Environmental Monitoring and Assessment (2005) 109: 243–253
DOI: 10.1007/s10661-005-6284-z

c Springer 2005
SPATIAL ASSESSMENT OF THE ALDER TREE IN KUSHIRO MIRE,JAPAN USING REMOTELY SENSED IMAGERY – EFFECTS OF THE
SURROUNDING LAND USE ON KUSHIRO MIREKAZUO OKI∗ , TSUTOMU AWADU, HIROYUKI OGUMA and KENJI OMASA
Department of Biological and Environmental Engineering, The University of Tokyo,
Graduate School of Agricultural and Life Sciences, Tokyo, Japan(∗ author for correspondence, e-mail: agrioki@mail.ecc.4-tokyo.ac.jp)(Received 7 June 2004; accepted 12 November 2004)

Abstract. The relationship between alder (Alnus japonica) distribution and surrounding land use inKushiro Mire was spatially assessed using remotely sensed imagery. From the result, it was foundout that the expanding area of alder trees in Kushiro Mire was affected by the agricultural land areain the upper course of the river basin and flooding in the lower course of the river. The soil sediments
flowing into the Kushiro Mire from the agricultural land resulted in heavy sedimentation that favors
the growth of alder trees. Consequently, the number and density of alder trees has increased. The
future distribution of alder trees was predicted based on the mechanism of expansion of the alder-tree
area in Kushiro Mire, and it was found that large vegetation areas in Kushiro Mire will be changed toareas with alder trees.
Keywords: agricultural land, flooding, Landsat, remote sensing, soil sediments, spatial assessment

1. Introduction
Wetlands are estimated to cover about 4–6% of the world’s land area (Mitsch andGosselink, 1993), and covers more than 20% of the landscape in boreal regions
where great expanses of peat lands are found (Gorham, 1991). One of the mostimportant roles of wetlands is its function as linchpins of global climate changethat sequesters and releases major portion of fixed carbon in the biosphere (Mitsch
and Wu, 1995). Costanza et al. (1997) estimated that wetlands are 75% morevaluable than lakes and rivers, 15 times more valuable than forests, and 64 times
more valuable than grasslands and rangelands. Wetlands also serve as an important
relay ground or habitat for migratory birds. They are an important site of wildlife
conservation and wildfowl, and genetic pools of various and precious flora and fauna(Adams and Hollis, 1988; Adams, 1993; Hollis et al., 1993; Mitsch and Gosselink,
1993; Thomas et al., 1993). Moreover, it is also important for the generation ofcarbon dioxide and methane gases, which cause global warming. Natural wetlands
are major source of methane (CH4 ), emitting approximately 21% of the total global
emissions to the atmosphere (Intergovernmental Panel on Climate Change (IPCC,
1995)).

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Wetlands are often heterogeneously distributed in many landscapes, particularly
in glaciated regions. These wetlands generally appear as small isolated patches
that are strongly influenced by their surrounding matrix. The patchy nature ofwetlands resemble ‘biogeographical islands’ at a local scale, but a shift in scale may
reveal that individual wetland patched may cluster to form a large wetland complex(Whited et al., 2000). Wetland assessment techniques have generally focused on
rapid evaluation. But a method in which the land cover distribution of this large
wetland complex is measured precisely to assess environmental change is necessary
because large wetland complexes are a delicate environment that are easily affectedby human development.
The Kushiro Mire, with 18,000 ha, is the largest wetland area in Japan. The importance of preserving the biodiversity of the Kushiro Mire wetlands was discussed
at the Ramsar Convention (Iwakuma, 1996). Most of the Kushiro Mire consists offen covered with reeds and sedge grasses, while some parts of the wetland are bog
areas covered with sphagnum moss. The northern part of the wetland is covered
with alder (Alnus japonica) (Oguma and Yamagata, 1997). The number, canopy
area, and density of alder trees in the Kushiro Mire have increased dramaticallyover the last 50 years. Alders are sensitive to small changes in the environment.
They grow best in areas where soil accumulates due to sedimentation and waterlevel has stabilized. It has been reported that alders can be used as an index ofaridity and eutrophication in wetlands (Yamagata, 1999).
In recent years, nutrient-rich water and soil sediment have been flowing into theKushiro Mire from the north due to rapid development in the surrounding land. As
a result, the vegetation distribution pattern in the wetland has undergone a rapidchange (Nakamura et al., 1997; Nagasaka and Nakamura, 1999). In particular, thewetland vegetation has been changed due to the dramatic increase in the number
and density of alder trees, which express aridity. However, previous studies have notconsidered the full distribution of alders over the entire mire. Hence, it is necessarythat the relationship between alder tree distribution and environmental changes
around Kushiro Mire be spatially assessed to better understand and explain thedramatic increase in the number and density of alder trees. As it will be difficultand costly to evaluate the alder distribution and the surrounding land use in Kushiro
Mire, by field survey, remotely sensed imagery was considered to be potentially
useful for the task (Yasuoka et al., 1994).
Several case studies have used remotely sensed data to classify vegetation in
Kushiro Mire (Yasuoka et al., 1994; Oguma and Yamagata, 1997; Yamagata, 1999).
These papers utilized a vegetation classification map of Kushiro Mire produced by
the National Institute for Environmental Studies of Japan based on Landsat Thematic Mapper data. There has also been a case study in which the precise area ofalders in Kushiro Mire was determined from TM imagery (Oki et al., 2002). However, there have been no spatial evaluation of the relationship between alder distribution and surrounding land use in Kushiro Mire using remotely sensed imagery.
Therefore, this study used remotely sensed imagery to evaluate the relationshipSPATIAL ASSESSMENT OF THE ALDER TREE IN KUSHIRO MIRE

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between alder distribution and surrounding land use in Kushiro Mire. The objective is to explain the mechanism of alder-area expansion in Kushiro Mire, andconsequently predict the future distribution of alder trees.

2. Data and Methods
2.1. C HARACTERISTICS OF THE KUSHIRO MIRE
The Kushiro Mire, which is about 18,000 ha, is the largest wetland area in Japan.
It is located in the eastern part of the Hokkaido region (Figure 1). The wetland wasformed by accumulation of peat over the last 400 years with depth ranging from 1 to
4 m. The average temperature in the area is about 5.5 ◦ C, and the annual precipitation
averages to 1100 mm. The wetland is recognized as one of the most important
ecosystems in terms of species diversity, and its conservation was proposed at the
Ramsar Convention (Iwakuma, 1996; Yamagata, 1999).
Most of the Kushiro Mire area consists of fen covered with reeds and sedge
grasses, while some parts of the wetland are bog areas covered with sphagnum moss.

Figure 1. Location of the Kushiro Mire in Hokkaido.

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The northern part of the wetland is covered with alder (Alnus japonica) (Oguma andYamagata, 1997). Fen is defined here as peat-producing wetland influenced by soil
nutrients from water flowing through the system. A bog area is a peat-producing
wetland in moist climate, where organic material has accumulated over long periods.
Water and nutrient goes into the system through precipitation and runoff. In recent
years, nutrient-rich water and soil sediment have been flowing into the Kushiro
mire from the north due to rapid development in the surrounding agricultural areas.
As a result, the vegetation distribution pattern in the wetland has undergone a rapidchange (Nakamura et al., 1997; Nagasaka and Nakamura, 1999). In particular, thenumber and density of alder trees have increased dramatically during the last 50
years. Because alder trees can grow well in areas where there’s accumulation ofsoil due to sedimentation, this resulted in rapid changes in vegetation in wetlands.
Therefore, it is necessary that the relationship between alder tree distribution andenvironmental changes around Kushiro Mire be spatially assessed.
2.2. S ATELLITE DATA
We used Landsat Multispectral Scanner (MSS) and Thematic Mapper (TM) data toevaluate the spatial relationship between alder tree distribution and environmental
changes around Kushiro Mire. The MSS is an optical sensor mounted on Landsat
1 to Landsat 5. Landsat 1 with the MSS was launched in 1972 as a first sensor.
The MSS has four bands, which are 0.5–0.6 µm (band 4), 0.6–0.7 µm (band 5),
0.7–0.8 µm (band 6), and 0.8–1.1 µm (band 7) in the visible to the near-infrared
region. The spatial resolution is approximately 80 m. On the other hand, the TM is
an optical sensor mounted on Landsat 4 and Landsat 5. The TM has seven bands,
namely 0.45–0.52 µm (band 1), 0.52–0.60 µm (band 2), 0.63–0.69 µm (band 3),
0.76–0.90 µm (band 4), 1.55–1.75 µm (band 5), 10.40–12.50 µm (band 6), and2.08–2.35 µm (band 7). The spatial resolution of these bands except for band 6 is
30 m. Band 6 has 120 m spatial resolution. In comparison with the MSS, the TM
has higher number of spectral bands and spatial resolution.
2.3. ALDER TREE MAPS
In this study, we produced alder tree maps in order to evaluate the change of spatial
patterns of alder tree areas in Kushiro Mire. The maps were classified into three
categories (alder, water, and other) by the ISODATA method using Landsat MSS(7 June 1979) and TM data (25 August 1981, 27 July 1985, 7 June 1990, 1 July
1993, 26 August 1996, 15 July 1998, and 22 September 2000) based on vegetation
maps made by field survey. The ISODATA method is an unsupervised classification,
which identify statistical patterns in the data without any ground truth data. The
clustering method uses the minimum spectral distance formula to form clusters(ERDAS, 1997). Also, Landsat TM is better than MSS data for evaluating theKushiro Mire, because its spatial resolution is 30 m, versus 80 m for MSS data.

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The use of Landsat TM began in the 1980s, whereas MSS imagery was used toevaluate the wetlands in the 1970s. TM imagery does not use the thermal infrared
band (band 6) in the classification. In this study, each Landsat MSS/TM image
was corrected geometrically using the TM imagery of 25 August 1981. A nearestneighbor interpolation method was used to prevent the original pixel values frombeing annulled. As a result, the error of superposed Landsat MSS/TM imagery wasless than 1.0 pixel.
Figure 2 shows sample alder tree maps made from Landsat imagery in Kushiro
Mire taken 7 June 1979 and 26 August 1996, and Figure 3 shows the changeof alder-tree area calculated from alder tree maps in Kushiro Mire from 1979 to
2000. From Figures 2 and 3, it can be seen that the alder-tree area has increased
dramatically, particularly in the Kuchoro and Setsuri River basins.

Figure 2. Alder trees maps made from landsat imagery observed on (a) 7 June 1979 and (b) 26 August
1996.

Figure 3. The change of alder-tree area calculated from alder tree maps in Kushiro Mire from 1979
to 2000.

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3. Results and Discussion
3.1. RELATIONSHIP BETWEEN ALDER TREE DISTRIBUTION AND FLOODEDAREA

It has been reported that the increase of the alder-tree area is closely related toflooding in Kushiro Mire. This is because alder trees grow well in sites with soil
accumulation caused by sedimentation (Nakamura et al., 1997; Yamagata, 1999).
In this section, the relationship between alder tree distribution and flood area wasevaluated spatially using remotely sensed imagery.
In general, flooding of Kushiro Mire occurs in the snowmelt season in May andthe typhoon season in September. However, it is difficult to monitor the Kushiro
Mire using remotely sensed imagery in September because of heavy cloud coverage.
Therefore, Landsat imagery from May 1994 and 1999 was used to determine theflood area. Figures 4(a) and 4(b) show the flood area of Kushiro Mire determinedfrom maps, which are classified into three categories (alder, water, and other) by
the ISODATA method using Landsat TM data from 17 May 1994 and 31 May
1999.
Figures 4(a) and 4(b) show the flooding in the lower course of the Kuchoro and
Setsuri Rivers. Flooding was very slight in the Chiruwatsunai River basin. From
Figures 2 and 4(a) and 4(b), it can be seen that there is a relationship between aldertree distribution and flood area in Kushiro Mire. The increase in flooded area results
in increase in density of alder tree after flooding. Therefore, using remotely sensed
imagery, it was confirmed spatially that the increase of the alder tree area is closely
related to the flood in Kushiro Mire.

Figure 4. The flood area of Kushiro Mire determined from maps classified into three categories (alder,water, and others) by the ISODATA method with Landsat TM data from (a) 17 May 1994 and (b) 31
May 1999.

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Figure 5. Enlargements of the imagery of the Kuchoro and Setsuri River basins.

Figure 5 shows the enlargements of the imagery of the Kuchoro and Setsuri
River basins. From Figure 5, it can be seen that the shape of the Kuchoro and Setsuri
Rivers was straight in contrast to the shape of the Chiruwatsunai River (flooding
was slight). Construction work to enhance the linearity of the Kuchoro and Setsuri
Rivers began in 1960s. This construction project was designed to improve thedrainage of agricultural land located in the upper course of the Kuchoro and Setsuri
Rivers. However, the force of water has strengthened the flow, as the rivers grew
steeper as a result of the construction work. Thus flooding became more likely inthe lower course of the rivers. This would seem to be the cause of the flooding in thelower course of the Kuchoro and Setsuri Rivers. From the remotely sensed imagery
shown in Figures 4 and 5, it was also confirmed that the flood was generated in thelower course of the Kuchoro and Setsuri Rivers.
3.2. RELATIONSHIP BETWEEN ALDER TREE DISTRIBUTION AND LAND USE
In this section, we analyze the land-use conditions around Kushiro Mire using
remotely sensed imagery in order to spatially assess the source of sedimentation andaccumulation of soil in Kushiro Mire. Figure 6(a) is the Landsat TM data on 17 May
1994 showing the Kushiro Mire (black) and the area surrounding area. Figure 6(b)shows the agricultural land in the upper course of the Kuchoro, Chiruwatsunai,and Setsuri Rivers enlarged from Figure 6(a). The agricultural land in Figure 6(b)(yellow) was extracted from a map classified by the ISODATA method. The mainarea of the extracted agricultural land consisted of meadows.
From the remotely sensed imagery in Figure 6(b), it was confirmed that there
was little agricultural area in the upper course of the Chiruwatsunai River, but there

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Figure 6. Kushiro Mire and the area around Kushiro Mire observed by Landsat TM data on 17 May
1994. Part (b) shows agricultural land in the upper course of the Kuchoro, Chiruwatsunai, and Setsuri
Rivers enlarged from (a).

was abundant agricultural area in the upper course of the Kuchoro and Setsuri
Rivers. Therefore, the alder tree distribution of Kushiro Mire is closely related tothe agricultural land area around Kushiro Mire.
3.3. P REDICTION OF EXPANDING ALDER- TREE AREA IN KUSHIRO MIRE
From the findings described in Figures 2 and 4–6, the mechanism of the expansionof alder-tree area in Kushiro Mire can be summarized as follows.
(1) The agricultural land area in the upper course of the Kuchoro and Setsuri Riverbasins has expanded.
(2) The eroded soil from the agricultural land located in the upper course of the
Kuchoro and Setsuri River basins has been flowing into the respective rivers.
(3) Flooding has been occurring in the lower course of the Kuchoro and Setsuri
Rivers as a result of the construction works to improve the drainage of agricultural land located in the rivers’ upper courses.
(4) Soil sediments have been flowing into the Kushiro Mire from the north due toflooding.
(5) Consequently, the number and density of alder trees have increased because
the sedimentation and accumulation of soil favor its growth.
On the basis of the mechanism of expansion of the alder tree in the areaof Kushiro Mire, the future distribution of alder trees was estimated from theSPATIAL ASSESSMENT OF THE ALDER TREE IN KUSHIRO MIRE

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flood area. Therefore, it is necessary to spatially observe the extent of floodingin Kushiro Mire. However, as it is difficult to evaluate the extent of flooding using
Landsat MSS or TM imagery because of revisit interval of 16 days, which also
hinders the assessment of flood dynamics even in relatively cloud-free areas, wecannot be certain that the extent of flooding is accurately evaluated by Landsat
imagery.
In this study, the future distribution of alder trees was estimated by overlaying
the flood imagery observed on 17 May 1994 with the alder trees imagery observed
on 22 September 2000. Landsat imagery of 17 May 1994 showed the most widely
flooded area among the images collected from 1979 to 2000. Thus, it is predictedthat the flood area in Kushiro Mire, with the exception of the alder-tree area in 2000,
will eventually change to alder-tree area. Figure 7 shows the future distribution ofalder trees predicted from the overlaid images in Kushiro Mire. In Figure 7, areas
with red color show the region that will eventually be changed to areas with aldertrees at the least. It was found that large vegetation areas such as reeds and sedge
grasses in Kushiro Mire will change to areas with alder trees. Furthermore, because
the coverage of the evaluated flood area may not maximally expand, it should beconsidered that the large vegetation area in Kushiro Mire shown in Figure 7 may
be underestimated.

Figure 7. The future distribution of alder trees predicted from the overlaid images in Kushiro Mire.

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4. Conclusions
The relationship between the alder (Alnus japonica) distribution and the surrounding land use was assessed using Landsat imagery with an objective of evaluating theeffects of the surrounding environmental changes on Kushiro Mire. On the basis of
the analytical results from the Landsat imagery, the expanding mechanism of thealder-tree area in Kushiro Mire was characterized as follows.
(1) The agricultural land area in the upper course of the Kuchoro and Setsuri Riverbasins has expanded.
(2) The eroded soil of the agricultural land located in the upper course of the
Kuchoro and Setsuri River basins has been flowing into the respective rivers.
(3) Flooding has been occurring in the lower course of the Kuchoro and Setsuri
Rivers as a result of the construction works to improve the drainage of agricultural land located in the rivers’ upper courses.
(4) Soil sediments have been flowing into the Kushiro Mire from the north due toflooding.
(5) Consequently, the number and density of alder trees have increased because
the sedimentation and accumulation of soil favor its growth.
Furthermore, the future distribution of alder trees was predicted by overlaying
the flood imagery observed in 1994 with the alder trees imagery observed in 2000.
As a result, it was found that large vegetation areas such as reeds and sedge grasses
in Kushiro Mire will change to areas with alder trees.
Lastly, this study concluded that the use of remote sensing techniques is generally
effective for areas like Kushiro Mire, which is a difficult region to evaluate throughfield survey because of expansive areas with various land cover types.
Acknowledgments
The authors would like to thank the National Space Development Agency of Japan(NASDA) for providing Landsat data for this research.
References
Adams, W. M. and Hollis, G. E.: 1988, ‘Hydrology and Sustainable Resource Development of a
Sahelian Floodplain Wetland’, Report for the Hadejia-Nguru Wetlands Conservation Project.
Adams, W. M.: 1993, ‘Agriculture, Grazing and Forestry’, in G. E. Hollis, W. M. Adams and M.
Aminu-Kano (eds), The Hadejia-Nguru Wetlands: Environment, Economy and Sustainable
Development of a Sahelisan Floodplain Wetland, IUCN, Gland.
Costanza, R., d’Arge, R., de Groot, R., Farber, S., Grasso, M., Hannon, B., Limburg, K., Naeem,
S., O’Neill, R. V., Paruelo, J., Raskin, R. G., Sutton, P. and Belt, M. V.: 1997, ‘The value of theworld’s ecosystem services and natural capital’, Nature 387, 253–260.

