Assessment of Land-Use/Cover Changes and Its Ecological Effect in Rapidly Urbanized Areas—Taking Pearl River Delta Urban Agglomeration as a Case

: Based on the land-use data of 2000 and 2015, this study makes a quantitative analysis of the ecological environment effect in Pearl River Delta using the ecological environment quality index and the ecological contribution rate of land-use change types. The results showed the following: (1) During 2000–2015, the land-use changes in Pearl River Delta mainly manifested in the reduction of cultivated land, forest land, water area, and unused land, while the area of construction land and grassland showed an increasing trend. The quality of ecological environment in the Pearl River Delta was largely stable but slightly declined overall; (2) Over the past 15 years, the comprehensive ecological environment index of the Pearl River Delta urban agglomeration has decreased by 0.02. With an average annual decrease of 0.11%. The spatial expansion caused by urbanization had the most profound impact on the decline of the ecological environment quality in the Pearl River Delta; (3) The eco-environmental quality indices of various cities in the Pearl River Delta declined to varying degrees. The city with the largest decline was Dongguan, followed by Shenzhen and Zhongshan. The spatial differentiation characteristics of the eco-environmental quality index indicate that the ecological quality preferences of cities distributed around the study area and close to the inland areas, while the ecological quality of the central coastal cities are biased. The quality of the ecological environment is related to the basis of the regional ecological environment. The research results have important practical signiﬁcance for maintaining regional ecological balance and promoting the sustainable use of land resources, and they provide a reference for the study of the ecological and environmental effects of land-use changes in key cities in economically developed areas.


Introduction
The ecological environment is the basic guarantee for human survival and the material basis for social development [1]. With the development of society, the relationship between human activities and the ecological environment has become increasingly close, which has caused great damage to the global ecosystem, and the ecological environment problems have become more and more serious [2,3]. In particular, the rapid development of urbanization in recent years has accelerated the damage caused to the surface environment by human activities, resulting in increasingly prominent urban ecological and environmental problems, which seriously threaten the urban ecological security [4,5]. Due to the changes in the ecological environment caused by the continuous advancement of the urbanization process, what methods should be used to dynamically monitor the ecological environment quality of the urban agglomeration area in a comprehensive, multiscale, and long-term

Data Sources
This study is based on the land-use data produced by the Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences. The obtained data were based on the interpretation of Landsat image data. After field verification, the classification accuracy is 87.94%, which meets the mapping requirements [30]. Land-use classification includes the first-level classification system (6 categories) and the secondlevel classification system (25 categories). The land-use types in the study area were merged and analyzed. The six types in the first-level classification (cultivated land, woodland, grassland, water area, construction land, and unused land in the first-level classification) were analyzed. Figure 2 presents the land-use classification map of the Pearl River Delta urban agglomeration based on the first-level classification system.

Data Sources
This study is based on the land-use data produced by the Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences. The obtained data were based on the interpretation of Landsat image data. After field verification, the classification accuracy is 87.94%, which meets the mapping requirements [30]. Land-use classification includes the first-level classification system (6 categories) and the second-level classification system (25 categories). The land-use types in the study area were merged and analyzed. The six types in the first-level classification (cultivated land, woodland, grassland, water area, construction land, and unused land in the first-level classification) were analyzed. Figure 2 presents the land-use classification map of the Pearl River Delta urban agglomeration based on the first-level classification system.

Analysis of the Land-Use Transfer Types
With the support of GIS, through spatial superposition of remote sensing images and land-use maps in different periods, the transfer matrix of land-use types was obtained, and then the process of land-use change was analyzed. In practical application, according to the principle of map algebra [31], for any two periods (k and k + 1), a land-use type map ( k i j A × and can be produced. The calculation formula for the land-use transfer matrix is then as follows: where i j C × is a land-use change map from k to k + 1; k i j A × is the land-use type map of period k; is a map of land-use types in the period k + 1; and i and j represent the different types of land use. When the values of i and j are in the range of 1-10, this formula can be used to calculate land-use transfer.

