Keywords

4.1 Introduction

4.1.1 Biodiversity

“Biodiversity,” a term coined only 30 years ago, refers to the multiformity of living organisms in terrestrial, marine, and other aquatic ecosystems. Biodiversity is the central issue in nearly all environmental concerns. At the 10th Conference of the Parties to the Convention on Biological Diversity (COP-CBD), held in Nagoya (Japan) in 2010, biodiversity was the keyword for the delegates’ ongoing campaign.

Although the term “biodiversity” is becoming increasingly familiar worldwide, the concept remains ambiguous. For the CBD, biological diversity refers to the variability among living organisms in all habitats including, among others, terrestrial, marine, and other aquatic ecosystems, and the ecological complexes of which they are part; this concept includes diversity within species, between species, and among ecosystems. Thus, biodiversity originally referred to the conditions supporting the great variety of life forms in diverse ecosystems.

Ecosystem services based on biodiversity provide a multitude of benefits to people (The Economics of Ecosystems and Biodiversity (TEEB) 2010). Evidence shows that biodiversity loss reduces the efficiency of ecological communities in: (1) capturing biologically essential resources; (2) producing biomass; (3) decomposing organic material; and (4) recycling biologically essential nutrients (TEEB 2010).

4.1.2 Current Status of Biodiversity

Mass loss of biodiversity is a global concern. Daily species’ extinction rates are now up to 1000-fold higher than natural rates (International Union for Conservation of Nature (IUCN) 2016). Extinction of individual species, habitat destruction, land conversion for agriculture and other human uses, climate change, pollution, and the spread of invasive species are only some of the threats responsible for today’s biodiversity crisis. The global biodiversity outlook issued by the Secretariat of the CBD (2014) emphasized that all major pressures on biodiversity are increasing.

A Japanese biodiversity outlook was published by the Ministry of the Environment of Japan (MoE) (2010) to provide a summary of the status of biological diversity in the country. The report identified four principal pressures (habitat change, abandonment of agricultural landscape management, pollution caused by the introduction of chemicals and invasive alien species, and climate change) that are directly driving biodiversity loss in Japan (Table 4.1). These crises have been addressed through a variety of responses, which have been partially effective. However, the socio-economic drivers of modern societies markedly limit the force of these responses.

Table 4.1 Four biodiversity crises in Japan (Numata 2014, after MoE 2010, 2012)
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4.2 Natural Environments and the Current Status of Biodiversity in Tokyo

The administrative area of the Tokyo Metropolitan Government includes the 23 special wards area of Tokyo to the east, 26 cities to the west, and two outlying island chains (Izu and Bonin Archipelagos) (Figs. 4.1 and 4.2). Although Tokyo covers a relatively small area, it supports rich biodiversity that should be maintained through conservation efforts.

Fig. 4.1
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Locations of the Tokyo Metropolis and the Izu and Bonin Archipelagos (Numata 2014)

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Fig. 4.2
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Location of the Bonin Islands

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Tokyo has two ecosystem types: (1) urban, secondary forest, and agricultural (Satoyama) systems, and (2) oceanic island systems. The different types of landscape support different habitat specialists.

4.2.1 Wildlife and Threatened Species

The Bureau of Environment of the Tokyo Metropolitan Government (BE-TMG) (1998) listed 4323 and 51 species of wild plants and mammals, respectively, found in Tokyo (Fig. 4.3a). Species richness was relatively low on the Izu and Bonin Islands, but endemism was high. The environs of Tokyo supported 4323 wild higher plant species, 51 mammal species, 422 avian species, 30 reptile species, 18 amphibian species, 18 freshwater fish species, and 2648 insect species. Among the higher plants, 3421 species occurred on the mainland, 1313 on the Izu Islands, and 654 on the Bonin Islands. Among mammals, only one wild species (Bonin fruit bat: Pteropus pselaphon) was found on the Bonin Islands, whereas 43 species occurred on the mainland. Evidence shows that wild species have either been extirpated in Tokyo or exist in small, threatened populations. Hence, monitoring is essential to keep track of surviving taxa.

