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Forest regeneration in urban areas: planting green forests as close to nature as possible | nippon.com

Vegetation ecologist Akira Miyawaki argues that reforestation should be accompanied by scientific data to map what forests will look like decades from now. The researchers who took Kaoru Miyawaki told us about the importance of creating forests in cities to protect the environment.

Today, when the era of global warming is said to have become familiar with the terms carbon neutrality and carbon offsetting, the ideal form of “green” is receiving more attention than ever before. It is said that due to the disappearance and destruction of satoyama, the forested areas left unattended and becoming more forested due to changing lifestyles, Japan’s current forest area is more saturated than ever. However, in urban areas with concentrated populations and increasing residential land use, green space is extremely scarce. In this case, I want to think about what kind of green is needed.

Vegetation method based on massive data of vegetation survey

Here, as an example of urban greening maintenance, I would like to consider the reforestation of urban areas using the example of “Environmental Forest” by Professor Emeritus Miyawaki Akira of Yokohama National University. Sadly, the teacher passed away in July 2021 at the age of 93. Pray for everyone and introduce the environmental protection forest afforestation advocated, guided and vigorously carried out by the teacher.

Professor Miyawaki is also a well-known vegetation ecologist, and served as the president of the Ecological Society of Japan. “Japanese Vegetation Magazine” has a total of 10 volumes. It has been extensively investigated at home and abroad, and it has compiled massive domestic data, which is an unprecedented achievement. Make full use of massive data for the formation of green forests.

Environmental protection forests have been introduced in vegetation survey reports, papers, and many books since the 1970s. In addition, a detailed explanation of the International Research Center of the Institute for Global Environmental Strategies (IGES) headed by Professor Miyawaki.“A Brief History of Deciduous Tree Environmental Protection Forest Research” has been published.

In 1972, as a greening of the factory of Nippon Steel (now Nippon Steel) Oita Works, the tree planting of the eco-friendly forest began, but as part of environmental improvement, it was gradually expanded beyond the factory. The name “Furusato no Mori”, which is still in use today, was used by Professor Miyawaki from the very beginning. In 1974, he compiled “Plant Sociology of the Formation of School Environmental Protection Forest: Based on the Field Vegetation Survey of 158 Schools in the Country”, and in 1976, an environmental protection forest was created in the campus of Yokohama National University.

The process of forming a school environmental protection forest near the main entrance of Yokohama National University.  1. A simple earth retaining wall built with exotic flowers and plants on a 2-3 meter wide slope.  2. The remaining soil in the city is used for soil seed dressing, and potted seedlings such as castanopsis, oak, and oak are mixed.  3. It grows taller in the third year after planting, reaching a height of 3 meters.  4. More than 10 years later, the tree has grown to over 10 emails (Photo courtesy of Akira Miyawaki)
The process of forming a school environmental protection forest near the main entrance of Yokohama National University. 1. A simple earth retaining wall built with exotic flowers and plants on a 2-3 meter wide slope. 2. The remaining soil in the city is used for soil seed dressing, and potted seedlings such as castanopsis, oak, and oak are mixed. 3. It grows taller in the third year after planting, reaching a height of 3 meters. 4. More than 10 years later, the tree has grown to over 10 emails (Photo courtesy of Akira Miyawaki)

Since then, it has spread to various places, and recently it has been working on the establishment of tidal forests in the tsunami-affected areas of the Great East Japan Earthquake. In the past 50 years, about 900 sites in Japan and more than 300 sites in Southeast Asia, Amazon, Chile, and China have been planted with environmentally friendly forests.

Creation of plantation forests close to natural forests

The idea of ​​creating an environmental protection forest is to identify the natural vegetation (potential natural vegetation) of the land and, based on its constituent species, create a plantation forest that is as close as possible to a natural forest. It features random dense planting of seedlings of natural forest constituent tree species with various proprietary technologies listed below.

1. The original tree species on which the land was planted

The most important point is the selection of tree species from the constituent tree species of the natural forest. In urban areas where no natural forest remains, select “potential natural vegetation”. Potential natural vegetation is the judgment of natural vegetation on land based on vegetation research results, land use characteristics and location environmental characteristics. At that time, the ancient giant trees in the area and the shrine forest that served as the guardian forest were clues. Recently, in the abandoned Satoyama, evergreen broad-leaved trees such as white oaks and castanopsis have been regenerated, and it can be said that these forests are also potential natural vegetation. In addition, since it depends on various conditions such as climate, topography and soil, it is necessary to judge according to the planned planting site. Plant tree species, according to the local environment, try to choose tall tree species, medium tree species, shrub species, etc. Recently, about 40 species have been planted.

2. Seeds from native species

Seeds for planting tree species are collected from native species around the planned site to grow seedlings. Castanopsis, oak, oak and other trees are often left in old villages and houses to plant the seeds of these trees. In addition, from the perspective of preventing gene damage, it should be noted that the current guidelines stipulate that the introduction of genes from different regions should be avoided. Local production for local consumption is also important for tree planting.

