沙漠研究 19-1, 65- 68 (2009 )Journal of Arid Land Studies“Desert Technology IX ”
Refereed Paper

Relationships between Soil, Topography and Tree Growthin a Water Harvesting System in the Loess Plateau, China
Tadaomi SAITO1, Hiroshi YASUDA1, Khumbulani DHAVU1, Takayuki KAWAI1,Mohamed A.M. ABD ELBASIT1, Atsushi TSUNEKAWA1, Shiqing LI2
Abstract: The Loess Plateau in northwestern China is one of the most seriously affected
regions by soil erosion in the world. We conducted investigations in a field afforestation sitein the north of Loess Plateau to clarify the relationships between soil, topography and tree
growth in a small scale water harvesting system, called “fish-scale-pit (FSP)”. The site (200 ×50 m) was located on a northern slope (0 – 25˚) of a hill. There were 314 FSPs in the site.
The survival rates of the planted trees at near hilltop and near gullies were lower than the otherarea. The tree height showed weak and positive correlations with slope angle (R = 0.43).
Bottom of hills were better areas to make FSPs than hilltops, considering their water balances.
Although the difference in the average tree heights between large-leaf and small-leaf trees wassmall, the bearing rate of the large-leaf trees was much higher than small-leaf trees.
Keywords: Fish-scale-pit, Loess Plateau, Topography, Tree growth, Water harvesting

1. Introduction
The Loess Plateau in northwestern China is a plateau that covers an area of some 640,000 km² in theupper and middle of the Yellow River. Loess is the name for the silty sediment that has been depositedby wind storms onto the plateau over the ages. The Loess Plateau is one of the most seriously affected
regions by soil erosion in the world. Soil erosion has drastically deteriorated land resources,environments and ecosystems in this region. Furthermore, the enormous amount of the eroded soil isaggrading the river bed of the Yellow River. Therefore, the Yellow River is an “above ground river” thatis seriously threatening the security of its lower reach. Chinese government has been promoting a large
national greening project since 1999, called “Grain for Green Project”, as a countermeasure against thisproblem. The main objective of this project is to reduce soil erosiona)by converting croplands on steep slopes and degraded lands tograsslands and tree-cover. For afforestation on steep slopes in theLoess Plateau, a small scale water harvesting system, called“fish-scale-pit (FSP)”, is commonly used to reduce erosion andincrease soil water storage.
The FSP is a pit dug in an
ellipsoidal-semicircular shape (Fig. 1a); the typical depth of a pit is 0.2– 0.4 m, and the lengths of major and minor axes of the lipb)
are 0.5 – 1.5 and 0.5 – 1.0 m, respectively (Tang, 2004).
FSPs were named after pits deployed on a large scale
looked like fish scales (Fig. 1b). To evaluate theeffectiveness of FSP systems, we have conducted twotypes of investigations in the north of Loess Plateau: i)water balance analysis and modeling of FSPs in anexperimental site using various monitoring devices (Saitoet al., 2008) and ii) investigations on soil, topography andtree growth in a field afforestation site. In this study, we
mainly focused on the afforestation site. The objective of
this study was to clarify the relationships between soil, Fig. 1. Pictures of fish-scale-pits (FSPs): a)typical design of FSPs in Yanan andtopography and tree growth in the FSP systems and tob) FSPs deployed on a large scale inobtain beneficial information for afforestation using FSPs.
Yuilin.
12Arid Land Research Center, Tottori University, 1390 Hamasaka, Tottori 680-0001, Japan;
Institute of Soil and Water Conservation, The Chinese Academy of Sciences and Ministry of Water Resources,Shaanxi, China; Fax no. +81-857-29-6199, tel. no. +81-857-23-3411, email: saito@alrc.tottori-u.ac.jp

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2. Materials and Methods
The investigations on FSPs have been conducted in
Liudaogou Basin (lat 38˚47′N, long 110˚21′E) located in
Shenmu District, Shaanxi Province, China (Fig. 2). The
average annual temperature of this region is 8.4 ˚C. The
average annual precipitation for this region is about 440 mm
and hence categorized as semi-arid. More than 70% of theannual precipitation falls from Jun to September.
Figure 3 shows the sketch of the field afforestation site.
The site (200 × 50 m) was located on a northern slope (0 –25˚) of a hill. On both sides of the site, along the slope,
were deep eroded gullies. There were 314 FSPs on the site.
Each pit had a 2-3 m long runoff area. The site was divided
into three zones (Fig. 3): Zone A (top area of the hill: 119pits), Zone B (middle area of the hill: 69 pits) and Zone C(bottom area of the hill: 126 pits). There were steps
between the zones.
A plum tree (Prunus armeniaca var. ansu Maxim) had
been planted in each FSP in 2000, by farmers. The farmers
replaced dead trees with new seedlings when they found deadtrees. The seeds of the trees can be sold as materials forherbal medicines. Minimum threshold precipitation for forest
establishment in the Loess Plateau is about 500 mm, hence it isdifficult for the trees to survive on the hillslopes without theFSPs. The leaf types of the trees in this site were divided
into two groups: large-leaf and small-leaf.
We investigated tree heights, leaf types, survival rate,
bearing rate, slope angles of the runoff areas and positions ofthe pits in the site. Volumetric soil water content, θ (m3 m-3),
and soil bulk electrical conductivity, σb (dS m-1), from the soil
surface to a depth of 10 cm, were also measured using WET
sensor (Delta-T Devices Ltd., Burwell, UK) at every pit andrunoff area. The σb values were converted to the electricalconductivity of the soil solution, σw (dS m-1), using the θ values
and a preliminarily determined calibration function. All
investigations were conducted in May and October in 2008.

Fig. 2. Location of the investigation site.
Curvesaremean
annualprecipitation in mm.

Fig. 3. Sketch of the field afforestationsite.

3. Results and Discussion
Table 1 lists the results of tree growth investigations. In 252 of the 314 pits, trees are living andaverage tree height was 130.0 cm. Although the farmers have replanted new seedlings some times, 20 %of trees were dead in total. The trees in Zone C (bottom area of the hill) showed highest survival rate andaverage tree height.
Figure 4 shows differences in survival rates at different locations of the pits. We defined two rowsof the pits across the slope nearest to the hilltop (21 pits) as “near hilltop” and two columns of the pits
along the slope nearest to the gullies (70 pits) as “near gully”. The survival rates at near hilltop and near
gully were lower than the other area. In particular, more than 60 % of trees were dead at near hilltop.
These results suggest afforestation should not be performed near hilltops and gullies.
Relationship between slope angles of runoff areas and tree heights is presented in Figure 5. The treeheight showed weak and positive correlations with slope angle (R = 0.43), meaning that increase in theslope angle might increase the tree height. This is probably because increase in slope angle increases
runoff generation. However, even in low angle areas (angle < 10˚), where enough runoff generation can
not be expected, many trees were living and grew to over average tree height (130 cm). These results

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Table 1. Results of tree growth investigations.
Number ofLiving

DeadSurvival

Average tree height &pits

trees

trees

rate (%)(Standard deviation) (cm)Total

3142526280

130.0 (45.2)

Zone A

11991

2876

126.2 (52.0)

Zone B

69462367

123.7 (34.0)

Zone C

1261151191

135.5 (43.1)

Table 2. Comparison of average soil water content (θ) and electrical conductivity of the soil solution (σw).
Average θ (m3 m-3)

Date

Average σw (dS m-1)

in FSPs

runoff areas

in FSPs

runoff areas

thMay 14 , 2008

0.13

0.10

1.82

1.85

th

0.14

0.11

1.63

1.62

Oct 13 , 2008

250

100
80

200

63.9 %
Tree height (cm)Survival rate (%)

85.8 %

60
40

38.1 %

2021 pits

70 pits150
y = 4.17x + 70.24
R = 0.43

100

Zone A
Zone B
Zone C
Regression line

223 pits
500
near hilltop

near gullyother area

Fig. 4. Differences in survival rates atdifferent locations of the pits.

005

1015

202530Slope angle (dgree)

Fig. 5. Relationship between slope angles of thesuggest that the FSPs can function as “waterrunoff areas and the tree heights. The treebasins” for collecting rain water falling directly
heights of the dead trees were assigned a value
into the pits, and runoff water from the slope mayof 0 cm. The data from “near hilltop” andbe used as supplementarily water to grow the“near gully” were excluded in this analysis.
trees.
Average θ in the FSPs was slightly higher than that in the runoff area (Table 2). One of the reasonsfor this tendency would be that rainfall and runoff water had been stored in the pits. In addition, shadows
made by the walls of the pits and canopy cover of the tree might reduce evaporation from the soil surface
in the pits; the same tendency have been observed in the experimental site (Saito et al., 2007). The
average σw values were low, and no significant difference in the σw was found between in the FSPs andrunoff areas, meaning that the problem of salt accumulations has not occurred in the FSPs.
Jiang (1997) indicated that soils at bottom area of hills generally have higher water content than soils
at hilltop areas in the Loess plateau. Our measurements also supported their results; e.g., average θ ofrunoff areas in Zone C (0.14 m3 m-3) was higher than that in Zone A (0.07 m3 m-3) on Oct. 13th, 2008.
This is because evaporation is high at hilltop due to strong wind and insolation, in contrast, runoff watertends to gather at bottom areas of hills.
As can be seen in Figure 5, most of the steep slope areas (angle < 10˚), where enough runoff
generation can be expected, were observed in Zone B and C. The same tendency was observed in otherhills in the investigation region. In conclusion, bottoms of hills are better areas to make FSPs thanhilltops, considering their water balances.
Comparison of average tree height and bearing rate between leaf types are shown in Figure 6. There6850
Average tree height
Bearing rate

20040150301002050

100

Bearing rate (%)

Average tree height (cm)2500
Large-leaf trees

Small-leaf trees

Fig. 6. Comparison of average tree height andbearing rate between leaf types. The error
bars are standard deviation.

Fig. 7. Picture of bare runoff areas. Grass covers
were completely cut by farmers.

were 156 large-leaf trees and 96 small-leaf trees in the investigation site. Although the difference in theaverage tree heights between large-leaf and small-leaf trees was small, the bearing rate of the large-leaf
trees was much higher than small-leaf trees. This indicates that selecting large-leaf type seedlings may
contribute to increase in bearing rate when farmers plant trees.
In several afforestation sites in the investigation region, grass covers of runoff area were completely
cut by farmers (Fig. 7). This treatment may contribute to growth of trees in pits through increase in
runoff generation and decrease in wasteful transpiration from grasses. However, bare runoff slopes arevery weak against wind and water erosion. Therefore, this treatment by farmers, removing vegetation
cover, is not suitable for the original objective of the Grain for Green Project. Further education on
ecology for farmers may be needed for successful results of the project.
4. Recommendations
The location of the pit and the slope angle were major contributing factors to the tree growth in theFSPs on the hillslope. We list some recommendations for successful afforestation using FSPs;• We should not make FSPs on gentle slopes and near hilltops and gullies, since the survival rate of theplanted trees will be low in such areas.
• Bottoms of hills are better areas to make FSPs than hilltops.
• Selecting large-leaf type seedlings may contribute to increase in bearing rate and hence income offarmers.
• Further education on ecology for farmers will contribute to successful results of the Grain for GreenProject.
Acknowledgements
This research was partially supported by a grant from the Global COE Program and Core University
Program by Japan Society for the Promotion of Science.
References
Jiang D. (1997): Conservation patterns for soil and water loess in the Loess Plateau. China Water Power Press, Beijing. (in Chinese)
Saito T., Kawai T., Yasuda H., Tsunekawa A., Zheng J., Zhang X. (2008): Evaluation and improvement of the soil water storage in awater harvesting system in the Loess Plateau, China. 9th International Conference on Dryland Development, Alexandria, Egypt.
Nov. 2008.
Saito T., Yasuda H., Tsunekawa A., Zheng J., Zhang X. (2007): Evaluation and improvement of fish scale pits in the Loess Plateau,China. CAS-JSPS Core University Program Japan-China Joint Open Seminar on Combating Desertification and Development inInland China of Year 2007, pp.33-34, Yangling Shaanxi Province, P.R. China.
Tang K. (2004): Soil and Water Conservation in China. pp.540-543, Science Press, Beijing. (in Chinese)