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A multiscale analysis of urbanization effects on ecosystem services supply in an urban megaregion
Science of the Total Environment 662 (2019) 824–833
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Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv
A multiscale analysis of urbanization effects on ecosystem services supply in an urban megaregion Jiali Wang a, Weiqi Zhou a,b,⁎, Steward T.A. Pickett c, Wenjuan Yu a, Weifeng Li a a b c
State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China University of Chinese Academy of Sciences, Beijing 100049, China Cary Institute of Ecosystem Studies, Box AB, Millbrook, NY 12545, USA
H I G H L I G H T S
G R A P H I C A L
A B S T R A C T
• Increased ecosystem services in BeijingTianjin-Hebei megaregion during 2000–2010. • Inversed U-shaped relationships between food production and population growth, and economic development. • Regulating services decreased with population growth and economic development. • All ecosystem services significantly decreased with urban land expansion. • Relationships between urbanization and ecosystem services are consistent across scales.
a r t i c l e
i n f o
Article history: Received 20 December 2018 Received in revised form 17 January 2019 Accepted 18 January 2019 Available online 23 January 2019 Editor: Deyi Hou Keywords: Urbanization Ecosystem services Multiscale Urban megaregion Urban ecology
a b s t r a c t The rapid and large-scale urbanization leads to drastic land-use conversion and impacts on ecosystem services. The relationship between urbanization and ecosystem services not only depends on the characteristics of the study area, but is closely related to the selected ecosystem services types and the indicators to measure urbanization level. Exploring the relationship in specific study area is necessary to support regional planning for sustainability. In this study, we analyzed the impacts of urbanization on ecosystem services from 2000 to 2010 in the Beijing-Tianjin-Hebei (BTH) urban megaregion in China. We quantified four critical ecosystem services, food production, carbon sequestration and oxygen production, water conservation, and soil retention, and identified the hotspots of ecosystem service provision. We measured the urbanization level from three aspects, namely, population growth, economic development and developed land expansion. The impacts of urbanization on the selected ecosystem services were examined at the hotspots scale and urban megaregion scale. We found both ecosystem services and urbanization level in the BTH region increased. There was an obvious spatial heterogeneity in the hotspots of ecosystem services, showing hotspots of food production aggregately distributed in the southern plain while hotspots of regulating services mainly located in the north mountainous areas with dense forest. The relationship between population growth, economic development and food production were represented by an inverse U-shaped curve, while it displayed a decreasing trend with regulating services. Both food production and regulating services decreased dramatically with urban land expansion. Additionally, the relationships between urbanization and ecosystem services were consistent across scales. Effective measures should be implemented for the hotspots of different types of ecosystem services to mitigate the loss of ecosystem services during rapid urbanization. The results can provide insights for enhancing urban sustainability in the BTH region, as well other urban megaregion with similar characteristics throughout the world. © 2019 Elsevier B.V. All rights reserved.
⁎ Corresponding author at: State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China. E-mail address: [email protected] (W. Zhou).
https://doi.org/10.1016/j.scitotenv.2019.01.260 0048-9697/© 2019 Elsevier B.V. All rights reserved.
J. Wang et al. / Science of the Total Environment 662 (2019) 824–833
1. Introduction The past decades have witnessed rapid urbanization in China, with the proportion of urban population increasing from 11.8% in 1950 to 54.8% in 2014 (Ye et al., 2018). The urban land also experienced rapid and continuous expansion. The national urbanization level which measured by the proportion of urban population is projected to reach approximately 60% in 2020 (Yang and Shi, 2017). Urbanization makes a significant contribution to social improvement and economic development, while simultaneously posing a grave threat to the health of non-urban ecosystems. During the process of urbanization, forest, pastoral, and agricultural ecosystems have been converted into human-dominated ecosystems at an unprecedented scale and pace. This process inevitably disturbs the structure and function of the antecedent ecosystems, resulting in the loss of ecosystem services (Alberti, 2010; J. Liu et al., 2017). It is widely assumed that urbanization will continue, which puts increasing pressure on ecosystems. Urban sustainability has become one of the most pressing issues facing humanity today (Grimm et al., 2008). Understanding the relationship between urbanization and ecosystem services is critically important for providing informative suggestions for urban planning to achieve urban sustainability (Zhou et al., 2017). Considerable research has demonstrated the urbanization is one of the main driving forces for the change of ecosystem services (GarcíaNieto et al., 2018; B. Li et al., 2016; Zhou et al., 2018). However, the effects of urbanization on ecosystem services are not consistent among different studies, and in some cases, research results are contradictory. For example, a number of studies have revealed ecosystem services were negatively correlated with urbanization (Faulkner, 2004; Su et al., 2014; Zhang et al., 2017). The main reason is that the increasing natural and semi-natural ecosystems transform to impervious surface during rapid urbanization, which causes a drastic decrease of the ecosystem services supply. However, some studies have found the opposite results - ecosystem services would increase during the urbanization process. For instance, Buyantuyev and Wu (2009) found that urbanization boosted productivity of plant communities and improved net primary productivity of ecosystem in the Phoenix metropolitan region of USA. Zhou et al. (2018) demonstrated that the value of ecosystem services increased in the Beijing-Tianjin-Hebei region with the rapid urbanization during the period 1996–2014. In addition, previous research demonstrated that a non-linear relationship, represented by an “inverse U” shape, between urbanization and ecosystem services may occur, as suggested by several studies (Li et al., 2010; Wan et al., 2015). That is, ecosystem services increase first at the earlier stage of urbanization, but after reaching a certain threshold value, it starts to decline. The main reason for these variability can be summarized as two aspects. First, multiple land use changes occur during rapid urbanization, the increases in forest, grassland and waters in non-urban areas may offset the decrease in ecosystem services caused by urban expansion (Zhou et al., 2018). Second, the relationship between urbanization and ecosystem services is highly dependent on the environmental context of study area. For example, a desert city, Phoenix, is intensely irrigated in the process of urbanization, thus greatly improved the productivity and biodiversity of the plant communities. To sum up, the relationship between ecosystem services and urbanization is complex. Extending the obtained results to other study area might lead to erroneous conclusions (Kindu et al., 2016). It is necessary to detect the relationship between ecosystem services and urbanization in specific research area in order to provide scientific basis for making reasonable urban planning and ecosystem management measures. Additionally, the relationship between urbanization and ecosystem services varies by both the types of ecosystem services and the selected indicators that used to measure urbanization level. There was no unanimous variation in the different ecosystem services types. For example, when investigating the relationship between ecosystem services and urbanization in the Guangzhou-Foshan Metropolitan Area, China, Ye et al. (2018) found gas regulation, soil formation and retention, and
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climate regulation occurred substantial decline, but the waste treatment and recreation and culture services increased. Furthermore, the relationship between ecosystem services and urbanization may also vary when using different indicators to measure urbanization levels. For example, some research suggested an “inverse U” shape relationship between ecosystem services and urbanization when the degree of urbanization was measured by population and economy (Wan et al., 2015). However, a negative relationship was found when the degree of urbanization was measured by developed land (e.g., Hu et al., 2015; Peng et al., 2017b). Therefore, fully understanding the relationship between multiple ecosystem services and different component of urbanization is of great significance for minimizing the negative impact of urbanization on ecosystems and realizing urban sustainability. Megaregions are now and will continue to be a prominent form of urbanization in China (Yu and Zhou, 2018; Li et al., 2019). More and more megaregions are emerging in recent decades, such as the BeijingTianjin-Hebei region, the Yangtze River Delta, and the Pearl River Delta. Although rapid and large-scale urbanization brings huge economic growth, the ecosystems of urban megaregions have experienced serious degradation (Cai et al., 2017), which not only poses threats to the regional ecological security, but also restrains the future economic development. Furthermore, the demand for valuable natural resources and excellent living environment are growing rapidly as large numbers of people congregate in the urban megaregion. Investigation the impacts of urbanization on ecosystem services in the urban megaregions have great significance for achieving the double-win situation for both economic development and environmental protection. A large number of studies have been conducted to investigate the impacts of urbanization and ecosystem services in the urban megaregion (Li et al., 2010; Zhang et al., 2017), but most have concentrated on analyzing the change of ecosystem services caused by urban land expansion at the whole urban megaregion (Sun et al., 2018; Ye et al., 2018). Few studies, however, have examined the hotspots of ecosystem services provision and the relations with urbanization. These hotspots are locations where the key ecosystem services are provided and thus contribute a disproportionate importance of ecosystem services provision to the region (Ouyang et al., 2016). If the hotspots of ecosystem services provision were overly developed, the ecosystems will be degraded, which is not conducive to the coordinated development of the urban megaregion. Hence, it is necessary to investigate the relationship between urbanization and ecosystem services in the hotspots, in addition to the whole urban megaregion. Based on the above review of the literature, this study was designed to explore the impact of urbanization on ecosystem services in the BeijingTianjin-Hebei region (BTH), China. The study had three components. First, four types of ecosystem services, including food production, carbon sequestration and oxygen production, water conservation, and soil retention, were selected to quantitatively assess ecosystem services and their change from 2000 to 2010. Second, the spatiotemporal patterns of change in urbanization were quantified using the three aspects of population growth, economic productivity, and land conversion. Finally, we identified the hotspots of each type of ecosystem services and explored the relationship between urbanization and ecosystem services in the hotspots and the whole urban megaregion. Our results are expected to provide quantitative information for realizing coordinated development of economy and environment and enhancing urban sustainability in the BTH region and other urban megaregion with similar characteristics throughout the world. 2. Material and methods 2.1. Study area and data sources The BTH region lies between 36.07°N–42.65°N and 113.46°E– 119.79°E in North China. It includes two municipalities that are directly under the control of the national government, Beijing city and Tianjin city, and another 11 municipalities in Hebei Province (Fig. 1). There are 202 counties in the BTH region, the number in Beijing city and
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Fig. 1. Location of the study area and the land use/land cover (LULC) in 2010.
