A decision made 70 years ago to reforest vast swathes of Japan with just two kinds of trees has coming back to haunt the country.
70年前作出的一项决定——只用两种树为日本大片地区重新造林——如今反过来困扰着这个国家。
In February, videos showing what looked like waves of smoke blowing off an evergreen forest went viral in Japan.
今年 2 月，一些视频在日本走红，画面中看起来像是一阵阵烟雾从常绿森林上方吹散开来。
It wasn't smoke – it was pollen, and the videos were a warning to tens of millions of residents of the archipelago nation: prepare your masks and allergy medicine.
那不是烟，而是花粉；这些视频是在提醒这个群岛国家的数千万居民：准备好口罩和抗过敏药。
Every spring (which is already arriving earlier in Japan due to climate change) you'll seeing people of all ages wearing masks on the streets of cities across the country.
每年春天，你都会看到日本全国各地城市的街道上，各个年龄段的人都戴着口罩；而由于气候变化，日本的春天已经来得更早了。
The reason: hay fever, driven by all the pollen.
原因是花粉症，而罪魁祸首正是大量花粉。
Hay fever – also known as allergic rhinitis – has now become a national crisis in Japan, with an estimated 43% of the population experiencing medium to severe symptoms.
花粉症，也称过敏性鼻炎，如今已成为日本的一场全国性危机，估计有43%的人口出现中度至重度症状。
This compares to 26% in the UK and 12-18% in the US.
相比之下，英国的这一比例为26%，美国为12%至18%。
As well as the discomfort, these allergies could leading to sleep loss and poor concentration, and sufferers are more likely to experience other conditions such as asthma and food allergies.
除了带来不适之外，这些过敏还可能导致睡眠不足和注意力不集中，患者也更容易出现哮喘、食物过敏等其他疾病。
At the peak of Japan's hay fever season, the economic impact from both sick days and lower consumer spending is estimated at $1.6bn (£1.2bn) per day.
在日本花粉症季节的高峰期，病假和消费者支出下降造成的经济影响估计每天高达16亿美元（12亿英镑）。
So why does Japan have such worse allergies?
那么，为什么日本会有如此严重的过敏问题呢？
The reason has little to didn't with poor health or pollution, or even the natural environment, but decisions made by leaders more than 70 years ago in the decades after World War Two.
其原因与健康状况差、污染，甚至自然环境都关系不大，而是源于二战后数十年间领导人在70多年前作出的决定。
During the war, oil and gas shortages led Japan to turning to the nation's most abundant natural resource – forests – as a source of fuel for home and industry.
战争期间，石油和天然气短缺促使日本转而利用本国最丰富的自然资源——森林——作为家庭和工业燃料来源。
The result was widespread deforestation of natural forests, with the mountains around major cities like Tokyo, Osaka and Kobe completely stripped bare of trees.
结果是天然森林遭到大范围砍伐，东京、大阪和神户等大城市周围的山林被彻底砍光。
"After World War Two, many of Japan's mountains became barren, causing disasters in various regions," says Noriko Sato, a professor and forestry researcher at Kyushu University in Fukuoka, Japan.
日本福冈九州大学教授兼林业研究人员佐藤纪子说：“二战后，日本许多山地变得荒芜，导致各地发生灾害。”
(Bare mountains can increase the incidence of landslides and flooding).
（裸露的山地会增加山体滑坡和洪水发生的概率。）
"large-scale afforestation was carried out by public works, funded by tax revenues, to prevent soil erosion."
“为防止水土流失，政府通过由税收资助的公共工程开展了大规模造林。”
Aiming for rapid reforestation, the government chose to plant reams of only two different native, fast-growing evergreen species that could quickly reforest landscapes and provide wood for future use in construction: the Japanese cedar, sugi, and the Japanese cypress, hinoki.
为了快速重新造林，政府选择大量种植仅两种不同的本土速生常绿树种，它们既能迅速让土地重新成林，又能为未来建筑用途提供木材：日本柳杉（sugi）和日本扁柏（hinoki）。
Today, these hinoki and sugi plantation forests still cover around 10 million hectares (25 million acres) – a fifth of Japan's entire land areas.