Ecological Quality Indicators of Land-Use Types
In this study, combined with expert scoring and analytic hierarchy process (AHP) and referring to the relevant domestic research, the ecological environment quality of land-use types under the second-level classification system was evaluated by using the fuzzy method. The results are shown in Table 1. Because the second-level classification

Analysis of the Land-Use Transfer Types
With the support of GIS, through spatial superposition of remote sensing images and land-use maps in different periods, the transfer matrix of land-use types was obtained, and then the process of land-use change was analyzed. In practical application, according to the principle of map algebra [31], for any two periods (k and k + 1), a land-use type map (A k i×j and A k+1 i×j ) can be produced. The calculation formula for the land-use transfer matrix is then as follows: where C i×j is a land-use change map from k to k + 1; A k i×j is the land-use type map of period k; A k+1 i ×j is a map of land-use types in the period k + 1; and i and j represent the different types of land use. When the values of i and j are in the range of 1-10, this formula can be used to calculate land-use transfer.

Ecological Quality Indicators of Land-Use Types
In this study, combined with expert scoring and analytic hierarchy process (AHP) and referring to the relevant domestic research, the ecological environment quality of landuse types under the second-level classification system was evaluated by using the fuzzy method. The results are shown in Table 1. Because the second-level classification system of land use has a high resolution and reflects clear ecological differences, the ecological environment quality of land-use types under the second-level classification system can be evaluated and combined with the types and processes of land-use change. By establishing Sustainability 2021, 13, 5075 5 of 16 the correlation between land-use/land cover and regional ecological environment quality, it is possible to quantitatively analyze the temporal and spatial variation characteristics of regional ecological environment quality by tracking changes in land-use types, quantities, and spatial characteristics.

Regional Eco-Environmental Quality Index
The overall situation of the ecological environment quality is quantitatively characterized through considering the ecological quality and area proportion of each land use in the region. It can be estimated as follows [32,33]: where EV t is the regional ecological environment quality index; LU i and C i are the area and eco-environmental indices of the i land-use types in the region during the t period, respectively; TA is the total area of the region; and N is the number of land-use types in the region.

Ecological Contribution Rate of Regional Land-Use Change Types
The ecological contribution rate refers to the change of regional ecological quality caused by the change of a land-use type and can be expressed as follows [20]: where LEI is the ecological contribution rate of land-use change type; LE t+1 and LE t reflect the ecological quality index of the initial and final stages of land-use change, respectively; LA is the change area of this type; and TA is the total area of the region.  Table 2 showed that in 2000, the order of land-use types in the Pearl River Delta was ranked according to the size of the area, which is consistent with the findings of 2015 (forest > cultivated land > construction land > water area > grassland > unused land). However, there was a clear expansion of construction land over the study period with an associated loss of cultivated land and forest. In the past 15 years, the land-use types in Pearl River Delta mainly depended on forest, cultivated land, construction land, and water areas, of which forest and cultivated land accounted for more than 25%. In particular, the area of forest was higher than 50%, indicating high forest cover in the Pearl River Delta. The proportion of unused land was less than 0.1%, the proportion of grassland was about 2%, and the area of construction land and water area was equivalent, accounting for about 7%.

