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Preface to the Second Number of the Special Issue:
Natural Environmental and Biotic Features and Ecological History
of Biotic Migrations and Invasions into the Japanese Archipelago
from Geological to Modern Ages
Izumi WASHITANI
Institute of Agriculture and Life Sciences, University of Tokyo,
Bunkyo-ku, Tokyo 113-8657, Japan

Prologue
Modern biological invasions in Japan are having various types of serious impacts on ecosystems
and human life, and appropriate countermeasures are urgently needed (Washitani, 2004). In contrast,
when historically viewed on a much longer time scale, major factors responsible for the unique indigenous flora and fauna of contemporary Japan included geo-biotic exchanges with the Eurasian Continentaccompanied by intermittent isolations of the Japanese Archipelago, as well as its unique environmental
conditions.
In the present essay, as a preface to the second number of the special issue, ‘Biological invasion in
Japan,’ I will briefly summarize the natural environmental features, including geological, climatic andbiotic, and the geological-ecological histories of the Japanese Archipelago, which have also interactedwith human history and are relevant to the biotic exchanges with Eurasian Continent, in order to contrast them with modern biological invasions.
Key words: biological invasion, ecological history, migration

1. Geo-biotic Histories, Environmental Features and Biota
1.1 Geological origins of the Japanese Archipelago
The distribution of volcanic and sedimentary rocks
in northeastern and lowland Japan suggests the date offormation of the geological basis of the present Japanese Archipelago was in the Miocene era (approximately 22 million years ago) (Taira, 1983). The Sea ofJapan is a young marginal basin located between
Japan and the Asian Continent and is inferred to havebeen formed in the middle Miocene, i.e., about 15 million years ago (Chinzei, 1991). Before that geologicalage, the Japanese islands were not separated from theEurasian Continent, but formed the eastern end of thecontinent.
During earlier geological ages, parts of the Japanese Archipelago were assembled at the eastern borderof the Eurasian Continent through stepwise fusions oflandmasses conveyed by oceanic plate movement(Hashimoto, 1991). The first arrival of a landmass,
which had been derived from an old equatorial continent, was dated to the beginning of the Mesozoic era.
Global Environmental Research8(2)/2004: 103-116
printed in JapanThe second arrival occurred in the Jurassic to early
Cretaceous era when the main parts of the present
Honshu, Shikoku, and Kyushu were assembled. At thenext stage during the Cretaceous to Miocene era, thesouthwestern borders of Honshu, Shikoku and Kyushu
and the main part of Hokkaido were added.
Deviation of magnetism of early Miocene rocks
from that of older rocks supports the hypothesis that
the Japanese Archipelago was located closer to the
Asian continent before the middle Miocene when thesouthwestern and northeastern halves independently
started to rotate clockwise and counterclockwise, respectively, to settle in the present position and configuration (Otofuji & Matsuca, 1984). This model well
explains the current topographic and petrologic coincidences that can be recognized between the continental and Japanese coastlines facing the Sea of Japan.
The present island arc/submarine trench system became active at the beginning of the Tertiary (approximately 30 million years ago), when the basic nature of
the relative movements of the Pacific plate andEurasian plate was fixed.

©2004 AIRIES

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1.2 Volcanoes and rich natural disturbances
Natural or human disturbances play importantroles in dynamic transitions of local biota, including
biological invasions, through the generation of wellilluminated gaps within dense vegetation or the release of resources occupied by competitive dominant
species. Volcanic and seismic activities and flooding
are the main causes of large-scale natural disturbances,which are major natural driving forces for biologicalinvasions or transitions.
Around the globe, the spatial distribution of volcanoes is remarkably uneven, and more than 80% areclumped along continental borders or island arcs adjacent to trenches where ocean plates sink beneath continental plates (Machida, 2002). The Japanese Archipelago, which forms a northeast-southwest arc stretching along the eastern end of the Eurasian Continent
over approximately 2,400 km, consists entirely of
relatively new volcanic belts along a conspicuous
plate subduction zone, where the plates of the western
Pacific Ocean, i.e., the Pacific and Philippine plates,
sink beneath the North American and Eurasian plates,
respectively. Therefore, the Archipelago is especiallyrich in natural disturbances accompanying volcanicand seismic processes. More than the one tenth (86out of 800 total) of active volcanoes in the world, including both active and dormant ones, are found along
two lines consisting of the eastern and western Japanese volcanic zones (Sakaguchi et al., 1976) where
one-tenth of the portion of the earth energy responsible for volcanic eruptions and earthquakes is emitted,
despite covering only 1/400 of the total land area of
the globe (Ito, 1987).
Many volcanoes have their peaks at elevations
above 3,000 m. Representative of those is Mt. Fuji,
the highest mountain in Japan, rising to 3,776 m on
the Pacific coast in central Honshu, the last eruptionof which was recorded in 1707. Volcanic ash and othervolcanic ejecta that are widely found in strata throughout the Japanese Archipelago enable us to infer thetimes, scales and impacts of past volcanic eruptions.
The most violent eruption that occurred within the
recent 10,000 years was that of the Kikai caldera in
the sea near southern Kyushu located between thesouth end of Kyushu and Yakushima Island and dated
back to 6,300 years ago (Machida, 2001). During theeruption, the pyroclastic flow spread across the sea not
only to the mountain ranges of Yakushima Island but
also an immense tract of the southern Kyushu region.
One can easily imagine disasters sweeping away all
animals and plants within range and vast void niches
formed for biological invasions. On a time scale oftens of thousands of years, volcanic activities arelikely to be one of the most important factors influencing the biota of the Archipelago.
Volcanic ash soils named andisols that are characterized by black color and fine particle size, andthus have large specific surface areas are widely distributed across temperate humid Japan, covering

