著：（日）森本幸裕 譯：康寧

理查德·瑞吉斯特（Richard Register）在Ecocity Berkeley（1987）一書中寫道：“庭園是自然的載體，城市是文化的載體……現(xiàn)如今，兩者的功能都失去了均衡?！盵1]

那么如何使城市建設(shè)與自然保護(hù)相得益彰？城市的發(fā)展勢(shì)必破壞生物的基本棲息空間，然而某些物種仍然要在城市生存。有些物種已成功適應(yīng)了城市環(huán)境，城市即已成為新的棲息地類型。這些情況都是在進(jìn)行城市建設(shè)時(shí)所要面臨的。日本有著人與自然和諧共生的文化，如水邊的“花、鳥、風(fēng)、月”景觀，模仿自然的傳統(tǒng)園林，以及由古樹構(gòu)成的神社圣林等。上述這些具有文化特質(zhì)的自然可以作為建設(shè)城市的借鑒，使得城市中的原生動(dòng)植物，在城市發(fā)展過程中得以繼續(xù)棲息繁衍。

2012年，日本政府頒布《2012—2020生物多樣性國家戰(zhàn)略》[2]，其中明確了4類生物多樣性喪失危機(jī)。第1類：由人類活動(dòng)和社會(huì)發(fā)展引起；第2類：由人為管理減少引起；第3類：由人為引進(jìn)物種引起；第4類：由全球氣候變化引起。該項(xiàng)國家戰(zhàn)略的頒布，旨在促進(jìn)形成自然豐富的城市，以實(shí)現(xiàn)“愛知生物多樣性目標(biāo)”。基于此，我們亟須找到創(chuàng)建“生物多樣性豐富的城市”的解決途徑和實(shí)現(xiàn)方法。

筆者從日本城市自然生境營造項(xiàng)目中選取了3個(gè)具有代表性的先進(jìn)案例，分別展現(xiàn)不同場(chǎng)地尺度、營造方法和生境功能。3個(gè)案例均已建成超過20年，筆者參與了建成后的動(dòng)態(tài)監(jiān)測(cè)和管理過程。因此，可以通過研究小組20多年的監(jiān)測(cè)結(jié)果來討論開創(chuàng)性的規(guī)劃設(shè)計(jì)理念與自然過程之間的關(guān)系。1）大阪萬博紀(jì)念公園：日本歷史上最大尺度的城市森林自然恢復(fù)工程。其具有創(chuàng)新的規(guī)劃理念，規(guī)劃目標(biāo)為創(chuàng)建“自我維持的城市森林”，形成自然植物群落。該項(xiàng)工程是在“生物多樣性”概念出現(xiàn)之前的一個(gè)創(chuàng)新型項(xiàng)目。通過幾十年的監(jiān)測(cè)數(shù)據(jù)和管理成果的驗(yàn)證，可借鑒其為實(shí)現(xiàn)自然森林群落，采取的城市森林生境營造方法和獨(dú)特的管理技術(shù)。2）梅小路公園“生命之森”：日本第一個(gè)位于城市中心公園中的生境營造項(xiàng)目。其設(shè)計(jì)理念是生物多樣性保護(hù)和恢復(fù)。具體設(shè)計(jì)方法為通過地形塑造及鄉(xiāng)土植被種植，模擬京都盆地自然生態(tài)系統(tǒng)。我們對(duì)場(chǎng)地建成后的生物群落進(jìn)行了長達(dá)數(shù)十年的監(jiān)測(cè)，可以清晰地驗(yàn)證其設(shè)計(jì)方法和管理成效。3）平安神宮生境花園：日本傳統(tǒng)庭園中再現(xiàn)自然生境的項(xiàng)目。雖然平安神宮庭園是一種人工景觀，但其在面臨琵琶湖生物多樣性危機(jī)時(shí)，作為生物多樣性庇護(hù)所的生境功能近年卻愈發(fā)凸顯。基于此案例，探討日本傳統(tǒng)園林造園設(shè)計(jì)和管理的特點(diǎn)，以及如何實(shí)現(xiàn)生境功能。

以上3個(gè)案例在城市生態(tài)網(wǎng)絡(luò)中發(fā)揮的重要作用均得到了廣泛認(rèn)可：1）日本國土交通省于2006年將大阪萬博紀(jì)念公園列為“近畿地區(qū)城市環(huán)境基礎(chǔ)設(shè)施規(guī)劃”的重要組成部分；2）梅小路公園的重要性不僅經(jīng)常在學(xué)術(shù)論文中被提及，而且京都市長在第一屆全球城市和地方政府生物多樣性峰會(huì)上介紹了“梅小路公園作為城市生物多樣性核心”的作用；3）《京都府紅皮書2002》中高度評(píng)價(jià)了平安神宮庭園在琵琶湖流域生態(tài)網(wǎng)絡(luò)中發(fā)揮的生境功能。

此外，幾十年來，上述3個(gè)案例因其尺度和特征的不同分別采用了相應(yīng)的管理方法，取得了豐碩成果，這些都可以從生物多樣性監(jiān)測(cè)結(jié)果中看出，因此上述3個(gè)案例也可以為城市生境適應(yīng)性管理提供借鑒。

1 大阪萬博紀(jì)念公園植物群落設(shè)計(jì)與人工林窗再生

1.1 自我維持的城市森林

為紀(jì)念1970年召開的世博會(huì)，在大阪北部千里山丘陵地區(qū)的世博會(huì)舊址上，建造了大阪萬博紀(jì)念公園。紀(jì)念公園面積較大，達(dá)340 hm2，公園建成后成為大阪北部地區(qū)快速城市化進(jìn)程中保留下來的大型綠色核心。

自然文化區(qū)是公園的主要組成部分，占地約100 hm2，其目標(biāo)設(shè)定為“自我維持的森林”，以此恢復(fù)因舉辦世博會(huì)而受到大規(guī)模干擾的原生常綠闊葉林（地帶性頂級(jí)群落）和半自然次生林（里山林）[3]。在城市區(qū)域內(nèi)恢復(fù)包含地帶性頂級(jí)群落的自然森林，是一個(gè)開創(chuàng)性的舉措，甚至從全球角度來看，其理念也處于前沿。公園的總體規(guī)劃由高山英華（Eika TAKAYAMA）負(fù)責(zé)，其中自然文化區(qū)由吉村元男（Motoo YOSHIMURA）設(shè)計(jì)，筆者作為項(xiàng)目組成員，負(fù)責(zé)種植設(shè)計(jì)工作。公園的歷史沿革如圖1。

1.2 植物群落種植單元及種植方法

依照植物演替規(guī)律，在日本形成穩(wěn)定的頂級(jí)群落可能需要數(shù)百年的時(shí)間。由于本項(xiàng)目計(jì)劃在2000年之前建成能夠自我維持的森林，所以設(shè)計(jì)團(tuán)隊(duì)的首要任務(wù)是盡快探明實(shí)現(xiàn)成熟森林生態(tài)系統(tǒng)的方法。

