187

Outline of Mires in Hokkaido, Japan, and Their Ecosystem
Conservation and Restoration
Hiroko FUJITA
Botanic Garden, Field Science Center for Northern Biosphere
Hokkaido University
North 3, West 8, Chuo-ku, Sapporo 060-0003, Japane-mail: hiro@fsc.hokudai.ac.jp

Abstract
Most of the wetlands on Hokkaido Island are peat-forming mires and constitute one of the mostimportant principal ecosystems characterizing the natural landscapes of Hokkaido. However, more than
70% of the original mire area has been lost through transmigration and land reclamation since the Meiji era(approximately 130 years ago). Nowadays, 150 wetlands remain in both mountainous regions and lowland
areas. They are characterized by various types, formations and development processes and there is an urgent
necessity to protect and restore them. Especially regarding lowland mires, there are serious problems suchas land subsidence, declining water tables due to drainage and increasing mineral soil or eutrophic waterrun-off from rivers and agricultural lands. As a result, mire vegetation has been undergoing retrogressive
succession. A number of scientific research projects are being carried out in order to clarify the processes
and mechanisms of mire ecosystem change and degradation. In addition, methods of conservation andrestoration of mire ecosystems have been advancing. Furthermore, enforcement of the ‘Law for promotionof nature restoration’ and revisions of various laws have promoted the activities of non-governmentalorganizations, administrations and researchers.
Key words: buffer zone, citizens’ partnership, peatland, retrogressive succession, wetlands

1. Introduction
Hokkaido Island has more peatlands than anywhere
else in Japan, as its climate conditions have facilitated
the formation of various types of wetlands. Lowland
mires such as Kushiro Mire, Sarobetsu Mire andKiritappu Mire present a grand landscape, and mountainmires such as Numanohara Mire, Genshigahara Mire,
Uryu Numa Mire and Ukishima Mire also form an
important element of natural landscapes in Hokkaido.
Wetlands greater than 1 ha total 150 in number, with a
combined area of 59,881 ha (Fujita et al., 1997). They
constitute 86% of the remaining wetlands of Japan(Geographical Survey Institute, 2000). The numerous
Japanese wetlands are located on alluvial plains in lowlands which are the main regions of human activity,
especially in the area south of central Honshu, where
they have been lost to development or converted to
paddy fields. By contrast, many wetlands are still relatively intact in Hokkaido. However, during the past 100
years, nearly 70% of the original wetlands in Hokkaido
have been lost (Fujita, 1997), and the decline in wetlandarea and degradation of mire ecosystems have continued
up to the present.
Global Environmental Research
11: 187-194 (2007)
printed in Japan

Until recently, people had treated wetlands as useless,with thorough reclamation of wetlands continuing fromthe 1950s to the 1970s without thought of conservationor preservation of the natural environment or biodiversity. In recent years, wetlands have been recognized ashabitat for unique, rare animals and plants and to havevarious functions. Thus, conservation and restoration ofremaining wetlands have become an important emergent
issue.
The aims of this paper are: (1) to summarize thecharacteristics of wetlands in Hokkaido, (2) to present
the problems regarding mire ecosystem degradation and(3) to introduce scientific research, and NPO andadministrative actions for conservation and restoration.

2. Wetlands in Hokkaido
The greatest feature of the wetlands of Hokkaido isthat most of them are on peatlands. Sakaguchi (1961)
pointed out that there is a fairly good correlation
between the 20˚C July isotherm and the southern limitof abundant mire formation, and that the 25˚C July isotherm coincides with the southern limit of peat formation in the lowlands. Hokkaido falls into the zone with
©2007 AIRIES188

