The Global-DEP: A Research Programme to Promote Sustainability of Dryland Social-Ecological Systems

Abstract

In light of the escalating pace and heightened intensity of contemporary climate change and human interventions, a more systematic and comprehensive approach to research has become imperative for the realization of the Sustainable Development Goals (SDGs) within dryland regions. In 2017, a collaborative research consortium comprising experts from diverse nations proposed the Global Dryland Ecosystem Programme (Global-DEP). This initiative was designed to address the intricate challenges inherent in the diverse and fragile social-ecological systems (SESs) of drylands. Drawing from a synthesis of preceding studies on dryland SESs and insights garnered from extensive regional consultations, the consortium crafted the conceptual framework of Global-DEP, with SESs as its fundamental underpinning. Key elements of the frame-work encompass driving forces, impacts, feedback loops, and scale. The team identified four pivotal themes: (1) dryland SES dynamics and driving forces, (2) dryland SES structure and functions, (3) dryland ecosystem services and human well-being, and (4) ecosystem management and sustainable livelihoods in drylands. The intricate interconnections among these themes were meticulously examined to delineate 12 critical research priorities. Anchored upon this conceptual framework and the identified research imperatives, the Global-DEP science plan was formulated. This plan is poised to expedite actionable interdisciplinary research within dryland SESs, tailored to the regional and cultural nuances of these areas. The final aim is to bolster dryland research endeavors, catering to the requirements of land practitioners and policymakers, while effectively contributing to the attainment of SDGs in drylands.

1.1 An Overview of Drylands and SDGs

Drylands encompass land areas characterized by a mean annual precipitation to mean annual potential evapotranspiration ratio (known as the aridity index) below 0.65. The aridity index defines four distinct dryland subtypes: hyper-arid (aridity index < 0.05), arid (0.05 ≤ aridity index < 0.20), semi-arid (0.20 ≤ aridity index < 0.50) and dry sub-humid (0.50 ≤ aridity index < 0.65). This definition classifies drylands as covering approximately 41% of the Earth's land surface, sustaining diverse ecosystems that deliver essential goods and services to over 2 billion inhabitants residing in these regions (Millennium Ecosystem Assessment (MEA) 2005).

Drylands are a critical part of the Earth’s systems functioning due to their contribution to the global carbon cycle and their role in climate regulation both regionally and globally, as well as being a major reservoir of biodiversity (including the original genotypes of many key cereals) and host to immense human cultural diversity (Buisson et al. 2022; Castro et al 2018; Maestre et al. 2022; Safriel et al. 2005; Wang et al. 2022). Their ability to deliver these services compared to other terrestrial environments is challenged due to low water availability (Prăvălie 2016), long dry spells (Wang et al. 2012), and hard to recovery from degradation due to the reduced social-ecological resilience (Cowie et al. 2018; Stafford-Smith et al. 2009). The hydrological balance plays a central role in dryland regions (Verstraete et al. 2009). Extended periods of limited water availability result in sparse vegetation cover with great temporal and spatial fluctuation, and great vulnerability to global environment changes and anthropogenic disturbances (Safriel & Adeel 2008). An estimated 1 billion of dryland human inhabitants depend directly on ecosystem services for their livelihoods; despite being attuned to the challenges of dryland conditions when undisturbed, this population rapidly becomes vulnerable when these challenges are exacerbated—becoming a ‘canary in the coalmine’ for global change.

Dryland ecosystems offer a wealth of ecosystem goods and services for human well-being (Safriel et al. 2005; Stafford-Smith et al. 2009). Ecosystem services (ES) in drylands are water constrained, highly variable, and vulnerable to environmental changes; and there are clear trade-offs and synergies among ES such as water supply, food production and regulation services such as carbon fixation and soil conservation (D'Odorico et al. 2013). Water crises, land degradation and desertification are pervasive and have the potential to lead to a collapse of life support systems in the absence of appropriate conservation and utilization strategies. This presents profound implications for the livelihoods of marginalized communities on a local scale and can also trigger migration, unrest, and economic instability at regional and global levels—extending well beyond the boundaries of dryland areas.

Over recent decades, international scientific programmes and initiatives have addressed drylands as part of their mandates. The UNESCO’s Man and the Biosphere Programme (MAB) in its early years took the arid and semi-arid zones as one of its focal ecosystem types and developed a plenty of projects in different regions, especially in Africa (Vannucci 1982). The Millennium Ecosystem Assessment specifically assessed the magnitude of desertification (i.e., land degradation in drylands) and its causal factors (Millennium Ecosystem Assessment (MEA) 2005), significantly warning that the conditions of global dryland ecosystems can deteriorate due to feedback loops between desertification, climate change, and biodiversity loss. The United Nations Food and Agriculture Organization (FAO) published reports on cereal production, forest and land use change in dryland (Koohafkan & Stewart 2008; Food and Agriculture Organization (FAO) 2016).

