沙漠研究 19-1, 141- 144 (2009 )Journal of Arid Land Studies“Desert Technology IX ”
Refereed Paper

Improvement Effect of Semi-Arid Land Afforestation on Soil Environment
Toshinori KOJIMA1, 2, Kosuke INABA1, Suguru KOYANAGI1, Hideki SUGANUMA1, Katuhiko KUROSAWA1,Satoko KAWARASAKI3, Hiroyuki TANOUCHI3, Richard HARPER4, Koichi YAMADA1, 2, Hiroyuki HAMANO1, 2, 5
Abstract: Carbon fixation by afforestation in semi-arid land has been proposed as one of themost promising countermeasures against the global warming issue. Our demonstration areafor carbon fixation suffered some serious problems, such as salinization and water logging,which we attempted to solve. We tried to reduce the groundwater level by taking advantageof the transpiration of planted trees. The two sites used were identified as D-low and D-high.
In this study, the transpiration of planted trees, soil water change, and groundwater level weremeasured. E. sargentii and E. occidentalis were considered to be optimum. From theanalyses of the groundwater and soil water contents, water was found to gather at the D-low
site. However, analysis of the Neutron Moisture Meter (NMM) data indicated that thevolumetric water content did not rise. Through the transpiration of planted trees, groundwater
was absorbed via tree roots located in deep soil. Thus, the groundwater level was expected todecrease, but this decrease was prevented by the collected water. On the other hand, due toafforestation at the D-high site, where it was difficult for water to gather, a decreasing tendency
in the amount of groundwater was clearly shown by the volumetric water content.
Furthermore, the precipitation water trickled down through the soil surface layer, which wasexpected to mitigate the salt accumulation in topsoil. Soil improvement effects byafforestation, i.e., desalination and the prevention of water logging through the transpiration ofplanted trees, were confirmed in our research area.
Keywords: Afforestation, Carbon fixation, Groundwater, Salinization

1. Introduction
Global warming has become one of the most serious environmental problems. The main cause is theincrement in the amount of carbon dioxide in atmosphere. As a promising countermeasure, carbon
fixation by afforestation in arid and semi-arid areas has been proposed (Yamada et al., 1999; Kojima et al.,2006). An afforestation experiment was also conducted at a farm (named Martin’s Farm) in a semi-arid
land of Western Australia as a case study. The location (UTM data) of this farm, scale, and annualprecipitation are shown in Figure 1. In this research area, the original native forest had been felled, andthe land had been turned into farmland. As a result, transpiration per unit area had decreased, and thegroundwater level had risen. Thus, there are currently some serious problems, such as salinization andwater logging. In this research, two sites, identified as the D-low and D-high sites, were selected forcomparison. The D-high site is shown in the upper area of Figure 1. The D-low site is shown in thelower area of Figure 1. In this research, we attempted to lower the groundwater level through thetranspiration of planted trees. We aimed to achieve both the improvement of the agricultural conditions
and carbon sequestration by afforestation.
2. Materials and Methods
The transpiration of planted trees, soil water content, and groundwater level were measured.
Comparing the measured data, the influence of afforestation in the research area was evaluated. Below is
an explanation of the objectives and installation position of each measurement item.
2.1. Transpiration
We selected four tree species as candidates for afforestation: Pinus radiata, Eucalyptus sargentii,
1

Department of Materials and Life Science, Seikei University, 3-3-1, Kichijoji-kitamachi, Musashino, Tokyo,180-8633, Japan.
2
Edith Cowan University, 100 Joondalup Drive, Joondalup, Western Austraia 6027, Australia.
3Forestry and Forest Products Research Institute, 1 Matsunosato, Tsukuba, Ibaraki 305-8687, Japan.
4
Forest Products Commission, 117 Great Eastern Highway, Rivervale, WA, 6103, Australia.
5
Asian Environment Research Group, National Institute for Environmental Studies, Ibaraki, 305-8506, Japan.

142

D -h ig h site T 1 line
W 51
W 52

W 11W 12W 13
W 14
W 15W 53

D -low site
W 54

T 5 line： N M M installed

Fig. 1. Martin’s Farm (annual mean precipitation; 314mm: S32.46˚; E117.40˚).
R ainfall ave

P. radiata

average [m 3/(d・tree)]

0.82×10

E. sargentii-2

1.31×10

E. globulus-2

0.74×10

E. occidentalis-2

1.22×10 -2020

2.0×10-2
2.0E-0240
1.5×10-2
1.5E-0260

1.0×10-2
1.0E-02

80

Rainfall [mm]Transpiration [m3/(d・tree)]

2.5×10-2
2.5E-02100

5.0×10-3
5.0E-03120
00.0E+00

140
123456789101112Time [month]Fig. 2. Comparison of the transpiration amount of trees in 2006.
Eucalyptus globules and Eucalyptus occidentalis. Thermal Dissipation Probes (TDP) were installed tomeasure the transpiration rates in their trunks in our research area (D-high and D-low). Data of TDP weremeasured every 30 minutes for three samples per tree species. Trees were planted at 3 m intervals within
the rows, giving an initial stocking of 1111 trees/ha in June 2000. TDP data were analyzed, andtranspiration rates were compared among four species for optimum tree species selection. Data fromJanuary 2006 to December 2006 were available.
2.2. Groundwater level
Piezometers were installed at the points indicated by W11-W54 in Figure 1. In this study, the T1
and T5 lines were selected for analysis because they were across the D-high and D-low sites. The data143obtained in 2005 were available.