Tianjin city is 16, respectively, and the remaining 170 belong to Hebei province. The area of the BTH region is 216,500 km2, accounting for 2.2% of the total area of China (D. Li et al., 2017). The study area has a typical temperate continental monsoon climate, with the annual average temperature of 3 °C–15 °C and annual average rainfall of 304–750 mm (Xie et al., 2016). The elevation decreases from the northwest to the southeast, ranging from 2836 m to −52 m. The BTH region is the center of national politics, economy, culture, and technology (Zhang et al., 2016). The total population was 111.42 million and the population density reached 515.8 person/km2 at the end of 2015. The study area is considered as the largest economic hub in North China, with a gross domestic product (GDP) exceeding 6935.89 billion Yuan (or, approximately 1100 billion dollars) in 2015. Spatial data and statistical data were used in this study to analyze the link between urbanization and ecosystem services. The Shuttle Radar Topography Mission (SRTM) digital elevation model (DEM) with spatial resolution of 90 m was obtained from the Geospatial Data Cloud site, Computer Network Information Center, Chinese Academy of Sciences (http://www.gscloud.cn). The precipitation, temperature, and other meteorological data were obtained from the Chinese meteorological data network (http://data.cma.cn/). The spatial meteorological data were interpolated using the inverse distance weighted method. The soil data were obtained from harmonized world soil database supplied by the International Institute for Applied Systems Analysis and the Food and Agriculture Organization (http://webarchive.iiasa.ac.at/ Research/LUC/External-World-soil-database). The net primary productivity (NPP) data from the MOD17A3 dataset were supplied by NASAUSGA (https://lpdaac.usgs.gov/). The land cover data were interpreted based on Landsat TM and ETM data with 30 m resolution using an approach that integrates object-based classification and a backdating method (Yu et al., 2016). The landscape was classified into 6 categories, namely forest, grass, water, farmland, developed land, and barren land. The population and GDP data at a spatial resolution of 1 km × 1 km were provided by the Data Center for Resources and Environmental Sciences, Chinese Academy of Sciences (RESDC) (http://www.resdc.cn). The statistical data, such as grain output and other production supply, were
obtained from Beijing Statistical Yearbook, Tianjin Statistical Yearbook and Hebei Statistical Yearbook. 2.2. Quantifying ecosystem services 2.2.1. Food production (FP) Food production is crucial for food security and regional sustainable development (B. Li et al., 2016). We calculated the crop production provided by farmland and assigned the results to raster data at a spatial resolution of 1 km × 1 km. According to related studies (Xie et al., 2018; Zhang et al., 2017), we selected grain, oil crops and vegetables to assess the food production as provisioning services. The production data were derived from Statistical Yearbooks of Beijing, Tianjin and Hebei Province. The equation for food production is as follows:
Px ¼
C X
AP
ð1Þ
c¼1
where Px is the total food production for pixel x, the size of the pixel is 1 km × 1 km. A refers to the area of cropland in pixel x. P represents the average yield of the selected grain, oil crops and vegetables per unit area. 2.2.2. Carbon sequestration and oxygen production (CSOP) We calculated the amount of carbon sequestration and oxygen production with NPP data based on the principle of photosynthesis, in which the production of 1 kg of dry matter can fix 1.63 kg of CO2 and release 1.2 kg of O2 (Li and Zhou, 2016). C x ¼ 1:63 NPPx þ 1:2 NPP x
ð2Þ
where Cx represents the amount of carbon sequestration and oxygen production for pixel x, NPPx is the amount of NPP for pixel x.
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2.2.3. Water conservation (WC) Water conservation refers to the capacity of ecosystems to hold part of water input from precipitation within a certain period. The amount of water conservation for each pixel on the landscape was obtained by the equation described as follows, the required runoff coefficient values were derived from Ouyang et al. (2016). WC ¼
j X
ðP i −Ri −ET i Þ Ai
ð3Þ
i¼1
Ri ¼ P i a
ð4Þ
where WC is the total amount of water conservation, Pi is the precipitation, Ri is the storm runoff, ETi is evapotranspiration, Ai is the area of the ecosystems as defined by land cover types, and a is the runoff coefficient, i is the index for each ecosystem, and j is total number of ecosystems within the pixel. 2.2.4. Soil retention (SR) Soil erosion reduces the soil fertility and increases the frequency of flood disaster, which has been considered to be an important ecological problem in the BTH region. The soil retention service was quantified using the universal soil loss equation (USLE) implemented in the sedimentation module of InVEST model. The annual soil loss of different land use types for each pixel was computed as follows (Sun et al., 2018): USLEx ¼ Rx ∙K x ∙LSx ∙C x ∙P x
ð5Þ
where Rx is the rainfall erosivity for pixel x, Kx is the soil erodibility factor for pixel x, LSx is the slope length-gradient factor, Cx is the crop management factor for pixel x and Px is the support practice factor for pixel x. Crop management and support practice factors for each land use type were modified according to Li (2014) and Wu et al. (2013). 2.3. Mapping urbanization levels Population growth, economic development, developed land expansion, and other social-economic indicators were widely applied to measure urbanization levels (Su et al., 2012). In this study, we characterized the urbanization levels of the BTH region from three aspects: population growth, economic productivity, and land conversion. The population density (person/km2) was used to reflect population urbanization, Gross Domestic Product (GDP) density (104 yuan/km2) was applied to describe economic urbanization, and the proportion of construction land in a specific grid (1 km2) was used to represent land conversion (Peng et al., 2017b). 2.4. Hotspot analysis of the selected ecosystem services Hotspot analysis is a specific spatial analysis technique that has been used for identifying areas where high values for a variable of interest occur. It has been widely applied to identify priority areas for both biodiversity and ecosystem services conservation (Y. Li et al., 2017; Schröter et al., 2017; Timilsina et al., 2013). We used Gi⁎ statistics, a tool integrated in ArcGIS 10.3, to identify the locations which can provide large amounts of ecosystem service. The detailed steps to obtain the distribution of hotspots for ecosystem services are as follows. First, zonal statistics were used to calculate the sum of each selected ecosystem service type for every county in the BTH region. Then we used the Hotspot Analysis (Getis-Ord Gi*) tool to identify the hotspots of ecosystem service provision. 2.5. Analyzing the relationship between ecosystem services and urbanization The relationship between ecosystem services and urbanization is complex, and linearity, “inverted U” shape, “S” shape and other non-
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linear relationship may occur. We applied curve estimation to identify the relationship between ecosystem services and urbanization. Curve estimation in SPSS 13.0 for windows, was used to analyze the relationship between ecosystem services and the three components of urbanization: population density, GDP density, and the proportion of the developed land. The relationship between ecosystem services and urbanization were explored in the specific hotspots and throughout the whole urban megaregion. The basic unit for curve estimation was the county. Due to the different size and unit for the indicators of population density and GDP density, the raw value of these two indicators were log transformed before conducting curve estimation. 