NAIROBI, Kenya — Many African cities are now characterized by deafening traffic noises and suffocating gas emissions, and are becoming limitless concrete jungles as urbanization takes hold and human settlements squeeze out natural forests.

But, in Kenya’s capital city of Nairobi, a unique restoration technique known as the Miyawaki method is restoring local ecosystems, which have been lost due to urban sprawl and competing needs, by creating forest islands in urban areas.

The technique, which is a unique approach to afforestation and ecological restoration, was developed by Japanese botanist Akira Miyawaki.

To illustrate the extent of the loss of green space, according to the Nairobi-headquartered International Livestock Research Institute, Nairobi’s forest cover decreased from 14% to 3% between 1976 and 2000. Additionally, bushland cover decreased from 22% to 13% during the same period.

The Miyawaki technique was developed in the 1970s, with the basic objective of densifying native green cover within a small parcel of land. This involves planting degraded lands with fast growing native tree species at close quarters, which then grow quickly to form a dense canopy.

In the Kenyan experiment, a total of 16 species were selected: Schrebera alata, Rawsonia lucida, Cassipourea malosana, Vepris simplicifolia, Drypetes gerrardii, Elaeodendron buchananii, Croton megalocarpus, Brachylaena huillensis, Calodendrum capense, Ficus thonningii, Warburgia ugandensis, Olea europaea ssp. africana, Olea capensis ssp. hochstetteri, Ehretia cymosa, Markhamia lutea and Cordia africana.

The beautiful natural forest not only attracts tourists and nature lovers, but also serves as carbon sinks and improves the natural environment through water retention and biomass creation, providing ecosystem services.

“The Miyawaki method offers the best technique to create natural forests in small areas with fast growth and less maintenance costs,” says Samuel Kiboi, a faculty member in the biology department at College of Biological and Physical Sciences in Nairobi. Kiboi is part of a team of researchers spearheading Miyawaki research in Kenya.

“The method is relevant for [the] creation of natural mini forests in urban areas,” adds Kiboi, who is also an associate professor of ecology and environmental sciences.

Since 2007, Kenya’s Miyawaki project has successfully established mini forests in the country, including in three areas in Nairobi — they have planted over 236,212 seedlings.

“We have established several mini forests at the University of Nairobi’s Chiromo campus, where plantations were done between 2012 and 2018,” Kiboi tells Mongabay. “In addition, other mini forests have been done in Ngong Road Forest as well as the largest inside Karura Forest over several years.”

But, while the Miyawaki method has numerous advantages such as rapid regeneration and biodiversity enhancement among others, it has been cited as having several disadvantages, such as the requirement of a lot of resources ― labor, materials and land ― potential disruption of non-native species, a complicated process of species selection, and maintenance requirement.

“The challenges are usually that, first, one has to understand the natural species composition in that area. This is termed as the potential natural vegetation, or PNV,” says Kiboi, who made a virtual presentation to the African Forum on Urban Forests in Johannesburg in March on his experiences using the Miyawaki method to create mini forests in urban settings in Kenya.

He says that this can only be done by carrying out scientific studies in relatively undisturbed forest areas in the surrounding ecosystem. “In our case, we did this by studying vegetation structure in relatively undisturbed forest areas of Ngong, Oloolua, Ngong Road and Karura forests. It is from this data that the species selection for restoration or creation of mini forests is done.”

“The good thing is that, once the baseline data is available, successive forests in the area can be done without going through the process again,” Kiboi says.

The other challenge, he adds, is that obtaining seedlings can be difficult since most nurseries will grow what is in high demand.

“Initially, seed availability may be a challenge since one has to know when and where to get the seeds from and also know how to grow each species. Thirdly, because of the high-density requirements, the method can be expensive, but once established, the benefits far outweigh the initial costs.”

About the method being disruptive to non-native species, Kiboi explains that if the aim is to establish a mini forest with potential natural vegetation, then there is no disruption to non-native species.

“If the aim is for other landscaping aesthetics, then this is possible. However, there is no need to mix the two approaches.”

Simon Kage, director at the Kenya-based Integrated Forest Consultancy and Management Services — the company contracted by Japan’s Yokohama City University to carry the project in Nairobi and Nakuru cities, says the initial costs of the method can be prohibitive due to the sheer number of seedlings to be used.

“In a normal reforestation project, we normally use between 1,000-1,100 seedlings per hectare [2.47 acres]. But with Miyawaki, we must use between 8,000-10,000 seedlings per hectare since the seedlings must be planted very close to each other,” Kage tells Mongabay.

He notes that the maintenance costs remain very low once the forests have established. “Subsequent maintenance costs once the forests [are] established are negligible to zero because the canopy smothers all the invasive species — with only successive native species able to grow.”

The method has a beneficial knock-on effect on the local communities through the supply of tree seedlings and forest maintenance activities.

According to Joseph Kamau Machina, a resident of Karura, the project has benefited the local community immensely.

“Personally, I have supplied over 30,000 seedlings to the company since the project started a few years ago. Currently, I’m employed to weed the seedlings in Karura Forest, replace trees that have died and water them occasionally,” he tells Mongabay.

Banner image: Loita forest in Kenya. Image by Rhett A. Butler / Mongabay.