Ongoing greening initiatives in the Middle East: An untapped potential to enhance our understanding of hyperarid ecosystems

To sustain its unique biodiversity into the future, it is crucial to promote the resilience and health of hyperarid ecosystems, particularly given the compound pressures of anthropogenic influence and climate change. These are key objectives of the Saudi and Middle East Green Initiatives, which aim to protect up to 30% of Saudi Arabia’s land and sea territories and plant up to 10 and 40 billion trees within the Kingdom and across the Middle East, respectively (https://www.greeninitiatives.gov.sa/about-sgi/ and https://www.greeninitiatives.gov.sa/about-mgi/, respectively). Other actions supported by these initiatives include the increase of renewable energy capacity – which has already risen by 300% in Saudi Arabia, restoring degraded lands – 94,000 hectares have been rehabilitated across Saudi Arabia at the moment – and rewilding endangered species that play a key role in the ecological balance of these ecosystems. It is also expected that the Saudi Green Initiative will play a significant role in achieving the recent commitment of Saudi Arabia to reach net zero emissions by 2060, with the Middle East Green Initiative aiding broader regional objectives towards carbon neutrality. Moreover, the Saudi Green Initiative’s ambition to protect at least 30% of Saudi Arabia’s territories by 2030 is in harmony with the global “30x30” target adopted under the Kunming-Montreal Global Biodiversity Framework of the Convention on Biological Diversity (CBD, 2022). Although this is a challenging objective, 18.1% and 6.49% of Saudi Arabia’s terrestrial and marine areas are already protected.

Both greening initiatives will protect some of the region’s iconic terrestrial fauna, which are classified at varying levels of threat, ranging from vulnerable to critically endangered, according to the International Union for Conservation of Nature (IUCN) Red List of Threatened Species. Additionally, they will protect mangroves, coral reefs and salt marshes, which have coevolved in this region to create some of the most resilient marine ecosystems globally (McCabe et al., Reference McCabe, AlShalan, Hejazi, Beck, Maestre, Guirado, Wada, Al-Ghamdi, AlSaud, Underwood, Magistretti, Gallouzi and KAUST2023). Some of the Saudi Green Initiative activities include the creation of national reserves, such as the King Salman bin Abdulaziz Royal Reserve, located in the north of the Arabian Peninsula. Covering approximately 130,000 km², this reserve hosts vulnerable species of mammals (e.g., Capra nubiana, Canis lupus arabs) and birds (e.g., Torgos tracheliotos, Falco cherrug). Additionally, urban areas are targeted by these initiatives. Cities like Riyadh and Makkah in Saudi Arabia are seeing an increase in the number of trees planted and the creation of new green areas, enhancing human well-being and biodiversity (Cox et al., Reference Cox, Shanahan, Hudson, Fuller, Anderson, Hancock and Gaston2017; Gaston, Reference Gaston2010).

The Saudi and Middle East Green Initiatives should also learn from past actions and seek not only to ecologically transform broad landscapes but also to shape societies and economies. For example, the Great Green Wall for the Sahara and the Sahel Initiative (GGWSS), which emerged in 2007, involves over 20 countries bordering the Sahara to establish plantations on 100 million ha from Eritrea’s Red Sea coast to Senegal’s Atlantic coast (Sileshi et al., Reference Sileshi, Dagar, Kuyah and Datta2023). The GGWSS was built upon earlier initiatives aimed at combating desertification in the Sahel region’s countries (Mbow, Reference Mbow2017). One such initiative was Algeria’s Green Dam Initiative, started in 1972, which aimed to establish a three million ha band of plantations to halt the northward advance of the Sahara Desert (Benhizia et al., Reference Benhizia, Kouba, Szabó, Négyesi, Négyesi and Ata2021). Other projects, such as the Acacia operation project and the Support for the rehabilitation and extension of the Nouakchott green belt in Mauritania, engaged local communities and national authorities in restoring inland and coastland ecosystems (Berte, Reference Berte2010). Projects in the Sahel region have shown that where policies and incentives are favorable, farmers actively promote the natural regeneration of trees, resulting in vast areas now being covered by trees (e.g., Haglund et al., Reference Haglund, Ndjeunga, Snook and Pasternak2011). A participatory approach involves extensive community engagement and enhances accountability and stewardship in land-restoration efforts. Initially, a centralized approach, heavily reliant on forest department control and substantial investment in equipment, marginalized local communities. Recognizing community ownership has enabled Sahelian countries to mitigate conflicts between development and environmental goals (Kumar, Reference Kumar2003). However, land privatization in the Sahel often fails due to diverse landscape uses and stakeholder needs (Schoneveld, Reference Schoneveld2017). These failures underscore the necessity for stakeholder-supported, site-specific solutions that enable ongoing improvement across countries and implementation sites. Learning from experiences in the Sahel region, local actions that can be scaled up with positive results include the zoning of grazing areas, ensuring water availability for livestock and promoting fodder trees (Mbow, Reference Mbow2017).