種植設(shè)計(jì)謹(jǐn)遵植物科學(xué)，以地帶性成熟森林的植被組成為種植設(shè)計(jì)單元藍(lán)本。然而，以場(chǎng)地現(xiàn)有生土的土壤條件、開敞性的立地環(huán)境來看，難于恢復(fù)森林植被。所以本項(xiàng)目在場(chǎng)地中央平坦地帶（包括湖泊和設(shè)施）周圍的山脊上修建了一條水道，濕潤灌溉加速土壤熟化，以創(chuàng)造近成熟的森林環(huán)境。在種植計(jì)劃實(shí)施過程中，利用混合種植先鋒樹種或肥料樹種等各種獨(dú)創(chuàng)性舉措來促進(jìn)森林生態(tài)系統(tǒng)的建立[4]303-321。

1.3 土壤改良促進(jìn)森林形成

然而，在種植施工完成后的第1個(gè)10年，樹木生長狀態(tài)很差，依此情況，幾乎難于在2000年形成一個(gè)成熟的森林生態(tài)系統(tǒng)。樹木生長不良的原因是山體切割后暴露的海相黏土層形成了酸性硫酸鹽土壤，而且在建設(shè)初期平整土地時(shí)重型機(jī)械又將土壤壓實(shí)。筆者加入了由小橋澄治（Sumiji KOBASHI）領(lǐng)導(dǎo)的監(jiān)測(cè)小組，并探明了土壤條件與樹木生長狀態(tài)之間的關(guān)系[5],[6]184-195，研究發(fā)現(xiàn)排水不良的土壤是限制樹木生長的最重要因素，此結(jié)論促成了森林生長環(huán)境改良措施的實(shí)行。

然而，直至20世紀(jì)80年代末，筆者才意識(shí)到恢復(fù)自然森林生態(tài)系統(tǒng)的困難。恰逢此時(shí)，“生物多樣性”一詞出現(xiàn)，而另一創(chuàng)新概念“適應(yīng)性管理”在20世紀(jì)90年代得到認(rèn)可，用于管理過于復(fù)雜的生態(tài)系統(tǒng)。此外，筆者研究還發(fā)現(xiàn)對(duì)森林樹種生長不利的排水不良場(chǎng)地，也是大阪市內(nèi)殘存的野生灌木和草本群落的生境[7]。

1.4 類似“萌生林”的結(jié)構(gòu)狀態(tài)，結(jié)構(gòu)單一、樹齡相同

20世紀(jì)90年代，隨著森林的逐漸形成，生物多樣性問題變得嚴(yán)峻。因?yàn)樯种脖粵]有長成多層復(fù)合結(jié)構(gòu)，而是呈現(xiàn)出層次單一、密度過高的狀態(tài)，即形成了由有限樹種構(gòu)成的類似“萌生林”的結(jié)構(gòu)狀態(tài)。盡管在制定種植計(jì)劃和進(jìn)行種植施工時(shí)選擇了多樣的樹種，但是當(dāng)年栽植的樹苗幾乎是同一世代的，這些樹苗長大的結(jié)果是森林地被層消失、物種多樣性和葉層高度多樣性（foliage height diversity）降低。

1.5 人工林窗動(dòng)態(tài)理論

基于維持自然成熟森林生物多樣性的“林窗動(dòng)態(tài)”理論，筆者提出啟動(dòng)“人工林窗動(dòng)態(tài)”計(jì)劃的建議，以實(shí)現(xiàn)形成“自我維持的森林”的種植設(shè)計(jì)初始目標(biāo)。

該計(jì)劃不僅需要?jiǎng)?chuàng)造約15 m×15 m的林窗，還需引入各種“林窗動(dòng)態(tài)”舉措，包括引入大阪市內(nèi)與場(chǎng)地相鄰的成熟森林表土等。大阪萬博紀(jì)念公園是城市建成區(qū)中的一個(gè)孤島，所以依靠自然力量，周邊森林的物種很難自行遷移到公園內(nèi)。鑒于此種情況，我們提取周邊未開發(fā)區(qū)域森林的表土，引入到公園需修復(fù)的場(chǎng)地內(nèi)，讓表土種子庫中蘊(yùn)藏的種子自由萌發(fā)。

經(jīng)過適應(yīng)性管理指導(dǎo)委員會(huì)[8]的討論，人工林窗項(xiàng)目于2003年開始實(shí)施，這也是在日本城市公園中進(jìn)行的第1例林窗實(shí)驗(yàn)（圖2）。相關(guān)工作內(nèi)容和實(shí)驗(yàn)成果已在名古屋舉行的生物多樣性條約第10次締約國會(huì)議（COP10）①中發(fā)表。截至目前，已經(jīng)形成由多樣動(dòng)植物共存、生態(tài)系統(tǒng)穩(wěn)定的自然森林。

2 “生命之森”城市生境營造

2.1 基于提高城市生物多樣性的生境花園

為慶祝京都建都1 200周年，京都市建成了第一個(gè)以恢復(fù)市區(qū)自然生境為目標(biāo)的城市公園（0.66 hm2）——梅小路公園。公園于日本城市綠化博覽會(huì)召開之后開建，原址為京都車站附近的梅小路鐵路貨運(yùn)站，經(jīng)過更新設(shè)計(jì)后成了城市公共園林（圖3）。其中“生命之森”生境花園于1996年對(duì)外開放。筆者負(fù)責(zé)成立并協(xié)調(diào)由生態(tài)學(xué)家和景觀設(shè)計(jì)師組成的研究小組。

公園對(duì)外開放后，在專家、學(xué)生和市民的合作下成立了志愿監(jiān)測(cè)小組。此后，本研究團(tuán)隊(duì)帶領(lǐng)監(jiān)測(cè)小組持續(xù)20多年觀測(cè)“生命之森”建成后的生物多樣性情況，定期舉辦自然教育活動(dòng)，每年發(fā)表1份調(diào)查報(bào)告[4]15-22?！吧睆呢涍\(yùn)站工業(yè)遺址成功地演變?yōu)槌鞘兄兄匾膭?dòng)植物棲息地。研究小組甚至發(fā)現(xiàn)了超出預(yù)期的生物在此棲息，比如曾經(jīng)在城市地區(qū)消失的翠鳥以及某種松露。在名古屋舉辦的生物多樣性條約第10次締約國會(huì)議（COP10）“城市生物多樣性”分會(huì)（2010年10月24—26日）中，京都市市長門川大作（Daisaku KADOKAWA）介紹了“生命之森”和研究小組的相關(guān)活動(dòng)。日本政府在2011年發(fā)表的白皮書中也對(duì)研究小組的志愿活動(dòng)有所闡述。

2.2 目的和宣言

建設(shè)“生命之森”的基本目的概述如下：1）為城市做出貢獻(xiàn)，使市民能夠享受大自然的季相變化；2）發(fā)揮/促進(jìn)發(fā)揮生態(tài)系統(tǒng)服務(wù)功能，減少諸如熱島現(xiàn)象的城市環(huán)境問題；3）為市民提供康養(yǎng)景觀，兒童可以體驗(yàn)、發(fā)現(xiàn)并向自然學(xué)習(xí)，促進(jìn)健康成長；4）保護(hù)城市化進(jìn)程前還未滅絕的本土物種，構(gòu)建“山城荒野”（Yamashiro Wilderness）。盡管“生命之森”面積很小，但研究小組仍將其建設(shè)的基本目標(biāo)設(shè)定為在京都市中心創(chuàng)造一個(gè)生物生境。