one-sixth of the total land surface and 27% of all agricultural lands (Takahashi & Shoji, 2002; Shoji &Takahashi, 2002).
1.3 Active geomorphological processes and rapid
riversThe mountainous condition of the Japanese Archipelago is the natural consequence of frequent volcanic
eruptions and seismic activity. The mountains tend tobe formed by volcanic ejecta or seismic land upheavals. More than three-quarters of the land surface ofJapan consists of mountains that form the solid backbone of the Japanese Archipelago, while flat lands,
including plateaus and lowlands, occupy only 26% of
the total land area of Japan.
Due to steep mountainous topographies and climatic conditions with abundant precipitation, aquaticsoil erosion and sedimentation occur actively throughout Japan. The volume of gravel and sand removed byerosion along a representative rapid river, the Kurobe
River of central Honshu, is estimated to be as large as
6,000 m3/km2 per year (Hamada & Nakamura, 1999).
Such a high erosion rate is globally exceptional.
Active production and sedimentation of gravel, sand,silt and clay are the most conspicuous features of
rapid Japanese rivers, and most plains in Japan aredeltas or alluvial fans formed by riparian sedimentation during the recent 10,000 years (Kodansha International, 1999). Deposition of alluvial sediments as
thick as 50-90 m is exceptionally rare world wide, butrather common in lowland Japan.
Various types of geomorphic processes on various
scales which prevail over the islands result in afine-grained mosaic of physical land conditions, inother words, highly spatially heterogeneous environmental conditions. Both scenic beauty and frequent
natural disaster are the results of high geomorphic
activities of the Japanese Archipelago. In addition tofrequent disturbances, spatially heterogeneous environmental conditions consisting of a fine-grained
mosaic are the most pronounced feature of the Japanese natural environment, enhancing biological diversity.
1.4 Climatic features
The present climate of Japan is generally temperatewith annual mean temperatures of 10-18°C, although
there are large seasonal fluctuations in both temperature and precipitation (Fukui, 1977). Compared toother regions at the same latitude, Japan is characterized by abundant annual precipitation and a large annual fluctuation of temperature characterized by summer heat comparable to the tropics and winter chillingcomparable to the frigid zone (Kira et al., 1976).
In addition to such a large thermal fluctuation,
there are marked seasonal changes due to alteration of
the circulation system. A global circulation patterncharacterized by tropical monsoon systems is basically constant year round, but in the northern hemi-Preface to the Second Number of the Special Issue

sphere entire circulation systems shift north during
summer (Study Group for Climate Impact and Application, 2002, 2004). Japan is located just at the latitudinal zone where tropical circulation systems alternatewith subtropical, and extra-tropical with polar
seasonally (Hamada & Nakamura, 1999). Therefore,
within the range of the Japanese Archipelago, tropicalcirculation prevails in summer, but extra-tropical circulation, in autumn, winter, and spring. The meteorology under the influence of the tropical circulation system is characterized by the absence of fronts and migratory anticyclones. The weather is relatively invariable day-to-day, but variable within a day. In contrast,
the extra-tropical circulation system brings about
cyclically changing weather with a cycle of several
days, according to the migration of fronts and migratory anticyclones from west to east.
In addition to the marked seasonality, there are
great spatial thermal variations over the islands, which
occur both horizontally (depending on latitude) andvertically (depending on altitude). An altitude a little
below 2,000 m on the northern island of Hokkaido
thermally corresponds that of 3,000 m in central
Honshu. Mountainous tundra characterized by dwarf
pine vegetation of Japanese stone pine (Pinus pumila)occurs above the altitude of 3,000 m in Honshu, but
above 1,500 m in Hokkaido (Fukui, 1977).
Throughout the archipelago, annual precipitation
generally ranges from 1,000 to 2,500 mm with anaverage of 1,700 mm (Fukui, 1977). Seasonal precipitation patterns contrast between the Pacific Ocean and
the Japan Sea sides due to the monsoon, i.e., prevailing winds changing direction seasonally (southwest insummer vs. northeast in winter) as well as the presence of mountains along the backbone of the mainland(Yoshino, 1980a,b). The winter monsoon, from late
September to late March, deposits rain and snow on
the Japan Sea side and brings dry, windy weather tothe Pacific side. In contrast, the summer monsoon
from mid-April to early-September brings rain to the
Pacific coast. Destructive typhoons often occur in latesummer and early fall, causing natural disturbancessuch as landslides and floods.
In addition to this overall pattern, minor climatic
variations resulting from the topographical complexityof the islands widen the range of variation of climaticconditions in Japan (Sakaguchi et al., 1976). For example, a drier climate with annual precipitation of lessthan 1,000 -1,600 mm prevails in the area around theSeto inland sea, while annual precipitation reaches
more than 8,000 mm in the mountainous regions ofYakushima Island off southern Kyushu (Hamada &Nakamura, 1999).
Abundant rainfall and prevailing mild temperatures
throughout most of the country produce a lush vegetation cover and enable a variety of crops to be raised,
except on mountainous terrain or in waterlogged regions.

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1.5 Biomes
Biomes are major communities of plants and animals sharing similar life forms and environmental
conditions. Individual biomes characterized by dominant types of vegetation are largely determined bymajor climatic conditions.
Most areas of Japan are blessed with abundant precipitation and temperatures mild enough to foster forests. Forest vegetation varies according to the great
spatial thermal variations over the islands (Kira et al.,1976), which occur both vertically (depending on latitude) and horizontally (depending on altitude). The
warmth index (WI), the yearly accumulation ofmonthly mean temperatures in excess of 5°C (Kira &Yoshino, 1967), is useful for predicting the major
biome types of a given region: WI>=180, subtropicalevergreen forests; 180>WI>=80, warm temperatebroad-leaved evergreen forests; 80>WI>=45, cooltemperate broad-leaved deciduous forests; 45>WI>=15, sub-arctic coniferous evergreen forests; andWI<15, alpine tundra found at high altitudes.
The range of broad-leaved evergreen forests
extends from Kyushu to Honshu’s northern lowlands.
Moving northwards along the Japanese Archipelago,
the evergreen-deciduous demarcation descends gradually from above 1,000 m in Kyushu to sea level innorthern Honshu. Representative deciduous trees are
beech (Fagus crenata), katsura (Cercidiphyllum
japoicum), maples such as Acea japonicum and Aceamono, oak (Quercus mongolica), and birch (Betula
ermanii); while coniferous trees such as Abies sacalinensis and Picea jezoensis predominate in the north andon the eastern periphery of Hokkaido up to an altitudeof 700 m (Kira et al., 1976). There are semitropicalrainforests in the Rukyu and Bonin (Ogasawara) islands of southern Japan.
Such a wide range of climatic conditions enables
biological invasions from various climatic zones tooccur with ease. Moreover, currently, the heat island
phemomenon in mega-cities, where alien plants oranimals are first introduced, is likely to facilitate theestablishment subtropical animals and plants.
The large difference in winter snowfall between
the Pacific and Japan Sea sides affects the actual
ranges of individual biomes and also the distributionof tree species. Heavy snowfall on the side facing theJapan Sea results in specific adaptation in plants, andwe can find certain evolutionary group pairs, ecotypes
or species, one distributed only on the side facing the
Pacific Ocean and the other, only on the side facing
the Japan Sea (Ohwi, 1953). Susceptibility to biological invasions is likely to be somewhat lower in theregions facing the Japan Sea, where only plants andanimals adapted to heavy snow can attain high fitness.