如今，这些扁柏和柳杉人工林仍覆盖约1000万公顷（2500万英亩），占日本全部国土面积的五分之一。
The problem is, sugi and hinoki trees also produce large amounts of lightweight pollen which can easily drift into cities.
问题在于，柳杉和扁柏也会产生大量轻质花粉，而这些花粉很容易飘进城市。
It's this pollen, often released all at once from the monoculture plantations, that is responsible for most seasonal allergies in Japan.
正是这种常常从单一树种人工林中一次性大量释放的花粉，导致了日本大多数季节性过敏。
The issue has become all the worse since these trees release ever more pollen after maturing at 30 years of ageing – now the case for nearly all of them.
问题变得更加严重，因为这些树在约30年成熟后会释放越来越多的花粉，而如今几乎所有这些树都已到了这个阶段。
"Pollen allergies have become a national health issue in Japan," says Sato.
佐藤说：“花粉过敏已成为日本的全国性健康问题。”
"Addressing this problem is urgent."
“解决这个问题刻不容缓。”
In 2023, Japan declared allergies a national social problem and the central government set out an ambitious plans – reduce pollen by 50% in 30 years.
2023年，日本宣布过敏已成为全国性的社会问题，中央政府并提出了一项雄心勃勃的计划：在30年内将花粉量减少50%。
As a first step, it aims to reduce the forest areas covered with high-pollen sugi trees by 20% by 2033.
作为第一步，它的目标是到 2033 年将覆盖有高花粉柳杉树的森林面积减少 20%。
But swapping out forests covering over 2% of Japan in 10 years is a massive endeavour.
但要在10年内替换掉覆盖日本国土面积超过2%的森林，是一项庞大的工程。
Plus, simply cutting these trees down won't being enough – they also needs to be replaced with new forests to avoid soil erosion or accidentally undercutting Japan's own climate targets.
此外，单纯砍掉这些树还不够；还需要用新的森林取而代之，以避免水土流失，或无意中削弱日本自身的气候目标。
Walking through sugi or hinoki plantation forests is eerie – all the trees are the same height and there are few birds or insects.
走在杉树或扁柏人工林中会让人感到阴森诡异：所有树木都一样高，鸟类和昆虫也很少。
The ground is spongy with dry needles, and there's little light or sound.
地面铺满干枯的针叶，踩上去松软，周围几乎没有光线，也听不到什么声音。
It's a stark contrast to Japan's natural forests, which teem with biodiversity and sound.
这与日本的天然森林形成了鲜明对比；天然森林里生物多样性丰富，也充满各种声响。
With their diverse tree species like red pine, larch and maple, these forests support more of all kinds of wildlife.
这些森林拥有赤松、落叶松和枫树等多样树种，能养育更多各类野生动物。
Japan's unique geography has made it one of the world's biodiversity hotspots, but habitat loss and invasive species have led much of its unique wildlife to become increasingly at risk.
日本独特的地理环境使其成为世界生物多样性热点之一，但栖息地丧失和入侵物种已使其许多独有野生生物面临越来越大的风险。
With the monoculture plantation forests causing so many problems, it makes sense that Japan is now trying to replace them with something better.
鉴于单一树种的人工林造成了这么多问题，日本如今试图用更好的东西取代它们是合情合理的。
But it's a daunting challenge.
但这是一项艰巨的挑战。
The reason?
原因是什么？
Japan has a lot of forests.
日本有大量森林。
In fact it's one of the most forested industrialised nations in the world, with forests covering 68% of its land, a third of which are sugi and hinoki plantations.
事实上，日本是世界上森林覆盖率最高的工业化国家之一，森林覆盖了其68%的土地，其中三分之一是柳杉和扁柏人工林。
The US, by contrast, is 34% forested; the UK just 13%.
相比之下，美国的森林覆盖率为 34%；英国只有 13%。
Across Japan, forests can be found right by cities.
在日本各地，城市旁边就能见到森林。
Japanese even has a word for the transition area between city and forest: satoyama.
