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Restoration of Biologically-diverse Floodplain
Wetlands Including Paddy Fields
Izumi WASHITANI
Institute of Agricultural and Life Sciences, The University of Tokyo,
1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japane-mail: awashi@mail.ecc.u-tokyo.ac.jp

Abstract
In Japan, like other developed nations, restoration of floodplain wetlands has recently become an
important social and scientific issue, after drastic reduction in area and ecological integrity. In an economical evaluation of global ecosystem services, lowland wetland or floodplain ecosystem types are most highly
valued among the ecosystem types evaluated. Floodplain ecosystems, which are characterized by both spatial heterogeneity and temporal variability due to seasonal and unpredictable floods and traditional humaninterventions, i.e., plant resource collection causing also intermediate disturbances, can be regarded as shifting mosaics consisting of a variety of aquatic and non-aquatic habitats. The system of paddy fields interconnected not only to each other, but also to irrigation ponds and rivers by extensive canal networks is thecommonest wetland type in Japan, and have provided substituting habitats for a large variety of wetland
species after the loss of natural floodplain by development. However, recently-introduced intensive farmingwith heavy application of chemicals and seasonal drying of paddies after the rice harvest has caused rapid
loss of biodiversity from agricultural landscapes. One promising measure to recover biodiversity, which has
become practiced in a certain leading areas is winter flooding, i.e., continuous wetting of paddies during
winter in combination with no or much reduced chemical applications compared to conventional modern
farming.
Key words: agricultural landscape, biodiversity, floodplain wetland

1. Floodplain Wetlands as Human Habitats
Floodplain wetlands have been the major habitats ofhumans, Homo sapiens, probably since early in theevolution of our species (Tattersal, 1998). Until recently,
wetlands had long held importance in human mental
maps as resource-rich spaces. In addition to drinking
water, wetlands provide foods, such as fish, shells, andherbs, and plant materials including grasses such as
Phragmites australius, Miscanthus species, sedges, willows, and alders, which have been used in roof thatching,construction, handcrafts, domestic animal feeding, fuels
and so on. Furthermore, wetlands perform a number of
ecological and hydrological functions that benefit local
and regional communities and also provide opportunities for transportation of human and goods.
However, in the modern age, wetlands have been
wiped out from both real and mental maps through various types of development, draining or transforming
them, especially in developing countries, including
Japan. Floodplain ecosystems are among the ecosystem
types that have lost the largest proportions of their areas,
and/or have been altered in their states and conditions,Global Environmental Research
11: 135-140 (2007)
printed in Japanespecially as agricultural modernization has intensified(Bobbink et al., 2006 ).
Japanese wetlands are no exception. During the 20th
century, approximately 60% of the total area of natural
wetlands was lost (Geographical Survey Institutehttp://www1.gsi.go.jp/geowww/lake/shicchimenseki2.html) mainly through reclamation. Furthermore, most remaining wetlands have lost their ecological integrity, or
been subjected to environmental deterioration, mainly
through nutrient pollution, biological invasion anddestruction of ecotone vegetation by the construction ofvertical concrete shore protection (Washitani, 2004a).
Simultaneously, paddy fields, which used to be themajor wetland type in Japan, have lost their wetness andecosystem health simultaneously through reclamation to
improve farming conditions and application of chemicals to increase productivity.

2. Attempts to Recognize Existent and Lost
Values: Ecosystem Services
After substantial loss of various types of wetlands
through the 1960-1980s, there has been a rapid surge of©2007 AIRIES

