Hyperarid drylands, areas with an aridity index (precipitation/potential evapotranspiration) below 0.05, represent some of the most extreme environments on Earth. Despite the perception as being inhospitable to life, they host a diverse set of biota and ecosystems, including rangelands that provide grazing for nomadic tribes (Johnson, Reference Johnson1993), biocrusts that contribute to carbon sequestration (Kidron et al., Reference Kidron, Li, Jia, Gao and Zhang2015) or coastal mangroves and salt marshes that support fisheries and modulate nutrient cycling (El-Regal and Ibrahim, Reference El-Regal and Ibrahim2014). Encompassing an area of around 10 million km2, the extent of hyperarid regions is expected to grow by the end of the century due to increasing aridity driven by climate change. Current projections estimate the expansion of hyperarid land by 2050 to range from 6% under moderate scenarios to as much as 12% in the most pessimistic scenarios (Huang et al., Reference Huang, Yu, Guan, Wang and Guo2016). While more than 100 million people currently live in hyperarid drylands (MEA, 2005), population growth rates as high as 65% by 2100 have been projected for developing countries in these regions (Huang et al., Reference Huang, Yu, Guan, Wang and Guo2016), placing further strain on these ecosystems.
Hyperarid ecosystems remain poorly studied compared to other dryland and nondryland ecosystems (Brito et al., Reference Brito and Godinho2014; Šmíd et al., Reference Šmíd, Sindaco, Shobrak, Busais, Tamar, Aghová, Simó‐Riudalbas, Tarroso, Geniez, Crochet and Els2021). Research on their biodiversity, structure and function is limited, representing less than 3% of all dryland studies (Groner et al., Reference Groner, Babad, Berda Swiderski and Shachak2023). These ecosystems are not only challenging to access (Ficetola et al., Reference Ficetola, Bonardi, Sindaco and Padoa-Schioppa2013) but also vastly under-protected, with just 6.7% of their total area designated for conservation (Lewin et al., Reference Lewin, Murali, Rachmilevitch and Roll2024). The inaccessibility of hyperarid areas, coupled with the misconception that they are barren and devoid of life, has resulted in their neglect of conservation efforts (Durant et al., Reference Durant, Pettorelli, Bashir, Woodroffe, Wacher, De Ornellas, Ransom, Abáigar, Abdelgadir, El Alqamy and Beddiaf2012). Consequently, there is a widespread but incorrect belief that these environments are either ecologically insignificant or incapable of further degradation (Martínez-Valderrama et al., Reference Martínez-Valderrama, Guirado and Maestre2020). Contrary to this view, hyperarid drylands are rich in biodiversity. For example, the Algerian Sahara alone is home to at least 1,200 plant species (Ozenda, Reference Ozenda2004). Due to the unique adaptations of organisms in these extreme environments, hyperarid ecosystems offer valuable insights into how dryland systems might respond to future climate change. They serve as natural laboratories for studying the impacts of, and adaptations to, climatic change that could affect other dryland regions (Groner et al., Reference Groner, Babad, Berda Swiderski and Shachak2023; Grünzweig et al., Reference Grünzweig, De Boeck, Rey, Santos, Adam, Bahn, Belnap, Deckmyn, Dekker, Flores, Gliksman, Helman, Hultine, Liu, Meron, Michael, Sheffer, Throop, Tzuk and Yakir2022). Furthermore, as nondryland areas face increasing water scarcity, mechanisms governing ecosystem functioning in drylands are expected to become relevant in these regions (Allan et al., Reference Allan, Barlow, Byrne, Cherchi, Douville, Fowler, Allan, Barlow, Byrne, Cherchi, Douville, Fowler, Gan, Pendergrass, Rosenfeld, Swann, Wilcox and Zolina2020). Many of these changes are anticipated in densely populated regions, particularly in the subtropics and mid latitudes, with significant implications for food production and societal well-being (Grünzweig et al., Reference Grünzweig, De Boeck, Rey, Santos, Adam, Bahn, Belnap, Deckmyn, Dekker, Flores, Gliksman, Helman, Hultine, Liu, Meron, Michael, Sheffer, Throop, Tzuk and Yakir2022). Beyond ecological insights, studying the adaptations of organisms in hyperarid drylands holds great promise for biotechnological and biodiversity applications (Bull and Asenjo, Reference Bull and Asenjo2013).