H. FUJITA

mean July temperatures below 20˚C except for a few
areas in the south, along the Sea of Japan coast and inbasins in central Hokkaido, and therefore has climaticconditions that are suitable for the formation andaccumulation of peat.
Figure 1 shows the distribution of peatlands and currently existing wetlands on an elevation map of
Hokkaido. Many of the peatlands are in lowland areas,
and a large number of the remaining wetlands are in theeastern and northern parts of Hokkaido. The peatland
areas before reclamation was 200,642 ha and most werein lowland alluvial plains. Low-moor peat accounts for
71%; transition-moor peat, 12%; and high-moor peat,
17% (Hokkaido Development Agency, 1963). The threelargest mires were located in the basins of the Ishikari
River, Kushiro River and Sarobetsu River, and theyaccounted for 46% of all peatlands in Hokkaido(Hokkaido Development Agency, 1963). The loss of
wetlands was particularly severe in the western and central parts of Hokkaido, where most lowland mires wereconverted to arable land for rice and other crops. On theother hand, mountain mires (above 400 m in altitude)
avoided the major effects of development. However,construction of forestry roads and an increasing numberof tourists have become a problem.
Three main geomorphologic and climatic factors canbe distinguished that have contributed to the formationof mires in the lowlands of Hokkaido: (1) formation ofpoorly drained alluvial plains along rivers, (2) terrestrialization of coastal lakes and lagoons and (3) highhumidity and low temperatures during the summer due
to sea fog (Fujita et al., 2007). In many cases, one ofthese factors can be singled out as the most importantone, but especially in the largest lowland mires, i.e., theIshikari Mire complex, Kushiro Mire and Sarobetsu
Mire, factors (1) and (2) or even all three (in the case of
the Kushiro Mire) have played a role (Fujita et al.,2007). Most of the lowland mires are distributed on alluvial plains along the lower reaches of rivers and can beclassified as minerotrophic fens. However, in the
Sarobetsu, Ishikari, Kushiro, Bekanbeushi, Furen,
Shibetsu and other mires, some areas have developed toa very oligotrophic, possibly ombrotrophic bog stage.
Stratigraphical investigations have shown that the mires
were initially influenced by flooding and graduallydeveloped into ombrotrophic bogs (Iizuka & Seo, 1955,
1956, 1966; Inoue, 1997; Matsumi et al., 1966;
Sakaguchi, 1958; Shoji et al., 1966a, 1966b, 1966c;
Tachibana et al., 1997; Uragami et al., 1954).
As compared with those in Europe and North
America, lowland mires in Hokkaido have some features such as a warm climate with abundant precipitation under the influence of a temperate monsoon, abundant calcium-less water or spring water, flooding events
caused by snowmelt in early spring or heavy rainfall inthe typhoon season and deposits of ash or volcanic
tephra in the peat layers (Fujita et al., 2007). These features are the background for the characteristics of lowland mires in Hokkaido.
There are 43 mountain mires among the 150 wetlands on the inventory and their area is 923 ha, that is,
only 1.5% of the total wetland area (Fujita, 1997). However, they have a variety formations, landscapes andvegetation. Hokkaido has many volcanoes, so numerous
mountain mires of diverse ages have developed in the
volcanic mountain ranges. Many have developed onlava plateaus and gentle slopes formed by lava flows(Fujita et al., 2007). Apart from these, there are a num-N

Peatlands
Current existing
wetlands

Elevation (m)

0

50

100

150

200 kmFig. 1 Distribution of peatlands and current existing wetlands in Hokkaido.

0 - 10
10 - 20
20 - 40
40 - 100
100 - 200
200 - 300
300 - 400
400 - 800
800 - 2500

Outline of Mires in Hokkaido, Japan, and Their Ecosystem Conservation and Restoration

ber of mires that have developed in depressions formedby landslides. They have widely varying dates of onsetof formation that are closely related to the time when thelandslides occurred (Fujita et al., 2007). The mountainmires of Hokkaido are mostly characterized as oligotrophic flat or sloping mires or as mesotrophic sloping
mires, often with a well developed microtopographyof elongated ridges and hollows (frequently calleda “Kermi-Schlenke complex” in a combination of
Swedish and German mire terminology) (Fujita et al.,2007).
Sakaguchi (1961) pointed out that the majority ofJapanese mires (he used the term “peatlands”) aredistributed in areas with Quaternary volcanic rocks or
on alluvial plains north of central Honshu. He found thata variety of topographic situations in volcanic landscapes are conducive to mire formation in mountain
ranges, e.g., basins dammed by lava or mudflows, shallow depressions on lava or mudflows, gentle slopes withweathered volcanic ash layers and slopes or seepage
areas with a continuous water supply from springs at thefoot of volcanoes. From this observation he concluded
that volcanic landforms play an analogous role inmountain mire formation in Japan as glacial landforms
do in many parts of Europe and North America.

3. Mire Ecosystem Degradation
3.1 Effects of drainage and land subsidence
The Ishikari Mire, located in the lower reaches of the
Ishikari River, once had an area of 55,000 ha, making it

189

the largest peatland complex in Japan (Hokkaido Development Agency, 1963). Mires in their natural condition,
however, were reduced to 119 ha by 1983 due to agricultural development (Miyaji & Kohyama, 1997). The
Bibai Mire is one of the two remaining mires of theoriginal Ishikari Mire (Fig. 2). The National Agriculture
Research Center for the Hokkaido Region preserves partof its 50 ha site. Using this mire, various research projects have been carried out for peatland reclamation
since 1919 (Kasubuchi et al., 1994). Nowadays, approximately 22 ha of area survives as wetlands, andvarious investigations have been carried out concerning
the functions of mire ecosystems or conservation ofmire systems (Itoh et al., 2001; Iiyama et al., 2005;
Kasubuchi et al., 1994, 1995; Nagata et al., 2005;
Shiozawa et al., 1995; Takakai et al., 2005).
The most crucial cause of mire degradation is declining ground water levels and progressive aridification
caused by drainage ditches surrounding the mire. Here,a deep drain was dug between the remaining mire andthe adjacent agricultural land. From this drain, theground water runs off (Fig. 2C). Figure 3 shows a geological cross section of the area (Kasubuchi et al., 1995).
The effect of drainage is very apparent especially on thewestern side of the plot (Shiozawa et al., 1995). From acomparison of the elevation of agricultural land withthat at the center of the mire, the subsidence in the
agricultural land seems to have been up to three meters
during these 40 years (Miyaji et al., 1995). In the
Ishikari Peatland the depth of peat layers sometimes
exceeds five meters, so if subsidence continues, prob-

Ａ

Ｂ

Ｃ

Ｄ

Fig. 2 Present condition of the Bibai Mire.
A: bog vegetation (Moliniposis japonica-Sphagnum papillosum community)，B: invasion of Sasa
palmate and Rhus trichocarpa into the bog (Rhus trichocarpa-Sasa palmate community)，C: drainage
ditch between the mire and adjacent cultivated land，D: area dominated by Sasa palmate (Rhustrichocarpa-Sasa palmate community)．

190

H. FUJITA

lems such as influences on irrigation facilities, increasing risks of inland flooding, etc., may occur (Kasubuchi
et al., 1994, 1995).
The degradation of the mire ecosystem is so clearthat the mire vegetation has changed. In old times, bog
vegetation covered the Bibai Mire, but at present only
two hectares of the central part remains as bog. Most of
the mire vegetation has been undergoing retrogressive
succession and has changed to Sasa palmata (Bean)
Nakai dominant communities (Fig. 2B, 2D). This is atypical case of retrogressive succession of bog vegetation to Sasa vegetation caused by the effect of drainage
that can be seen in the southwestern part to the northernend of Hokkaido (Fujita & Inoue, 2005; Fujita &Tachibana, 1998; Fujita & Takeda, 2002; Tachibana &Ito, 1980).
Figure 4 shows fluctuations of the ground water levelin the bog area and Sasa area in the Bibai Mire
(Fujimoto et al., 2006) with data from the bog area in
the Sarobetsu Mire where typical bog vegetation exists
with little human impact (Inoue, unpublished). The
difference in the two fluctuation patterns of the groundwater level between retrogressive vegetation (Sasa
community) and bog vegetation in the Bibai Mire is not
so clear in the warm weather period (Fujimoto et al.,
B

A

east

paddy field

19

west

drainage ditchroaddrainage ditch

HeightHeight(m)
(m)

18

road

17

cultivated land

16
dressed soil and topsoil
high-moor peat

15transitional-moor peat
low-moor peat14

clayey peat
peaty clay

13

clay

600

500

400

300 200
Distance(m)(m)
Distance

100

ground water level0

Fig. 3 Geological cross section of the Bibai Mire.
(Kasubuchi et al., 1995)

Groundwater(cm)
Groundwater level
level (cm）20

10Ground surface

0

-10

-20

-30
1-Jul.

1-Aug.

1-Sep.

1-Oct.

2005

Sarobetsu bog

Bibai bog

Bibai Sasa

Fig. 4 Fluctuations of the water tables of the Bibai Mire andSarobetsu Mire.
(Fujimoto et al., 2006; Inoue, unpublished data)

1-Nov.

2006). In summers with less precipitation, the groundwater level is low in both areas because of the large
evapotranspiration. On the other hand, the fluctuation of
the water level in the Sarobetsu Mire is within 10 cm.
According to observations of fluctuations in the groundwater level from 1994 to 1997 in the Bibai Mire (Itoh etal., 2001), the record level of 2005 (Fujimoto et al.,2006) is very similar to them. In 1994, however, thegroundwater level dropped approximately 50 cm below
the ground surface due to a record drought (Itoh et al.,2001). The occurrence of such unusual years causes
extreme aerobic conditions in the peat, and it may cause
retrogressive succession in the remaining mire.
It has been pointed out that the duration of retentionof snow melt water in late spring is important forthe preservation of mire ecosystems (Hayama &Nakatsugawa, 2004; Nakatsugawa et al., 2005). At the
Bibai Mire, though, the melting snow water runs off in ashort period along a land slope formed by the drainage
effect (Kasubuchi et al., 1994; Takada et al., 2004).
3.2 Sedimentation and eutrophication
In the Kushiro Mire, on increase of alder trees in themire has become a concern. It is said this is due to anincrement in sedimentation and eutrophication related tochanges in land use in the upper river basin and river
short-cuts. However, the relationship between vegetation change and soil sedimentation is not yet clear in theplaces where the alders have increased. The reason therelationship is unclear is the difficulty of peat soil
sampling under wet conditions such as inundation.
We therefore developed a new method of sampling by
freezing a soil column using a special borer. We analyze
the 137Cs contents and carbon volume of these samples(Fig. 5; Kato et al., 2006). 137Cs is a radioactive nuclide
content with a half-life of 30.2 years produced by
nuclear tests, and its content can be used for dating
sedimentation. In Japan, the maximum 137Cs fallout wasrecorded in 1963. We analyzed several aerial photographs from 1967 and chose points with no vegetation
change (CH line; Fig. 5, upper figure), and points withchanged vegetation from reeds and sedges to alderforests (K2, K3 and K4 on the K line; Fig. 5, lower
figure). On the CH line, the carbon volume is highabove the peak of the 137Cs level, indicating sedimentation did not occur. On the other hand, the carbon volume
on the K line is low above the peak of the 137Cs level
and this indicates the occurrence of sedimentation after
1963 at the K line points. The K line is located near thebank of the Kuchoro River, which was improved andstraightened with short-cuts from 1966 to 1980, withan accompanying increase in inflow of sediment(Kameyama et al., 2001; Mizugaki & Nakamura, 1999;
Nakamura et al., 1997). The CH line is located in thebasin of the Chiruwatsunai River which has kept its
pristine river form. Around the K line, the ground waterlevel is high and stable (Fujimura et al., 2006), so thefactor in the alder forest increment here is not drainage
but reinforced sedimentation.

Outline of Mires in Hokkaido, Japan, and Their Ecosystem Conservation and Restoration
137Cs

0

0

（Bq/kg dry soil）

100

200

300

5

Ｄｅｐｔｈ (ｃｍ）

0.2

Carbon content （％）
400

0

0

20

40

60

10

15

15

20

20

0.1
0

5

10

191

- 0.1
- 0.2

CH1 (alder forest）

25

- 0.3
- 0.4
0.2

25

CH2 （sedge & reed ）

30

0.1

30

0
- 0.1

137Cs

Ｄｅｐｔｈ (ｃｍ）

0

（Bq/kg dry soil）

100

200

300

Carbon content （％）
0

400

20

40

60

- 0.2

0

0

- 0.3

5

5

- 0.4

10

10

15

15
20

20
25
30

K1 (95m from the bank）
K2 (150m from the bank)K3 （220m from the bank）
K4 (250m from the bank）

25

Fig. 6 (a) Simulated groundwater table profiles around a trenchfor various evapotranspiration rates. (b) The simulation of
the higher groundwater table rise than in the case of thesigle trench if two trenches were constructed in parallel tothe original one. (Iiyama et al., 2006)

30

Fig. 5 137Cs content and carbon volume of frozen soilcolumnar samples from the Kushiro Mire (upper: CH
line on the Chiruwatsunai River, lower: K line on the
Kuchoro River). (Kato et al., 2006)

