![\"Sumiko](\"https:\/\/www.japantimes.co.jp\/japantimes\/uploads\/images\/2026\/08\/09\/555578.jpg\" "\\"Sumiko")
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\n Sumiko Sasamoto and her son measure temperatures in Tokyo’s Nakano Ward on Aug. 2 as part of a citizens’ initiative to study how to increase tree coverage in the ward.
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Later, at around 2 p.m., in a shaded area of a street lined with Japanese white oak trees, temperatures were in the 36 C range both at 50 cm and 130 cm. The street felt even cooler than that thanks to good wind circulation.<\/p>\n
As extreme heat fueled by human-induced climate change drives daily highs into the upper 30s and even 40s across Japan, the presence or absence of tree canopy makes a world of difference, especially in urban areas, where asphalt roads and concrete structures absorb and radiate heat, and intensify the heat island effect.<\/p>\n
And while experts agree that urban greening is crucial to mitigating the impact of urbanization and climate change, trees are becoming even more scarce in Japanese cities.<\/p>\n
In Tokyo\u2019s central 23 wards, \u201ctree canopy cover,\u201d the proportion of land area covered by tree crowns (branches and leaves) when viewed from above, declined from 9.2% in 2013 to 7.3% in 2022, according to a study<\/a> by Kinya Shiraishi and Toru Terada, both researchers at the University of Tokyo, that was published in 2024.<\/p>\n Tree canopy cover has become one of the widely used metrics for measuring and setting urban greening targets around the world. Tokyo\u2019s 7.3% is considerably lower than other global cities, such as New York (23.4%), Paris (21%), Barcelona (25%) and Melbourne (15.3%), according to data released by each city.<\/p>\n <\/p>\n <\/a><\/p>\n \u201cConsidering that Tokyo\u2019s tree canopy cover is less than 10%, the situation is grim,\u201d Shiraishi says.<\/p>\n It\u2019s not just Tokyo.<\/p>\n According to the National Institute for Land and Infrastructure Management, as of 2022, the number of roadside trees was 6.29 million, down by half a million from the peak recorded in 2002.<\/p>\n While cities in North America and Australia commonly set numerical tree canopy cover targets, Japan has yet to adopt the benchmark. Most local governments currently use broader indicators such as \u201cgreen coverage ratio,\u201d which includes not only tree canopy but also other vegetation such as grass and shrubs, and \u201cgreen ratio,\u201d which includes even paved squares within parks and water surfaces.<\/p>\n \u201cTokyo, despite confronting rising annual average temperature and the heat island effect, has yet to incorporate urban forestry into its urban planning framework,\u201d Shiraishi writes in the paper.<\/p>\n Myriad benefits<\/p>\n On top of providing shelter from the sun, which reduces ground surface temperatures and can keep buildings cooler, reducing energy consumption, experts point to multiple benefits of urban forestry. Unlike concrete, trees hold a lot of moisture, which, when evaporated by heat, helps cool the air. Tree crowns intercept rain and reduce stormwater runoff, preventing floods, too.<\/p>\n Urban trees are known to improve water quality by absorbing pollutants such as oxidized nitrogen and reactive phosphorus from rainwater, while offsetting traffic-related carbon dioxide emissions through photosynthesis and removing ozone, a key component of smog, from the atmosphere.<\/p>\n Furthermore, urban forestry has therapeutic effects: Shinrin-yoku<\/a> (forest bathing) is known to reduce stress hormones in the blood, activate natural killer cells \u2014 a type of white blood cell \u2014 and generally improve people\u2019s mood.<\/p>\n <\/p>\n <\/a><\/p>\n \n In Tokyo\u2019s central 23 wards, \u201ctree canopy cover,\u201d the proportion of land area covered by tree crowns (branches and leaves) when viewed from above, declined from 9.2% in 2013 to 7.3% in 2022. With all of these benefits in mind, why is the tree canopy decreasing?<\/p>\n Based on satellite imagery and land-use data, Shiraishi analyzed where and how the canopy coverage is declining in Tokyo. He discovered that, over the 10 years through 2023, tree cover fell by 38% on public land and 57% on private land.<\/p>\n Residential areas saw the highest percentage of tree cover loss, with single-family houses seeing drops of 39.8%, along with roads (14.7%), educational and cultural facilities (10.8%) and parks (10.4%).<\/p>\n Many old houses in residential districts of Tokyo used to have large gardens with trees on their premises. But with the aging of many landowners, there has been a trend toward selling land to reduce tree maintenance costs.<\/p>\n Shiraishi also points out that Japan\u2019s inheritance tax rate is prohibitively high, with the maximum rate at 55%. When an occupant of a property dies, their families often have no option but to pay the tax with money gained from selling parts of their land. Since land prices are going up in Tokyo, property developers divide the land into several plots to build smaller detached homes on each, sacrificing trees in the process.<\/p>\n <\/p>\n <\/a><\/p>\n \n University of Tokyo researcher Kinya Shiraishi says that while many cities around the world, such as New York, are trying hard to stem the decline of or restore tree cover, in Japan, the legal protection of urban forestry is very weak. Many municipal governments in Tokyo encourage private homeowners with large trees to keep them by designating them as \u201cprotected trees\u201d and providing pruning subsidies and other support, such as regular checkups by arborists. But such designations are not forceful enough, and owners of protected trees can fell them without punishment if they so desire.<\/p>\n \u201cUrban trees are decreasing abroad as well,\u201d Shiraishi says, noting that redevelopment pressures remain strong in many cities. Urban environments, where roadside space is very limited, also create exceedingly harsh growing conditions for trees.<\/p>\n \u201cBut many cities, such as New York, are trying hard to stem the decline or restore tree cover. In Japan, the legal protection of urban forestry is very weak,\u201d he says.<\/p>\n Citizen effort<\/p>\n To reverse the trend, Shiraishi says the government should provide more incentives for residential owners with large trees on their land to keep them. He also believes that Japan should fully embrace the concept of urban forestry, which requires a holistic, long-term approach to growing and maintaining trees, while also maximizing their value.<\/p>\n At the same time, the negative impact of increasing tree cover in cities should be weighed as well, he says. Some people may frown on the cost of maintaining trees or the darkness that dense canopies bring, while others may suffer from allergies. Others may also dislike having the ground covered in fallen leaves or lament the bugs and birds that are something of a package deal with trees.<\/p>\n \u201cConcerns are varied, depending on individuals, communities or nations, so policies should weigh people\u2019s views (carefully), not ignore them,\u201d he says.<\/p>\n<\/p>\n<\/p>\n
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