The effect of environmental factors on spatial variability in land use change in the high-sediment region of China s Loess Plateau

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1 J. Geogr. Sc. 2013, 24(5): DOI: /s Scence Press Sprnger-Verlag The effect of envronmental factors on spatal varablty n land use change n the hgh-sedment regon of Chna s Loess Plateau LUO Ya 1,2, YANG Shengtan 1, * ZHAO Changsen 1, LIU Xaoyan 3, LIU Changmng 4,5, WU Lnna 1,6, ZHAO Hagen 1, ZHANG Ych 1 1. State Key Laboratory of Remote Sensng Scence, School of Geography, Bejng Normal Unversty, Bejng Key Laboratory for Remote Sensng of Envronment and Dgtal Ctes, Bejng , Chna; 2. School of Geographc and Envronmental Scences, Guzhou Normal Unversty, Guyang , Chna; 3. Yellow Rver Conservancy Commsson, Zhengzhou , Chna; 4. College of Water Scence, Bejng Normal Unversty, Bejng , Chna; 5. Key Laboratory of Land Water Cycle and Surface Processes, CAS, IGSNRR, CAS, Bejng , Chna; 6. College of Resource and Envronment Engneerng, Guzhou Unversty, Guyang , Chna; Abstract:In areas wth topographc heterogenety, land use change s spatally varable and nfluenced by clmate, sol propertes, and topography. To better understand ths varablty n the hgh-sedment regon of the Loess Plateau n whch sol loss s most severe and sedment dameter s larger than n other regons of the plateau, ths study bulds some ndcators to dentfy the characterstcs of land use change and then analyze the spatal varablty as t s affected by clmate, sol property, and topography. We buld two ndcators, a land use change ntensty ndex and a vegetaton change ndex, to characterze the ntensty of land use change, and the degree of vegetaton restoraton, respectvely. Based on a subsecton mean method, the two ndcators are then used to assess the spatal varablty of land use change affected by clmatc, edaphc, and topographc elements. The results ndcate that: 1) Land use changed sgnfcantly n the perod The total area experencng land use change was 42,302 km 2, accountng for 22.57%of the study area. Hgh-coverage grassland, other woodland, and forest ncreased sgnfcantly, whle low-coverage grassland and farmland decreased n 2010 compared wth ) Land use change occurred prmarly west of the Yellow Rver, between 35 and 38 degrees north lattude. The four transformaton types, ncludng (a) low-coverage grassland to medum-coverage grassland, (b) medum-coverage grassland to hgh-coverage grassland, (c) farmland to other woodland, and (d) farmland to medum-coverage grassland, were the prmary types of land use change, together consttutng 60% of the area experencng land use change. 3) The spatal varablty of land use change was sgnfcantly affected by propertes of dryness/wetness, sol condtons and slope gradent. In general, land use changed dramatcally n sem-ard regons, remaned relatvely Receved: Accepted: Foundaton: Natonal Key Technologes R&D Program, No.2012BAB02B00; Publc Welfare Foundaton of the Mnstry of Water Resources of Chna, No ; The Fundamental Research Funds for the Central Unverstes Author: Luo Ya (1979 ), Assocate Professor, specalzed n LUCC and sol eroson. E-mal: luoya2002@163.com * Correspondng author: Zhao Changsen (1977 ), PhD, specalzed n applcaton of RS n water resources and water envronment. E-mal: hzjohnson2003@163.com www/sprngerlnk.com/content/ x

2 LUO Ya et al.: The effect of envronmental factors on spatal varablty n land use change n Chna s Loess Plateau 803 stable n ard regons, changed sgnfcantly n clay-rch sol, remaned relatvely stable n clay-poor sol, changed dramatcally n steeper slopes, and remaned relatvely stable n tablelands and low-lyng regons. The ncrease n vegetaton concded wth ncreasng changes n land use for each physcal element. These fndngs allow for an evaluaton of the effect of the Gran to Green Program, and are applcable to the desgn of sol and water conservaton projects on the Loess Plateau of Chna. Keywords: spatal varablty; land use change; dryness/wetness; sol propertes; slope