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2. Japanese Biota and Factors Responsiblefor its Diversity
2.1 Species richness patterns
Ecologists have been trying hard to understand andtheorize global biodiversity patterns such as spatial
variability of species richness. A currently influential
hypothesis is the so-called ‘species richness-energy
hypothesis’ (Currie, 1991) or more generally, the ‘species richness-climate hypothesis’ (Rosenzweig, 1995).
The hypothesis predicts that regional species diversity
increases with increasing heat and water availability(Kerr, 2001). The empirical patterns of many taxonomic groups including terrestrial insects, vertebrates,and plants, and marine and aquatic taxa across most of
the world strongly support this model (Gaston, 2000),
although various other factors affecting regional or
local species richness are well known (Rosenzweig,
1995; Huston, 1994).
The Japanese Archipelago is generally temperate,
so intermediate species richness is expected according
to the general ‘species richness-energy’ hypothesis(Huston, 1994). However, if the current species richness is compared with those of other island countries
in temperate regions such as the British Isles and New
Zealand, marked species richness, both total and perarea, can be observed for mammals, reptiles, amphibians, freshwater fishes, and vascular plants (Table 1).
Dragonfly taxa are notable, consisting of nearly 200
species (Sugimura et al., 1999). In addition to climatic
variability due to the large south-north range and geographical variation, active natural disturbances andfine-grained spatial heterogeneities resulting fromunique geomorphic conditions would also be partially
responsible for the biological diversity of the JapaneseArchipelago.
Moreover, the biological-geographical history including that of human-nature interactions greatly influences the current pattern of regional species diversity, since species diversity is affected by the balanceamong immigration, speciation and extinction. As to
extinction and immigration (transportation), humans
have been exerting huge influences since prehistoricages as will be described later.
The wealthy flora and fauna of the country embracing more than five thousand wild vascular plant
species, 188 mammals, 250 breeding birds, 87 reptiles,
61 amphibians (WRI, 2001), and 197 dragonflies(Ishida, 1996), are ascribed not only to the various

modes and scales of the present environmental variability throughout the country, but also to its uniqueland and biotic histories, as described below. Moreover, it is also related to the fact that the islands wereleast affected by the last glaciations, so that tertiary
floral and faunal components have been well preserved.
2.2 Geographic separation leading to diversification
Populations of plants or animals of the same originthat have become mutually isolated due to geographical separation or other reasons are expected to evolve
along different paths, not only by chance but also as
the result of different environmental conditions exerting different selective forces (Hey, 2001; Tuewlli etal., 2001).
Plate tectonic landmass movement and other geomorphic processes as well as colonization of organisms into the new regions provide opportunities for
producing ‘geographically separated conditions’ facilitating species diversification. In addition, geomorphic
processes and climatic changes may bring out new
selective forces for biological diversification. Although species differ greatly in their abilities to disperse and adapt to new environments, and thus respond to environmental changes differently, largescale geomorphic events such as landmass movement
or the formation of geographic barriers, i.e., seas,
continents and mountain ranges affects the wholebiota.
At the beginning of the Triassic, the present continents of the world were part of one large super-continent named Pangaea, which covered about one-quarterof the Earth’s surface. Late in the Triassic Period (245to 208 million years ago), Pangaea began to breakapart and its segments, Laurasia (the origin of all thepresent-day northern continents) and Gondwanaland(the origin of all of the present-day southern continents), gradually separated, resulting in the formationof the Atlantic Ocean. Probably reflecting the Pangaea
splitting events, we can recognize floral or faunal regions characterized by their distinctive plant or animal
life. The present geographical position of Japan canhardly explain the marked resemblance of its flora tothat of Atlantic America, or that of the Himalayan region, but we can predict the similarities when considering the origin of the Japanese Archipelago as a resultof landmass assemblies and splitting.

Table 1 Current species richness compared with those of two other island countries in temperateregions, as the British Isles and New Zealand (according to the data table from WRI 2001).

Preface to the Second Number of the Special Issue

2.3 Endemism and conditions responsible forpreserved biota
Although the flora and fauna are closely related tothose of continental East Asia due to the geologicalhistory, the endemism of both the flora and fauna ofJapan is remarkable. We have 188 mammal species
including 42 (22%) endemics (WRI, 2001). The Japanese mammalian fauna shares 41% of its species with
East Russia, 34% with Korea, 40% with continental
China, 12% with Taiwan, and 9% with Southeast Asia.
In any taxonomic group, the numbers of total species and endemics are high, but amphibian and dragonfly richness is especially noteworthy. The close
combination of woodlands and wetlands is the mostconspicuous feature of Japanese landscapes. Amphibians and dragonflies are strongly associated with sucha combination of landscape components. One of theold names for Japan is AKITSUSHIMA meaning ‘The
Island of the Dragonfly’ (Hearn, 1901). Japan has
continued to be a woodland country rich in wetlands
at least for 10,000 years, even since the human activities came to prevail in the archipelago. Suchcontinuity has well preserved the ancient biota including forest plants and animals, which escaped the impacts of Quaternary climatic changes, repeated alternations of warming and glaciation, by shifting theirrange to the north or south along the islands, extending 2,000 km in a southwest to northeast direction.
The wealthy tree flora is well preserved, consistingof approximately a thousand species including many
relict endemics, and is remarkable if compared withthat of the British Islands, which preserve only 143
tree species surviving the losses during the Wuerm
and Riss Ice Ages (Hamada & Nakamura, 1999).
The flora of the cool temperate regions, including
the mountainous heights of southwestern Japan andhills and lowlands of northeastern Japan, contains
many species and genera endemic to Japan or East
Asia (Nakanishi et al., 1983), and this is especiallytune of areas with abundant precipitation. An endemic
species group, called the ‘Sohayaki’ elements, isfound in the southwestern mountainous regions on theside facing the Pacific Ocean, while the ‘Japan Sea’elements are distributed in snowy mountains on theside facing the Japan Sea (Ohwi, 1953). The cool temperate deciduous forests are characterized by tertiary
circa-Arctic elements, many of which are now distributed in East Asia and North America, in an isolatedmanner. The flora of the warm temperate regions, in
low altitude southwestern areas, has fewer but a considerable proportion of endemics. Compared to thetemperate regions, the sub-frigid regions at high altitudes in the central part of Honshu embrace much
fewer endemics and the flora is enriched by circaArctic elements, which are widely distributed aroundthe Arctic (Ohwi, 1953).
In addition to many endemics on the islands,
Japan’s flora and fauna contain many components
common to easten continental Asia, because compared107