研究小組確保要建成一個(gè)生態(tài)系統(tǒng)[4]3-14，該生態(tài)系統(tǒng)必須：1）盡可能豐富本地物種多樣性；2）盡可能具有發(fā)展性或可持續(xù)性；3）包含與京都密切相關(guān)并被市民熟悉的物種；4）包含未來會(huì)被喜愛的物種；5）具有較低數(shù)量的入侵物種。研究小組認(rèn)為，對(duì)于公園的管理強(qiáng)度不應(yīng)過大，而應(yīng)控制在適中水平，并且要兼顧自然的發(fā)展進(jìn)程。

2.3 設(shè)計(jì)

筆者認(rèn)為，針對(duì)面積有限的“生命之森”生境設(shè)計(jì)，需有如下舉措：1）以收費(fèi)促進(jìn)生境的保護(hù)，通過與日本庭園朱雀之庭（Suzaku-no-niwa）的聯(lián)系實(shí)現(xiàn)；2）日常使用“樹冠回廊”作為通行設(shè)施以減少地面步行系統(tǒng)對(duì)生境的干擾，以及設(shè)立封閉區(qū)域，該區(qū)域每年僅向游客開放幾天；3）開發(fā)包括土崖在內(nèi)的多樣化地形，促進(jìn)翠鳥筑巢；4）通過挖井抽取地下水以滿足多類型池塘的用水需求；5）引入多種生態(tài)系統(tǒng)資源要素，如自然生態(tài)系統(tǒng)中的粗木碎屑（Coarse Woody Debris，簡稱CWD）、鄉(xiāng)村樹籬、由河石壘成的石墻（Nozurazumi）、樹樁、里山中出現(xiàn)的薪材堆等。

2.4 結(jié)果

令人驚訝的是：研究小組觀察到了“生命之森”生境的動(dòng)態(tài)演替進(jìn)程，尤其在建成后的第1個(gè)10年[9-10]。棲息地中物種的遷入與滅絕動(dòng)態(tài)變化顯著。根據(jù)監(jiān)測(cè)記載，“生命之森”中的顯花植物種類在1999年到達(dá)峰值，隨后逐漸減少。就鳥類而言，其種類在最初建成幾年呈現(xiàn)出顯著增加趨勢(shì)，隨后進(jìn)入幾乎穩(wěn)定或稍微增加的階段。而在真菌方面，地上真菌和菌根的種類也有所增加（表1）。

表1 “生命之森”建成后生境恢復(fù)的典型生態(tài)事件（按時(shí)間順序選定）Tab. 1 Chronological selected ecological events in the “Inochi-no-mori” restored habitat after construction

2.5 “生命之森”城市生境營造的挑戰(zhàn)

盡管建成后的“生命之森”在自然演替過程中呈現(xiàn)出積極的發(fā)展趨勢(shì)，但隨后還是出現(xiàn)了一些具有挑戰(zhàn)性的問題。

第1個(gè)挑戰(zhàn)是外來入侵物種。豐富的蜻蜓種群數(shù)量因牛蛙的出現(xiàn)而大大減少（建造后第2年記錄）；因小龍蝦造成的損害，水生植物逐漸減少，隨后滅絕；女貞（Ligustrum lucidum）在森林環(huán)境的邊緣和內(nèi)部都具有入侵性。第2個(gè)挑戰(zhàn)是在有限的空間內(nèi)，如何權(quán)衡生態(tài)系統(tǒng)演替與物種多樣性之間的關(guān)系[11]。以草本先鋒植物為主的干擾依賴物種，在建成第3年后開始減少。

2.6 展望與挑戰(zhàn)

“生命之森”項(xiàng)目可以說是在工業(yè)遺產(chǎn)（如貨運(yùn)火車站）生態(tài)恢復(fù)后形成的城市孤立生境中，精確記錄自然演替過程的第一個(gè)例子。這些監(jiān)測(cè)記錄也為未來采用新的科學(xué)技術(shù)提供了寶貴的信息。目前，環(huán)境DNA檢測(cè)是用于環(huán)境監(jiān)測(cè)的創(chuàng)新性方法。如研究小組對(duì)于真菌的監(jiān)測(cè)數(shù)據(jù)，可以為環(huán)境DNA研究提供有價(jià)值的信息。但是對(duì)于實(shí)際存在的龐大的真菌種群來說，基于觀察得來的監(jiān)測(cè)數(shù)據(jù)只是其中非常有限的一部分?！吧笔且粋€(gè)孤立生境，其水源來自雨水和地下井水。環(huán)境DNA研究可以分析“生命之森”的水體，從而揭示多樣的真菌類型（operational taxonomic unit，簡稱OTU），其數(shù)量遠(yuǎn)遠(yuǎn)超過我們?nèi)庋郾O(jiān)測(cè)的記錄。

此外，當(dāng)前項(xiàng)目面臨的另一個(gè)重要問題是如何應(yīng)對(duì)從具有較小樹木和開放冠層的異質(zhì)生境，向具有較高樹木和封閉冠層的同質(zhì)生境的自然演替。在此種演替趨勢(shì)下，顯花植物物種多樣性正在逐漸減少。日本橡樹枯萎事件也在演替進(jìn)程中產(chǎn)生了負(fù)面效應(yīng)。而自然生態(tài)系統(tǒng)中的有利干擾，例如洪水干擾、風(fēng)力干擾都不會(huì)在“生命之森”這種城市公園中蘊(yùn)藏的小規(guī)模生態(tài)系統(tǒng)內(nèi)發(fā)生。

近年來，由于京都市周邊森林中梅花鹿數(shù)量的增多，造成了森林生物多樣性的嚴(yán)重破壞。所以，我們可以期待，未來城市建成區(qū)中的生物生境將有可能發(fā)揮巨大的作用，可以成為瀕危物種的避難所。

綜上，筆者認(rèn)為需調(diào)整對(duì)于城市生境生態(tài)系統(tǒng)的管理策略，即從被動(dòng)的管理（等待新物種的自然遷移定居）轉(zhuǎn)為主動(dòng)管理，如引入瀕危物種，為其創(chuàng)建相應(yīng)的棲息地環(huán)境等。這也是為實(shí)現(xiàn)“沒有物種滅絕的城市”而進(jìn)行的適應(yīng)性管理舉措之一。

3 平安神宮生境花園

3.1 概述

2019年，一項(xiàng)大規(guī)模、精心管理的污泥疏浚工程在平安神宮庭園中的池塘展開，這也是其40年來的首次疏浚。工程現(xiàn)場(chǎng)安設(shè)了大型污泥處理設(shè)施，共有1 000人參與疏浚，盡管污泥處理耗時(shí)3個(gè)月，但是池塘里的生物種群卻得到很好的保護(hù)。因?yàn)楣こ虝r(shí)刻在監(jiān)督委員會(huì)的監(jiān)控下進(jìn)行，該委員會(huì)成員包括生態(tài)學(xué)專家、景觀和文化遺產(chǎn)方面的專家、京都市政府工作人員等。施行此種舉措不僅源于平安神宮作為國立名勝的文化價(jià)值，還因?yàn)槠涫蔷┒汲鞘谢字幸粋€(gè)重要的生物棲息地。