In Asia, the Great Green Wall of China (GGWC), initiated by the Chinese government in 1978, aims to combat desertification and reduce the eolian transport of dust from the Gobi Desert (Parungo et al., Reference Parungo, Li, Li, Yang and Harris1994). Scheduled for completion in 2070 (Lu et al., Reference Lu, Hu, Sun, Zhu, Liu, Zhou, Zhang, Shi, Liu, Wu and Zhang2018), this project builds on China’s experience with shelterbelt programs (Qi and Dauvergne, Reference Qi and Dauvergne2022). While the GGWC has yielded benefits, such as reduced dust movement and increased vegetation, during its first stages, many of the dryland areas targeted for afforestation were found to be better suited for grasslands and steppes than woodlands or forests (Cao et al., Reference Cao, Tian, Chen, Dong, Yu and Wang2010; Mátyás et al., Reference Mátyás, Sun and Zhang2013), often leading to significant water pressures on water resources (Li et al., Reference Li, Fu, Wang, Stringer, Wang, Li, Liu and Zhou2021a). Not only tree survival rates were low but also irrigation was necessary in drier areas within many of these projects (e.g., Wang et al., Reference Wang, Peng, Xu, Zhang and Zhang2020). Nevertheless, subsequent research has demonstrated the benefits of shelterbelts in drylands for reducing net erosion (Su et al., Reference Su, Zhou, Zhang, Wang, Wang, Zhou, Zhang, He and Zhang2021) and improving crop productivity (Zheng et al., Reference Zheng, Zhu and Xing2016). Additionally, studies on biocrusts in China’s drylands have shown that breeding them can effectively control land degradation (Li et al., Reference Li, Hui, Tan, Zhao, Liu and Song2021b) by reducing dust emissions and increasing soil nutrient content (He et al., Reference He, Hu and Jia2019; Li et al., Reference Li, He, Zerbe, Li and Liu2010). Because of these experiences, new strategies in China now focus on science-based activities, encouraging natural regeneration, creating multispecies plantations, matching species to local conditions and emphasizing water conservation (Turner et al., Reference Turner, Davis, Yeh, Hiernaux, Loizeaux, Fornof, Rice and Suiter2023).

Over the past four decades, Australia has also made significant advancements in restoring its drylands through sustained efforts and community involvement (Campbell et al., Reference Campbell, Alexandra and Curtis2017). Initiatives in Australia learned from small-scale efforts and led to a shift in policies towards large-scale activities, biodiversity conservation, water quality improvement and greenhouse gas mitigation. Successful restoration programs underscored community capacity and commitment, yet it was also recognized that community efforts alone were insufficient for sustainable resource management on a landscape or continental scale without technically and economically viable land use and farming systems. These lessons are particularly important in drylands, where synergistic interactions such as grazing intensification, drought, climate change, reduced fire frequency and changes in atmospheric chemistry or small animal populations can collectively overwhelm the effects of individual factors (Fu et al., Reference Fu, Chen, Wang, Yu and Yu2021a).

Restoration in the Middle East cannot be based only on planting trees in the desert

