Keywords

1 Background

Drylands are regions where the Aridity Index (AI, determined by dividing mean annual precipitation by potential evapotranspiration) is below 0.65 (Huang et al. 2017a). Globally, drylands occupy ~41% of terrestrial land surface, supporting more than 38% of the world’s population, of which approximately 90% are in developing countries (Berdugo et al. 2017; Reynolds et al. 2007). Drylands are characterized by scarce and highly variable annual precipitation, high potential evapotranspiration, low fertility of soils, and sparse vegetation (Huang et al. 2017a; Smith et al. 2019). Dryland ecosystems play an important role in providing numerous services such as water, food, fiber, habitat, biodiversity, and carbon sequestration (Ahlström et al. 2015; Bestelmeyer et al. 2015; Poulter et al. 2014). However, the sustainability of these ecosystem services is a concern, as drylands are considered to be fragile ecosystems and extremely sensitive to land degradation induced by climate change and human activities (Costanza et al. 2014; D’Odorico et al. 2013; Huang et al. 2017a; Maestre et al. 2016; Middleton and Sternberg 2013). Studies have reported that global aridity is increasing, and that the world will be drier in the future due to climate change (Huang et al. 2016; Li et al. 2023; Lian et al. 2021; Park et al. 2018). For example, it is estimated that drylands will expand up to 56% of the Earth’s surface under the RCP8.5 scenario, or up to 50% under the RCP4.5 scenario, respectively (Huang et al. 2016). One recent aridity database analysis (covering 1950–2000) showed that global drylands have expanded by almost 4% in this time period, with major expansion in the arid (+3.4%) and semi-arid (+0.9%) regions (Prăvălie et al. 2019). Aridity is increasing in almost all continents except for Europe and South America, focusing on low and middle latitudes (Prăvălie et al. 2019). However, these findings are inconsistent with observed increases in greenness over drylands (He et al. 2019). Several studies have found that the AI is not an accurate proxy for defining drylands, as it fails to consider the key role of varying atmospheric CO2 concentrations that drive climate change and its impacts on vegetation (Berg and McColl 2021; Stringer et al. 2021). The expansion of global drylands with a decreasing AI contrast with findings from other studies that use variables such as precipitation and soil moisture to identify drylands (Berg and McColl 2021; Lian et al. 2021; Roderick et al. 2015; Zhang et al. 2020a).

Of all the countries with drylands in the world, China ranks second in its extent of dryland areas after Australia (Prăvălie 2016). More than half of China’s land surface (56.48%) is defined as dryland (Prăvălie 2016). China’s drylands are home to approximately 580 million people, accounting for 20% of the world’s population living in drylands (van der Esch et al. 2017). China alone accounts for almost one third of increases in dryland expansion worldwide (Prăvălie et al. 2019). Desertification is land degradation in drylands and is prevalent in China’s drylands, challenging water supply, food security, and carbon sequestration (Wang et al. 2008). China leads globally in large-scale land conservation and restoration programs to combat desertification, greening the country’s drylands (Bryan et al. 2018). However, large-scale ecological restoration projects also impose substantial pressure on these water-limited environments (Cao 2008; Wang et al. 2010).

During the last two decades, increasing research effort has been devoted to understanding China’s dryland ecosystems and their responses to ongoing global change (Ci and Yang 2010; Huang et al. 2017a; Wang et al. 2008; Yang et al. 2011). This chapter aims to provide a comprehensive understanding of the basic characteristics, changes, and drivers of China’s drylands. It reviews the key fronts on which progress has been made, suggests research priorities in both the near- and long-term, and proposes possible strategies to address the main remaining research gaps. It is essential to advance understanding and develop appropriate strategies to cope with continued climate changes and ecosystem dynamics. Such efforts can help inform actions to advance towards the sustainable development goals (SDGs) in China’s drylands, offering insights for other global drylands.

This chapter is structured to provide the following:

  1. (1)

    A review of the major characteristics of China’s drylands, including their distribution, climate, soil, land uses, land degradation, eco-hydrological processes, and social and economic development;

  2. (2)

    A synthesis of current understanding of the changes in China’s drylands, covering dryland dynamics, structure and functions, ecosystem services, and human well-being, and considering the livelihoods of local communities;

  3. (3)

    A discussion of the factors affecting ecosystem structure and functioning of dryland ecosystems under environmental change;

  4. (4)

    A synthesis of major research priorities and potential approaches to address them.

2 Major Characteristics of Drylands in China

2.1 Distribution and Landforms

Based on the AI, drylands can be further classified as hyper-arid (AI < 0.05), arid (0.05 <= AI < 0.20), semi-arid (0.20 <= AI < 0.50), and dry sub-humid (0.50 <= AI < 0. 65) areas (Huang et al. 2017a). China’s drylands cover an area of approximately 657.52 × 104 km2, accounting for about 66% of the terrestrial surface (Fig. 12.1a), among which the hyper-arid, arid, semi-arid, and dry sub-humid areas are 84.20 × 104 km2 (8.55%), 208.64 × 104 km2 (21.17%), 256.46 × 104 km2 (25.99%), and 108.23 × 104 km2 (10.96%), respectively. China’s drylands are mainly located in latitudes between 30° and 50° N, and in longitudes between 75° and 135° E (Fig. 12.1a).

Fig. 12.1
2 maps. A. It represents the spatial distribution of dryland and subtypes in China. The legend at the bottom represents Beijing, borders, rivers, provincial boundaries, hyper-arid, arid, semi-arid, dry sub-humid, and humid. B. represents landforms and locations in China. The locations are marked 1 to 12.

a Spatial distribution of drylands and four subtypes in China. Data is derived from the Global Aridity Index database (Trabucco and Zomer 2009). b Landforms and location of deserts in China’s drylands. Data is derived from data sets provided by Data Center for Resources and Environmental Sciences, Chinese Academy of Sciences (RESDC) (http://www.resdc.cn)

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Drylands are mainly located in north China, covering 17 provinces, municipalities, and autonomous regions, including Xinjiang, Tibet, Qinghai, Inner Mongolia, Gansu, Ningxia, Shaanxi, Shanxi, Hebei, Henan, Shandong, Jiangsu, Heilongjiang, Jilin, Liaoning, Beijing, and Tianjin. Among all the provinces that have drylands, Xinjiang and Inner Mongolia have the largest dryland areas, with 173.46 × 104 km2 and 114.25 × 104 km2, respectively (Table 12.1). Drylands in Xinjiang are dominated by hyper-arid and arid regions, covering 65.29 × 104 km2 and 87.84 × 104 km2, respectively.