The Middle East accounts for over 30% of the world’s hyperarid drylands. This region hosts diverse biomes that have developed unique ecoevolutionary adaptations over thousands of years of biotic and abiotic interactions. They support more than 8,000 unique species of vascular plants (Hegazy and Doust, Reference Hegazy and Doust2016) and encompass a diverse range of ecosystems present in other regions, albeit under more favorable conditions. These ecosystems span from mangroves along the coastal fringes of the Red Sea to grasslands and shrublands extending across Turkey and Iraq (Box 1). Despite the geographic and historical interest the Middle East has generated, much of the research undertaken in this region has predominantly focused on the description of the flora in individual countries, such as Iran (e.g., Rechinger, Reference Rechinger1963–2005), Israel and Palestine (e.g., Danin, Reference Danin2004; Zohary, Reference Zohary1962), Lybia (e.g., Jafri and El-Gadi, Reference Jafri and El-Gadi1977–1993), Oman (e.g., Ghazanfar, Reference Ghazanfar1992; Ghazanfar and Fisher, Reference Ghazanfar and Fisher1998), Saudi Arabia (e.g., Mandaville, Reference Mandaville2013; Migahid, Reference Migahid1978), Turkey (e.g., Davis et al., Reference Davis, Mill and Tan1988, Reference Davis, Heywood and Hamilton1994) or Yemen (e.g., Brown and Mies, Reference Brown and Mies2012; Kilian et al., Reference Kilian, Hein and Hubaishan2002). Other studies described the vegetation of the Middle East from geobotanical and phytogeographical perspectives (e.g., Zohary, Reference Zohary1971, Reference Zohary1973). Similarly, the fauna of the Middle East has drawn significant interest due to the extreme environmental conditions these species endure, with several biodiversity hotspots in the region. For example, the Arabian Peninsula hosts a high number of endemic vertebrate species, 21.6% of which are unique to this region (Mallon, Reference Mallon2011). Additionally, the Middle East serves as an essential stopover for migratory bird species along major migratory routes that connect Africa, Asia and Europe (Schekler et al., Reference Schekler, Smolinsky, Troupin, Buler and Sapir2022). Countries like Israel have been extensively studied for their key role in bird migration routes for decades already (e.g., Leshem and Yom-Tov, Reference Leshem and Yom-Tov1996). However, except for Hegazy and Doust (Reference Hegazy and Doust2016), the life stories of many Middle Eastern species have not been comprehensively investigated and described while concurrently considering this region’s geography, plant evolution and ecology. Moreover, these studies have yet to integrate the complex interactions between human societies and ecosystems, particularly in the face of the additional pressures imposed by climate change.
Box 1. Hyperarid drylands in the Middle East are much more than barren landscapes.
The Middle East is home to diverse ecosystems that, while also found in other regions under more favorable conditions, can thrive in some of the driest environments on Earth. Gaining a deeper understanding of these ecosystems offers valuable insights into their functioning, restoration potential and relevance for addressing climate change, land degradation and desertification. For instance, mangroves (1) along the coasts of the Red Sea and Arabian Sea (Almahasheer, Reference Almahasheer2018; Blanco-Sacristán et al., Reference Blanco-Sacristán, Johansen, Duarte, Daffonchio, Hoteit and McCabe2022) are a key vegetation type in the Middle East. These ecosystems provide nursery grounds for marine life, support local communities through commercial species and protect coastlines from erosion. However, mangroves in this region endure extreme saline stress due to limited freshwater inputs and increasing groundwater extraction, on which they heavily rely (Adame et al., Reference Adame, Connolly, Turschwell, Lovelock, Fatoyinbo, Lagomasino, Goldberg, Holdorf, Friess, Sasmito, Sanderman, Sievers, Buelow, Kauffman, Bryan-Brown and Brown2021). Additionally, these mangroves face significant human pressures (Almahasheer et al., Reference Almahasheer, Aljowair, Duarte and Irigoien2016). Understanding how mangroves survive in such arid conditions offers a unique opportunity to predict how global mangrove ecosystems might respond to climate change, including the effects of human activities, sea-level rise and microclimatic shifts (Osland et al., Reference Osland, Enwright, Day, Gabler, Stagg and Grace2016). Similarly, the grasslands (2) of the Middle East, such as those in Iran’s Taftan mountains (Burrascano et al., Reference Burrascano, Naqinezhad and Fernández2018) and the southwestern Arabian Peninsula (Ghazanfar and Fisher, Reference Ghazanfar and Fisher1998), provide a valuable opportunity to study the interactions between abiotic and biotic factors across altitudinal and latitudinal gradients. As global aridity increases, understanding the dynamics of these grasslands – ranging from Mediterranean grasslands to semi-arid steppes – can offer crucial insights for improving grassland health in other dryland regions. This is particularly important given the extreme climatic conditions in which these grasslands exist, which mirror those in many other arid and semi-arid ecosystems globally, such as the grasslands in the Namib Desert (Evans et al., Reference Evans, Todd-Brown, Jacobson and Jacobson2020; Logan et al., Reference Logan, Jacobson, Jacobson and Evans2021) and Australia (Keast, Reference Keast2013). By studying how these Middle Eastern grasslands thrive, researchers can gain a deeper understanding of the resilience and adaptive strategies of grassland ecosystems, crucial for managing the effects of climate change on grasslands worldwide. Shrublands (3), which dominate much of the Middle East – such as the eastern Arabian Peninsula, parts of Jordan (e.g., Jebel Ajloun) and northern Israel (Upper Galilee) – also play a critical ecological role. They provide habitats for insects and small rodents and host biocrusts – communities of photo- and heterotrophic organisms living on the soil surface in large, unvegetated drylands. Biocrusts are essential for maintaining dryland ecosystem health by influencing soil respiration, nutrient cycling and runoff dynamics. While biocrusts have been extensively studied in regions like the Negev Desert and the Arava Valley in Israel (e.g., Galun and Garty, Reference Galun and Garty2003; Kidron and Tal, Reference Kidron and Tal2012), research across other Middle Eastern countries is limited. Studies from countries like Iran (Bashtian et al., Reference Bashtian, Sepehr, Farzam and Bahreini2019), Iraq (Hamdi et al., Reference Hamdi, Yousef, Al-Azawi, Al-Tai and Al-Baquari1978), Jordan (El-Oqlah et al., Reference El-Oqlah, Hawksworth and Lahham1986), Oman (Abed et al., Reference Abed, Al-Sadi, Al-Shehi, Al-Hinai and Robinson2013) and Saudi Arabia (Alotaibi et al., Reference Alotaibi, Sonbol, Alwakeel, Suliman, Fodah, Jaffal, AlOthman and Mohammed2020) suggest that biocrust composition is relatively uniform across the region (Galun and Garty, Reference Galun and Garty2003), but more research is needed to fully understand their distribution and composition in the Middle East. With its long history of land use and anthropogenic impacts under climate change (Kaniewski et al., Reference Kaniewski, Van Campo and Weiss2012), the Middle East offers valuable insights into how human activities shape biocrust communities under extreme environmental conditions. Studying the interactions between biocrusts and human-induced changes – such as grazing, agriculture and urbanization – can inform strategies for managing and mitigating these impacts, both regionally and globally. Leveraging remote sensing technologies (e.g., satellites, drones and eddy-covariance towers) alongside in situ data collection could enhance ecosystem surveys, providing timely insights into their functioning. This data could also support the establishment of new monitoring networks, such as eddy covariance flux networks, which remain underrepresented in hyperarid drylands worldwide (Smith et al., Reference Smith, Dannenberg, Yan, Herrmann, Barnes, Barron-Gafford, Biederman, Ferrenberg, Fox, Hudson and Knowles2019).
Here, we elaborate on how research on the biodiversity and ecology of Middle East hyperarid drylands can advance our understanding of dryland ecosystems globally while also contributing to the success of ongoing Saudi and Middle East Green Initiatives (https://www.greeninitiatives.gov.sa/). With an initial investment of more than USD 180 billion, these green initiatives aim to restore degraded marine and terrestrial environments, enhance biodiversity and mitigate the impacts of climate change throughout the Middle East. We argue that if these initiatives are successfully developed and implemented, they might serve as the foundation for further experimental and theoretical studies on the impacts of extreme climates on dryland ecosystems globally. Furthermore, the Saudi and Middle East Green Initiatives could establish the base for applied solutions aimed at preserving and/or rehabilitating the biodiversity and ecosystem services of global drylands, mitigating climate change and addressing land degradation and desertification.
