uses the plant density that is used for these mini-forests.

I’ll use the example of my home town. They took an area of 5,400 sqft (500 sqm) and planted 1,300 native trees, shrubs and groundcovers using 56 different species. Such an area is only large enough for 3 fully grown trees.

The History of Mini-Forests

The concept was started in Japan by Akira Miyawaki in the 1970s. The work was noticed by Shubhendu Sharma in India who became fascinated with the concept and felt that it could be of great benefit to his homeland. He modified and improved the method through a new company called Afforestt. They introduced the concept into Europe where it was recently adopted in the UK, The Netherlands, Belgium and France.  According to its website, Afforestt has planted 450,026 trees in 44 cities across 10 countries. The history of the movement is well documented in the book, Mini-Forest Revolution, by Hannah Lewis.

More recently mini-forests have been started in North America and several Asian countries. Even Japan is planting more of them.

In reviewing the history of this method it became obvious that although it is becoming more popular, most of the plantings are quite recent. Many have been planted in the last 15 years and there are few old growth mini-forests that are well documented.

The Science of Mini-Forests

What does the science say about Miyawaki forests? Do they work?

I looked for research studies that have evaluated this technique but found very few. I talked to the staff at Guelph to see if they had done a review of such studies before implementing the forest. They hadn’t and did not know of any studies. I also contacted Green Communities Canada which is promoting the forests across Canada. Neither they nor their consulting partners have any studies.

An extensive review of the mini-forests in Belgium has been done, but this review does not compare this method to other reforestation methods. The only conclusion you can reach from it is that this method creates forests, that forests have the above mentioned benefits when compared to non-forest areas. But there is no evidence that the mini-forest method is better than other reforestation methods. Similar conclusions are reached by evaluations that were done by The Netherlands by Wageningen University.

forest and meadow showing temperatures, forest is cooler than the meadow
Belgium mini-forest review concludes that forests are cooler than meadows or gravel, source: Urban Forests

A study in Malaysia compared 18 year old Miywaki forests to natural forests and concluded that the trees in the new forest did grow faster and they seemed to sequester carbon faster, but supporting data is limited.

A research paper by Akira Miyawaki himself declared, “We have proved that it is possible to restore quasi-natural multi-stratal forest ecosystems in 20 to 30 years if we take the ecological method”. It does show that some 550 mini-forests have been created in Japan and Malaysia, but it presents no evidence that these are similar to natural forest ecosystems. They might be, but the study does not show that they are similar and even Akira uses the term “quasi-natural”.

Statements such as, “The result is a densely packed pioneer forest that grows in 20 to 30 years instead of taking 150 to 200 years” are not supported by any science I found. A mature 200 year old oak will simply not be developed in 30 years!

This phenomena has taken hold and is being adopted in many places without any clear evidence that it works better than other methods.

Not Everyone is Sold on Them

The Miyawaki method assumes that all ecosystems are the same and that provided native species are selected, the resulting forest will be a natural forest. It does not take into account local ecosystem differences. In an extreme example, a mini forest in a semi-arid area produced a planting that did not resemble the native ecosystem. Two ecologists, Fazal Rashid and Somil Daga, visiting a three-year-old Miyawaki native forest had this to say, “Plants comfortable in deep, moist situations dominated the canopy. The rest, at least the ones we managed to identify through the thicket, were hunkering below, assuming lanky forms, unlike anything we’d seen in natural open situations. This was straitjacketed wilderness at its worst: a veritable botanical zoo, but a badly designed one that created neither beauty nor allowed plants to express their real character. Here they were, the caged plants, packed like sardines. The ironic thing about the Miyawaki system is that it’s wildly unreasonable, illogical and inappropriate. But it seems like we live in wildly absurd times where common sense is no longer common.”

Does the Miyawaki Method Work?

There is no doubt it builds forests and therefore it adds all the benefits that accompany a new forest. But that is not the question that should be asked. As discussed above, the thing that makes these forests unique is the very dense planting. The real question that needs to be asked is, does this dense planting produce benefits over and above a less dense planting?

For example, the planting in Guelph uses 5,400 sqft (500 sqm) of space for 1,300 native trees, shrubs and groundcovers. What if that same number of plants were planted in 10,000 sqft? Would the forest grow as well? The cost would be about the same but the size of forest would be much bigger. If this larger forest provides the same degree of diversity, same number of organisms, same amount of water purification etc., then the close planting is not justified and the Miyawaki method does not fully work.

It amazes me that given the thousands of planted mini-forests, this comparison has not been properly tested.

