Impact Assessments of Land-Use Change on Valued Ecosystem Services

Urban areas in NCP increased to 12,648 km² in 2008 from 6036 km² in 1988, with a change percentage of 108.54 %. The annual expansion ratio of urban areas in NCP reached 5.48 % a year. Urban areas expanded faster in western NCP, i.e., regions around Beijing, central Hebei, central Henan, and northwestern Shandong, with urbanization ratios over 300 % (Fig. 3.3). Urban expansion ratios are lower in southeastern NCP, i.e., regions in northern Anhui and Jiangsu provinces. Most of the urban expansion ratios in these areas were less than 50 % during 1988–2008 (Fig. 3.3).

Ratio of cultivated land loss due to urban expansion reached 76.48 % in NCP during 1988–2008. In addition, about 19.89 % of expanded urban areas were converted from other construction land (i.e., rural settlement, industrial, and mining land). The lost proportions of forestry areas, grassland, and water areas due to urban expansion are as low as 0.75, 1.19, and 1.36 %, respectively. Cultivated land contributed to most of the expanded urban areas. The spatial pattern of cultivated land loss ratio in urban expansion is opposite to that of urban expansion ratio. The ratio of cultivated land loss in urban expansion is higher in southeastern NCP, ranging from 90 to 100 % (Fig. 3.3). Urban expansion consumes less cultivated land in western NCP, with a ratio of cultivated land loss lower than 60 %.

The value of total ecosystem service of converted cultivated land in 1988 is about 3911.17 USD/ha (e.g., in 2008 USD) (Table 3.2). Value percentage of nutrient cycling, water conservation, gas regulation, provision of organic production, and soil conservation are 0.32, 22.77, 15.69, 51.17, and 10.05 %, respectively. After the conversion from cultivated land to urban areas, the value of total ecosystem service decreased by 8.94 % (349.33 USD/ha) during 1988–2008. Three kinds of ecosystem services presented a decreasing trend, while two ecosystem services increased.

The ecosystem service of water conservation vanished (decreased by 100 %) when cultivated land was converted to urban areas. The ESV of soil conservation and nutrient cycling also decreased by 5.50 and 3.18 %, respectively. However, ESV of gas regulation and organic production increased by 21.54 and 21.54 %, respectively. The changes in ESV are the combined results of climate and land-use change.

According to the buffer comparison method, we assessed the effects of land-use change on ESV when converting cultivated land to urban areas. Land-use change led to the overall decrease of ESV except for soil conservation in the conversion (Table 3.3). Urban expansion resulted in the complete loss of water conservation function. Ecosystem service functions of nutrient cycling, gas regulation, and organic production also decreased by 31.91, 7.18, and 7.18 %, respectively. However, urban expansion improved the function of soil conservation with an increase of ESV of 2.40 %.

Land-use change significantly reduced the total ESV in central NCP (decreased by 43–100 %), while it increased the ESV in western NCP (ranging from 15 to 128 %) (Fig. 3.4). Except for several regions in northwest, the water conservation function all decreased by 100 % in NCP. The soil conservation function was improved in 65.28 % of the counties in NCP due to urban expansion. The increase of the soil conservation function is particularly significant in eastern NCP, i.e., Shandong Peninsula. However, it decreased remarkably in southwestern NCP (Fig. 3.4).

Organic material production and the gas regulation function decreased in 70.91 % of counties in NCP, while the nutrient cycling function decreased in over 98 % of counties in NCP. The decrease of nutrient cycling is more significant than that of organic production and gas regulation. The decrease of nutrient cycling is larger in central NCP than that in western NCP. The regions that the gas regulation and organic production increased was scattered across the entire NCP. However, the number of counties experiencing increase in gas regulation and organic production gradually decreased from the western NCP to eastern NCP.

In the conversion from cultivated land to urban areas, land-use change accounted for 57.40 % of the changes in ESV, while climate change resulted in 42.60 % of the changes in ESV. For different ecosystem services, land-use change accounted, on average, for 52.62, 80.63, 19.99, 19.99, and 23.30 % of changes in ESV for nutrient cycling, water conservation, gas regulation, organic production, and soil conservation, respectively (Fig. 3.5). Land-use change has a major influence on water conservation and nutrient cycling, while the main effects of climate change are on gas regulation, organic production, and soil conservation.

