中国园林·刊首语(2021-05) | 王向荣：生物多样是城市本应具有的状态

本期主题：生物多样性

生物多样是城市本应具有的状态

2020年上半年，因为一场突发的疫情，我所在的大学一直处于封闭的状态。没有了学生和老师，平时拥挤热闹的小小校园异常宁静。出人意料的是，春天过后，校园里出现了不少可爱的小动物——刺猬。刺猬本应生存在远离人类活动区域的乡野荒地和灌丛中。捷克动画片《鼹鼠的故事》中有一个场景：因为人类砍伐森林、建造城市，鼹鼠和它的好朋友刺猬失去了生活的家园，它们尝试用香肠堵住汽车排气管来保护自己的生存环境，结果却是徒劳。这个故事讲述了一个无情的事实：人类社会的发展是建立在掠夺野生动植物的生命和资源的基础上的。在人类到来以前，每一片土地都曾是野生动植物的家园，然而人类建造的城市却将许多生物驱逐出这片土地。疫情期间人类被迫收缩自己的活动空间，却不经意地促进了野生动物的回归。刺猬重新出现在高密度城市建成区中意味着城市生物多样性在一定程度上的提高，虽然这可能仅仅是暂时的。

城市生物多样性是指城市中生物的种类，包括植物、动物和微生物的丰富程度。城市是一个以人为中心的社会，城市中人口密集、高楼林立、路网纵横、车水马龙，人类活动不断挤压着本土野生动植物的生存空间。生活在城市里的人似乎已经忘记了这片土地上曾经还有丘陵小岗、丛林草滩、原野湖泽、瓜田菜园，曾经还生活着许多其他的生物，不少人以为生物多样性对于城市既不现实，也没有意义。 

事实上，城市生物多样性是保证城市生态平衡的基础，是生态系统服务的保障，在调节城市气候、维护水的自然循环和水源清洁、保持土壤肥力等方面均发挥着重要的作用。生物多样的城市才有可能成为生态系统良好、运转平衡稳定的城市。城市生物多样性也与城市居民的生活和健康息息相关。科学研究表明，与在乡村长大的人相比，童年在城市中度过的人更容易在特定的季节出现一些过敏症状。原因在于，乡村的微生物远比城市的微生物多样复杂，与在城市成长的孩子相比，在乡村生活的孩子接触了更多的微生物，他们的免疫系统经过与这些微生物的博弈，身体已经适应它们。而在城市中长大的人却没有这样的经历，在成年后，一旦遇到某些免疫系统从未接触过或不认识的微生物，就比较容易染病。 

城市生物多样性的前提是复杂多样的生境条件。尽管城市在不断建设和扩张中改变了土地原有的生态系统、水文状况和地表结构，城市中的自然空间既有限又破碎，但是要在一定程度上实现城市生物多样性却并非如我们想像的那样困难重重。从疫情期间校园里出现的刺猬来看，如果一片土地没有或少有人进入，让自然自由生长、自我维系，这片土地就会成为当地乡土植物和动物栖息的天堂。所以要实现生物多样性，城市中需要有无人进入和无人干扰的区域，让自然本身控制这片土地，让物种自主竞争、栖息繁衍。 

中国的城市中有很多大尺度的公园、绿道、水岸等城市绿色空间，承载着生态保护、市民游憩等综合功能。在这些项目中，完全可以划出一定范围的、不设任何道路和基础设施的区域，形成荒野地，放任自然过程自由发展，维护群落的自然演替状态，为动植物提供多样的生境条件和栖息地。这样的荒野不仅是城市生物多样性的重要载体，也能成为公众自然教育的课堂，让人们直观地观察和了解一片土地在没有人干扰的情况下本身应该具有的自然面貌。

在密集的城市建设区域，其实也有机会在一定程度上实现生物多样性。2年前丹麦著名风景园林师Stig Andersson曾带我参观了他新近完成的位于哥本哈根市街区及办公楼周边的6个小尺度项目。在很好地满足了各种使用功能的基础上，这些项目或是模拟当地的植物群落，创建出城市中的野境；或是通过再野化的途径，对原有的公园进行近自然化的改造，提升群落结构的复杂性和生态服务能力。所有设计都采用乡土植物，林下保留部分枯木，通过近自然的种植方式，为城市动植物提供多样的生境条件。这种低维护、可持续、接近原生状态、由自然过程主导的城市中微小的野境，促进了城市生物多样性的恢复和土壤微生物群落的构建，也使得城市更加充满了自然的气息。

Stig Andersson的实践给予我们许多启示——即使在闹市中的小尺度绿地设计，我们也应该摒弃仅仅依据人的视觉喜好和固有的审美习惯来选择植物和营建绿地的方式，因为这样的绿地生态功能极为有限。我们应该更加深入地研究地带性的生境类型， 更多地采用近自然群落的种植方式，以维持和改善城市的生态环境，为本地动植物提供适宜的生境，丰富城市栖息地类型和物种多样性，也为城市带来不断生长变化、充满自然气息的景观面貌。

当然，要实现城市生物的多样性，城市还必须具有完善的自然系统。城市需要有一张将更大区域中的森林、河湖、湿地、农田连接成一体的生态网络，这张网络能将自然引入城市，将原本破碎、独立、分散的绿色空间联系起来，为城市生物提供连续的栖息地和迁徙廊道，从而在更大的区域尺度上丰富城市的生物多样性。 

由于地理分布和气候条件的差异，不同城市的生物多样性会有各自的特点。自人类出现之始就与自然界各种生物一起竞争共生，生物多样不应该仅仅是城市的理想，更应该是城市必须具有的基本状态。