The year 2015 witnessed a pivotal milestone with the United Nations’ adoption of “Transforming our World: The 2030 Agenda for Sustainable Development,” delineating 17 Sustainable Development Goals (SDGs) (United Nations (UN) 2015). This framework provides a structured approach to balance essential human needs derived from ecosystem services (ES), such as food, water, and energy security, with human developmental aspirations encompassing poverty eradication, health, equity, education, and livelihoods. Addressing these complex trade-offs and potential synergies across values and governance domains, including infrastructure, urban development, and consumption patterns, has been a key consideration (Fu et al. 2019).

Drylands emerge as a pivotal resource both vital and interconnected in the attainment of the 2030 Agenda (Stafford-Smith & Metternicht 2021). SDG target 15.3 stands as a unique global objective, aiming to achieve land degradation neutrality (LDN) by 2030. The objective seeks to maintain or enhance the conservation of natural capital linked to land resources and the ecosystem services they provide. As a result, a systematic strategy becomes imperative for meeting human needs while sustaining the ecosystems and the benefits they yield within drylands across the globe. Moreover, the SDG target 15.3 cannot achieve only for itself considering the high links among SDG15 (Life on Land), SDG13 (Climate Action), SDG6 (Clean Water and Sanitation), SDG1 (No poverty), SDG2 (Zero Hunger), and other pertinent SDGs in the context of drylands (Yao et al. 2021). Thus, the success of SDG 15.3 hinges on addressing numerous other SDGs, including poverty, hunger, water access, energy, climate, and broader issues of equity, peace, and prosperity (Stafford-Smith & Metternicht 2021). The SDGs offer an optimal framework for navigating the intricate landscape of potential synergies and trade-offs encompassing the diverse array of resources and services offered by drylands (Fig. 1.1).

Fig. 1.1

More-or-less depletable services and resources delivered by drylands, loosely classified into the four categories of ecosystem services (wheel spokes), surrounded by key shared attributes of drylands (wheel tyre), and surrounding key aspects of governance needed for a GEC (wheel axle) (Stafford-Smith and Metternicht 2021)

1.2 Recent Developments in Dryland SES Research

Socio-ecological systems (SESs) are complex adaptive systems arising from dynamic interactions between ecosystems and human societies (Folke et al. 2016; Preiser et al. 2018). In dryland regions, human inhabitants draw upon local ecosystems to extract diverse resources, ranging from water to food, all in service of enhancing human well-being. The management of these ecosystems is profoundly influenced by an array of factors, including governmental policies, subsidies, payments for ecosystem services, and markets spanning local to global scales. These social processes hold pivotal significance, shaping the very fabric of SESs in drylands—encompassing their structure, attributes, and intricate interactions (Maestre et al. 2016). While the ramifications of climate change reverberate globally, adaptive strategies predominantly manifest at the local or regional level, necessitating the holistic consideration of ecological, social, and economic stimulants and responses inherent to specific SESs, particularly within dryland contexts (Scheffer et al. 2015). Evident shifts in the functioning of ecosystem goods and services serve as society's barometer of ecosystem change, potentially inciting societal reactions that, in turn, exert further impacts on ecosystems, thereby triggering a cycle of iterative feedback and response (McCollum et al. 2017).

Drylands are thus strongly coupled SESs, which are heavily influenced by people and by global change, with complex social-ecological interactions and feedbacks across scales (Reynolds et al. 2007). In light of this, the sustainability of dryland SESs necessitates a comprehensive approach rooted in an understanding of the dynamic interplays between nature and society. This entails an equal emphasis on the ways in which social transformations mold the environment, and conversely, how environmental shifts shape societal dynamics (Clark and Dickson 2003). This understanding extends to encompass social institutions, cycles, and order (Redman et al. 2004). Here we build on the recent development of dryland SES research through four lenses: SES dynamics and drivers, SES structure and function, ecosystem services in SES, and sustainability of SES.

