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Spatial distribution pattern changes of oasis soil types in Manasi River Basin, arid northwestern China
Catena 87 (2011) 253–259
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Catena j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / c a t e n a
Spatial distribution pattern changes of oasis soil types in Manasi River Basin, arid northwestern China Pujia Yu a, b, c, Hailiang Xu a,⁎, Shiwei Liu a, b, Mu Qiao a, Qingqing Zhang a, Hongyan An a, Jinyi Fu a a b c
State Key Laboratory of Desert and Oasis Ecology, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi 830011, China Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Changchun 130012, PR China Fukang Station of Desert Ecology, Chinese Academy of Sciences, Urumqi 830011, PR China
a r t i c l e
i n f o
Article history: Received 20 June 2010 Received in revised form 2 March 2011 Accepted 4 June 2011 Keywords: Spatial distribution pattern Soil type Landscape index Manasi River Basin Soil map
a b s t r a c t Soil distribution pattern play a significant role in the stability conservation and economic development of oasis in arid regions. Hence, ecologists and agrology scientists have a central interest in understanding the spatial distribution changes of soil types. The aim of this study was to analyze the main processes of soil distribution pattern changes from 1987 to 2006 through the landscape indexes. Soil types and soil distribution pattern changes were assessed and compared by using two soil maps made in 1987 and 2006. 14 soil types were classified and analyzed in the study area. Results indicated many differences among the changes of different soil types. During the period from 1987 to 2006, there were widespread changes in spatial distribution of soil types in Manasi River Basin at class-level. The area of Petrocambids decreased, whereas Aquicambids increased. The small patches began to coalesce into large ones and the patch numbers decreased during the past 20 years, which brought about the fragmentation decrease in Manasi River Basin. In contrast to the decrease of the patch density, the average patch area of 12 soil types increased. With the increasing man-made disturbance, more soil type patches, especially the agricultural soil patches were close to square in shape. During the recent 20 years, the decreased patch shape indexes occupied about 57% of all while the increased patch shape indexes were over 40%. The split index of most soil types has also declined during the same period. The landscape-level indexes also reflected the spatial distribution changes of oasis soil types. The landscape diversity index and landscape evenness index have increased while the landscape dominance index has decreased in the recent 20 years, which showed that more equirotal soil patches were formed and various soil types dominated the soil landscape in Manasi River Basin. Changes of different soil types are one of major indictors to show environment changes and impacts of human activities. Therefore, it is necessary to emphasize the study of soil type changes in the arid and semiarid region. © 2011 Elsevier B.V. All rights reserved.
1. Introduction For centuries, human have been altering the Earth's surface to produce food through agricultural activities. In most regions, these changes are thought to be driven by socioeconomic factors and environment change (Forman, 1995; Fu et al., 2006). Changes in Earth's surface or removal of natural vegetation have a drastic effect on the physical, chemical, and biological properties of soil and hence change the quality of soil (Kaleem Abbasi et al., 2007). In recent decades, the changes of land-use and land-cover have appeared all over the world (Guo et al., 2008; López et al., 2010; Martinez-Montoya et al., 2010). The changes of soil quality lead to the changes of soil type and spatial distribution pattern. Soil change is a long-standing environmental issue in academic world. Discussing the mechanism ⁎ Corresponding author at: 818 South Beijing Road, Urumqi 830011, Xinjiang, PR China. Tel.: + 86 0991 7885418; fax: + 86 0991 7885320. E-mail address: [email protected] (H. Xu). 0341-8162/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.catena.2011.06.001
of soil type changes is conducive to understanding of the environment and land use change. As a major issue concerning environmental change, soil change has recently received a wide attention (Fairhead and Scoones, 2005; Wang et al., 2007). Soil type change, which is associated with the long-term changes of ecosystem functions, changes physical structure and chemical component of soil, reduces soil nutrients, land productivity, and biodiversity, and diminishes economic viability (Abbasi and Rasool, 2005; Melegy, 2005; Rasiah and Kay, 1995; Sahani and Behera, 2001). The previous studies on soil showed the limited concern to the changes of soil type and the spatial distribution pattern (Kaleem Abbasi et al., 2007; Rozhkov, 2009). There are many soil types in a region, whereas each soil type contains a great deal of patches. Landscape ecology provides an integrated approach in studying the spatial distribution pattern changes of the regional soil types. Various landscape indices (Baker and Cai, 1992; Jaeger, 2000; Wu, 2000) can be used to describe the spatial distribution pattern of soil types characteristically. Soil structure and composition is evolving continuously in space and time. Soil
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distribution pattern impacts the physical, chemical, and biological processes of soil. Therefore soil type change is incompatible with sustainable development, and it is necessary to evaluate it on regional scale. Oasis is the unique intrazonal landscape in arid and semi-arid regions all over the world. In China, it is mainly distributed in desert of the northwest arid climate area (Pan and Chao, 2003). There are two opposite processes in oases evolution in arid and semi-arid regions: one is oasification, and another is desertification (Jia et al., 2004). Desert–oasis ecotone is an interaction area between desert and oasis ecosystems, and plays an important role in arid region (Wang et al., 2007). Xinjiang of China, an extremely arid region, is located in the middle of Eurasia. The specific morphologic character that two basins (Junggar Basin and Tarim Basin) lie among the three mountains (Altay Mountain, Tianshan Mountain and Kunlun Mountain) developed oases. The study area, Manasi River Basin, is a typical region in Xinjiang because the oasis here is one of the largest areas for agriculture and one of highly developed regions for industry (Yu et al., 2010a,b). In addition, it is a focus region of human activities, so it is the representative place in exploring the soil spatial distribution change. In this exploratory study, on basis of two maps of soil type in the study area (1987 and 2006), the spatial distribution pattern change of soil types was analyzed. This report is the continuation of our previous study (Yu et al., 2010a,b), in which the same study area was sampled just once in a year. Such studies will help to show how to control the soil type changes. Moreover, the analysis on changes of soil spatial distribution pattern can provide decisions and policy-making processes at regional and national levels. 2. Materials and methods 2.1. Study area The study area (latitudes 46°00′ ~ 44°00′N and longitudes 84°30′ ~ 86°30′E) is located in the northern piedmont of Tianshan Mountains, Xinjiang, arid northwestern China, with total area of 22,301 km 2 (Fig. 1). Its southern boundary is the eastern Tianshan Mountains and its north adjoins the Gurbantunggut Desert. The general topography of Manasi River Basin is that the southern is higher than the northern part. The highest elevation is up to 5243 m in the study area. Relying on the water supply from Manasi River Basin, the oases, showing zonal and patchy in distribution are spread over the piedmont alluvial-pluvial fan, alluvial fan marginal belt, and alluvial plain (Liu et al., 2009). The climate of the study area belongs to the temperate continental arid climate. The annual and daily temperature changes are great. The mean annual temperature is 6.5 °C, and the annual average precipitation and potential average evaporation are 170 mm and 1800 mm respectively. The water resources in Manasi River Basin are abundant with the total amount of 2.6 × 10 9 m 3 (Liu et al., 2009). There are five rivers in this area, which are Taxi river, Manasi river, Ningjia river, Jingou river, and Bayingou river. Most regions of the study area are relatively flat, and the soil potential for agriculture is great. Soil types mainly include Aquicambids, Halaquepts, and Ustipsamments (Table 1). Crops grown well on the cultivated lands including corn (Zea may L.), wheat (Triticum spp.) and cotton (Gossypium hirsutum L.). Formerly, the natural landscapes were covered by types of desert grasslands, saline or alkaline lands, but the surface landscapes have been transformed to oasis landscapes since 1949. From 1989 to 2005, the cropland area increased rapidly, which had expanded 8.9% of the total study area (Li et al., 2008). 2.2. Data sources and research method A GIS database was developed to study the structure, spatial patterns and changes of soil type in Manasi River Basin. The soil type
Fig. 1. Location map of study area in arid northwestern China.
