A Solution to the Lack of Urban Vegetation解决城市植被缺乏的方法

The relentless spread of buildings and roads turns urban areas into heat islands， discomforting residents and exacerbating dangerous heatwaves， which are in any case likely to become more frequent as the planet warms.

高楼和道路的疯狂扩张将城市地区变成热岛，导致居民不适，加剧危险热浪强度。随着全球变暖，以上情况无论如何都有可能变得更加频繁。

A possible answer to the problem of heat is trees. Trees cool things down. Besides transpiration， they provide shade. Their leaves have， after all， evolved to intercept sunlight， the motor of photosynthesis.

针对高温问题，种树是一个可行的解决方式。树木可以降温。除了蒸腾作用，树木还提供阴凉，毕竟树叶进化出了拦截光照的特性，而光照正是光合作用的动力。

To cool an area effectively， though， trees must be planted in quantity. In 2019 researchers at the University of Wisconsin found that American cities need 40% tree coverage to cut urban heat back meaningfully. Unfortunately， not all cities—and especially not those now springing up in the world’s poor and middle-income countries—are blessed with parks， private gardens or even ornamental street trees in sufficient numbers.

然而，要想给一个区域有效降温，种植的树木必须成大体量。2019年，威斯康星大学的研究员发现，美国城市的树木覆盖率达到40%才能有效给城市降温。不幸的是，并不是所有的城市都有数量充足的公园、私人花园，或者行道树，全球贫困和中等收入国家中正在兴起的城市尤其欠缺植被。

Under the greenwood tree

绿林荫下

One group of botanists believe they have at least a partial solution to this lack of urban vegetation. It is to plant miniature simulacra of natural forests， ecologically engineered for rapid growth. Over the course of a career that began in the 1950s their leader， Miya-waki Akira， a plant ecologist at Yokohama National University， in Japan， has developed a way to do this starting with even the most unpromising derelict areas.

一组植物学家认为，对于城市植被缺乏，至少存在可以解决部分问题的方案。这个方案便是建造天然林的微型模拟物，借助生态学手段快速造林。这组植物学家的领导者、日本横滨国立大学的植物生态学家宫胁昭自20世纪50年代着手此事，他已经研究出一种方案，可以从最无望的废弃区域开始试验。

Dr Miyawaki’s insight was to deconstruct and rebuild the process of ecological succession1， by which bare land develops naturally into mature forest. Usually， the first arrival is grass. Shrubs sprout later， followed by small trees and， finally， larger ones. Incipient and mature woodlands therefore contain different species. The Miyawaki method skips some of the early phases and jumps directly to planting the kinds of species found in a mature wood.

宫胁博士的观点是解构和重建生态演替过程，即裸地自然发展为成熟林的过程。通常情况下，最先出现的是草，随后灌木发芽，接着是小树，最后是大树。因此，幼林地和成熟林地包含的物种不同。宫胁造林法跳过了早期几个阶段，直接种植成熟林地中的物种。

When starting a Miyawaki forest， those involved， who often refer to themselves as gardeners， first analyse the soil in which it will grow. If necessary， they improve it by mixing in suitable fertilisers. They then select 100 or so local plant species to deploy. These are chosen by surveying the nearby area on foot instead of relying on published guidebooks， which have a habit of being out of date or even simply wrong.

建造宫胁森林之初，参与这项工作的人——他们通常称自己为“园工”——首先会分析待种土地的土壤。如果有必要，他们会在土壤中混入适当肥料来改善土质。接着，园工们会选择100种左右的当地植物搭配种植。这些植物物种都是园工们实地调研周边区域后选出来的，没有参考已出版的指南，因为这些指南通常已过时，甚至是完全错误的。

Using a wide mix of species， not all of them trees， is important. Most plantations， having been created for commercial purposes， are monocultures. But trees， shrubs and ground-covering herbs all coexist in natural forests， and the Miyawaki versions therefore have this variety from the start. Not only does that pack more greenery into a given space， it also encourages the plants to grow faster—for there are lots of positive ecological relations in a natural forest. Vines rely on trees for support. Trees give shade to shrubs. And， beneath the surface， plants’ roots interact with each other， and with soil fungi， in ways that enable a nutrient exchange which is only now beginning to be understood.

很重要的一点是，宫胁森林中要混种各种各样的植物，而非全都种上树。大多数为商业目的而建的种植园里种的都是单一植物物种，但是天然林中树木、灌木和地被草本植物共存，因此宫胁森林从一开始就体现了这种多样性。这样不仅能在给定的空间里种植更多绿色植物，还能加速植物生长——因为天然林中存在许多积极的生态关系。例如：树木给藤本植物以支撑，还能为灌木遮荫；地表之下，植物根系之间相互作用，还与土壤真菌相互作用，以各种方式交换养分，而这一点人们才刚刚有所了解。

After selecting their species， the gardeners gather seeds and plant them at random， rather than in rows. And they plant at high density. The seedlings therefore have to fight for sunlight， so only the fastest-growing survive. Trees planted in this way can shoot up2 as much as 14% more rapidly than normal. For three years， the gardeners water and nurture their handiwork. Then it is left to fend for itself3. A couple of decades later the whole thing reaches maturity.

选好植物物种后，园工们收集种子，但不会成行播种，而是随意播种，种植密度也很高。因此，幼苗必须争夺光照，只有生长最快的才能存活。以这种方式种植的树木生长起来比正常情况下快14%。播种后的3年里，园工们会浇灌、培育他们亲手种下的植物，随后便任其自行生长。几十年后，整个森林便成熟了。

Dr Miyawaki has supervised the planting of more than 1，500 of these miniature forests， first in Japan， then in other parts of the world. Others are now following in his footsteps. India is particularly keen. In Mumbai， more than 200，000 trees are found in Miyawaki forests throughout the city and its suburbs. In Bangalore， more than 50，000. A group in Chennai has set up 25 such forests. The authorities in Tirunelveli， in the country’s south， use the Miya-waki method to create green cover in the city’s schools. Hyderabad started growing the largest individual forest of the lot， across four hectares， in 2020.

宫胁博士已经指导建造了1500多个微型森林，先是在日本，然后在世界其他地方。其他国家与地区正跟随宫胁的脚步，印度尤其热衷于此。在孟买，整个城市及其郊区的多个宫胁森林中共有20多万棵树。在班加罗尔，这一数量超过了5万。金奈的一个园工小组已经建造了25个宫胁森林。印度南部蒂鲁内尔维利当局使用宫胁造林法在当地学校里建立绿色植被。2020年，海德拉巴开始建造单体最大的微型森林，面积达4公顷。