4. Approaches to Mire Ecosystem
Conservation and Restoration
4.1 Scientific research on conservation andrestoration methods
Even in bogs under good natural conditions, theground water level usually drops in July and August,because the amount of evapotraspiration is larger than
precipitation in the summer season. In addition, the effects of drainage cause mire degradation. Therefore, forthe remaining mires surrounded by drains, like the Bibai
Mire, steps should be taken to stop or dam up the
run-off from the mire. For the first attempt at hydrological conservation, in the Bibai Mire, a blocking sheet wasburied on the lower three sides of the bog, but the effectcould not be sustained for long periods (Itoh et al.,2001). After that, from 2003, a subsequent attempt wasmade to raise the groundwater level by trench irrigationin an area invaded by Sasa (Iiyama et al., 2005, 2006).
A trench 28 m long, 20 cm deep and 23 cm wide wasdug and supplied irrigation water from neighboring
paddy fields for the period from early May to the end of
August. The water table level in the trench was kept
within 5 cm of the soil surface by an automatic irrigation tap (Iiyama et al., 2005). The irrigation water
spread over a distance of only about 15 m on both sidesof the trench (Iiyama et al., 2005, 2006). The irrigatedarea was limited to several meters from the trench, because the lateral ground water flux in a peatland is notvery large (Iiyama et al., 2005). It has therefore beensuggested that in order to spread irrigation water over alarger area, construction of several trenches in parallel
form would be required (Fig. 6; Iiyama et al., 2005,
2006).
In the Sarobetsu Mire, obvious subsidence and retrogressive succession has occurred due to the influence ofa drainage ditch constructed between the mire and theadjacent agricultural grassland. After reclamation of themire into grassland in the mid 1980s, the subsidence andsurface bumpiness became more apparent year by year.
In addition, some parts of the field show poor drainage
conditions so that the grass yield has declined and theworkability has also dropped (Nakase et al., 2006). For
improvement of field conditions together with restoration of mire hydrological conditions, an experiment wasstarted in 2006 setting a buffer zone between the mire
and the grassland in a project conducted under the ‘Law
for the promotion of nature restoration.’ A 25 m wide
strip of grassland next to the mire across the drainage
ditch was leased from the farmer as a buffer zone. A
new drain was dug next to the grassland to enhancedrainage of the grassland, while the old ditch locatedbetween the mire and the grassland was dammed up
using peat material dug from the new drain. (Fig. 7;
Nakase et al., 2006). Damming this up kept the
groundwater table in the mire high and the buffer zone
formed a suitable gradient for the groundwater level
between the mire and the grassland (Fig. 8). Monitoring
and keeping multiyear data is important for theconsideration and creation of restoration methods.
4.2 Efforts by NPOs and local governments toconserve and restore mires
Degraded mires surrounded by agricultural land arescattered throughout the Ishikari peatland. They are very

192

H. FUJITA

BeforeOld drain

Grassland

Miregroundwater level
Mire

Grassland

After setting up the buffer zone
balancing pool（old drain）

Bufferzone

Mire

Grassland
New drain

old ditch filled with
peat

Mire

Buffer zone

Grassland

BeforeAfter

25m

Fig. 7 Plan of the buffer zone between the Sarobetsu Mire andits adjacent grasslands. (after Wakkanai Development andConstruction Department)

Grassland

Mire
25 m

Buffer zone

tion, the Ishikari branch office decided to introduce
irrigation water for rice farming to this wasteland to stop
further degradation due to low groundwater levels. They
built an inlet for irrigation water on an adjacent irrigation pipeline and started supplying water from the springof 2006 (http://www.ishikari.pref.hokkaido.lg.jp/ss/csi/
news/deitansitti-1.htm). This attempt is the first case ofaction to preserve mires taken directly by administrative
authorities, and it will be necessary to monitor its effectover the long term. Furthermore, in the summer of 2007,
an NPO was established for the conservation andrestoration of mires and rural areas originating on
peatland. In Hokkaido, several NPOs and groups are inaction for conservation of mires.
In urban areas, efforts for the conservation andrestoration of remaining mires are more active. The
karakaneitotonbo (Nehalennia speciosa), a kind ofdamselfly, has been designated an endangered species. It
has been found in a small wasteland (20 ha) in an urban
area of Sapporo city. This area was formerly a part of
the Ishikari Mire, and degraded bog vegetation still remains, but it is in very serious condition due to heavy
human impacts such as drainage, peat cutting, and landfilling. Also, the land is privately owned but divided
among numerous land owners (Fujita & Inoue, 2005). In
1997 the local citizens organized a conservation group,
and in 2004 they raised it to an NPO status (http://
www.host.me-h.ne.jp/tombo/). From 2005, this NPO
started purchasing several pieces of lands by using a
grant from the Association of National Trusts in Japan.
Though the purchased area is still very small, an initial
step has been taken towards restoration of the mire
ecosystem.
As stated above, we may expect that various wetland
conservation and restoration activities may be carriedout, not only by administrative authorities but also by
partnerships of citizens.

Acknowledgment
Fig. 8 A picture of the buffer zone between the mire and grasslands at the Sarobetsu Mire.

small in size and the vegetation in them has changed toforest or Sasa grassland. In some cases, however, mireplants or endangered plants may barely be surviving.
Recently, a movement has been started to preserve thesedegraded mires as a place for keeping local gene resources and biodiversity.
The wasteland at Numanohata in Shinshinotsu Murais a privately owned small mire (2.3 ha). The Ishikari
branch office of the Hokkaido Government has madepositive efforts to preserve this wasteland. This area wasopened about 100 years ago, and the wasteland also suffers the effect of drainage from several old ditches. A
flora survey showed there to be 158 plant species,
including wetland plants and endangered species (Katoh& Fujita, unpublished). After several years of considera-

I thank Dr. Takashi Inoue, for reviewing a draft ofthis paper and giving significant suggestions.
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