Analysis of Land-Use Transfer Matrix
Using the spatial analysis function of GIS, the land-use data in 2000 and 2015 were analyzed by spatial overlay, and the land-use type change range (Table 3), spatial distribution map (Figure 3), and land-use type transfer matrix of the Pearl River Delta (Table 4)   Land-Use Cultivated Forest Grass-Water Construc-Unused Total   The area of cultivated land decreased significantly, from 14,343.63 km 2 in 2000 to 12,403.83 km 2 in 2015 ( Table 3). The cumulative reduction area was 1939.8 km 2 , which accounted for approximately 15.64% of the cultivated land in 2015.The main destinations for the transfer of cultivated land were construction land, water areas, and forest, for which the percentages of transfer were 11.66%, 1.49%, and 0.6% (Table 4), respectively. There was a clear urban expansion trend through the occupation of cultivated land in the suburban plain. A total of 213.15 km 2 of cultivated land was transferred to water areas because the phenomenon of reclaiming land from lakes changed to returning farmland to lakes. This shows that the policy of returning farmland to lakes in Guangdong province has achieved remarkable results.
The area of forest decreased considerably, with a total reduction of 846.11 km 2 (Table 3), which accounted for 2.9% of the forest land in the Pearl River Delta region. The main destinations for forest transfer were construction land and grassland, with transfer percentages of 2.72% and 0.49% (Table 4), respectively. Of the forests, 147.55 km 2 was degraded into grassland, indicating that there has been clear forest ecosystem damage in the Pearl River Delta region, which should be addressed.
The grassland area increased by 33.26 km 2 over the study period, accounting for 3.01% of the grassland ratio in 2015. The increase of grassland was mainly dependent on the conversion of construction land and forest land. The construction land transferred by 6.03%, and the forest transferred by 5.12%. The transfer of construction land to grassland is the embodiment of urban greening. The area under water bodies decreased over the study period. The water area reduced by 287.18 km 2 , which was 7.45% of the total water area in 2015. The main direction of water transfer is construction land, and the percentage of transfer was 12.32%.
Construction land showed the largest increase of all land uses over the study period. The construction land area of the Pearl River Delta has increased by 3044.02 km 2 . The increase accounted for 42.1% of the total construction land in 2015. The increase of construction land was mainly related to cultivated land, forest, and water areas with percentages of transfer of 23.09%, 11.29%, and 7.04%, respectively. Construction land expansion was concentrated in Guangzhou, Foshan, Dongguan, Zhongshan, and other cities. With the remarkable acceleration of spatial urbanization, a large amount of cultivated land, forest, and water areas became occupied by construction land.
Unused land showed the smallest change of area, with a decrease of 2.56 km 2 . Construction land and cultivated land were the main destinations of unused land.

Overall Characteristics of the Eco-Environment Effects
The regional eco-environmental quality index of the Pearl River Delta in 2000 and 2015 was calculated according to Formula (2). The results were 0.63 and 0.61, respectively, indicating that the regional eco-environmental quality index of the Pearl River Delta urban agglomeration decreased over the study period, with an average annual decrease of 0.11%. This shows that the ecological environmental quality of the Pearl River Delta region deteriorated between 2000 and 2015, which maintains the dynamic stability of the regional ecological environment overall.
The regional ecological quality tends to improve and deteriorate at the same time, while maintaining the overall stability of the regional ecological environment. These two trends offset each other in a certain region to a considerable extent, which leads to relative stability overall. The trend of ecological environmental improvement and deterioration can be drawn from the analysis of secondary land-use type change. Tables 5 and 6 show the area and contribution rates of the main land-use change types that led to the improvement and deterioration, respectively, of the ecological environment in the Pearl River Delta region over the study period. Table 5. The major land-use transformation types that were improving the regional eco-environment.   Table 5 showed that the types of land-use change that resulted in the improvement of the ecological environment quality in the Pearl River Delta region from 2000 to 2015 mainly included returning farmland to forest, returning farmland to water, and mutual transformation within forests. Among them, the ecological contribution rate of the internal conversion part of forest land was 67.16%, mainly because other forest land was converted into forest land; the ecological contribution rate of returning farmland to forest was 10.66%, mainly due to the conversion of dry land to forest land; the ecological contribution rate of returning farmland to water was 4.18%, mainly due to the conversion of dry land into reservoir ponds. Table 6 showed that the main driving factors leading to the deterioration of the ecological environmental quality in the Pearl River Delta region during 2000-2015 were the expansion of construction land and land degradation. The expansion of urban and rural construction land scale was mainly manifested in the transformation of cultivated land, forest, and water areas to urban and rural construction land. The conversion of landuse types into urban and rural construction land accounted for 46.55% of the ecological contribution rate, mainly due to the encroachment of construction land into the ecological space with forest land. The main manifestation of land degradation was the degradation of forest land into grassland or other forest land. The land degradation part accounted for 35.79% of the ecological contribution rate, mainly due to the encroachment of construction land into the ecological space with forest land. Overall, there were two trends of ecological improvement and deterioration in the Pearl River Delta region, but its overall habitat quality had maintained a stable trend