to whole length of the history of continuity, only abrief time has lapsed since the complete separation of
the Japanese Archipelago from the continent.
2.4 Vegetation and disturbances
Species compositions of individual communities
tend to adjust to the particular types and frequencies
of disturbances occurring in the region, as such individuals and species best adapted to those types andfrequencies have the highest survival rate and reproductive success, so that they dominate the community.
The establishment of equilibrium conditions is prevented when disturbances in combination with environmental fluctuations suppress competing species,
altering the balance of competitive interactions(Huston, 1994).
Biodiversity of the Japanese Archipelago would
have been enhanced by the active natural disturbances
caused by frequent typhoons, and high volcanic, seismic and geomorphic activities causing landslides, fires,storms and flooding, which destroy established vegetation on various spatial and temporal scales, increasing α-diversity, as well as increasing β-diversity
through enhanced regional or local environmental
heterogeneity. The Japanese flora contains many disturbance tolerant or even dependent plant species(Washitani, 2001).
In primeval ecosystems, natural disturbances playvital roles in maintaining a shifting mosaic of habitat
patches and contribute to retention of a subset of thenatural biodiversity (Huston, 1994). If natural processes are left in complete absence of disturbances,
light-demanding species, which can grow only insunny habitats, are lost as succession proceeds.
2.5 Vegetation and natural and anthropogenic
disturbances
Even today, intensive exploitation of the land for
agriculture has been mostly confined to densely populated lowlands and hilly regions of the islands, thoughconifer plantations occupy more than half of themountainous regions at the sacrifice of natural vegetation (Ministry of Environment, 2002).
Humans have influenced the Japanese Islands forat least tens of thousands of years, and now none of its
ecosystems is entirely wild or natural. Japanese ecosystems have been subjected to a long history of human interventions, but humans have been only one
among many influences, including active natural disturbances.
Clearing primeval forests to develop agriculturallands and settlements may have led to the extinctionof closed-canopy specialist species. However, certain
types of human intervention played certain roles inpreserving local flora and fauna of older ages against
the natural courses of ecosystem change due to nonanthropogenic climatic changes. Intermittent clearing
of woods would serve to maintain the deciduous forests even after domination by northwardly advancing

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broad-leaved evergreen forests due to climatic warming, which started about 10,000 years ago. Deciduousness is the necessary condition for preserving many
plants and insects adapted to deciduous forests ofcooler temperate climates (Moriyama, 1988). It is increasingly recognized that the sensitivity of species tocurrent threats may reflect ‘extinction filters’ imposedby past events (Balmford, 1996).
Active natural disturbances prevailing in the Japanese Archipelago which destroy established vegetation,i.e., floods, landslides, volcanic eruptions and associated fires, have continuously exerted selective forces
for disturbance-resilience or resistance of species.
Simultaneously, by creating gaps or void niches, frequent disturbances have facilitated biological invasions.

3. Chronology of Biotic Exchanges andInvasions
3.1 Migrations and isolations during glacial andinterglacial ages
It is well known that the climate cycle of the alternation of glacial and interglacial ages, which has repeated seven times during the past 700,000 years,
greatly influenced biotic communities around theglobe, and that the evolution and development ofhominids were also governed by such environmental
fluctuations (Pavlov et al., 2001).
The lower sea level during glacial periods
generated land bridges connecting the Japanese Archipelago to the Eurasian Continent, one between the
Korean Peninsula and Kyushu and the other, between
Sakhalin and Hokkaido (Nogami et al., 1980). These
conditions may have elicited active biotic migrations.
Many colonization events including those of humans
from the continent may have occurred and profoundly
affected the Japanese fauna and flora of later ages.
Extant and extinct mammals may have migrated fromthe Asian Continent through the land bridges.
Fossil mammoths, which have been excavatedfrom southeastern Hokkaido, and a fossil elephant,
Palaeodoxodon naumanii, excavated from various
regions of Japan, suggest that large mammals could
move from the continent by land when the Japaneseislands were connected to the continent (Kamei, 1991).
P. naumanii is inferred to have moved from northern
China 300,000 years ago by the southern route andfirst entered Kyushu. The fossil elephants lived in theJapanese Archipelago until approximately 16,000
years ago, when a cooler climate intermittently prevailed and fostered coniferous forests of Pinaceae,
Taxodiaceae, and Cupressaceae, which covered thepresent warm temperate regions. Fossil evidence suggests that in the same era, big horn deer, Japanese deer,brown bears, rabbits, mice, and bean geese lived with
P. naumanii (Kawamura, 1991). Migrations of large
mammals may also facilitate the migration of plants
through seed dispersal mechanisms which depend on

mammals (Washitani, 2002).
Fossil records suggest that P. naumanni rapidly
declined during the last interglacial period. The climate was fairly mild, so climate factors are inconceivable as the major factor in its extinction. Active human hunting (Cardillo & Lister, 2002) is evidenced bystone and bone tools yielded with the elephant bones,
including knives and scrapers, and suggest that wasamong the reasons for extinction of active hunting of
P. naumanni by Paleolithic man (Kamei, 1991).
During the last ice age which lasted from 20,00018,000 years BP, thick ice sheets covered Canada,
Greenland and Scandinavia and more than 30% of theland area of the world was covered by glacial ice. The
sea level was depressed by 80-130 m globally, as acounter-balance against ice sheet development. In theJapanese Archipelago, however, glaciers were poorly
developed due to a somewhat dry climate (Nogami,1998), and older flora and fauna survived the age well.
In central Japan, the ice sheet covered only mountainpeaks above an altitude of 2,500 m, and a large part of
the region escaped the influence of glaciers.
Post-ice age warming caused extensive marinetransgression with a 40 m sea level elevation in total
during the 4,000 years from 10,000 year ago when thesea level rose continuously by 1 cm per year. In theearly Jomon period, i.e., 6,000 years ago, the climate
was relatively warm and the sea level was about 3 mhigher than now (Hamada, 1999).
3.2 Pre-historic migrations of humans and large
mammals
When and who first lived in the Japanese Archipelago is the most fascinating question enthralling not
only anthropologists and archeologists but also thegeneral public. Current interdisciplinary research activities concerning this question (Omoto, 1996;
Urabayashi & Tozawa, 2001; Baba, 2001), which include genetic analysis of old human bones with DNA
markers, have revealed dynamic human migrations
and interactions in and around the pre-historic sceneof the Japanese Archipelago (Fig. 1).
Numerous stone tools dated back to 10,000 to
30,000 years ago have been found through recent archeological excavations throughout the Japanese Archipelago (Okamura, 2000), but no firm evidence ofold human settlements in Lower and Middle Paleolithic Japan has been obtained until today.
Underground preservation of old bones is extremely difficult in the acidic soils prevailing over theJapanese Islands, so old human bones are rarely foundand only in special regions or under conditions such as
in limestone soil or shell heaps (Amano, 2001). Although more than 5,000 Paleolithic remains have beenfound throughout the Archipelago, only one fossil human skeleton of that age (dated to 18,000 years ago)
is available for sufficient analysis. The nearly complete set of fossil human bones called ‘Minatogawa
hominid,’ which were excavated from a site onPreface to the Second Number of the Special Issue