maps were provided by the National Key Technology Program “Study on Ecology—economic Regionalization and Ecological Compensation in the South of Junggar Basin” (a project studying the structure of ecology–economic system, the principles and references of regionalization, and the grade of ecological security in Manasi River Basin, Xinjiang). The original soil map of 1987 was designed by Fan and Hou (1995), which was a product of Second National Soil Survey of China. These soil type data were generated by automated scanning of the soil maps and manual digitization. The soil map of 2006 was designed by Xu, Fan, Qiao and Yu, which was a product of the National Key Technology Program “Study on Ecology—economic Regionalization and Ecological Compensation in the South of Junggar Basin”. The map is a newly created digital version of Manasi River Basin. More information of the map can be gained by the references of Yu et al. (2010a,b). The scales of the two soil maps (1987 and 2006) were 1:100,000. Based on these soil type data, the soil type maps (the shape file) of Manasi River Basin were compiled and used to analysis the changes among 20 years (Fig. 2). The soil classification used for the two maps was the Chinese Genetic Soil Classification System and translated into US Soil Taxonomy according to the China Soil Scientific Database (http://www.soil.csdb.cn) and the references of Shi et al. (2004, 2006 and 2010). There are 7292 soil profiles collected throughout China in the China Soil Scientific Database. The soil profile attributes are used as the initial link between Chinese Genetic Soil Classification System and US Soil Taxonomy. The basic attributes for each soil profile are composed of descriptive and quantitative data, recorded in thematic sections. One section lists classification (soil order, suborder, great group, subgroup, family and series), geographic Table 1 Soil types in study area. Code
Soil type
Code
Soil type
11 21 23 24 32 41 61
Aquicambids Anthracambids Haplocambids Halaquepts Plaggepts Xerumbrepts Aquisalids
64 71 72 81 82 83 91
Haplosalids Petrocalcids Petrocambids Ustipsamments Xeropsamments Ustifluvents Other types
P. Yu et al. / Catena 87 (2011) 253–259
255
Fig. 2. Soil type maps of 1987 and 2006.
2.3. Landscape index Studying the theory and methodology of landscape structure quantification and landscape index application is important in landscape ecology research (Guo et al., 2008). Lots of landscape indexes have been developed during the last decades (Bu et al., 2005; Frohn, 1998; Turner and Gardner, 1991). With the view of quantifying the spatial distribution pattern changes of oasis soil types, a series of landscape indexes were calculated at both class level and landscape level by using GIS software (Table 2). They included the mean patch area (MPS), patch density(PD), mean patch shape index(MSI), and split index(S) at the class level, largest patch index(LPI), landscape diversity index(H), landscape evenness index(E), and landscape dominance index(D) at landscape level. 3. Results and discussion 3.1. The area of each soil type The characteristics of soil types around Manasi River Basin are shown in Fig. 3. Xeropsamments was the dominant soil type,
accounted for 23.73% in 1987 and 24.44% in 2006. Haplocambids was the secondary soil type with the proportion of 15.5% in 1987 and 16.19% in 2006. Plaggepts, Xerumbrepts, Haplosalids and Ustifluvents were relatively rare in the study area. Compared with 1987, there were smaller changes in the area of soil types in the past 20 years. The area of Petrocambids decreased from 2907.98 to 2110.93 km 2, whereas the area of Aquicambids increased from 2351.38 to 2766.66 km 2 during the same period. The process of soil type changes was complex and indigestible. Simplifications are needed in studying the soil type changes. Comparative correlations of soil and land use bring about a visual Table 2 Description of landscape pattern indices used in the soil spatial distribution pattern analysis. Landscape index
Calculation
Mean patch area (MPS) Patch density (PD):
MPS = PD = m
Mean patch shape index (MSI) Split index (S)
Largest patch index (LPI)
Range MPS ≥ 0, without limit
A N
N A n
∑ ∑
0:25pij pffiffiffiffi
S=
1 2
PD ≥ 0, without limit
,
aij
i=1 j=1
N
qffiffiffiffiffiffiffiffi n i A
=
distribution, major soil properties, profile characteristics and production capacity (Shi et al., 2010). A group of experienced pedologists consulted the US soil classification again in order to make sure that the translate procedure can be used by us. The version of US Soil Taxonomy used in these maps was the Soil Survey Staff (1992). According to the American Soil Taxonomy, the soil of the study area was classified into 14 soil types (Table 1). GIS is a powerful tool to collect, store, extract, transform, and display spatial data, which are necessary to the data use and the study of the landscape dynamic changes (Guo et al., 2008).The area measurements of soil types were carried out by using the ArcView GIS version 3.3 (Li et al., 2008). In order to define the transition of soil types and the spatial pattern in the study area, the ArcGIS software and its spatial analysis module of Arcmap were used in the analysis procedure.
rffiffiffiffiffiffiffiffiffi . A i
LPI = Maxða1 ;⋯;an Þ
A
H = − ∑ ðPi Þ lnðPi Þ E=
H
i=1
=H max Þ × 100% m
D = H max + ∑ ðpi Þ lnðPi Þ i=1
S ≥ 0, without limit
A
m
Landscape diversity index (H) Landscape evenness index (E) Landscape dominance index (D)
MSI ≥ 1, without limit
100 ≥ LPI ≥ 0 H ≥ 0, without limit 1≥E≥0 D ≥ 0, without limit
Note: A, the total area of the soil type; N, total number of soil type patches; Pi, probability of the ith soil type in the total area; m, total number of soil types in the area; Hmax = ln(m); p, perimeter of each patch; a, area of each patch; pij, probability of the jth patch belong to the total ith landscape area; aij, area of the jth patch belong to the ith landscape; ni, total number of patches in the ith soil type; Ai, total area of patches in the ith soil type.