Fig. 4.3
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Wildlife species in metropolitan Tokyo. (a) Numbers of wildlife species listed for mainland Tokyo and the Izu and Bonin Archipelagos. (b) Numbers of endangered wildlife species listed for mainland Tokyo and the Izu and Bonin Archipelagos (Numata 2014)

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The BE-TMG (2010, 2011) listed threatened wild species in Tokyo, including 800 mainland plant species (Fig. 4.3b). Of these, 182 (22.8%) species have been recognized as threatened by the MoE. The Tokyo Metropolitan Government listed 384 threatened plant species on the Izu Islands; of these, 99 were listed as threatened by the MoE (BE-TMG 2011). The Tokyo Metropolitan Government listed 169 threatened species of plants on the Bonin Islands; among these, 35 species were listed as threatened by the MoE (BE-TMG 2011).

Among the threatened mammal species, 37, 5, and 1 occur on the mainland, the Izu Islands, and the Bonin Islands, respectively. The Japanese wolf (Canis lupus) and the Japanese river otter (Lutra lutra nippon) are now extinct on the mainland.

Eight-hundred mainland plant species have been listed as either extinct (68 species) or threatened (BE-TMG 2010). Among the latter species, 9 and 24 are listed as IA (critically endangered) and IB (endangered), respectively, by the MoE.

Small and mid-sized mammals were found in the city center area before the Second World War, but 20 species, including the Japanese water shrew (Chimarrogale platycephala) and the red fox (Vulpes vulpes japonica), are now considered extinct. Many mid-sized mammals, including the masked palm civet (Paguma larvata) and the raccoon dog (Nyctereutes procyonoides) occur in the North and South Tama areas. Common and threatened mammals, such as the Asian black bear (Ursus thibetanus), the stoat (Mustela ermine), and the Japanese serow (Capricornis crispus), occur in West Tama in the montane sector of Chichibu-Tama-Kai National park.

4.2.2 Protected Areas in Tokyo

Three national parks and one quasi-national park are located in the Tokyo administrative area. Chichibu-Tama-Kai National Park is located at the intersection of Saitama, Yamanashi, Nagano, and Tokyo Prefectures. The park contains eight peaks over 2000 m high, scattered over 1250 km2 of terrain, with numerous hiking trails and ancient shrines. Fuji-Hakone-Izu National Park is a collection of dispersed tourist sites that dot Yamanashi, Shizuoka, and Kanagawa Prefectures and the western Tokyo Metropolis. The total area is 1227 km2. The park includes Mount Fuji, Fuji Five Lakes, Hakone, the Izu Peninsula, and the Izu Islands. Ogasawara National Park is located on the Ogasawara (Bonin) Islands ca. 1000 km to the south of Tokyo. The park was established in 1972 within the municipality of Ogasawara, which is part of Tokyo. In 2011, the Ogasawara Islands were included in the UNESCO World Heritage List.

Meiji no Mori Takao Quasi-National Park is located around Mount Takao in Hachioji City, Tokyo. Established in 1967 for the centennial celebrations of the accession of Emperor Meiji, it is the smallest of the quasi-national parks. Mount Takao, rising to 599 m above sea level, is a massif of low mountains that formed in the Mesozoic era. The area supports dense pristine forests of momi fir (Abies firma), Japanese red pine (Pinus densiflora), and Japanese beech (Fagus crenata).

4.2.3 Mainland

The mainland area of Tokyo is divided into the 23-ward (east) and Tama (west) areas (Fig. 4.1). The highest concentration of urban zones is within the 23-ward area. Natural and secondary vegetation, including subalpine conifer forest, broad-leaved deciduous forest, broad-leaved evergreen forest, and plantations, are predominant in the western part of mainland Tokyo (Fig. 4.4). Most land is urban, and only 0.1% (42.4 ha) of the 23-ward area supports natural forest, secondary vegetation, or tree plantations (BUD-TMG 2008). The proportional covers of forest and agricultural land in the Tama area are 48.7% (56,458 ha) and 5.5% (2590 ha), respectively (BUD-TMG 2009).