136

I. WASHITANI

public recognition of wetland values and ecosystem services wetlands provide us (Bobbink et al., 2006).
Wetland restoration has thus become one of the mostimportant social issues, especially as ecosystem sustainability has become highly valued together with ecological efficiency and social fairness. The wise-use concept,
which provides the framework of the Ramsar Convention for wetland conservation (http://www.ramsar.org/
index_about_ramsar.htm), depends on the recognition of
the ecological functions of wetlands, which can be ofvalue in multiple economic and non-economic ways tohuman society.
Coinage of the ecosystem services’ concept by Dailyet al. (1997) greatly enhanced value assessment of ecosystems including wetlands. ‘Ecosystem services’ aredefined by the conditions and processes through which
natural ecosystems and the species that make them up
sustain and fulfill human life. The production of goods
and life-support functions are the two major classes of
ecosystem services that can be assessed in money．
According to Costanza et al. (1997), who evaluatedglobal ecosystem services economically, lowland
wetland or floodplain ecosystem types are most highly
valued among those of 16 ecosystem types evaluated fortheir ecosystem services. Services from floodplain/
lowland wetlands had a total value of $19,580/ha/year
on average, which is by far higher than the values of
those from temperate forests, $302/ha/year. The service
categories of “flood control” ($7,240/ha/year), “watersupply” ($7,600/ha/year), and “trapping poisonous substances” ($1,659/ha/year) were especially highly priced.
The ecosystem services’ concept played a key role in
the Millennium Ecosystem Assessment (MA), aninternational work program designed to meet the needsof decision makers and the public for scientific information concerning the consequences of ecosystem change
for human well-being and options for responding tothose changes (MA, 2005a). Ecosystem services aredefined as the benefits people obtain from ecosystems,
and can be recognized on the basis of understanding
their relationship to human well-being. The MA analyzed the present status and past 50 years’ changes inecosystem services and their influence on humanwell-being.
The MA stressed that wetland ecosystems, including
rivers, lakes, marshes, rice fields, and coastal areas,
could provide many services that contribute to humanwell-being and poverty alleviation by providing many
non-marketed and marketed benefits to people. In
particular, in a world threatened by the present rapidly-progressing climate change (IPCC, 2007), wetlands
such as mangroves and floodplains can play a criticalrole in physical buffering of the catastrophic impacts
caused by sea level rise and increases in storm surges(MA, 2005b). The MA placed high certainty on thestatement that the total economic value of unconverted
wetlands is often greater than the converted wetlands.
Major drivers for conversion are known to developmentof infrastructure such as dams, dikes and levees, land

conversion, water withdrawal, pollution and the introduction of invasive alien species. Global climate change
and nutrient loading are also expected to become
increasingly important drivers in the next 50 years (MA,2005b).

3. Floodplain Ecosystem Mosaics and Traditional Usage as Paddies and Satoyama
Systems in East Asia
Floodplain ecosystems are characterized by both spatial heterogeneity and temporal variability, principally
due to seasonal and unpredictable floods exerting
spatially variable effects of inundation, erosion andsedimentation (Middleton, 1999). Therefore, they can be
regarded as shifting mosaics (Pickett & White, 1985),
which consist of a variety of aquatic and non-aquatic
habitats (Fig. 1). They includes channels, backwaters,
ponds, wet and moist grasslands, banks and riparian
forests. In addition to the diversity of habitats (β diversity in the sense of Whittaker, 1960), “moderate
disturbances” (Connell, 1978) caused by flooding and/or
traditional human activities concerning the use of wetland resources may contribute to the maintenance ofhigh biodiversity within the individual habitats (α diversity in the sense of Whittaker, 1960).
In a less converted floodplain with minor anthropogenic modification, there are diverse aquatic habitats
with different ecological features: seasonal and temporal
ponds (Collinson, 1995) and creeks and channels, which
are mutually connected during floods. Such a networkof aquatic habitats provides a suitable condition for
fresh aquatic fish, which spawn in shallow still water,
but live in streams, lakes or other larger water bodies intheir adult stage.
A high diversity of flora in a wide environmental
range from wet to moist conditions can support highfauna diversity. One of the major types of lowland wetland vegetation is moist tall grassland dominated by
Miscanthus sacchariflorus or Phragmites australis, witha high variety of herbaceous plant species grown under
the grass canopy (Masuda & Washitani, 1990;
Washitani & Masuda, 1990). The plant species diversityof such grasslands is mostly conferred by the underlayer plants, which are thought to be maintained by
disturbances caused by floods and/or human interventions associated with traditional use of the grasses.
These floods and interventions create well-illuminatedmicro-habitats without accumulation of grass litter
which would interfere with sprouting or emergence of
herbaceous plants of short stature (Washitani, 2001). In
recent years, however, moist grasslands have rapidly
lost their ecological integrity and species diversity ofnative plants due to abandonment and/or environmental
deterioration, probably due to eutrophication and biological invasion of alien plants such as Solidago altissima native to North America (Washitani, 2004b;
Miyawaki & Washitani, 2004)
In the Watarase wetland, the largest wetland in cen-Restoration of Biologically-diverse Floodplain Wetlands Including Paddy Fields