P. Yu et al. / Catena 87 (2011) 253–259
6000
measure the fragmentation degree of each soil type, which is determined by both the number and the total area of the soil type. Smallest value of the average patch area and largest value of patch density indicate that the fragmentation degree of this soil type is great or there are more patches of same soil type per square kilometer. Significant difference of the average patch areas appeared in different soil types. Xeropsamments had the biggest average patch area with the value of 170.69 km 2 in 1987. The second was Petrocalcids, followed by Aquisalids, Other types and Anthracambids. Halaquepts, Xerumbrepts and Haplosalids had the smallest average patch area, with the value of 3.06 km 2, 2.64 km 2, and 2.67 km 2. In 2006, Xeropsamments, served as the landscape matrix, still had the biggest average patch area. Anthracambids was the second, followed by the Petrocalcids, Petrocambids and Haplocambids. The average patch area of Xerumbrepts and Haplosalids was on the increase in 2006. Additionally, Halaquepts still had the average patch area in 2006, which almost unchanged during the period. From 1987 to 2006, the average patch area of 12 soil types increased, while 2 soil types decreased, which indicated that the fragmentation degrees of 12 soil types was higher and 2 soil types were lower. The average patch area of Xeropsamments rises from 170.69 km 2 to 495.56 km 2, while the patch density decreased from 0.006 to 0.002. These changes reflected a decline of fragmentation degree in landscape matrix. There were similar changes in properties of Anthracambids, Haplosalids, and so on. Contrary to the Xeropsamments and Anthracambids, the value of average patch area of Aquisalids decreased from 50.94 km 2 to 28.28 km 2. During the same period, the value of patch density increased from 0.02 to 0.137, reflecting a rise of fragmentation degree in Aquisalids. There revealed numerous remarkable points in results of Table 3. The first point was the rapid increase of average patch area of Haplosalids, Xerumbrepts, and Anthracambids, which increased 2540%, 1025% and 581%, respectively. The second was the decline of patch density of Haplosalids, Xerumbrepts, and Aquicambids, which decreased 99.02%, 91.11%, and 85.32%, respectively. The third was the rapid increase of patch density of Aquisalids, which increased 0.117 or 598%. The average patch area of most soil types had an increasing trend between 1987 and 2006 except for some types such as Aquisalids. The results indicated that the small patches began to coalesce into large ones and the patch numbers decreased. The patches density of Anthracambids and Aquicambids decreased in 2006 result from the maturity of irrigation techniques, the popularization of mechanization and the population growth. The distribution of soil types became more aggregative during the past 20 years, which resulted in the fragmentation degree declining. The mean patch shape index indicates to what extent an isodiametric patch (square) contains most of the patch interiors (Forman and Godron, 1986). If the soil type patch is mainly the square
1987 2006
4000
3000
2000
1000
0 32
41
61
64
71
72
81
82
83
91
Soil type Fig. 3. The total area of each soil type in Manasi River Basin in 1987 and 2006.
overview of different landscapes (Mandera et al., 2010). Using the data of soil type distribution and GIS, we obtained the spatial distribution pattern information of oasis soil types in Manasi River Basin. GIS had been proved to be useful tools for indentifying geomorphologic process and environmental assessment (Guo et al., 2008). It was useful to identify the spatial distribution pattern and investigate the spatial changes of soil types. In continuous landscapes, soil and land use patterns have similar autocorrelation values (Mandera et al., 2010). Changes of different soil types were the major indicators to show the environmental changes. The human activities and natural changes were the main reasons for the soil type changes in this region. With the population growing in the study area (Fig. 4), the area of farmland and living space was on the rise (Fig. 4). The urban/build-up land area increased 0.6% during the 20 years, and the increase was related to population growth and improved quality of life. Furthermore, the grassland area decreased form 34.9% to 27.6% in 1987–2006 because of the unreasonable soil utilizations and population growth (Li et al., 2008). The changes of landscapes also leaded to the changes of soil types. The natural soil types (e.g. Anthracambids, Petrocambids) decreased and the Anthrosols soil types (Aquicambids, Haplocambids, Halaquepts, Xerumbrepts and Plaggepts) increased (Fig. 3). 3.2. Analysis of the class-level index Table 3 showed the landscape indices of each soil type in Manasi River Basin. The average patch area and the patch density are used to
110
Population
1850
Planting area
1800 1750
4
Population (10 )
105
1700 100
1650 1600
95
1550 1500
90
1450 1400
Year Fig. 4. Population and planting area in the study area during 1987–2006.
2006
2005
2004
2003
1 997
1 996
1 995
1 994
1 993
1 992
1 991
1 990
1 988
1 989
1 987
85 2002
24
2001
23
2000
21
1 999
11
1 998
The value of area(km2)
5000
Planting area (km2 )
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P. Yu et al. / Catena 87 (2011) 253–259 Table 3 The average patch area and patch density for each soil type in 1987 and 2006. Soil type
11 21 23 24 32 41 64 61 71 72 81 82 83 91
1987
2006
MPS (km2)
PD (number/km2)
MPS (km2)
PD (number/km2)
5.09 34.09 8.80 3.06 11.02 2.64 2.67 50.94 55.77 20.06 12.14 170.69 23.52 38.86
0.196 0.029 0.114 0.327 0.091 0.378 0.375 0.020 0.018 0.050 0.082 0.006 0.043 0.026
25.15 232.22 53.08 3.71 27.53 29.75 70.39 28.28 86.37 54.13 27.06 495.56 36.62 33.56
0.040 0.004 0.019 0.270 0.036 0.034 0.004 0.137 0.012 0.018 0.037 0.002 0.027 0.030
patch or less complexity, the value of the mean patch shape index will be small. The more the value of patch shape index deviates from 1, the more the patches deviate from the square patch. In 1987, the values of the mean patch shape index were from 1.38 to 3.54 (Fig. 5). The maximum was found in Ustifluvents, followed by Haplosalids, Anthracambids, and Xeropsamments, which meant that the shape of these soil types was most complex in all soil types. The minimum was found in Plaggepts, followed by Other types and Xerumbrepts. These values implied that the patches of Plaggepts, Other types, and Xerumbrepts were significantly dominated by lots of regular patches. In 2006, the values of the mean patch shape index were from 1.43 to 3.16. The largest value was still found in Ustifluvents, followed by Xeropsamments, Petrocambids and Petrocalcids, but the smallest value changed to other types. Form 1987 to 2006, the decreased patch shape indexes occupied about 57% of all soil types while the increased patch shape indexes were over 40% (Fig. 5). The soil type in rapid increase was Xeropsamments, which had expanded 0.79 or 35.02%. The second was the Xerumbrepts, which had expanded 0.43 or 28.74%. It indicated that the soil types were more complex in 2006. During the same time, some soil types became simple. There was a significant decrease from 2.32 to 1.90 in the value of Anthracambids. So did Anthracambids in Haplosalids, Ustifluvents, Aquisalids and so on. These results showed the typical characteristics of agricultural oasis evolvement.
