Spatial heterogeneity of urban land-cover landscape in Guangzhou from 1990 to 2005

Transcription

1 J. Geogr. Sci. (2009) 19: DOI: /s y 2009 Science in China Press Springer-Verlag Spatial heterogeneity of urban land-cover landscape in Guangzhou from 1990 to 2005 GONG Jianzhou 1,2, LIU Yansui 2, XIA Beicheng 3 1. School of Geographical Sciences, Guangzhou University, Guangzhou , China; 2. Institute of Geographic Sciences and Natural Resources Research, CAS, Beijing , China; 3. School of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou , China Abstract: Urbanization has been the most important process that changed land cover landscape in Guangzhou since reformation, especially since It is essential for monitoring and assessing ecological consequences of urbanization to understand landscape quantitative characteristics and its changes. Based on four land-cover type maps interpreted from remote sensing TM images of 1990, 1995, 2000 and 2005, combining gradient analysis with landscape metrics, the quantified spatial pattern and its dynamics of urbanization in Guangzhou was got. Three landscape metrics were computed within different regional areas including the whole study area, two transects along two highways (one N S and the other W E) and radiation zones with equal distance outwards the city center were set. Buffer zones for transects N S and W E were outlined along highways. The following questions should be answered in this paper: What responses were implied with changing spatial grain size or extent for landscape pattern analysis? Could gradient progress of urbanization be characterized by landscape pattern analysis? Did landscape metrics reveal urban expanding gradually? Were there directional differences in land cover landscape pattern during urbanizing development? The results gave some affirmative answers. Landscape pattern exhibited obviously scale-dependent to grain size and extent. The landscape metrics with gradient analysis could quantitatively approach spatial pattern of urbanization. A precise location for urbanized area, like city center and sub-center, could be identified by multiple landscape metrics. Multiple adjunctive centers occurred as indicated by analysis of radiation zones around the city center. Directional differences of landscape pattern along the two transects (N S and W E) came into being. For example, fragmentation of landscape in the transect W E was obviously higher than that in the transect N S. All in all, some interesting and important ecological implications were revealed under landscape patterns of two transects or radiation zones, and that was the important step to link pattern with processes in urban ecological studies and the basis to improve urban environment. Keywords: spatial heterogeneity; land-cover landscape; scale; Guangzhou Received: Accepted: Foundation: National Natural Science Foundation of China, No ; Guangzhou Science & Technology Program, No.08C027 Author: Gong Jianzhou (1970 ), Postdoctoral, specialized in the study of environmental ecology and management, 3S application. gongjzh66@126.com

2 214 Journal of Geographical Sciences 1 Introduction Urban land cover is the most prominent landscape on the earth surface influenced by human activities. Not only the macroscopic change in land use and pattern caused by urbanization could be recorded objectively, but also its location and time (spatial and temporal), i.e., where/when changes occurred could be reproduced by studying land use cover change (LUCC) (Liu et al., 2008; He et al., 2005). Remote sensing data and GIS technology have become the most important methodology. LUCC affects directly eco-system, such as system structure and function. Some inherent relationships in ecosystem could not be characterized by land cover landscape expression. The essential concept about ecosystem and landscape is spatial heterogeneity or spatial distribution. Besides spatial characteristics, landscape pattern also has temporal characteristics, and generally dynamics is used. It is very important to realize that urbanization can not be suspended and ecosystem structure and function could be improved by controlling change of regional earth surface or land cover. So the methodology of landscape pattern analysis will be a basic or prerequisite tool to interpret and control the changing speed of earth surface. Landscapes are often spatial heterogeneous (Liu et al., 2002), while spatial heterogeneity is ubiquitous across all scales and forms the fundamental basis of the structure and function of landscapes (Luck et al., 2002). In physical meaning, heterogeneity must be scale-dependant. Thus, to get a better understanding of regional landscape needs an appropriate scale, and the scale also regards to landscape structure and function. As we know, landscape pattern responds scale changing in a range. What is the range? Is there a threshold scale for a certain landscape case? What is the most appropriate scale for the study? Urbanization has been the most important process of land cover change (Darla et al., 2005) and would be even more significant with the majority of the world s population swarming into cities (Zhang, 2004). This process, in turn, has profoundly changed the structure and function of urban ecosystems (Yu et al., 2007). And always, with different factors or locations during different development periods, urban landscape showed temporal-spatial heterogeneity. To understand how urban landscapes affect, and are affected by, biophysical and socioeconomic activities, their spatial heterogeneity will be helpful, and the quantified heterogeneity could reveal more characteristics deeply in academy. Some researches had revealed that spatial heterogeneity was scale-dependent (Wu et al., 2004, Gong et al., 2006). So further study should consider setting baseline to interpret scale-dependent and make the research reliable, such as change of landscape patterns with scale. The scale in ecological field is important but very complicated. In many research projects it was ignored or purposefully avoided, and then mentioned lightly that the scale should be understood. It is obvious that all ecological phenomena take place spatially in heterogeneous environments with a series of scales and that the relationship between subjects and their environment is the very subject of ecology (Wu et al., 2000). Here a detailed discussion about scale was performed for exploring the landscape heterogeneity in Guangzhou, the study area of the paper. Gradient analysis is a useful tool to understand vegetation change under some environmental variables spatially and temporally. Some researchers found inter-landscape in the space of suburbs, between urban and rural areas, such as Joshua (2000), Luck (2002), Zhang