Table 12.1 Area and proportion of drylands and sub-types in different provinces and cities of China
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The topography of China’s drylands varies greatly, and is mainly composed of inland basins (e.g., Tarim Basin, Junggar Basin), high plateaus (i.e., Qinghai-Tibet plateau, Loess Plateau, Inner Mongolia Plateau), and high mountain systems (e.g., Himalayas Mountains, Tianshan Mountains, Kunlun Mountains and Qilian Mountains). Deserts and Gobi landforms are widely distributed in China’s drylands (Fig. 12.1b). Deserts cover an area of 56.34 × 104 km2, among which Taklimakan Desert and Gurbantunggut Desert are the largest. Gobi is mainly distributed around the Tarim Basin, Junggar Basin, the foothills of the Kunlun Mountain, Tianshan Mountains, and Hexi Corridor. Gobi is mainly formed by external forces such as wind and water power, and its surface is mainly gravel, which is different from sandy land. Loess landforms are mainly distributed on the Loess Plateau, showing large hilly and gully areas with loose soils that are easily eroded and transported by running water.

2.2 Climate, Soil, Land Uses, and Land Degradation

The formation and evolution of landforms in drylands result from the combined effects of abiotic factors (e.g., rainfall, temperature, soil), biotic attributes (e.g., vegetation), and land degradation.

Climate

Most of the drylands in China are located in the central Eurasian continent surrounded by high mountains and plateaus, where the moist summer monsoon from the Pacific Ocean cannot penetrate deep into the northwest hinterland; and nor can the wet summer monsoon from the Indian Ocean due to the barrier of the Himalayas Mountains and the high Qinghai-Tibet Plateau (Li and Ling 1992). These areas are consequently characterized by water scarcity and drought. Water resources are limited as precipitation (mean: 304.0 mm; Std: 22.6 mm) is typically much lower than potential evapotranspiration (mean: 814.9 mm; Std: 25.5 mm) (Fig. 12.2a, b). Precipitation is both temporally and spatially highly variable. Rainfall during the year usually occurs as short-duration and high-intensity rainstorms during a relatively short rainy season from June to September. Multiple precipitation pulses occur alternately with dry periods. The interannual variation of rainfall is typically high, in particular in hyper-arid and arid regions (Li et al. 2021). Rainfall varies greatly over short geographical distances, with high rainfall in mountainous regions but scarce rainfall in the surrounding plains. Rainfall differs across the gradient of hyper-arid, arid to semi-arid and dry sub-humid areas, increasing gradually from the northwest towards the east, south, and southeast (Fig. 12.2a). Runoff in response to rainfall events in China’s drylands is dominated by infiltration-excess overland flow (runoff production when the rainfall intensity is greater than the soil infiltration capacity), while saturation-excess overland flow (runoff production when the unsaturated zone and saturated portion of the soil profile is saturated by long periods of rainfall) is seldom observed. High intensity events during the rainy season frequently lead to flashy runoff and low infiltration, while rainfall with low intensity seldom produces runoff due to the high temperatures and the associated rapid and high rates of water loss to evaporation and transpiration. The spatial pattern of rainfall and evapotranspiration leads to runoff in upland drylands with altitude greater than 1,000 m, while the lowland drylands have no runoff production at all (Chen et al. 2015). Consequently, river networks across China’s drylands landscapes are poorly dissected and dominated by ephemeral streams (existing only for a short period following rainfall or snowmelt) and intermittent streams (streams that exist for longer periods than an ephemeral stream but not all year round).

Fig. 12.2
A set of 6 maps in the drylands of China. A. represents the precipitation range from less than 200 to greater than 800. B. represents the potential evapotranspiration range from less than 400 to greater than 1300. C. represents temperature from less than negative 10 to greater than 20. D. represents soil type, e. it represents land uses. F. it represents land degradation processes.

Spatial distribution of basic characteristics in the drylands of China, including a precipitation, b potential evapotranspiration, c temperature, d soil types, e land uses, and f land degradation processes

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Mean temperature in the drylands of China ranges from −30 to 30 °C (Li and Ling 1992), and varies greatly between southern and northern parts (Fig. 12.2c). The maximum recorded temperature (49.6 °C) in China was documented in the famous “Fire Prefecture” of Turfan in Xinjiang, while nearby Fuyun was recorded one of the lowest minimum temperatures (−51.5 °C). The diurnal temperature range is substantial, with the temperature difference in the Tarim Basin as much as 15–20 °C. This big difference in temperature between night and day is observed in an old saying: “Cotton-padded jacket in the morning, T-shirt at noon, and enjoy watermelons around the stove”. Both altitude and terrain influence temperatures. The temperature decreases by 5–6 °C with an increase of 1,000 m in altitude. In the northern Qinghai-Tibet Plateau where the altitude is approximately 4,000–5,000 m above sea level, the mean temperature in July stays below 10 °C.

Drylands in China are rich in solar and wind energy. The total annual duration of sunshine varies from 2,500 to 3,000 h, with annual solar radiation from 136 to 160 kcal/cm2 (Li and Ling 1992). High solar radiation usually occurs in the Qinghai-Tibet Plateau, the Tarim Basin, and Hexi Corridor in Northwest China.

Soil

There are many kinds of soil both in horizontal and vertical zonality which has resulted from the varied patterns of climate, rock formation, topography, vegetation, and the long history of agricultural development in China’s drylands (Li and Ling 1992). The 1:1,000,000 soil database in the drylands of China was tailored from the 1:1,000,000 soil database in China that was based on the 1:1,000,000 soil maps of China compiled and published by the National Soil Census Office in 1995. The spatial database was based on the soil genetic classification of China, including 12 orders, 61 groups, and 227 subgroups (Shi et al. 2004b). From arid, semi-arid in the northwest to sub-humid in the middle and east of the China’s drylands, the major soil type ranges from desert soil to steppe soil, and to the forest-steppe soil sequences (Li and Ling 1992). The largest soil order in China’s dryland is Alpine soil (Fig. 12.2d), which is widely distributed on the Qinghai-Tibet Plateau, covering a total dryland area of 168.89 × 104 km2. Alpine soils are further classified into felty soils, dark felty soils, frigid calcic soils, cold calcic soils, cold brown calcic soils, frigid desert soils, cold desert soils, and frigid frozen soils. Alpine soils are mainly in the high-altitude cold region where soil erosion by freezing and thawing is substantial, so the soil layers generally have frozen layers and permafrost. Soil biological function in Alpine soil areas is weak due to the poor hydrothermal conditions, resulting in sparse vegetation cover and slow accumulation of humus. Primarosols are widely distributed in the arid and semi-arid regions of China, such as the Tarim Basin, Zhungeer Basin, and the Loess Plateau, with a total area of 122.58 × 104 km2. Primarosols in the Taklimakan Desert is further classified as aeolian sandy soil, and that in the Loess Plateau is Loessial soil. Desert soil and Aridsols are widely distributed in northeastern Xinjiang, northwestern Gansu, and western Inner Mongolia, with the total area of 62.67 × 104 km2 and 31.76 × 104 km2, respectively. These two types of soil are vulnerable to erosion, with low nutrients and poor fertility, meaning they are not conducive to vegetation growth and farming. Alkali-saline soils are widely distributed in low altitude areas such as the plains, basins, and valleys of arid and semi-arid inland regions where the groundwater table is high and there is considerable evaporation of surface water, making soluble salts in the subsoil easily drawn up into the topsoil.