257
In the recent decades, the economic conditions improved dramatically in the study area. The gross output value of industry and agriculture had reached 140.6 × 10 8 in 2006, 15 times as much as that in 1987. With the agricultural activities becoming more purposeful and mature, the shape of irrigated farmland became more regular; the patch area was much bigger, and thus the value of mean shape index was on the decrease. Compared with 1987, the mean shape index of 6 soil types decreased in 2006, which showed that the shape of these soil types became simple during the recent 20 years. The split index represents the degree of isolation in landscape spatial distribution. There were significant differences in split indexes of different soil types in 1987–2006. In 1987, the values of the split index were from 0.08 to 5.29 (Fig. 6). This meant that the degrees of isolation in different soil types were variable. The largest value of split index was found in Haplosalids, followed by Xerumbrepts, Halaquepts, Plaggepts and so on. However, the maximum was the Aquisalids, followed by Halaquepts in 2006. In 2006, the degrees of isolation of different soil types became smaller. The values of the split index were from 0.05 to 1.84. Some findings could be gained from the results (Fig. 6). Firstly, there was a significant decrease from 5.29 to 0.10 in the value of Haplosalids and from 2.96 to 0.76 in Xerumbrepts in 2006 in contrast to 1987. So did Xerumbrepts in Plaggepts, decreasing from 2.26 to 0.96, and Halaquepts decreased from 2.35 to 1.68. The second finding was the rapid increase of Xerumbrepts, the value of which had increased 1.63 or 795.24%, it meant that the human disturbances was increasingly prominent during the past 20 years. The split index analyses indicated that the small patches coalesced into larger ones in the study area, but that there appeared the interspersion of opposing soil types in some area. The Haplosalids and Xerumbrepts patches coalesced into the fewer but larger patches. The patches of Aquicambids, Anthracambids, Haplocambids, and Halaquepts had the same change trend. The reason was that these soil types, supporting crops planting, were more integrated and connective in 2006. This phenomenon reflected the influence of population growth (Fig. 4) and the land policy shift. The patches of some types like Aquisalids were separated from other soil type patches or distributed sporadically among other soil type patches, which leaded to the spilt index increase. 3.3. Analysis of the landscape-level index Results of the landscape-level indexes reflected the spatial distribution pattern changes of oasis soil types in Manasi River
4.0 5.50
1987 2006 5.25
3.0
The spilt index
The patchshape index
3.5
1987 2006
2.5
2.0
5.00 2.5 2.0 1.5
1.5
1.0 0.5
1.0 11 21 23 24 32 41 61 64 71 72 81 82 83 91
soil
0.0 11 21 23 24 32 41 61 64 71 72 81 82 83 91
soil type Fig. 5. The mean patch shape index of each soil type in Manasi River Basin in 1987 and 2006.
Fig. 6. The split index of each soil type in Manasi River Basin in 1987 and 2006.
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P. Yu et al. / Catena 87 (2011) 253–259
Table 4 The landscape-level index of the study area in 1987 and 2006. Year
H
E
D
PD (number/km2)
MPS (km2)
LPI (%)
1987 2006
2.126 2.220
0.886 0.926
0.272 0.178
0.066 0.022
15.233 44.603
9.480 10.210
Basin (Table 4). The variation of landscape-level indexes was quite remarkable in Manasi River Basin during the study period. The landscape diversity index is used to measure the patch diversity of the given landscape structure, which is determined by both the number and the proportional area distribution of different patch types. The landscape diversity index was 2.216 in 1987 and 2.220 in 2006 in the study area. It implied that the patch diversity of the area was relatively low during the past 20 years. The landscape diversity index of the study area was low both in 1987 and 2006, but it had a slightly increasing trend as the result of the increasingly intensive human disturbances. Both the landscape dominance index and the landscape evenness index are calculated to decide the extent to which one or a few soil patch types dominated the landscape structure. High values of the landscape dominance index indicated that the local landscapes were dominated by one or few soil types in study area, and a value close to 0 showed that different soil types have equivalent overages. When the value of landscape dominance index was over 0.70, the landscape was dominated by few soil types (Hulshoff, 1995). The value of landscape evenness index was high with value of 0.886 in 1987 and 0.926 in 2006. By contrast, the landscape dominance index was relatively low with the value of 0.272 in 1987 and 0.178 in 2006. The value of the landscape dominance index decreased 0.094 or 34.56%, which meant that more equirotal soil patches were formed during the past 20 years, and some soil types (e.g., Xeropsamments, Haplocambids, Anthracambids and Petrocambids) dominated the soil landscape in the study area. The patch density at the landscape level was used to describe the extent to which the landscape is fragmented. The values of PD in the study area were 0.066 in 1987 and 0.022 in 2006, respectively. The values were relatively lower and indicated that the landscape fragmentation was not serious during the past 20 years. Table 4 showed that the value of the mean patch shape index and the largest patch index, which were also used to describe the degree of landscape fragmentation, was on the rise from 1987 to 2006, which also indicated that the soil landscape fragmentation of the study area was less serious. Previous researches had found that the land use patterns depended on the local land use policy and natural condition, and in turn influence the biophysical and socioeconomic environment (Gonzalez-Abraham et al., 2007; Guo et al., 2008; Theobald et al., 1997). The above results showed the soil type change and indicated that the soil type changes have a close relationship with the local social and economic development. The study area, as a typical agricultural region, was facing some problems in soil use and management. Solving these problems will help to accelerate the sustainable development of the typical agricultural oasis. 4. Conclusions The oasis around Manasi River Basin is a significant ecosystem in the north of Xinjiang. In order to investigate the changes of spatial distribution pattern of oasis soil types in Manasi River Basin, a number of landscape metrics including the area, patch density, average patch area, mean patch shape index, split index, and landscape-level index are used frequently in the oasis research. A thorough comprehension of the historical soil type changes as well as the explicit spatial distribution pattern will be helpful to develop sustainable oasis management systems and preserve essential oasis functions. From 1987 to 2006, there are widespread changes in spatial distribution pattern of soil types took place in Manasi River Basin in
class-level index. Petrocambids decreased by 797.05 km 2, while Aquicambids increased by 415.28 km 2. According to the analysis of landscape indices, the fragmentation degree in Manasi River Basin was on the decline and the shape of artificial soil type patches became regular. The split index of most soil types have also decreased during the same time. The results indicated that those soil type patches were the agricultural soil patches primarily. The average patch area of most soil types increased and the patch density of most soil types decreased. It showed that the small patches had begun to coalesce into large ones and the patch numbers decreased. Due to increasing man-made disturbance, more soil type patches were nearly square in shape. From 1987 to 2006, the decreased patch shape indexes occupied about 57% of all while the increased patch shape indexes were over 40%. At landscape-level, the landscape-level indexes also reflected the spatial distribution changes of oasis soil types. The landscape diversity index and landscape evenness index had increased by 0.094 and 0.16, respectively. The landscape dominance index had decrease by 0.094 in the recent 20 years. It showed that more equirotal soil patches were formed and various soil types dominated the soil landscape in Manasi River Basin. Analyzing spatial patterns of landscape is the first step to understand the local ecological process. Therefore, what was discussed here provides an initial basis and guidelines for the further detailed analysis on these issues. Although the results implied the explicit spatial distribution and changes of soil types in Manasi River Basin, the particular driving force behind the soil type change was not analyzed in our study. The study area is an important region in the north of Xinjiang. Socio-economic and natural driving forces such as machinery, population, political decisions, precipitation and others may influence the soil type changes. Our future study will be directed towards the detection of the socio-economic and natural driving forces, which influence the soil type and spatial patterns changes in the Manasi River Basin.