gradent; the hgh-sedment regon of Chna s Loess Plateau 1 Introducton The Loess Plateau of Chna s the man source of the Yellow Rver sedment. The plateau has a fragle ecology and suffers severe sol loss. Ths study focuses on the hgh-sedment regon of the Loess Plateau n whch sol loss s most severe and sedment dameter s larger than n other regons of the plateau. Sgnfcant changes n land use have occurred n ths regon snce the Gran to Green Program (GTGP) launched n 1999 (Pe et al., 2003; L et al., 2007; Fu et al., 2011). Accompaned by ths rapd change, the sol organc carbon and lable organc carbon stores changed (Zhang et al., 2012), and water yeld reductons on many of the branches of the Yellow Rver have also been observed (Lü et al., 2012; Xn et al., 2012). The more that s known about ths land use change, the more ts relatonshp to eco-hydrologcal varatons n the regon can be understood. There s a close relatonshp between envronmental factors and land use change (Chen et al., 2001; Fu et al., 2006), and envronmental factors are more nfluental n areas wth greater topographc heterogenety (Opršal et al., 2013). Among the factors, clmate, sol propertes, and topography would be expected to affect land use change on the Loess Plateau, an area wth hgh topographc heterogenety. Studyng the spatal varablty of land use change affected by envronmental factors may be helpful for an evaluaton of the effect of sol and water conservaton. To date, scholarly attenton has focused on the spatal varaton of land use change and ts possble nfluences (L et al., 2009; Zhang et al., 2008). These studes carefully analyzed the changes n areas of all land use types, and ther effect on water yeld. Studes have rarely smultaneously focused on the spatal varablty of land use change as t s affected by clmatc, edaphc, and topographc elements, however, ths spatal varablty clearly merts further research. Ths study has two prmary objectves. Frst, we buld two ndcators, a land use change ntensty ndex and a vegetaton change ndex, to characterze the ntensty of land use changes, and the degree of vegetaton restoraton, respectvely. Second, the two ndcators, from macroscopc to mcrocosmc, are used to analyze the spatal varablty of land use change affected by envronmental factors, ncludng clmatc (ndcated by dryness/wetness), edaphc (ndcated by sol texture), and topographc (ndcated by slope gradent) elements on the Loess Plateau n the perod Descrpton of study area The hgh-sedment regon of the Loess Plateau s the prmary sedment source of the Yellow Rver (Fgure 1), and s located at the juncton of Shaanx, Shanx, Inner Mongola, Nngxa,

3 804 Journal of Geographcal Scences and Gansu. It s stuated between E to E and N to N, encompassng 187,422 km 2, wth an elevaton rangng from 388 to 3747 m above sea level. The area s characterzed by dramatc spatal varaton; ts gully densty s 2 5 km/km 2. Average annual precptaton vares from 300 to 650 mm. Nearly 80% of the precptaton s domnated by ranstorms that occur durng the rany season, from June to September. Approxmately 90% of the area s covered by loess, wth severe sol loss. Fgure 1 Locaton of the study area 3 Methodology 3.1 Two ndcators that characterze land use change Accurate data on the ntensty of land use change and the effect of envronmental restoraton are useful n an evaluaton of the trends and consequences of land use change. The study thus uses two ndcators to characterze the ntensty of land use change and the effect of envronmental restoraton, respectvely. (1) Land use change ntensty ndex The land use change ntensty ndex (D) was used to characterze ts ntensty. For a gven regon, the value of D was calculated as the area of land use change dvded by the total area of a regon: D = A/S 100% (1) where D s the land use change ntensty ndex rangng from 0 to 1, n %; A s the area of land use change, n km 2 ; S s the total area of the regon, n km2. The hgher the value of D, the more ntense the land use change s n a gven regon, and vce versa.