3. Results 3.1. Spatial pattern of ecosystem services in the BTH region The spatial pattern of the four selected ecosystem services exhibited clear heterogeneity, and the ecosystem services had great change during 2000 to 2010 (Fig. 2). Food production increased remarkably, with an average food production of 152.29 t/km2 in 2000, increasing to 196.06 t/km2 in 2010. The high-yield area was located on the plains in the south of the BTH region, such as the western part of the Shijiazhuang, Baoding, Xingtai and Handan, while the low-yield region mainly distributed in Zhangjiakou and Chengde in the north of the study area. Although the highest value of COSP were lower in 2010, the COSP service improved between 2000 and 2010, the average values were 3820.88 t/km2 and 4027.94 t/km2, respectively. The values of COSP service were higher in the central parts of the study area that was covered by forest and farmland, while the values were lower in the eastern part of Zhangjiakou and the coastal areas in Tianjin, Tangshan, Langfang and Cangzhou. The average amount of water conservation increased greatly during 2000–2010. The areas that had higher water conservation values were located in the north of the BTH region. The soil erosion situation of the study area has greatly improved; the average value of soil retention increased from 959.39 t/km2 to 1347.34 t/km2. The high-value regions of soil retention were located in the mountainous area that were covered with dense forest. 3.2. Spatial pattern of urbanization level in the BTH region The urbanization levels of the BTH region in 2000 and 2010 are shown in Fig. 3. The results indicated that the population density and GDP density of each city in the BTH region have greatly increased, the area of developed land has been expanding constantly during 2000–2010. The spatial pattern of population growth, economic productivity, and land expansion is similar, with great variations among different cities. The areas with higher urbanization levels were located in the already existing urban districts of the 13 cities in the BTH region, especially the 2 megacities, Beijing and Tianjin. While the areas in Chengde and Zhangjiakou presented the lowest levels of urbanization. The results of population urbanization suggested that the population density were the highest in Beijing, and the average values were 658 person/km2 and 1195.6 person/km2 in 2000 and 2010, respectively. The level of economic urbanization was the highest in Tianjin, and the average values of the GDP density increased from 1409.77 yuan/km2 to 4105.06 yuan/km2 during the study period. The developed land experienced rapid expansion in 2000–2010, for example the proportion in Tianjin was 15.54% in 2000, while the value reached 23.16% in 2010. 3.3. Identifying hotspots of ecosystem services in 2000 and 2010 The hotspots with different confidence levels of the selected ecosystem services in 2000 and 2010 were shown in Fig. 4. It is generally recognized that P b 0.05 (i.e., 95% confidence level) is defined as statistically significant (Y. Li et al., 2017). Thus we focused on hotspots with confidence levels above 95% in this study, which were considered as the
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Fig. 2. Spatial patterns of ecosystem services in 2000 and 2010 (FP - food production; COSP‑carbon sequestration and oxygen production; WC-water conservation; SR-soil retention).
key areas for ecosystem services provision. The hotspots were aggregated in space, but the spatial patterns of hotspots of different ecosystem services were distinct. The hotspots of food production were located on the plain in the southern and eastern part of the study area, including many counties in Hengshui, Cangzhou, Xingtai, Shijiazhuang and Tangshan. The spatial distributions of the hotspots of COSP, WC,
and SR were similar, which were situated in the northern BTH region, including Chengde, the east part of Zhangjiakou and the northern part in Beijing. The spatial pattern of hotspots did not changed significantly during 2000–2010. We also found that the areas with higher levels of urbanization, such as the two megacities of Beijing and Tianjin, have fewer hotspots of ecosystem service provision.
Fig. 3. Spatial patterns of urbanization levels in 2000 and 2010 (Pop_D - population density; GDP_D - GDP density; DLP-developed land proportion; Yuan is the Chinese currency, at an exchange rate of 1.00 USD = 6.75 Yuan as of January 2019).
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Fig. 4. Hotspots of ecosystem services with different confidence levels in 2000 and 2010.
3.4. The relationship between urbanization and ecosystem services in the BTH region The relationships between urbanization and ecosystem services in the hotspots and the whole BTH region were explored in this study. The spatial pattern of COSP, WC, and SR in hotspots were similar (Fig. 4); thus we considered the sum of COSP, WC, and SR as regulating service and identified the shared hotspots for these services, then analyzed the correlation between ecosystem services and urbanization over the period of 2000–2010. 3.4.1. The relationship between urbanization and ecosystem services in the hotspots There was an “inverse U” shape relationship between food production and the urban parameters of population density and GDP density (Fig. 5). The increase of population density and economic development intensity had a positive impact on food production in areas with low levels of urbanization, which indicated that ecosystems have sufficient capacity to resist the negative effect of urbanization. After a certain level of growth, food production decreased significantly with increasing population density and GDP density. Whereas, there was an obvious negative relationship between developed land proportion and food production, food production consistently decreased significantly with the increase of urbanization level. The main reason was that the expansion of the developed land often takes place at the expense of farmland, resulting in a decrease in food production. For regulating services, the ecosystem services drastically declined with an increase of population density, GDP density and developed land. 3.4.2. The relationship between urbanization and ecosystem services in the BTH region The characteristic of the relationship between urbanization and ecosystem services in the whole BTH region was similar to that in the hotspots (Fig. 6). There was an “inverse U” shape relationship between food production and population density and GDP density in 2000 and 2010. In terms of the parameter of population density, when the value reached 444.79 person/km2 in 2000, food production decreased
significantly with an increase of population, while the threshold value declined to 345.31 person/km2 in 2010. The main reason is that the growing population puts great pressure on ecosystem, and the carrying capacity of the ecosystem reduced. For the indicators that were used to measure economic productivity, the maximum value of GDP density that caused a reduction in food production increased during the study period. The threshold value was 2.5 million yuan/km2 in 2000, and it reached 5.97 million yuan/km2 in 2010. The food production was negatively correlated with land urbanization. The regions with higher levels of urbanization were located in the center of the cities, where the area of farmland was relatively small, so the crop yield was low. In view of regulating services, there was a prominent negative relationship between ecosystem services and urbanization. The main reason was that the regulating services is mainly provided by forest ecosystems. Rapid urbanization leaded to a significant reduction in forest ecosystems, thus decreasing the supply of ecosystem service. 4. Discussion 4.1. The relationship between urbanization and ecosystem services The relationship between urbanization and ecosystem services has received widespread attention in recent years (Cao et al., 2017; Jiang et al., 2017), but with inconsistent results from previous studies. Overall, ecosystem services in the BTH urban megaregion had a trend of growth, even though the region experienced rapid and intense urbanization from 2000 to 2010. Such improvement in ecosystem services was consistent with that from the China Ecosystem Assessment at the national scale (Ouyang et al., 2016), and from other studies (Viña et al., 2016). Such improvement, similar to that at the national scale, may be mainly attributed to China's national conservation policies started in 2000, which have effectively alleviated the ecological deterioration (Ouyang et al., 2016). Under the effect of ecological conservation policies, the area of forest in the study area increased from 70,309.44 km2 to 71,603.64 km2 over the past decade, which greatly improved the regulating services. Large areas of farmland have been occupied along with
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Fig. 5. Relationship between ecosystem services and urbanization in hotspots.