3 GONG Jianzhou et al.: Spatial heterogeneity of urban land-cover landscape in Guangzhou 215 et al. (2004), Yu et al. (2007), and so on. Forman et al. (1986) postulated that patch characteristics exhibit generally predictable patterns along a landscape modification gradient. Zhang (2004) demonstrated that the center and spatial pattern of urbanization could be quantified by using the combined method of landscape metrics and gradient analysis. In this field, gradient analysis of urban land cover became a preferred method that could reveal spatial heterogeneity of urban landscape recommended by most of the landscape ecologists. Highways are the important corridors in urban areas, and the results disturbed directly by human activities. Also highways could indicate social and economic development. Correspondingly, highways must affect some land cover types of landscape patches and urban population aggregation, called corridor effects by scholars (Liu et al., 2000, Zhu et al., 2006, Zong et al., 1999). The gradient landscape characteristics have been developing along highways, too. In this study, four land cover maps, interpreted from four Landsat TM images, 1990, 1995, 2000 and 2005, were used as the original analysis data. Grain size and extent were factors to affect landscape pattern and characteristics, hence defining appropriate grain size is very important to explore urban landscape characteristics ecologically. So, analysis of scale-dependent was designed firstly in the paper. Then, two transects were set on each map respectively, one is the North South directional Jing Zhu Highway, the other is the West East directional Guang Yuan Thruway, together with radiation zones cutting away from city center towards peripheral areas. Gradient analysis in the following sections could quantitatively characterize regional spatial heterogeneity and developmental dynamics of the metropolis of Guangzhou. All were assumed to address the following questions: (1) What were the characteristics of landscape change of land cover along highway or the radiation zones? (2) Could urbanization gradients be detected by using landscape pattern analysis? (3) Could urban center or sub-centers be detected by landscape pattern metrics? (4) Was landscape metrics analysis an adaptable method for landscape pattern? 2 Study area Guangzhou, the biggest city and economic, political and cultural center of South China, is located at the center of the Pearl River Delta, lying between 22º26 23º56 N and 112º57 114º3 E and covering approximately an area of km 2 (Figure 1). Guangzhou is characterized by southern subtropical monsoon climate, with an average annual temperature of The topography is characterized by mountains and hills in north or northeast, basin and alluvial plain in south or southwest. Historically, that is before 2005, the administrative division of Guangzhou was composed of ten districts and two counties, including Fangcun district, Liwan district, Yuexue district, Dongshan district, Haizhu district, Tianhe district, Huangpu district, Baiyun district, Panyu district, Huadu district, Conghua county and Zengcheng county. After 2005, the districts were adjusted slightly and one new district was set within the Huangpu and Baiyun districts. For data consistency. this paper still adopted the old administrative division scheme, which could not affect the study results.