4 LUO Ya et al.: The effect of envronmental factors on spatal varablty n land use change n Chna s Loess Plateau 805 (2) Vegetaton change ndex Vegetaton s an mportant ndcator of the effect of envronmental restoraton. The vegetaton change ndex (I) was used to characterze the degree of vegetaton restoraton. For a gven regon, the values of I are obtaned from the followng formula: I = R 2010 R 1998 (2) where I s the vegetaton change ndex, n %; R 1998 and R 2010 are the percentage of vegetaton n 1998 and 2010, respectvely. The area of vegetaton was obtaned from the land use map, and equals numercally the sum of forest, shrub, hgh-coverage grassland, and medum-coverage grassland. If the value of I s greater than 0, t shows that vegetaton ncreased. The greater the value of I, the faster the vegetaton ncreased. If the value of I s less than 0, t shows that vegetaton decreased. The greater the absolute value of I, the faster the vegetaton decreased. If the value of I equals 0, t shows that the vegetaton was unchanged. 3.2 Land use nformaton extracton and valdaton In order to record land use change n the perod , we nterpreted 30 m resoluton satellte mages (Landsat-5TM n 1998 and HJ-CCD n 2010).Based on the land use classfcaton standard of Chna (GB/T ), land use was classfed nto 11 types, ncludng farmland, forest, shrub, open woodland, other woodland, hgh-coverage grassland, medum-coverage grassland, low-coverage grassland, water body, constructon land, and unused land. Usng the man-machne nteractve vsual nterpretaton technque (Yang and Zhu, 2000), land use raster datasets n 1998 and 2010 were obtaned. Three feld verfcatons were carred out to assess the accuracy of the nterpretaton of the land use data. Nearly 32% of the survey area was verfed. For the 2010 land use data, nterpretaton accuracy was assessed by vsual verfcaton. The results confrmed that 121 out of 129 ponts were correctly nterpreted n 2010, wth an accuracy of 93.8%. For the 1998 land use data, multple sources of nformaton and multdscplnary expertse were used to assess the nterpretaton accuracy, ncludng referencng hstorcal documents and maps and ntervewng local resdents. The results showed that 118 out of 129 ponts were correctly nterpreted n 1998, wth an accuracy of 91.47%. 3.3 Dryness/wetness dentfcaton In order to characterze the spatal varablty of land use change that s affected by clmate, the ardty ndex (K) was used to dentfy the dryness/wetness of a regon based on annual precptaton and evaporaton n the perod at 104 weather statons. The ardty ndex was estmated usng the followng formula (Yang et al., 2002; Mao et al., 2011): P K (3) E where K s the ardty ndex; P s annual precptaton, n mm; E s annual evaporaton, n mm. A regon can be classfed nto three types: humd (K s greater than 0.5), sem-ard (K ranges from 0.2 to 0.5), and ard (K s less than 0.2). 3.4 Sol texture dentfcaton As a fundamental sol property, texture affects many other basc physcal and chemcal characterstcs. Clays are typcally the most mportant mneral consttuents of sols. Because

5 806 Journal of Geographcal Scences of ther small sze, the small clay partcles wth ther large specfc surface area are most mportant n determnng the fundamental propertes of sol (Balba, 1995). The clay rato of sol can be used to dentfy sol texture. In ths study, the (sand+slt)/clay rato (Bouyoucos, 1935) was used to represent the clay rato for purposes of dentfyng sol texture. Based on the Chnese 1:1,000,000 scale sol map, sol property nformaton was obtaned. Three sol textures could then be classfed usng the nternatonal classfcaton system: loam or sand ((sand+slt)/clay rato more than 5.67 or clay rato less than 15%), clay loam ((sand+slt)/clay rato rangng from 3 to 5.67 or clay rato rangng from 15% to 25%), and clay ((sand+slt)/clay rato less than 3 or clay rato more than 25%). 3.5 Slope gradent classfcaton Global Dgtal Elevaton Model (GDEM) data at a resoluton of 30 m were used to extract the slope gradent nformaton needed for the study. The slope gradent can be classfed nto fve classes: less than 2, 2 to 6, 6 to 15, 15 to 25, and greater than Sample regon selecton The Gran to Green Program (GTGP) profoundly mpacted land use n the hgh-sedment regon of the Loess Plateau (Fu, 2011). Each provnce mplemented GTGP dfferently because of dfferent strategc goals and development models. In order to elmnate the mpact of these vared strategc goals and development models on land use change, the sample regon needed to represent as unform a GTGP mplementaton background as possble. Among the fve provnces nvolved n the hgh-sedment regon, the vegetaton restoraton effect of Shaanx Provnce was most sgnfcant, each area wthn the provnce mplemented GTGP smlarly. We thus selected 21 basns n Shaanx Provnce as sample regons (Fgure 1). 3.7 Subsecton mean method for expressng the relatonshps between envronmental factors and land use change The relatonshps between envronmental factors and land use change are dffcult to express usng a lnear fttng method because of the complexty of land use change. Accordngly, we propose a subsecton mean method to express these relatonshps. The subsecton mean method can be descrbed as follows: 1) Takng a basn as a computng unt, we calculate the means of a) land use change ntensty ndex, b) vegetaton change ndex, c) ardty ndex, d) (sand+slt)/clay rato, and e)slope gradent of the 21 basns. Among them, the means of a) and b) represent land use change characterstcs, expressed by the dependent varables Y 1 and Y 2, respectvely. The means of c), d) and e) represent envronmental factors, expressed by the ndependent varables X 1, X 2 and X 3, respectvely. For each basn, the relatonshps between envronmental factors and land use change can be represented by (X 1, Y 1 ), (X 1, Y 2 ), (X 2, Y 1 ), (X 2, Y 2 ), (X 3, Y 1 ) and (X 3, Y 2 ) coordnate pars. 2) Independent varables X (=1,2,3) of 21 basns are arranged as a seres from small tolarge and then dvded nto three subsectons. m mn max mn Subsecton 1: X ~ X ( X X )

6 LUO Ya et al.: The effect of envronmental factors on spatal varablty n land use change n Chna s Loess Plateau 807 Subsecton 2: Subsecton 3: mn max mn mn max mn X ( X X )~ X 2( X X ) mn max mn X 2( X X ) ~ X m 3) The mean of dependent varables of X can be found by the followng functon: Y j (j=1,2; =1,2,3) correspondng to each subsecton Y j 1 N m 0 jm Y N (4) where Yj s dependent varables Y j correspondng to X ; Yj s the mean of dependent varablesy ; m s the number of the plots (X, Y j ) for whch X s ncluded wthn the range of a j gven subsecton. 4) Last we use Yj to represent the land use change characterstcs correspondng to each subsecton of envronmental propertes. 4 Results and dscusson 4.1 General characterstcs of envronmental factors and land use change n the hgh-sedment regon of the Loess Plateau Spatal varaton of envronmental factors The spatal varaton of dryness/wetness, sol texture, and slope gradent s shown n Fgures 2A and 2B, and Tables 1 and 2. Area and dstrbuton of each envronmental factor category are descrbed below. Fgure 2 Spatal varaton of envronmental factors and land use change n the hgh-sedment regon of the Loess Plateau (A) ardty ndex and the (sand+slt)/clay rato, (B) slope gradent, (C) land use change n the perod Low=Low-coverage grassland, Med=Medum-coverage grassland, Hg=Hgh-coverage grassland, Far=Farmland, Oth=Other woodland, Shr=Shrub, For=Forest, Ope=Open woodland 1) Dryness/wetness condtons As shown n Fgure 2A and Table 1, the ardty ndex ranges from 0.15 to 0.45, the areas of ardty ndex less than 0.2, are 38,545 km 2 (20.57% of the study area) and 148,877

7 808 Journal of Geographcal Scences Table 1 Area of each category of ardty ndex and the (sand+slt)/clay rato Ardty ndex (dmensonless) Area (km 2 ) Proporton (%) The (sand+slt)/clay rato (dmensonless) Area (km 2 ) Proporton (%) < , < , , > > , Total 187, Total 187, Table 2 Area of each category of slope gradent Slope (degree) Area (km 2 ) Proporton (%) < 2 26, , , , > 25 14, Total 187, km 2 (79.43% of the study area), respectvely. Ard clmate (ardty ndex less than 0.2) s prmarly dstrbuted west of the Zhaoshyao-Wangdaohengta-Hequ lne, whle the rest of the study area has a sem-ard clmate (ardty ndex from 0.2 to 0.5).The results show that the study area s domnated by a sem-ard clmate. 2) Sol texture In Fgure 2A and Table 1, we also see that the areas where the (sand+slt)/clay rato s less than 3, , and more than 5.67 are 4,616 km 2 (2.46% of the study area), 129,925 km 2 (69.32% of the study area), and 52,881 km 2 (28.21% of the study area), respectvely. Clay ((sand+slt)/clay rato less than 3) s sporadcally dstrbuted n the Lupan Mountans and Qnlng Mountans, sand and loam ((sand+slt)/clay rato rangng from 3 to 5.67) are prmarly dstrbuted west of the Qngyangcha-Shenjawan-Gaojabao-Gaoshya lne, whle the rest of the study area s covered by clay loam. The results show that most of the study area s covered by clay loam sol. 3) Slope gradent The slope gradent of the study area s shown n Fgure 2B and Table 2.The areas wth a slope gradent less than 2, 2 6, 6 15, 15 25, and more than 25 are 26,169 km 2 (13.96% of the study area), 33,221 km 2 (17.73% of the study area), 68,726 km 2 (36.67% of the study area), 45,247 km 2 (24.14% of the study area), and 14,059 km 2 (7.5% of the study area), respectvely. Flat land of less than 6 accounts for just 31.69% of the study area, s dstrbuted west of the Qngyangcha-Shenjawan-Gaojabao-Wangdaohengta lne, and reaches from Jaqao to Jngcun along the Jnghe Rver. The results show that the study area s domnated by a steep slope gradent General characterstcs of land use change By overlayng the 1998 and 2010 land use maps, a land use change map for the perod (Fgure 2C), and the areas of each category of land use n 1998 and 2010 were

8 LUO Ya et al.: The effect of envronmental factors on spatal varablty n land use change n Chna s Loess Plateau 809 obtaned (Table 3). Table 3 shows that grassland areas totaled 82,623 km 2 (44.08% of the study area) n 1998 and 83,355 km 2 (44.47% of the study area) n 2010; that farmland n the same years totaled 66,769 km 2 (35.62% of the study area) and 58,538 km 2 (31.23% of the study area), respectvely; and that, n the perod , hgh-coverage grassland, other woodland, and forest, ncreased sgnfcantly, whle low-coverage grassland and farmland decreased n 2010 compared wth The results show that the pattern of land use has changed, but land cover remans domnated by grassland and farmland. It should be noted that changes n water bodes were not analyzed, because the total area of water was small and appeared to be affected by precptaton. Table 3 Area of each category of land use n 1998 and 2010 Land use type km 2 % km 2 % km 2 % Farmland 66, , Forest Shrub 13, , Open woodland 6, , Other woodland , , Hgh-coverage grassland , , Medum-coverage grassland 44, , Low-coverage grassland 31, , , Water body Constructon land Unused land Total 187, ,422 As llustrated n Fgures 1 and 2C, land use change occurred prmarly west of the Yellow Rver, between 35 and 38 degrees north lattude, ncludng the upper reach of the Jnghe Rver basn, the upper and mddle reaches of the Beluo Rver basn, the Yanhe Rver basn, the Qngjan Rver basn, and the upper and mddle reaches of the Wudng Rver basn. In addton to these regons, land use east of the Yellow Rver, from north to south along the Yellow Rver, also changed sgnfcantly. As shown n Table 4, the area of land use change was 42,302 km 2, accountng for 22.57% of the study area. Among 84 transformaton types, the area of four types, ncludng (a) low-coverage grassland to medum-coverage grassland, (b) medum-coverage grassland to hgh-coverage grassland, (c) farmland to other woodland, and (d) farmland to medum-coverage grassland, represented more than 60% of the area experencng land use change. Results ndcate that land use change n the perod was dramatc and domnated by these four types. 4.2 Spatal varablty of land use change affected by clmate As one of the ndcators of clmate, dryness/wetness was an mportant factor affectng the

9 810 Journal of Geographcal Scences Table 4 Prmary land use change transformaton types n the perod Transformaton type Area Proporton (%) Note Low to Med 11, Med to Hg 9, Far to Oth 2, Far to Med 2, Low=Low-coverage grassland Low to Hg 1, Med=Medum-coverage grassland Shr to For 1, Hg=Hgh-coverage grassland Far=Farmland Far to Low 1, Oth= Other woodland Far to Hg 1, Shr= Shrub Far to Ope For= Forest Med to Shr Ope= Open woodland Other 77 types 9, All of the changed 42, Non-change 145, Total 187,422 spatal dstrbuton of sol mosture and thereby affectng agrcultural actvtes, and was a key factor n lmtng the transformaton drecton of land use change (Brown et al., 2011). After calculatng the means of the land use change ntensty ndex (D), the vegetaton change ndex (I), and the ardty ndex (K) of each sample basn, the