Acknowledgments This study was supported by the National Basic Research Program of China (973 Program, 2009CB421102), National Natural Science Foundation of China (30600092,30970549,40971284) and National Key Technology Program (2007BAC17B01) of China.
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Catena j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / c a t e n a
Spatial distribution pattern changes of oasis soil types in Manasi River Basin, arid northwestern China Pujia Yu a, b, c, Hailiang Xu a,⁎, Shiwei Liu a, b, Mu Qiao a, Qingqing Zhang a, Hongyan An a, Jinyi Fu a a b c
State Key Laboratory of Desert and Oasis Ecology, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi 830011, China Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Changchun 130012, PR China Fukang Station of Desert Ecology, Chinese Academy of Sciences, Urumqi 830011, PR China
a r t i c l e
i n f o
Article history: Received 20 June 2010 Received in revised form 2 March 2011 Accepted 4 June 2011 Keywords: Spatial distribution pattern Soil type Landscape index Manasi River Basin Soil map
a b s t r a c t Soil distribution pattern play a significant role in the stability conservation and economic development of oasis in arid regions. Hence, ecologists and agrology scientists have a central interest in understanding the spatial distribution changes of soil types. The aim of this study was to analyze the main processes of soil distribution pattern changes from 1987 to 2006 through the landscape indexes. Soil types and soil distribution pattern changes were assessed and compared by using two soil maps made in 1987 and 2006. 14 soil types were classified and analyzed in the study area. Results indicated many differences among the changes of different soil types. During the period from 1987 to 2006, there were widespread changes in spatial distribution of soil types in Manasi River Basin at class-level. The area of Petrocambids decreased, whereas Aquicambids increased. The small patches began to coalesce into large ones and the patch numbers decreased during the past 20 years, which brought about the fragmentation decrease in Manasi River Basin. In contrast to the decrease of the patch density, the average patch area of 12 soil types increased. With the increasing man-made disturbance, more soil type patches, especially the agricultural soil patches were close to square in shape. During the recent 20 years, the decreased patch shape indexes occupied about 57% of all while the increased patch shape indexes were over 40%. The split index of most soil types has also declined during the same period. The landscape-level indexes also reflected the spatial distribution changes of oasis soil types. The landscape diversity index and landscape evenness index have increased while the landscape dominance index has decreased in the recent 20 years, which showed that more equirotal soil patches were formed and various soil types dominated the soil landscape in Manasi River Basin. Changes of different soil types are one of major indictors to show environment changes and impacts of human activities. Therefore, it is necessary to emphasize the study of soil type changes in the arid and semiarid region. © 2011 Elsevier B.V. All rights reserved.
1. Introduction For centuries, human have been altering the Earth's surface to produce food through agricultural activities. In most regions, these changes are thought to be driven by socioeconomic factors and environment change (Forman, 1995; Fu et al., 2006). Changes in Earth's surface or removal of natural vegetation have a drastic effect on the physical, chemical, and biological properties of soil and hence change the quality of soil (Kaleem Abbasi et al., 2007). In recent decades, the changes of land-use and land-cover have appeared all over the world (Guo et al., 2008; López et al., 2010; Martinez-Montoya et al., 2010). The changes of soil quality lead to the changes of soil type and spatial distribution pattern. Soil change is a long-standing environmental issue in academic world. Discussing the mechanism ⁎ Corresponding author at: 818 South Beijing Road, Urumqi 830011, Xinjiang, PR China. Tel.: + 86 0991 7885418; fax: + 86 0991 7885320. E-mail address: [email protected] (H. Xu). 0341-8162/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.catena.2011.06.001
of soil type changes is conducive to understanding of the environment and land use change. As a major issue concerning environmental change, soil change has recently received a wide attention (Fairhead and Scoones, 2005; Wang et al., 2007). Soil type change, which is associated with the long-term changes of ecosystem functions, changes physical structure and chemical component of soil, reduces soil nutrients, land productivity, and biodiversity, and diminishes economic viability (Abbasi and Rasool, 2005; Melegy, 2005; Rasiah and Kay, 1995; Sahani and Behera, 2001). The previous studies on soil showed the limited concern to the changes of soil type and the spatial distribution pattern (Kaleem Abbasi et al., 2007; Rozhkov, 2009). There are many soil types in a region, whereas each soil type contains a great deal of patches. Landscape ecology provides an integrated approach in studying the spatial distribution pattern changes of the regional soil types. Various landscape indices (Baker and Cai, 1992; Jaeger, 2000; Wu, 2000) can be used to describe the spatial distribution pattern of soil types characteristically. Soil structure and composition is evolving continuously in space and time. Soil
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distribution pattern impacts the physical, chemical, and biological processes of soil. Therefore soil type change is incompatible with sustainable development, and it is necessary to evaluate it on regional scale. Oasis is the unique intrazonal landscape in arid and semi-arid regions all over the world. In China, it is mainly distributed in desert of the northwest arid climate area (Pan and Chao, 2003). There are two opposite processes in oases evolution in arid and semi-arid regions: one is oasification, and another is desertification (Jia et al., 2004). Desert–oasis ecotone is an interaction area between desert and oasis ecosystems, and plays an important role in arid region (Wang et al., 2007). Xinjiang of China, an extremely arid region, is located in the middle of Eurasia. The specific morphologic character that two basins (Junggar Basin and Tarim Basin) lie among the three mountains (Altay Mountain, Tianshan Mountain and Kunlun Mountain) developed oases. The study area, Manasi River Basin, is a typical region in Xinjiang because the oasis here is one of the largest areas for agriculture and one of highly developed regions for industry (Yu et al., 2010a,b). In addition, it is a focus region of human activities, so it is the representative place in exploring the soil spatial distribution change. In this exploratory study, on basis of two maps of soil type in the study area (1987 and 2006), the spatial distribution pattern change of soil types was analyzed. This report is the continuation of our previous study (Yu et al., 2010a,b), in which the same study area was sampled just once in a year. Such studies will help to show how to control the soil type changes. Moreover, the analysis on changes of soil spatial distribution pattern can provide decisions and policy-making processes at regional and national levels. 2. Materials and methods 2.1. Study area The study area (latitudes 46°00′ ~ 44°00′N and longitudes 84°30′ ~ 86°30′E) is located in the northern piedmont of Tianshan Mountains, Xinjiang, arid northwestern China, with total area of 22,301 km 2 (Fig. 1). Its southern boundary is the eastern Tianshan Mountains and its north adjoins the Gurbantunggut Desert. The general topography of Manasi River Basin is that the southern is higher than the northern part. The highest elevation is up to 5243 m in the study area. Relying on the water supply from Manasi River Basin, the oases, showing zonal and patchy in distribution are spread over the piedmont alluvial-pluvial fan, alluvial fan marginal belt, and alluvial plain (Liu et al., 2009). The climate of the study area belongs to the temperate continental arid climate. The annual and daily temperature changes are great. The mean annual temperature is 6.5 °C, and the annual average precipitation and potential average evaporation are 170 mm and 1800 mm respectively. The water resources in Manasi River Basin are abundant with the total amount of 2.6 × 10 9 m 3 (Liu et al., 2009). There are five rivers in this area, which are Taxi river, Manasi river, Ningjia river, Jingou river, and Bayingou river. Most regions of the study area are relatively flat, and the soil potential for agriculture is great. Soil types mainly include Aquicambids, Halaquepts, and Ustipsamments (Table 1). Crops grown well on the cultivated lands including corn (Zea may L.), wheat (Triticum spp.) and cotton (Gossypium hirsutum L.). Formerly, the natural landscapes were covered by types of desert grasslands, saline or alkaline lands, but the surface landscapes have been transformed to oasis landscapes since 1949. From 1989 to 2005, the cropland area increased rapidly, which had expanded 8.9% of the total study area (Li et al., 2008). 2.2. Data sources and research method A GIS database was developed to study the structure, spatial patterns and changes of soil type in Manasi River Basin. The soil type
Fig. 1. Location map of study area in arid northwestern China.