Regional Characteristics of the Eco-Environment Effects
According to Formula (2), it was found that land-use changes in the Pearl River Delta region between 2000 and 2015 led to various levels of change in the ecological environment quality of cities (Figures 4 and 5). Based on the spatial scale, Zhaoqing, Huizhou, and Jiangmen moderately had the higher eco-environment index values, which are scattered around the Pearl River Delta region. In contrast, Dongguan, Foshan, and Zhongshan which were concentrated in the central region of the Pearl River Delta, and they had the lowest eco-environment index. Guangzhou, as the capital of Guangdong province, had relatively good ecological quality, ranking fourth. Therefore, the ecological environment of the Pearl River Delta region was characterized by poor environmental quality of the central cities and good environmental quality of the surrounding cities. The eco-environmental index of cities in the Pearl River Delta region moderately decreased between 2000 and 2015.
That of Dongguan, Shenzhen, and Zhongshan deteriorated considerably, with the ecoenvironmental index decreasing by 0.051, 0.047, and 0.046, respectively. Huizhou, Zhuhai, and Jiangmen showed much less deterioration, with decreases to the eco-environment index of 0.007, 0.007, and 0.008, respectively.   These findings reveal that for cities such as Huizhou, with overall good ecological quality, there was a small ecological environment deterioration trend, whereas for cities such as Dongguan with relatively poor ecological quality, the deterioration trend was much greater. Therefore, the government should strengthen environmental protection supervision and balance the changing trend of the ecological environment quality for each city (Figure 6).   These findings reveal that for cities such as Huizhou, with overall good ecological quality, there was a small ecological environment deterioration trend, whereas for cities such as Dongguan with relatively poor ecological quality, the deterioration trend was much greater. Therefore, the government should strengthen environmental protection supervision and balance the changing trend of the ecological environment quality for each city (Figure 6). These findings reveal that for cities such as Huizhou, with overall good ecological quality, there was a small ecological environment deterioration trend, whereas for cities such as Dongguan with relatively poor ecological quality, the deterioration trend was much greater. Therefore, the government should strengthen environmental protection supervision and balance the changing trend of the ecological environment quality for each city ( Figure 6).

Assessment of the Eco-Environmental Quality in the Pearl River Delta
The eco-environment index of the Pearl River Delta region was clustered by using the Euclidean distance method in SPSS v.20 software (Table 7). According to the clustering results, nine administrative units in the study area were divided into five ecological quality grades (Figures 7 and 8). Table 7. Standards for grading of eco-environmental quality in Pearl River Delta.

