Multi-scale analyses on the ecosystem services in the Chinese Loess Plateau and implications for dryland sustainability
Introduction
Dryland areas cover about 47% of the world terrestrial land surface and support nearly 40% of the global human population [1•]. Therefore, the globally established sustainable development goals (SDGs) for 2030 cannot be fulfilled without the contribution from dryland areas and the people living there. Because of the limitation of water resources availability and the challenging climate change impacts, dryland areas are also victims of persistent land degradation problems that has resulted in desertification of 3.6 billion hectares. Consequently, halt and reverse land degradation has been incorporated as critical components of the 15th SDG ‘Life on Land’. As a prerequisite to accomplish this sub goal, land degradation neutrality (LDN) has to be guaranteed in general and particularly in dryland areas. LDN is defined as a stable or increasing state of land resources on the amount and quality to support ecosystem functions and services within specified temporal and spatial scales and ecosystems [2]. This necessitates the outweighing of ecological restoration over land degradation. Ecological restoration is thus the critical approach to address this SDG component. To keep soils and land healthy is prerequisite for successfully implementing ecological restoration and realization of LDN [3].
However, a top-down quantitative analysis revealed that meeting the global land restoration and protection targets can incur land use conflicts, which call for the harmony between land management and policy pursuits [4•]. This is highly relevant to dryland areas because of their inherent ecological vulnerability, harsh human-nature relations, and mounting challenges to be addressed in resolving the aforementioned conflicts. Along this line, the sustainable use and management of the soil-water system and the relevant ecosystem services according to their geographical differentiations can be critical for conflict resolution and facilitating LDN [5,6]. As to the literature on ecological restoration in dryland areas, most of them are restricted to site or landscape scales and focusing on technological issues concerning restoration such as the water harvesting technics [7], planting technics of restoration islands [8], and dryland restoration modeling [9]. These are important to inform best working methods for restoration manipulations. But the success of dryland restoration programs is closely linked to both ecological and socioeconomic opportunities and limitations largely beyond the scope of technical issues. Therefore, more efforts are urgently required to move global dryland restoration forward by regional scientific understanding of the tradeoffs and synergies triggered by restoration initiatives and their sustainable management [10].
As the third largest country in the world, China has long been suffering from land degradation resulted from comparatively low resources and environmental carrying capacity but the world highest human population pressure. To combat the widespread land degradation problem, China has invested huge amount of money and other resources in large scale ecological conservation and restoration programmes that have brought about significant gains in ecosystems (e.g. forests and grasslands) and their services on desertification control, soil conservation, and water quality maintenance [11••]. Within China, the Loess Plateau (LP) as a typical dryland region ranked the highest in ecosystem restoration after the implementation of the Grain for Green Program (GGP) [12]. The LP region lies in the north central of mainland China covering about 640 thousand km2 (Figure 1). It is the pilot and demonstration area for the GGP that returns the croplands on steep hillslopes to grass and woodlands to improve environmental stability and ecosystem services. After the regional implementation of GGP, the vegetation coverage has been significantly restored in 62% of the LP region, which is much more than the area with significant vegetation degradation at only 2.2% of the LP region during 2000–2015 [13]. This is very positive and ideal for addressing the LDN component of the 15th SDG at regional scale from the vegetation restoration perspective. LDN requires actions at local, regional, and national scales for the ecological restoration of degraded lands on both ecosystem state and functionality. Therefore, the LP is a typical regional case of global dryland for addressing the LDN target and some sustainable land management practices from the LP have been incorporated in the United Nations Convention to Combat Desertification recommended global sustainable land management database of World Overview of Conservation Approaches and Technologies [2].
After 20 years of intensive ecological restoration and management, the significant land cover and ecosystem changes in the LP region have promoted changes in ecosystem services and their interactions represented as tradeoffs and synergies across spatiotemporal scales, which are also critical scientific concerns supporting the LDN [14]. This paper will summarize the research progress on this topic and discuss its implications on dryland sustainability. It can provide evidence-based insights for facing the LDN on drylands that have not been met so far and are still tough challenges in the future [4•,15•].
Section snippets
Field-based monitoring and multi-scale analyses on ecosystem services
Field-based monitoring of ecosystem properties and changes can provide essential data sources for the research on ecosystem services. The usability of this approach depends on the monitoring design of the target ecosystems which can be site-specific and also stretch to a large region along environmental gradient in forms of transects. All these field-based approaches have been adapted in the LP region. Supported by these monitoring campaigns, the changes of ecosystem services and their
Modeling-based multi-scale analyses on ecosystem services
Field-based monitoring and experiments are fundamental as ground truth strongly supporting ecosystem service research and applications. But they are time and resources consuming. Therefore, much more researches have adopted model-based approaches on ecosystem services assessments and simulations.
Some researches focused on the assessment or modelling of one specific ecosystem service. As the LP is a typical dryland region, water, carbon, and also temperature regulation services have been
Implications for the ecosystem service research and applications on drylands towards sustainability
The sustainability of drylands as socio-ecological systems depends on both the ecological adaptability and resilience of the ecosystems and endurable level of human use pressure that is well within the carrying capacity of the dryland ecosystems in changing environment across local to global scales. More specifically, the ecological restoration in drylands have to exceed degradation for realizing the sustainable development goal of LDN [49]. For this mission, it is highly required to advance
Research challenges and directions
With the aid of a relevant literature search and analysis for the latest five years (Supplementary information), it is clear that the LP has been the most intensively studied dryland region both in China and internationally. The most distinctive feature of the current ecosystem service research in the LP region is the quantitative investigations of the trade-offs and synergies among various ecosystem services driven by land use changes, and policy motivated soil conservation and vegetation
Conclusion
With the promotion of the 2030 sustainable development goals, ecological restoration will be increasingly used as powerful tool for realizing the target of land degradation neutrality. This is particularly important and challenging in global drylands. The ecosystem service research has provided scientific support for quantifying the effectiveness and impacts of ecological restoration on drylands just as those reflected from the research progresses reviewed in this paper on the Chinese Loess
References and recommended reading
Papers of particular interest, published within the period of review, have been highlighted as:
• of special interest
•• of outstanding interest
Declaration of Competing Interest
The authors report no declarations of interest.
Acknowledgements
This research was funded by the National Key Research and Development Program of China (No. 2016YFC0501601), the Strategic Priority Research Program of the Chinese Academy of Sciences (No. XDA23070201), and the International Partnership Program of Chinese Academy of Sciences, (No. 121311KYSB20170004).
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