3.2 作為野生動(dòng)植物生境的日本傳統(tǒng)園林

平安神宮始建于1895年，是日本工業(yè)促進(jìn)博覽會(huì)的展館，同時(shí)其建成也是為了紀(jì)念京都建都1 100年。這座面積3.3 hm2的神社園林由著名的景觀設(shè)計(jì)師第七代小川治兵衛(wèi)（Jihei OGAMA，1860—1933）設(shè)計(jì)建造，人們也稱他為第七代“植治”，其曾在日本京都市東山地區(qū)建造了許多優(yōu)秀的現(xiàn)代園林作品，包括山縣有朋的私產(chǎn)無鄰庵庭園等。這些庭園的特點(diǎn)是廣泛應(yīng)用“借景”，以及創(chuàng)造溪流、池塘等自然式水體景觀，水源全部來自琵琶湖疏水路（圖4）。平安神宮庭園于1975年被認(rèn)定為日本國立名勝，本研究主要強(qiáng)調(diào)其作為城市基底中生物生境的作用。

3.3 庭園中的生物多樣性

翔實(shí)的調(diào)查報(bào)告[12]記錄了平安神宮庭園中豐富的生物多樣性：年間共發(fā)現(xiàn)約200種木本植物、300種草本植物、106種苔蘚、40種蕨類植物、4種海龜和40種鳥類，足見該庭園作為城市基底中孤立生境的重要作用。

3.4 分形，形成自然生境多樣性的重要因素

平安神宮庭園生物多樣性豐富的原因可以在設(shè)計(jì)中找到，即“縮景”（微縮自然）[13]621-625,14[375-388]。庭園中每個(gè)池塘的形態(tài)都可以看作是一個(gè)分形[15]615-618，這種現(xiàn)象在自然界景觀中是廣泛存在的（圖5）。

簡單地說，分形理論表示局部形態(tài)和整體形態(tài)是相似的，且每一部分都（至少近似地）是整體縮小后的形狀，稱為自相似。我們分析了日本傳統(tǒng)園林中池塘形態(tài)、種植設(shè)計(jì)、置石分布的特征，發(fā)現(xiàn)分形維數(shù)是日本傳統(tǒng)園林形式和風(fēng)格的一個(gè)重要量化特征[14]375-388。此外，分形現(xiàn)象可以為不同大小的生物提供多樣的生境。綜上，基于分形理論的“微縮自然”是日本園林的一個(gè)特征[15]615-618，使其能夠作為野生生物的庇護(hù)所而存在。

3.5 城市基底中瀕危物種的孤立保護(hù)區(qū)

平安神宮庭園發(fā)揮生境功能的一個(gè)有意義的成果是瀕危物種縱帶鱊（Acheilognathus cyanostigma）的棲息[13]621-625?？v帶鱊是一種廣受歡迎的魚類，原本生存在琵琶湖中。1996年滋賀縣立琵琶湖博物館展出此魚，但是發(fā)現(xiàn)博物館里的縱帶鱊種群是平安神宮池塘中種群的后代。那么為什么縱帶鱊沒有在琵琶湖中聚集，卻能在平安神宮的池塘里存活下來？

縱帶鱊很可能是一路順著琵琶湖疏水路（連接琵琶湖和京都的運(yùn)河）從平安神宮而來，但是如果平安神宮庭園里只有一個(gè)孤立的池塘，縱帶鱊就不能繁殖。因?yàn)槠浞敝承柰ㄟ^在大型雙殼軟體動(dòng)物中插入一根長的輸卵管產(chǎn)卵，發(fā)育后的幼魚仍然要依靠埋藏在沙中的底棲貝類生存。而雙殼軟體動(dòng)物的幼體則需要寄生在小的底棲魚類上，如吻鰕虎魚屬（Rhinogobius）。從縱帶鱊的生活史和生態(tài)習(xí)性來看，縱帶鱊的存在即證明平安神宮庭園中的池塘已經(jīng)形成了一個(gè)多生境的生態(tài)系統(tǒng)。此外，1983年琵琶湖發(fā)生第一次淡水赤潮時(shí)，為防止污水進(jìn)入，琵琶湖入水口安裝了砂濾池，該過濾器有效防止了外來物種對(duì)池塘生境的入侵，如藍(lán)鰓太陽魚（Lepomis macrochirus）和大口黑鱸（Micropterus salmoides）等。

3.6 對(duì)于適應(yīng)性管理的需求

在2000年左右，平安神宮庭園中的鯉魚種群數(shù)量因錦鯉皰疹病毒（KHV）的流行而顯著下降，湖底污泥堆積問題變得嚴(yán)峻，雙殼軟體動(dòng)物棲息地惡化，縱帶鱊種群急劇減少，被稱為“微型琵琶湖”的平安神宮庭園池塘生態(tài)系統(tǒng)危機(jī)頻現(xiàn)。

為了應(yīng)對(duì)此問題，我們?cè)诘谄叽爸仓巍钡娜沼浿姓业搅藢?duì)其建園理念的描述[16]，彼時(shí)他剛剛完成了京都清風(fēng)荘（Seifuso）庭園（山縣有朋的別墅）的建造工作。第七代“植治”親自去鴨川捕捉小魚，并將它們放進(jìn)庭園中的池塘。這一描述清晰地表明了第七代“植治”恢復(fù)庭園自然的意圖。因此，為了保持和傳承設(shè)計(jì)者所期望的自然景觀，必須對(duì)平安神宮庭園中的池塘進(jìn)行人為清淤疏浚管理，而不是僅僅依靠幾十年一遇的自然干擾。

4 討論

城市生境對(duì)于維持和豐富城市生物多樣性發(fā)揮著重要作用，是建設(shè)“防止物種滅絕的可持續(xù)城市”的基礎(chǔ)。筆者重點(diǎn)介紹了經(jīng)人為恢復(fù)和營造的城市生境，并沒有討論諸如自然保護(hù)區(qū)、神社森林、城市農(nóng)業(yè)用地、河流、水庫等各類已經(jīng)存在的自然生境。這些生境都是維持城市生物多樣性的基礎(chǔ)。隨著城市化進(jìn)程的加快，城市生物多樣性已經(jīng)顯著降低，城市生境的恢復(fù)和營造對(duì)于實(shí)現(xiàn)2015年聯(lián)合國可持續(xù)發(fā)展峰會(huì)提出的可持續(xù)發(fā)展目標(biāo)（Sustainable Development Goals，簡稱SDG）就必不可少。

4.1 斑塊面積

大型棲息地斑塊能夠棲息更多樣的物種[17]，提供更多的生態(tài)系統(tǒng)服務(wù)。但是在城市中心地區(qū)建立新的大型生境以應(yīng)對(duì)生物多樣性危機(jī)，是昂貴和困難的，也是不現(xiàn)實(shí)的。本文中3個(gè)案例的建設(shè)都有特殊歷史意義：亞洲舉辦的第一屆世博會(huì)、京都建都1 200周年紀(jì)念和1 100周年紀(jì)念。我們需要從生物多樣性的角度探討棲息地斑塊面積大小與城市孤立生境效能之間的關(guān)系。

