城市荒野與城市生境

城市的生態(tài)系統(tǒng)非常復(fù)雜，生境條件也極為多樣。城市生境包含了綠地、林地、農(nóng)田、濕地、水體、荒地這些自然或近自然的區(qū)域，同時也包括了建筑、橋梁、各種管網(wǎng)、軌道等構(gòu)筑物或基礎(chǔ)設(shè)施。

在各種城市生境中，我更關(guān)注城市中的荒野。城市生境的大量消失，棲息地和生物物種的減少都與荒野的消失相關(guān)。所以，城市生境和棲息地的問題，關(guān)鍵在荒野。

中國城市建成區(qū)綠地率已達30%以上，但大多數(shù)城市生物多樣性的表現(xiàn)卻非常弱，實際上城市綠地面積的增加并不一定意味城市生態(tài)功能、特別是生境和棲息地質(zhì)量的增強。麥克哈格在《設(shè)計結(jié)合自然》一書中寫到，“城市中重要的系統(tǒng)有兩個，一個是自然的系統(tǒng)，一個是人工的系統(tǒng)，一個好的城市中這兩個系統(tǒng)是互相平衡的。而自然的系統(tǒng)并非指綠色的自然，而是能夠真正按照自己的演變進程發(fā)展的自然”。城市中的荒野就屬于這一類自然。

城市荒野指城市中以自然而非人為主導(dǎo)的土地，這片土地能夠在人的干預(yù)之外進行自然演替，它的主人是土地本身和其上自由棲息的生命。

荒野之于城市的價值體現(xiàn)在其經(jīng)濟和高效的生態(tài)服務(wù)功能。在城市中，由自然過程主導(dǎo)的荒野是一種最接近原生狀態(tài)的穩(wěn)定的生態(tài)系統(tǒng)，具有低維護、低影響、可持續(xù)的特性。自然狀態(tài)下的植物群落能夠自發(fā)生長，相互競爭適應(yīng)，從而形成適宜場地環(huán)境和氣候條件的種群形態(tài)和穩(wěn)定、優(yōu)越的生態(tài)系統(tǒng)?；囊盀楫?dāng)?shù)貏又参锶郝涮峁┝诉m宜的生境條件，它是城市中最重要的生物棲息地類型之一。

城市文明和工業(yè)文明的繁榮發(fā)展使勞動創(chuàng)造的事物顯現(xiàn)出更多的價值，而自然原生事物的價值卻往往被人們忽視。人們普遍認為荒野與“荒蠻”“雜亂”“野蠻”等消極的意象相關(guān)，在城市中的荒野更是荒蕪的野地，與城市生活和城市景觀格格不入，沒有保留和維護的必要。隨著城市的發(fā)展與技術(shù)的進步，人類對土地的改造變得更加容易，在城市的迅速更新和擴張過程中，城市及周邊大量的原生或次生的荒野地被徹底開發(fā)用于城市建設(shè)。長期生活在城市環(huán)境中，人們習(xí)慣于欣賞靜態(tài)的、人工的、可控的景觀，并將自然環(huán)境視為凝固的景象而忽視其時間變化的維度，因而逐漸失去對生命自然狀態(tài)的關(guān)注和對自然景物變化的敏感。一些原來的荒野地被進行大規(guī)模地“美化”，改造為公園綠地。城市中能夠按照自然本身的進程進行演變的土地日益減少，在城市中，荒野早已逐漸淡出人們的視野。

幸運的是，在城市發(fā)展中，有時一些荒野地會由于特殊的原因被保留了下來。城市中也會有一些土地由于各種因素而被廢棄多年，從而演變成一種次生荒野。這為我們在城市中保護和維護荒野創(chuàng)造了機會和條件。

如1999——2003年間，杭州西湖一次大規(guī)模疏浚的淤泥輸送到了一個名叫江洋畈的山谷里，形成了容積約100萬m3的淤泥庫。隨后植物在淤泥上逐漸萌發(fā)出來，并隨著地表含水量的變化呈現(xiàn)出明顯而有趣的自然演替過程，形成了城市中一片由自然主導(dǎo)的次生荒野，后來依托這片土地建造了江洋畈生態(tài)公園。這是一個自然系統(tǒng)能夠按照自身的規(guī)律進行演替的公園，是一個將人類活動與荒野景觀和諧統(tǒng)一在一起的公園。今天，有幾十種鳥類棲息于此，泥塘中生活著野生的魚、小龍蝦和蟹，科學(xué)家們在這里共發(fā)現(xiàn)了42種蝴蝶。

江洋畈位于一個山谷之中，周圍有優(yōu)越的自然條件，不過即使在高密度的城市街區(qū)里，一些面積較小的類似荒野的綠地也具有獨特的生境與棲息地價值。如位于英國倫敦伊斯林頓區(qū)(London Borough of Islington)的吉萊斯皮公園（Gillespie Park）最早曾是一片農(nóng)地，后來成為鐵路邊的一片工業(yè)原料堆積地，1960年廢棄后開始了數(shù)十年的自然演替過程。21世紀(jì)初，這片土地被保留并建成了一個面積僅為1.6hm2的野生動植物公園（Wildlife Park），公園中有200余種植物，包括一些在城市中十分罕見的植物，并棲息著大量的鳥類和昆蟲。這里還成為人們第一次記錄到長尾藍蝶繁殖的地方。

其實早在20世紀(jì)70年代，歐洲的一些城市公園里就開始專門劃出一片區(qū)域，使之成為不受人為干擾的類荒野地，為當(dāng)?shù)氐膭又参锾峁⒌膱鏊６搅?1世紀(jì)，歐洲許多城市公園在滿足市民休閑活動的前提下，更是放任自然過程在公園中自由發(fā)展，最大限度地維護土地的自然演替狀態(tài)，并使自然演替成為公園自主設(shè)計的一部分，讓植物依條件自我選擇，自由地萌發(fā)、生長和變化，以此來為城市創(chuàng)造出適應(yīng)當(dāng)?shù)丨h(huán)境的生境和棲息地。

城市生境和棲息地是城市生態(tài)與生物多樣性的重要基礎(chǔ)，而荒野在城市生境和棲息地的維護方面具有不可替代的價值。我們應(yīng)該認識到，城市中不僅需要綠地，也需要按自然本身演替過程繁衍的綠地，需要城市中的荒野。

主編：王向榮教授

2019年1月1日

PREFACE

Urban Wilderness and Urban Habitat

The ecosystem of city is highly complex, and the habitat condition is also extremely diverse. Urban habitats include green space, forest, farmland, wetland, water bodies, wasteland and other natural or near-natural areas, as well as structures or infrastructures such as buildings, bridges, pipe networks, railways, etc.

Among all kinds of urban habitats, I pay special attention to the spaces with wildness feature in the city (here termed with urban wilderness). The vanish of urban habitats and biological species are related to the loss of wilderness. Therefore, the key to urban habitat is wilderness.

The green space ratio of urban built up area in China has reached 30%, but the biodiversity performs infirmly in most cities.In fact, the increase of urban green space area does not necessarily indicate the enhancement of urban ecological function, especially the enhancement of habitat quality. Ian Lennox McHarg, in his book Design and Nature, regard it so: There are two important systems in the city, one is the natural system, the other is the artificial system,and the two systems are balanced in a well-developed city, the natural system does not mean the green space, but the space that can develop according to its own evolution process. The wilderness in the city falls into this category of nature.

Urban wilderness refers to the land in a city dominated by nature rather than human beings, which is capable of natural succession beyond human intervention, and is owned by the land itself and the life upon which lives freely.

The value of wilderness to the city lies in its efficient ecological service function. In cities, the wilderness, dominated by natural processes, is a stable ecosystem closest to its native state, with lower maintenance, lower impact, and sustainable characteristics. The plant communities in natural state can grow spontaneously and compete with each other to form a stable and advantageous ecological system suitable for the site environment and climate conditions. Wilderness provides suitable habitat conditions for local animal and plant communities, and it is one of the most important habitat types in urban areas.

The prosperity of urban civilization and industrial civilization make the things created by labor show more value, but the value of natural or original things is often ignored. It is widely believed that wilderness is associated with negative images such as “Savage”,“Disorder”, and “Barbarism”, etc., or wilderness is desolate field,which is incompatible with urban life and urban landscape feature,and is not necessary to preserve and maintain. With the development of cities and the progress of technologies, transforming land becomes much easier. A large number of primary or secondary wilderness land around the city is thoroughly developed for urban construction in the process of rapid urban renewal and expansion.After living in urban environments for a long time, people are used to appreciating static, artificial, controllable landscapes, and viewing the natural environment as a solidified landscape, ignoring its dimension of temporal change. As a result, the attention to the natural state of life and the sensitivity to the changes of natural scenery are gradually lost. Some of the original wilderness areas have been extensively “beautified” and transformed into urban park. The land that can evolve according to the process of nature itself in the city is decreasing gradually, the urban wilderness has gradually faded out of people’s view.

Fortunately, some wilderness land sometimes survives in urban development for special reasons. Also, some land in the city, being abandoned for years for a variety of factors, turns into secondary wilderness, creating opportunities and conditions for us to preserve and maintain the wilderness in our cities.

For instance, between 1999 and 2003, a large amount of dredged-silt from West Lake in Hangzhou was transported into a valley called Jiangyangfan, forming a silt reservoir with a capacity of about 1 million cubic meters. Then the plants germinated gradually from the silt, with the change of water content on the land surface,obvious and interesting natural succession processes occurred, a secondary wilderness dominated by nature was formed in the city.Later, with this piece of land, Jiangyangfan Eco-Park was built. This is a park in which the natural system can follow its own laws, and a park that harmonizes human activities with the wilderness landscape.Today, dozens of species of birds inhabit here, the bog is home to wild fishes, crayfishes and crabs, where scientists have found also 42 species of butterflies.

Jiangyangfan is located in a valley, surrounded by superior natural environment, but even in high-density urban neighborhoods,some smaller wilderness-like greenbelts have unique value of habitat.For example, Gillespie Park in London Borough of Islington was originally a piece of farmland, later became an industrial storage area for raw material along the railroad, and since it was abandoned in 1960, decades of natural succession began. At the beginning of the 21st century, the land was preserved and built into a small 1.6-hectare Wildlife Park with more than 200 species of plants, including some species rare to be seen in the city, also a large number of birds and insects. It is the first urban space to record the breeding of longtailed blue butterflies.

In fact, as early as the 1970s, some urban parks in Europe began to line out a special area as undisturbed wilderness, providing habitat for local animals and plants. Still in this century, on the premise of satisfying the leisure activities of the citizens, many urban parks in Europe allow the natural process to develop freely in the parks,maximize the maintenance of the natural succession of the land, and make succession progress a part of the park’s autonomous design,allowing plants to compete and germinate themselves according to the site environment, to grow and transform freely, so as to create biotopes and habitats which are adaptive to the local environment in the cities.

Urban biotope and habitat are important foundations for urban ecology and biodiversity, while wilderness has irreplaceable value in its maintenance. As we should realize, the city needs not only green space, but also the green space that able to develop according to the succession of nature itself, and the wilderness in the city is indispensable.