137

Floodplain Wetlands
Moist tall
grassland
River
ChannelRiparian forest
Seasonal
Pond

Moist tall
grassland
Meadow
Pond

Cutting grassfieldsRice paddies
Irrigation ponds

Coppices

Modernization・Urbanization

Restoration

loss of ecotone vegetation
loss of habitat diversity
crowded by invasive
alien species

Abandonment
Fig. 1 Schematic representation showing original and traditional land use of afloodplain with a variety of habitats constituting a shifting mosaic, with thepresumed restoration routes.

tral Japan, winter burning, a traditional management
practice for preserving good condition of cut grass fields,
is continuing even now, and thus there remain the typical moist tall grasslands inhabited by more than 50
endangered plant species listed in the national red list
(Ministry of the Environment, 2007), such as Amsonia
elliptica (Thunb.) Roem. et Schult., Apodicarpum ikenoi
Makino, Thalictrum simplex var. brevipes Hara, etc.
(Ishii & Washitani, 2008).

4. Rice Cultivation in Floodplain Wetlands by
Neolithic Settlers
In East Asia, since approximately eight thousands
years ago when the cultivation of rice (Oriza sativa)
originated in the Yangzi delta (Zong et al., 2007), floodplain wetlands were gradually transformed to paddy
fields. A recent archeological investigation by Zong’s
team at the Kuahuqiao Neolithic site revealed that early
Neolithic communities selected floodplain swamps forrice cultivation and settlement. The Neolithic paddy
fields, dated to 7,700 years in age, were excavated froma location where there was a coastal swamp at that time.
Evidence suggests that the site supported rice farming
until around 7,550 years ago, when rising sea levels suddenly deluged the area.
Zong et al. (2007) inferred that exploitation of
aquatic perennial wild rice (Oryza rufipogon) growing
in floodplain swamps by sedentary foragers might havebeen a prelude to the cultivation of rice. Evidence showsthat the Neolithic settlers used fire to clear alderdominated wetland scrub to prepare the site for occupation, then maintained wet grassland vegetation of paddy
types. It is also inferred that they controlled seasonal
flooding of slightly brackish water by “bunding” tomaintain crop yields.

5. Paddy Systems as Substitute Habitats ofFloodplain Wetlands
After most of Japanese lowland floodplains werealtered to paddy fields, paddy field became the commonest wetland type in Japan. In a traditional agricultural landscape, paddy fields were interconnected not138