Land Uses

China’s drylands are dominated by grasslands (2.3 million km2, 34%), desert (1.4 million km2, 21%), and croplands (1.1 million km2, 16%) (Fig. 12.2e). Large amounts of unused land including Gobi, sandy land, and bare rocky land account for 33% of the total dryland area (Fig. 12.3). Most of these areas are barren land with sparse vegetation due to natural conditions and human activities such as overgrazing (Li and Ling 1992). The spatial pattern of land uses in China’s drylands shows that cultivated land, urban and rural settlements are mainly in the North China Plain. Large areas of sandy land and Gobi are concentrated in northern Xinjiang, western Inner Mongolia, and western Gansu.

Fig. 12.3
2 pie chart depicts the proportion of land use in China. The data are grassland 34%, unused land 33%, arable land 16%, woodland 11%, waters and urban and rural settlements 3%, salt lick, and bare land 2%, Gobi, bare rock texture, and sand 9%, everglade and others 1%.

Pie chart showing the proportion of land uses in China’s drylands in 2020. Data is derived from data sets provided by Data Center for Resources and Environmental Sciences, Chinese Academy of Sciences (RESDC) (http://www.resdc.cn)

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Ecohydrology

Plant growth is mainly determined by the available soil moisture during the growing season (Bai et al. 2004; Wu et al. 2011). The spatial and temporal patterns of available water strongly govern dryland vegetation (Scott et al. 2014). Hydrological processes influence the distribution, structure, function, and dynamics of biological communities, while feedbacks from biological communities affect the water cycle (Fig. 12.4a). Investigating the two-way interactions between and interdependence of ecological and hydrological processes is essential to better understand ecosystem dynamics in drylands (Brauman et al. 2007; Newman et al. 2006; Turnbull et al. 2008; Scott et al. 2014).

Fig. 12.4
A schematic illustration of the water cycle and ecosystem interactions in drylands. It includes water table, soil development infiltration, soil stabilization, plant water use, flow attenuation, buffer strip filtration, and wetland filtration.

Water cycle and ecosystem interactions in drylands (after Brauman et al. (2007)). At the watershed scale, dryland ecosystems affect water through canopy interception, evaporation, transpiration, water use by plants (i.e., forest, shrub, and grass), flow attenuation, and ground surface modification. The hydrological cycle driven by solar energy includes precipitation, infiltration, surface flow, ground flow, and evaporation. Water fluxes are indicated by arrows. The water balance equation is expressed as precipitation = evapotranspiration (transpiration + evaporation) + discharge (surface + ground water) + change in water storage (surface + ground water)

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Dryland vegetation is typically patchy and heterogeneous. Studies conducted at multiple spatial scales (e.g., plot, hillslope, catchment) have found that the patchy vegetation affects the temporal and spatial pattern of water, sediment and nutrients, soil microbial biomass, and functional diversity (Hu et al. 2010; Li et al. 2008), and ultimately the functioning of China’s drylands (Fu et al. 2003; Wang et al. 2001).

Land Degradation

In ancient China, most drylands were covered by dense forests and grasses, and the soil was fertile for agriculture development and grazing (Li and Ling 1992). However, the once-productive ecosystem has been historically deteriorated by human activities (e.g., land reclamation, farming) during the last 6,000 years, leading to natural hazards such as widespread drought, soil erosion, and salinization. Erosion by wind, water and freeze–thaw are three key processes of desertification in China’s drylands (Shi et al. 2004a), which together affect 95.4% of the country’s dryland area (Li et al. 2021). Breaking this down, the dryland regions affected by wind erosion, water erosion, and freeze–thaw erosion cover 2.28 million km2 (34.5% of China’s total drylands), 2.46 million km2 (37.4% of total drylands), and 1.55 million km2 (23.5% of total drylands), respectively. More than half (56.2%) of drylands affected by wind erosion (mostly in northwestern and northern arid and hyper arid regions) experience strong (5000–8000 tons km−2 yr−1), extremely strong (8,000–15,000 tons km−2 yr−1), and dramatic (>15,000 tons km−2 yr−1) magnitudes of erosion. However, the drylands affected by water erosion and freeze–thaw erosion are predominantly influenced by minor, mild, or moderate erosion (<5,000 tons km−2 yr−1), which accounts for 92.9% and 94.6% of the water erosion and freeze–thaw erosion regions, respectively.

Since the establishment of the People’s Republic of China in 1949, a series of important policies and measures (e.g., Three-North Shelterbelt Development Program, Grain for Green Program) have been adopted to develop the drylands (Li and Ling 1992). Land degradation increased thereafter and peaked in the early 1980s (Wang et al. 2008). The widespread land degradation in China’s drylands seriously constrained socioeconomic development, especially before the end of the twentieth century (Lü et al. 2012). However, the land degradation trend has been reversed since 1980s as observed by Normalized difference vegetation index (NDVI) (Piao et al. 2005). NDVI has usually been used as a proxy assessment of land degradation or improvement, but it fails to consider other influencing factors such as climate which could be represented by rain-use efficiency (RUE). Land degradation as measured by RUE-adjusted annual sum NDVI analysis showed that 80% of degrading areas are in the humid and cold-climate zone (i.e., non-dryland areas); while drylands have a much lower proportion of degrading areas, with 10% in the dry sub-humid, 5% in the semi-arid, and 5% in the arid and hyper-arid areas (Bai and Dent 2009).

2.3 Social and Economic Development

China’s drylands have a population of 580 million, representing 41.6% of the total population of the country. The areas with the highest population densities in China’s drylands are in the southeast provinces of Beijing, Tianjin, Shandong, Hebei, and Henan. Coastal areas of Northeast China are also densely populated (Fig. 12.5a). The western region is sparsely populated, and there are large areas devoid of human populations.