urban expansion. As shown in Table S1 in the Appendix, 3108.47 km2 of farmland has been converted to developed land from 2000 to 2010. However, the agriculture yield remarkably increased, with the average food production of the BTH region increasing from 152.29 t/km2 to 196.06 t/km2, which was largely attributed to the technology improvement and industrial structure upgrade in agriculture sectors. When considering different types of ecosystem services, and their relationships with levels of urbanization measured by different indicators, the impacts of urbanization and ecosystems services may vary. For example, the provisioning services had an “inverse U” shape relationship with economic dimensions of urbanization, but had a significantly negative linear one with urban expansion. This is likely because the impact of
population growth and economic development on the ecosystem is reflected by developed land expansion (Peng et al., 2017b). At the early stage of urbanization, the negative impact of developed land expansion on ecosystem is insignificant, where ecosystem can resist the interference of human activities. But with continuous urban expansion and economic development, increased yield per unit area was not enough to compensate the loss caused by conversion of arable land to developed land. In contrast to provisioning services, regulating services were negatively correlated with all the three urbanization indicators. Expansion of developed land can directly drive the decline of ecosystem's regulating services, which also can be indirectly reflected by population growth and economic development (Peng et al.,
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Fig. 6. Relationship between ecosystem services and urbanization in the BTH region.
2017b). For example, conversion of forested land to developed land would inevitably reduce the supply of regulating services provided by forest ecosystems. In the future, many effective measures should be implemented to realize the harmonious development of urbanization and ecological environment. For the hotspots of provisioning services that are located in the middle and south of the study area, agricultural infrastructure should be upgraded in order to increase crop production (Peng et al., 2017a). In addition, we need to strictly observe the red line for protecting farmland and control the expansion of developed land. For the hotspots of regulating services that are situated in the north of the study area, ecological conservation policy should continue to be implemented, including a strengthening of forest ecosystem protection.
Furthermore, the population density and economic development scale should be controlled to realize the coordinated development of urbanization and ecological environment. 4.2. The implication of hotspots analysis In addition to the commonly conducted analysis at the city or megaregion scale, we also analyzed the relationship between urbanization and ecosystem services for the hotspots. Increasing interest has been focused on mapping and specifically identifying the hotspots of ecosystem services in recent years. A large number of relevant research has been performed by using hotspots analysis to identify the critical areas of ecosystem services supply (e.g., G. Li et al., 2016; Timilsina
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et al., 2013). Although numerous studies have emphasized the necessity to incorporate the concept of ecosystem services into landscape planning and ecosystem management, practical applications are still largely lacking (Daily et al., 2009; Groot et al., 2010). Identifying the hotspots of the different types of ecosystem services alone can provide insights for decision makers to more effectively determine the protection priority areas. Our results showed that the hotspots of regulating services (COSP, WC, SR) were located in the northern of the study area, which was primarily covered by high dense forest. Ecological degradation of these sites could cause a significant decline in multiple ecosystem services (Qiu and Turner, 2013), which poses a serious threat to human well-being. Thus these areas should be treated as the priority areas for ecological protection to ensure regional ecological security. Moreover, the conservation budgets are usually not sufficient to conserve all sites (Y. Li et al., 2017), the efficiency of ecological conservation strategies would be improved greatly by focusing on hotspots. Our results of hotspot analysis also showed great spatial mismatch between hotspots distribution of provisioning and regulating services. The hotspots of food production were aggregated in the south plain, while the hotspots of COSP, WC, and SR mainly were distributed in the north mountainous part of the study area that covered with dense forest. This finding was consistent with previous studies that indicated topography and ecosystem service type were the two important factors that caused spatial heterogeneity in the hotspots of ecosystem services (Cai et al., 2017; Y. Li et al., 2017; S. Liu et al., 2017). Such information on spatial mismatch can also provide insights on identify protection priority areas, and suggest consideration of tradeoffs among different types of ecosystem services. 4.3. Limitations and future perspectives In this study, the relationship between urbanization and ecosystem services was explored for both hotspots and the whole BTH region. The BTH region is composed of 13 cities with various urbanization levels, and the development direction of each city is different. For instance, as the political, economic and cultural center, Beijing experienced rapid development, especially the hi-tech Industries. The cities of Chengde and Zhangjiakou, which are located in the northern part of the BTH region, have been considered to be important ecological protection zones, as a result of their vital roles in water conservation and sandstorm prevention. In contrast, Xingtai, Handan, and other cities in the southern part of the BTH region not only have abundant mineral resources, but also provide vast agricultural production. In view of the distinct characteristics of each city, the relationship between urbanization and ecosystem services at the city scale should be further explored to obtain more comprehensive view on achieving the goal of sustainable development. In addition, we only considered four types of ecosystem services, but not others, such as the cultural services. With the beautiful scenery and invaluable cultural heritage, the study area is an important national and international tourist destination in China. The development of tourism also exerts an influence on ecosystem services. The cultural ecosystem services need to be considered in future research. 5. Conclusion The relationship between urbanization and ecosystem services is complicated. This study documented that there are diverse relations between urbanization and ecosystem services. In particular, there are different relationships depending upon the type of ecosystem services examined and the different indicators used to measure urbanization levels. Our study explored the relationship between urbanization and ecosystem services in the BTH region from the hotspots scale and the whole urban megaregion scale. The results showed that there was an “inverse U” shape relationship between food production and urbanization measured by population density and economic density; however,
food production declined sharply with increasing of urban land conversion. In contrast, the regulating services were negatively correlated with the three urbanization indicators. In the future, effective measures should be taken to promote the reasonable development of population and economy, and control the expansion of developed land for realizing urban sustainable development. Acknowledgements This research was funded by the project of “Developing key technologies for establishing ecological security patterns at the Beijing-TianjinHebei urban megaregion” of the National Key Research and Development Program (2016YFC0503004), the Key Research Program of Frontier Sciences, CAS (QYZDB-SSW-DQC034), and the National Natural Science Foundation of China (Grant No. 41590841). Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi. org/10.1016/j.scitotenv.2019.01.260. References Alberti, M., 2010. Maintaining ecological integrity and sustaining ecosystem function in urban areas. Curr. Opin. Environ. Sustain. 2, 178–184. Buyantuyev, A., Wu, J., 2009. Urbanization alters spatiotemporal patterns of ecosystem primary production: a case study of the Phoenix metropolitan region, USA. J. Arid Environ. 73, 512–520. Cai, W., Gibbs, D., Zhang, L., Ferrier, G., Cai, Y., 2017. Identifying hotspots and management of critical ecosystem services in rapidly urbanizing Yangtze River Delta Region, China. J. Environ. Manag. 191, 258–267. Cao, W., Li, R., Chi, X., Chen, N., Chen, J., Zhang, H., et al., 2017. Island urbanization and its ecological consequences: a case study in the Zhoushan Island, East China. Ecol. Indic. 76, 1–14. Daily, G.C., Polasky, S., Goldstein, J., Kareiva, P.M., Mooney, H.A., Pejchar, L., et al., 2009. Ecosystem services in decision making: time to deliver. Front. Ecol. Environ. 7, 21–28. Faulkner, S., 2004. Urbanization impacts on the structure and function of forested wetlands. Urban Ecosyst. 7, 89–106. García-Nieto, A.P., Geijzendorffer, I.R., Baró, F., Roche, P.K., Bondeau, A., Cramer, W., 2018. Impacts of urbanization around Mediterranean cities: changes in ecosystem service supply. Ecol. Indic. 91, 589–606. Grimm, N.B., Faeth, S.H., Golubiewski, N.E., Redman, C.L., Wu, J., Bai, X., et al., 2008. Global change and the ecology of cities. Science 319, 756–760. Groot, R.S.D., Alkemade, R., Braat, L., Hein, L., Willemen, L., 2010. Challenges in integrating the concept of ecosystem services and values in landscape planning, management and decision making. Ecol. Complex. 7, 260–272. Hu, X., Hong, W., Qiu, R., Hong, T., Chen, C., Wu, C., 2015. Geographic variations of ecosystem service intensity in Fuzhou City, China. Sci. Total Environ. 512-513, 215–226. Jiang, W., Deng, Y., Tang, Z., Lei, X., Chen, Z., 2017. Modelling the potential impacts of urban ecosystem changes on carbon storage under different scenarios by linking the CLUE-S and the InVEST models. Ecol. Model. 345, 30–40. Kindu, M., Schneider, T., Teketay, D., Knoke, T., 2016. Changes of ecosystem service values in response to land use/land cover dynamics in Munessa–Shashemene landscape of the Ethiopian highlands. Sci. Total Environ. 547, 137–147. Li, M., 2014. Ecosystem Services Evaluation Based on the InVEST Model: A Case Studies of Yanqing, Beijing. Beijing Forestry University, Beijing. Li, J., Zhou, Z.X., 2016. Natural and human impacts on ecosystem services in Guanzhong Tianshui economic region of China. Environ. Sci. Pollut. Res. 23, 6803–6815. Li, T., Li, W., Qian, Z., 2010. Variations in ecosystem service value in response to land use changes in Shenzhen. Ecol. Econ. 69, 1427–1435. Li, B., Chen, D., Wu, S., Zhou, S., Wang, T., Chen, H., 2016. Spatio-temporal assessment of urbanization impacts on ecosystem services: case study of Nanjing City, China. Ecol. Indic. 71, 416–427. Li, G., Fang, C., Wang, S., 2016. Exploring spatiotemporal changes in ecosystem-service values and hotspots in China. Sci. Total Environ. 545-546, 609–620. Li, D., Wu, S., Liu, L., Liang, Z., Li, S., 2017. Evaluating regional water security through a freshwater ecosystem service flow model: a case study in Beijing-Tianjian-Hebei region, China. Ecol. Indic. 81, 159–170. Li, Y., Zhang, L., Yan, J., Wang, P., Hu, N., Cheng, W., et al., 2017. Mapping the hotspots and coldspots of ecosystem services in conservation priority setting. J. Geogr. Sci. 27, 681–696. Li, W., Zhou, W., Han, L., Qian, Y., 2019. Uneven urban-region sprawl of China's megaregions and the spatial relevancy in a multi-scale approach. Ecol. Indic. 97, 194–203. Liu, J., Li, J., Qin, K., Zhou, Z., Yang, X., Li, T., 2017. Changes in land-uses and ecosystem services under multi-scenarios simulation. Sci. Total Environ. 522–526. Liu, S., Yin, Y., Cheng, F., Hou, X., Dong, S., Wu, X., 2017. Spatio-temporal variations of conservation hotspots based on ecosystem services in Xishuangbanna, Southwest China. PLoS One 12, e0189368.
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Contents lists available at ScienceDirect
Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv
A multiscale analysis of urbanization effects on ecosystem services supply in an urban megaregion Jiali Wang a, Weiqi Zhou a,b,⁎, Steward T.A. Pickett c, Wenjuan Yu a, Weifeng Li a a b c
State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China University of Chinese Academy of Sciences, Beijing 100049, China Cary Institute of Ecosystem Studies, Box AB, Millbrook, NY 12545, USA
H I G H L I G H T S
G R A P H I C A L
A B S T R A C T
• Increased ecosystem services in BeijingTianjin-Hebei megaregion during 2000–2010. • Inversed U-shaped relationships between food production and population growth, and economic development. • Regulating services decreased with population growth and economic development. • All ecosystem services significantly decreased with urban land expansion. • Relationships between urbanization and ecosystem services are consistent across scales.
a r t i c l e
i n f o
Article history: Received 20 December 2018 Received in revised form 17 January 2019 Accepted 18 January 2019 Available online 23 January 2019 Editor: Deyi Hou Keywords: Urbanization Ecosystem services Multiscale Urban megaregion Urban ecology
a b s t r a c t The rapid and large-scale urbanization leads to drastic land-use conversion and impacts on ecosystem services. The relationship between urbanization and ecosystem services not only depends on the characteristics of the study area, but is closely related to the selected ecosystem services types and the indicators to measure urbanization level. Exploring the relationship in specific study area is necessary to support regional planning for sustainability. In this study, we analyzed the impacts of urbanization on ecosystem services from 2000 to 2010 in the Beijing-Tianjin-Hebei (BTH) urban megaregion in China. We quantified four critical ecosystem services, food production, carbon sequestration and oxygen production, water conservation, and soil retention, and identified the hotspots of ecosystem service provision. We measured the urbanization level from three aspects, namely, population growth, economic development and developed land expansion. The impacts of urbanization on the selected ecosystem services were examined at the hotspots scale and urban megaregion scale. We found both ecosystem services and urbanization level in the BTH region increased. There was an obvious spatial heterogeneity in the hotspots of ecosystem services, showing hotspots of food production aggregately distributed in the southern plain while hotspots of regulating services mainly located in the north mountainous areas with dense forest. The relationship between population growth, economic development and food production were represented by an inverse U-shaped curve, while it displayed a decreasing trend with regulating services. Both food production and regulating services decreased dramatically with urban land expansion. Additionally, the relationships between urbanization and ecosystem services were consistent across scales. Effective measures should be implemented for the hotspots of different types of ecosystem services to mitigate the loss of ecosystem services during rapid urbanization. The results can provide insights for enhancing urban sustainability in the BTH region, as well other urban megaregion with similar characteristics throughout the world. © 2019 Elsevier B.V. All rights reserved.
⁎ Corresponding author at: State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China. E-mail address: [email protected] (W. Zhou).
https://doi.org/10.1016/j.scitotenv.2019.01.260 0048-9697/© 2019 Elsevier B.V. All rights reserved.
J. Wang et al. / Science of the Total Environment 662 (2019) 824–833
1. Introduction The past decades have witnessed rapid urbanization in China, with the proportion of urban population increasing from 11.8% in 1950 to 54.8% in 2014 (Ye et al., 2018). The urban land also experienced rapid and continuous expansion. The national urbanization level which measured by the proportion of urban population is projected to reach approximately 60% in 2020 (Yang and Shi, 2017). Urbanization makes a significant contribution to social improvement and economic development, while simultaneously posing a grave threat to the health of non-urban ecosystems. During the process of urbanization, forest, pastoral, and agricultural ecosystems have been converted into human-dominated ecosystems at an unprecedented scale and pace. This process inevitably disturbs the structure and function of the antecedent ecosystems, resulting in the loss of ecosystem services (Alberti, 2010; J. Liu et al., 2017). It is widely assumed that urbanization will continue, which puts increasing pressure on ecosystems. Urban sustainability has become one of the most pressing issues facing humanity today (Grimm et al., 2008). Understanding the relationship between urbanization and ecosystem services is critically important for providing informative suggestions for urban planning to achieve urban sustainability (Zhou et al., 2017). Considerable research has demonstrated the urbanization is one of the main driving forces for the change of ecosystem services (GarcíaNieto et al., 2018; B. Li et al., 2016; Zhou et al., 2018). However, the effects of urbanization on ecosystem services are not consistent among different studies, and in some cases, research results are contradictory. For example, a number of studies have revealed ecosystem services were negatively correlated with urbanization (Faulkner, 2004; Su et al., 2014; Zhang et al., 2017). The main reason is that the increasing natural and semi-natural ecosystems transform to impervious surface during rapid urbanization, which causes a drastic decrease of the ecosystem services supply. However, some studies have found the opposite results - ecosystem services would increase during the urbanization process. For instance, Buyantuyev and Wu (2009) found that urbanization boosted productivity of plant communities and improved net primary productivity of ecosystem in the Phoenix metropolitan region of USA. Zhou et al. (2018) demonstrated that the value of ecosystem services increased in the Beijing-Tianjin-Hebei region with the rapid urbanization during the period 1996–2014. In addition, previous research demonstrated that a non-linear relationship, represented by an “inverse U” shape, between urbanization and ecosystem services may occur, as suggested by several studies (Li et al., 2010; Wan et al., 2015). That is, ecosystem services increase first at the earlier stage of urbanization, but after reaching a certain threshold value, it starts to decline. The main reason for these variability can be summarized as two aspects. First, multiple land use changes occur during rapid urbanization, the increases in forest, grassland and waters in non-urban areas may offset the decrease in ecosystem services caused by urban expansion (Zhou et al., 2018). Second, the relationship between urbanization and ecosystem services is highly dependent on the environmental context of study area. For example, a desert city, Phoenix, is intensely irrigated in the process of urbanization, thus greatly improved the productivity and biodiversity of the plant communities. To sum up, the relationship between ecosystem services and urbanization is complex. Extending the obtained results to other study area might lead to erroneous conclusions (Kindu et al., 2016). It is necessary to detect the relationship between ecosystem services and urbanization in specific research area in order to provide scientific basis for making reasonable urban planning and ecosystem management measures. Additionally, the relationship between urbanization and ecosystem services varies by both the types of ecosystem services and the selected indicators that used to measure urbanization level. There was no unanimous variation in the different ecosystem services types. For example, when investigating the relationship between ecosystem services and urbanization in the Guangzhou-Foshan Metropolitan Area, China, Ye et al. (2018) found gas regulation, soil formation and retention, and
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climate regulation occurred substantial decline, but the waste treatment and recreation and culture services increased. Furthermore, the relationship between ecosystem services and urbanization may also vary when using different indicators to measure urbanization levels. For example, some research suggested an “inverse U” shape relationship between ecosystem services and urbanization when the degree of urbanization was measured by population and economy (Wan et al., 2015). However, a negative relationship was found when the degree of urbanization was measured by developed land (e.g., Hu et al., 2015; Peng et al., 2017b). Therefore, fully understanding the relationship between multiple ecosystem services and different component of urbanization is of great significance for minimizing the negative impact of urbanization on ecosystems and realizing urban sustainability. Megaregions are now and will continue to be a prominent form of urbanization in China (Yu and Zhou, 2018; Li et al., 2019). More and more megaregions are emerging in recent decades, such as the BeijingTianjin-Hebei region, the Yangtze River Delta, and the Pearl River Delta. Although rapid and large-scale urbanization brings huge economic growth, the ecosystems of urban megaregions have experienced serious degradation (Cai et al., 2017), which not only poses threats to the regional ecological security, but also restrains the future economic development. Furthermore, the demand for valuable natural resources and excellent living environment are growing rapidly as large numbers of people congregate in the urban megaregion. Investigation the impacts of urbanization on ecosystem services in the urban megaregions have great significance for achieving the double-win situation for both economic development and environmental protection. A large number of studies have been conducted to investigate the impacts of urbanization and ecosystem services in the urban megaregion (Li et al., 2010; Zhang et al., 2017), but most have concentrated on analyzing the change of ecosystem services caused by urban land expansion at the whole urban megaregion (Sun et al., 2018; Ye et al., 2018). Few studies, however, have examined the hotspots of ecosystem services provision and the relations with urbanization. These hotspots are locations where the key ecosystem services are provided and thus contribute a disproportionate importance of ecosystem services provision to the region (Ouyang et al., 2016). If the hotspots of ecosystem services provision were overly developed, the ecosystems will be degraded, which is not conducive to the coordinated development of the urban megaregion. Hence, it is necessary to investigate the relationship between urbanization and ecosystem services in the hotspots, in addition to the whole urban megaregion. Based on the above review of the literature, this study was designed to explore the impact of urbanization on ecosystem services in the BeijingTianjin-Hebei region (BTH), China. The study had three components. First, four types of ecosystem services, including food production, carbon sequestration and oxygen production, water conservation, and soil retention, were selected to quantitatively assess ecosystem services and their change from 2000 to 2010. Second, the spatiotemporal patterns of change in urbanization were quantified using the three aspects of population growth, economic productivity, and land conversion. Finally, we identified the hotspots of each type of ecosystem services and explored the relationship between urbanization and ecosystem services in the hotspots and the whole urban megaregion. Our results are expected to provide quantitative information for realizing coordinated development of economy and environment and enhancing urban sustainability in the BTH region and other urban megaregion with similar characteristics throughout the world. 2. Material and methods 2.1. Study area and data sources The BTH region lies between 36.07°N–42.65°N and 113.46°E– 119.79°E in North China. It includes two municipalities that are directly under the control of the national government, Beijing city and Tianjin city, and another 11 municipalities in Hebei Province (Fig. 1). There are 202 counties in the BTH region, the number in Beijing city and
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Fig. 1. Location of the study area and the land use/land cover (LULC) in 2010.
Tianjin city is 16, respectively, and the remaining 170 belong to Hebei province. The area of the BTH region is 216,500 km2, accounting for 2.2% of the total area of China (D. Li et al., 2017). The study area has a typical temperate continental monsoon climate, with the annual average temperature of 3 °C–15 °C and annual average rainfall of 304–750 mm (Xie et al., 2016). The elevation decreases from the northwest to the southeast, ranging from 2836 m to −52 m. The BTH region is the center of national politics, economy, culture, and technology (Zhang et al., 2016). The total population was 111.42 million and the population density reached 515.8 person/km2 at the end of 2015. The study area is considered as the largest economic hub in North China, with a gross domestic product (GDP) exceeding 6935.89 billion Yuan (or, approximately 1100 billion dollars) in 2015. Spatial data and statistical data were used in this study to analyze the link between urbanization and ecosystem services. The Shuttle Radar Topography Mission (SRTM) digital elevation model (DEM) with spatial resolution of 90 m was obtained from the Geospatial Data Cloud site, Computer Network Information Center, Chinese Academy of Sciences (http://www.gscloud.cn). The precipitation, temperature, and other meteorological data were obtained from the Chinese meteorological data network (http://data.cma.cn/). The spatial meteorological data were interpolated using the inverse distance weighted method. The soil data were obtained from harmonized world soil database supplied by the International Institute for Applied Systems Analysis and the Food and Agriculture Organization (http://webarchive.iiasa.ac.at/ Research/LUC/External-World-soil-database). The net primary productivity (NPP) data from the MOD17A3 dataset were supplied by NASAUSGA (https://lpdaac.usgs.gov/). The land cover data were interpreted based on Landsat TM and ETM data with 30 m resolution using an approach that integrates object-based classification and a backdating method (Yu et al., 2016). The landscape was classified into 6 categories, namely forest, grass, water, farmland, developed land, and barren land. The population and GDP data at a spatial resolution of 1 km × 1 km were provided by the Data Center for Resources and Environmental Sciences, Chinese Academy of Sciences (RESDC) (http://www.resdc.cn). The statistical data, such as grain output and other production supply, were
obtained from Beijing Statistical Yearbook, Tianjin Statistical Yearbook and Hebei Statistical Yearbook. 2.2. Quantifying ecosystem services 2.2.1. Food production (FP) Food production is crucial for food security and regional sustainable development (B. Li et al., 2016). We calculated the crop production provided by farmland and assigned the results to raster data at a spatial resolution of 1 km × 1 km. According to related studies (Xie et al., 2018; Zhang et al., 2017), we selected grain, oil crops and vegetables to assess the food production as provisioning services. The production data were derived from Statistical Yearbooks of Beijing, Tianjin and Hebei Province. The equation for food production is as follows:
Px ¼
C X
AP
ð1Þ
c¼1
where Px is the total food production for pixel x, the size of the pixel is 1 km × 1 km. A refers to the area of cropland in pixel x. P represents the average yield of the selected grain, oil crops and vegetables per unit area. 2.2.2. Carbon sequestration and oxygen production (CSOP) We calculated the amount of carbon sequestration and oxygen production with NPP data based on the principle of photosynthesis, in which the production of 1 kg of dry matter can fix 1.63 kg of CO2 and release 1.2 kg of O2 (Li and Zhou, 2016). C x ¼ 1:63 NPPx þ 1:2 NPP x
ð2Þ
where Cx represents the amount of carbon sequestration and oxygen production for pixel x, NPPx is the amount of NPP for pixel x.
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2.2.3. Water conservation (WC) Water conservation refers to the capacity of ecosystems to hold part of water input from precipitation within a certain period. The amount of water conservation for each pixel on the landscape was obtained by the equation described as follows, the required runoff coefficient values were derived from Ouyang et al. (2016). WC ¼
j X
ðP i −Ri −ET i Þ Ai
ð3Þ
i¼1
Ri ¼ P i a
ð4Þ
where WC is the total amount of water conservation, Pi is the precipitation, Ri is the storm runoff, ETi is evapotranspiration, Ai is the area of the ecosystems as defined by land cover types, and a is the runoff coefficient, i is the index for each ecosystem, and j is total number of ecosystems within the pixel. 2.2.4. Soil retention (SR) Soil erosion reduces the soil fertility and increases the frequency of flood disaster, which has been considered to be an important ecological problem in the BTH region. The soil retention service was quantified using the universal soil loss equation (USLE) implemented in the sedimentation module of InVEST model. The annual soil loss of different land use types for each pixel was computed as follows (Sun et al., 2018): USLEx ¼ Rx ∙K x ∙LSx ∙C x ∙P x
ð5Þ
where Rx is the rainfall erosivity for pixel x, Kx is the soil erodibility factor for pixel x, LSx is the slope length-gradient factor, Cx is the crop management factor for pixel x and Px is the support practice factor for pixel x. Crop management and support practice factors for each land use type were modified according to Li (2014) and Wu et al. (2013). 2.3. Mapping urbanization levels Population growth, economic development, developed land expansion, and other social-economic indicators were widely applied to measure urbanization levels (Su et al., 2012). In this study, we characterized the urbanization levels of the BTH region from three aspects: population growth, economic productivity, and land conversion. The population density (person/km2) was used to reflect population urbanization, Gross Domestic Product (GDP) density (104 yuan/km2) was applied to describe economic urbanization, and the proportion of construction land in a specific grid (1 km2) was used to represent land conversion (Peng et al., 2017b). 2.4. Hotspot analysis of the selected ecosystem services Hotspot analysis is a specific spatial analysis technique that has been used for identifying areas where high values for a variable of interest occur. It has been widely applied to identify priority areas for both biodiversity and ecosystem services conservation (Y. Li et al., 2017; Schröter et al., 2017; Timilsina et al., 2013). We used Gi⁎ statistics, a tool integrated in ArcGIS 10.3, to identify the locations which can provide large amounts of ecosystem service. The detailed steps to obtain the distribution of hotspots for ecosystem services are as follows. First, zonal statistics were used to calculate the sum of each selected ecosystem service type for every county in the BTH region. Then we used the Hotspot Analysis (Getis-Ord Gi*) tool to identify the hotspots of ecosystem service provision. 2.5. Analyzing the relationship between ecosystem services and urbanization The relationship between ecosystem services and urbanization is complex, and linearity, “inverted U” shape, “S” shape and other non-
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linear relationship may occur. We applied curve estimation to identify the relationship between ecosystem services and urbanization. Curve estimation in SPSS 13.0 for windows, was used to analyze the relationship between ecosystem services and the three components of urbanization: population density, GDP density, and the proportion of the developed land. The relationship between ecosystem services and urbanization were explored in the specific hotspots and throughout the whole urban megaregion. The basic unit for curve estimation was the county. Due to the different size and unit for the indicators of population density and GDP density, the raw value of these two indicators were log transformed before conducting curve estimation. 3. Results 3.1. Spatial pattern of ecosystem services in the BTH region The spatial pattern of the four selected ecosystem services exhibited clear heterogeneity, and the ecosystem services had great change during 2000 to 2010 (Fig. 2). Food production increased remarkably, with an average food production of 152.29 t/km2 in 2000, increasing to 196.06 t/km2 in 2010. The high-yield area was located on the plains in the south of the BTH region, such as the western part of the Shijiazhuang, Baoding, Xingtai and Handan, while the low-yield region mainly distributed in Zhangjiakou and Chengde in the north of the study area. Although the highest value of COSP were lower in 2010, the COSP service improved between 2000 and 2010, the average values were 3820.88 t/km2 and 4027.94 t/km2, respectively. The values of COSP service were higher in the central parts of the study area that was covered by forest and farmland, while the values were lower in the eastern part of Zhangjiakou and the coastal areas in Tianjin, Tangshan, Langfang and Cangzhou. The average amount of water conservation increased greatly during 2000–2010. The areas that had higher water conservation values were located in the north of the BTH region. The soil erosion situation of the study area has greatly improved; the average value of soil retention increased from 959.39 t/km2 to 1347.34 t/km2. The high-value regions of soil retention were located in the mountainous area that were covered with dense forest. 3.2. Spatial pattern of urbanization level in the BTH region The urbanization levels of the BTH region in 2000 and 2010 are shown in Fig. 3. The results indicated that the population density and GDP density of each city in the BTH region have greatly increased, the area of developed land has been expanding constantly during 2000–2010. The spatial pattern of population growth, economic productivity, and land expansion is similar, with great variations among different cities. The areas with higher urbanization levels were located in the already existing urban districts of the 13 cities in the BTH region, especially the 2 megacities, Beijing and Tianjin. While the areas in Chengde and Zhangjiakou presented the lowest levels of urbanization. The results of population urbanization suggested that the population density were the highest in Beijing, and the average values were 658 person/km2 and 1195.6 person/km2 in 2000 and 2010, respectively. The level of economic urbanization was the highest in Tianjin, and the average values of the GDP density increased from 1409.77 yuan/km2 to 4105.06 yuan/km2 during the study period. The developed land experienced rapid expansion in 2000–2010, for example the proportion in Tianjin was 15.54% in 2000, while the value reached 23.16% in 2010. 3.3. Identifying hotspots of ecosystem services in 2000 and 2010 The hotspots with different confidence levels of the selected ecosystem services in 2000 and 2010 were shown in Fig. 4. It is generally recognized that P b 0.05 (i.e., 95% confidence level) is defined as statistically significant (Y. Li et al., 2017). Thus we focused on hotspots with confidence levels above 95% in this study, which were considered as the
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Fig. 2. Spatial patterns of ecosystem services in 2000 and 2010 (FP - food production; COSP‑carbon sequestration and oxygen production; WC-water conservation; SR-soil retention).
key areas for ecosystem services provision. The hotspots were aggregated in space, but the spatial patterns of hotspots of different ecosystem services were distinct. The hotspots of food production were located on the plain in the southern and eastern part of the study area, including many counties in Hengshui, Cangzhou, Xingtai, Shijiazhuang and Tangshan. The spatial distributions of the hotspots of COSP, WC,
and SR were similar, which were situated in the northern BTH region, including Chengde, the east part of Zhangjiakou and the northern part in Beijing. The spatial pattern of hotspots did not changed significantly during 2000–2010. We also found that the areas with higher levels of urbanization, such as the two megacities of Beijing and Tianjin, have fewer hotspots of ecosystem service provision.
Fig. 3. Spatial patterns of urbanization levels in 2000 and 2010 (Pop_D - population density; GDP_D - GDP density; DLP-developed land proportion; Yuan is the Chinese currency, at an exchange rate of 1.00 USD = 6.75 Yuan as of January 2019).
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Fig. 4. Hotspots of ecosystem services with different confidence levels in 2000 and 2010.