Fig. 4.4
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Vegetation map of mainland metropolitan Tokyo. Natural and secondary vegetation (subalpine coniferous forest, broad-leaved deciduous forest, and broad-leaved evergreen forest zones) and plantations are indicated. Data sourced from the results of the Sixth and Seventh Vegetation Surveys conducted by the Ministry of the Environment of Japan (Numata 2014)

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4.2.3.1 The 23-Ward Area

An urban ecosystem dominates the 23-ward area, where the natural vegetation would have been temperate evergreen forest. Little natural or semi-natural vegetation occurs in housing and factory areas (Fig. 4.4). The urban ecosystem is unique, but poor in biota because of habitat destruction, pollution, and overuse of natural biological resources (Puppim de Oliveria et al. 2011). The imperial residence and urban parks in the central ward area contain large-scale natural or semi-natural environments. Wild species have been recorded within the imperial residence area: 1366 wild plant species, 69 avian species, and a few mid-sized mammals, including the masked palm civet and the raccoon dog, have been reported there (Endo et al. 2000; Koyama et al. 2000; Takeda et al. 2000).

4.2.3.2 Tama Area

Forests occur in the Tama area. Many are secondary stands of deciduous oaks and plantations of cedar trees (Fig. 4.4). Natural stands that include climax species of temperate deciduous forests (Fagus creanata) have a limited occurrence in west Tama. The post-war new town development of Tama had significant effects on the natural environment. The development included the Satochi-Satoyama sector, which contained managed secondary forests of deciduous oaks (Quercus serrata and Q. acutissima), agricultural land with rice paddies and dry fields, artificial lakes, ponds, and grasslands before the Second World War (Numata and Obara 1982). Many secondary forests of deciduous oaks were reconfigured to residential land during the Tama new-town development in the 1960s (Miyawaki 1986). Ichikawa et al. (2006) examined changes in the Satoyama landscape, located in the urban fringe of the Tokyo metropolitan area, during the period 1880–2001. They found that in the Tsurukawa area (Machida, Tokyo): (1) the cover of woodland and agricultural land began to decrease rapidly by 1961; (2) large-scale development increased during the 1960s and 1970s; (3) the decrease in woodland and agricultural land cover slowed after 1974, but the rate of urbanization (conversion to urban land) remained unchanged after 1974; and (4) urban land use was predominant (60% of the total area), with large-scale development accounting for 6.1% of the area in 2001; woodland, crop field, and paddy field cover decreased to 20%, 7.4%, and 1.1% of the total area, respectively.

4.2.4 Izu Islands

The Izu Islands are volcanic; two of the islands, Hachijo-jima and Aoga-shima, are oceanic. The flora of the Izu Islands is part of a vegetation zone that includes the Izu peninsula and the Hakone volcano. However, ocean currents isolate the islands, which have floristic elements that differ from those of the Izu and Boso peninsulas (Miyawaki 1986). Differences in geological history and area account for the variation in vegetation and plant species richness among the islands (Table 4.2).

Table 4.2 Areas and numbers of vascular plant species on 11 islands of the Izu Archipelago (Numata 2014, data from Kachi 2011)
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Although some differences exist among the islands, climax evergreen forests with Castanopsis sieboldii and Machilus thunbergii occur throughout the Izu Archipelago (Kamijo and Okutomi 1993). The vegetation of the evergreen forests, which differs from that of the Honshu mainland, is characterized by the absence of indigenous oak species (Miyawaki 1986). Anthropogenic impacts (Oyama 1999) and diverse stages of plant succession (BE-TMG 2011) also characterize the Izu Islands.

A distinctive biodiversity feature of the archipelago is the high number of endemic and sub-endemic species (Miyawaki 1986). Eighteen vascular plant species, 21 variant species, 1 variety, and 1 hybrid are endemic to the islands (Oba and Akiyama 2002).

The terrestrial mammalian fauna of the archipelago is poorer than that of the Honshu mainland. Nineteen mammal species, including the Japanese sea lion (Zalophus japonicus), are found in this area. Five rodents and shrews may have been artificially introduced (Takada et al. 1999, 2004). Other mammals, including the Taiwan squirrel (Callosciurus erythraeus thaiwanensis), the Formosan rock macaque (Macaca cyclopis), Sika deer (Cervus nippon), the Japanese weasel (Mustela itatsi), and goats (Capra hircus), may also have been introduced. Five mammal species, including the greater horseshoe bat (Rhinolophus ferrumequinum) and the large Japanese field mouse (Apodemus speciosus), are listed as threatened species (BE-TMG 2011).

4.2.5 Bonin (Ogasawara) Islands

The oceanic Bonin Islands are part of a remote Japanese archipelago in the northwestern Pacific Ocean. More than 30 islands and rocks belong to three islands groups: the Mukojima, Chichijima, and Hahajima groups. The three Volcano Islands (Ioretto) and three small, isolated islands (Nishinoshima, Minamitorishima, and Okinotorishima) are sometimes regarded as members of the Bonin Archipelago (Figs. 4.1 and 4.2). The climate of the Bonins is subtropical; the mean monthly temperature range on Chichijima is 18–28 °C. The monthly rainfall range is 60–170 mm, and the annual precipitation is ca. 1300 mm.

The biota of the Bonin Islands is distinct from that of the Honshu mainland (Miyawaki 1989; Hata and Kachi 2011). The islands have been less impacted by anthropogenic effects than have other islandsnear Japan mainland. Prehistoric remains (ca. 800–2000 years old) have been found on Kitaiwo-to (one of the Volcano Islands) and Chichi-jima (Kawakami and Okochi 2010). Prehistoric peoples disappeared prior to the recent human repopulation of the archipelago in 1830. Members of the second wave of settlers were European and Polynesian. A whaling industry existed around the islands (Kawakami and Okochi 2010), and farmland replaced some of the forests. Domestic animals, such as goats, were introduced to the islands and eventually became feral.

Vegetation and plant species richness differ across the archipelago due to the diversity of bedrock, geological history, and island area (Fig. 4.2; Table 4.3). The degree of plant species endemism is high: 69 endemic plant species (67% of the flora) occur in lowland dry forests. However, natural disasters and the elevated browsing pressure from feral goats have become major threats to the vegetation of the islands. Rhododendron boninense is one of a group of rare plant species with population sizes smaller than 100 individuals. Two wild mammal species have been recorded on the islands, but one of them, the Bonin pipistrelle (Pipistrellus sturdeei), is now extinct, leaving the Bonin fruit bat (Pteropus pselaphon) as the only extant wild mammal. This species is listed as critically endangered (CR) by the MoE. The bat sometimes becomes an agricultural pest because its habitat overlaps human dwelling spaces (Inaba et al. 2002). Some of the island avian species are also threatened by habitat degradation. However, Bryan’s Shearwater (Puffinus bryani), which was considered to be extinct, was rediscovered in 2012 (FFPRI 2012). The endemic and threatened species on the islands highlight the ecological significance of the Bonins.

Table 4.3 Areas and numbers of vascular plant species on 14 islands of the Bonin Archipelago (Numata 2014, data from Kachi 2011)
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Mesic forest (Elaeocarpus-Ardisia), with trees greater than 20 m in height, is part of the diagnostic vegetation of the Bonin Islands. The islands provide a suitable habitat with good soil for tall tree species, including Elaeocarpus photiniaefolius and Pisonia umbellata (Shimizu 2003). Another diagnostic vegetation type is a low, dry forest with trees 5–8 m high. This vegetation occurs in habitats with thin, dry soils. The forest contains many shrubby tree species, including Distylium lepidotum and Schima mertensiana (Shimizu 2003). The beech family (Fagaceae) is notably absent from the Bonin Islands (Miyawaki 1989).