Fig. 12.5
2 maps. A. represents the spatial distribution of population density, which ranges from 0 to 1 to greater than 5000. B. represents gross domestic productivity high at 63, and low at 0. C. represents the night light map for the G D P value range from 0 to greater than 3000. D. horizontally stacked bar graph depicts year versus G D P for hyper-arid, arid, semi-arid, and dry sub-humid. The highest value is 2015.

a Spatial distribution of population density, b Gross Domestic Productivity (GDP), c Night Light Map (NLM), and d trends of GDP in the drylands of China. The DN value represents the brightness value of remote sensing image pixels, and records the gray scale of ground objects in the range of 0–63. The larger the DN value, the brighter it is

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Nighttime lights offer an important indicator to measure the degree of regional economic and social development. Lighting information based on satellite sensors is closely related to urban development and human activities. The nighttime light map of China’s drylands (Fig. 12.5b) shows a distribution highly consistent with the distribution of GDP and population. The eastern part of the drylands, especially the North China Plain, is densely populated with towns and high levels of economic development, and these areas have larger brightness values of remote sensing image pixels. There are also several bright spots in the Northeast parts of the drylands, in the provincial capitals.

Gross Domestic Product (GDP) is usually used to measure the total value of all final products and services produced by a country or region in a one-year cycle. The size of GDP is closely related to population distribution and urban development (Fig. 12.5c). In 2015, the annual GDP of China’s drylands was about 26,095 billion yuan (Fig. 12.5d), accounting for 41.9% of national GDP. The GDP of the semi-arid and dry sub-humid regions accounted for 39.5% of the national GDP. The GDP of China’s drylands is mainly provided by the two dryland sub-types in the eastern part of China’s drylands. The GDP contribution of the hyper-arid area is maintained at a low level with no significant growth over the past 20 years. The GDP of China’s drylands decreases from southeast to northwest. The Qinghai-Tibet Plateau and southern Xinjiang have extremely low GDP levels due to their sparse populations.

3 Changes to Drylands in China

3.1 Structure and Functions

Climate Change

China’s drylands have experienced temperature increases of 4.12 °C during 1980–1997 and 4.93 °C during 1997–2015, with an average annual increase of 0.013 °C (Fig. 12.6a). However, precipitation showed non-significant trends (p > 0.1) in general (Fig. 12.6b). Potential evapotranspiration increased from 798.74 mm during 1980–1997 to 831.09 mm during 1997–2015, with average annual increases of 1.30 mm (Fig. 12.6c). The changing trends of temperature, precipitation, wind speed, and potential evapotranspiration followed a cycle of 2–4 years (Fig. 12.7).

Fig. 12.6
A set of 4 multi-line graphs depicts the annual temperature, precipitation, potential evapotranspiration, and wind speed versus years from 1980 to 2014. The values fluctuate and are labeled drylands, dry sub-humid, semi-arid, arid, and hyper Arid.

Annual climate change in China’s drylands and four subtypes during 1980–2015. a, b, c, d show the interannual variation of mean temperature, precipitation, potential evapotranspiration, and wind speed, respectively

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Fig. 12.7
A set of 4 multi-line graphs depicts the trend of annual temperature, precipitation, potential evapotranspiration, and wind speed versus years from 1980 to 2014 for drylands, dry sub-humid, semi Arid, arid, and hyper-arid. The values of the curves are highly fluctuating in all graphs.

Trend of annual climate change in China’s drylands and four subtypes during 1980–2015. a, b, c, d show the dynamics of the trend of annual temperature, precipitation, potential evapotranspiration, and wind speed, respectively

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Except in a few areas in the northwest (hyper arid areas) and northeast, temperature increased in the most of drylands of China (Fig. 12.8a). Precipitation declined in northeastern China, but increased in the northern arid and semi-arid areas (Fig. 12.8b). Wind speed declined in some of northeastern and northwestern China, but increased in the northern and southwestern arid and semi-arid areas (Fig. 12.8c). Potential evapotranspiration increased in most of the drylands except the western Tibetan Plateau (Fig. 12.8d).

Fig. 12.8
A set of 4 maps of the dry land of China. The legend at the bottom represents Beijing, provincial boundaries, borders, temperature change, precipitation change, wind speed, and potential evapotranspiration.

Spatial trend of climate change in the drylands of China during 1980–2015. a, b, c, d show the trend of temperature, precipitation, wind speed and potential evapotranspiration respectively

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Land Use/Cover Change

Land use/cover change in China’s drylands showed a decrease in forest from 1970 to 2000, and an increase from 2000 to 2015 (Fig. 12.9). Grassland showed a continued decrease by 5.4 × 104 km2 from 1970 to 2015, with reductions in all high, moderate and low coverage grassland. Cropland and construction land increased during the 1970–2015 by 5.8 × 104 km2 and 3.4 × 104 km2, respectively. The area of unutilized land reduced by 1.5 × 104 km2 from 1970 to 2015 mainly in the sub-types of Gobi and Sandy land (Fig. 12.9).

Fig. 12.9
A set of 6 bar and line graphs depicts changes in land use distribution versus years from 1970 to 2015. The values of the bars are both increasing and showing increasing trends. The bar value indicates area, and the line value indicates percentage.

Changes in land use distribution during the period 1970–2015 in the drylands of China. The primary Y-axis shows the area and the secondary Y-axis shows the percentage. Land uses considered include: a cropland; b forest; c grassland; d water body; e construction land; f unutilized land

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Vegetation Indices Change

Numerous vegetation indices have been developed to investigate vegetation growth dynamics, including vegetation productivity, vegetation greenness, and vegetation cover (Ding et al. 2020). Due to the various indices to depict vegetation growth dynamics and great uncertainty in the estimation of vegetation change (Piao et al. 2020), it is essential to determine the consistency of vegetation growth dynamics using multiple indices (Ding et al. 2020). In this section, three widely used satellite-derived vegetation indices were applied to assess 2000–2015 vegetation growth trends in China’s drylands. Specifically, net primary productivity (NPP), Normalized Difference Vegetation Index (NDVI), and the leaf area index (LAI) were used to characterize vegetation greenness, vegetation cover and productivity, respectively. Results showed that NPP, NDVI, and LAI increased in the drylands of China during 2000–2015 (Fig. 12.10a–c). The spatial distribution of the vegetation growth trends showed that there was a combination of vegetation improvement and degradation (Fig. 12.10d–f). Generally, vegetation indices increased in the central and eastern semi-arid and dry sub-humid regions, and decreased in the northwestern drylands. The area over which vegetation growth was enhanced was generally greater than the area with degraded vegetation. Overall, the distribution of vegetation growth trends was similar among NPP, NDVI, and LAI, but there are areas where distinct differences existed among different vegetation indices.