relatonshps between land use change and clmate could be revealed based on the subsecton mean method descrbed n secton 3.7. As llustrated n Fgure 3, accordng to the subsecton mean method, the average ardty ndex rangng from 0.16 to 0.35 s dvded nto three subsectons, ncludng , ,and The means of the land use change ntensty ndex (D) n the three subsectons are then 18.49%, 56.54%, and 42.62%, respectvely (Fgure 3A). In addton, the means of the vegetaton change ndex (I) n these subsectons are 5.79%, 26.27%, and 12.9% (Fgure 3B). Taken together, these results ndcate that generally, land use change n the sem-ard regon s more dramatc than n the ard regon, and the vegetaton restoraton effect s also more pronounced n the sem-ard than n the ard regon. Wth regard to clmate, long-term drought condtons play a key role n the drecton of land use change and lmt the vegetaton restoraton effect n large-scale ard and sem-ard regons. Most ard regons n the study area are dstrbuted n the upper reaches of the rvers. These regons have low water-resource avalablty and hgh rrgaton costs resultng n a lower survval rate for artfcal vegetaton than occurs n sem-ard regons, and natve vegetaton that s domnated by low-coverage grassland. As a result, land use change and vegetaton restoraton levels are lower n ard than n sem-ard regons. More specfcally, as shown n Fgure 3A and 3B, the land use change ndex and vegetaton change ndex n the ardty ndex subsecton are both less than n the subsecton , ndcatng that land use change n the regons n whch the ardty ndex ranges from s more dramatc than n the range, and the vegetaton restoraton effect n the regons n whch the ardty ndex ranges from s more evdent than n the range. There appear to be two reasons for ths phenomenon. Frst,

10 LUO Ya et al.: The effect of envronmental factors on spatal varablty n land use change n Chna s Loess Plateau 811 because the regons n whch the ardty ndex ranges from are mostly dstrbuted n the lower reaches of the rvers (Fgure 2A), there s better water resource avalablty, and less farmland s beng converted to woodland and grassland, so the land use change ndex s lower than n regons n whch the ardty ndex ranges from Second, land use change n these regons s domnated by two transformaton types, medum-coverage grassland to hgh-coverage grassland and shrub to forest (Fgure 2C), and accordng to Equaton 2, the total vegetaton area was not greater than the sum of forest, shrub, hgh-coverage grassland, and medum-coverage grassland. The vegetaton change ndex s thus lower relatve to regons n whch the ardty ndex ranges from Fgure 3 Relatonshps between land use change and dryness/wetness condtons (A) land use change ntensty ndex and ardty ndex; (B) vegetaton change ndex and ardty ndex 4.3 Spatal varablty of land use change affected by sol propertes Sol affects mosture retenton and thereby nfluences land use. Dfferences n sol propertes affect water content (O'Geen, 2012), and so also affect the ntensty of land use change and vegetaton restoraton. After calculatng the means of the land use change ntensty ndex (D),the vegetaton change ndex (I), and the (sand+slt)/clay rato for each sample basn, the relatonshps between land use change and sol propertes were revealed. Fgure 4 llustrates these relatonshps. Based on the subsecton mean method, the average (sand+slt)/clay rato that ranges from 4.1 to 16.7 s dvded nto , , and subsectons. Accordngly, the mean land use change ntensty ndex (D) for the three subsectons are 36.21%, 22.58%, and 14.8%, respectvely (Fgure 4A). The mean vegetaton change ndex (I) for the subsectons are 13.26%, 10.34%, and 4.14% (Fgure 4B). The smaller the (sand+slt)/clay rato, the greater the values of D and I. The results ndcate that the more the clay content of sol, the more changes n land use occurred and the more vegetaton was restored. Sol propertes had a clear effect on land use change. Water storage and redstrbuton are a functon of sol pore space and pore-sze dstrbuton, whch can be governed by texture (Chlds 1940). Clay-rch sols have the largest pore space, hence the greatest total water-holdng capacty (O'Geen, 2012). Because vegetaton s more lkely to survve n clay-rch sols, land use changed more dramatcally and vegetaton was more clearly restored n regons wth a hgh clay rato.