Between 1991 and 2005, global drylands expanded by 4%, as highlighted by Feng and Fu (2013). Projections under the pessimistic climate change scenario (RCP8.5) suggest a further 23% increase in global dryland expansion by 2100, potentially accounting for 56% of the total global land area (Huang et al. 2016). The dynamics of drylands are intricate, characterized by multifaceted patterns encompassing both linear and nonlinear, gradual and abrupt shifts. These transformations are propelled by intricate interplays between biophysical and socio-economic factors, all underpinned by fundamental drivers that encompass abiotic elements (e.g., climate and soil properties), attributes of biological communities (e.g., diversity and spatial pat-terns), and human activities (e.g., grazing and agriculture) (Ruppert et al. 2015; Maestre et al. 2016). Many dryland landscapes have undergone marked degradation, often transitioning from productive vegetation-pattern states to barren, unproductive conditions (Zelnik et al. 2013). Widespread catastrophic shifts have been documented in dryland landscapes globally (Berdugo et al. 2017). Climate change exacerbates negative impacts on vegetation diversity and coverage, while disruptions in species interaction networks and suboptimal management practices—some of which manifest slowly—compromise the landscape resilience of dryland SESs in the face of extreme events (Hoover et al. 2014). Given the sparse nature of dryland vegetation, the efficacy of vegetation indices in reflecting actual changes becomes compromised, leading to ambiguous outcomes. A notable instance occurred between 1982 and 2013, when an increased global vegetation index masked the stark fact that actual vegetation had, in fact, declined on a global scale (Pan et al. 2018).

With the projected escalation in aridity and the anticipated rise in the frequency of drought occurrences across global drylands, the prevalence of abiotic factors governing land degradation, especially hydrological and aeolian soil erosion processes, could intensify (Ravi et al. 2010). The foreseen increase in aridity linked to climate change stands to adversely affect the multifaceted functions and services furnished by dryland ecosystems worldwide (Delgado-Baquerizo et al. 2016). Such amplified aridity levels have the potential to exacerbate soil erosion, land degradation, and desertification (Reynolds et al. 2007; Feng and Fu 2013). The employment of dynamic modeling techniques emerges as essential for gaining valuable insights into comprehending the trajectories of future dynamics within dryland SESs and the fundamental driving mechanisms steering these changes (Pelletier et al. 2015).

The intricate interplay between structure and function across various spatial scales unveils how SESs respond to the ongoing wave of global transformations, simultaneously playing a fundamental role in determining state shifts within drylands (Maestre et al. 2016; Mayor et al. 2013; Saco et al. 2018). The structures and functions of drylands, and how they interact may change significantly, even leading to shifts among alternative stable states (D’Odorico et al. 2013). When a critical threshold is crossed, SESs can undergo catastrophic change and reorganize into a different state (Angeler and Allen 2016; Turnbull and Wainwright 2019). However, the mechanisms that underlie the interactions between structure and function, and the resulting impacts on the state of SES are still controversial and poorly understood (Loreau and Mazancourt 2013). We must handle the complexity caused by multiple feedbacks among biotic and abiotic elements (Mayor et al. 2013; Turnbull et al. 2012), by interactions between structures and functions (Saco et al. 2018; Turnbull et al. 2012), and by the scale issues that challenge our ability to reveal how the structure and function of dryland SESs evolve (Berdugo et al. 2017). Climate changes usher in changes in nutrient input and loss rates, rates of plant photosynthesis, grazing patterns and intensities, soil fertility depletion, temporal and spatial water availability reductions, and the occurrence of dust storms; these extreme climatic events can even swiftly reshape landscape configurations (Lucatello et al. 2020). Consequently, abrupt or even catastrophic shifts in dryland SESs, accompanied by corresponding losses or gains in ecological and economic assets, might occur (Ursino 2019). However, the realm of predicting and confirming abrupt responses to a changing environment remains inadequately explored, leaving landscape response to stress highly variable and unpredictable (Zelnik et al. 2013). Regime shifts within dryland SESs can emerge from gradual or rapid reactions to alterations in external drivers and feedback loops, culminating in gradual, abrupt, or catastrophic outcomes (Saco et al. 2020). Although regime shifts within single dimensions are often addressed on an ecosystem scale due to the relatively straightforward relationships between variables, the nonlinearity, intricacies of feedback systems, and the presence of behavioral thresholds in dryland SESs render comprehensive and realistic predictions challenging (Burthe et al. 2016).