根據(jù)我們以京都為對(duì)象的研究發(fā)現(xiàn)，約1 hm2的孤立生境（如梅小路公園中的“生命之森”、平安神宮庭園）可以成為日本食蟲山雀（Parus minor）的棲息地； 3～10 hm2的棲息地可以為小型猛禽棕鷹（Ninox scutulata）提供生境；而蒼鷹則需要100 hm2的區(qū)域棲息（如大阪萬博紀(jì)念公園）[18-20],[21]23-34。由此可見，大型棲息地比小型棲息地發(fā)揮更大的作用。但是，景觀生態(tài)學(xué)領(lǐng)域的經(jīng)典議題“單個(gè)大型棲息地或幾個(gè)小型棲息地”（Single Large or Several Small，簡稱SLOSS）：單個(gè)大型棲息地（Single Large，簡稱SL）與幾個(gè)小型棲息地（Several Small，簡稱SS）相比，哪種方式更好？由以上研究可以發(fā)現(xiàn)，就稀有物種的數(shù)量和創(chuàng)建稀有物種的棲息地而言，SS比SL更具優(yōu)勢(shì)。盡管SS的棲息地面積很小，但是棲息地的獨(dú)特性非常重要。

雖然生境面積大小是決定物種多樣性的非常重要的正向參數(shù)，但是該參數(shù)的實(shí)際影響力因物種而異。蕨類植物、草本植物[21]23-24、螞蟻[22]和苔蘚[23]更易受到小生境多樣性的影響[24]。從此視角來看，日本園林作為生境的意義非常重要，尤其對(duì)于小型生物來說。

4.2 緊循自然過程的生境管理

城市生境作為城市生態(tài)網(wǎng)絡(luò)，旨在保護(hù)和維持地區(qū)原生生物多樣性。景觀生態(tài)學(xué)中要素、格局、過程這3個(gè)自然的屬性是解析城市孤立生境物種多樣性的關(guān)鍵[25]。大阪萬博紀(jì)念公園案例表明僅僅進(jìn)行景觀要素（生態(tài)系統(tǒng)類型、物種等）和格局（創(chuàng)建不同類型森林斑塊、塑山造河）的設(shè)計(jì)，還不足以恢復(fù)自然森林，還需重點(diǎn)引入“干擾形成景觀生態(tài)多樣性”這一概念，作為自然過程（如“林窗動(dòng)態(tài)”和洪水干擾）的替代對(duì)其進(jìn)行適應(yīng)性管理。同理，從景觀要素和格局的角度來看，梅小路公園設(shè)計(jì)得當(dāng)，然而隨著森林的生長，會(huì)發(fā)現(xiàn)其生境由最初的異質(zhì)鑲嵌格局轉(zhuǎn)變?yōu)榫鶆蚪Y(jié)構(gòu)，并出現(xiàn)干擾依賴型植物物種多樣性顯著降低這個(gè)問題。平安神宮庭園作為微縮自然（見池塘的形狀、材料、微生境分布以及與琵琶湖的連接等）發(fā)展出獨(dú)特而豐富的生物多樣性，但是目前面臨缺乏洪水干擾等自然過程的問題。

人工修復(fù)或營造形成的生境的可持續(xù)性很大程度上取決于適應(yīng)性管理水平，如池塘清淤疏浚即可以看作是自然洪水干擾的替代。對(duì)于大阪萬博紀(jì)念公園這類大尺度的生境來說，一定程度的自然干擾可以發(fā)揮生態(tài)系統(tǒng)的自我調(diào)節(jié)作用。所以在自然的3個(gè)屬性中，過程屬性是最具挑戰(zhàn)的議題（表2）。

從景觀要素和格局視角來看，本文3個(gè)項(xiàng)目都是成功案例。蒼鷹被發(fā)現(xiàn)在大阪萬博紀(jì)念公園這種大型斑塊內(nèi)筑巢，梅小路公園和平安神宮庭園也成為瀕危物種的避難所。然而，最重要的是需通過人工干擾進(jìn)行適應(yīng)性管理，以代替自然干擾，即“過程”是維持生物多樣性和場(chǎng)地生境功能的一個(gè)重要屬性。

所以，在進(jìn)行生境恢復(fù)設(shè)計(jì)時(shí)，不僅要針對(duì)場(chǎng)地進(jìn)行景觀要素、空間格局設(shè)計(jì)，還要對(duì)自然和人為管理制定相應(yīng)程序。雖然自然干擾可能會(huì)造成災(zāi)害，但一定程度的自然干擾對(duì)生境的健康是必不可少的。生境的適應(yīng)性管理與“綠色基礎(chǔ)設(shè)施”和“生態(tài)災(zāi)害降低”（Ecosystem-based Disaster Risk Reduction， 簡稱Eco-DRR）密切相關(guān)[27]，如雨水花園不僅可以成為城市中的小型生境，還可以緩解熱島現(xiàn)象以及全球氣候變暖導(dǎo)致的暴雨災(zāi)害[28]。

注釋(Note)：

①“生物多樣性條約第10次締約國會(huì)議(簡稱COP10)于2010年10月11—29日在日本愛知縣名古屋市舉行，會(huì)議公布2010年瀕危動(dòng)物名單，通過遺傳資源利益分配的相關(guān)議定書，提出2010—2020年保護(hù)生物多樣性目標(biāo)。

圖表來源：

圖1由大阪府政府提供，圖2、4由作者提供，圖3由京都市政府提供，圖5由伊藤早介提供；表1由作者自繪，表2來源于參考文獻(xiàn)[26]。

（編輯/劉昱霏）

Richard Register wrote in his bookEcocity Berkeley(1987): “ The Garden is the paradise of nature, and the City is the paradise of culture. Or at least they could be…. Today, both are out of balance.”[1]

How can we harmonize city construction with nature conservation? City development inevitably degrades the essential habitat of creatures; however, some species also live in urban areas. Moreover, some species successfully adapt to living in an urban environment as their new habitat. In Japan, we sometimes notice the traditional culture of living with nature and celebrating the “Flower, Bird, Wind, Moon” along the waterside, natureoriented landscape gardens, and sacred shrine forests with old trees. It seems that such cultural nature could act as a clue to building cities where the species that originally lived will not be extinct.

The Cabinet of Japan approved the National Biodiversity Strategy of Japan 2012—2020 (Government of Japan 2012)[2], which takes into account four types of biodiversity loss: the first crisis (caused by human activities including development), second crisis (caused by a reduction in human activities), third crisis (caused by artificially introduced factors), and the fourth crisis (caused by changes in the global environment). The strategy aims to promote the development of urban areas that are rich in nature in order to achieve the Aichi Biodiversity Targets. We need to identify a better method for creating cities that are rich in biodiversity.