Okinawa Island (Baba, 2001), was recently demonstrated to be morphologically and genetically similar
to the Wajaku hominids who lived in prehistoricIndonesia (Tagaya, 2001). However, the sample size
is too small to permit any statistical analysis, and large
ambiguity still remains on his relation to later Japanese such as the Jomon or other Asian hominids.
A specific type of fine stone razors found withmany Paleolithic remains throughout Japan suggests
the immigration of mammoth hunters from Siberia
during the coldest period of the latest Ice Age(Urabayashi ＆ Tozawa 2001). The stone razors,
which were designed to be used by setting into bonearrow heads just like modern replaceable razor blades,
were a unique invention of prehistoric Siberian mammoth hunters, who left remains at the Marita site near
Irkutsk that can be dated back to about 20,000 years
ago (Kimura, 2001). They hunted mammoths andreindeer, ate meat, and utilized fur, bones, and horns
to manufacture housing, tools, accessories, etc. The
fine stone razors, which probably were essential tomammoth hunting, started to be used in Siberia about
21,000 years ago, while the oldest stone razor of thistype found in Japan dates to approximately 20,000
years ago.
During that period (20,000-18,000 years ago), theglobe was in the worst part of the last Ice Age, andvast tracts of Siberia were covered with so called‘mammoth steppe,’ a grassland that mainly consistedof Poa, Carex and Eriphorum (Kawamura, 2001).
Together with woolly rhinoceros, reindeer, bison, wild
horses, arctic foxes and wolverines, mammoths inhabited the middle and northern latitudes of Eurasia, andextended their range into the cool steppes of North
America where average temperatures were 7 or 8 degrees colder than today (Urabayashi & Tozawa,
2001).
The supposed age of mammoth migration from
Siberia to northern Japan is also around 20,000 years
ago when the habitat of the mammoth, i.e., drier
steppes with scattered conifers or open woodlands,

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reduced in area and/or shifted southwards (Kawamura,2001). During the coldest period of the latest Ice Age,
open woodlands or Mammoth steppes advanced tocover not only Hokkaido but also the northern part ofHonshu. With such an environmental change in mind,
it is easy to imagine that mammoths migrated tonorthern Japan along with mammoth hunters, pursuing
the game.
At the end of the glacial age 10,000 to 13,000
years ago the mammoths became extinct. Slaughteringby hominids in combination with climatic changes isthought to be partially responsible for the extinction(Kawamura, 2001).
3.3 Prehistoric human life facilitating biotic
migration
The Japanese Neolithic Age, the Jomon period andthe Yayoi period are characterized by unique types ofearthenware common to the remains of the ages. The
Jomon (meaning ‘cord marks’ in Japanese) type of
pottery with cord mark patterns pressed into the clay,
were first discovered in the early Meiji Period by an
American zoologist Edward Sylvester Morse whotaught zoology at Tokyo Imperial University as a professor (Sahara, 1998a). Since the first discovery of
Jomon pottery by Morse near Tokyo, numerous Jomon
type potteries have been excavated from all overJapan. The period of Jomon pottery usage began about
12,000 years ago and lasted to 2,300 years ago.
Simpler potteries having bullet-shaped bases without special surface patterns, which are presumed to be
an ancestral type for the Jomon ones, were unearthedfrom several remains dated to about 13,000 years ago.
Representative clay pottery without cord marks, dated
12,000 years ago, was excavated from Shinjuku inTokyo (Abe, 2001). This type of pottery is very similar to the world’s oldest earthenwares found in
Siberian remains located in the Amur basin, but aremuch thinner and have bullet-shaped bases, suggesting that the earthenware was used to boil food byplacing it over a fire (Abe, 2001).

Fig. 1 Prehistoric global migrations of Homo sapiens and interactions around Japan(redrawn from Baba, 2001).

110

I. WASHITANIThe descendents of mammoth hunters migrated
from Siberia with their fine razor stones and bullet-shaped potteries, probably facing dramatic climaticchanges due to global warming, and had to modify
their lifestyle and culture to fit well in their new environment (Urabayashi & Tozawa, 2001). Arid, cool
steppes were rapidly disappearing and gradually displaced by dense forests. Such environmental changes
caused extinctions of large mammals, which weregrazers strongly depending on the grasslands. The
Jomon people had to innovate their dietary life drastically, and one of the solutions to the challenge may
have involved cooking techniques with fire.
In addition to the above-mentioned evidence (i.e.,the shared features of stone tools and earthenware),morphological and genetic analyses of old humanbones also suggest Paleolithic human immigrationfrom Siberia to the Japanese Archipelago before thebeginning of the Jomon period.
The first old human bones were excavated by E. S.
Morse who found seven sets of human bones from ashell midden site in Omori, southern Tokyo, in 1877.
Since then, several thousand sets of Jomon humanbones have been excavated from various regions ofJapan (Amano, 2001). Old bones of the Jomon people
have been found all over the Japanese Islands, fromthe north end of Hokkaido to south end of Southeastern Islands.
Multivariate craniofacial analysis and genetic
analysis with DNA markers strongly suggest a close
relationship between the Jomon and existent mongoloids of Siberia and other regions of the east Eurasiancontinent (Omoto, 2001). Shinoda (cited by Omoto,2001) compared mitochondrial DNA sequences registered in a DNA bank for the Jomon and modern peoples of various areas of the World and obtained exciting results. Among 29 Jomon investigated, 17 shared
identical sequences with the existent Buryats living
near Lake Baikal, and three others, with Koreans,
Taiwan Chinese and Thais, respectively.
The results strengthened the inference that the
Jomon, or proto-Japanese, may have had multiple origins, but possibly one of the dominant lineages wasdescendants from Paleolithic Siberian mammoth hunters. They partially merged with peoples from othercontinental Asian regions and spread throughout thearchipelago (Tozawa, 2001), gradually adapting to theislands’ natural environments. The Ainu, a minority
race of northern Japan, is known to be genetically andcraniofacially close to the prehistoric Jomon (Brace etal., 2001). Linguistic evidence also suggests that acertain people speaking a language belonging to the
Ural-Altaic family moved eastward across Siberia andentered Japan via Sakhalin Island and Hokkaido(Amano, 2001).
A recent investigation based on craniofacial
morph-metric comparisons (Brace et al., 2001) also
showed that the prehistoric Jomon and the Ainu ofcontemporary Japan are actually closer to prehistoricand existent European groups than the core populations of continental Asia. Along with the Ainu and theJomon, the Polynesians of Oceania are shown to beclose to Eurasians. The study also revealed that
American natives living in the border region between
Michigan and Alberta, Canada, are very similar to the
Jomon and the Ainu. Figure 1 is a schematic representation of the placement of the original populations
involved in the thus presumed initial human expansions and their subsequent movements and combinations (Brace et al., 2001).
Therefore, it is suggested that the Japanese Archipelago was a focal place, where Paleolithic peoples
with different migration histories interacted, andmerged, and the dominant group was people closely
associated with those starting on the trip to the New
World, with some among them migrating afterwards
to South Asia and Polynesia. Such dynamic humanmigrations might be accompanied by both intentional
and unintentional plant and animal migrations, as
described later.
Most modern Japanese are genetically not so close
to the Jomon. After the end of the Pleistocene, development of agriculture led to a major expansion of thecore population of continental East Asia, and many
immigrants from the continent entered in the JapaneseArchipelago (Tozawa, 2001). Immigrant lineages had
become dominant in the Yayoi period, as describedlater.
3.4 Presumed plant transportation by prehistoric
humansDynamic migrations of mammals including hominids during and after the last Ice Age should havebeen accompanied by dispersal of the seeds of grassland plants as well as ruderals, a type of weedy plant.
Ruderals are plants that grow on well-illuminatednutrient rich sites such as bare grounds formed bytrampling by mammalian herds, whose discharge of
bodily wastes creates especially nutrient-rich conditions (Grime, 1979).
The dynamic Paleolithic migrations and/or range
expansions of mammals including humans surely
helped such sun-loving nutrient-consuming plants that
disperse their seeds by hitchhiking on mammals externally or internally. In addition to clinging to wooly
body parts, adhesion to legs or hoofs of mammals
with mud is thought to be one of the most effectual
means of seed dispersal for ruderals (Fenner, 1985).
Upright-standing humans with an exceptionally largefoot sole area relative to body size may be the mostefficient seed dispersers for such plants.
The Ice Age, when land bridges or shallows connected the Asian continent with the Japanese Archipelago (Fig. 2), was a great migration age, whenplants and animals including hominids actively migrated long distances. Short grass steppes or tundra
could be more easily traversed by large mammals,
including humans, than forests, although only species

