The Mini-Forests of Miyawaki

By Julie Boudreau

Mini-forests, microforests, urban forests… so much relatively new vocabulary in our horticultural conversations. And through it all, the Miyawaki method surfaces from time to time. Let’s take a closer look at who this famous Miyawaki is and what are the main principles behind his approach to urban reforestation.

Akira Miyawaki was a Japanese-born botanist and ecologist who conducted most of his work between the 1970s and the 2000s. His work had such a great impact on ecological approaches that he received dozens of honorary awards in the environmental field. A bit like Masanobu Fukoka inspired the work leading to the democratization of permaculture, Miyawaki has, without doubt, offered important solutions for the restoration of natural forest environments. Thousands of urban forests have been created around the world using the Miyawaki approach.

The Main Principles of the Urban Forest, According to Miyawaki

The Miyawaki method consists of densely reforesting a small plot of land, using native plants perfectly adapted to the existing environment. The selection of plants generally includes three layers, namely large trees (the canopy), what could be described as pioneer species (the tree layer) and shrubs (the shrub layer). This, of course, is adapted depending on the countries and existing vegetation zones.

Another element that defines the Miyawaki method is the random nature of the plantings. We plant more or less randomly, without any precise order, trying, at the very least, to have the three strata of vegetation in relative proximity. This is why it is so interesting to involve children in microforest projects.

Also, one of the main objectives of microforests is to be sanctuaries of biodiversity. It is therefore completely natural to work as much as possible with plants produced from seeds (and not by grafting or cuttings). We thus enrich the landscape with a beautiful genetic diversity, ideal for natural selection to take place, in the face of extreme conditions and invasions of parasites.

Four Easy Steps!

The Miyawaki method is based on four main steps which form the very heart of its approach. A microforest can be created on an area as small as a thousand square feet (100 m²)

1. Observe, Analyze and Design the Future Forest

Creating a microforest requires an initial planning stage. Carry out a good soil analysis, studying the conditions of the site. Even go for a walk in the natural forests around the plantation site. These walks aim to identify which native species are already growing in this territory. If the site is in a highly urbanized area, research will be done to find out what historically grew there.

It is with this palette of plants that we will design the new forest. Taking into account the quality of the soil and the conditions of the site, we will choose around thirty species, all native and distributed in the different strata of vegetation.

The analysis stage can also be used to identify invasive exotic plants: those that we do not want to see appear in our project. This information will be useful for the maintenance phase of the project.

2. Prepare the Ground

In order to stimulate good root development and increase the chances of survival of young trees, the soil will be generously enriched. A generous amount of compost, manure or natural fertilizers will be applied. Depending on site conditions, the soil is sometimes tilled to lighten it.

Miyawaki quickly understood that the quality of the soil was an important condition in the success of these plantations. We are looking for maximum fertility here.

3. Plant Densely and Randomly

As mentioned above, there is no real plan for planting in a microforest , except when site conditions vary greatly from one area to another. In general, arrive with all the plants and go there at random. Try as much as possible to alternate between large trees, smaller ones and shrubs, so that the three layers cover the entire surface.

We must emphasize the importance of working with native species. The microforest wants to get as close as possible to what it would look like if it were natural and spontaneous. The very concept of microforests invites us to plant very young plants, approximately one or two years old. These are planted close together, at a ratio of approximately 3 plants per square meter. Yes, the plants are packed, but that’s intentional.

Do not expect all of these plants to survive. The idea behind these dense plantations is to reproduce a form of healthy competitiveness between plants. This competition promotes height growth. This planting density also has a very important advantage in the maintenance phase. If plants quickly cover the surface of the site, this leaves less room for weeds and unwanted plants. Since smaller plants are more economical, a certain compensation is obtained which absorbs the expected losses. It is estimated that between 61% and 84% of what is planted will disappear. All this is intended.

Planting is completed with a thick layer of straw or organic mulch. Also, on all the projects I have observed so far, the microforest is surrounded by a barrier or a fence. In rural areas, it could protect the young plantation from grazing quadrupeds. In an urban environment, it is to protect the trees from small and large humans!

4. Maintenance Leading to Self-management

This step is absolutely crucial to ensure the success of the project. Left completely to their own, small trees will be overrun by weeds and invasive plants will take over the plot!

This is why these projects very often include 2 to 3 years of maintenance following planting. Once or twice a year, we control growth around the small trees, pull out large weeds and control invasive plants. In southern Quebec, we will closely monitor the arrival of undesirable plants such as the Siberian elm (Ulmus pumila), Norway maple (Acer platanoides), common buckthorn (Rhamnus cathartica) and glossy buckthorn (Frangula alnus).

This sustained maintenance will allow native plants to develop well and quickly cover the entire surface. Thus, we arrive at a point where the forest manages itself. The least adapted species will be expected to disappear. Sick or damaged plants will leave more room for their vigorous neighbors.

Too Good to Be True?

To some, Miyawaki’s approach seemed revolutionary. Many people have praised his work. Of course, some critics have also raised.

For example, it is claimed that the microforests created by Miyawaki are not real forests. On this point, we can only agree. It is literally impossible, in a disturbed environment, to recreate to perfection what nature took centuries, if not millennia, to create. However, we must admit that these naturally artificial (or artificially natural) forests are a very good premise for the establishment of an environment which will gently and slowly tend towards a true forest ecosystem. After all, how many beautiful ancient forests are the results of abandoned fields?

We often praise the astonishing speed of growth of microforests , going so far as to say that they grow 10 to 20 times faster than spontaneous forests. This is based on the fact that competitiveness between densely planted plants forces trees to grow taller faster. Everyone struggles for brightness. However, there is little research that validates the speed of growth.

Also, some detractors claim that Miyawaki did not invent anything. Already in the 1950s, the German Reinhold Tüxen was exploring “potential natural vegetation”. There is a correlation to be made between these two approaches and Miyawaki was indeed invited to Germany to participate to the work of Tüxen.

Nonetheless, there are many decades-old microforests all over the world that have proven their merit. They have become islands of greenery in disturbed environments. And they provide all the ecological services expected of forests, such as purifying the air, carbon sequestration and countering the harmful effects of heat islands. Microforests are fascinating laboratories for better understanding the main principles of natural selection and resilience.