The effects of land-use change on ESV are more significant in northwestern NCP than any other region in NCP (Fig. 3.5). Land-use change in these areas accounted for over 60 % of the changes in ESV. However, in northern NCP, the effects of land-use change on ESV are generally lower than 45 %. The influence of land-use change on water conservation gradually decreased from northwestern NCP to southeastern NCP. The effects of land-use change on soil conservation is particular significant in a northeast–southwest strip (Fig. 3.5). The effects of land-use change on organic production, gas regulation, and nutrient cycling are similar, i.e., they gradually decreased from the east to the west in NCP.

There are many trade-offs in ecosystem service in urban expansion, i.e., an increase in soil conservation, while there is a decrease of water conservation, nutrient cycling, gas regulation, and organic production. Urban areas are mostly soil sealed, which means that soil erosion does not easily occur. However, cultivated land usually leads to soil erosion under certain conditions, such as in sloping areas, low vegetation cover, and heavy rainfall.

For the soil sealing in urban areas, urban land almost has no water conservation function. When cultivated land was converted to urban areas, the water conservation function almost vanished. The nutrient content of nitrogen in cultivated land is similar to that of an urban ecosystem. However, the nutrient content of phosphorus and potassium in urban ecosystem is far below than that in cultivated land. Therefore, in the conversion from cultivated land to urban areas, the nutrient cycling value of phosphorus and potassium significantly decreased.

Theoretically, if expanded urban areas are all soil sealed, the functions of organic material production and gas regulation will significantly decrease for the loss of vegetation. In this study, we found that land-use change resulted in a decrease of 7.18 and 7.18 % for the organic material production and gas regulation. It can be explained from two perspectives. First, we utilized the land-use change data with a spatial resolution of 1 km. There will be many mixed pixels of urban areas and cultivated land. Although many pixels in land use were classified as urban areas, vegetation could still emerge in these pixels forming functions of organic material provision and gas regulation. Second, there may be many mistaken classification errors in urban areas, i.e., much of the cultivated land close to cities was reclassified as urban areas.

Separating the effects of land-use change from climate change on ESV has always been difficult for the complicated mutual influences between them. In the previous researches, two approaches were usually adopted to do this work, i.e., econometrics analysis and scenario analysis. Econometrics analysis identifies the effects of land-use and climate change on ESV by regression or correlation analysis (Heubes et al. 2012). For example, Su and Fu (2013) found that precipitation in the Chinese Loess Plateau significantly influenced the water yield, while the land-use conversion from cropland to grass/woodland significantly influences the sediment control. Econometrics analysis can judge whether land-use or climate change significantly influences ESV, while it fails to assess the degree of the influence.

In scenario analysis, three scenarios were generally developed, i.e., pure climate scenario (no land-use change), pure land-use change scenario (no climate change), and combined scenario (changes in both climate and land use) (Geng et al. 2014). The influence of land-use and climate change on ESV can be clearly presented by assessing the changes in ESV under different scenarios. The contribution of climate and land-use change on ESV can also be assessed in scenarios analysis. However, scenario analysis still faces great challenges in scenario creation. Many pure scenarios of climate and land-use change are difficult to be created for the complicated mutual effects between them. For example, soil erosion is determined by a great deal of factors, e.g., precipitation, land use, slope, and vegetation coverage. Precipitation, land use, and slope can be easily controlled in scenario creation. However, the vegetation coverage, which is usually directly calculated by remote sensing, is a combined result of land-use and climate change. It is difficult to create a pure climate vegetation coverage without the influences of land-use change and vice versa. Therefore, the application of scenario analysis method is greatly limited.

The buffer comparison method developed in this study can directly assess the contribution of land-use and climate change on ESV. It could be viewed as an improved scenario analysis method. Buffer comparison method factually developed two scenarios, i.e., pure climate scenario and combined scenario. The influence of land-use change on ESV was indirectly deduced by the two scenarios. Since there is no land-use change in buffer zones, pure climate scenario can be easily created and applied in all ESV assessment. The application range of this method is widely enhanced.

The MEA classifies the functions of ecosystem services into provisioning (e.g., provision of food and fiber), regulation (e.g., regulation of climate through carbon storage), cultural (e.g., recreational values), and supporting services (e.g., nutrient cycling and soil formation). Because of the lack of available data and method in mapping cultural services, we only assessed five ecosystem functions in provisioning, regulation, and supporting services. The cultural function changes in the process of urbanization were not assessed, which added much uncertainty in the assessment.

The spatial resolution of the data we utilized to assess ESV and urban expansion is 1 km. The data could be a little coarse for analyzing urban expansion and generate many mixed pixels of urban areas and other land-use types. If the mixed pixels were classified as urban areas, the NPP and NDVI in urban areas could be overestimated. The ESV closely related NPP and NDVI (e.g., organic material production, nutrient cycling) could be consequently overestimated.