maps were provided by the National Key Technology Program “Study on Ecology—economic Regionalization and Ecological Compensation in the South of Junggar Basin” (a project studying the structure of ecology–economic system, the principles and references of regionalization, and the grade of ecological security in Manasi River Basin, Xinjiang). The original soil map of 1987 was designed by Fan and Hou (1995), which was a product of Second National Soil Survey of China. These soil type data were generated by automated scanning of the soil maps and manual digitization. The soil map of 2006 was designed by Xu, Fan, Qiao and Yu, which was a product of the National Key Technology Program “Study on Ecology—economic Regionalization and Ecological Compensation in the South of Junggar Basin”. The map is a newly created digital version of Manasi River Basin. More information of the map can be gained by the references of Yu et al. (2010a,b). The scales of the two soil maps (1987 and 2006) were 1:100,000. Based on these soil type data, the soil type maps (the shape file) of Manasi River Basin were compiled and used to analysis the changes among 20 years (Fig. 2). The soil classification used for the two maps was the Chinese Genetic Soil Classification System and translated into US Soil Taxonomy according to the China Soil Scientific Database (http://www.soil.csdb.cn) and the references of Shi et al. (2004, 2006 and 2010). There are 7292 soil profiles collected throughout China in the China Soil Scientific Database. The soil profile attributes are used as the initial link between Chinese Genetic Soil Classification System and US Soil Taxonomy. The basic attributes for each soil profile are composed of descriptive and quantitative data, recorded in thematic sections. One section lists classification (soil order, suborder, great group, subgroup, family and series), geographic Table 1 Soil types in study area. Code
Soil type
Code
Soil type
11 21 23 24 32 41 61
Aquicambids Anthracambids Haplocambids Halaquepts Plaggepts Xerumbrepts Aquisalids
64 71 72 81 82 83 91
Haplosalids Petrocalcids Petrocambids Ustipsamments Xeropsamments Ustifluvents Other types
P. Yu et al. / Catena 87 (2011) 253–259
255
Fig. 2. Soil type maps of 1987 and 2006.
2.3. Landscape index Studying the theory and methodology of landscape structure quantification and landscape index application is important in landscape ecology research (Guo et al., 2008). Lots of landscape indexes have been developed during the last decades (Bu et al., 2005; Frohn, 1998; Turner and Gardner, 1991). With the view of quantifying the spatial distribution pattern changes of oasis soil types, a series of landscape indexes were calculated at both class level and landscape level by using GIS software (Table 2). They included the mean patch area (MPS), patch density(PD), mean patch shape index(MSI), and split index(S) at the class level, largest patch index(LPI), landscape diversity index(H), landscape evenness index(E), and landscape dominance index(D) at landscape level. 3. Results and discussion 3.1. The area of each soil type The characteristics of soil types around Manasi River Basin are shown in Fig. 3. Xeropsamments was the dominant soil type,
accounted for 23.73% in 1987 and 24.44% in 2006. Haplocambids was the secondary soil type with the proportion of 15.5% in 1987 and 16.19% in 2006. Plaggepts, Xerumbrepts, Haplosalids and Ustifluvents were relatively rare in the study area. Compared with 1987, there were smaller changes in the area of soil types in the past 20 years. The area of Petrocambids decreased from 2907.98 to 2110.93 km 2, whereas the area of Aquicambids increased from 2351.38 to 2766.66 km 2 during the same period. The process of soil type changes was complex and indigestible. Simplifications are needed in studying the soil type changes. Comparative correlations of soil and land use bring about a visual Table 2 Description of landscape pattern indices used in the soil spatial distribution pattern analysis. Landscape index
Calculation
Mean patch area (MPS) Patch density (PD):
MPS = PD = m
Mean patch shape index (MSI) Split index (S)
Largest patch index (LPI)
Range MPS ≥ 0, without limit
A N
N A n
∑ ∑
0:25pij pffiffiffiffi
S=
1 2
PD ≥ 0, without limit
,
aij
i=1 j=1
N
qffiffiffiffiffiffiffiffi n i A
=
distribution, major soil properties, profile characteristics and production capacity (Shi et al., 2010). A group of experienced pedologists consulted the US soil classification again in order to make sure that the translate procedure can be used by us. The version of US Soil Taxonomy used in these maps was the Soil Survey Staff (1992). According to the American Soil Taxonomy, the soil of the study area was classified into 14 soil types (Table 1). GIS is a powerful tool to collect, store, extract, transform, and display spatial data, which are necessary to the data use and the study of the landscape dynamic changes (Guo et al., 2008).The area measurements of soil types were carried out by using the ArcView GIS version 3.3 (Li et al., 2008). In order to define the transition of soil types and the spatial pattern in the study area, the ArcGIS software and its spatial analysis module of Arcmap were used in the analysis procedure.
rffiffiffiffiffiffiffiffiffi . A i
LPI = Maxða1 ;⋯;an Þ
A
H = − ∑ ðPi Þ lnðPi Þ E=
H
i=1
=H max Þ × 100% m
D = H max + ∑ ðpi Þ lnðPi Þ i=1
S ≥ 0, without limit
A
m
Landscape diversity index (H) Landscape evenness index (E) Landscape dominance index (D)
MSI ≥ 1, without limit
100 ≥ LPI ≥ 0 H ≥ 0, without limit 1≥E≥0 D ≥ 0, without limit
Note: A, the total area of the soil type; N, total number of soil type patches; Pi, probability of the ith soil type in the total area; m, total number of soil types in the area; Hmax = ln(m); p, perimeter of each patch; a, area of each patch; pij, probability of the jth patch belong to the total ith landscape area; aij, area of the jth patch belong to the ith landscape; ni, total number of patches in the ith soil type; Ai, total area of patches in the ith soil type.