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Biodiversity is What a City Should Have

In the first half of 2020, due to the sudden pandemic, my  university was being closed. Without students and teachers, the usually crowded and lively small campus was extremely quiet. Unexpectedly, after that spring, many cute little animals like hedgehogs appeared on the campus. Hedgehogs are supposed to live in rural wastelands and shrubs far away from human activities. There was a scene in the Czech cartoon "The Mole": because humans cut down the forest to build the city, the mole and its good friend hedgehog lost their homes. They tried to plug the car exhaust pipe with sausages to protect their survival environment, but resulting in vain. This story tells a ruthless fact: the development of human society is based on plundering the lives and resources of wild animals and plants. Before humans came, every piece of land was once home to wild animals and plants, but the cities built by humans expelled many creatures from the land. During the pandemic, humans were forced to shrink their space for activities, but they inadvertently promoted the return of wild animals. The re-emergence of hedgehogs in high-density urban built-up areas meant that urban biodiversity was increased to a certain extent, although this might only be temporary.

Urban biodiversity refers to the abundance of biological species in the city, including plants, animals, and microorganisms. The city is a people-centered society, densely populated, with tall buildings, road networks, and busy traffic, and human activities continue to squeeze the living space of native wild animals and plants. People living in cities seem to have forgotten that there used to be hills, jungles, grass lands, beaches, plains, lakes, fruit and vegetable farms on this land, many other creatures once living there, and many people think that biodiversity is neither realistic nor meaningful for the city.

In fact, urban biodiversity is the basis for ensuring urban ecological balance and the guarantee of ecosystem services. It plays an important role in regulating urban climate, maintaining natural water circulation and clean water sources, and maintaining soil fertility. Only a city with diverse biodiversity can become a city with a sound ecosystem and a balanced and stable operation. Urban biodiversity is also closely related to the lives and health of urban residents. Scientific research shows that compared with people who grew up in the countryside, people who spent their childhood in the city are more likely to have some allergic symptoms in certain seasons. The reason is that the microbes in the countryside are far more diverse and complex than the ones in cities. Compared with the children who grow up in cities, the children living in the countryside are exposed to more various microbes, and their immune systems have gone through the game with these microbes. The body has been adapted to them. However, people who grew up in cities have no such experience. When they are adults, once they encounter certain microorganisms that the immune system has never been in contact with or do not recognize, they are more susceptible to infection.

The premise of urban biodiversity is complex and diverse habitat conditions. Although the original ecological system, hydrological conditions and surface structure of the land have been changed by the continuous construction and expansion of the city, the natural space in the city is limited and fragmented, but the realization of urban biodiversity to a certain extent is not so difficult as we think. Judging from the hedgehogs that appeared on campus during the pandemic, if a piece of land has no or few people entering it, allowing nature to grow freely and sustain itself, this land will become a paradise for local native plants and animals. Therefore, to achieve biodiversity, cities need to have areas that no one enters and no one interferes with, so that nature itself can control this land and allow species to compete independently, inhabit and multiply.

There are many large-scale parks, greenways, waterfronts and other urban green spaces in Chinese cities, which carry comprehensive functions such as ecological protection and citizen recreation. In these projects, it is possible to delineate a certain range of areas without any roads and infrastructure to form wilderness, allow the free development of natural processes, maintain the natural succession state of the community, and provide diverse living conditions and habitats for animals and plants. Such wilderness is not only an important carrier of urban biodiversity, but also a classroom for public nature education, allowing everyone to intuitively observe and understand the natural appearance of a piece of land without human interference.

In dense urban construction areas, there are also opportunities to achieve biodiversity to a certain extent. Two years ago, the famous Danish landscape architect Stig Andersson took me to see his six newly completed small-scale projects located in the neighborhoods or around office buildings in Copenhagen. Beyond satisfying various functions, these projects either simulate the local plant community to create a wild environment in the city, or re-wild the original parks to be near-natural, to enhance the complexity of the community structure and ecological service capabilities. All designs adopt native plants, and some dead woods are reserved under the forest, to provide diverse habitat conditions for urban animals and plants through a near-natural planting method. This low-maintenance, sustainable, close to native state, and tiny wilderness in the city dominated by natural processes promotes the restoration of urban biodiversity and the construction of soil microbial communities, and makes the city more natural.

Stig Andersson's practice has given us a lot of enlightenment: even in the small-scale green space design in the downtown area,  we should abandon the way of selecting plants and constructing green space only based on people's visual preferences and inherent aesthetic habits, because the function of such green space ecology is extremely limited. We should study more in-depth zonal habitat types and adopt more planting methods that are close to natural communities to maintain and improve the urban ecological environment, provide suitable habitats for local animals and plants, and enrich urban habitat types and species diversity, and also bring to the city a landscape of continuous growth and change, full of natural flavor.

Of course, to realize the biodiversity of the city, the city must also have a complete natural system. It needs to have an ecological network that connects forests, rivers, lakes, wetlands, and farmland in a larger area. This network can introduce nature into the city, link the originally fragmented, independent, and scattered green spaces, and provide continuous habitats and migration corridors for urban plants and animals, to enrich the biodiversity of the city on a larger regional scale.

The biodiversity of different cities will have their own characteristics due to the differences in geographic distribution and climatic conditions. Human beings have been competing and coexisting with various creatures in the natural world since their emergence. Biodiversity should not only be the ideal of a city, but a basic condition that a city must  have.

本刊主编：王向荣 教授

Prof. Dr.-Ing. WANG Xiangrong

Chief Editor

引文格式

王向荣.生物多样是城市本应具有的状态[J].中国园林，2021，37(5)：2-3.

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