I. WASHITANI

only to each other, but also to irrigation ponds and rivers
by extensive canal networks. Therefore, aquatic habitat
networks including seasonal and more permanent pools
with creeks interconnecting them were preserved after
the natural floodplains were converted to agriculturallandscapes. Paddy fields are thus the surrogates fornatural shallow nutrient-rich seasonal pools in floodplains, and have been habitats for such animals andplants that were previously adapted to riparian seasonal
pools (Washitani, 2007). However, they are more reliable in occurrence and continuation due to regional ricecultivation calendars and several thousands years of ricecultivation history in Japan may have been enough tobring about adaptive evolutionary changes in insects,
fogs, fishes and mollusks with relatively short generation times.
Until at least several decades ago, even in densely
populated areas, Japanese paddies were not only places
for agricultural production of rice, but also wetlands fullof creatures: a variety of fogs, fishes, dragonflies, water
beetles, and fireflies, whose life cycles are well adapted
to the seasonal farming practices in paddies. Agricultural production, as it was practiced, teamed up with a
network of life and ecosystem integrity. For carp andmany small fish species, paddies are a reproductive
habitat where they spawn their eggs. In spring, lukewarm water flowing from irrigated paddy fields stimulates fish in rivers and lakes, causing them to swim
against the stream. The temperature gradient from shallow paddies to the rivers leads the fish to the paddy
fields.
Before the modernization of farming, paddy fields inJapan were the habitat of a variety of wetland plants andanimals the original habitats of which had been floodplain pools. Ponds and channel networks for irrigation
not only made adequate substitutes for floodplain
aquatic habitats for certain wetland species, but also
worked as dissimilation routes for fish and mollusks in
combination with river systems.
At one time, bounties of wet paddy fields were notconfined to rice, the staple food in Japan, but included
many other foods, such as fish and pond snails, theoriginal habitats of which were floodplain wetlands.
However, in recent decades, aquatic habitat networks
consisting of paddies, rivers and lakes connected withirrigation canals and creeks have been lost or fragmented due to drying of the paddies and/or replacementof irrigation canals by pipelines to modernize farming
conditions. In concert with excess application of agricultural chemicals, these changes in physical conditions
have brought about a mounting crisis threatening to animals and plants once common in agricultural landscapes,
many of which are now listed in the national red list
(Ministry of the Environment, 2007). Intensive farming
and seasonal drying of paddies after the rice harvest
have caused loss of habitats for various wetland species,
i.e., water birds, common fresh aquatic fish, amphibians
and aquatic insects including dragonflies, fireflies andwater beetles (Nishihara et al., 2006).

6. Signs of a Surge in Restoration Activities for
Paddy Wetland Functions and Biodiversity
If managed appropriately, paddies, one of the world’s
dominant forms of agriculture, can provide valuable
habitats for water birds, as Elphick (1998) concluded in
his study examining the equivalence of flooded paddy
fields to semi-natural wetlands in California. In Europe,
winter flooding has been practiced in the Ebro delta,
located in northeastern of Spain, which is the third mostimportant aquatic habitat of the western Mediterraneanfollowing the Carmargue (in France) and Doñana Park(in southern Spain). About 65% of the delta surface iscultivated with rice. Supportive agri-environmental
measures by the European Union (Regulation CEE
1257/1999) for sustainable rural development, especially in areas with environmental restrictions, havebeen adopted in the Ebro delta: (1) to maintain floodingof the paddy surface at least four months (in autumn-winter time) so as to favor aquatic fauna and (2) toeliminate mechanical techniques mixing weed with soil
and water in order to minimize pesticide contamination(Serra et al., 2007).
In Japan, there has been more activity in monitoring
and restoring biodiversity to agricultural landscapes in
the last decade. One promising measure to recover
paddy biodiversity is winter flooding, that is, continuous
wetting of paddies during winter when rice plants are
not growing in the paddies, in combination with no ormuch reduced chemical applications compared toconventional modern farming. This new biodiversity-friendly farming is named “fuyumizu-tanbo” meaning ‘winter flooded paddy fields’ in Japanese. Such a
biodiversity-friendly farming practice has been rapidly
dissimilated after being tested at a new Ramsar site,“Kabukuri-numa and surrounding paddies” located in
the former town of Tajiri (the present Oosaki City) in
Miyagi Prefecture (Kurechi, 2008).
“Kabukuri-numa” is a swamp 150 ha in area which
is a major wintering habitat for migratory geese in Japan.
In 1995, the swamp faced a crisis of thorough dredging
to increase in its water storage capacity for flood control.
The plan, however, was canceled to preserve conditions
for the wintering of migratory geese by maintaining
natural habitats of various wetland animals and plants.
Instead of dredging it, 50 ha of paddy fields adjacent tothe swamp were restored to natural wetland. The aims of
the restoration were not only to increase the flood control capacity, but also to improve the wintering conditions for the geese. Simultaneously the “fuyumizutanbo” farming method was introduced into neighboring
paddy fields included in the Ramsar site. Thoughnormally, paddy fields are seasonally dried up after therice harvest in the modern conventional farming method,when they are flooded in winter they become wetlands
full of wildlife including water fowl, frogs, worms andmicroorganisms. Participatory monitoring by farmers
has revealed that the activities of these creatures yieldnatural fertilizer to enrich and develop a nutrient-rich