Fig. 12.10
A, B, and C. The line graph of annual N P P, N D B I, and L A I versus years from 2000 to 2015 for drylands, dry sub-humid, semi-arid, arid, and hyper-arid. The values are slightly increasing and decreasing in all graphs. D, E, and F. Represent the spatial pattern map of China for N P P, N D V I, and L A I.

Temporal and spatial patterns of NPP, NDVI, and LAI changes in the drylands of China during 2000–2015. Panels a, b, and c show the trends of annual NPP, NDVI, and LAI, respectively, in China’s drylands and sub-types. Panels d, e, and f show the spatial pattern of NPP, NDVI, and LAI, respectively. The gray area represents no data

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The combination of changes in vegetation productivity, vegetation greenness, and vegetation cover in China’s drylands showed a diversity of vegetation growth dynamics (Fig. 12.11). 62.98% of the vegetated area exhibited an increase or decrease in all three aspects. In most of the eastern dry sub-humid and semi-arid areas, NPP, NDVI, and LAI all increased, but in some semi-arid areas of the Qinghai-Tibet plateau, all three vegetation indices decreased. 37.02% of the vegetated area experienced inconsistent trends in vegetation productivity, vegetation greenness, and vegetation cover. 15.98% of the vegetation area experienced enhanced vegetation productivity and cover, with degraded greenness, especially on the edges of semi-arid and arid areas (Fig. 12.11). Regions with increased greenness (NDVI) but decreased productivity (NPP), and vegetation cover (LAI) accounted for 1.85% of the vegetated area in drylands. Another noteworthy vegetation growth pattern is found in the regions where only vegetation productivity increased while greenness and cover decreased. Those areas accounted for 4.77% of the vegetated area and were concentrated in the northeastern Inner Mongolia region’s drylands.

Fig. 12.11
A map exhibits a combination of trends in N P P, N D V, and L A I in China. The unshaded region indicates no data. The scale at the bottom represents 500 to 2000 kilometers.

Combination of trends in NPP, NDVI, and LAI of the drylands in China during 2000–2015. The gray area represents no data

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3.2 Ecosystem Services

Water is the principal driver of ecological processes. Among the various services provided by ecosystems (Fig. 12.12), hydrological services (e.g., water supply) are the basis for realizing other services such as soil generation, carbon sequestration, and recreation (Brauman et al. 2007). To better understand and quantify water-related ecosystem services, it is essential to link ecohydrological processes (e.g., water, carbon, energy, and nutrient cycling) to ecosystem services (water and food security, and climate moderation) (Brauman et al. 2007; Sun et al. 2017). Water scarcity drastically limits dryland ecosystem services, particularly supporting and regulating services which are of great importance for soil formation, nutrient cycling, and water and climate regulation (Prăvălie 2016). The low freshwater availability of dryland ecosystems implies that water is insufficient to accommodate China’s dryland population of 580 million while also ensuring optimal ecosystem functionality.

Fig. 12.12
A schematic illustration of hydrological and other services such as provisioning, regulating, supporting, and cultural services for timber, non-timber forest products, wildlife habitat, local climate modification, flood mitigation, recreation, water supply, soil development, and carbon sequestration.

Examples of hydrological and other services that a watershed produces, such as water supply, timber and non-timber forest products, soil development, carbon sequestration, and local climate modification and recreation. Based on the categories used by The Millennium Ecosystem Assessment (2005), provisioning services refer to the products obtained directly from ecosystems such as water, food, and timber; regulating services indicate that ecosystems have the ability to regulate processes such as climate, and the water cycle; supporting services are indirect services which are important for soil formation, nutrient cycling and so on; and cultural services refer to benefits that ecosystems provide to people including tourism, education, recreation, and aesthetic values

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Dryland ecosystems in China are important in providing a wide range of ecosystem services including water yield, soil conservation, carbon sequestration, and habitat quality (Lü et al. 2012). Based on the datasets of ecosystem services evaluated by Xu et al. (2020), the changes in the four major ecosystem services in China’s drylands (e.g., water yield, soil conservation, carbon sequestration, and habitat quality) during 2000–2015 were examined. Results showed a strong correlation between the studied ecosystem services and aridity, indicating that the values for all four ecosystem services followed the order: dry-sub-humid > semi-arid > arid > hyper-arid.

Water yield, soil conservation, carbon sequestration, and habitat quality in dry sub-humid regions are the highest among the four dryland sub-types (Fig. 12.13). Significant conversions of farmland to woodland and grassland have resulted in enhanced soil conservation and carbon sequestration, but decreased regional water yield under a warming and drying climate trend. Water yield generally increased from 2000 to 2010, and then decreased from 2010 to 2015 (Fig. 12.13a). The spatial pattern showed that water yield increased in general but declined in southeastern and southwestern drylands. Soil conservation showed a non-significant trend during 2000–2015 (Fig. 12.13b). Spatially, soil conservation declined in southeastern and southwestern drylands, where water erosion and freeze–thaw erosion are serious, respectively. Carbon sequestration generally increased during 2000–2015, especially in eastern dry sub-humid and semi-arid areas, but decreased in some of the southwestern semi-arid and arid areas (Fig. 12.13c). The finding is consistent with the vegetation change, showing that NPP, NDVI, and LAI increased in most of eastern dry sub-humid and semi-arid areas, but decreased in some semi-arid areas of the Tibetan plateau. Habitat quality is highest in the northeastern semi-arid area and southwestern semi-arid and arid areas such as the Qinghai-Tibet Plateau. Habitat quality increased in arid and hyper arid areas, but decreased in dry sub-humid and semi-arid areas, especially in the east and northeast drylands (Fig. 12.13d).

Fig. 12.13
A set of 4 grouped bar graphs depicts annual water yield, annual soil conservation, annual carbon sequestration, and annual habitat quality versus years from 2000 to 2015 for dry sub-humid, semi-arid, arid, and hyper-arid. The estimated highest value is dry sub-humid in all graphs.

Ecosystem service change in China’s drylands and sub-types. a, b, c, and d are the water yield, soil conservation, carbon sequestration, and habitat quality, respectively

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4 Driving Forces of Dryland Change

The ecosystem structure, functioning and delivery of ecosystem services by drylands are substantially affected by multiple drivers, including climate change, dryland conservation practices, livestock grazing and fencing, and nitrogen deposition (Fu et al. 2021; Maestre et al. 2016). The following parts of this section give an overview of the drivers of change in the drylands of China.