4 216 Journal of Geographical Sciences Figure 1 Landscape maps showing two transects and radiation zones series for gradient analysis of landscape patterns in Guangzhou 3 Data and methods 3.1 Data and data processing The basic data used in this study included: (1) remote sensing data, including four Landsat Thematic Mapper (TM) images taken on , , and , respectively, and WRS =122/ The nominal resolution was 25 m; (2) a topographic map of 1984, compiled by the Guangzhou Institute of Surveying and Drawing (1:50,000); and (3) an auxiliary zoning scheme map of 2000 of Guangzhou. The processing procedure of source data was as follows: (1) To derive land cover maps from TM data by user-computer interactive interpreting method and make field survey to check some points in the field and on maps. Eight land cover types were classified, and the accuracy of land cover classification was reported as 76.1%. (2) To unify the geo-reference. Coordinate system is Universe Transverse Mercatol Projection (UTM) with original longitude 117ºE, original latitude 0ºN, WGS84 geodetic datum and WGS84 ellipsoid. (3) To split maps of each year into map sets of different areas, with rectangular equal-area analysis units. All vectors were converted to grids, with a pixel of m 2 using buffer technology. Data were compiled using Arc/Info, Erdas Image 8.6 and Arcview Analysis of map compilation and landscape metrics calculation In this paper, grain size and extent were emphasized to analyze scale response. To understand response of landscape characteristics to grain size and extent change, land cover type map of 2005 was analyzed. When the extent was kept the same as the original data sets, the

5 GONG Jianzhou et al.: Spatial heterogeneity of urban land-cover landscape in Guangzhou 217 grain size was systematically changed from 1 1 to 20 20, 30 30, and pixels for creating different landscapes, respectively. The resampling rule for the majority was followed, which was so far one of the most popular methods for data resampling in ecology and remote sensing (Wu, 2004). That was to say, a new aggregated areal unit was assigned to the patch type that was most dominant among others. Note that the aggregation at each successive grain size started still at original data (1 1). This might be the independent aggregation scheme (Wu et al., 2002), which compiled new maps directly aggregating the original data set, instead of using a cumulative procedure that might introduce more errors. To study response of landscape to the changing extent, a rectangle landscape was cut first in the center of Guangzhou. It was a sample range with the largest area where could be created, an area of 1632 by 1693 pixels, signed 1700 (Figure 1). It could be nested with a series of rectangles from one apex of the rectangle and along the diagonal to S E apex. Secondly, choosing the N W apex of the rectangle and taking 100 pixels as an increment to create new rectangle from the start apex. Then a series of rectangles were followed: , ,, , and To detect the direction differentiation of land cover landscape pattern, two transects, along west east (W E) and south north (S N), were set to study landscape patterns. The two transects were across Guangzhou at city center. The W E transect was along Guang Yuan Thruway, and the N S transect was along Jing Zhu Highway. Both had the same width of 10 km (Figure 1b), while cutting landscape maps were complied by using buffer technology. All images of four years were performed with the same processing and analyzing procedures. As Figure 1b shows, the controlled stations along the S N transect included the northern border of Jing Zhu Highway, southward to Tuhua crossroad, and to Longxue Island as the southern end. Accordingly, from east to west, the controlled stations were Shizijiao, where it is near the border, westward along Guangyuan Expressway to Guangyuan Dong Road, to Guangyuan Zhong Road, to Huancheng Highway, then to Xunfengzhou where it is the western end. Both transects intercrossed at Tangxiazhan. Based also on buffer technology, the gradient characteristics of land cover landscape pattern were detected, and the city area, enclosed by highway, was considered as urban core area, the first radiation zone (signed 1). Then, a series of radiation zones of land cover type maps were cut from core towards peripheries in the study area, and their radiation zones were marked with serial numbers, such as 1, 2, 3, and so on, from core towards periphery orderly. The responses of gradient change of landscape patterns were analyzed by comparing all of those radiation zones. The core area of Guangzhou was enclosed interiorly by Huancheng Highway, and separated the whole area into two parts, i.e., northern part and southern part. The numbers of southern serial radiation zones was 0 15, while the northern was 0 22, and both series of zones are departed from the fifth radiation zone (Figure 1a). Based on maps set by the above steps, three landscape metrics, including patch density (PD), mean fractal metrics (FRAC_MN) and Shannon s diversity metrics (SHDI), had been got. The landscape pattern analysis package, FRAGSTATS (Landscape Ecology Program, 2008), was used to compute the landscapes metrics at landscape level for the above maps, including scale effect in the study area, the landscape patterns in the whole area, in the two highway zone landscapes and radiative transect landscapes away.