11 812 Journal of Geographcal Scences Fgure 4 Relatonshps between land use change and sol texture (A) land use change ntensty ndex and the (sand+slt)/clay rato; (B) vegetaton change ndex and the (sand+slt)/clay rato 4.4 Spatal varablty of land use change affected by topography As an mportant ndcator of topography, slope gradent has a clear effect on the ntensty of sol eroson (Quan et al., 2001), and thereby affects sol fertlty and patterns of land use. After calculatng the means of the land use change ntensty ndex (D), the vegetaton change ndex (I), and the slope gradent of each sample basn, the relatonshps between land use change and topography could be obtaned. Fgure 5 llustrates the relatonshp between land use change and topography. Based on the subsecton mean method, the average slope gradent rangng from 2.1 to 16.6 s dvded nto , and subsectons. Accordngly, the mean land use change ntensty ndex (D) for the three subsectons s 14.8%, 15.75%, and 43.6%, respectvely (Fgure 5A). In addton, the mean vegetaton change ndex (I) for the subsectons s 4.14%, 6.25%, and 15.93% (Fgure 5B). The results ndcate that the greater the slope gradent, the more dramatc the change n land use and the more vegetaton was restored. Land use changed wth topography. Steeper slopes generally have rapd runoff, less mosture enterng the sol (Balba, 1995), and lower gran productvty. Farmers n the study Fgure 5 Relatonshps between land use change and topography (A) land use change ntensty ndex and slope gradent; (B) vegetaton change ndex and slope gradent

12 LUO Ya et al.: The effect of envronmental factors on spatal varablty n land use change n Chna s Loess Plateau 813 area prefer to grow crops on tablelands and n low-lyng areas wth a smaller slope gradent n order to mprove gran self-suffcency, whch helps to explan why land wth a smaller slope gradent s more dffcult to transform nto woodland and grassland. Land use changed more dramatcally and vegetaton was thus more restored at steeper slopes. 4.5 Relatonshp between land use change ntensty and vegetaton restoraton effect GTGP, launched n 1999, was prmarly amed at changng land use n order to acheve vegetaton restoraton. To further evaluate the consstency between these two ams, the relatonshp between land use change ntensty and vegetaton restoraton are dscussed usng a lnear regresson method. As shown n Fgure 6, the vegetaton change ndex ncreases wth the land use change ntensty ndex; the correlaton coeffcent (R 2 ) of both s The results ndcate that the ncrease n vegetaton concded wth the growth n land use change, achevng the purpose of GTGP. Fgure 6 Relatonshp between land use change ntensty and vegetaton restoraton effect 5 Conclusons We constructed two ndcators to evaluate the spatal varaton of land use change as t s affected by envronmental factors n the hgh-sedment regon of the Loess Plateau. The results ndcate that land use changed dramatcally n the perod We found frst that the study area s domnated by a sem-ard clmate, clay loam sol, and steep slope gradent. The area affected by land use change was 42,302 km 2, accountng for 22.57% of the study area. Hgh-coverage grassland, other woodland, and forest ncreased sgnfcantly, whle low-coverage grassland and farmland were lower n 2010 compared wth The pattern of land use has changed, but land cover stll was domnated by grassland and farmland. Second, we found that land use change occurred prmarly west of the Yellow Rver, between 35 and 38 degrees north lattude, ncludng the upper reaches of the Jnghe Rver basn, the upper and mddle reaches of the Beluo Rver basn, the Yanhe Rver basn, the Qngjan Rver basn, and the upper and mddle reaches of the Wudng Rver basn. In addton to these regons, land use east of the Yellow Rver, from north to south along the Yellow Rver, also changed sgnfcantly. Four transformaton types, (a) low-coverage grassland to medum-coverage grassland, (b) medum-coverage grassland to hgh-coverage grassland, (c) farmland to other woodland, and (d) farmland to medum-coverage grassland, were the prmary types of land use change, representng together 60% of the total area experencng land use change. Thrd, sgnfcant spatal varaton n land use change affected by the dryness/wetness, sol texture and slope gradent was found. In general, land use changed dramatcally n sem-ard regons, remaned relatvely stable n ard regons, changed sgnfcantly n clay-rch sol,