Ambitious tree-planting objectives are not a new concept, even in drylands (Bond et al., Reference Bond, Stevens, Midgley and Lehmann2019). Unfortunately, many previous dryland afforestation efforts have often delivered tree monocultures, which risks reducing sustainable development by negatively affecting ecosystem functioning (Yao et al., Reference Yao, Xiao and Ma2021). Apart from avoiding planting regimes that are incompatible with the landscape, the inherent constraints of water availability in drylands and the increased pressures that large-scale tree planting places on these, are critical considerations when designing greening and restoration efforts (Schwärzel et al., Reference Schwärzel, Zhang, Montanarella, Wang and Sun2020). Although intrinsically appealing from a policy perspective (i.e., planting trees is a socially recognizable and acceptable climate action), excessive focus on afforestation using trees can miss opportunities for broader and longer-term benefits. For instance, mono-specific tree plantations may achieve a narrow accounting-based objective (in terms of trees planted or carbon captured) but they can reduce ecosystem diversity (e.g., Maestre and Cortina, Reference Maestre and Cortina2004), jeopardize water resources for humans and ecosystems (e.g., Feng et al., Reference Feng, Fu, Piao, Wang, Ciais, Zeng, Lü, Zeng, Li, Jiang and Wu2016) and amplify the risk of future carbon loss following any ecosystem disturbance (e.g., forest fires and pests; Anderegg et al., Reference Anderegg, Trugman, Badgley, Anderson, Bartuska, Ciais, Cullenward, Field, Freeman, Goetz, Hicke, Huntzinger, Jackson, Nickerson, Pacala and Randerson2020). In other parts of the world, regions deemed degraded have been mistakenly considered as potential areas for afforestation, simply by failing to carefully assess their suitability for tree planting (e.g., soil health, environmental gradients). Such areas have included grasslands and shrublands (Veldman et al., Reference Veldman, Aleman, Alvarado, Anderson, Archibald, Bond, Boutton, Buchmann, Buisson, Canadell and Dechoum2019), which represent two of the more common environments found in the Middle East (Box 1; Hegazy and Doust, Reference Hegazy and Doust2016).

Recognizing the limitations and unintended consequences of prior afforestation strategies underscores the importance of adopting a more nuanced approach to ecosystem restoration, particularly in hyperarid regions. Increased biodiversity is considered an indicator of healthier and more resilient ecosystems, allowing faster recovery from disturbance and providing ecosystem services that contribute to more sustainable and stable human development (Jactel et al., Reference Jactel, Bauhus, Boberg, Bonal, Castagneyrol, Gardiner, Gonzalez-Olabarria, Koricheva, Meurisse and Brockerhoff2017). Thus, restoration and conservation efforts should act in concert to increase biodiversity, thereby bolstering the resilience of all naturally occurring ecosystems. This holistic view is crucial if the goal is to restore the multifaceted ecosystems of hyperarid lands, considering the variety of services they provide (Box 1). For example, biocrusts are key players in dryland development and function that increase soil carbon and nutrient contents, impact multiple components of the hydrological cycle and reduce soil erosion and dust emissions (Eldridge et al., Reference Eldridge, Reed, Travers, Bowker, Maestre, Ding and Havrilla2020; Rodríguez-Caballero et al., Reference Rodriguez-Caballero, Stanelle, Egerer, Cheng, Su, Canton, Belnap, Andreae, Tegen, Reick, Pöschl and Weber2022), benefitting both the environment and human societies. Therefore, the development of a biocrust research program is urgently needed to understand their ecology, distribution and potential to restore degraded habitats and mitigate climate change in the Middle East.