3. Growing in Vinyl Pots

The collected seeds are germinated in toro boxes and then transplanted into multiple pots to make “potted seedlings”. A polypot is a vinyl nursery pot, usually 10.5 cm in diameter. Healthy potted seedlings filled with roots in pots have very good survival rates and growth rates after transplanting, but the choice is important because the quality of the seedlings has a big impact. Various tree species are produced by specialists, but can also be produced individually in small batches. Many organizations grow potted seedlings as part of their environmental education.

1. Transplant seedlings that sprout in Toro boxes (right) into vinyl pots.  2. Potted seedlings are maintained in a nursery in a container.  3. Take the jujube seedlings out of the pot. The root system is well developed.  4. Potted seedlings waiting to be shipped out. You can bring the transport net together (photo by the author)
1. Transplant seedlings that sprout in Toro boxes (right) into vinyl pots. 2. Potted seedlings are maintained in a nursery in a container. 3. Take the jujube seedlings out of the pot. The root system is well developed. 4. Potted seedlings waiting to be shipped out. You can bring the transport net together (photo by the author)

4. Arbor Day that doubles as environmental education

Planting is carried out by building mounds for planting under conditions such as soil improvement, usually by densely planting Class 3 seedlings at 3 or more intervals within 1 square meter, usually about 50 cm high. Since it can be easily planted with transplanting iron, even a few people can do it on a small scale. But if the area is large, a large number of seedlings must be planted and participants are invited to hold an “arbor day”. 10,000 participants planted 100,000 saplings at a large tree-planting festival 50 meters wide and hundreds of meters long.

In some cases, a group of like-minded people is born with Arbor Day, each starting their own tree planting activities. Since there are many children, it is an environmental protection activity as well as an environmental education that will lead the next generation.

Arbor Day.  1. Construction of planting mounds.  2. Potted seedlings waiting to be planted.  3. Plant potted seedlings. Various tree species are mixed.  4. After planting, spread the straw on the floor and fix it with straw rope (photo by the author).
Arbor Day. 1. Construction of planting mounds. 2. Potted seedlings waiting to be planted. 3. Plant potted seedlings. Various tree species are mixed. 4. After planting, spread the straw on the floor and fix it with straw rope (photo by the author).

5. Fertile soil promotes growth

The survival rate and growth rate of potted seedlings are high, and the afforestation is fast. Adjacent trees grow, high branches meet, the space above the forest has no gaps, wind and light do not enter, together with the straw applied at planting to prevent the soil from drying out and weeds. About 3 to 5 years after planting, weeding is no longer required, and straw and fallen leaves are eroded and decomposed, forming fertile soil for soil microorganisms and small animals to inhabit. When this happens, the green forest grows rapidly. As described by Dr. Miyawaki at 1 meter per year, it grows into a forest of nearly 10 meters in 10 years depending on environmental conditions. The green forest is planted with the constituent tree species with potential natural vegetation, and with the growth of these tree species, a forest imitating a natural forest with a height of more than 20 meters is formed.

“The Best Masterpiece of the Forest” Meiji Shrine

In large cities such as Tokyo and Osaka, the population density is high, the houses are dense, and the surface is mostly paved. Therefore, the greens represented by the forest are extremely thin. Active tree planting can also help alleviate the heat island phenomenon. In addition, it also shows high disaster prevention effect against house collapse and fire spread caused by major earthquakes. Therefore, attention should be paid to the development of environmental protection forests in urban areas from the perspective of disaster prevention.

The forest of Meiji Jingu is such an urban plantation forest. More than 100 years after planting in 1920, there are many reports about the excellent forest functions in the vast forest, which can be said to be a veritable “forest masterpiece” created by human beings. In modern times, however, building such a vast forest would be difficult.

Therefore, instead of regenerating a large forest in one place, it is better to arrange small-scale forests with disaster prevention, sound insulation, climate mitigation functions, and high biodiversity in various parts of the city. It scatters the miniatures of the Meiji Jingu Forest. One of the most suitable ways to achieve this is the Environmental Forest Law.

From potted seedlings to environmental protection forests (in the Higashi-Ogishima Thermal Power Station in Kawasaki City, Tokyo Electric Power Company). Immediately after planting.  In the 1980s, I planted one plant per 1 square meter. After that, it was densely planted on three trees (left) over time. Eco-friendly forest 10 years after planting. The trees are not very tall, but they form a dense forest (Photo credit: Akira Miyawaki).
From potted seedlings to environmental protection forests (in the Higashi-Ogishima Thermal Power Station in Kawasaki City, Tokyo Electric Power Company). Immediately after planting. In the 1980s, I planted one plant per 1 square meter. After that, it was densely planted on three trees (left) over time. Eco-friendly forest 10 years after planting. The trees are not very tall, but they form a dense forest (Photo credit: Akira Miyawaki).

Banner photo = Environmental protection forest in Nippon Steel Oita Works. The saplings planted in 1972 have grown into a forest surrounding the factory after about 50 years. Taken in 2021 (Photo courtesy of Green Elm)

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