I selected three representative cases from the viewpoint of the history of the designed natural landscape in urban areas in Japan. The points of selection are the scale, design method and habitat function of the designed landscape. All selected three cases have been managed over 20 years since construction, and I am involved in the monitoring and management process; therefore, we can discuss the relationships between planning or design concept with natural processes through verifying outcomes and troubles. 1) EXPO’70 Commemorative Park is the largest scale of natural forest restoration on the disturbed urban site in Japan ever. And the innovative planning concept to set the goal as “self-sustaining forest” that means natural plant communities. The project was an innovative one before the concept of biodiversity was born. We can study the outcome of the initial plant community design method and unique forest management techniques to realize natural forest communities through the data of monitoring and management over decades. 2) “Inochi-no-mori” is the first urban habitat project in a city park in the city center, with the theme of biodiversity conservation and restoration in Japan. The design method is to mimic the remnant ecosystems of Kyoto basin introducing trees and plants with topography arrangement. Because of the intensive monitoring of the biota of the site, we can discuss the outcomes of the design method and the needed management through decades. 3) Garden of Heian Shrine is one of the famous traditional Japanese gardens that intend to reproduce natural landscapes. Although it is a manmade landscape, habitat function as a biodiversity refuge is highlighted recently, facing the biodiversity crises in the original nature, Lake Biwa. Habitat function of the Japanese landscape gardens could be discussed by considering characteristics of the design and management.

All three cases are widely recognized for their importance in urban ecological networks; 1) Ministry of Land, Infrastructure, Transport and Tourism of Japan nominated the EXPO park area as an element of “Urban Environmental Infrastructure Plan of Kinki District” in 2006, 2) the significance of ‘Inochi-no-Mori’ is not only discussed in papers, but also the Mayor of Kyoto introduced it as the core of biodiversity in the First Global Biodiversity Summit of Cities & Subnational Governments, 3) habitat function of the Garden of Heian Shrine in the ecological network of the Lake Biwa basin is highly valued in theRed Data Book of Kyoto Prefecture(2002).

Over the decades, these cases have been uniquely managed with different characteristics, while examining the monitoring results from a biodiversity perspective. These cases therefore provide meaningful insights into considering desirable adaptive management of urban habitat.

1 Plant Community Design and Artificial Gap Regeneration in EXPO’70 Commemorative Park

1.1 “Self-Sustaining Forests” in Urban Areas

EXPO’70 Commemorative Park is a large park (340 hm2) that was the former site of the world EXPO held in 1970 at Senri hills in northern Osaka and now stands as a commemorative park to that event. It comprises a green core of open space that was preserved amidst the process of the urban development in northern Osaka that marked the beginning of the era of high economic growth in Japan.

The main part of the park is the Nature-Culture Zone, covering around 100 hm2, the goal of which was set as “Self-Sustaining Forest” with the aim of restoring natural evergreen broad-leaved forests (climatic climax forests) and semi-natural secondary forest (Satoyama forests) to the ground that had seen large-scale disturbance resulting from the hosting of EXPO’70 (Commemorative Organization for the Japan World Exposition’70, 1972)[3]. It was a pioneering approach, even from a global perspective, to restore natural forests including climax forests in urban areas.

The master plan of the whole park was supervised by Dr. Eika TAKAYAMA (and the Nature-Culture Zone was designed by Mr. Motoo YOSHIMURA). I was involved in the project team as a member of planting design staff (Fig. 1).

1.2 Plant Community Design Unit and Planting Methods

Plant succession theories tell us that climax forests are likely to need several hundred years in order to become established in Japan. However, the target year for completion of the “Self-Sustaining Forest” was set as 2000. Therefore, the mission of the design team was to propose methods for realizing the mature forest ecosystem as rapidly as possible. The planting design was based on vegetation science, considering the species composition of existing forest vegetation as a design unit. However, the open environment and immature soils could have proved too tough for the forest vegetation. Therefore, in order to bring it closer to the mature forest environment, a unique attempt was made to construct a water channel along the ridge surrounding the central flat part that contains the lakes and facilities. The planting sought to mix pioneer species or fertilizer trees, and various other unique methods were designed to enhance the establishment of the forest ecosystem[4]303-321.

1.3 Edaphic Improvement for the Forest Growth

However, in the first decade after planting, the tree growth was so poor that it seemed difficult to establish a mature forest by the year 2000. The reasons for poor growth are acid sulfate soil that resulted from the layer of marine clay exposed by the cutting of the hills, and the compacting of soil by the heavy machines used in the land reclamation.

I joined the monitoring team led by Dr. Sumiji KOBASHI and clarified the relationship between the soil conditions and tree growth[5],[6]184-195. I contributed to enhancing the forest growth environment by providing the finding that the poorly drained soil was the most important factor in limiting normal tree growth.

However, it was in the late 1980s that I came to realize exactly how difficult it is to restore real natural forests. That was when the term “biodiversity” was born, while the concept of “adaptive management”, which is an innovative concept for managing ecosystems that are too complex to understand in their entirety, became recognized in the 1990s.

I realized that the poor drainage sites that provided poor conditions for the growth of forest species were also unique sites of wild grassland and bush communities that were about to disappear from the Osaka city area as a result of rapid urbanization[7].

1.4 “Sprout Forests”, Single Layer and Same Age

The next issue became serious in the 1990s. While forests are seemingly formed gradually, problems were detected from the viewpoint of biodiversity. Indeed, forests were not multi-layered but rather single-layered overcrowded forests, so-called “Sprout Forests” consisting of limited species. In spite of the diverse species selected, the trees planted were considered to be of almost the same generation. As such, the vegetation on the forest floor disappeared, while the diversity of species and range of foliage heights also decreased.

1.5 Artificial Gap Dynamics

Therefore, taking into account the “Gap Dynamics” theory, which explains the mechanism by which the biodiversity of a natural mature forest is maintained, I made a proposal to the decisionmaker to launch an “artificial gap dynamics” project as a means of realizing the original theme of “Self-Sustaining Forest”. This would entail not only creating a gap of around 15 m × 15 m but also introducing various types of gap dynamics, including spreading the surface soil from the surrounding forests of Osaka. We expected soil seed bank of various species to recruit. The soils could be taken from another, adjacent urban developing site, considering the EXPO’70 park is an isolated patch in the urban matrix, so that it is hard for new species to colonize from surrounding forests.

From 2003 onward, what was probably the first trial (Fig. 2) of applied gap dynamics in urban parks was carried out based on a discussion by the adaptive management steering committee[8]. Those activities and outcomes were also widely announced at a side event of the CBD COP10 in Nagoya.

2 Urban Habitat, “Inochi-no-mori”

2.1 Habitat Garden for Urban Biodiversity

The first project as a city park aimed at restoring natural habitat in urban areas (0.66 hm2) in Kyoto took place on the occasion to celebrate 1 200 years since Kyoto became the capital. The site of the former Umekoji railway freight train yard, near Kyoto Station, was developed as a public park in Kyoto City following the National Urban Greening Fair (Fig. 3). “Inochi-no-mori” (Living Forest) was opened in 1996. The author was in charge of coordinating the study group for the project alongside ecology and landscape design specialists. After the park opened, a volunteer monitoring group was set up with the cooperation of experts, students, and citizens. We have continued to conduct intensive monitoring with citizens and hold nature study tours, and have published a report every year[4]15-22. The forest grew into a significant habitat on the former freight train yard that was far from nature. Not only have unexpected creatures colonized the area, such as the kingfisher, once extinct from urban areas, and a kind of truffle, but the ongoing valuable monitoring has enabled several students to utilize the monitoring data and gain a doctoral degree. At the occasion of the City Biodiversity Summit 2010, held in the City of Nagoya, Aichi Prefecture, Japan (from 24 to 26 October 2010) as a side event for the 2010 Convention on Biological Diversity, COP10, Mr. Daisaku KADOKAWA, the mayor of Kyoto, introduced “Inochi-no-mori” and our activities in his presentation speech. Our voluntary activities were also introduced in a white paper by the Japanese Government in 2011.