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6000
measure the fragmentation degree of each soil type, which is determined by both the number and the total area of the soil type. Smallest value of the average patch area and largest value of patch density indicate that the fragmentation degree of this soil type is great or there are more patches of same soil type per square kilometer. Significant difference of the average patch areas appeared in different soil types. Xeropsamments had the biggest average patch area with the value of 170.69 km 2 in 1987. The second was Petrocalcids, followed by Aquisalids, Other types and Anthracambids. Halaquepts, Xerumbrepts and Haplosalids had the smallest average patch area, with the value of 3.06 km 2, 2.64 km 2, and 2.67 km 2. In 2006, Xeropsamments, served as the landscape matrix, still had the biggest average patch area. Anthracambids was the second, followed by the Petrocalcids, Petrocambids and Haplocambids. The average patch area of Xerumbrepts and Haplosalids was on the increase in 2006. Additionally, Halaquepts still had the average patch area in 2006, which almost unchanged during the period. From 1987 to 2006, the average patch area of 12 soil types increased, while 2 soil types decreased, which indicated that the fragmentation degrees of 12 soil types was higher and 2 soil types were lower. The average patch area of Xeropsamments rises from 170.69 km 2 to 495.56 km 2, while the patch density decreased from 0.006 to 0.002. These changes reflected a decline of fragmentation degree in landscape matrix. There were similar changes in properties of Anthracambids, Haplosalids, and so on. Contrary to the Xeropsamments and Anthracambids, the value of average patch area of Aquisalids decreased from 50.94 km 2 to 28.28 km 2. During the same period, the value of patch density increased from 0.02 to 0.137, reflecting a rise of fragmentation degree in Aquisalids. There revealed numerous remarkable points in results of Table 3. The first point was the rapid increase of average patch area of Haplosalids, Xerumbrepts, and Anthracambids, which increased 2540%, 1025% and 581%, respectively. The second was the decline of patch density of Haplosalids, Xerumbrepts, and Aquicambids, which decreased 99.02%, 91.11%, and 85.32%, respectively. The third was the rapid increase of patch density of Aquisalids, which increased 0.117 or 598%. The average patch area of most soil types had an increasing trend between 1987 and 2006 except for some types such as Aquisalids. The results indicated that the small patches began to coalesce into large ones and the patch numbers decreased. The patches density of Anthracambids and Aquicambids decreased in 2006 result from the maturity of irrigation techniques, the popularization of mechanization and the population growth. The distribution of soil types became more aggregative during the past 20 years, which resulted in the fragmentation degree declining. The mean patch shape index indicates to what extent an isodiametric patch (square) contains most of the patch interiors (Forman and Godron, 1986). If the soil type patch is mainly the square
1987 2006
4000
3000
2000
1000
0 32
41
61
64
71
72
81
82
83
91
Soil type Fig. 3. The total area of each soil type in Manasi River Basin in 1987 and 2006.
overview of different landscapes (Mandera et al., 2010). Using the data of soil type distribution and GIS, we obtained the spatial distribution pattern information of oasis soil types in Manasi River Basin. GIS had been proved to be useful tools for indentifying geomorphologic process and environmental assessment (Guo et al., 2008). It was useful to identify the spatial distribution pattern and investigate the spatial changes of soil types. In continuous landscapes, soil and land use patterns have similar autocorrelation values (Mandera et al., 2010). Changes of different soil types were the major indicators to show the environmental changes. The human activities and natural changes were the main reasons for the soil type changes in this region. With the population growing in the study area (Fig. 4), the area of farmland and living space was on the rise (Fig. 4). The urban/build-up land area increased 0.6% during the 20 years, and the increase was related to population growth and improved quality of life. Furthermore, the grassland area decreased form 34.9% to 27.6% in 1987–2006 because of the unreasonable soil utilizations and population growth (Li et al., 2008). The changes of landscapes also leaded to the changes of soil types. The natural soil types (e.g. Anthracambids, Petrocambids) decreased and the Anthrosols soil types (Aquicambids, Haplocambids, Halaquepts, Xerumbrepts and Plaggepts) increased (Fig. 3). 3.2. Analysis of the class-level index Table 3 showed the landscape indices of each soil type in Manasi River Basin. The average patch area and the patch density are used to
110
Population
1850
Planting area
1800 1750
4
Population (10 )
105
1700 100
1650 1600
95
1550 1500
90
1450 1400
Year Fig. 4. Population and planting area in the study area during 1987–2006.
2006
2005
2004
2003
1 997
1 996
1 995
1 994
1 993
1 992
1 991
1 990
1 988
1 989
1 987
85 2002
24
2001
23
2000
21
1 999
11
1 998
The value of area(km2)
5000
Planting area (km2 )
256
P. Yu et al. / Catena 87 (2011) 253–259 Table 3 The average patch area and patch density for each soil type in 1987 and 2006. Soil type
11 21 23 24 32 41 64 61 71 72 81 82 83 91
1987
2006
MPS (km2)
PD (number/km2)
MPS (km2)
PD (number/km2)
5.09 34.09 8.80 3.06 11.02 2.64 2.67 50.94 55.77 20.06 12.14 170.69 23.52 38.86
0.196 0.029 0.114 0.327 0.091 0.378 0.375 0.020 0.018 0.050 0.082 0.006 0.043 0.026
25.15 232.22 53.08 3.71 27.53 29.75 70.39 28.28 86.37 54.13 27.06 495.56 36.62 33.56
0.040 0.004 0.019 0.270 0.036 0.034 0.004 0.137 0.012 0.018 0.037 0.002 0.027 0.030
patch or less complexity, the value of the mean patch shape index will be small. The more the value of patch shape index deviates from 1, the more the patches deviate from the square patch. In 1987, the values of the mean patch shape index were from 1.38 to 3.54 (Fig. 5). The maximum was found in Ustifluvents, followed by Haplosalids, Anthracambids, and Xeropsamments, which meant that the shape of these soil types was most complex in all soil types. The minimum was found in Plaggepts, followed by Other types and Xerumbrepts. These values implied that the patches of Plaggepts, Other types, and Xerumbrepts were significantly dominated by lots of regular patches. In 2006, the values of the mean patch shape index were from 1.43 to 3.16. The largest value was still found in Ustifluvents, followed by Xeropsamments, Petrocambids and Petrocalcids, but the smallest value changed to other types. Form 1987 to 2006, the decreased patch shape indexes occupied about 57% of all soil types while the increased patch shape indexes were over 40% (Fig. 5). The soil type in rapid increase was Xeropsamments, which had expanded 0.79 or 35.02%. The second was the Xerumbrepts, which had expanded 0.43 or 28.74%. It indicated that the soil types were more complex in 2006. During the same time, some soil types became simple. There was a significant decrease from 2.32 to 1.90 in the value of Anthracambids. So did Anthracambids in Haplosalids, Ustifluvents, Aquisalids and so on. These results showed the typical characteristics of agricultural oasis evolvement.