日语甚至有一个词专门指城市与森林之间的过渡地带：里山。
Still, even before the 2023 government declaration, some local actors and non-profits had begun efforts to turn these forests into biodiverse ecosystems, and some are already seeing the benefits.
尽管如此，早在政府2023年发布声明之前，一些地方行动者和非营利组织就已经开始努力把这些森林转变为具有生物多样性的生态系统，其中一些已经看到了成效。
The small town of Nishiawakura, Okayama, for example, has created an entire economy around reducing the 84% of its forests made up only of hinoki and sugi, turning wood into heating for eel farms as well as chopsticks and timber.
例如，冈山县的西粟仓町围绕减少当地仅由扁柏和杉树构成的84%森林，已经发展出一整套经济模式，把木材转化为鳗鱼养殖场所需的热能，也制成筷子和木材。
In 2020, Kobe, a larger port city in central Japan with a dense urban core and vast forests within its city limits, began an effort to turn more than 180 hectares (445 acres) of plantation back into natural broadleaf forests in a 15-year cycle.
2020 年，神户这座位于日本中部、城市核心区密集且市界内拥有大片森林的大型港口城市，开始了一项为期 15 年的行动，将 180 多公顷（445 英亩）人工林恢复为天然阔叶林。
Every year, an area is selectively clear-cut, removing sugi, hinoki but also other invasive species like bamboo.
每年都会有一片区域被选择性皆伐，清除杉木、扁柏，也清除竹子等其他入侵物种。
Broadleaf trees are left, and with more sun coming through to the ground, they grow back, along with other new seedlings either planted by staff or brought by birds or animals.
阔叶树会被保留下来，随着更多阳光照到地面，它们会重新生长，同时还有工作人员种下的，或由鸟类和动物带来的其他新幼苗也会长起来。
With its scheme now about halfway done, local government workers say they have been pleasantly surprised by how quickly biodiversity has returned.
随着该计划目前大约完成了一半，地方政府工作人员说，生物多样性恢复得如此之快令他们感到惊喜。
"Our wildlife monitoring is showing more animals and insects returning, including badgers, pond turtles, many species of frogs, and rare insects too, which is encouraging," says Atsushi Okada, head of the Kobe City Environmental Bureau.
神户市环境局局长冈田敦说：“我们的野生动物监测显示，越来越多动物和昆虫正在回归，包括獾、池龟、多种青蛙，以及稀有昆虫，这令人鼓舞。”
As well as addressing the pollen issue, the scheme aims to fulfil the Kobe's pledge to increase its protected areas to 30% of all land by 2030.
除了应对花粉问题外，该计划还旨在履行神户市的承诺：到2030年将受保护地区增加到全市土地的30%。
More diverse forests should also protect the city against the landslides and natural disasters poised to become more frequent due to climate change, says Daisuke Tochimoto, a forester with the City of Kobe.
神户市林务员栃本大辅说，多样性更高的森林还应能保护城市免受山体滑坡以及因气候变化而可能变得更加频繁的自然灾害侵袭。
As for the cut trees, they are used for heating, furniture production and Japanese white charcoal, a smoke-free barbeque fuel which could also be used in industrial processes.
至于被砍伐的树木，它们被用于取暖、家具生产以及制作日本白炭；这种无烟烧烤燃料也可用于工业过程。
The hope is that, over time, the project can become financially sustainable and not reliant on public funds, says Okada.
冈田说，他们希望随着时间推移，该项目能够在财务上实现可持续，不再依赖公共资金。
Similar projects are beginning in other parts of Japan.
类似项目也正在日本其他地区启动。
One project in Hotani, Osaka, is now restoring wetlands and grasslands.
大阪穗谷的一个项目目前正在恢复湿地和草地。
And the largest effort aims to turn 10,000 hectares (25,000 acres) of plantation forests in Gumna prefecture to meadows and mixed deciduous woodland.