330
W54

surface328
Altitude [m]2.3. Soil water content
Data from Neutron Moisture Meter (NMM)
probe tubes installed at two sites (D-high andD-low, as shown in Figure 1) were analyzed, andthe characteristics of the land and soil watercontent change at five points in depth (30 cm-270cm) were discussed. These data were measured
twice a year and averaged. The data from March
2002 to December 2004 were available.

2005 ground water level
D-low site

326

Creek324

W51

W53
W52322320
0100200300
Distance [m]400500Fig. 3. D-low site groundwater data.
344
342

Altitude [m]3. Results and Discussion
3.1. Transpiration
E. sargentii and E. occidentalis wereconsidered to be optimum tree species because
their transpiration rate was larger than that of otherspecies (Fig. 2). Their transpiration rate wasaround 1.20×10-2 [m3/(d･tree)].

340

surface338

2005 ground water levelW11336

W12334

W13332

D-high site

W14330328

W15326
324
322
050

100

150200250300350400450

Distance [m]Fig. 4. D-high site groundwater data.
W15

W14W13

W11W12324.6
324.4

Altitude [m]3.2. Groundwater
Results of the groundwater level are shown inFigures 3 and 4. As also shown in Figure 1, thedistance from W54 across the D-low site and thatfrom W15 across the D-high site are shown in thex-axis of Figures 3 and 4.
Figure 3 indicates that the groundwater levelis high at the D-low site. Thus, the D-low site
was found to be easily salinized and water-logged.
This could be because the D-low site was locatednear a creek, where it was easy for water to gather.
At the D-high site, it was found that the soil
surface was far from the groundwater level.
Figure 5 indicates that the groundwater level
slowly decreased at the D-high site.

324.2
324.0

D-high site

323.8

2004 rainfall 276.7mm
2003 rainfall 369.8mm
2002 rainfall 182.6mm

323.6

2001 rainfall 303.8mm
323.4
050

100

150

200

250

300

350

400

450

Distance [m]Fig. 5. Changes in the groundwater level at theD-high.
depth [cm]000.4101020200.3

3030
404050500.230
Rainfall [mm/month]

Volumetric water content [-]3.3. Soil water content
Results of the soil water content are shown inFigures 6 and 7. At the D-low site, the results
indicated that the soil volumetric water content
remained stable for all of five points in depth.
The analysis of Piezometer data (Fig. 3) indicatedthat the soil water content might have risen due tothe groundwater level; however, no clear effectfrom the groundwater level was found from thedata in Figure 5.
At the D-high site, thevolumetric water content decreased at all fiveobservation points.
Moreover, the measured
value of the soil water content was not found to beaffected by the groundwater level as measured by
the piezometer.

90
150
210

60
60
70
70

0.1

Mar-028080

Sep-02Mar-03

Sep-03Time

Mar-04270
Rainfall

Sep-04

Fig. 6. Variation of volumetric soil water content
measured by NMM in D-low site.

144000.4

depth [cm]

1010
2020

0.3

3030
4040
5050

0.2

30
Rainfall [mm/month]

Volumetric water content [-]4. Conclusions
4.1. D-high
The D-high site was characterized by a deep
groundwater level, i.e., 12 meters deep from thesoil surface. The surface altitude of the D-highsite was high; thus, water hardly collected at theD-high site. The analysis of NMM data pointed
to a decreasing tendency with time in thevolumetric water contents. Soil improvement
effects, i.e., desalination and the prevention ofwater logging through the transpiration of plantedtrees, were confirmed in our research area.
Finally, the hydrological mechanism of theimprovement effect by afforestation wasexplained.

90

150

210

6060

270
7070

Rainfall0.1
Mar-028080

Sep-02Mar-03

Sep-03
TimeMar-04

Sep-04

Fig. 7. Variation of the volumetric soil water content
measured by NMM at the D-high site.

4.2. D-low
The D-low site was characterized by a high groundwater level. In addition, water was found togather at the D-low site. However, analysis of the NMM data indicated that the volumetric water contents
did not rise. This contradiction is explained as follows. Through the transpiration of planted trees,
groundwater was absorbed via the roots of trees located in the deep soil. The groundwater level at theD-high site slowly decreased, while that at the D-low site remained almost constant. However, thegroundwater level at the D-low site is expected to decrease in the near future. Furthermore, theprecipitation water which trickles down through the soil surface layer was expected to mitigate the salt
accumulation at the topsoil. Thus, salt in the top soil was considered to move down to the root zone andto be leached out by groundwater. Soil improvement effects, i.e., desalination and the prevention of water
logging through the transpiration of planted trees, were confirmed in our research area.
Acknowledgements
This work was supported by grants from the Mitsui & Co., Ltd. Environment Fund and from theGlobal Environment Research Fund of The Ministry of the Environment (GHG-SSCP Project).
References
Kojima T., Hamano H., Abe Y., Tanouchi H., Egashira Y., Saito M., Law J., Takahashi N., Yamada K. (2006): Basic Data ofResearch Project on Large Scale Afforestation of Arid Land for Carbon Fixation near Leonora in Western Australia. J. of Arid
Land Studies, 16(3): 167-174.
Yamada K. Kojima T., Abe Y., Williams A., Law J. (1999): Carbon sequestration in an arid environment near Leonora, WesternAustralia. J. Arid Land Stud., 9: 143-151.