Restoration of Biologically-diverse Floodplain Wetlands Including Paddy Fields

mud layer, which can prevent weed seed germination by
burying them after rice planting in the next season. The
new farming method, therefore, has potential merits
both for biodiversity conservation and as an organic
farming method suited to East Asian rice cultivation.
The rice produced by “fuyumizu-tanbo” is highly valuedby consumers and selling at reasonable prices.
A similar farming method combining winter floodingwith no or less chemical application has been also
adopted in Toyooka City in Hyogo Prefecture where a
project to re-introduce white stork (Ciconia boyciana)
once extinct in the wild is being attempted. In the project, birds bred in a sanctuary were released after theappropriateness of release had been checked geneticallyand ecologically (Naito et al., 2008). Simultaneously,
restoration of the ecological integrity of various types of
wetlands including paddy fields where the birds canfeed has been underway. Paddy fields and drainage
canals are important feeding habitats for white storks,
since loaches and aquatic insects are their major food.
Wetland restoration to develop extensive shallow
swamps along river channels has also been implemented
in the variety of the Maruyama River as a part of civil
works for flood control

7. Potential Value of Floodplain Wetlands
Contributing to Synergy between Climate
Change Mitigation and Biodiversity
Conservation
According to the United Nation’s Intergovernmental
Panel on Climate Change (IPCC), global climate change
is rapidly progressing and the average global surface
temperature has risen by approximately between 0.6°C0.2°C over the 20th century (IPCC, 2007). The IPCC
predicts further global warming of 1.4°C-5.8°C by theend of the 21st century. More floods, storms, droughts,
heat waves and increases in threats of diseases and pests
are forecasted as the result of climate change. In order tomitigate climate change, reduction in the release ofgreenhouse gases is needed.
Therefore, reduction in fossil carbon emissions to
mitigate climate change has the first priority in actions
to secure human sustainability. Industrialized countries
have agreed under the Kyoto Protocol to reduce theirgreenhouse gass emissions by at least five percent relative to 1990 levels, by the years 2008 to 2012. Morethorough reductions in emissions should be agreed toafter 2012 to stabilize the climate as needed (IPCC,
2007). Reducing gasoline consumption is one of the
major measures to reduce the release of greenhousegases.
Bio-fuels are among the important solutions for the
reduction of carbon emissions from large-scale consumption of fossil fuel. Landuse for biomass production
for bio-gasoline is expected to increase rapidly in thenear future, and this may have various negative consequences on wetland conditions. Therefore, cellulosic
ethanol production from presently unused biomass is139

expected to be an environmentally-friendly measure(Sanderson, 2006). In addition to a number of wellappreciated services provided by floodplain wetlands(Costanza, 1997), moist tall grass biomass of inwetlands is a promising energy resource substituting forfossil fuels.
The moist tall grasslands dominated by P. australis
and/or M. sacchariflous, which are the commonest wetland vegetation types in Japan, have long been used tocollect cutting grasses and were periodically burned for
management, probably since the Neolithic Age.
Abandonment of traditional use and/or management of
the grasslands, i.e., cutting and burning are among the
major causes of biodiversity loss in moist tall grasslands(Washitani, 2001). If the biomass of these grasses wereused as material for the production of cellulosic ethanol,
a fully renewable, advanced bio-fuel that can be used intoday’s cars (Sanderson, 2006), it would contribute to
the solutions for both global warming and conservation
and/or recovery of wetland biodiversity in Japan.
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