13 814 Journal of Geographcal Scences remaned relatvely stable n clay-poor sol, changed dramatcally n steeper slopes, and remaned relatvely stable n tablelands and low-lyng regons. Moreover, the ncrease n vegetaton concded wth the ncrease n land use change for all of the envronmental factors studed. Overall, the fndngs help to evaluate the effect of the Gran to Green Program and are applcable to future desgns for sol and water conservaton n Chna s Loess Plateau. Acknowledgement Thanks to Wenlong Song, Xu Zhou, Lpeng Hou et al. for assstng n land use nformaton extracton and feld verfcaton. References Balba A M, Management of Problem Sols n Ard Ecosystems. CRC Press. Boca Raton, Florda, 250 p. Bouyoucos G J, The clay rato as a crteron of susceptblty of sols to eroson. Journal of the Amercan Socety of Agronomy, 27: Brown Ian, Poggo Laura, Gmona Alessandro et al., Clmate change, drought rsk and land capablty for agrculture: Implcatons for land use n Scotland. Regonal Envronmental Change, 11(3): Chen L D, Wang J, Fu B J et al., Land-use change n a small catchment of northern Loess Plateau, Chna. Agrculture, Ecosystems and Envronment, 86: Chlds E C, The use of sol mosture characterstcs n sol studes. Sol Scence, 50: Fu B J, Lu Y, Lü Y H et al., Assessng the sol eroson control servce of ecosystems change n the Loess Plateau of Chna. Ecologcal Complexty, 8: Fu B J, Qu J Z, Chen L D et al., Temporal change n land use and ts relatonshp to slope degree and sol type n a small catchment on the Loess Plateau of Chna. Catena, 65: L G, Lang W, Yang Q K, Analyss of land use pattern change n coarse sandy regon of mddle reaches of Yellow Rver. Scence of Sol and Water Conservaton, 7(3): (n Chnese) L L J, Jang D J, L J Y et al., Advances n hydrologcal response to land use/land cover change. Journal of Natural Resources, 22(2): (n Chnese) Lü Y H, Fu B J, Feng X M et al., A polcy-drven large scale ecologcal restoraton: quantfyng ecosystem servces changes n the Loess Plateau of Chna. Plos One, 7: Mao F, Sun H, Yang H L, Research progress n dry/wet clmate zonng. Progress n Geography, 30(1): (n Chnese) O'Geen A T, Sol Water Dynamcs. Nature Educaton Knowledge, 3(6): 12. Opršal Z, Šarapatka B, Kladvo P, Land-use changes and ther relatonshps to selected landscape parameters n three cadastral areas n Morava (Czech Republc). Moravan Geographcal Reports, 21(1): Pe X F, Gan Z M, Lu X, A study on the problem of returnng farmland to forests n Yellow Rver Basn. Journal of Ard Land Resources and Envronment, 17(3): (n Chnese) Quan B, M J M Römkens, L R et al., Effect of land use and land cover change on sol eroson and the spato-temporal varaton n Lupan Mountan Regon, southern Nngxa, Chna. Fronters of Envronmental Scence & Engneerng n Chna, 5(4): Xn Z B, Ran L S, Lu X X, Sol Eroson Control and Sedment Load Reducton n the Loess Plateau: Polcy Perspectves. Internatonal Journal of Water Resources Development, 28(2): Yang J P, Dng Y J, Chen R S et al., The nterdecadal fluctuaton of dry and wet clmate boundares n Chna n recent 50 years. Acta Geographca Snca, 57(6): (n Chnese) Yang S T, Zhu Q J, Affect of man-computer nteractve nterpretaton method n sol eroson survey of large scale by remote sensng. Journal of Sol and Water Conservaton, 14(3): (n Chnese) Zhang L H, Xe Z K, Zhao R F et al., The mpact of land use change on sol organc carbon and lable organc carbon stocks n the Longzhong regon of Loess Plateau. Journal of Ard Land, 4(3): Zhang X P, Zhang L, Wang Y et al. Tempo-spatally responses of the annual streamflow to LUCC n the mddle reaches of Yellow Rver, Chna. Scence of Sol and Water Conservaton, 7(1): (n Chnese)