2.2 Purpose and Declaration

The basic purposes of establishing “Inochino-mori” are summarized as follows: 1) to contribute to a city where you can enjoy the blessings of the four seasons of nature, 2) to enable/facilitate enjoyment of ecosystem services, reducing urban environmental problems such as the heat island phenomenon, 3) to provide a healing landscape for citizens where children can experience, discover, and learn from the abundant nature for their healthy growth, 4) to contribute to a city without extinction of native species before urbanization: “Yamashiro Wilderness” .

While the area of the habitat is very limited, we nevertheless summarized the basic goal as the creation of a habitat before the urbanization of the city of Kyoto.

So we pledged[4]3-14to nurture an ecosystem that would 1) be as rich as possible in native species diversity, 2) be as developmental or sustainable as possible, 3) contain species that are closely related to Kyoto and are familiar to citizens, or 4) include species that would be loved in the future, and 5) have a low population of invasive species that may degrade the biodiversity.

We also agreed that the management should not be so intensive but instead kept to a moderate level and with regard for natural processes.

2.3 Designs

I suggest that successful design methods for the habitat of the limited area should have the following objectives: 1) to protect the area as a paid area connected to the Japanese garden “Suzaku-no-niwa”, 2) to limit the footpaths used on a daily basis including “Canopy Corridor Bridge”, and for closed areas to be opened to the public for guided tours on several days a year, 3) to develop a diverse topography, including soil cliffs, to encourage the kingfisher to nest, 4) for the several types of ponds to be supplied with water by digging a well, 5) to introduce diverse ecosystem resources including CWD (Coarse Woody Debris) in the natural ecosystems but also elements such as a country hedge, “Nozurazumi” (a dry-stone wall using river stones), tree stumps, and firewood deposit in the Satoyama ecosystems.

2.4 Outcomes

We were surprised to observe the dynamic ecological succession[9-10]of the “Inochi-no-mori” habitat, especially during the first decade. The trends of colonization and extinction of species in the habitat varied considerably by taxon.

The maximum number of flowering plant species in Inochi-no-mori was recorded in 1999; however, it then gradually decreased. In the case of avifauna, an increasing phase during the first several years was followed by an almost stable or slightly increasing phase, while in the case of fungi, there appeared to be an increase in the number of epigean and mycorrhiza species. Selected events are shown in Table 1.

2.5 Challenges in the Urban Habitat Project

In spite of the positive trends seen in the natural succession, a number of challenging issues subsequently arose, as described in the yearly reports, which are available on the website.

The first challenge was the invasive alien species. The very rich dragonfly fauna, which was recorded in the second year after construction, was drastically reduced by bullfrogs. The aquatic plants were gradually reduced and then died out due to damage caused by feeding crayfish. Glossy Privet (Ligustrum lucidum) was invasive both at the edge of and within the forest environment.

The second challenge is how to deal with the tradeoff between ecosystem succession and species diversity in the limited area[11]. Disturbancedependent species, mostly herbaceous pioneer plants, began to decrease after the third year.

2.6 Further Challenges

“Inochi-no-mori” was almost the first example of the succession process to be precisely recorded in an urban isolated habitat restored from unnatural land use such as a freight train yard. Therefore, the monitoring records provide precious information for new science and technology. For example, the environmental DNA detection method has recently become an innovative technology for environmental monitoring; however, verification of the results presents a challenge in terms of the standardization of the method. Inochi-no-mori is an isolated habitat whose water source is rainwater and the water from the well on the site. Therefore, our monitoring data on fungi provides valuable information for environmental DNA research due to the fact that we are able to observe very limited fractions of the total rich biodiversity. The ongoing environmental DNA study using the water of Inochi-no-mori is now revealing the various taxonomic fungi (OTU), far more than the species recorded by the monitoring.

The current important issue is how to deal with natural succession from the heterogeneous habitat with smaller trees and open canopies to the homogeneous habitat with taller trees and closed canopies. And the species diversity of flowering plants is gradually decreasing. The Japanese oak wilt event created a slight counter process in the succession trends; however, none of the types of natural disturbances seen in a natural ecosystem, such as floods and windfall of large trees, occur in the limited area of the urban park.

Recently, considering the increasing loss of biodiversity owing to the severe damage caused by feeding sika deer in the surrounding forests of Kyoto city, we might expect a further significant event in the urban habitat, in that it could become a refuge for endangered species. As such, we amended the policy from a passive attitude, waiting for the natural colonization of new species, to one based on active management, which included introducing endangered species by preparing the condition of the habitat. This is one of the actions involved in adaptive management to realize “the city without species extinction.”

3 Garden of Heian Shrine as a Habitat Garden

3.1 Introduction

This year, a large but carefully managed sludge dredging project was undertaken in the ponds of Heian Shrine for the first time in about 40 years. A large sludge treatment plant was installed, and a total of 1,000 people worked on it for 3 months while conserving the biota of the ponds. The project was conducted under the supervision of a committee that included specialists in ecology, Japanese gardens, and cultural properties, working alongside Kyoto city administration staff. The project was carried out because the garden is not only a cultural property in the form of a National Place of Scenic Beauty but also a significant patch of habitat in the urban matrix of the city of Kyoto.

3.2 Japanese Garden as a Wildlife Habitat

Heian Shrine (Heian-jing) was originally constructed in 1895 as a pavilion for the National Exposition for Promoting Industries held in Kyoto, commemorating 1,100 years of the transition of the capital to Kyoto. The 33,000 m2sacred garden was built by notable landscape artist OGAWA Jihei VII (1860—1933), also known as Ueji, who had previously built many excellent modern landscape gardens across the Higashiyama area (foot of the eastern mountains of Kyoto), including the Murinan garden of Aritomo YAMAGATA. Those gardens are characterized by their borrowed sceneries and natural waterside landscapes of streams and ponds using water drawn from the epoch-making canal that leads from Lake Biwa. The sacred garden of Heian Shrine was registered as a National Place of Scenic Beauty in 1975 (Fig. 4). We should emphasize not only the aspect of its scenery but also its function as a habitat in the urban matrix.

3.3 Biodiversity of the Garden

The intensive research report[12]recorded the astonishing fact of the rich biodiversity: about 200 tree species, 300 herbaceous plant species, 106 moss species, 40 fern species, four turtle species, and 40 bird species in a year.

Thus, the garden functions as a significant isolated habitat within the urban matrix of the city of Kyoto.

3.4 Fractals as an Important Element of Natural Habitat Diversity

Important reasons for the rich biodiversity may be found in its design[13]621-625,[14]375-388: a kind of miniature nature, “Shukkei” (miniaturizing nature). The shape of each pond in the garden can be considered as a fractal[15]615-618, which is often observed in natural landscapes (Fig. 5).

Fractal intuitively means that the part and the whole are similar, and they exhibit similar patterns at increasingly small scales, called self-similarity. We analyzed the fractal dimensions of the pond shapes and tree and stone distributions of historical Japanese gardens. And we confirmed that the fractal dimensions of Japanese traditional gardens could be a significant quantitative property of their form and style[14]375-388. Furthermore, fractals can provide habitat diversity for various sizes of organisms; therefore, “miniaturizing nature” is an important concept within Japanese gardens[15]615-618that enables them to function as a sanctuary for wildlife.