6 218 Journal of Geographical Sciences 4 Results and discussion 4.1 Effects of grain size on landscape metrics Generally, a significant effect on values of landscape metrics should occur when grain size was changed (Gong et al., 2006). The magnitude and pattern of these responses varied always with metrics and landscapes. The effects of changing grain size of the metrics selected exhibited the following characteristics as shown in Figure 2. All three metrics showed scale-dependent, but the responses have different intensities with the increase of grain size. The total tendency of the three metrics was decreasing with the increase of grain size, except PD in small grain size. However, the ranges of variation of different metrics in value differ obviously, such as PD decreased sharply from the above 1.2 to almost zero approaching, whereas FRAC_MN and SHDI declined slightly, indicating different aspects of landscape pattern differ from each other at distinctive grain size. Besides, PD increased at first till the gain was up to 3, but declined rapidly (almost linearly) as grain size increased constantly. The curves showed jump points at grain size 20 for metrics PD and SHDI. Generally it is called threshold. Many researches relative to scale reported that the threshold should be avoided when a general result was analyzed. In this study, a basic grain size 1 pixel (1 1) was chosen. So no threshold response would occur in the following analysis. 4.2 Effects of extent on landscape metrics Effects of extent on landscape pattern analysis have been ignored for a long time, particularly, in gradient or heterogeneity analysis. Generally, the changing extent also has significant influence on the values of landscape metrics. Extent is an absolute spatial concept, and its variation should be variable. The effect maybe hides under some other relative or non-relative phenomenon. But we are not aware of doing any study on effects of changing extent or avoid purposely scale effect. Actually, an appropriate extent could be helpful to get a proper or accurate result, and even avoid subjectivity. Similar to the case of grain size change, the responses of landscape metrics to extent change could also be different from metrics. Metrics PD greatly decreased with the increase of extent (Figure 3). It declined rapidly at first with the extent of 100 to 400. SHDI showed a complex track line, increasing Figure 2 Response curves of landscape index to changing grain size in 2005 Figure 3 Response curves of landscape index to changing extent in 2005

7 GONG Jianzhou et al.: Spatial heterogeneity of urban land-cover landscape in Guangzhou 219 with the increase of extent when extent was less than 400, and fluctuating with the increase of extent when extent was greater than 400. FRAC_MN was almost constant under different extents, without response to extent change. Obviously, the three metrics approached three parallel and stable levels when the extent was bigger than The curves of metrics PD and SHDI showed an important extent 400. PD declined sharply before extent 400, and declined slowly after extent 400. SHDI increased before extent 400, and decreased or fluctuated after extent 400. It is distinctly evident that there was a threshold extent for these metrics in this study area. The above results revealed that changing extent significantly affect the values of landscapes metrics, extent 400 might be a sensitive one for the characteristics of landscape patterns in the study area. It is worth noting that the result of the following analysis can avoid consciously the corresponding sensitive area of 140 km 2. In other words, the scale consideration of the paper for gradient analysis was designed and sensitive extent was avoided, based on this procedure, the corresponding results might be reliable. 4.3 General characteristics of land cover change For the total landscape pattern, the dynamics of three metrics were compared covering 4 years of the study period (Figure 4). The metrics FRAC_MN was constant throughout the study period. This means that shape of the urban landscape was not so prominent. The metrics PD and SHDI had an ascending period, but the periodicity differed from each other. PD ascended from 1990 to 2000, and SHDI ascended from 1990 to They could interpret that land use cover change would be damaged in this period. An increasing PD showed that many large patches would be fragmentized, and an increasing SHDI meant that continuous and similar-neighboring patches would be deducted in a landscape system. All the results showed that the landscape approached a stable stage in recent years. We can find that three metrics were basically smooth (Figure 4). Even in PD and Figure 4 Curves of landscape index in Guangzhou SHDI ascending periods, the increasing part was only a small portion of the metric values. It may tell us that landscape in Guangzhou was elementarily balanced. 4.4 Direction differentiation of land cover heterogeneity Two transects, one N S and the other W E, were set to study directional differentiation. Three metrics used in the study were calculated based on 4-year remote sensing images and the results were listed in Table 1. The data indicated how the values of landscapes metrics differed from two different directions and periods of time. Values of PD in S N transect were obviously less than that in W E transect. This meant that there were more patches in a unit area in W E transect than in N S transect, indicating that urbanization was more developed in W E transect. Considering the changing rates, PD values (Table 1) were 15.49% 9.61% 1.89% at N S transect landscape, while 4%