4.1 Climate Change

Climate projections indicate that hotter, drier conditions and extreme rainstorms will continue to intensify over the twenty-first century (Feng and Fu 2013; Fu and Feng 2014), and are assumed to result in dryland expansion and further desiccation and degradation (Huang et al. 2016, 2017c, 2020). Ecosystems in the transitional regions (e.g., semi-arid regions) are fragile and highly sensitive to warming and drying, and are generally agricultural districts with large populations, leading to great challenges for both the ecosystem and human wellbeing (Huang et al. 2017a). Semi-arid drylands are highly sensitive to climate change (Huang et al. 2017b; Poulter et al. 2014), and the largest contributor to land-based carbon sink interannual variability, vital in regulating the climate (Ahlström et al. 2015). An expansion of 33% in China’s semi-arid regions from 1948 to 2008 (Li et al. 2015b) will have reduced soil organic carbon storage and emitted CO2 into the atmosphere (Maestre et al. 2016).

Global climate change is likely to produce higher aridity (Berdugo et al. 2020), which will cause negative ecological consequences by limiting soil moisture and disrupting vital C, N, and P biogeochemical cycles (Delgado-Baquerizo et al. 2013). Key ecosystem structures and the functional properties in drylands showed a strong nonlinear change with increasing aridity, indicating that dryland ecosystems could pass an irreversible tipping point as aridity increases (Berdugo et al. 2020; Delgado-Baquerizo et al. 2013; Wang et al. 2014a; Wardle 2013). Different climatic change drivers affect vegetation in different ways. Rising atmospheric CO2 enhances water-use efficiency and plant growth (Li et al. 2013), while an increase in aridity negatively affects water availability and plant productivity (Berdugo et al. 2020; Maestre et al. 2016). However, it is still not known whether the positive effects of CO2 fertilization can buffer the negative effects of increased aridity.

4.2 Livestock Grazing and Fencing

Due to increasing demand for meat, milk, and other livestock products, many dryland regions in China are seeing grazing intensification (Su et al. 2005). Overgrazing is an important driver of widespread declines in biodiversity, ecosystem functioning, and services in the arid and semi-arid grasslands of China (Bai et al. 2007; Deng et al. 2014; Li et al. 2017b; Su et al. 2005). Overgrazing decreases plant species diversity and productivity (Bai et al. 2007), reduces the C, N and P pools in above-ground biomass, and alters C:N:P stoichiometry of steppe ecosystems (Bai et al. 2012); results in soil compaction through trampling and reducing soil infiltration rate, and enhances topsoil exposed to water and wind erosion (Li et al. 2015a, 2017b). A synthesis analysis based on 61 studies from 88 independent research sites within the Qinghai-Tibetan Plateau showed that livestock grazing significantly increased plant species diversity, but decreased aboveground biomass by 47.15%, soil organic carbon by 12.41% and soil total nitrogen by 12.75% (Lu et al. 2017). To mitigate the negative impacts of climate change in the arid and semi-arid grasslands of China, reducing the stocking rate is essential, particularly to sustain native steppe biodiversity, and conserve ecosystem functioning (Bai et al. 2012).

Fencing is widely used as a restoration and management practice in grassland ecosystems worldwide (Deng et al. 2014; Wu et al. 2009, 2010). Fencing improves soil quality by increasing soil organic carbon, soil total nitrogen, the soil C:P ratio and N:P ratio within the 0–100 cm soil profile, and increases vegetation coverage, biomass, and plant diversity (Deng et al. 2014; Wang et al. 2014b). Fencing grassland with grazing exclusion decreased bulk density, pH, and forbs (Wang et al. 2014b). 8-year grazing exclusion significantly affected C pools but had no significant influence on the soil N pool (Wang et al. 2014b). More attention should be given to identifying the main soil and plant characteristics that drive C and N dynamics after grazing exclusion (Wang et al. 2014b). The effects of grazing management are influenced by local environmental factors such as climate, elevation, slope, and water availability (Gao et al. 2010; Lu et al. 2017).

4.3 Desertification

China’s drylands are seriously threatened by desertification (Qi et al. 2012), leading to declines in ecosystem functions and services (Prăvălie 2016). Desertification is the outcome of coupled processes which primarily result from climate variation exacerbated by human activities (Chi et al. 2019; Liu et al. 2008; Wang et al. 2008). This section describes the key processes of desertification including wind erosion, water erosion, salinization, freeze–thaw erosion, and rocky desertification (Fig. 12.14).

Fig. 12.14
A map represents desertification in the drylands of China. It highlights salinization, wind erosion, water erosion, rocky desertification, and freeze-thaw weathering. The legend at the top right represents rivers, hyper Arid, arid, Semi-Arid, dry sub-humid, and humid.

The major external forces that cause desertification in drylands of China. Generally, desertification is caused by wind erosion and aeolian processes; water erosion and alluvial processes; freezing and thawing processes on cold plateaus; soil salinization and alkalization processes; and rocky desertification in the dry-sub-humid karst areas

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Wind erosion is a key driver of desertification in global drylands (Poesen 2018; Shi et al. 2004a). China’s drylands affected by wind erosion are mostly in the country’s northwestern and northern arid and hyper arid regions, where the majority of wind erosion intensity is characterized by strong, extremely strong, and dramatic magnitudes. Wind erosion results in loss of soil nutrients (Wang et al. 2006b; Yan et al. 2005) and reduction in NPP and the provisioning services of croplands, grasslands, and forests (Zhao et al. 2017). Wind erosion impacts the lives of 200 million people going as far back as half a century (Wang et al. 2010). Sand and dust storms caused by wind erosion have adverse impacts on air quality, public health, safety of transportation, communication, and irrigation infrastructure, and have significant impacts on the economy (Jiang et al. 2018; Shen et al. 2018; Wang et al. 2016b). Wind erosion dynamics are driven by a combination of climatic factors (i.e., global atmospheric circulation, wind speed) (Jiang et al. 2018; Zhang et al. 2018), soil properties (i.e., surface roughness and erodibility) (Chi et al. 2019), and human activities (i.e., land use/cover change) that leave the soil more exposed (Zhao et al. 2017).