Beyond the provisioning of essential services like food, freshwater, and fuel, the critical regulating services such as soil conservation, hydrological regulation, and cli-mate regulation, alongside the cultural services offered by the distinctive biodiversity, ecosystems, and landscapes of drylands, stand as paramount indicators of human well-being within dryland SESs (Fu et al. 2013). Global shifts in the environment have profoundly reshaped the provision of ecosystem services in drylands, along with their intricate supply-and-demand dynamics and the inherent trade-offs that manifest across diverse scales (Lu et al. 2018). To quantitatively assess alterations in dryland ecosystem services across spatial and temporal scales, an array of mapping and scenario analysis tools have been devised for regional simulations of ecosystem services (Hu et al. 2015; Smith et al. 2011). The interactions within dryland SESs encompass multifaceted dimensions, encompassing service types (e.g., food, water, energy, and services related to ecological security), beneficiaries (e.g., farmers, retailers, and environmentalists), locations (e.g., upper or lower reaches of watersheds), and temporal periods or generations (Seppelt et al. 2011). These interactions are further shaped by public infrastructure elements like roads, dams, drinking water pipelines, and cultural amenities, which facilitate residents in remote regions to access the supply or transportation of local ecosystem services to areas with demand beyond the realm of drylands (Castro et al. 2014; Miyasaka et al. 2017).

Human well-being emerges as a state intricately intertwined with specific environmental conditions. It encompasses material circumstances, freedom of choice, health, social relations, security, inner tranquility, and spiritual experiences—all essential for maintaining a high quality of life (Summers et al. 2012). Through intensive land use practices encompassing cultivation, grazing, deforestation, resource extraction, and excessive utilization of freshwater resources, human activities within dry-lands can potentially induce various forms of land degradation and water resource deterioration. These impacts are often exacerbated by climate change, leading to consequential effects on the delivery of ecosystem services (D’Odorico and Bhattachan 2012). Elevated levels of human well-being can indirectly yield benefits to ecosystem services, as the adverse consequences on ecosystem services are frequently mediated by institutional, cultural, and governance factors, along with conflicts. These mediating factors might operate more effectively at higher levels of human well-being (Lucatello et al. 2020).

Under the influence of degrading factors, dryland ecosystem services come under pressure, curbing human access to necessities like food, water, energy, and ecological security, thereby compromising sustainable livelihoods to varying extents across distinct dryland SESs (Keesstra et al. 2018). In recent times, nature-based solutions (NBS) have gained prominence as approaches aimed at safeguarding, sustainably managing, and restoring natural or altered ecosystems to effectively and adaptively address societal challenges. NBS stands as a prospective framework to reverse the trajectory of degradation evident in dryland ecosystems, which threatens both biodiversity and human well-being. NBS aligns conservation and development objectives, offering a pathway to counteract the detrimental effects of degradation (Cohen-Shacham et al. 2019; Keesstra et al. 2018).

The primary biophysical constraints challenging the sustainability of dryland SESs encompass natural resource limitations and ecosystem degradation, with high emphasis on water scarcity and encroaching desertification (Huber-Sannwald et al. 2012). Social and economic constraints, such as limited access to markets and resources, weak governance structures, and inadequate information about alternative production technologies, further curtail the available options for inhabitants of drylands (van Ginkel et al. 2013). The disparity between the supply and demand of ecosystem services in drylands stands as a significant hurdle for landowners, producers, land managers, land use planners, and policymakers. This challenge is amplified as land quality sits at the juncture of ecosystem functioning and human security, encompassing vital elements like clean water, air, food, and energy—the bedrock of livelihood development in dryland SESs (Reed et al. 2015). Consequently, there exists a pressing need to guide and facilitate transdisciplinary and participatory research efforts aimed at combating land degradation and harmonizing dryland ecosystem services. This calls for collaboration from all stakeholders, including academia, governmental and nongovernmental organizations, civil societies, local stakeholders, and policymakers, with a goal to foster collective knowledge generation, continuous system monitoring, reevaluation, and capacity enhancement in dryland stewardship across all tiers (Challenger et al. 2018).To cultivate resilient livelihoods within dryland SESs, innovative approaches are essential from all participants—ranging from primary producers to policymakers—to identify, quantify, and address the driving forces and interactions that shape and constrain the development and progression of dryland livelihoods (King et al. 2018).

Good governance in drylands involves institutions for decision making by a range of stakeholders, including individuals, both in formal positions of power and as ‘ordinary’ citizens, households, communities and organizations (Lopez-Porras et al. 2018). Building capacity in education, health, gender equality, technology, and comprehensive analysis is also closely related to promotion of dryland SES governance (Reed and Stringer 2016; Cherlet et al. 2018; Middleton 2018). This in turn helps regions and countries ensure future water, food, energy, and ecological security, to mitigate climate change, and to advance the capacity for good governance (Griggs et al. 2013). The SDGs can be regarded as a major governance instrument to combat desertification, drought, and land degradation that combine and scale up established socioeconomic principles (Rica et al. 2018); and the logic of analysing the interconnections between SDGs permits the potential to mainstream sustainability (Bautista et al. 2017).