3.4. The relationship between urbanization and ecosystem services in the BTH region The relationships between urbanization and ecosystem services in the hotspots and the whole BTH region were explored in this study. The spatial pattern of COSP, WC, and SR in hotspots were similar (Fig. 4); thus we considered the sum of COSP, WC, and SR as regulating service and identified the shared hotspots for these services, then analyzed the correlation between ecosystem services and urbanization over the period of 2000–2010. 3.4.1. The relationship between urbanization and ecosystem services in the hotspots There was an “inverse U” shape relationship between food production and the urban parameters of population density and GDP density (Fig. 5). The increase of population density and economic development intensity had a positive impact on food production in areas with low levels of urbanization, which indicated that ecosystems have sufficient capacity to resist the negative effect of urbanization. After a certain level of growth, food production decreased significantly with increasing population density and GDP density. Whereas, there was an obvious negative relationship between developed land proportion and food production, food production consistently decreased significantly with the increase of urbanization level. The main reason was that the expansion of the developed land often takes place at the expense of farmland, resulting in a decrease in food production. For regulating services, the ecosystem services drastically declined with an increase of population density, GDP density and developed land. 3.4.2. The relationship between urbanization and ecosystem services in the BTH region The characteristic of the relationship between urbanization and ecosystem services in the whole BTH region was similar to that in the hotspots (Fig. 6). There was an “inverse U” shape relationship between food production and population density and GDP density in 2000 and 2010. In terms of the parameter of population density, when the value reached 444.79 person/km2 in 2000, food production decreased
significantly with an increase of population, while the threshold value declined to 345.31 person/km2 in 2010. The main reason is that the growing population puts great pressure on ecosystem, and the carrying capacity of the ecosystem reduced. For the indicators that were used to measure economic productivity, the maximum value of GDP density that caused a reduction in food production increased during the study period. The threshold value was 2.5 million yuan/km2 in 2000, and it reached 5.97 million yuan/km2 in 2010. The food production was negatively correlated with land urbanization. The regions with higher levels of urbanization were located in the center of the cities, where the area of farmland was relatively small, so the crop yield was low. In view of regulating services, there was a prominent negative relationship between ecosystem services and urbanization. The main reason was that the regulating services is mainly provided by forest ecosystems. Rapid urbanization leaded to a significant reduction in forest ecosystems, thus decreasing the supply of ecosystem service. 4. Discussion 4.1. The relationship between urbanization and ecosystem services The relationship between urbanization and ecosystem services has received widespread attention in recent years (Cao et al., 2017; Jiang et al., 2017), but with inconsistent results from previous studies. Overall, ecosystem services in the BTH urban megaregion had a trend of growth, even though the region experienced rapid and intense urbanization from 2000 to 2010. Such improvement in ecosystem services was consistent with that from the China Ecosystem Assessment at the national scale (Ouyang et al., 2016), and from other studies (Viña et al., 2016). Such improvement, similar to that at the national scale, may be mainly attributed to China's national conservation policies started in 2000, which have effectively alleviated the ecological deterioration (Ouyang et al., 2016). Under the effect of ecological conservation policies, the area of forest in the study area increased from 70,309.44 km2 to 71,603.64 km2 over the past decade, which greatly improved the regulating services. Large areas of farmland have been occupied along with
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Fig. 5. Relationship between ecosystem services and urbanization in hotspots.
urban expansion. As shown in Table S1 in the Appendix, 3108.47 km2 of farmland has been converted to developed land from 2000 to 2010. However, the agriculture yield remarkably increased, with the average food production of the BTH region increasing from 152.29 t/km2 to 196.06 t/km2, which was largely attributed to the technology improvement and industrial structure upgrade in agriculture sectors. When considering different types of ecosystem services, and their relationships with levels of urbanization measured by different indicators, the impacts of urbanization and ecosystems services may vary. For example, the provisioning services had an “inverse U” shape relationship with economic dimensions of urbanization, but had a significantly negative linear one with urban expansion. This is likely because the impact of
population growth and economic development on the ecosystem is reflected by developed land expansion (Peng et al., 2017b). At the early stage of urbanization, the negative impact of developed land expansion on ecosystem is insignificant, where ecosystem can resist the interference of human activities. But with continuous urban expansion and economic development, increased yield per unit area was not enough to compensate the loss caused by conversion of arable land to developed land. In contrast to provisioning services, regulating services were negatively correlated with all the three urbanization indicators. Expansion of developed land can directly drive the decline of ecosystem's regulating services, which also can be indirectly reflected by population growth and economic development (Peng et al.,
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Fig. 6. Relationship between ecosystem services and urbanization in the BTH region.
2017b). For example, conversion of forested land to developed land would inevitably reduce the supply of regulating services provided by forest ecosystems. In the future, many effective measures should be implemented to realize the harmonious development of urbanization and ecological environment. For the hotspots of provisioning services that are located in the middle and south of the study area, agricultural infrastructure should be upgraded in order to increase crop production (Peng et al., 2017a). In addition, we need to strictly observe the red line for protecting farmland and control the expansion of developed land. For the hotspots of regulating services that are situated in the north of the study area, ecological conservation policy should continue to be implemented, including a strengthening of forest ecosystem protection.
Furthermore, the population density and economic development scale should be controlled to realize the coordinated development of urbanization and ecological environment. 4.2. The implication of hotspots analysis In addition to the commonly conducted analysis at the city or megaregion scale, we also analyzed the relationship between urbanization and ecosystem services for the hotspots. Increasing interest has been focused on mapping and specifically identifying the hotspots of ecosystem services in recent years. A large number of relevant research has been performed by using hotspots analysis to identify the critical areas of ecosystem services supply (e.g., G. Li et al., 2016; Timilsina
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et al., 2013). Although numerous studies have emphasized the necessity to incorporate the concept of ecosystem services into landscape planning and ecosystem management, practical applications are still largely lacking (Daily et al., 2009; Groot et al., 2010). Identifying the hotspots of the different types of ecosystem services alone can provide insights for decision makers to more effectively determine the protection priority areas. Our results showed that the hotspots of regulating services (COSP, WC, SR) were located in the northern of the study area, which was primarily covered by high dense forest. Ecological degradation of these sites could cause a significant decline in multiple ecosystem services (Qiu and Turner, 2013), which poses a serious threat to human well-being. Thus these areas should be treated as the priority areas for ecological protection to ensure regional ecological security. Moreover, the conservation budgets are usually not sufficient to conserve all sites (Y. Li et al., 2017), the efficiency of ecological conservation strategies would be improved greatly by focusing on hotspots. Our results of hotspot analysis also showed great spatial mismatch between hotspots distribution of provisioning and regulating services. The hotspots of food production were aggregated in the south plain, while the hotspots of COSP, WC, and SR mainly were distributed in the north mountainous part of the study area that covered with dense forest. This finding was consistent with previous studies that indicated topography and ecosystem service type were the two important factors that caused spatial heterogeneity in the hotspots of ecosystem services (Cai et al., 2017; Y. Li et al., 2017; S. Liu et al., 2017). Such information on spatial mismatch can also provide insights on identify protection priority areas, and suggest consideration of tradeoffs among different types of ecosystem services. 4.3. Limitations and future perspectives In this study, the relationship between urbanization and ecosystem services was explored for both hotspots and the whole BTH region. The BTH region is composed of 13 cities with various urbanization levels, and the development direction of each city is different. For instance, as the political, economic and cultural center, Beijing experienced rapid development, especially the hi-tech Industries. The cities of Chengde and Zhangjiakou, which are located in the northern part of the BTH region, have been considered to be important ecological protection zones, as a result of their vital roles in water conservation and sandstorm prevention. In contrast, Xingtai, Handan, and other cities in the southern part of the BTH region not only have abundant mineral resources, but also provide vast agricultural production. In view of the distinct characteristics of each city, the relationship between urbanization and ecosystem services at the city scale should be further explored to obtain more comprehensive view on achieving the goal of sustainable development. In addition, we only considered four types of ecosystem services, but not others, such as the cultural services. With the beautiful scenery and invaluable cultural heritage, the study area is an important national and international tourist destination in China. The development of tourism also exerts an influence on ecosystem services. The cultural ecosystem services need to be considered in future research. 5. Conclusion The relationship between urbanization and ecosystem services is complicated. This study documented that there are diverse relations between urbanization and ecosystem services. In particular, there are different relationships depending upon the type of ecosystem services examined and the different indicators used to measure urbanization levels. Our study explored the relationship between urbanization and ecosystem services in the BTH region from the hotspots scale and the whole urban megaregion scale. The results showed that there was an “inverse U” shape relationship between food production and urbanization measured by population density and economic density; however,
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