刊首語(yǔ)

生態(tài)系統(tǒng)服務(wù)

記得20世紀(jì)80—90年代的校園，夏季時(shí)白色的蝴蝶不時(shí)飛舞過(guò)操場(chǎng)，蜻蜓在空中盤旋，傍晚燕子在家屬區(qū)低飛，時(shí)而還能聽(tīng)到蛙聲，看到蝙蝠和發(fā)著藍(lán)光的螢火蟲。可是現(xiàn)在這種景象都已消失，在北京我已經(jīng)許多年沒(méi)有再見(jiàn)到蝴蝶飛舞和蜻蜓盤旋的景象了。

上面提到的這些小生物都是人類的朋友，也是自然生態(tài)鏈中不可或缺的重要環(huán)節(jié)。如果沒(méi)有蝴蝶，世界上就少了一支龐大的授粉大軍，植物的繁衍就會(huì)受到影響；如果沒(méi)有蜻蜓、燕子、青蛙和蝙蝠，蚊蠅等害蟲就沒(méi)有了天敵。伴隨著一些物種的減少或消失，它們所提供的生態(tài)服務(wù)也會(huì)隨之減弱或消失。

僅僅從指標(biāo)上來(lái)看，這些年來(lái)中國(guó)城市的綠地面積和綠地率并沒(méi)有減少，甚至還有不同程度的增加。比如我們學(xué)校東面不遠(yuǎn)處新建了近7km2的森林公園，北面緊鄰學(xué)校又建了1 km2的郊野公園，綠地大大增加了，然而為什么人們反而看不到蝴蝶和蜻蜓等物種呢？

麥克哈格曾說(shuō)“城市中重要的系統(tǒng)有兩個(gè)，一個(gè)是自然的系統(tǒng)，一個(gè)是人工的系統(tǒng)，一個(gè)好的城市中這兩個(gè)系統(tǒng)是互相平衡的。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(jìn)程發(fā)展的自然”。這樣的自然實(shí)際上是城市中以自然而非人為主導(dǎo)的土地，植被遵循自然演替的規(guī)律而發(fā)展，各種植物相互競(jìng)爭(zhēng)、逐步適應(yīng)，從而構(gòu)成適宜當(dāng)?shù)丨h(huán)境的群落，并形成穩(wěn)定和優(yōu)越的生態(tài)系統(tǒng)。這片自然中的主人是土地本身和其上自由棲息的生命，在維持和改善城市生態(tài)環(huán)境方面，這樣的自然較之那些精心設(shè)計(jì)和建造，靠高強(qiáng)度人工管理來(lái)維護(hù)的綠地更具有優(yōu)越性，因?yàn)槿斯す芸叵碌某鞘芯G化，植物按照人的要求來(lái)選擇，生長(zhǎng)也受到人的控制，群落的自然特性相對(duì)薄弱，生態(tài)系統(tǒng)單一，自我構(gòu)建和修復(fù)的能力已經(jīng)萎縮，并不具備為當(dāng)?shù)匾恍┪锓N提供棲息地的生態(tài)服務(wù)條件。

如此看來(lái)，蝴蝶和蜻蜓在城市中大幅減少的原因，并非由于城市中缺少綠地，而在于城市中能夠真正按照自然的演變進(jìn)程發(fā)展的土地和水域已基本消失，在近30年的快速城市化進(jìn)程中，我們的城市生態(tài)環(huán)境已經(jīng)發(fā)生了根本的變化。一方面是城市的快速拓張蠶食了城市中和城市外圍的原野、樹林、湖澤和丘陵；另一方面，城市中新建的綠地都是按照按人的使用、欣賞和審美來(lái)設(shè)計(jì)的，追求的是有裝飾效果的、穩(wěn)定的和可控的景觀。由于這些綠色環(huán)境并不具備完整的生態(tài)系統(tǒng)服務(wù)能力，許多物種必然失去棲息的家園。

城市如此，整個(gè)地球也面臨同樣的窘境。近些年世界上用的最多的詞匯之一就是“地球”，在地球上經(jīng)歷了百萬(wàn)年的進(jìn)化后，人類已經(jīng)十分適應(yīng)這個(gè)環(huán)境，然而地球的生態(tài)功能正在惡化，森林在破壞，濕地在縮減，草地在退化、生物多樣性在銳減、海平面在上升、水土流失和沙漠化的范圍在擴(kuò)大，人類對(duì)資源的消耗已經(jīng)超過(guò)了地球的再生能力，地球的生態(tài)系統(tǒng)實(shí)際上是在赤字地運(yùn)轉(zhuǎn)。

幾年前我曾給孩子買了本書《筆記大自然》(Keeping a Nature Journal)，希望通過(guò)閱讀這本書，他能夠更好地觀察自然和理解自然。書上前言中的一句話非常深刻：“人類追求輝煌和成功的夢(mèng)想，最終將使得自身成為大自然的敵人。人類在揮霍自身智慧的同時(shí)，也在殆盡自己立足的家園?！苯?jīng)濟(jì)的發(fā)展和科技的進(jìn)步使得人類的自我意識(shí)不斷膨脹，人類似乎具有了無(wú)窮的能力，可以按自己的意愿，任意改變環(huán)境。地球表面的陸地已有83%的土地被人類改造利用，這種改造都影響著地球的生態(tài)系統(tǒng)。當(dāng)然有許多改造有利于生態(tài)系統(tǒng)的穩(wěn)定和生態(tài)功能的提高，但是更多的改造在不同程度上都導(dǎo)致了生態(tài)功能的退化甚至喪失。

本期的專題是“生態(tài)系統(tǒng)服務(wù)”。生態(tài)系統(tǒng)的服務(wù)是非常全面和廣泛的，比如為人類提供食物、原材料。生態(tài)系統(tǒng)可以調(diào)節(jié)氣候、凈化污染、涵養(yǎng)水源、保持水土、防風(fēng)固沙、減輕災(zāi)害、保護(hù)生物多樣性，進(jìn)而為人類的生存與發(fā)展提供良好的環(huán)境。當(dāng)然生態(tài)系統(tǒng)也為我們提供文化、精神、宗教、審美、休閑、旅游和教育等方面的服務(wù)。

生態(tài)系統(tǒng)為地球上所有的生命提供了賴以生存的各種條件，但是生態(tài)系統(tǒng)的維護(hù)與人對(duì)發(fā)展的追求之間往往又存在著矛盾。我們應(yīng)該認(rèn)識(shí)到，無(wú)論科技如何發(fā)展，世界怎樣變化，人類與自然的關(guān)系也不會(huì)改變。路邊最不起眼的野草或池塘中最低等級(jí)的微生物，也遠(yuǎn)比人類發(fā)明創(chuàng)造的任何裝置要復(fù)雜和難解。生態(tài)系統(tǒng)的許多功能是人類科技不能提供的，也是金錢無(wú)法購(gòu)買的。我們只有維系好人與自然之間共生互惠的關(guān)系，做到與自然和諧地相處，才能維護(hù)和建設(shè)好地球良性的生態(tài)系統(tǒng)。

主編：王向榮教授

2017年1月25日

Ecosystem Service

I remember what our campus was like back in the 80's and 90's of 20 century. White butterflies and dragonflies were dancing in the air, swallows were cruising low over the residential buildings, with frogs croaking, bats and glowing fireflies circling around. I have not seen butterflies and dragonflies for years.

They are our friends, and also essential to the functioning of ecosystem. Butterflies play a vital role in plant pollination and multiplying, dragonfly, swallow, frog and bat are natural enemies to mosquito and fly. With them gone, so is the provision of their ecological services.

Judging merely from the numbers, the percentage of public green spaces in cities of China are actually rising. Like the Olympic Forest Park east of the campus is 7 km2and the newly-built country park right north of the campus is 1 km2. How come we don’t see butterflies and dragonflies even with more green spaces?

Ian McHarg once identified that nature and built environment are two important systems in a city, and a good city owns a balance between these two. Here nature is a self-evolving system rather than simply the green spaces. It refers to urban land that regulated by nature instead of men. Plants grow under natural laws, while the competitive and adaptive ones eventually form adaptive local communities and reach ecosystem stability. Land and all living things on it rule this optimal system essentially. Compared to those high-maintenance greens that are carefully designed and built, natural system is much more preferred to sustain and improve urban ecology. Some natural attributes of plant community are weakened by artificial selection and human-regulated growth. Systems with reducing biodiversity no longer have the capacity of self-construction and restoration, lest to provide ecological services for some local species.

The diminishing of self-regulated land and water system, rather than the lack of green spaces, is the main reason butterflies and dragonflies are vanishing. Urban ecology has been drastically changed during the thirty year’s fast urbanization, which is encroaching rural lands, woods, lakes and hills. Meanwhile, urban green spaces are designed for people's amenity, aesthetic pleasure, pursuing decorative, stable and manageable characters. They are not capable of providing intact ecosystem services thus habitat loss is inevitable.

What urban cities are going through is reflective of the entire planet. PLANET is a buzzword in recent years. Human went through million years of evolution to adapt to and thrive on this planet. However, they are now facing ecological degradation with extensive deforestation, wetland shrinking, grassland degradation, biodiversity loss, sea level rising, water and soil erosion, even desertification. We are consuming nature's capital faster than it can regenerate and humanity has been running an ecological deficit with the earth.

I bought my kid a book called Keeping a Nature Journal a couple of years ago, hoping he could learn to better see and understand nature. In the preface it says that human’s desire for glory and success drove nature against us. We are destroying our habitat with our own hand. Money and technology make people think they are omnipotent and free to do anything to the environment. Many dramatic changes in the earth ecology are due to human influence, and human has taken up and transformed 83 percent of the total land surface. Some changes are favorable to the ecosystems stability and ecological functions improvement, but some are causing degradation and loss of certain ecological functions to some degree.

This issue will focus on ecosystem services. Besides provisioning food and resources, these services are comprehensive and wide, regularly involving climate regulation, pollution mediation, water conservation, windbreak and erosion control, disaster mitigation and biodiversity conservation, thus providing a better habitat for human survival and development. Moreover, ecosystem also offers us with cultural, spiritual, religious, aesthetic, leisure, tourism and educational services.

Ecosystem nourishes all living things on earth, but there’s a tradeoff between sustaining vital ecosystem services and pursuing economic development. It should be concerned that the relationship between human and nature will never change despite the development of science and technology. Even the humblest roadside weeds and inconspicuous microbes in a pond are far more complex than any man-made device. Functioning of the ecosystem cannot be replaced by artificial technologies or be purchased. A well-functioning ecosystem is only based on reciprocal and harmonious relationship between human and nature.

Translator: WANG Qian

Proofreader: WANG Xi-yue

Chief Editor: Prof. Wang Xiang-rong

January. 25th, 2017