1.3 Global-DEP and Its Conceptual Framework

In recent decades, a plenty of frameworks for understanding Social-Ecological Systems (SESs) have been put forth, with Ostrom's framework standing out as one of the most widely employed (Ostrom 2009; McGinnis and Ostrom 2014). The SES framework offers valuable insights into evaluating the intertwined social and ecological facets contributing to sustainable resource utilization and management. This framework can be applied in a spatially explicit, quantitative manner to identify opportunities and trade-offs when striving for the sustainability of interconnected SESs (Leslie et al. 2015). Several other frameworks have also emerged, each engaging with varying aspects of the SES perspective. One such framework is the Composition-Structure-Process-Service framework, designed to dissect the underlying mechanisms driving Ecosystem Services (ES) production. Functioning as an application-oriented linking framework, it bridges landscape patterns, ecosystem processes, and ES, while also embracing landscape design for sustainable ecosystem management across different scales (Fu et al. 2013). An enhanced iteration of this framework, named the Pattern-Process-Service-Sustainability framework, has been refined to incorporate the dynamics of interconnected natural and human systems (Fu & Wei 2018). Another integrated framework synthesizes the core tenets of the ES cascade concept and the Driver-Pressure-State-Impact-Response (DPSIR) framework. This amalgamation aims to position ES within a broader SES context, encompassing the cycle of ES provision, societal feedback, and analytical depiction of social-ecological interactions. It aims to serve as a valuable instrument for policy development that promotes the sustainability of dryland ecosystems and thereby safeguards the livelihoods of their associated users (Nassl and Löffler 2015).

The Dryland Development Paradigm (DDP), introduced by Reynolds et al. (2007), has gained considerable influence as a guiding framework for dryland development. Drawing on empirical analyses within dryland systems science, Stringer et al. (2017) derived an updated version of the DDP (DDP#2). This iteration comprises three integrative principles and advocates a shift away from a research-for-development approach. The DDP emphasizes the need to always consider both human and environment aspects of dryland systems, but also to avoid careless generalization, highlighting for research to be concerned with the diversity of global drylands and their social-ecological characteristics. For example, Safriel et al. (2005) highlighted the interrelationships between major ES, between ES and biodiversity, and between ES and the livelihoods that ecosystems support across the aridity gradient. As another example, Stafford-Smith et al. (2011) formalized a conceptual systems model of key migration processes in drylands globally, which recognizes a series of factors at local and broader scales that contextually affect how critical ES are to local livelihoods and how these then interact with what adaptive capacity households may have to stay or move. Furthermore, Huber-Sannwald et al. (2012) amalgamated the DDP and other conceptual frameworks, coupling them with an exhaustive analysis of biophysical, socio-economic, and historical data. Their study assessed challenges and opportunities for livelihood development within the Amapola dryland ecosystem, a semi-arid region in Mexico. Their findings called for an effective, flexible, and viable policy framework that could enhance the biotic and cultural diversity of drylands locally, ultimately transforming drylands across the globe into a resilient biome, in the face of global environmental and social shifts.

The Global Dryland Ecosystem Programme (Global-DEP) was approved as a key international cooperation project under the International Partnership Program (IPP) of Chinese Academy of Sciences (CAS) in August 2017. It is an international cooperation initiative jointly proposed by Prof. Bojie Fu from the CAS and Dr Mark Stafford-Smith from the Commonwealth Scientific and Industrial Research Organization (CSIRO) in Australia, with an aim of developing an actionable research plan to address the challenges facing diverse and fragile dryland SESs. A Scientific Committee was established to orchestrate the development of the program's Science Plan, and a dedicated Secretariat was put in place to provide essential technical support. In addition, the program created four thematic work groups and five regional work groups, featuring principal investigators from CAS as well as counterparts from nations such as the United States, Spain, Senegal, and Australia, among others (Fig. 1.2).