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In the recent decades, the economic conditions improved dramatically in the study area. The gross output value of industry and agriculture had reached 140.6 × 10 8 in 2006, 15 times as much as that in 1987. With the agricultural activities becoming more purposeful and mature, the shape of irrigated farmland became more regular; the patch area was much bigger, and thus the value of mean shape index was on the decrease. Compared with 1987, the mean shape index of 6 soil types decreased in 2006, which showed that the shape of these soil types became simple during the recent 20 years. The split index represents the degree of isolation in landscape spatial distribution. There were significant differences in split indexes of different soil types in 1987–2006. In 1987, the values of the split index were from 0.08 to 5.29 (Fig. 6). This meant that the degrees of isolation in different soil types were variable. The largest value of split index was found in Haplosalids, followed by Xerumbrepts, Halaquepts, Plaggepts and so on. However, the maximum was the Aquisalids, followed by Halaquepts in 2006. In 2006, the degrees of isolation of different soil types became smaller. The values of the split index were from 0.05 to 1.84. Some findings could be gained from the results (Fig. 6). Firstly, there was a significant decrease from 5.29 to 0.10 in the value of Haplosalids and from 2.96 to 0.76 in Xerumbrepts in 2006 in contrast to 1987. So did Xerumbrepts in Plaggepts, decreasing from 2.26 to 0.96, and Halaquepts decreased from 2.35 to 1.68. The second finding was the rapid increase of Xerumbrepts, the value of which had increased 1.63 or 795.24%, it meant that the human disturbances was increasingly prominent during the past 20 years. The split index analyses indicated that the small patches coalesced into larger ones in the study area, but that there appeared the interspersion of opposing soil types in some area. The Haplosalids and Xerumbrepts patches coalesced into the fewer but larger patches. The patches of Aquicambids, Anthracambids, Haplocambids, and Halaquepts had the same change trend. The reason was that these soil types, supporting crops planting, were more integrated and connective in 2006. This phenomenon reflected the influence of population growth (Fig. 4) and the land policy shift. The patches of some types like Aquisalids were separated from other soil type patches or distributed sporadically among other soil type patches, which leaded to the spilt index increase. 3.3. Analysis of the landscape-level index Results of the landscape-level indexes reflected the spatial distribution pattern changes of oasis soil types in Manasi River
4.0 5.50
1987 2006 5.25
3.0
The spilt index
The patchshape index
3.5
1987 2006
2.5
2.0
5.00 2.5 2.0 1.5
1.5
1.0 0.5
1.0 11 21 23 24 32 41 61 64 71 72 81 82 83 91
soil
0.0 11 21 23 24 32 41 61 64 71 72 81 82 83 91
soil type Fig. 5. The mean patch shape index of each soil type in Manasi River Basin in 1987 and 2006.
Fig. 6. The split index of each soil type in Manasi River Basin in 1987 and 2006.
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Table 4 The landscape-level index of the study area in 1987 and 2006. Year
H
E
D
PD (number/km2)
MPS (km2)
LPI (%)
1987 2006
2.126 2.220
0.886 0.926
0.272 0.178
0.066 0.022
15.233 44.603
9.480 10.210
Basin (Table 4). The variation of landscape-level indexes was quite remarkable in Manasi River Basin during the study period. The landscape diversity index is used to measure the patch diversity of the given landscape structure, which is determined by both the number and the proportional area distribution of different patch types. The landscape diversity index was 2.216 in 1987 and 2.220 in 2006 in the study area. It implied that the patch diversity of the area was relatively low during the past 20 years. The landscape diversity index of the study area was low both in 1987 and 2006, but it had a slightly increasing trend as the result of the increasingly intensive human disturbances. Both the landscape dominance index and the landscape evenness index are calculated to decide the extent to which one or a few soil patch types dominated the landscape structure. High values of the landscape dominance index indicated that the local landscapes were dominated by one or few soil types in study area, and a value close to 0 showed that different soil types have equivalent overages. When the value of landscape dominance index was over 0.70, the landscape was dominated by few soil types (Hulshoff, 1995). The value of landscape evenness index was high with value of 0.886 in 1987 and 0.926 in 2006. By contrast, the landscape dominance index was relatively low with the value of 0.272 in 1987 and 0.178 in 2006. The value of the landscape dominance index decreased 0.094 or 34.56%, which meant that more equirotal soil patches were formed during the past 20 years, and some soil types (e.g., Xeropsamments, Haplocambids, Anthracambids and Petrocambids) dominated the soil landscape in the study area. The patch density at the landscape level was used to describe the extent to which the landscape is fragmented. The values of PD in the study area were 0.066 in 1987 and 0.022 in 2006, respectively. The values were relatively lower and indicated that the landscape fragmentation was not serious during the past 20 years. Table 4 showed that the value of the mean patch shape index and the largest patch index, which were also used to describe the degree of landscape fragmentation, was on the rise from 1987 to 2006, which also indicated that the soil landscape fragmentation of the study area was less serious. Previous researches had found that the land use patterns depended on the local land use policy and natural condition, and in turn influence the biophysical and socioeconomic environment (Gonzalez-Abraham et al., 2007; Guo et al., 2008; Theobald et al., 1997). The above results showed the soil type change and indicated that the soil type changes have a close relationship with the local social and economic development. The study area, as a typical agricultural region, was facing some problems in soil use and management. Solving these problems will help to accelerate the sustainable development of the typical agricultural oasis. 4. Conclusions The oasis around Manasi River Basin is a significant ecosystem in the north of Xinjiang. In order to investigate the changes of spatial distribution pattern of oasis soil types in Manasi River Basin, a number of landscape metrics including the area, patch density, average patch area, mean patch shape index, split index, and landscape-level index are used frequently in the oasis research. A thorough comprehension of the historical soil type changes as well as the explicit spatial distribution pattern will be helpful to develop sustainable oasis management systems and preserve essential oasis functions. From 1987 to 2006, there are widespread changes in spatial distribution pattern of soil types took place in Manasi River Basin in
class-level index. Petrocambids decreased by 797.05 km 2, while Aquicambids increased by 415.28 km 2. According to the analysis of landscape indices, the fragmentation degree in Manasi River Basin was on the decline and the shape of artificial soil type patches became regular. The split index of most soil types have also decreased during the same time. The results indicated that those soil type patches were the agricultural soil patches primarily. The average patch area of most soil types increased and the patch density of most soil types decreased. It showed that the small patches had begun to coalesce into large ones and the patch numbers decreased. Due to increasing man-made disturbance, more soil type patches were nearly square in shape. From 1987 to 2006, the decreased patch shape indexes occupied about 57% of all while the increased patch shape indexes were over 40%. At landscape-level, the landscape-level indexes also reflected the spatial distribution changes of oasis soil types. The landscape diversity index and landscape evenness index had increased by 0.094 and 0.16, respectively. The landscape dominance index had decrease by 0.094 in the recent 20 years. It showed that more equirotal soil patches were formed and various soil types dominated the soil landscape in Manasi River Basin. Analyzing spatial patterns of landscape is the first step to understand the local ecological process. Therefore, what was discussed here provides an initial basis and guidelines for the further detailed analysis on these issues. Although the results implied the explicit spatial distribution and changes of soil types in Manasi River Basin, the particular driving force behind the soil type change was not analyzed in our study. The study area is an important region in the north of Xinjiang. Socio-economic and natural driving forces such as machinery, population, political decisions, precipitation and others may influence the soil type changes. Our future study will be directed towards the detection of the socio-economic and natural driving forces, which influence the soil type and spatial patterns changes in the Manasi River Basin.
Acknowledgments This study was supported by the National Basic Research Program of China (973 Program, 2009CB421102), National Natural Science Foundation of China (30600092,30970549,40971284) and National Key Technology Program (2007BAC17B01) of China.
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