8 220 Journal of Geographical Sciences Table 1 Dynamics of landscape characteristics of land-cover along transects in two directions in Guangzhou, PD PRAC_MN SHDI PD FRAC_MN SHDI PD FRAC_MN SHDI PD FRAC_MN SHDI N S W E Note: N S indicates transect landscape from south to north; and W E indicates transect landscape from east to west. 0.39% 14.05% at W E transect landscape. The results showed landscape fragmentation in S N transect were highly significant during 1990 to 1995 and 1995 to 2000, while the landscape fragmentation suspended and the PD value went down during 2000 to But a reverse result appeared in W E transect. Especially, from 2000 to 2005, a fast landscape fragmentation occurred. It was true that just within the period, Guangzhou made a new plan to build new towns in the eastern part. Besides the main industries were concentrated there, a new district, Luogang, was established in 2005, and it was arranged to make preparations in a few years before The situation of PD was coincident with the actual facts of Guangzhou urban development distribution, key area of industrial development of Guangzhou lies in the eastern, such as new economic development zone of Huangpu district. FRAC_MN is a metric to describe mean shape complexity across a landscape. By viewing FRAC_MN values, the directional differentiation of landscape shapes was very weak, indicating urban landscapes tend to be simple for patch shape spatially. To quantify the distribution and configuration of all land cover types in two transects, SHDI value was considered. SHDI increased as the number of different patch types increased and/or the proportional distribution of area among patch types became more equitable, thus expressing the complexity of composition and configuration of a landscape. As shown in Table 1, it was clear that dynamics of SHDI value varied with direction. SHDI at S N increased at first, then decreased, and then increased again. But at the same time, SHDI at W E transect decreased monotonously. The decreasing SHDI meant that landscape patches were more similar with the neighboring patches under the situation that urbanization and landscape characteristics tended to be simpler. All these showed the urban development was different in the two transects. The built-up area took an increasing proportion year by year, such as at W E. The monotonously decreasing tendency of SHDI revealed that this is just the characteristics in the built-up area. It also meant that the municipal built-up area was almost the single dominant land cover type. Meanwhile, the attributes of transect landscapes could verify the changing characteristics further, for example, the percentages of the built-up area were 29.92%, 41.71%, 46.82% and 48.33%, respectively, corresponding to four years of 1990, 1995, 2000 and The two transects implied many characteristics, such as being similar to the above mentioned or some being functional, such as corridor. City expressway and highway could be used to study urban landscapes with buffer technology. 4.5 Gradient of land cover outwards The three metrics varied spatially in different radiation zones (buffer zone) (Figure 5). It also revealed differentiation in different directions.

9 GONG Jianzhou et al.: Spatial heterogeneity of urban land-cover landscape in Guangzhou 221 Figure 5 Changes of landscape indices along the buffer zones in different directions Buffer zones (indicating the numbers away the urban core zone marked 1, 2, ) North indicating the northern radiation transect area and South the southern transect area as shown in Figure 1a (1) PD PD had a similar gradient tendency at two directions southwards and northwards. The values of metrics went down gradually from the city center to the peripheral suburban and rural areas. In four years the PD values were dynamical almost parallel in two directions outwards from the city center. It meant that fragmentation of landscape at two-direction landscapes had the same tendency temporally and spatially. Looking northwards, the metrics PD showed three peaks in buffer zones 7, 12 and 15 respectively, where there was strong fragmentation of landscape. And similarly southwards, there were two peaks in buffer zones 8 and 12 respectively. Checking the location of those buffer zones, buffer zones 7 and 12 northwards was crossing Huadu and Conghua districts, respectively. Buffer zone 8 southwards was crossing Nansha Economic Development District. All those increasing PD at each buffer zone indicated high fragmentation of landscape. This result implied that some sub-centers had occurred outside the city center of Guangzhou. A proposal should be raised to improve the status of over aggregating in the old city center. A multi-center pattern had already formed and it could be detected by gradient analysis method under 3S technology. Besides the above characteristics, valleys of PD curves were also clearly identified in some protective zones, where landscape was in an original state, at buffer zones northwards and southwards. Correspondingly, those northern zones were distributed