Restoration and greening initiatives in the Middle East should focus not only on what is visible above ground but also on soils. Over 32% of the world’s soil organic pool is stored in drylands worldwide (Plaza et al., Reference Plaza, Zaccone, Sawicka, Méndez, Tarquis, Gascó, Heuvelink, Schuur and Maestre2018a), with significant loss of carbon occurring in major cropland and grazing areas (Sanderman et al., Reference Sanderman, Hengl and Fiske2017). However, although soils’ potential to mitigate climate change has been long recognized (Bossio et al., Reference Bossio, Cook-Patton, Ellis, Fargione, Sanderman, Smith, Wood, Zomer, von Unger, Emmer and Griscom2020), their role in dryland restoration and mitigation efforts remains underexplored. Soil organic carbon can act as a stable carbon sink, showing resilience to land-use changes and disturbances, unlike above-ground biomass. Carbon-rich soils also enhance water and nutrient retention, enhancing ecosystem resilience to disturbances like droughts (e.g., Iizumi and Wagai, Reference Iizumi and Wagai2019). However, regional evaluations of soil organic carbon in drylands remain limited, with existing studies often producing inconsistent results (Fu et al., Reference Fu, Stafford-Smith, Wang, Wu, Yu, Lv, Ojima, Lv, Fu, Liu and Niu2021b). Furthermore, understanding the impact of land-use changes on regional soil carbon is hindered by insufficient data quality, poor representativeness and a lack of historical land-use information (Hendriks et al., Reference Hendriks, Stoorvogel and Claessensa2016). Comprehensive assessment of soil carbon stocks requires robust sampling methods that can scale site-specific data to broader regional levels (Ciais et al., Reference Ciais, Bombelli, Williams, Piao, Chave, Ryan, Henry, Brender and Valentini2011), an ongoing challenge in terrestrial carbon studies (Zhang and Hartemink, Reference Zhang and Hartemink2017). As such, a regional dataset combining soil organic carbon, land-use and soil properties for the Middle East would enhance our understanding of how climate influences physical processes in global drylands. For instance, increasing aridity is known to reduce soil carbon and nitrogen levels (Delgado-Baquerizo et al., Reference Delgado-Baquerizo, Maestre, Gallardo, Bowker, Wallenstein, Quero, Ochoa, Gozalo, García-Gómez, Soliveres and García-Palacios2013) and disrupt the nutrient balance in dryland soils (Maestre et al., Reference Maestre, Eldridge, Soliveres, Kéfi, Delgado-Baquerizo, Bowker, García-Palacios, Gaitán, Gallardo, Lázaro and Berdugo2016). Carbon accumulation in soils is influenced by factors such as parent material, topography, microclimatic conditions and species diversity (Ramesh et al., Reference Ramesh, Bolan, Kirkham, Wijesekara, Kanchikerimath, Rao, Sandeep, Rinklebe, Ok, Choudhury and Wang2019), while human activities can accelerate carbon emissions (Lal, Reference Lal2004a; Schlesinger, Reference Schlesinger2000). Although improved management strategies (e.g., grazing regimes, organic amendments, cover crops, crop rotation and conservation tillage) can enhance carbon stocks in dryland soils (Lal, Reference Lal2004b, Reference Lal2018; Plaza et al., Reference Plaza, Gascó, Méndez, Zaccone, Maestre, García, Nannipieri and Hernández2018b), they can be less effective in these environments due to their coarser texture and lower clay content, which protects organic matter from decomposition (Lehmann and Kleber, Reference Lehmann and Kleber2015; Six et al., Reference Six, Conant, Paul and Paustian2002). It is, therefore, crucial to evaluate the interactions between biotic, abiotic and human factors to understand soil C dynamics in the Middle East.

Concluding remarks

Hyperarid lands have been largely missing from existing large-scale global dryland field surveys (Maestre et al., Reference Maestre, Quero, Gotelli, Escudero, Ochoa, Delgado-Baquerizo, García-Gómez, Bowker, Soliveres, Escolar and García-Palacios2012, Reference Maestre, Le Bagousse-Pinguet, Delgado-Baquerizo, Eldridge, Saiz, Berdugo, Gozalo, Ochoa, Guirado, García-Gómez and Valencia2022b). The Saudi and Middle East Green Initiatives provide a unique opportunity to gain insights into the processes that govern the structure, functioning and responses to climate change of hyperarid drylands. Knowledge gaps that need to be addressed include understanding: (i) the drivers for the unexpected high functional diversity in dryland plants (Gross et al., Reference Gross, Maestre, Liancourt, Berdugo, Martin, Gozalo, Ochoa, Delgado-Baquerizo, Maire, Saiz and Soliveres2024); (ii) how plants will adapt to water scarcity and respond to increased inter-annual precipitation variability (Garcia-Pichel and Sala, Reference Garcia-Pichel and Sala2022); (iii) developing a region-wide understanding of the distribution, characteristics and functioning of biocrusts (e.g., Abed et al., Reference Abed, Tamm, Hassenrück, Al-Rawahi, Rodríguez-Caballero, Fiedler, Maier and Weber2019) and (iv) the mechanisms, both physiological and genetic, behind the ability of soil microorganisms to endure extreme conditions (Makhalanyane et al., Reference Makhalanyane, Valverde, Gunnigle, Frossard, Ramond and Cowan2015). Further, many remote sensing-derived products ignore hyperarid drylands based on the assumption that vegetation is largely absent. As a result, hyperarid drylands are often excluded from remote sensing products typically used in global studies and vegetation estimates (e.g., Harris et al., Reference Harris, Gibbs, Baccini, Birdsey, De Bruin, Farina, Fatoyinbo, Hansen, Herold, Houghton and Potapov2021; Sabatini et al., Reference Sabatini, Jiménez-Alfaro, Jandt, Chytrý, Field, Kessler, Lenoir, Schrodt, Wiser, Arfin Khan and Attorre2022). This is problematic, as vegetation (and trees in particular) is more abundant in hyperarid areas than initially thought (Brandt et al., Reference Brandt, Tucker, Kariryaa, Rasmussen, Abel, Small, Chave, Rasmussen, Hiernaux and Diouf AA Kergoat2020; Reiner et al., Reference Reiner, Brandt, Tong, Skole, Kariryaa, Ciais, Davies, Hiernaux, Chave, Mugabowindekwe and Igel2023). More generally, international networks evaluating ecosystem carbon, water and energy fluxes, such as FLUXNET (Baldocchi et al., Reference Baldocchi, Falge, Gu, Olson, Hollinger, Running, Anthoni, Bernhofer, Davis, Evans, Fuentes, Goldstein, Katul, Law, Lee, Malhi, Meyers, Munger, Oechel, Paw, Pilegaard, Schmid, Valentini, Verma, Vesala, Wilson and Wofsy2001), lack sites in hyperarid environments, despite these representing around 8% of the global land surface (Prăvălie et al., Reference Prăvălie, Bandoc, Patriche and Sternberg2019). Developing an augmented flux network that includes sites in the Middle East would provide invaluable information on hyperarid drylands and contribute to filling existing gaps in flux databases that preclude obtaining more precise carbon cycling and climate change impact estimates.

Many of the actions discussed here will occur in complex and unpredictable contexts, where human realities should be considered alongside ecological and biophysical factors. Drylands exhibit sensitivity to changes in structure–function relationships due to extreme climate conditions (D’Odorico and Bhattachan, Reference D’Odorico and Bhattachan2012; Reynolds et al., Reference Reynolds, Smith, Lambin, Turner, Mortimore, Batterbury, Downing, Dowlatabadi, Fernández, Herrick and Huber-Sannwald2007), and human interventions can alter the resilience and stability of these systems (Robinson et al., Reference Robinson, Ericksen, Chesterman and Worden2015). Interactions between natural and human-induced processes affect dryland dynamics at specific scales (Fu et al., Reference Fu, Chen, Wang, Yu and Yu2021a), varying by social, cultural and economic context (Stringer et al., Reference Stringer, Reed, Fleskens, Thomas, Le and Lala-Pritchard2017). Therefore, understanding the complex and adaptive nature of drylands in the Middle East should involve dynamic interactions between its ecosystems and human societies (Folke et al., Reference Folke, Biggs, Norström, Reyers and Rockström2016), requiring interdisciplinary efforts (Bautista et al., Reference Bautista, Llovet, Ocampo-Melgar, Vilagrosa, Mayor, Murias, Vallejo and Orr2017).

Research in the Middle East should focus on the interplay between ecosystem services and human well-being to optimize services that enhance drylands’ health and human well-being in the long term (Fu et al., Reference Fu, Stafford-Smith, Wang, Wu, Yu, Lv, Ojima, Lv, Fu, Liu and Niu2021b). Identifying local limiting factors and their impacts can improve knowledge of ecosystem functioning and livelihoods through sustainable development (Reed et al., Reference Reed, Stringer, Dougill, Perkins, Atlhopheng, Mulale and Favretto2015; Turner et al., Reference Turner, Kasperson, Matson, McCarthy, Corell, Christensen, Eckley, Kasperson, Luers, Martello and Polsky2003). An interdisciplinary approach, which evaluates ecological and social perspectives together, will allow for assessing ecological dynamics and their driving forces in the Middle East. It will not only enable an understanding of the macroscopic differences among various dryland systems in this region but also help identify management or policy responses likely to deliver successful outcomes in different types of drylands (Fu et al., Reference Fu, Stafford-Smith, Wang, Wu, Yu, Lv, Ojima, Lv, Fu, Liu and Niu2021b).

Developing a comprehensive research program on ecosystem structure and functioning across multiple spatio-temporal scales in the Middle East is a critical step to provide the scientific underpinning needed for the success of ongoing green initiatives and climate change and desertification mitigation actions in this region. The creation of a Middle East collaborative network of researchers, practitioners and decision-makers, and the set-up of standardized regional surveys using standardized protocols following models successfully implemented in other large-scale and global surveys (e.g., Maestre et al., Reference Maestre, Eldridge, Gross, Bagousse-Pinguet, Saiz, Gozalo, Ochoa and Gaitán2022a; Maestre and Eisenhauer, Reference Maestre and Eisenhauer2019), would be a fundamental step forward towards achieving this aim. Doing so would not only be key to creating the basis for long-term monitoring of ecosystem changes in the region but would provide us with invaluable insights to advance our understanding of hyperarid drylands and to better comprehend and react to the increasingly drier conditions being experienced and forecasted across the globe.