Testing the Miyawaki method in our urban greenspaces through the Trees Outside Woodland project

Through the collaborative Trees Outside Woodland project, we have been investigating the use of the Miyawaki method in a UK local authority context to find out whether it could be a cost-effective and reliable new approach to successfully establish urban trees and maximise their ecosystem services.  

The Miyawaki methodology is based on a woodland establishment and management approach developed by Japanese botanist Dr Akira Miyawaki. Its aim is to quickly reconstruct indigenous woodlands on deforested land or areas with degraded soils, and the method has been successfully utilised in Asia for over 50 years for the purpose of environmental conservation, water retention, and protection against natural hazards.  

The method involves densely planting a wide selection of native climax tree species suited to the site into aerated, enriched soil, mulching and then maintaining the plot for two to three years, from which point minimal interventions should be made. 

Since 2021, we have planted 16 urban adapted Miyawaki method plots adjacent to comparison plots (which used standard local authority planting methods), across four English local authorities. Sites were chosen for their record of past planting failure and the poor quality of their soils.  

Paired experimental and comparison plots used whips comprising the same species mix, from the same nurseries, and were equally maintained through the first three years following planting. 

Initially, the total cost to plant the trees using the Miyawaki method was higher compared to the comparison plots. This is because it’s a more resource heavy process and around three times the number of trees are planted. However, our findings so far show a significantly greater survival in the Miyawaki plots (an average of 79 per cent) compared to the comparison plots (47 per cent), bearing in mind this was achieved during a drought in summer 2022.  

The average median cost of the Miyawaki method was £10 per survived tree, against £50 for standard practice planting methods. The higher cost of creating a Miyawaki method plot appears to have been outweighed by higher tree survival to date, resulting in a lower cost per surviving tree than in the comparison plots. Results have also shown much less cost variability per surviving tree in the Miyawaki plots, which suggests that the method is more reliable.  

Growth rates have been higher across the Miyawaki method plots. After three and a half years the trees generally resemble a dense thicket of early successional woodland, with some of the biggest trees measuring around 15 feet. All species are thriving. Some are faster growing than others, but many are flowering and producing seed already, and wildlife is making a home within the plots. Most of the surviving trees in the comparison areas are also doing well but some have been vandalised and they are significantly smaller than those in the Miyawaki plots.   

Since we planted our first experimental Miyawaki plots in February 2021, Kent County Council (KCC) has now adopted the approach as part of Plan Tree – Kent’s Tree Establishment Strategy, through which a number of small-scale Miyawaki method planting projects have been delivered across the county, with many more planned for the future. 

One of the key aims of planting using the Miyawaki method is that once the trees become established, usually after two to three years, the mini-woodland becomes stable and self-sustaining and no further maintenance is required, this can help to reduce on-going costs for a local authority. Planting at such high-density promotes rapid, light-seeking upward growth, creating a shady, humid micro-climate, and minimising invasion by light-demanding weeds. Any trees that do not survive within the plot will nurture the others as they decay. 

Since the methodology was developed for a sub-tropical Japanese climate, challenges remain for the adaptation of the method to other areas. We will not know whether the European plots will succeed for another 50 years, as the only proof of concept has been successfully achieved in Asia. The data produced from our trials is, however, adding to the growing body of research and experimentations with the methodology across the rest of the world.  

We have found that although urban tree planting can be difficult and costly, adapting the Miyawaki method appropriately to suit the challenges of individual urban sites can be an effective way to establish trees. 

The use of the Miyawaki method is growing worldwide, not only for small urban plots but also for larger scale restoration projects, where it can be used as a step towards the recovery of degraded habitats and ecosystems to help combat the biodiversity and climate crises. 

Additionally, through volunteer engagement, these projects can be used to cultivate better environmental awareness and inspire people  – particularly children – to have a more harmonious and sustainable relationship with the natural world.