10 222 Journal of Geographical Sciences in forest areas and those in southern zones were located nearby the estuary of the Pearl River, respectively. Comparing temporally, the changing PD curves were relatively similar and consistent. In 2000, the peak values out of the city center were much higher than that of the other three years. This meant that the period around 2000 or was the key period for establishing the sub-centers. Huadu, Conghua and Zengcheng districts had got a rapid development during the period But in contrast with the zone number, relatively stable peak values extending southward or northward by one zone from each other among four years, might indicate urbanization direction and speed. Another characteristic of PD curves showed a warning signal. It is the end part of PD curve of 2005 that presented an increasing trend compared with the other years. This information must be paid much attention for protecting both the northern and southern parts of Guangzhou, where there exist some landscapes undisturbed or disturbed lightly. (2) FRAC_MN The metrics FRAC_MN was nearly approaching constant in different periods of time and in different radiation zones except in buffer zones northwards and buffer zones southwards. In the zones southwards, the southern end located in the estuary of the Pearl River where landscape was mainly sea water body or wetland artificially enclosed, and the northern end was in forest area where there was a big reservoir named Liuxihe. In those buffer zones the patch shape complexity of landscape might be simplified or complicated. In those zones of northern end it became more complicated, and in those zones of the southern end it became simplified. The results might hint the responses to borderlines between natural and artificial landscapes. For example, Nansha Port and Nansha Economic Development District started to be developed after 2000, so in buffer zone 14 southwards there were the lowest FRAC_MN metrics because the landscape was mainly sea water body or simple inning mound. (3) SHDI The diversity of landscape, characterized by SHDI, is an important landscape characteristic. It implied diversities of landscape types, patch shape and patch number and their inlay pattern. There was a valley of SHDI in buffer zones 9 10 northwards, and also a similar valley of SHDI in buffer zones 6 7 southwards. Following this valley the SHDI decreased sharply both southwards and northwards for all four years. These two valleys were located between city center and the sub-centers. The first valley was just located between Baiyun District and Huadu and Conghua districts, and the second valley was located in Shawan Channel of Xijiang River, where it is the planned intergradation zone for New City of Guangzhou, such as Asian Game Village being built to the south of Shawan Channel. In the northern part of the zone the SHDI was gradually lower northwards starting from buffer zone 13 because of the forest, an absolutely dominant land cover type. A segment, which started from buffer zone 15 northwards, of SHDI curve of 2005 showed an exceptional tendency, which was separated upwards from other three curves of 1990, 1995 and It must be a strong warning to tell the landscape fragmentation in the northern part of Guangzhou, owing to the construction of the Jing Zhu Highway around The result indicated the increasingly intense human activities. The above results agreed with the anterior analysis for metrics PD. Those metrics mentioned above revealed that landscape of land cover change had multi-

11 GONG Jianzhou et al.: Spatial heterogeneity of urban land-cover landscape in Guangzhou 223 ple dimensional heterogeneities, and a joint use of different metrics could get more information from their dynamics. 5 Conclusions Global urbanization and a series of problems caused by urbanization have been regarded. To understand urban land use/cover changes and reveal the characteristics of urban landscape patterns would be helpful to resolve some problems ecologically. Statistical approach could be used to quantify landscape patterns, but the spatial characteristics of landscapes might be ignored. Some methodologies were developed to interpret structural characteristics of landscapes, such as landscape metrics (Wu, 2004). Spatial, temporal and digital characteristics are very complicated to be scale-dependent, which are important or even vital to the study effectively. However, it is very difficult to integrate those characteristics of landscape metrics and physical land use/cover change. Many literatures told us that the problems could be resolved by selecting appropriate metrics, choosing exact grain/extent for the study area and minimizing scale effects. The paper selected three landscape metrics, which were designed to give expression to fragmentation, shape and diversity. The changing grain size and extent were performed to analyze responses of landscape patterns to land use/cover change. The response to grain size existed throughout the study period, but it was different from metrics, such as PD was the most remarkable intensity to respond to scale, while FRAC_MN responded less intensely to scale. Meanwhile, a likely threshold of grain size presented at around 20 pixels, corresponding to 600 m. Similarly, extent change responded intensely to landscape patterns. Among those three metrics, PD was sensitive to extent, PD and SHDI showed a divergence at extent value 400 (an area about 144 km 2 ). It corroborated that landscape characteristics of urban land use/cover change were evidently scale-dependent and the heterogeneity was multiple dimensional, like spatial and temporal, being also responsive to scale. The results revealed that landscape patterns of land use/cover change in Guangzhou did not conspicuously fluctuate in the studying period of 1990 to Only curves of PD exhibited a relatively more changeable feature during 1990 to 1995, when the rapid development stage was in social economic, and urban aspects. Based on integrated gradient analysis of transect and radiation zone, different landscape metrics could describe multiple aspects of landscape patterns about urban development in Guangzhou. Firstly, transect analysis showed that the urban landscape pattern differed in west east or south north corridor in landscape fragmentation, shape and diversity, especially for metric PD. It was coincident with the actual facts of developmental pattern in Guangzhou. A new industrial district has been set up in the eastern part, Luogang, where the old industrial district Huangpu was located and being also close to the Economic Development District. Secondly, analysis of three landscape metrics detected a new pattern of urban landscape, i.e., multiple sub-centers around city center of Guangzhou. The multiple sub-centers were distributed in different districts, including Huadu, Conghua, Zengcheng and Panyu. It also revealed when these sub-centers occurred, such as Huadu district in , Conghua and Zengcheng districts in , and Panyu in This significantly implied 3S technology could be used to detect dynamics of urbanization spatially and temporally.