Fig. 1.2

Global-DEP organizational structure

The conceptual framework of the Global-DEP was meticulously crafted by amalgamating insights from diverse disciplines and examining previous frameworks. This framework, grounded in the perspective of SES, underscores the imperative of comprehending several pivotal components. These encompass the drivers shaping SES, the intricate interplay of SES structure and functions, the critical realm of ecosystem services and its impact on human well-being, and the management responses required to actualize the SDGs. The framework draws attention to the interlinked and multi-scale nature characterizing dryland SESs, an insight resonant with the DDP. This recognition culminates in the proposition of a cohesive quartet of research themes, propelled by the forces of global environmental transformations and globalization. These research themes are strategically oriented towards achieving SDG objectives through a dynamic interplay of responses and feedback loops weaving together ecological and social facets (Fig. 1.3). This fundamental framework, though presented in a simplified manner, was further expanded upon by Fu et al. (2021). Its significance lies in its ability to engage researchers spanning ecology and social sciences, both converging on the realm of dryland SESs. Additionally, this framework provides the bedrock for the formulation of both the scientific and actionable agendas of Global-DEP.

Fig. 1.3

Simplified diagram of Global-DEP conceptual framework

1.4 Research Themes and Priorities

Based on the overarching framework of helping dryland SESs meet the SDGs, each of the four themes raises specific research priorities as described below.

Theme I: Dryland social-ecological system dynamics and driving forces

The dynamics inherent in dryland SESs are a product of the intricate amalgamation of diverse linear and non-linear patterns, coupled with both gradual and sudden shifts. These dynamics are propelled by an interplay of biophysical and socio-economic factors. This thematic exploration seeks to unveil the critical variables essential for comprehending these large-scale dynamics, thereby fostering an overarching understanding of the distinctions among distinct dryland SESs. Such insights serve as a fundamental platform for discerning transferrable findings across different locales and projecting the trajectories of pivotal drivers shaping SES dynamics in other thematic domains.

Research priority 1.1: what are the essential dryland variables (EDVs) of the macroscopic dynamics of dryland SES?

Essential variables are the minimum set of variables required to characterize change in a system (Reyers et al. 2017). Essential variables for climate, biodiversity, water, socio-ecological systems and SDGs have been proposed successively in recent years (Reyers et al. 2017). Social-ecological activities in drylands are dominated by water availability; and the responses of dryland SES to climate change and anthropogenic disturbances can be reflected by changes in land cover (Maestre et al. 2016). Dryland landcover is particularly characterized by sparse and patterned vegetation and soil biocrusts. Research to identify these sensitive essential variables and to enhance the monitoring of their dynamics is essential to underpin understanding of the driving forces behind them (Li et al. 2021), and to improve management of dryland SES.

Research priority 1.2: what are the driving forces of the macroscopic dryland SES dynamics?

Climate change and human activities notably loom as pivotal drivers of dryland SES dynamics, amplifying the risks of land degradation and desertification (MEA 2005). Moreover, dryland SESs are usually water-limited by definition. Remote sensing technology provides many key water-related products that can assist the macroscopic study of dryland SES dynamics, including patterns over space and time of soil moisture, precipitation, evapotranspiration, water stress of vegetation, and evapotranspiration partition (Wang et al. 2012). As an entry point to understand the contextualized contributions of climate change and human activities, the research frontier is to identify how these factors together determine the development and degradation of drylands across spatiotemporal gradients of water availability.

Research priority 1.3: what are the future trajectories of macroscopic changes in dryland SES?

Extreme climate events will become more frequent, widespread and intensified under projected trends of global warming, resulting in significant changes in dryland (Huang et al. 2017). With population growth, human activities, such as grazing, also impose greater pressures on dryland SES. Although a variety of models have been proposed and applied to simulate land use transformations in drylands, there is still a high uncertainty across models and scenarios. Tackling the intricate questions underlying future dryland SES trajectories necessitates predictive work encompassing varied climate scenarios, human interventions, and desertification trends based on observed trends in the foundational EDVs.

Theme II: Dryland social-ecological system structure and functions

Intrinsic to the stability and resilience of SESs in drylands are the intricate inter-plays of their structures, functions, and interactions. A comprehensive grasp of state shifts in local dryland SESs goes beyond predictions based solely on isolated indicators due to the substantial spatiotemporal variations, sensitivity, and vulnerability to natural and human-induced disturbances. This thematic exploration strives to uncover the intricate biotic and abiotic mechanisms governing regime shifts in dryland SESs. By adopting both comprehensive and context-specific viewpoints, this theme aims to elucidate how these SESs evolve under diverse circumstances, addressing queries about tipping points and alterations in regimes that could have profound ramifications for the provisioning of ES across varied dryland SESs.

Research priority 2.1: how do ses structure, functions and their interactions change in drylands?