Assessment of the Eco-Environmental Quality in the Pearl River Delta
The eco-environment index of the Pearl River Delta region was clustered by using the Euclidean distance method in SPSS v.20 software (Table 7). According to the clustering results, nine administrative units in the study area were divided into five ecological quality grades (Figures 7 and 8).     Overall, the ecological environment quality of all cities in the Pearl River Delta was higher than the low-value category; in 2000, the ecological environment quality was worst in Dongguan, and by 2015, the ecological quality of Foshan and Zhongshan had also been reduced from the moderate level to the same level as Dongguan, which is divided into lower levels. The quality of the ecological environment in most cities was at the moderate level and above. In 2000, the ecological index of Zhaoqing was higher than 0.75, and the quality of ecological environment was classified as high level. A specific analysis of these findings is presented below: (1) In the low-value zone of eco-environmental quality, the eco-environment index was lower than 0.30. The ecological quality index of cities in the Pearl River Delta region consistently exceeded 0.3, which shows that the overall level of the ecological environment quality in the Pearl River Delta is not the worst.
(2) In the lower zone of eco-environmental quality, the eco-environment index was between 0.3 and 0.45. In 2000, only Dongguan belonged to the lower ecological quality area. In 2015, this category included Dongguan, Zhongshan, and Foshan. This comparison shows that the ecological environment quality of Zhongshan and Foshan cities reduced Overall, the ecological environment quality of all cities in the Pearl River Delta was higher than the low-value category; in 2000, the ecological environment quality was worst in Dongguan, and by 2015, the ecological quality of Foshan and Zhongshan had also been reduced from the moderate level to the same level as Dongguan, which is divided into lower levels. The quality of the ecological environment in most cities was at the moderate level and above. In 2000, the ecological index of Zhaoqing was higher than 0.75, and the quality of ecological environment was classified as high level. A specific analysis of these findings is presented below: (1) In the low-value zone of eco-environmental quality, the eco-environment index was lower than 0.30. The ecological quality index of cities in the Pearl River Delta region consistently exceeded 0.3, which shows that the overall level of the ecological environment quality in the Pearl River Delta is not the worst.
(2) In the lower zone of eco-environmental quality, the eco-environment index was between 0.3 and 0.45. In 2000, only Dongguan belonged to the lower ecological quality area. In 2015, this category included Dongguan, Zhongshan, and Foshan. This comparison shows that the ecological environment quality of Zhongshan and Foshan cities reduced from the moderate level to the lower level. In the past 15 years, there has been rapid urbanization of Zhongshan and Foshan with areas of urban land increasing at the cost of land with a high ecological value such as forest and cultivated land.
(3) In the moderate zone of eco-environmental quality, the eco-environment index was between 0.45 and 0.60. In 2000, this category included Foshan, Zhongshan, Zhuhai, Shenzhen, and Guangzhou. In 2015, although the ecological environment quality of Shenzhen, Zhuhai, and Guangzhou declined, it remained within the moderate category. However, Foshan and Zhongshan declined from the moderate level to the lower level.
(4) In the higher zone of eco-environment quality, the eco-environment index was between 0.60 and 0.75. In 2000, the ecological quality of Jiangmen and Huizhou was divided into this grade, whereas in 2015, Zhaoqing also joined this category. The comparative study showed that the eco-environment quality of Zhaoqing was the best among the nine cities. Only the eco-environment quality of Zhaoqing reached the higher level in 2000. The ecological environment quality of Jiangmen and Huizhou remained within the higher zone. Because of the good ecological environment of Jiangmen and Huizhou, a large number of land-use types with high ecological value, such as forest and grassland, are distributed in this area, and few natural disasters occur in these inland cities.
(5) In the high-value zone of eco-environment quality, the eco-environment index is higher than 0.75. In 2000, the overall ecological quality of Zhaoqing reached this level. This was because the land use in Zhaoqing was mainly based on land-use types with high ecological value, such as woodland, water, grassland, and so on, and the ecological effect was good. The city did not maintain this eco-environmental quality index level in 2015 and was transferred to the higher zone.