12 224 Journal of Geographical Sciences Thirdly, the metrics curves gave much information for understanding important characteristics of land use/cover change, such as the curve of metrics FRAC_MN in 2000 and 2005 fluttered from other curves. It was a warning signal indicating where intense human disturbance could occur. It showed the place was Nansha, where a new construction area for modern port and heavy industries had been planned and put into effect. The metrics SHDI in 2005 northwards exhibited an obvious divergence starting from buffer zone 14, suggesting increasing intensity of human activities, where forest was the main type of landscape and the best choice for reclaiming new land. More attention should be paid to this important landscape area. References Darla K M, Cynthia C, Abigail M Y, Land use policy and landscape fragmentation in an urbanizing region: Assessing the impact of zoning. Applied Geography, 25: Gong Jianzhou, Xia Beicheng, Effects of spatial grain size on landscape pattern of land-cover types in the rapidly urbanized region. Acta Ecologica Sinica, 26(7): (in Chinese) Gong Jianzhou, Xia Beicheng, Remote sensing estimation of vegetation coverage in Guangzhou based on the correction of atmospheric radiation. Chinese Journal of Applied Ecology, 18(3): (in Chinese) Gong Jianzhou, Xia Beicheng, Study on Urban Landscape Ecology and Eco security: A Case Study in Guangzhou. Beijing: Science Press, (in Chinese) He Chunyang, Li Jinggang, Wang Yuanyuan et al., Understanding cultivated land dynamics and its driving forces in northern China during Journal of Geographical Sciences, 15(4): (in Chinese) Joshua D G, Analysis of urban rural gradients using satellite data. A Dissertation for Doctor Degree. University of Washington, Landscape Ecology Program-fragstats downloads, Liu J G, William W T, Integrating Landscape Ecology into Natural Resource Management. Cambridge University Press, Liu Shenghe, Wu Chuanjun, Shen Hongquan, A GIS based model of urban land use growth in Beijing. Acta Geographica Sinica, 55(4): (in Chinese) Liu Yansui, Wang Lijuan, Long Hualou, Spatio-temporal analysis of land-use conversion in the eastern coastal China during Journal of Geographical Sciences, 18(3): Luck M, Wu J G, A gradient analysis of urban landscape pattern: A case study from the Phoenix metropolitan region, Arizona, USA. Landscape Ecology, 17 (4): Shi Peijun, Today and future of the dynamics of human earth (earth surface) system. Earth Science Frontiers, 4(1/2): (in Chinese) Wu J G, Effects of changing scale on landscape pattern analysis: Scaling relations. Landscape Ecology, 19: Wu J G, Dennis E J, Jelinski et al., Multiscale analysis of landscape: Scale variance and pattern metrics. Geographic Information Sciences, 6(1): Wu J G, Shen W J, Sun W Z et al., Empirical patterns of the effects of changing scale on landscape metrics. Landscape Ecology, 17: Yu X J, Ng C N, Spatial and temporal dynamics of urban sprawl along two urban rural transects: A case study of Guangzhou, China. Landscape and Urban Planning, 79(1): Zhang L Q, Wu J P, Zhen Y et al., A GIS-based gradient analysis of urban landscape pattern of Shanghai metropolitan area, China. Landscape and Urban Planning, 69: Zhu Jianjun, Cui Baoshan, Yao Huarong et al., Landuse changes and expansion effects caused by road construction in longitudinal range-gorge region. Journal of Natural Resources, 21(4): (in Chinese) Zong Yueguang, The corridor effects in urban ecological landscape planning: A case study on Beijing. Acta Ecologica Sinica, 1999, 19(2): (in Chinese)