Low species richness, simple food webs, and high levels of endemism in the biota are typical characteristics of oceanic islands. Across five major islands in the Bonin Archipelago, 150 of 688 species of vascular plants are endemic. Southeast Asian elements are the major components of the flora with western origins. Polynesian elements are from the south, and Japanese mainland elements are from the north (Shimizu 2003). Some species advancing into the islands filled vacant niches and underwent adaptive radiation. The most remarkable example of adaptive radiation is found in the land snail genus Hirasea (12 species and 4 subspecies) (Tomiyama 1992). Each species has a particular shell shape that is adapted to a specific habitat (Shimizu 2003). Small, remote oceanic islands generally lack indigenous land mammals and amphibians.

4.3 Perspective on Biodiversity in Tokyo

4.3.1 Biodiversity Crisis in Tokyo

The four principal drivers of biodiversity loss are listed in Table 4.1 (MoE 2010). Pressures from these drivers are either constant or increasing within the environs of Tokyo.

The first biodiversity crisis in Tokyo was serious before the Second World War, but has receded in recent times. Large- and mid-sized mammal species (e.g., Japanese red fox and Japanese hare [Lepus brachyurus]) were found in the city center until the 1930s (Kishida 1934), but habitat loss caused by rapid modernization and the catastrophic damage inflicted during the war eliminated most of these species. After the war, small mammal populations were impacted by large-scale development in the Tama area (Chiba 1973). Most of the woodlands in the north Tama area had disappeared by the 1970s (NCB-MoE 1976).

Interest in green spaces and natural environments in urban areas increased after the 1980s, following a period of rapid economic growth and rising pollution. In 1972, the Tokyo Metropolitan Government issued new regulations for nature protection and recovery in Tokyo. The 10-year project for green spaces in Tokyo, launched in 2007, encouraged the improvement of “green road networking” and “Umino-mori” (“forest in the bay”) (BE-TMG 2007).

A conflict between humans and wildlife has emerged in green spaces. The ranges of some large- and mid-sized mammal species are expanding. For example, the ranges of wild boars have expanded considerably in West Tama, where damage to agriculture has become a serious issue. Some outdoor pests (e.g., wasps) have become a major problem in Tokyo (Hosaka and Numata 2016). Reducing conflicts with pests and appropriate science communication on the value of biodiversity are critical for sustainable biodiversity conservation in urban areas.

A weakening of the relationship between human beings and the Satoyama landscape through increased use of fossil fuels and chemical fertilizers is a second major crisis in Tokyo. The species composition and structure of managed forests used for agricultural purposes in Satoyama landscapes have changed, creating a biodiversity crisis in Japan. The endangered cherry species Tamano Hoshizakura (Cerasus tamaclivorum), for example, is found in Satoyama landscapes of the South Tama area (Ohara et al. 2004). Appropriate management of secondary forests by periodic logging and mowing will be important for the conservation of this species (Iki et al. 2014).

Satoyama management activities have been undertaken by local community groups. Volunteer-based management by these groups is recognized as an effective tool for mitigating the degradation of Satoyama woodlands (Kobori and Primack 2003). However, the problem of human aging is becoming a crucial issue in maintaining the staff required for management activities (Oku 2010). Participation by new members may be essential for the continuation of volunteer-based management by local community groups.

The alien species problem is the third crisis of special importance in the Bonin Islands. The direct impacts of alien species on endemic rare taxa are well known, and measures to control invaders have been implemented. The indirect impacts of alien species, e.g., pollination failure in indigenous plants, have also been emphasized recently (Abe et al. 2008; Abe 2009).

Problems caused by invasive species have been reported in mainland Tokyo. Although there is little quantitative information on the abundance of alien species in mainland Tokyo, Kitazawa (2010) detected significant increases in the numbers of alien plant individuals and species in four prefectures within the Kanto area. Some invasive species, such as the common raccoon (Procyon lotor), have caused serious problems through damage to agriculture by the vectoring of infectious diseases.

4.3.2 Strategies and Actions for Biodiversity Conservation

The outcomes of COP-10 have had great impacts on the policies and practices for conserving and managing biodiversity in Japan. The MoE established the National Biodiversity Strategy 2012–2020 with five goals: (1) raising public awareness of biodiversity; (2) developing human resources and a collaborative framework; (3) creating regions linked by ecosystem services; (4) national land conservation and management that accounts for the dwindling human population; and (5) strengthening the scientific knowledge base for the development of political measures (MoE 2012).

