Miyawaki - What’s that ?
The Miyawaki method, named after the Japanese botanist who developed it, is an approach to reforestation that aims to rapidly create dense and diverse ecosystems by imitating natural processes.
It establishes green oases at the heart of our cities and in suburban areas, and brings a multitude of benefits for the environment and human wellbeing. The method has solid scientific foundations and builds on a number of principles, as explained below.
The principles
The Miyawaki method involves planting young trees and shrubs that are exclusively native to the location, selected according to the Potential natural vegetation (PNV) of the region. These trees are planted very closely together to encourage natural competition as well as cooperation, thereby accelerating their growth. The canopy becomes dense very quickly because we use plants with differing sizes and spread. This encourages the development of rich biodiversity and reinforces the positive environmental impact. The method also restores life to the soil to improve its texture, fertility and water retention.
Mimicking the natural processes of forest regeneration makes it possible to create resilient ecosystems that can look after themselves and thrive without continuous human intervention. In general, we say that a microforest can sustain itself after three years. It is a technique that has been used successfully in many countries around the world.
The underlying philosophy is to encourage a better balance that links human activities harmoniously with nature. Miyawaki forests are forests for living in, integrated in the places where we live and work.
Preparing the soil
Revitalise the soil using natural additives, such as shredded mulch, compost, manure and straw for an inoculation with micro-organisms, while increasing moisture retention and aerating the soil. This preparatory work is a crucial step.
Diversity of trees
Select the plant community that best represents the primordial forest that once existed on the chosen site; plant a wide variety of species to develop the biodiversity of the ecosystem.
Planting density
Plant at high density and allow the vegetation to develop spontaneously with very little maintenance for the first two or three years. The density multiplies the expected environmental impact.
Speed is the key
A complex forest emerges more rapidly than if we rely on spontaneous regeneration.
The benefits
- Habitats for biodiversity
Microforests consist of highly diversified vegetation forming an ideal natural habitat for the region’s native flora and fauna. - An ally in the mitigation of climate change
By offering shade and encouraging evapotranspiration, microforests help reduce the ambient air temperature and create islands of coolness. - Improved air quality
Trees’ leaves trap fine particles and other pollutants in the air, cleaning up the atmosphere and reducing the impact on human health. - Soil protection
The soil is protected and absorbs rainwater much more effectively. This considerably reduces the risks of erosion and flooding, while maintaining the humidity of the soil. - A boost to human wellbein
Microforests provide places for relaxing and walking. This helps reduce stress and improve our wellbeing in general. - Better spaces for living
In aesthetic terms, microforests enhance urban landscapes and create a more harmonious environment for residents. They are a landscaping tool. - Support for education and awareness
Microforests can be used as educational aids to raise awareness among children and adults, especially in schools where we often plant them. Getting people actively involved has been shown to be particularly effective ! - Economic benefits
Microforests can be used to transform neglected plots of land into productive green spaces that benefit the environment and local residents. - Strengthening social ties
Involving citizens in creating and maintaining microforests can build social cohesion and impart feelings of belonging to a community.
How a microforest develops : in pictures
The development of a microforest is characterised by the transition from a landscape with a scattering of young plants to a more mature, balanced and self-sustaining community of plants in which biodiversity can thrive. Watch the accelerated evolution of a microforest.
The trees and shrubs are arranged randomly in the prepared ground to reflect how nature takes root without human intervention, establishing heterogeneous, organic compositions.
Plants grow vigorously to occupy the available space, rapidly forming a dense canopy. As the microforest develops, a diversity of plant species takes hold, creating a complex, interconnected ecosystem.
In time, the microforest achieves its full size and attains a dynamic equilibrium that includes continuous processes of regeneration and decomposition, ensuring the long-term survival of the ecosystem.
How a microforest develops : in pictures
The development of a microforest is characterised by the transition from a landscape with a scattering of young plants to a more mature, balanced and self-sustaining community of plants in which biodiversity can thrive. Watch the accelerated evolution of a microforest.
More details about the Miyawaki method
What does the upkeep involve ?
