One City Plan goals
Bristol Tree Forum has been working hard to support the aim in Bristol’s One City Plan to double the tree canopy by 2046. Our focus has been on retaining existing mature trees on the one hand whilst encouranging the planting of new trees on the other. Increasing tree canopy is a valuable strategy towards that other vital goal of net Carbon neutrality by 2030.
The One City Plan has other goals which may be in competition with canopy increase. The most obvious is the need for more housing and the ensuing loss of existing trees and green space. As we have shown with our CO2 calculator, replacement plantings take decades to balance the loss of a mature tree.
Another conflict is with the need to tackle the problem of declining biodiversity – The One City Plan visualises that “by 2050 ..biodiversity is at a level never before seen in the city” Unfortunately that goal may well be realised, but not in a good way.
Conflict between biodiversity and tree canopy arises because, whilst an isolated tree planted in a street or open space may go on to create a large canopy, interactions with other plants are needed to create biodiversity. On the other hand, natural rewilding will generate increased biodiversity but tree canopy will be slow to develop.
The Miyawaki method
The Japanese plant ecologist Akira Miyawaki observed that ancient forests provided the greatest biodiversity but of course take centuries to grow. He wondered if newly planted areas, particularly degraded urban areas, could be engineered to grow rapidly to achieve similar levels in years rather than decades. The ‘Miyawaki method’ requires species selection to mimic the old forest, extensive ground preparation and dense planting of a large number of species. In Japan, most of the native forest had been lost or replaced by exotic conifers, so Miyawaki’s first problem was to discover the species in the original deciduous forest and grow enough of them for planting.
Miyawiki inspired a Toyota engineer, Shubhendhu Sharma to found afforestt which has developed over 130 forests in 10 countries. Shubhendhu’s TED talk sparked global interest in the idea of developing small urban areas with dense planting. In the Netherlands, IVN (Institute for Nature Education and Sustainability) worked with Shubhendu to develop the idea for temperate conditions and plant over 100 ‘Tiny Forests’ of around 200 sq m with a planting density of 3 per sq m, each with a strong educational focus.
The claim is that Miyawaki forests can rapidly achieve the level of biodiversity found in mature forest. A detailed study of the first two ‘Tiny Forests’ developed by IVN found that soil biota after only 2 years approached the level in nearby mixed forest. Animal biodiverity was also considerable, covering 176 species. A report after 5 years is expected soon. These results are impressive but need to be compared with other planting schemes for a true comparison.
The UK experience
In the UK, take-up has been much slower. A few eco organisations have started to offer support to groups wishing to develop Miyawaki forests. Earthwatch, partnering with IVN, is supporting a scheme in Witney, Oxfordshire. Sugi are involved in an ambitious ‘Forest of Thanks’ in Barking and Dagenham.
Whilst researching this topic, I was delighted to find that Bristol City Council is planning a Tiny Forest in Southmead, as part of the One Tree per Child initiative, and there is interest in creating one in Caerphilly. It seems as if this approach to increasing biodiversity AND canopy coverage is finally taking off.
Where to start
Looking round the internet, the range of organisations now promoting the Miyawaki approach or its variants is rather baffling.
For me, the best starting point are the materials generously developed especially for self-help forest makers by Daan Bleichrodt of IVN. Daan provides not only an excellent handbook but a short online course, part of which is a most helpful and honest section on the pitfalls and ways to overcome them. Beyond the technical issues of soil analysis and species selection, the support and involvement of local groups is critical: schools to help with planting, weeding and long-term engagement; citizens scientists to monitor progress; local residents to help with watering, tidying litter and keeping the place safe; the media to help with fund raising. The woodland needs to be owned by the community rather than imposed on them and of course good project management is also a necessity.
The bottom line
Miyawiki or Tiny Forests are a promising approach to rewilding urban areas and we look forward to being involved in future schemes. However their contribution to overall tree canopy is limited by their size. In Bristol, to double tree canopy from 11.9 % (from the iTree Eco study) we need to add 1,300 hectares of canopy. To achieve this by the Miyawiki method alone, we would have to plant 65,000 tiny forests, a vivid illustration of the scale of the challenge.
Chris Wallace, Bristol Tree Forum.
First published as – https://kitwallace.tumblr.com/post/637044661031141376/miyawaki-forests