Discussion
Although the ecological environment of the Pearl River Delta maintained an overall balance during the period 2000-2015, it should not be ignored that the eco-environment index of each city decreased to varying degrees, with Dongguan, Shenzhen, and Zhongshan showing the greatest declines. The spatial differentiation of eco-environmental index was characterized by the high eco-environmental index of the surrounding and inland cities, such as Zhaoqing, Huizhou, and Jiangmen, whereas low eco-environmental index values were reported in the coastal cities of the central region, such as Dongguan, Foshan, and Zhongshan. These high and low eco-environmental index values were related to the difference in the regional ecological environment foundation. Therefore, efforts should be made to rebuild the ecological environment, limit, or avoid human activities that lead to negative development of the ecological environment, and make full use of the self-repairing function of the system.
From the research results, we can see that the urban expansion in the Pearl River Delta is prominent, and ecological spaces such as cultivated land, forest land, and wetland have been damaged to varying degrees. At the same time, part of the cultivated land has been turned into wetland, which shows that Guangdong Province has achieved remarkable results in implementing the policy of returning farmland to lakes. Therefore, relevant laws can be formulated to protect the corresponding ecological space of forest land. Regarding the protection of cultivated land, the management and control measures of the red line of cultivated land protection can be strictly observed. Regarding urban expansion, corresponding control policies can be formulated to limit the expansion of construction land, protect ecological space, and ensure regional ecological security.
In short, as one of the three major urban agglomerations in China, the Pearl River Delta has fulfilled the mission of ecological civilization development entrusted by the state and strived to build an "ecological plus" development strategy. However, this area is subject to a series of contradictions between man and land, such as the encroachment of cultivated land, forest, and water area; a sharp increase of population; and the decline of ecological environment quality. Firstly, we should make clear the basic ecological control line of the region, scientifically plan its ecological function structure, and invite environmental protection. Secondly, we should optimize the layout of regional industrial development, formulate the catalogues of industrial access for different groups, and guard against environmental risks from the source. Furthermore, we should fully implement the target responsibility system of energy conservation and emission reduction, adhere to intensive use of land resources, improve ecological carrying capacity, and leave room for the sustainable development of the Pearl River Delta urban agglomeration.
Although this paper studies the change trend and spatial pattern of land-use structure, it does not deeply explore the driving mechanism of land-use transformation in the Pearl River Delta region, which is a more concerned part in the study of land-use transformation. In the future, it is necessary to further study the driving mechanism of land-use transformation in various stages in combination with the economic and social development stages to further reveal the related problems of land-use transformation. At the same time, due to the lack of improvement on the existing ecological quality assessment methods, how to make the ecological environment quality index more in line with the objective reality, accurately determine the ecological environment quality index of different land-use types, and better evaluate the impact of different scales and different land-use classification systems on the assessment results needs to be further studied.

Conclusions
According to the interpretation results of Landsat satellite remote sensing images, the quantitative indexes such as land-use coverage, comprehensive ecological environment quality index, and ecological contribution rate were used to realize the quantitative evaluation of the ecological environment effect of the Pearl River Delta region by revealing the correlation between land-use/land-cover and regional ecological environment quality.
(1) During 2000-2015, the land-use change in the Pearl River Delta mainly manifested in the reduction of cultivated land, forest, water areas, and unused land, and the increase of construction land and grassland. From the perspective of spatial distribution, it was concentrated in Guangzhou, Foshan, Dongguan, Zhongshan, and other cities. There was clear spatial urbanization in the Pearl River Delta region.
(2) From 2000 to 2015, the ecological environment of the Pearl River Delta largely maintained a relative balance but declined slightly overall. From 2000 to 2015, the comprehensive eco-environment index of the Pearl River Delta urban agglomeration decreased by 0.02, among which forest, water areas, and cultivated land declined the most. The spatial expansion caused by urbanization had the most profound impact on the decline of regional ecological environmental quality.
(3) This modest overall decline masked more complex and extreme dynamics in the quality of ecological environment of individual city. Among them, Dongguan, Shenzhen, and Zhongshan are the cities with the largest decline. The spatial differentiation characteristics of the eco-environmental quality index indicate that the ecological quality preferences of cities distributed around the study area and close to the inland areas, while the ecological quality of the central coastal cities are biased. The quality of the ecological environment is related to the basis of the regional ecological environment. Decision analysis is required to support land-use planning to ensure the sustainability of ecosystem services for the wellbeing of the people of Pearl River Delta and other rapidly urbanizing areas in China and globally.
This study comprehensively evaluated the eco-environmental effects caused by the land-use change of the urbanization prominent region, revealed the problems existing in the process of land development and ecological construction in the Pearl River Delta urban agglomeration region, and provided policy suggestions for the coordinated development of urbanization and ecological environment in the region. At the same time, it also provided a reference for the research on the eco-environmental effects of land-use change in key cities in economically developed areas.  Institutional Review Board Statement: I choose to exclude this statement because the study did not involve humans or animals.
Informed Consent Statement: I choose to exclude this statement because the study did not involve humans.

Data Availability Statement:
This study is based on the land-use data produced by the Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences.