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Journal of Hydro-environment Research 3 (2009) 77e84www.elsevier.com/locate/jher

Research paper

Study on reforestation with seabuckthorn in the Pisha Sandstone area

Kang Zhang*, Mengzhen Xu, Zhaoyin Wang

State Key Laboratory of Hydroscience and Engineering, Tsinghua University, 100084 Beijing, China

Received 8 April 2009; revised 18 June 2009; accepted 25 June 2009

Abstract

In northwest China, an area of more than 11 000 km2 is covered by Pisha Sandstone, a kind of loosely bonded sandstone formed during theTertiary period. Pisha Sandstone is hard when it is dry but becomes loose when it is wet. Due the nature of this sandstone, this area of northwestChina is plagued with a high erosion rate (over 20 000 t/km2 yr) as well as poor vegetation. In order to reforest gullies and to control erosion inthe area, seabuckthorn (Hippophae rhamnoides Linn) was successfully used to reduce the erosion rate and help encourage vegetation growth inthis area. Field investigations have been carried out in the Xizhao gully to study the effects of the species on sediment trapping and ecologicalimprovement. Through these investigations, it was discovered that seabuckthorn encouraged the growth of Clinelymus dahurcus Turcz, andconsequently, the two species form a dense double-layer of vegetation with well-developed middle and understory plant communities. The forestwas planted in the late 1990s (first introduced in 1995), with a measured rate of sediment trapping efficiency of more than 90%. Rainstorm waterwas also stored in the gully within the trapped sediment. The water content in the reforested gully was approximately twice as high as the non-vegetated gully. Soil organic matter content was higher in the gully planted with seabuckthorn than compared with a non-vegetated gully. Theunderstory community was evaluated by the taxa richness, the thickness-coverage and the Simpson diversity of the sub-layer vegetation. Theunderstory community patterns found in the seabuckthorn vegetation was much better compared with those found in areas forested with poplaror willow vegetation.Crown Copyright � 2009 Published by Elsevier B.V. on behalf of International Association for Hydraulic Engineering and Research, AsiaPacific Division. All rights reserved.

Keywords: Seabuckthorn; Vegetation barriers; Soil erosion; Sediment trapping; Reforestation; Ecological restoration

1. Introduction

The Pisha Sandstone area mainly consists of loosely bondedsandstone formed during the Tertiary period, and covers most ofthe Ordos Plateau and Inner Mongolia Autonomous Region.Due to Pisha Sandstone’s loosely bonded composition, erosionoccurs frequently during and after rainfall. The erosion rate inthis area is commonly over 20 000 t/km2 yr (Zhen, 2005).Furthermore, the soil erosion problem and dryecold climateresult in poor vegetation condition in these areas, and only a fewspecies of plants grow well.

Vegetation barriers along the contour line can be used tocontrol soil erosion in arid or semi-arid areas. These vegetation

* Corresponding author. Tel.: þ86 10 62788787; fax: þ86 10 62772463.

E-mail address: zhang-k08@mails.tsinghua.edu.cn (K. Zhang).

1570-6443/$-seefrontmatterCrownCopyright� 2009PublishedbyElsevierB.V.onbehalfofInternat

doi:10.1016/j.jher.2009.06.001

barriers also give researchers direction in the management oferosion (Kiepe, 1995; Angima et al., 2000; Lal, 1989). Spaanet al. (2005) studied vegetation barrier by using the Andropo-gon gayanus (a species of dense grass) with remarkableeffectiveness in diminishing soil loss in the Africa sub-Saharansemi-arid area. Rao et al. (1991) managed Leucaena leucoce-phala as hedgegrows on Alfisols and Vertic Inceptisols in semi-arid area in India. It was found that hedgerow intercroppingwas beneficial in terms of soil richness and water conservation.

Qian (1986) proposed the utilization of seabuckthorn(Hippophae rhamnoides L.) to control soil erosion in theLosses Plateau area. Seabuckthorn and a Chinese relatedspecies have been widely planted and tested in the LossesPlateau in recent decades.

Seabuckthorn, belongs to the Elaeagnaceae family(Rousi, 1971), and it is native to Europe and Asia (Rongsen,1992). Seabuckthorn can grow in arid and cold areas and it easily

ionalAssociationforHydraulicEngineeringandResearch,AsiaPacificDivision.Allrightsreserved.

Fig. 1. Map of the Xizhao gully.

78 K. Zhang et al. / Journal of Hydro-environment Research 3 (2009) 77e84

spreads across landscapes (Schroeder, 1995). Due to its favor-able characteristics such as wide adaptation, fast-growing rate,strong coppicing, suckering habits, and efficient nitrogen fixa-tion this species is often the first woody species colonizing openareas (Rousi, 1965; Salo, 1989) Seabuckthorn is ecologicallysound, well-adapted for soil conservation and enhances thewildlife habitat (Schroeder, 1990).

In order to control erosion, Bi and Li (1998) proposed ‘‘flex-ible dams’’ in the Pisha Sandstone area in 1995. ‘‘Flexible dams’’may be formed by vegetation barriers which mainly consist ofseabuckthorn in the gullied areas on the Pisha Sandstone.

This paper describes a methodology to explore the ecolog-ical effects of seabuckthorn. Field investigations were alsocarried out in order to study the influence of the seabuckthorn ontrapping sediment and the effects of the seabuckthorn forestsediment water distribution and organic matter content.

2. Study areas

An investigation was conducted in the Xizhao gully, locatedin Zhungerr county of Inner Mongolia (Fig. 1). The Xizhao gullyis a third-order tributary of the Yellow River. It has a high gullydensity and erosion rates of over 40 000 t/km2 yr (Bi et al., 2003),in which the gully density is defined as the total length of gulliesper area. Three check dams have been constructed upstreamfrom the stem gully to control erosion. The upstream area of the

Table 1

Characteristics of the Xizhao gully classified with Horton-Strahler’s stream

ordering system.

Stream order Number of streams Length of stream (km)

1 210 21.589

2 41 11.436

3 9 5.462

4 2 5.122

5 1 1.586

first check dam is 3.46 km2. There are also 19 inferior orderbranch gullies with lengths larger than 200 m (Fig. 1). Thesebranch gullies are the main source area of sediment in smallwatersheds. Characteristics of the Xizhao gully classified withHorton-Strahler’s stream ordering system are shown in Table 1and Fig. 2.

Two branch gullies of the Xizhao gully were selected to bestudied. The East gully 1(EG1) is an inferior order branch ofXizhao gully (Fig. 1), with a total drainage area of 1.67 km2.Seabuckthorns were planted as a form of ‘‘flexible dams’’ inEG1 during 1994e1995(Bi et al., 2003); thus EG1 is the mainexperimental area. The East gully 4 (EG4) from Xizhao(Fig. 1) was also selected to be investigated, and seabuck-thorns were also planted in this branch gully in 2002.

3. Methods

3.1. Sediment deposition measurements

The depth of sediment deposition from 9 flexible dams inEG1 (Fig. 3) was measured with a water level meter in 2005(Table 2). Five or six crossing sections are marked by cementstakes and relative channel elevation is measured in order tocompare the change of sediment deposition from 1996 to 2005.

1

10

100

1000

1

10

100

1000

0 1 2 3 4 5 6

Length of stream

(km)N

umbe

r of

str

eam

s

Stream order

Number of streamsLength of streams

Fig. 2. Horton’s laws for the Xizhao gully basin.

1# check dam

0#

3#

5#

4#

2#6#

1+1#

6+1#1#

non-

vege

tate

d

gully

2# check dam

t heXi zhaogul l y

the

refo

rest

edgu

lly

C4C3C2CuCmCd

Sections where sediment deposition measured

C3C2CuCmCd

Sections where soil moisture and organic matter measured Sections where soil

moisture and organic matter measured

Fig. 3. Sketch of the EG1 branch gully.

79K. Zhang et al. / Journal of Hydro-environment Research 3 (2009) 77e84

Three sections Cu, Cm, Cd distributed along the seabuckthornforest are the sections of first line, middle line, and last line ofseabuckthorn arranged from upstream to downstream at eachflexible dam site. There are also three additional sections C2, C3

and C4 which are upstream 15 m, 30 m, and 45 m from the firstline of seabuckthorn in backwater direction. Thus, the longi-tudinal profile of sediment deposition may also be estimated ateach of the 9 flexible dam sites. This experimental layout isshown in Fig. 3.

3.2. Soil moisture content

Soil moisture content was measured in two ‘‘sub-branch’’gullies of EG1 on August 16th 2005, five days after rainfall.One ‘‘sub-branch’’ is covered by the No.6 seabuckthorn forest

Table 2

Depth of sediment deposition accumulated from 1996 to 2005 in EG1 in the ‘‘flex

Serial number

of seabuckthorn forest

Cu Cm

0# 0.404 0.551

3# 0.179 0.018

2# 0.351 0.401

1þ 1# 0.139 0.409

1# 0.051 0.611

5# 0.961 0.781

4# 0.261 0.601

6# 0.532 0.434

6þ 1# 0.152 0.555

Average sediment depth 0.337 0.485

Notes: 1. The respective depth values of sediment deposition for the serial numbers

not take into account the depth of deposition of the first year.

(the reforested gully), while the other branch has no shrubcover (non-vegetated gully) as illustrated in Fig. 5.

In order to analyze soil moisture content of the two gullies,three sections were chosen in each branch. The sections in thereforested gully are distributed along the seabuckthorn forest;the first section is located at the first line of seabuckthorn andthe third section at the last line. The three sections in the non-vegetated gully are located in parallel from upstream todownstream. In each section of the gully soil samples werecollected from the surface to substrate every 10 cm in the stemchannel, with a total excavation depth of 100 cm. All soilsamples were preserved in a sealed aluminum box and takenback to the laboratory. The samples were weighed and driedwith an alcohol burner, then weighed again.

Soil moisture content was measured again in the EG1 andEG4 gullies on September 2nd 2007, one day after an intense

ible dams’’ with seabuckthorn (m).

Cd C2 C3 C4

0.651 0.577 0.407 0.290

0.841 0.407 0.877 0.400

0.620 0.470 0.220 0.050

0.661 0.528 0.268 e

0.500 0.570 0.510 0.310

0.930 0.870 0.820 0.790

0.200 0.430 1.000 e

0.733 0.475 0.109 0.053

0.683 0.546 0.550 e

0.647 0.541 0.529 0.316

0#, 2# and 3#, in which the seabuckthorn were planted earlier, this table does

Table 3

Soil moisture content on-the-spot survey (%).

Soil depth (cm) The reforested gully Non-vegetated gully Average

Cu Cm Cd Cu Cm Cd The reforested

gully

Non-vegetated

gully

0 13.95 20.38 11.97 7.53 8.74 7.25 15.43 7.84

10 13.46 12.28 11.45 6.54 7.34 11.58 12.40 8.49

20 16.74 15.89 13.23 8.90 7.43 10.33 15.29 8.89

30 19.91 11.23 10.12 13.32 6.30 11.17 13.75 10.26

40 19.60 14.27 4.83 13.99 7.88 12.13 12.90 11.33

50 12.38 9.61 7.46 12.77 5.12 12.64 9.82 10.18

60 8.35 3.80 15.16 13.04 6.05 12.61 9.10 10.57

80 7.66 5.68 5.53 12.04 4.82 13.35 6.29 10.07

100 8.71 7.15 6.37 12.96 10.88 13.51 7.41 12.45

80 K. Zhang et al. / Journal of Hydro-environment Research 3 (2009) 77e84

rainfall. Return flow in EG4 was observed and saturated soilmoisture content was identified.

3.3. Soil organic matter

Soil organic matter content is a common index used toevaluate soil fertility. Soil samples were collected from sixdifferent sites: three located at the seabuckthorn forest gully andthree at the non-vegetated gully. Furthermore, soil samples fromeach site were classified into three different depths of soil every10 cm from the surface to 30 cm. Loss-on-ignition method (Lao,1988) was used to be evaluated soil organic matter content.

3.4. Vegetation investigation

In order to assess the ecological effect of the seabuckthornforest, a vegetation study was performed at four different sitesin EG4. These locations are the following: (1) under the sea-buckthorn forest in the EG4; (2) on the slope of the EG4 withno seabuckthorn planted; (3) under the poplar forest in thedepositional section at the mouth of the branch gully; (4)under the willow forest in the depositional section at the mouthof a branch gully.

4. Results

4.1. Effect of the seabuckthorn foreston sediment trapping

0102030405060708090

100

0 3 6 9 12 15 18

Soil

dept

h (c

m)

Soil moisture content rate ( )

reforested gully

non-vegetated gully

Fig. 4. Distribution of the average soil moisture content in the seabuckthorn

reforested gully and non-vegetated gully.

Field measurement in the EG1 gully in 2005 are shown inTable 2. The maximum depth of sediment deposition in thesections of ‘‘flexible dams’’ formed by seabuckthorn was0.961 m, and the average depth of sediment deposition in thesesections was 0.49 m (Zhang, 2006).

It can be observed from Table 2 that in general the depthvalues of sediment deposition gradually increases from theupstream (location C4) through location C3 and C2 to the firstline of seabuckthorns. However, the reverse trend is present inthe seabuckthorn forest sampling locations from Cu to Cd.Hence, the shape of deposition in the seabuckthorn dam is inthe form of delta which is similar to the sediment depositionpattern in a reservoir. This deposition pattern indicates

changes in the flow velocity of water passing through the areawith seabuckthorn. Similar result was also recorded in labo-ratory experiments (Qiu et al., 2003).

The seabuckthorn forest has ecological characteristics thatare important in trapping sediment and resisting erosion. Thisplant can easily form dense bushes that grow alongside Elymusdahuricus; therefore, vegetation cover in the seabuckthorn forestis extremely dense. Consequently, well-developed vegetationprevents raindrops from hitting bare soil directly; moreover, thevegetation also increases roughness and permeability of the soil.Dense branches and leaves efficiently increase flow resistanceand transform strand flow or concentrated flow into overlandflow. Accordingly, flow velocity and sediment transport capacitydecrease; thus, soil erosion is mitigated.

4.2. Effect of the seabuckthorn forest on water storage

Gullies with plentiful vegetation and weak erosion mainlyretain moisture by grass and shrub development. A portion of thewater flowing through the gully is absorbed by the roots of thesegrasses and shrubberies. As a result, these plants grow well andthe surfaces in these gullies have an increased moisture retentioncapacity. In fact, moisture retention is directly proportional tovegetation cover. This phenomenon can be confirmed bymeasuring soil moisture content after rain, as listed in Table 3.

Fig. 4 illustrates that soil moisture content of the landsurface in the reforested gully is almost twice as high as in

Fig. 5. Vegetation cover in different gullies (a) EG1; (b) EG4.

81K. Zhang et al. / Journal of Hydro-environment Research 3 (2009) 77e84

non-vegetated gully. Rainwater is retained in the soil of theseabuckthorn reforested gully. The seabuckthorn forests rootshelp retain this rainwater. Consequently, the stored water alsohelps sustain growth of grasses and shrub. Vegetation cover inthe reforested gully was measured at 95% in 2005, this increasein vegetation allows for greater efficiency in the storing waterand greater resistance to soil erosion. Contrastingly, water in thenon-vegetated gully moves deep into the soil, leaving the landsurface with too little soil moisture to support grass and shrubcover. The overall effects of the lack of seabuckthorn roots area lower vegetation cover of 20% and a high soil erosion rate.

There is little water flow in EG1 where the vegetation coveris up to 100% (Fig. 5a). However, water slowly flows from EG1to the latest deposited sediment in the seabuckthorn forest sitedat the mouth of gully EG4 (Fig. 5b), in which the vegetationcover approximates 80%. This phenomenon indicates that therain does not directly flow out of the gully as runoff. Water isstored in the deposited sediment up to the soil saturation rateand then slowly flows from the sediment delta formed bydeposition. Because of high vegetation cover in EG1, there islittle soil erosion and all moisture is retained by the vegetationor stored in the sediment; thus no water flows in the gully.

Additionally, when the soil moisture content is up to 36%a large soil reservoir for water is formed in the gully and rain-water is intercepted and stored. Rain is thereby converted intosoil moisture in the deposited sediment because under the sea-buckthorn that precipitation slowly flows downward into thedeposited sediment trapped by the seabuckthorn. This is a slowprocess and water can be seen in sediment one day after rain(Fig. 6).

4.3. Effect of the seabuckthorn foreston soil organic matter

Fig. 6. Water is stored in the sediment trapped by the seabuckthorn.

A comparison of the differences in the soil organic matter ofthe reforested gully and the non-vegetated gully are shown inTable 4. The values found in the gully planted with the sea-buckthorn forest were approximately two times more than thoseof the gully with no shrubs and were higher at all sampling depth.Thus, these results confirm that the seabuckthorn forest promotessoil fertility. The seabuckthorn forest is able to trap sediment inthe gully and also accumulate soil organic matter in the deposited

sediment (Li and Bai, 2003). Table 4 shows that the soil organicmatter content does not change obviously with the depth of soilin both of the reforested gully and the non-vegetated gully.

4.4. Ecological effects of the seabuckthorn forest

4.4.1. Taxa richnessThere are approximately 15 species of plants in the sub-layer

of the seabuckthorn forest in the EG4 gully (Table 5), and 90%of the sub-layer cover is Clinelymus dahurcus Turcz. The plantsspecies in the other three vegetation study sites, namely, on theslope, under the poplar forest, and under the widow forest, aremuch less numerous (the number of plants species are 9, 8, and10 respectively) than in the sub-layer of the seabuckthornshrubs. Taxa richness meant the number of total species per areawas calculated, and the difference of the understory coveragewas taken into consideration. The calculated taxa richness of theunderstory with seabuckthorn shrub is much higher if comparedto the other 3 sites (Table 5). It can be concluded that the sea-buckthorn forest assists in the development of other species.

4.4.2. Vegetation coverForest thickness (FT) can be used to measure and compare

the level of forest ecological development in different time atdifferent areas (Fan et al., 2008). This indicator can be express as

FT (mm)¼ Total forest stock volume (m3)/Total land area(m2)� 1000 (mm/m)¼ Forest stock volume per unit area (m3/ha)� Forest coverage/10 (mm).

Table 4

Soil organic matter content in reforested gully and contrastive gully (%).

Depth (cm) The reforested gully Non-vegetated gully Average

Cu Cm Cd Cu Cm Cd The reforested gully Non-vegetated gully

0e10 6.964 6.822 6.782 3.660 1.448 2.443 6.856 2.517

10e20 6.019 6.297 6.514 3.751 1.425 1.009 6.277 2.062

20e30 5.692 5.255 5.910 3.544 1.299 0.841 5.619 1.895

Table 5

The investigation of vegetation in the EG4.

Sites Area Understory

coverage

Taxa richness & proportion Average

height

Average taxa

richness (/m2)

Average

thickness-coverage

(m)

Simpson diversity

indexUnderstory community Proportion

Under the

seabuckthorn

shrub

6m2 95% Clinelymus dahurcus Turcz 90% 0.5 2.5 0.455 0.810

Youngia japonica 3% 0.1

Artemisia arenaria DC 2% 0.3

Milulotus officinalis-

(Madnle) Len

5% 0.4

Salsola collinaArtemisia gmelinii

Heteropappus altaicus

Echinops latifolius Tausch

Artemisina arayiOthersa

Total species: 15 100% 0.325 2.5 0.455 0.810

On the slope 6m2 60% S. breviflora Griseb 80% 0.3 1.17 0.174 0.649

Radix Stellerae Chamaejasmis 10% 0.3

Lespedeza davurica

(Laxm.) Schindl

10% 0.2

Salsola collinaArtemisia gmelinii

Cynanchum komarovii

Setaria viridis (Linn.) Beauv.

Othersb

Total species: 9 100% 0.267 1.17 0.174 0.649

Under the

poplar forest

6m2 90% Fimbristylisfusca(Nees) Benth 30% 0.3 1.33 0.261 0.172

Heleocharis yokoscensis 20% 0.25

Agrostis alba L. 15% 0.3

Heteropappus altaicus 10% 0.3

Medicago sativa 10% 0.4

Artemisia sacrorum Ledeb 5% 0.2

Setaria 10% 0.25

Othersc

Total species: 8 100% 0.286 1.33 0.261 0.172

Under the

willow forest

6m2 90% Herba Artemisiae Scopariae 15% 0.5 1.67 0.329 0.082

Medicago sativa 10% 0.15

Heteropappus altaicus 10% 0.25

Salsola collina 10% 0.2

Artemisia gmelinii 10% 0.3

Stipa capillata 10% 0.25

Paris tetraphylla A. Gray 5% 0.25

Artemisina arayi 20% 0.1

Othersd 10% 0.3

Total species: 10 100% 0.256 1.67 0.329 0.082

a Contains 6 species.b Contains 2 species.c Contains 1 species.d Contains 2 species.