其中规模最大的行动旨在把群马县1万公顷（2.5万英亩）的人工林改造成草地和混合落叶林。
Smaller-scale projects are also common, says Akira Mori, a professor of biodiversity and ecosystem services at the University of Tokyo, pointing to dozens of initiatives around Japan.
东京大学生物多样性与生态系统服务教授 Akira Mori 表示，规模较小的项目也很常见，并指出日本各地已有数十项相关行动。
Since the goal of removing 20% of the high-pollen sugi plantations was announced, the country has designated approximately 980,000 hectares (2.4 million acres) of sugi plantation forests as areas for focused logging and replanting.
自宣布清除20%高花粉柳杉人工林的目标以来，日本已将约98万公顷（240万英亩）的柳杉人工林指定为重点采伐和重新种植区域。
Still, not all of this is being turned into broadleaf forests: some of it is fresh plantations, often planted with low-pollen or pollen free sugi.
不过，并非所有这些土地都在转变为阔叶林：其中一部分是新的人工林，常常种植低花粉或无花粉柳杉。
Japan's ministry of agriculture, forestry and fisheries tells the BBC it plans to track the progress toward its targets for the reduction of high-pollen sugi- planted forests, but did not provide any numbers on progress so far.
日本农林水产省告诉 BBC，它计划跟踪减少高花粉柳杉人工林目标的进展，但没有提供迄今为止进展的任何数字。
Still, these efforts may not yet be large enough to make much of a difference to the pollen.
不过，这些努力目前规模可能还不够大，尚不足以对花粉问题产生多大影响。
And even if it achieves the goal, 80% of the plantation forests will remain.
即使实现了这一目标，仍会有80%的人工林保留下来。
So Japan is also trying other ways to tackle hay fever.
因此，日本也在尝试用其他方式应对花粉症。
Pollen data and forecasts, for example, are being used to better understand of where dispersion is likely, allowing authorities to selectively cut down the worst offending forests, and researchers are even looking at spraying trees with solutions to suppress pollen.
例如，花粉数据和预报正被用来更好地了解花粉可能扩散到哪里，从而让主管部门有选择地砍伐造成问题最严重的森林，研究人员甚至还在考虑向树木喷洒溶液来抑制花粉。
In 2023, one forecasting company distributed thousands of pollen-detecting robots – whose eyes going different colours depending on pollen levels – across Japan.
2023年，一家预测公司在日本全国投放了数千个花粉检测机器人，这些机器人的“眼睛”会根据花粉浓度变成不同颜色。
Medicine is another prong to the attack, with the development of new treatments to better ease the symptoms of pollen exposure.
药物是应对这一问题的另一条路径，人们正在开发新的治疗方法，以更好地缓解接触花粉后出现的症状。
One Japanese trial, for example, showed a long-acting under-the-tongue immunotherapy tablet was were still helping alleviate symptoms two years after treatment.
例如，日本的一项试验显示，一种长效舌下免疫治疗片在治疗结束两年后仍有助于缓解症状。
Other scientists have even been experimenting with genetically modified rice designed to alleviate allergy symptoms.
其他科学家甚至一直在试验一种旨在缓解过敏症状的转基因水稻。
(Read more about the new wave of effective cures for seasonal allergies ).
（阅读更多关于新一波有效治疗季节性过敏方法的内容。）
When the sugi and hinoki forests were first planted in the 1950s and 60s, they weren't meant to stand forever.
在20世纪50年代和60年代，杉木和扁柏林最初被种下时，并不是为了永远保留下去。
At the time, it was assumed they would be gradually cut down and replanted over time, as had been the case before the war.
当时，人们认为这些树会随着时间推移逐步被砍伐并重新种植，就像战前那样。
But as Japan's economy boomed in the late 60s and 70s, major cities like Kobe and Tokyo grew rapidly, and it ended up being cheaper to import wood from other countries such as Malaysia and Indonesia.
但随着日本经济在20世纪60年代末和70年代蓬勃发展，神户和东京等大城市迅速扩张，最终从马来西亚、印度尼西亚等其他国家进口木材变得更加便宜。
In 2011, though, Japan set a goal of relying less on forestry imports, and has seen its domestic wood use grow from 26% in 2010 to nearly 42% in 2020.