3.5 Isolated Sanctuary of Endangered Species in the Urban Matrix

The most interesting outcome is the surviving endangered fish species[13]621-625, striped bitterling (Acheilognathus cyanostigma), in Lake Biwa, the largest lake in Japan.

Originally a popular fish species, the striped bitterling has been displayed at the Lake Biwa Museum in Shiga prefecture, opened in 1996, as a species of Lake Biwa. But the population is the return of a descendant that survived at Heian Shrine. Why did it survive in this pond even though it was not collected in Lake Biwa? It is likely that the fish came from Lake Biwa through the canal that connects the lake to Kyoto; however, the fish cannot breed if there is only a pond. The striped bitterling lays its eggs by inserting a long oviduct into a large bivalve. Bitterling, as waterside fish, adapt to water level fluctuations and are characterized by a life cycle in which the juveniles survive on shellfish that are submerged in the sand, even during the drought season. The larvae of shellfish are also parasitic on small benthic fish species such as Yoshinobori (Rhinogobius), which is why the presence of the striped bittering indicates that an ecosystem of diverse habitats has been formed in the garden ponds. Moreover, when the first freshwater red tide occurred in Lake Biwa in 1983, a sand filter was installed at the inflow inlet from the canal, to prevent polluted water from entering the lake. It is important that the filter also prevented the invasion of the alien species Bluegill (Lepomis macrochirus)and Black Bass (Micropterus salmoides).

3.6 Need for Adaptive Management

In the early 2000s, however, following a remarkable decline in the carp population owing to a pandemic of koi herpes virus (KHV infection), the accumulation of sludge became prominent and the bivalve habitat deteriorated, which resulted in the crisis of a drastic decline in the striped bitterling population.

The garden ponds of Heian Shrine, also called mini Lake Biwa, have also suffered from sludge accumulations in recent years.

We found a description in the diary[16]of the landscape artist Ueji, from when he had just finished construction work on the garden of Seifuso (Aritomo YAMAGASTA’s Kyoto villa); he went to the Kamo river to catch small fish and released them into the pond. This description clearly shows his intent to restore nature in the garden. Thus, in order to inherit the natural scenery he intended, it is essential to undertake dredging instead of relying on the natural disturbance caused by flooding that occurs after heavy rains once every several decades.

4 Discussion

Urban habitats play an important role in urban biodiversity, serving as the basis of a sustainable city without species extinction. Here, I have only discussed the ecological aspects of a restored urban habitat and have not discussed the current existing habitat including various kind of reserves, sacred shrine forests, agricultural land left in urban areas, rivers, reservoirs, and so on. These are the fundamentals of urban biodiversity. However, because urban biodiversity has deteriorated due to the development so far, the restoration of habitats is indispensable for realizing the Sustainable Development Goals (SDGs), which was adopted by the UN Sustainable Development Summit held in 2015.

4.1 Patch Size

Large habitats are capable of inhabiting a variety of species[17]; and can be expected to have large ecosystem services. On the other hand, creating and managing new large habitats in urban areas to respond to the biodiversity crisis is costly and difficult. All three cases are associated with special events: the first world EXPO held in Asia, 1,200 years, and 1,100 years anniversary of capital establishment in Kyoto. We need to consider the significance of the size of fragmented habitats from the viewpoint of biodiversity.

According to our research in the city of Kyoto[18-20],[21]23-24, an isolated habitat in an area covering around 1 hm2(such as the garden of Heian Shrine and Inochi-no-mori in Umekoji park) could become a habitat for an insect-eating Japanese tit (Parus minor), an area of 3-10 hm2could be a habitat for the small raptor Brown hawk-owl (Ninox scutulata), while a goshawk could live in an area covering 100 hm2(such as EXPO’70 Commemorative Park). Thus, large habitats are better than smaller ones; however, the famous proposition, SLOSS: Single Large (SL) or Several Small (SS) habitats, which is better, tells us that SS is more advantageous than SL in terms of the number of species and the establishment of a habitat for rare species. Yet even if it is small, the restoration of a unique habitat has great significance.

Of course, the size of a habitat is a very important positive parameter for determining the species diversity. However, the actual significance of the area varies greatly depending on the taxonomic group. Ferns, herbs[21]23-24, ants[22], and mosses[23]are greatly affected by the diversity of micro-habitats[24]. Japanese landscape gardens as a habitat, particularly for small organisms, are significant for this reason.

4.2 Habitat Management Considering Natural Process

Important significance of urban habitats is to ensure the original biodiversity of the area, as an ecological network. Landscape ecological discussion using the concepts of “Elements/ Pattern/Process” is the key issue[25]to understand the species diversity of fragmented patches in urban areas (Tab. 2)[26].

EXPO case showed us the consideration of elements (such as ecosystem types, species) and patterns (such as several types of forest patch and making hills and rivers) are not enough to restore natural forests. More concern on the landscape ecological diversity formed by disturbances needed; and the adaptive management as an alternative to natural processes (such as gap dynamics and flooding). Inochino-mori case was well designed to set up the initial stage from the viewpoint of the elements and patterns of nature, however, growth of the forests made the initial heterogeneous mosaic pattern to change into more homogeneous structure. And the significant degradation of species diversity of disturbancedependent plants was observed. Heian Shrine case is characterized as miniaturized patterns of nature (such as shape, material, microhabitat distribution of ponds and the connection to Lake Biwa) that allowed to developing the unique and rich biodiversity of the garden. But lack of natural process such as flooding is the reason of the problem we faced recently.

However, the sustainability of restored habitats depends on adaptive management, such as mud dredging of pond bottoms as an alternative to natural flooding. In the case of a large habitat such as EXPO’70 park, it is possible to accept a certain degree of natural disturbance such as trees brought down in a typhoon. Among the three properties of nature shown in the Table, “Process” is the most challenging issue to deal with (Tab. 2).

All three cases originally had strong points in the construction; or in terms of “Elements”and ‘Pattern’, those were good practices. Goshawk successfully nested at the large patch, EXPO. Inochino-mori and the garden of Heian shrine are the refuge of endangered species. However, adaptive management of human disturbances as alternative to natural disturbances is the essential “Process” to maintain biodiversity and attractiveness of each site.

In a habitat restoration project, it is not only the design of the elements and patterns of the site that need to be studied carefully, but also the design of the management program in place for natural and human processes. Natural disturbances can cause disasters but are also essential for a healthy habitat. Therefore, adaptive management of habitat is closely related to “Green Infrastructure” and Eco-DRR “Ecological Disaster Reduction”[27]. The rain garden is very useful as a habitat in the city, as well as mitigating the heat island phenomenon and mitigating heavy rain disasters due to global warming[28].

Sources of Figures and Tables:

Fig. 1 Photo courtesy of Osaka Prefectural Government；Fig. 2, 4 Source of the author; Fig. 3 Photo courtesy of Kyoto City; Fig. 5 Photo courtesy of Mr. ITO Sosuke; Tab.1 drawn by the author; Tab. 2 Source of the paper written by reference [26].