A microforest does require a little bit of care during the first two or three years, after which it becomes self-sufficient.
We recommend two or three interventions per year during those first years : once in spring (May-June) and another at the end of the summer (September), while some work may also be needed in July or August, possibly including targeted watering if there is a prolonged dry period.
Essentially, the upkeep of the forest entails pulling out weeds by hand, which might otherwise suffocate the trees, and leaving the weeds on the ground to decompose in situ.
This is done as part of a natural management approach, which means maintaining areas in a way that encourages biodiversity and respects local ecosystems, rather than resorting to intensive maintenance practices such as regular mowing and the use of herbicides. Unlike a lawn or a traditional hedge or shrubbery, there is virtually no maintenance required once the microforest has become self-sufficient.
In our experience, two people take about three hours to do the necessary work for the upkeep of a 300m² area of microforest.
Urban Forests provides a simple forest care handout and provides follow-up support for each microforest until it is self-sufficient.
Why do we plant trees so close together ?
We generally plant saplings per square metre, including all species of trees and shrubs. Sometimes, in places further south, we plant four saplings per square metre.
This density encourages reciprocal protection by creating a favourable microclimate. It improves the capacity of the microforest to resist wind, heat, cold and human disturbance. The closeness of the saplings stimulates their growth and accelerates soil regeneration. Some of the sugars created by photosynthesis are injected into the soil by the trees to stimulate microbial life, which in turn releases food from the soil for the trees. As such, the planting density increases the positive feedback.
Trees and plants that grow in such dense conditions tend to adapt by rising rapidly towards the light, stimulated by the intense competition. The species we choose are those that can coexist harmoniously and even support one another.
Each species grows to occupy its own place, creating several layers of vegetation corresponding to the development of a freely evolving forest. This means a large number of trees can coexist, some of them growing into irregular shapes, creating a dynamic plant space and ideal habitat for animal life.
How do you choose what to plant ?
The composition of the vegetation to be planted for the microforest is based on an analysis of the local ecosystem: climate, soil, exposure, existing biodiversity, etc.
We determine the Potential Natural Vegetation (PNV) of a site by consulting a scientific database and cross-checking this information with observations at the site. This lets us compose the best adapted plant community for the area.
We choose 20 to 30 different native species, both trees and shrubs, with the aim of creating a multi-storeyed forest. The diversity of the forest provides an extraordinary environment for biodiversity, with twisted trees that intertwine and increase the number of possible habitats for animal life.
How long does it take to create a microforest ?
The Miyawaki method reduces the time needed for a quasi-mature forest to emerge by around 20 years, compared to the 200 years it takes for natural regeneration. This is possible thanks to the preparation of the soil and the diversity of tree and shrub species planted simultaneously at the outset, which encourages a rapid succession of vegetation to produce a dense, layered forest. This helps the forest ecosystem to recover more quickly.
The plant cover evolves naturally in stages in a process of ecological succession, with layers of vegetation succeeding one another as they attain their state of full development, known as the climax, which depends on the conditions prevailing at the site. The forest is dense and diverse (in terms of tree and shrub species as well as plant size). It is a forest like this that we call a mature forest.
What results and feedback have you gained at Urban Forests ?
Of 108 sites planted by Urban Forests in temperate and Mediterranean climates, only three have failed and two have achieved rather mediocre results. This was mainly due to a lack of protection from animals (rabbits, deer), or to extremely sandy soils at the Belgian coast. All the other microforests have given good, albeit variable, results.
After having practised this method for a number of years, our team wanted some reliable and objective data about the forests’ development. We carried out a detailed study of six of our sites in Belgium, the results of which were published in 2023. This gained accurate figures on the growth rates, mortality rates, plant cover, the state of the understorey, the soils and temperatures, and the water infiltration rates. The results are encouraging! According to this study, the trees in our microforests have a survival rate of 76%.
What’s more, we’ve improved our technique over time, paying increasing attention to the standard of soil preparation, the choice of species and the right maintenance, which has further improved the results.