One study does provide some insight into this question. Two mini-forests were planted in Italy, in a dry Mediterranean climate, and each was planted with a different density of trees. These two areas were also compared to two adjacent forests that had been planted in more traditional ways.

Table showing results from the Italy study
Study looking at tree planting density, source: Effectiveness of the Miyawaki method in Mediterranean forest restoration programs

Sites A and B are 12 year old mini-forests. Sites R15 and G15 are traditionally planted and their age is not specified. Site B used the dense planting similar to the Miyawaki method while site A used a density of about 1/3 as much. The rate of 21,000 trees per hectare is actually on the low side for this method which is normally in the range of 20,000 to 30,000. For example, the mini-forest in Hamilton, Ontario was planted at 30,000 trees per hectare.

One of the main overstory trees in the area is the maritime pine (Pinus pinaster) and the study has the most data for it. The results show that a more dense planting resulted in higher mortality and contrary to claims for this method, lower density resulted in taller maritime pines.

Did the dense planting of the Miyawaki method work? Not in this case. Dense planting had more mortality and shorter trees.

We know that dense planting does not grow trees with a normal structure. They end up being tall and thin with almost no lower branches. It is surprising to me that this method has become as popular as it has, given what we know about tree growth and the very limited number of studies that have examined such dense planting.

The Value of Mini-forests

Many of the concepts in the Miyawaki method are valid and when followed will make a good forest, including selecting native plants, using different types of plants, preparing the soil and allowing the forest to mature on its own.

It is also accepted that growing more forests on vacant land is good for the environment and for local plant and animal diversity. That is not being disputed. The idea of mini-forests are getting people to plant more forests and that may be the real value of this revolution.

However, I think it is important that we question the real difference in this method, namely planting close together. The evidence does not support that part of the method. At the very least, I would encourage any future plantings to be split into two simultaneous tests. One with the traditional spacing and the other with a more generous spacing. The two forests can then be compared over time. This is the only way we can tell if the spacing works.

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Robert Pavlis

I have been gardening my whole life and have a science background. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

3 thoughts on “Miyawaki Forest – Do Mini-Forests Really Work?”

  1. There are scientific journals that cover reforestation, I wonder if there’s anything published on this. The letters page of one such would be a great place to put a call for long-term monitoring of the technique, ideally with control plots as you say. A standard methodology to be used by all practitioners would be good. But first, one would have to do a search and maybe consult a reforestation expert, to make sure it’s not already under way.

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  2. My initial reaction was – what a mess! I still think it’s a waste of plants to plant this close together. I read about the site in your town and they planted things like raspberries alongside trees that get big. I think those raspberries will spread like crazy the first couple of years and then the trees will shade them out, if the trees live. I would love for you to do a follow-up on the mini-forest near you in a couple of years so we can see how it matures.

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  3. Another great article.
    I have been reforesting a small land area over the last 9 years. I’m in NewZealand. The land is 3000 sq m of steep dry clay. It was covered in exotic plants and invasive weeds. The first step was to clear it.
    I have planted a range of natives which would occur naturally here. I would plant no closer than 1m apart. 1.5 to 2m is the general rule. I use cardboard tree collars for protection. From what i can see the miyawaki method plants at around 0.5m.
    I would not plant species which grow on the margins where they will be shaded out by large trees. I would not plant some species at all until smaller trees have grown to provide shade. Harsh sunlight would otherwise kill them. I have deliberately planted fast growing nursery species which provide quick cover and attract birds. This gives conditions to encourage native species to self seed. This is working very well. Plants find their own optimal positions and spacings.

    I do not feed young trees. It encourages weeds such as grasses which stunt growth. Native trees are well adapted to local conditions.

    I am maintaining the plantings by removing invasive weeds. For the first two years I used irrigation but only in small selected areas which really needed it. Water is a precious resource.

    Plants are expensive and require resources to grow and plant. It seems wasteful to plant densely when you know that many plants will die. It seems wasteful to plant trees in shade when they thrive in light, and vice versa. How can you expect forest ground cover to flourish when you don’t yet have a forest?

    You could plant at half the density and donate the other half of your plants to a community who can’t afford to fund their own forest but have unused land.

    Ultimately forests grow in stages. Primary growth sets the conditions for secondary growth which leads on to mature tertiary growth. This takes decades if not centuries. We can help the process along but the shortcuts are limited.
    I don’t think that reforestation is a pursuit for those looking for instant gratification.
    Chris from Nelson NZ

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