Preface to the Second Number of the Special Issue

Fig. 2 Japan in early diluvium, approximately a million
years ago (a) and land bridges or shallows connecting the Japanese Archipelago to the continent during
the Würm Ice Age about 20,000-30,000 years ago(b) (redrawn from Hamada & Nakamura, 1999).

which had adapted to cooler climates, could actively
migrate.
Intentional introduction of plants probably originated just at the time when people first appreciated theroles of seeds or other dispersal agents in plant reproduction, although we can only resort to imagination toreconstruct such a history of the relationship between
humans and plants.
Patches or layers containing high densities of plantseeds found among Jomon remains are interpreted asdebris from squeezing berries to make juice or wine.
The discarded seeds were those of Sambucus, Raps,
Actinidia, Morus, and Vites species (Tsuji, 1999).
These shrubs and vines grow vigorously after fires orclearing of forests. Gaps created by natural or humandisturbances would be a food reservoir for easy collecting of delicious berries. People not only acted as
effective seed dispersers, but also unintentionally or
intentionally prepared suitable habitats for theseplants.
3.5 Active trade with the Asian continent
The Sannai Maruyama site in Aomori Prefecture,
one of the most representative Jomon remains, contains various types of dwellings, apparently accommodating approximately 500 people at its peak
(Watanabe, 2001). Various trade items excavated fromthe site, jade beads, raw amber, projectile points
attached with asphalt and pottery with patterns createdby pressing cone shells from the southwestern sea,suggest active trade across the Japan Sea by dugout
canoe.
Even after separation of the islands from theEurasian Continent because of sea elevation due toglobal warming after the last Ice Age, active movement of people and cultures may have continued. Rice
cultivation was probably introduced from South China
more than 2,500 years ago (Urabayashi, 2001). Jomon
rice is thought to have been introduced from the
Yunnan region, through southern mountainous regions
and the Shandong Peninsula. In the Jomon period, rice111

was generally cultivated in burned fields with othermiscellaneous cereals, but some paddies of the period
have been also unearthed (Urabayashi, 2001).
The Yayoi culture, which arose first in Kyushu
about 2,200 years ago while the Jomon culture wasstill undergoing development in other parts of theJapanese Islands, spread gradually eastward to overwhelm the Jomon culture as it went, until it reachedthe northern part of Honshu (Tozawa, 2001). The
name Yayoi derived from the name of a town in Tokyo
where, in 1884, pottery of this type was first foundand drew the attention of scholars. Yayoi pottery was
fired at higher temperatures than Jomon pottery andwas produced by turning on wheels (Sahara, 1998b).
During the Yayoi period, irrigated rice cultivation
became commoner and commoner (Urabayashi, 2001).
Analysis of plant opals, which are microfossils derived from grass leaf tissues, is helpful in revealing or
ascertaining sites where ancient paddy fields werelocated (Fujiwara, 1998). With the help of analytic
techniques, more than 100 paddy remains of the Yayoi
era (BC 3c - late AC 3c) have been excavated(Amano, 2001). The remains are located in lowlands
or valleys, where irrigation and drainage are feasible,
benefiting from the natural topography. These
constitute evidence demonstrating that rice cultivation
spread rapidly in the Yayoi period. Rapid developmentof agriculture would be associated with the introduction of ironware.
Probably certain paddy weeds were unintentionallyintroduced accompanying rice introduction (Maekawa,1943). However, they are originally wetland plants,
and considering the floristic resemblance of Japan andcontinental Asia, it is difficult to conclude that they
had never been native to Japanese wetlands.
3.6 Ancient to pre-modern agricultural ages
Similarly to human histories of many other regions,from an ecological viewpoint, Japanese history can bebroadly divided into the three familiar periods ofhunter-gatherer, agricultural and industrial societies(Totman, 2000). In Japan, a Japanese-style agricultural
system which was established in the Yayoi period on
the basis of the Jomon legacy and items imported
from continental East Asia lasted to the early 20th
century, when eddies of violent industrialization
shattered the traditional agricultural systems together
with their rural communities.
The early centuries of land clearance and lowintensity tillage significantly altered landscapes by
opening many scattered lowland areas to sunlight.
Moreover, the adoption of Chinese architectural practices and the creation of a succession of densely populated capital cities in the Kinai Basin led to deforestation of the basin, frequent eruption of wildfires thatswept through areas of recently created scrub growth,and erosion leading to gradual degradation of soil anddownstream flooding (Totman, 2000). By the eleventh
century, human exploitation had almost completely