不过，2011年日本设定了减少依赖林业进口的目标，并且其国内木材使用比例已从2010年的26%增长到2020年的近42%。
Japan's forestry ministry says promoting the growing demand for sugi wood is another countermeasure it is taking against pollen sources, alongside improving its forestry productivity and workforce.
日本林业主管部门表示，除了提高林业生产效率和加强劳动力外，推动对柳杉木材不断增长的需求，是其针对花粉来源采取的另一项应对措施。
Of course, if Japan is going to exploit its forests, it has to avoid the same mistakes made in Southeast Asia, where cheap wood means the clear-cutting of tropical forests.
当然，如果日本要开发利用本国森林，就必须避免东南亚曾犯下的同样错误：在那里，廉价木材意味着热带森林被皆伐。
Junichi Mishiba, forest project coordinator at the non-profit Friends of the Earth Japan, worries that more incentives to cut down trees is leading to bad environmental practices.
非营利组织“日本地球之友”的森林项目协调员三柴淳一担心，更多鼓励砍树的激励措施正在导致不良的环境做法。
"There is an increase in clear-cut areas resulting from policies promoting harvesting," he says.
他说：“促进采伐的政策导致皆伐面积有所增加。”
To support its efforts to replace the plantations, in 2024 the national government began collecting a new forest environment tax of 1000 yen ($6/£5) per year on all residents.
为支持替换这些人工林的努力，2024 年日本中央政府开始向所有居民征收一项新的森林环境税，每人每年 1000 日元（约合 6 美元/5 英镑）。
The money is being used to support sustainable forestry, including reducing plantation forests and replacing older sugi with new, low-pollen seedlings, especially in urban areas.
这笔资金正被用于支持可持续林业，包括减少人工林，并用新的低花粉树苗替换较老的杉树，尤其是在城市地区。
Data on its impact is not yet available, but Mori argues the support is not enough, with municipalities often lacking the capacity and expertise to design and monitor such changes to forests.
关于其影响的数据尚不可得，但森认为这种支持还不够，因为市町村往往缺乏设计和监测此类森林变化所需的能力与专业知识。
A 2023 report by the Forest Declaration Assessment noted that in recent years, only 30-40% of Japan's newly harvested land has been replanted.
森林宣言评估组织2023年的一份报告指出，近年来，日本新近采伐过的土地中只有30%至40%得到了重新造林。
Japan's forestry ministry says that it has since improved its methodology on how it calculates this harvesting area, and now calculates the figure to be approximately 50-60%.
日本林业主管部门表示，此后它已经改进了采伐面积的计算方法，现在计算出的这一比例约为 50% 至 60%。
Good forest management will be essential, agrees Mika Akesaka, an associate professor of economics at Kobe University.
神户大学经济学副教授明坂美香也认为，良好的森林管理将至关重要。
Leaving felled trees unmanaged, for example, can increase landslide risk and reduce water retention capacity, she says.
她说，例如，放任被砍倒的树木无人管理，可能会增加山体滑坡风险，并降低蓄水能力。
Mishiba, though, fears that by focusing only on seasonal allergies rather than wider ecological indicators, Japan is once again prioritising short-term solutions.
不过，三柴担心，日本只关注季节性过敏，而不是更广泛的生态指标，这意味着日本再次把短期解决方案放在优先位置。
The country needs to think 50 or even 100 years ahead, he says, considering biodiversity, climate and the role of the people who will live alongside these forests.
他说，日本需要放眼未来50年甚至100年，考虑生物多样性、气候，以及将与这些森林共生的人们所扮演的角色。
Japan's forestry ministry tells the BBC its forest planning system "requires that forest management be carried out with due consideration for the multiple functions of forests", therefore "no harm to the performance of [these forest] functions will be done by this policy initiative".
日本林业部门告诉BBC，其森林规划制度“要求在开展森林管理时充分考虑森林的多重功能”，因此“这项政策举措不会损害这些森林功能的发挥”。
Urgency to act is also growing because of another unplanned factor – climate change.