Water erosion and alluvial processes are important drivers of desertification in the semi-arid and dry sub-humid regions of China, with 1.39 million km2 and 0.80 million km2 affected by water erosion, respectively. In particular, the Loess Plateau in the arid and semi-arid regions is one of the hotspots suffering the most severe water-erosion-induced soil erosion problems in the world (Fu et al. 2017; Morgan 2009; Shi and Shao 2000; Wang et al. 2016a). Rainsplash, runoff energy and gravity are the three main active agents in water erosion processes such as splash erosion, interrill erosion, rill erosion, and gully erosion (Li et al. 2018b, c; Li and Pan 2020). Piping is a common subsurface erosion process in the semi-arid loess hilly and gullied regions of North China. Pipes are efficient pathways for water, sediment, and carbon transport, and have the potential to initiate or affect development of gullies through roof collapse or channel extension (Li et al. 2018b; Poesen 2018). Both process-based and empirical soil erosion models have been used previously in the arid and semi-arid Loess Plateau of China to understand these processes (see Li et al. (2017a) for a detailed review). However, it is still a challenge to understand how basic water erosion processes (gully erosion, pipe erosion) function and how the various erosion agents (e.g., rainsplash, runoff, gravity) interact.

Frost weathering is commonplace in the cooler high altitude climates of drylands on the Qinghai-Tibet Plateau (Cheng and Wu 2007). Frost weathering is important in producing eroding soil particles (Li et al. 2018a, b), enhancing heat exchange between the atmosphere and the soil surface and influencing the local and regional climate (Cheng and Wu 2007), and affecting surface and subsurface hydrological processes (Li et al. 2018a). Permafrost degradation could result in desertification and ecosystem deterioration on the Qinghai-Tibet Plateau. Changes in the active layer and permafrost conditions under climate warming scenarios are likely to increase emissions of major greenhouse gases (e.g., carbon dioxide and methane) stored in frozen soils (Cheng and Wu 2007; Yang et al. 2010; Zhang et al. 2020b). Despite the important role of frost weathering in changing carbon pools and fluxes on the Qinghai-Tibet Plateau, very little research has attempted to quantify the effects on carbon dynamics and the underlying hydrological processes (Yang et al. 2010).

Other processes such as salinization and alkalization could enhance desertification in drylands. Salinization affects approximately 0.17 million km2 of the arid and semi-arid regions where the surface soil is rich in sodium chloride and sulfate (>0.3%) (Arndt et al. 2004). Salinization has negative impacts on land productivity since high pH and salinity, and low nutrient levels, restrict plant growth. Rocky desertification is widely distributed in the southwest karst drylands (Jiang et al. 2014; Tong et al. 2018). Rocky desertification is caused by erosion of the thin soil layer (mostly <10 cm) and is induced by increasing human exploitation of natural resources, which has particularly taken place during the past half century (Jiang et al. 2014). However, rocky desertification is not a major land degradation issue in China’s drylands due to the relatively minor land area that it affects (<1% of the total drylands).

4.4 Interactions Among Different Drivers

Abiotic factors and biotic attributes of the ecosystem modify and are modified by each other, and ultimately change ecosystem multifunctionality (Fig. 12.15). Large rain pulses greater than a threshold of between 10 and 25 mm are capable of improving carbon sequestration capacity in the semi-arid steppe of northern China (Chen et al. 2009). Plant structures modulate abiotic properties through biotic-abiotic feedbacks (e.g., evapotranspiration) and associated hydrological responses (e.g., runoff, infiltration). Vegetated and bare surface patches determine whether and how patches interact, and affect the downslope routing of water, sediments and nutrients (Li et al. 2008). Additionally, vegetation patches affect runoff and erosion processes on a hillslope, and the spatial organization of bare and vegetated surfaces (e.g., size, length and connectivity of bare areas), which determines the operating processes at the hillslope scale.

Fig. 12.15
The conceptual framework of relationships and feedback for abiotic factors, biotic attributes, and global change drivers. The abiotic factors are rainfall, temperature, aridity, and topography. The biotic attributes are species richness, species abundance, spatial pattern, and biocrusts. The global change drivers are climate change, conservation practices, grazing and nitrogen deposition.

Conceptual framework showing the relationships and feedbacks among abiotic factors, biotic attributes, ecosystem processes, ecosystem functioning, and global environmental change drivers in drylands of China

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Wind, water, and freeze–thaw weathering are three major agents of desertification. In addition, the three erosion agents usually occur simultaneously and interact strongly with each other. For example, the effects of rainsplash and overland flow on soil erosion (soil particle detachment and available material transport) largely depend on antecedent conditions, including frost weathering which is important in increasing soil erodibility (Li et al. 2018b). Climate change (e.g., warming, CO2 elevation), human activities (e.g., cropland and settlement expansion, and overgrazing by livestock), and their interaction are key in initiating desertification in China’s drylands (Wang et al. 2006a).

Due to the fast-than-average warming rates and growing human consumption of resources, China’s dryland socio-ecological systems may experience systemic and non-linear changes (Fu et al. 2021; Lian et al. 2021), particularly in the semi-arid regions (Berdugo et al. 2020). These changes will negatively affect the key ecosystem services provided by drylands as well as the livelihoods of the substantial human population living in those areas. 2 °C warming has greater negative effects on ANPP in the arid and semi-arid grasslands than the dry sub-humid grasslands (Cheng et al. 2018). Climate projections point to a greater risk of extreme events (e.g., rainstorms and droughts) and aridification in the arid and semi-arid regions of China (Fu et al. 2008). Decreasing precipitation and increasing temperatures enhance soil drying, making soil suction increase, and available soil moisture for plant root uptake less accessible (Huang et al. 2017a). This soil moisture–temperature positive feedback leads to decreased evapotranspiration and increased sensible heat flux and temperature, a completely dry soil layer and desertification (Seneviratne et al. 2010). Expansion of drylands will increase the risk of water scarcity, land degradation, and declines in human wellbeing (Fu et al. 2021; Li et al. 2015b; Yao et al. 2020). While we see significant expansion in the drylands of northern China (Li et al. 2015b), there is conflicting evidence showing that China’s drylands will shrink under future 1.5 and 2.0 °C warming scenarios when using runoff and leaf area index (LAI) to delineate drylands instead of the AI (Zhang et al. 2020a). It is thus unclear that the country’s dryland boundaries will expand overall under climate change.