112

I. WASHITANI

stripped the basin of its old-growth forests and damaged enough soil in the metropolitan region so that theruling elite was unable to maintain the level of resource extraction essential to its urban civilization.
However, many regions outside the Kinai might wellhave preserved the integrity of their ecosystems tomodern ages (Totman, 2000).
After the age of warfare, Japanese society enteredan intensive agricultural stage (Tanaka, 2000), andfeudal rulers governed the agricultural communities.
As the agricultural society developed and its systems
became refined, farmers became tied to their villages
more and more tightly. The agricultural society was
sustained by yields or outputs from regional ecosystems, similarly to hunter-gather societies, while thecurrent industrial society is sustained by current output from spatially and temporally remote ecosystems,
i.e., biological output from different regions and yields
from ancient biomass (coal, oil and gas).
During the long-standing agricultural age, Japan
experienced many inland wars, through which thewarrier class took over real control form the Tenno(Emperor) court nobles. However, the country totallyescaped foreign invasion. The risk of subjection toforeign rulers was first heightened after the Chinese
Sung dynasty was overrun in 1279 by the Mongol
armies of Kublai Khan, who dispatched invadingarmies to northern Kyushu several times (Murai,2001). The last dispatched fleet was reported to contain 140,000 fighters, mostly Chinese, on 4,400 vessels. Dogged resistance and a fortuitous typhoon,
which has been called ‘divine wind’ in later legend,
wrecked the invading force on the beaches, and Japan
could evade the Mongol invasion.
3.7 National seclusion and escape from European
colonization
Pressure from abroad greatly increased after the
first arrival of Europeans on Tanegashima, an island
off the south of Kyushu in 1542, when a Chinese shipwith three Portuguese crew members drifted ashore at
the island and guns and gunpowder as well as Christianity were first introduced to Japan (Kamigaito, 2000).
Nagasaki port was opened to foreign trade in 1570,
and the Portuguese entered the harbor (Harada, 1999).
Firearms and new religions were accepted by theJapanese in the midst of a warring state period andhad great influences on Japanese society.
“After nearly a hundred years of Christianity andforeign intercourse, the only apparent results of thiscontact with another religion and civilization were theadoption of gunpowder, and firearms as weapons, theuse of tobacco, and the habit of smoking, the makingof sponge-cake (still called Castira ― the Japanese
form of Castile), the naturalization into the languageof a few foreign words, the introduction of new andstrange forms of disease, among which the Japanesecount the scourge of venereal virus, and the permanent
addition to that catalogue of terrors which priest andmagistrate in Asiatic countries ever hold as weapons
to overawe the herd.” (Griffis, 1883)
Hideyoshi Toyotomi, a prominent warrior who
stopped the warring state and brought the entire country under his control licensed both domestic and foreign trading ships, and Ieyasu Tokugawa who established the Tokugawa Shogunate systematized thislicensing by issuing sealed letters (Harada, 1999).
However, in the 1630s, the Tokugawa Shogunate forbade foreign trade to avoid a tangle of foreign complications that involved unruly European, Japanese, andother Asian traders as well as an increasing Manchu
assault on Korea and Ming China. Japanese were forbidden to go abroad. In 1639, Portuguese ships were
excluded from Japanese ports, and only the Dutch andChinese were allowed to trade, and they were only
allowed to trade, at an isolated port located in
Nagasaki. Therefore, foreign trade was restricted until
modern trade officially began in 1859 (Harada, 1999).
3.8 Opening the country and avenues to industrialization
During the agricultural periods, especially theperiod of Japan’s isolation, biological invasions werelikely to be rather trivial issues. However, 19th century European imperialism, which was itself driven
primarily by the carrot and stick of early industrial
empowerment and Western Europe’s ecological limitations, disturbed the Tokugawa political order bydepriving it of the stable and non-threatening geopolitical context in which it had operated (Totman, 2000).
The European intrusion also brought in not only its
wake, but also the rudiments of an alternative to intensive agriculture: namely, industrialization. From the1860s onward, Japanese leaders and an ever-growing
portion of the general populace began to tackle thetask of developing their own industrializing order withenthusiasm. In the late Edo period, active introductionof European plants and animals was made and somewere naturalized later. White clover (Trifolium repens
L) is believed to have been first introduced when it
was used as packing for boxes containing earthenware
imported from Holland (Osada, 1976), although later
repetitive intentional introductions as pasture plants orsoil erosion prevention material are rather responsible
for the current day prevalence of the species.
Japan’s modern foreign trade officially began in1859. Until then the Tokugawa Shogunate (16031867) had maintained a policy of National Seclusion(Asao, 1998). With the signing of the Harris Treaty(United States― Japan treaty of Amity and Commerce) in July 1858, Japan opened its doors toWestern commerce.
The Meiji revolution was a new departure forindustrialization of Japan. The society that hitherto
had been sustained by current output of the regional
ecosystem gave way to one that depends on a combination of current biological output from remote places
and yields from ancient biomass, i.e., fossil fuelsPreface to the Second Number of the Special Issue(Totman, 2000). It definitely opened the age of rapid
biological invasion into Japan.
Achieving equality with the West was one of the
primary goals of the Meiji leaders. Treaty reform,
aimed at ending the foreigners’ judicial and economic
privileges provided by extraterritoriality and fixedcustoms duties, was sought as early as 1871 when the
Iwakura mission went to the United States and Europe(Inoo, 1995). The Western powers insisted, however,that they could not revise the treaties until Japanese
legal institutions were thoroughly reformed along
European and American lines. In this context, ‘Westernization’ of social systems became synonymouswith the modernization that was the prerequisite toindustrialization of Japan. Many of Japan’s leaders atthat time had gone abroad to embassies and on study
tours, and the government had actively hired foreign
advisors and employees to help in the development of
new governing and educational institutions and newcommercial and industrial ventures. By 1875 some
520 foreign employees, mostly European, alreadyworked for the government, while hundreds more
were under taking private services, mainly as engineers and teachers (Griffis, 1883).
The efforts of central government were fully rewarded and in 1894, the treaty provisions for extraterritoriality were formally changed (Inoo, 1995).
Meiji leaders encouraged study abroad, and promoted
the learning of foreign languages and translation ofEuropean books. They accepted the introduction ofsuch cultural elements as contemporary European
food, dress, architecture, art, music, dance, drama,
literature and philosophy as well as science (Hearn,1904). Westernization gradually penetrated all socialand daily life of the Japanese especially in the new
metropolitan Tokyo.
3.9 Westernization and active biotic introduction
Japan was thus among the world’s first societies toindustrialize along with parts of Europe and North
America (Totman, 2000). With the slogan ‘Japanesesprit with Western learning,’ the government as wellas economic and academic circles strived to introduce
western cultures, technologies, and goods including
numerous biotic items. Therefore, the rush to introduce exotic plants and animals led to naturalization ofmany such introduced species. The first naturalizationof most contemporarily common non-native plant
species occurred in the Meiji period (Washitani, 2002).
Since that period, the number of naturalized species
has constantly increased. Several Solidago species including Solidago altissima, one of the most notorious
invasive plants in current-day Japan, were first introduced as ornamental plants at that time (Osada, 1976).
A pathogenic nematode (Bursaphelenchus xylophilus) that was unintentionally brought from North
America and has caused tremendous damage to pine
plantations throughout Honshu, Shikoku and Kyushu,
especially in recent years, was first recorded in