82 K. Zhang et al. / Journal of Hydro-environment Research 3 (2009) 77e84

83K. Zhang et al. / Journal of Hydro-environment Research 3 (2009) 77e84

Derived from the FT, average thickness-coverage could beused to measure the state of the vegetation cover and evaluateecological environment of given area. Average thickness-coverage can be calculated with the formula below:

TC¼A�Cu �

Xn

i�1

�Pi�Hi

�A

in which TC stands for average thickness-coverage, and n istotal species of understory vegetation, A, Cu, Pi, Hi means thesquare of study area, understory coverage of the study area,proportion of the i-th species in understory vegetation andaverage height of the i-th species in understory vegetationrespectively. The higher the average thickness-coverage value,the better the state of vegetation.

The average thickness-coverage under the seabuckthornshrub in the gully is 0.455 (Table 5); on the slope of the samegully with no seabuckthorn, this index is only 0.174. Its valueunder the poplar forest is 0.261 and 0.329 under the willowforest. The average thickness-coverage under the seabuckthornshrub is approximately twice as high as under the poplar forest,and nearly one and a half times higher than under the willowforest. It is clear that the state of the vegetation in the seabuck-thorn areas is better.

4.4.3. Simpson diversity indexSimpson diversity index is

D¼"XS

i¼1

�n2

i

N2

�#�1

in which ni is the number of individuals of the i-th species, and Nis the total number of individuals in the sample. Simpson’sindex as a dominant concentration index is commonly used toestimate species diversity in crops, home gardens, and natureforest. This index is usually lower than 1, but the higher theSimpson diversity index value, the better the biodiversity. Theincrease of the Simpson diversity index is directly proportionalto the biodiversity. The Simpson diversity index is 0.810 underthe seabuckthorn shrub and it is 0.649 on the slope of the samegully. Its value is 0.172 under the poplar forest and it is 0.082under the willow forest (Table 5). Therefore, it can be inferredthat planting a seabuckthorn forest in the gully may alsoimprove biodiversity to some extent.

5. Conclusions

Planting seabuckthorn in the Pisha Sandstone area isa successful method of trapping sediment in the gullies andcontrolling soil erosion. In the gully where the seabuckthornwere planted over 12 years ago, almost all the sediment istrapped; Seabuckthorn have also contributed to increase the soilmoisture content by storing water in the seabuckthorn’s rootzone and consequently improving the soil fertility. Organicmatter content is higher in the gully reforested with seabuck-thorn compared to the non-vegetated gully. Moreover, planting

seabuckthorn in the gully can promote growth of other plantspecies, especially the C. dahurcus Turcz, effectively improvebiodiversity and abundance. All the three parameters used toevaluate the understory community (the taxa richness, thethickness-coverage and the Simpson diversity index), suggestthat planting seabuckthorn vegetation is more advantageous forsoil health and prevention of erosion in the Pisha SandstoneXizhao gully compared to planting poplar or willow vegetation.

Acknowledgement

Research for this project was supported by the Ministry ofWater Resources of China (2007SHZ0901034), and the NationalNatural Science Foundation (Grant No. 50779027). Discussionswith Cifen Bi (Bureau of the Upper and Middle Reaches ofYellow River, Xi’an) and Huaien Li (Xi’an University ofTechnology) were instrumental in developing many ideas con-tained in this paper. Ordos City Water Science Institute providedfield experimental tools and the suitable infrastructure to ensurethe research work going on. Many postgraduate students inXi’an University of Technology took part in field investigation,and Xuehua Duan (Tsinghua University, Beijing) gave valuableproposals in draft paper, Dr. Fabio Souza (Tsinghua University,Beijing) paid great patience to review the draft paper and gavemany helpful suggestion, the authors are grateful to all of them.

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