Based on the National Biodiversity Strategy and the Basic Act on Biodiversity enacted in 2008, the Tokyo Metropolitan Government established a new green plan in 2012 to function as a regional biodiversity strategy. The plan aims to create 1000 ha of new green space by increasing urban park areas, coastal forests, wayside trees, and school yards with lawns (BE-TMG 2012). Furthermore, 11 of 62 districts (i.e., wards, cities, towns, and villages) in Tokyo had established their own regional biodiversity strategies by March 2015 (MoE 2015). These strategies aim to promote: (1) public understanding of biodiversity issues; (2) conservation of native species and their habitats; (3) control of alien species; (4) networking among the lay public, companies, institutions, and governments; and (5) community development through conservation activities. Thus, biodiversity conservation has become a central concept for green space management in Tokyo.

The private sector has also initiated new actions related to biodiversity. A 3600-m2 Satoyama forest was created alongside office buildings and a shopping complex in Otemachi in 2014 to mitigate heat-island effects and improve ecological networks in the city center. The forest supports 280 plant species, of which 160 were growing naturally one year after the forest was developed. The Satoyama attracts 8 and 66 species of birds and insects, respectively (Taisei Corporation 2014). the non-profit organization Ginza Honeybee Project keeps 150,000 honeybees on a rooftop in Ginza and collects 840 kg of local honey annually, aiming to strengthen public social networks and raise awareness of local biodiversity (Ginza Honey Bee Project 2016).

4.3.3 Ecosystem Disservices and Challenges

Although nature conservation has had significant positive effects on the maintenance of biodiversity in urban and agricultural landscapes, the negative impacts of biodiversity on the quality of urban life have recently been identified as ecosystem disservices (Lyytimäki and Sipilä 2009). Ecosystem disservices include allergen emissions, damage to human infrastructures, and people afflicted by falling branches, fear of and stress related to shaded green areas during darkness, and populations of pests and nuisance animals (Gómez-Baggethun and Barton 2013). Though most of these nuisances may be minor, they could be relevant to the quality of urban lifestyles and present challenges for biodiversity conservation activities (Lyytimäki et al. 2008). For example, human–wildlife conflicts may increase as green spaces expand within the urban or residential areas of western countries (Kretser et al. 2008; Soulsbury and White 2015). In Tokyo, the numbers of consultations on wasps, which account for 50% of total pest consultations, are higher in districts with high proportions of forested areas (Hosaka and Numata 2016). Local governments may face problems in handling the increasing numbers of consultations on wild animals in urban areas. Hence, the minimization of ecosystem disservices and the maximization of ecosystem services will contribute to sustainable biodiversity conservation. Public perceptions of ecological services and disservices are affected by many factors, including social and cultural contexts, and can be changed through education, interpretation, and media coverage (Lyytimäki and Sipilä 2009; von Döhren and Haase 2015). Thus, relevant scientific knowledge and environmental education, including information on the ecological functions of wild animals and appropriate ways of interacting with them, may greatly reduce the perceived disservices. Since most natural environments in Tokyo are influenced by human activities, promoting public understanding of biodiversity is the key to formulating an urban planning framework for the sustainable management of biodiversity.

4.4 Concluding Remarks

Tokyo, the capital of Japan, is one of the world’s largest cities. It spans the 23-special wards district to the east, 26 cities to the west (Tama), and 2 outlying island chains (Izu and Bonin Archipelagos). Although Tokyo is relatively small in area, it has rich biodiversity that should be maintained through conservation efforts. “Biodiversity” has become a key element in urban landscape design and in the management efforts of national and local governments, private companies, and citizen groups. The ecological disservices of wildlife, such as an increasing frequency of conflicts between wild animals and residents in urban areas, should not be overlooked. Appropriate scientific communication on biodiversity is the key to reducing ecosystem disservice levels.