113

Nagasaki in 1905. It is thought to have invaded byhiding in imported wood for shipbuilding (Tomigashi,
2002).
Successful establishment of introduced species
requires suitable habitats where they can live and reproduce. Distributions of most naturalized species
were principally confined to areas subjected to intensive human interventions for industrialization or urbanization (Washitani & Morimoto, 1993). During theearly modern industrial stage 1868-1945, agricultural
techniques changed only incrementally and in rather
familiar ways (Totman, 2000), and intact
SATOYAMA landscapes with wealthy indigenous
biodiversity (Washitani, 2001) were likely to be wellpreserved. Not only primeval forests but also intact
SATOYAMA landscapes were relatively resistant toinvasions by newcomers, though constantly influenced by humans in order to extract bio-resources
such as fuels, fertilizer, and building materials(Washitani, 2001).
In the course of the early modern industrial development of Japan, after fostering light industry, especially the textile industry, during 1897-1906, the government led development of basic industries such asrailroads and mining. Railways opened routes for invasive plant species to invade throughout the country.
Erigeron canadensis, which was unintentionally introduced from North America and spread along the railways in those days, was called the ‘railway plant’ inJapanese (Osada, 1976). The plant was regarded as asymbol of the early modern industrial development ofJapan.
Japan’s heavy industries, such as iron/steel andshipbuilding, grew rapidly from the 1930s (Kodansha
International, 1999). Remarkable industrial development resulted in domestic shortages of raw materials
and markets. The need to secure raw materials andmarkets in a hostile international trading environment
led to efforts to form the so-called ‘Greater East Asia
Co-prosperity Sphere’ in the years immediately preceding World War II. Imperialism accompanied bymilitarism stirred up Japanese pride and the will to
invade other Asian countries. Increased fur demand
related to military invasions of North China elicitedintroduction of fur animals such as Myocaster coypus,
which become naturalized after the war (Murakami,
2002).
The war was ended by the holocaust of the atomic
bombs dropped on Nagasaki and Hiroshima. The fall
webworm, Hyphantria cunea, which greedily strips awide range of deciduous trees, especially cherry trees,
was thought to be introduced attached to propaganda
bills the US Air Force distributed by airplane orintermingled with US Army munitions (Gomi, 2002).
3.10 Post-war economic growth and increased
invasions
As a result of its defeat, Japan was subjected to the
Allied Occupation, which lasted from August 1845 to114

I. WASHITANI

April 1952. Japan concluded a security treaty with theUnited States that permitted US military bases to remain on Japanese soil in return for an American commitment to protect Japan from foreign aggression. US
military bases are thought to be among the major gatesfor unintentional introduction of various exotic plants
and animals. An example is Polypedates leucomystax,
which was first recorded the early 1960s in Okinawa
where US armed forces were based and is thought tohave been introduced from Indochina attached tomilitary items (Ohta, 2002a). During 28 years from1945 to 1973, the Okinawa Islands were newly
invaded by a total of 12 nonindigenous insect species,
half of which were first found in the vicinity of the US
military bases (Kiritani, 2002).
During post war food shortage (1945 to 1955)
more than 25 species of cereal weevils invaded Japan
via cereal imports (Kiritani, 2002).
The Korean War (1950-1953) brought about a rushof special military procurements to support US andUnited Nations forces, enabling Japanese industry to
climb out the stagnation. Naturalization of various
alien plants and animals became tangible in the postwar era (Osada, 1976; Miyashita, 1977).
The rapid growth and bubble economy from themid-1960s brought about a new rush of naturalizationof introduced plants and animals especially those fromthe United States of America, the major trade counterpart exporting biotic items including cereals to Japan(Washitani, 2002).
Biological invasion depends on both opportunities
for invasion and the presence of habitats or niches
where the introduced species can establish. An example of establishment through intentional introduction
for farming can be found in Rana catesbeiana, which
was actively introduced for meat production(Hasegawa, 1999), though the attempt was soon abandoned. The species is now one of the most common
amphibian species in various aquatic habitats, is an
extraordinarily strong competitor species (Kiesecker
et al., 2001) and is thought to threaten native amphibians (Ohta, 2002b).
Chances for invasion may be extraordinarily elevated if the plants or animals are intentionally introduced in large amounts continuously into the region,
including vast areas of unoccupied habitats. As such,active introduction of non-native pasture grasses forvarious construction projects has caused serious problems of invasions of such grasses as Eragrostis
curvula (Muranaka & Washitani, 2004) and several
varieties of Festuca into wide ranges in Japan(Washitani, 2002).
The most notorious invaders attracting serious
public concern are introduced freshwater fishes of thesunfish family native to North America. These fishes
have been repeatedly released into lakes and ponds for
sport fishing and have multiplied explosively (Yodo,
2002), preying on a wide range of native species including aquatic fishes and insects such as dragonfly

larva (Suda, 2002). The large-mouth bass, reported inonly 23 prefectures of Japan in early 1970s, is now
distributed to all 49 prefectures.
During and after the rapid economic growth whichstarted in the 1960s, Japanese landscapes were greatlychanged by various types of development projects
according to a national plan to ‘remodel the Japanesearchipelago’ (Tanaka, 1972), which was inevitably
accompanied by drastic landform changes. Surging
waves of development projects for construction ofdams, ports, roads, industrial complexes, residential
areas, and recreational facilities such as golf courses,
destroyed large tracts of various types of natural orsemi-natural habitats such as woodlands, wetlands,
beaches, floodplains, and grasslands, leaving unoccupied sunlit habitats where invasive alien plant species
could easily establish large seed sources. Rural landscapes today are bright with escaped exotic ornamental plants, such as Slidago altissima and S. gigantean
var. leiophylla, Coreopsis lanceolata, Rubeckia
laciniata, Aster novae-angliae, and Aster novi-belgii,
most of which were introduced from North America in
the Meiji or Taisho periods, and we totally miss native
wild flowers familiar to elderly persons.
Anthropogenic landscape changes in concert withactive intentional and unintentional introductions associated with economic globalism are likely to be
most responsible for the current rush of invasions. The
rapid decline of native species replaced by prevailing
non-native species throughout the landscape is a major
aspect of the current biodiversity crisis of Japan.

EpilogueWithin less than 150 years, Japan has been transformed from a closed country of self-sustainable agricultural communities depending solely on regenerative bio-resources to one of the big industrial countries
exploiting resources worldwide. During this period,
naturalized alien species increased tremendously.
Today, in concert with other factors causing environmental deterioration, invasive alien species profoundly threaten the biodiversity and integrity of Japanese ecosystems, especially those in fresh water andagricultural landscapes. Social concern about the
problems has been growing rapidly (Washitani, 2004),
and Japanese society at last has started groping foreffective countermeasures to the problems (Mito &Uesugi, 2004), though whether or not we can establish
appropriate countermeasures depends largely on thescientific understanding of the problems by the general public as well as the officials responsible for thematter. I hope the present special issue will play animportant role in promoting such a wide scientificunderstanding.

Preface to the Second Number of the Special Issue

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(Received 13 December 2004, Accepted 23 December 2004)