由于另一个未曾预料的因素——气候变化，采取行动的紧迫性也在上升。
Around the world, temperature and weather shifts are impacting pollen spread and Japan saw its earliest pollen dispersal ever in 2025.
在世界各地，气温和天气变化正在影响花粉传播，而日本在2025年出现了有记录以来最早的花粉扩散。
"Pollen dispersal is greatly influenced by weather conditions such as temperature and wind," says Mai Sato, a spokesperson with the Japan Weather Association (JWA), a forecasting company which releases regular pollen forecasts to the public.
日本气象协会发言人佐藤舞说：“花粉扩散受到气温和风等天气条件的很大影响。”日本气象协会是一家向公众定期发布花粉预报的预报机构。
Japan's vast forests also themselves hold huge amounts of carbon, and sugi plantations are responsible for almost half the carbon sequestered by its forests each year.
日本广袤的森林本身也储存着大量碳，而杉木人工林贡献了其森林每年封存碳量的近一半。
Japan is leaning heavily on this carbon sequestration to achieve its net zero goal, and encourages it with a carbon credits scheme.
日本正高度依赖这种碳封存来实现净零目标，并通过碳信用计划来鼓励这种做法。
• The eccentric influence on a young Sir David Attenborough
• 对年轻的大卫·阿滕伯勒爵士产生影响的古怪人物
• Chernobyl's wildlife is different, but not in the ways you might think
• 切尔诺贝利的野生动物确实有所不同，但并不是你可能以为的那些不同。
• There's something special about Kangeroo Island's koalas
• Kangeroo岛的考拉有些特别之处
Still, since 2004 Japan has seen a declining trend in the yearly amount being absorbed which it attributes to the maturity of its forests.
不过，自2004年以来，日本每年吸收的碳量呈下降趋势，日本将其归因于森林逐渐成熟。
Research has shown that since ageing trees absorb less carbon, thinning forests of old trees and planting new, younger and more diverse species will be essential to keeping Japan's forests an effective carbon sink.
研究表明，由于老龄树木吸收的碳更少，疏伐老树森林并种植新的、更年轻且更多样化的树种，对于保持日本森林作为有效碳汇至关重要。
Japan's forestry ministry says it is thoroughly replanting sites where sugi forests have been harvested with low-pollen cedar seedlings or other tree species.
日本林业主管部门表示，它正在对柳杉林已被采伐的地点进行全面重新栽种，种上低花粉雪松幼苗或其他树种。
"Through this, we will continue to sustainably demonstrate the multiple functions of forests, including their role as a carbon sink, and contribute to Japan's climate targets," it says.
该部门表示：“通过这一做法，我们将继续以可持续方式发挥森林的多重功能，包括其作为碳汇的作用，并为日本的气候目标作出贡献。”
Before the 1960s, Japan didn't even have a word for hay fever.
在 20 世纪 60 年代以前，日本甚至没有表示花粉症的词。
Japanese cedar pollinosis was first identified in 1963 and, according to researchers at the time, was new to the country.
日本柳杉花粉症最早于1963年被发现，而据当时的研究人员称，这在日本还是一种新现象。
The hope is that with the return of more natural, diverse forests, Japan can one day go back to enjoying its springs – without the sneezes.
人们希望，随着更自然、更多样化的森林回归，日本有朝一日能重新享受春天，而不再喷嚏不断。
*This article was updated with a response from Japan's ministry of agriculture, forestry and fisheries on 20/5/26.
*本文于2026年5月20日更新，加入了日本农林水产省的回应。
For essential climate news and hopeful developments to your inbox, sign up to the Future Earth newsletter, while The Essential List delivers a handpicked selection of features and insights twice a week.
想在邮箱中收到重要气候新闻和充满希望的进展，可以订阅 Future Earth 新闻简报；The Essential List 每周两次推送精选专题和洞见。
For more science, technology, environment and health stories from the BBC, follow us on Facebook and Instagram.
想阅读更多 BBC 关于科学、技术、环境和健康的报道，请在 Facebook 和 Instagram 上关注我们。