Understanding interactions between the structure and functioning of dryland SES at multiple spatial scales can substantially improve our understanding of how drylands respond to ongoing global environment changes. The ecosystem structure of drylands interacts with function through multiple feedbacks, particularly hydrological feedbacks (D'Odorico and Bhattachan 2012). Therefore, connectivity, scale, and threshold behavior in hydrological systems are of common concern in dryland landscapes. The research frontier is revealing how ecohydrological and socioeconomic processes drive the evolution of SES structures, functions, and their interplay in diverse and scale-dependent dryland contexts.

Research priority 2.2: how do dryland SES structures and functions respond to climate change?

The intricate interplay between structure and function across various spatial scales affords insights into the SES responses to global transformations and how these dynamics underpin shifts in SES states (Fu et al. 2021; Maestre et al. 2016). Given the geographical heterogeneity inherent in different dryland SESs, predicting the trajectories of local dryland changes necessitates an in-depth comprehension of the mechanisms and resilience maintenance strategies in the face of climate change. This entails exploring how these structures and functions recalibrate under shifting climatic conditions.

Research priority 2.3: what is the SES mechanism for regime shifts in drylands?

Regime shifts, irreversible or sustained alterations, often bring detrimental impacts to drylands (Scheffer et al. 2015). These shifts can stem from gradual changes or swift responses to external drivers and feedbacks. Addressing these shifts necessitates a deep dive into the context-specific social-ecological feedback loops embedded in drylands, where threshold behaviors come to the forefront. Fostering a comprehensive understanding of these shifts involves developing holistic indicators, models, and multi-variable approaches capable of prognosticating the likelihood of regime shifts in dryland SESs moving forward.

Theme III: Dryland ecosystem services and human well-being in a changing environment and society

The intricate relationships between ES and human well-being in diverse dryland settings present a complex challenge. Discerning the dimensions of human well-being most pertinent to dryland ecosystems, as well as how changes in ES impact well-being within specific SESs, stands as the core objective of this theme. This exploration seeks to identify pathways that harness the value of ES for livelihood enhancement, catering to a wider array of beneficiaries both within and beyond SESs. This theme is set to propel the necessity for comprehensive monitoring to prevent the occurrence of collapse thresholds and amalgamate context-specific insights into the connections between ES and human well-being, thus influencing local management and policy choices in drylands.

Research priority 3.1: how do dryland ecosystem services change across space and time?

Dryland ES have high spatial and temporal variability due to the high variability in natural and social conditions, such as ecosystem type, climate, extreme events or disturbances, and economic development level. Enhancing our ability to model and predict the changes in these services across different scales in space and time is pivotal. This involves refining model structures, incorporating modules or parameters that account for the unique characteristics of dryland ecosystems, and generating more reliable estimates of ES at the local level. The research frontier includes biophysical modeling of ES at multiple scales, ES valuation not limited to monetary value, identification on the key drivers of ES change, and then simulating ES change in future scenarios.

Research priority 3.2: what are the interactions between multiple ecosystem services and supply–demand relationships?

Understanding the trade-offs and synergies resulting from interactions among various ES is essential for devising adaptable land use strategies within dryland SESs. Due to the spatial heterogeneity of ecosystems and population distribution in drylands, both the supply and demand of ES have high spatial variability (Castro et al 2014). With spatially heterogeneous and temporally dynamic human needs, the trade-offs between ES and people can be exacerbated, causing complex interactions among multiple beneficiaries, locations, and human generations. Therefore, the research frontier is to explore all the potential tradeoffs among the multiple dimensions of human demand for ES, particularly considering the future needs for ES under dryland environmental change; as well as to understand the supply–demand mismatches of dryland ES at different scales, and then track the potential dryland ES flows that depend on socioeconomic and environmental teleconnections.

Research priority 3.3: how are dryland ecosystem services linked to human well-being?

Clarifying how changes in ES alter their contribution to human well-being is key to the entangled dryland challenges, and to promoting the resilience of these SESs and finding solutions that balance ecological protection and socioeconomic development. This entails deciphering the ideal blend of natural and social capital for fostering well-being and understanding how other forms of capital, like technology and infrastructure, play a role in bolstering ES within dryland SESs. The research frontier is to understand the pathways and mediating factors that enable ES to deliver human well-being, to quantify the relationship between ES and human well-being, to optimize landscapes to produce ES, and to understand how best to provide payment for ES.

Theme IV: Ecosystem management and sustainable livelihoods in drylands

The immense diversity of global drylands – encompassing varying environments, degradation levels, social and cultural dimensions, and human reliance – underscores the necessity for nuanced and contextually-tailored management objectives and strategies. This theme is designed to forge connections between community development and ecosystem management, ensuring the attainment of SDGs within dryland SESs. Drawing upon insights from other themes, it aspires to proffer management and policy alternatives, while simultaneously pinpointing the EDVs, a contextual grasp of tipping point dynamics in ES provisioning, and the pathways by which these services translate into human well-being across distinct geographical contexts.