5 Ecological Management

5.1 Payments for Ecosystem Services

Payments for Ecosystem Services (PES) have been widely used as an effective tool for ecological conservation and restoration without restricting socioeconomic development (Salzman et al. 2018; Yang et al. 2013). China leads in its investment in global government-financed PES programs, implementing PES strategies at a scale and speed simply not possible in other countries (Salzman et al. 2018). During the last four decades, there has been a substantial increase in PES programs in China’s drylands (Bryan et al. 2018). Illustrative PES programs include the Grain to Green Program (regarded as the world’s largest PES program in terms of investment and area coverage), and the Natural Forest Conservation Program, focusing on logging bans and afforestation (Liu et al. 2008; Salzman et al. 2018). Many previous studies have reported the ecological and socioeconomic outcomes of PES programs. For example, Wu et al. (2019) used a framework that linked the Grain to Green Program, livelihood activities, and socioeconomic outcomes, to investigate how the Grain to Green Program affected the incomes of local households in the Yanhe watershed of the Loess Plateau. Wu et al. (2019) selected five livelihood activities, including crop production, orchard fruit production, non-farm work, labor migration, and greenhouse-grown vegetable production. ‘Non-payment income’ was selected as an indicator of the socioeconomic outcome, to represent income from sources other than payments from the Grain to Green Program. Several hypothesis was proposed including: (i) all the five livelihood activities are able to increase non-payment incomes; (ii) the Grain to Green Program is to convert steep croplands to forest and grassland, which has a negative impact on agricultural production; but positively affects orchard fruit production due to the increase in area of orchard fruit plantation; (iii) the Grain to Green Program has a positive impact on participation in non-farm work and labor migration in the household (Liu et al. 2008; Yin et al. 2014). In addition, it was hypothesized that different livelihood activities interact with each other. For instance, labor migration has greater earnings than local non-farm work and creates more job vacancies for local non-farm workers. Both labor migration and non-farm work have negative effect on crop production. Due to the limited labor in a household, the five livelihood activities were negatively correlated to each other. Wu et al. (2019) found that the implementation of the Grain to Green Program significantly increased participation in local non-farm jobs and household incomes. They suggested several ways to improve the socioeconomic outcomes by increasing non-farm work benefits and reducing the reliance of households on income from crop production.

5.2 Efforts to Combat Desertification

To combat desertification, China has implemented a wide range of large-scale land conservation and restoration programs (Fig. 12.16) in drylands (Bryan et al. 2018; Ouyang et al. 2016). Detailed descriptions were provided in Bryan et al. (2018), Li et al. (2021) and Kong et al. (2021). The Natural Forest Conservation Program and Grain for Green Program are two of the biggest programs offering PES in China and worldwide in terms of scale, payment, and duration (Liu et al. 2008). These ecological restoration projects have changed land-use patterns and exerted a significant influence on dryland ecosystems (Bryan et al. 2018; Cheng et al. 2018; Lu et al. 2018).

Fig. 12.16
A schematic timeline diagram represents 13 major programs. Programs such as the Shelterbelt Development Program in 1978, the Soil and Water Conservation Program in 1983, the Shelterbelt Development Program Five Regions in 1987, and the Soil and Water Conservation Program Yangtze in 1989.

The 13 major programs include: the Shelterbelt Development Program—Three North (China’s Great Green Wall) (1978–2050); Soil and Water Conservation Program—National (1983–2017); Shelterbelt Development Program—Five Regions (1987–2020); Soil and Water Conservation Program—Yangtze (1989–indefinite); Natural Forest Conservation Program (1998–2020); Grain for Green Program (1999–2020); Wildlife Conservation and Nature Protection Program (2001–2050); Sandification Control Program—Beijing/Tianjin (2001–2022); Fast-growing and High-yielding Timber Program (2001–2015); Forest Ecosystem Compensation Fund (2001–2016); Partnership to Combat Land Degradation (2003–2023); Rocky Desertification Treatment Program (2008–2020); and Grassland Ecological Protection Program (2011–2020)

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Ecological conservation and restoration projects have resulted in vegetation greening (Chen et al. 2019; Piao et al. 2020), reduced soil erosion and land degradation (Piao et al. 2020; Zhu et al. 2016), and enhanced ecosystem services through soil conservation and carbon sequestration (Lu et al. 2018; Tong et al. 2018). However, in many afforestation areas, large-scale plantations have experienced high mortality due to a lack of understanding of the suitability of planted species to the local environment and soil desiccation in the deep soil layer caused by over-planting (Cao 2008; Feng et al. 2016). Although some positive outcomes have been achieved over the last two decades, large uncertainties remain regarding long-term policy effects on the sustainability of the performance of the ecological conservation and restoration programs. Future research is needed to further explore the dynamic interactions between people and their living environments in a changing world (Lü et al. 2012).

China is a developing country that suffers from long-term and large-scale desertification in its drylands, and the country’s efforts to combat desertification produce many best management practices. For example, the State Forestry Administration of China has established the national desertification monitoring system and the China Desert Ecosystem Research Network (CDERN), to strengthen monitoring and research in desert regions (Wang et al. 2013). The CDERN network has 43 research stations across the arid, semi-arid, and dry sub-humid areas in North China, providing long-term observations and scientific demonstrations for the prevention and control of desertification and regional economic development. In addition, a series of standardization of desertification control technology and ecological protection measures have been approved by the National Standardization Technical Committee, including Technical specification for sand control, Closing (sand) technical specification for afforestation, Technical specification for oasis protection forest system construction (Bao et al. 2017). The normally used desertification control technology includes integrating a series of effective sand-stabilizing methods, selecting drought-tolerant sand-fixing plants, and promoting the fast recovery of vegetation through technology. China’s experience and lessons could be important for other developing countries in order to combat desertification and to improve livelihood of residents (Ci and Yang 2010).

6 Summary and Perspectives

Biotic and abiotic interactions through space and time are vital in determining vegetation dynamics and shaping ecosystem responses in China’s drylands. The key processes of desertification, including wind erosion, water erosion, salinization, freeze–thaw erosion, and rocky desertification, hamper the ability of China’s drylands to provide ecosystem goods and services. Expected increases in aridity will nevertheless negatively impact ecosystem structure and functioning in the drylands of China, even if there is no clear evidence that the country’s dryland boundaries will expand overall under climate change when using runoff and LAI to define drylands. Large-scale ecological restoration projects enhance the greening of China’s drylands, but also impose considerable pressure on these water-limited environments. The effectiveness of the restoration projects should be evaluated in a comprehensive way.

To unravel the complex and dynamic mechanisms of dryland structure and functioning, much work remains to be done on understanding the interactions between biotic attributes and abiotic factors, the two-way interactions between and interdependence of ecological and hydrological processes, and key desertification processes. Integrated research is needed based on multiple spatial–temporal scale observations alongside multidisciplinary studies.

This chapter is of major importance in improving our understanding of China’s drylands where a large proportion of the human population directly depends on ecosystem services from these environments. Due to their wide distribution and unique features, improved and synthesized knowledge about China’s drylands also contributes to the general understanding of how terrestrial ecosystems function and respond to ongoing global environmental changes in drylands around the world.