It is very important to avoid projects that claim to use the Miyawaki method without actually following its principles.
Is the Miyawaki method suitable for Europe ?
The Miyawaki method was developed in Japan, which is an archipelago with a multitude of very different climates, from north to south, and from coastal regions to inland mountains. It was therefore possible to test the method in all these contexts. Since then, the method has proved itself all over the world.
In Japan’s temperate climate, Miyawaki forests grow more slowly than in its tropical zones, but there is not much difference: depending on the stage of growth, the temperate forest catches up with the tropical forest in three to six years. Which is a fairly small gap in development for two such different climates. Professor Miyawaki emphasises the preeminent role of the soil rather than climate in forest development: “Field studies have taught us that it’s not climatic conditions but soil conditions that matter.” (Miyawaki, 1999; translated). Furthermore, a look at a biome map shows that similar types of forest grow in Japan and in Europe.
Our own experience and the accumulated evidence of several years in Europe demonstrate the effectiveness of the method here too. It is reasonable to suppose that our microforests will evolve in the long term to become beautiful ecosystems. There is every reason to believe that future studies will produce the same results as in Japan, albeit with regional differences that do not cast doubt on the validity of the method.
What data is available to us in Europe ?
As yet, the scientific data and publications remain limited, given the relatively recent introduction to Europe of the Miyawaki method. However, the preliminary results are very encouraging.
Voici quelques sources pertinentes :
Here are some relevant sources: A study by Urban Forest in 2023, which examined six microforests, provided accurate figures, albeit limited in terms of the number of forests. In terms of data collection and data quality, however, the measurements were rigorous and provide an accurate representation of the situation in Belgium.
Earthwatch Europe monitoring reports from 2022 and 2023 assessing the Tiny Forest programme. These provide an overview of the third season of growth of microforests planted in the UK, Ireland and the Netherlands. While monitoring 100 microforests, this report highlights findings in five areas of research: biodiversity; flood management; tree growth and carbon storage; thermal comfort and social benefits.
SUGi publishes an annual impact report that measures the human impact and provides statistical analyses of microforests. SUGi is a platform that collaborates with “Forest Makers” around the world. By early 2024, SUGi had supported, co-designed and planted 184 microforests in 40 cities in 24 countries worldwide.
Trees Outside Woodland (TOW), is an ongoing programme of evaluation as part of the National Ecological Capital Assessment (NCEA) of Great Britain. It aims to provide accurate information on the size, distribution, composition and condition of trees growing outside forests, as well as their interaction with ecosystems outside conventional woodland.
Since 2018, in partnership with academics from the Dutch Institute for Nature Education and Sustainability (IVN), Wageningen University in the Netherlands has been carrying out research on 11 Dutch Miyawaki forests . They have published their results.
Several French universities have also launched research into microforests, including Toulouse, Nantes and Metz. The United Nations supports the use of the method.
Can you share any statistics ?
Here are some important facts and figures.
Water absorption: Our own study showed that water infiltrates six times more quickly into the soil of a microforest than into a nearby lawn. Earthwatch UK has shown that, after just one or two years of growth, the infiltration rate inside a microforest is 24% faster than in areas around it.
Soil compaction : On average, soil compaction is 39% less severe in the forest than in the surrounding area.
Temperature : The average air temperature is 6°C cooler inside a microforest than outside, and the humidity is higher.
Biodiversity : on average, 37 groups of species are present in each forest. This is a lot more than the average of 15 to 30 species used to create a single Miyawaki forest at the outset.
We should, however, interpret these figures carefully. They need to be viewed in the context of their data-collection, which is not described here.
Professor Akira Miyawaki
Japanese botanist and professor, recognised around the world for his method of creating native forests. To begin with, he developed his method as a means of restoring damaged soil, particularly on industrial and urban sites. His work has shown that the planting of trees to mimic closely the composition and structure of a forest without human intervention results in rapid growth and ecological robustness.
He completed more than 2,000 projects worldwide between 1970 and 2021. In 2006 he received the Blue Planet Prize, the equivalent of a Nobel Prize for ecology.