Research priority 4.1: how can sustainable ecosystem management schemes be developed in drylands?

While instances of site-specific practices for sustainable ecosystem management exist, the development of universally effective strategies for diverse drylands remains a challenge. Nature-based solutions (NBS) offer a promising avenue, encompassing actions that shield, sustainably manage, and restore natural or modified ecosystems. These approaches, adaptable to shifting external circumstances and contextual nuances, can guide ecosystem management principles in drylands. To advance this, key steps include quantifying EDVs pertinent to dryland NBS, devising novel management techniques that accommodate uncertainty and extended timeframes, evaluating the limitations of NBS in the variable dryland climate, and comprehensively factoring in trade-offs, complexities, and impending climate shifts when applying NBS in these regions.

Research priority 4.2: how can livelihood be maintained in drylands?

Livelihoods are diverse across dryland ecosystems, but their differentiation and variation are based on adaptive responses to local environmental and social conditions. Site-specific environmental knowledge and the aspirations of resident populations remain largely unconsidered within expert assessments and management strategies in dryland SES. Understanding the prime drivers of livelihood changes—determined by EDVs—is crucial. Equally important is grasping how development strategies and socio-economic changes can fortify livelihood resilience and robustness, especially in times of mounting uncertainty and risk. The research frontier includes identifying the ecological capacity for livelihoods in different drylands, quantifying the responses of livelihood-related indicators and livelihood resilience to climate change in drylands, and developing strategies to enhance livelihood capital.

Research priority 4.3: how can sustainable governance be promoted in specific dryland SES contexts?

The SDGs serve as a significant global governance tool to combat land degradation, desertification, and drought. The relations between SDGs and their interconnections with drylands governance (Stafford Smith and Metternicht 2021) should be fully explored, since measures to promote access to food (SDG 2), water (SDG 6), and energy (SDG 7), if applied under an unsustainable governance regime, could be counterproductive in enabling sustainable consumption and production (SDG 12), could aggravate climate change (SDG 13), and could undermine conservation outcomes relevant to SDG 15 (Safriel 2017). Therefore, the research frontier includes evaluating and setting priorities for achieving SDGs in specific dryland SES contexts, and construction of a cross-scale and multilevel dryland SES case study database to help explore sustainable governance pathways.

1.5 Summary and Perspectives

The development of the conceptual framework and research priorities forming the cornerstone of the Global-DEP Science Plan for dryland SESs has been a collaborative effort, marked by substantial consultations during Scientific Committee meetings and regional workshops conducted in China, Australia, and Africa. The out-comes of these endeavors have been disseminated through special issues in international journals, which has circulated the program's concepts, data, and case studies (Fu et al. 2021). A pivotal stride towards the integration of the Global-DEP into the broader landscape of land system science has been the establishment of the Global Dryland SES working group under the aegis of the Global Land Programme (https://glp.earth/). This strategic move solidifies the linkages with the broader community of land system scientists, further facilitating cross-disciplinary and international collaborations.

In light of the escalating challenges confronting rapidly transforming dryland SESs, the paramount objective of Global-DEP remains to encapsulate pivotal concepts relevant to interdisciplinary comprehension and cross-cultural insight into dryland SESs. Its overarching structure is designed to resonate with the diverse contexts of drylands, enabling it to act as a responsive tool for fostering research collaboration, policy dialogue, management practices, and sustainable livelihoods in these ecosystems.

Though the above-presented conceptual framework constitutes a simplified depiction of dryland SESs, Global-DEP diligently follows a standardized approach aimed at informing transformative policies and practices across these systems, while engaging researchers, policymakers, practitioners, and local stakeholders on a global, regional, and local scale. The programme operates with the intention of incorporating feedback and engagement from diverse locales, capitalizing on local knowledge, and considering the perspectives, opportunities, and challenges experienced by stakeholders in drylands.

The fluidity of the conceptual framework reflects its adaptability to the evolving research landscape and the dynamic demands of sustainable development in global drylands. To this end, the Global-DEP framework is set to undergo regular updates and revisions to align with research progress and evolving requirements. This iterative approach ensures that the framework remains a living synthesis of research priorities, continually guiding efforts toward enhancing the well-being of dryland ecosystems, landscapes, and livelihoods in the face of an ever-changing environment and the imperative of sustainable development.