SPATIAL ASSESSMENT OF THE ALDER TREE IN KUSHIRO MIRE

253

ERDAS: 1997, Erdas Tour Guide, Erdas Inc., Atlanta, Georgia, USA.
Gorham, E.: 1991, ‘Northern peatlands: Role in the carbon cycle and probable responses to climatic
warming’, Ecol. Appl. 1, 182–195.
Hollis, G. E., Adams, W. M. and Aminu-Kano, M.: 1993, The Hadejia-Nguru Wetlands, IUCN Gland,
Switzerland and Cambridge, UK.
IPCC: 1995, in J. T. Houghton, L. G. Meira Filho, J. Bruce, Hosesung Lee, B. A. Callander, E. Haites,
N. Harris and K. Maskell (eds), Climate Change 1994, Radiative Forcing of Climate Change andan Evaluation of the IPCC IS92 Emission Scenarios, Cambridge University Press, New York,USA.
Iwakuma, T.: 1996, Mires of Japan: Environment of Kushiro Mire, National Institute for Environmental
Studies, Japan, pp. 99–104.
Mitsch, W. J. and Gosselink, J. G.: 1993, Wetlands, 2nd ed., Van Nostrand Reinold, New York.
Mitsch, W. J. and Wu, X.: 1995, ‘Wetlands and Global Change’, in R. Lal, J. Kimble, E. Levine and
B.A. Stewart (eds), Advances in Soil Science, Soil Management and Greenhouse Effect, CRC
Lewis Publishers, Boca Raton, FL, pp. 205–230.
Nakamura, F., Sudo, T., Kameyama, S. and Jitsu, M.: 1997, ‘Influences of channelization on dischargeof suspended sediment and wetland vegetation in Kushiro Marsh, northern Japan’, Geomorphology
18, 279–289.
Nagasaka, A. and Nakamura, F.: 1999, ‘The influences of land-use changes on hydrology and riparian
environment in a northern Japanese landscape’, Landsc. Ecol. 14(6), 543–556.
Oguma, H. and Yamagata, Y.: 1997, ‘Study on effective observing season selection to produce thewetland vegetation map’, J. Jpn. Soc. Photogram. Remote Sens. 36(4), 5–16.
Oki, K., Oguma, H. and Sugita, M.: 2002, ‘Mixel classification of alder trees using temporal Landsat
Thematic Mapper Imagery’, Photogram. Eng. Remote Sens. 68, 77–82.
Thomas, D. H. L., Jimoh, M. A. and Matthes, H.: 1993, ‘Fishin’, in G. E. Hollis, W. M. Adams and
M. Aminu-Kano (eds), The Hadejia-Nguru Wetlands, IUCN Gland, Switzerland and Cambridge,
UK.
Whited, D., Galatowitsch, S., Tester, J. R., Schik, K., Lehtinen, R. and Husveth, J.: 2000, ‘The
importance of local and regional factors in predicting effective conservation. Planning strategies
for wetland bird communities in agricultural and urban landscapes’, Landsc. Urban Plan. 49,
49–65.
Yamagata, Y.: 1999, Advanced Remote Sensing Techniques for Monitoring Complex Ecosystems:
Spectral Indices, Unmixing, and Classification of Wetlands, Research Report from the National
Institute for Environmental Studies, Japan, 148 pp.
Yasuoka, Y., Tmamura, M. and Yamagata, Y.: 1994, ‘Application of Remote Sensing to Environmental
Monitoring – Global Wetland Monitoring’, in Optical Methods in Biomedical and Environmental
Sciences, Elsevier Science, pp. 269–272.