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.
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Hyperarid drylands, areas with an aridity index (precipitation/potential evapotranspiration) below 0.05, represent some of the most extreme environments on Earth. Despite the perception as being inhospitable to life, they host a diverse set of biota and ecosystems, including rangelands that provide grazing for nomadic tribes (Johnson, Reference Johnson1993), biocrusts that contribute to carbon sequestration (Kidron et al., Reference Kidron, Li, Jia, Gao and Zhang2015) or coastal mangroves and salt marshes that support fisheries and modulate nutrient cycling (El-Regal and Ibrahim, Reference El-Regal and Ibrahim2014). Encompassing an area of around 10 million km2, the extent of hyperarid regions is expected to grow by the end of the century due to increasing aridity driven by climate change. Current projections estimate the expansion of hyperarid land by 2050 to range from 6% under moderate scenarios to as much as 12% in the most pessimistic scenarios (Huang et al., Reference Huang, Yu, Guan, Wang and Guo2016). While more than 100 million people currently live in hyperarid drylands (MEA, 2005), population growth rates as high as 65% by 2100 have been projected for developing countries in these regions (Huang et al., Reference Huang, Yu, Guan, Wang and Guo2016), placing further strain on these ecosystems.
Hyperarid ecosystems remain poorly studied compared to other dryland and nondryland ecosystems (Brito et al., Reference Brito and Godinho2014; Šmíd et al., Reference Šmíd, Sindaco, Shobrak, Busais, Tamar, Aghová, Simó‐Riudalbas, Tarroso, Geniez, Crochet and Els2021). Research on their biodiversity, structure and function is limited, representing less than 3% of all dryland studies (Groner et al., Reference Groner, Babad, Berda Swiderski and Shachak2023). These ecosystems are not only challenging to access (Ficetola et al., Reference Ficetola, Bonardi, Sindaco and Padoa-Schioppa2013) but also vastly under-protected, with just 6.7% of their total area designated for conservation (Lewin et al., Reference Lewin, Murali, Rachmilevitch and Roll2024). The inaccessibility of hyperarid areas, coupled with the misconception that they are barren and devoid of life, has resulted in their neglect of conservation efforts (Durant et al., Reference Durant, Pettorelli, Bashir, Woodroffe, Wacher, De Ornellas, Ransom, Abáigar, Abdelgadir, El Alqamy and Beddiaf2012). Consequently, there is a widespread but incorrect belief that these environments are either ecologically insignificant or incapable of further degradation (Martínez-Valderrama et al., Reference Martínez-Valderrama, Guirado and Maestre2020). Contrary to this view, hyperarid drylands are rich in biodiversity. For example, the Algerian Sahara alone is home to at least 1,200 plant species (Ozenda, Reference Ozenda2004). Due to the unique adaptations of organisms in these extreme environments, hyperarid ecosystems offer valuable insights into how dryland systems might respond to future climate change. They serve as natural laboratories for studying the impacts of, and adaptations to, climatic change that could affect other dryland regions (Groner et al., Reference Groner, Babad, Berda Swiderski and Shachak2023; Grünzweig et al., Reference Grünzweig, De Boeck, Rey, Santos, Adam, Bahn, Belnap, Deckmyn, Dekker, Flores, Gliksman, Helman, Hultine, Liu, Meron, Michael, Sheffer, Throop, Tzuk and Yakir2022). Furthermore, as nondryland areas face increasing water scarcity, mechanisms governing ecosystem functioning in drylands are expected to become relevant in these regions (Allan et al., Reference Allan, Barlow, Byrne, Cherchi, Douville, Fowler, Allan, Barlow, Byrne, Cherchi, Douville, Fowler, Gan, Pendergrass, Rosenfeld, Swann, Wilcox and Zolina2020). Many of these changes are anticipated in densely populated regions, particularly in the subtropics and mid latitudes, with significant implications for food production and societal well-being (Grünzweig et al., Reference Grünzweig, De Boeck, Rey, Santos, Adam, Bahn, Belnap, Deckmyn, Dekker, Flores, Gliksman, Helman, Hultine, Liu, Meron, Michael, Sheffer, Throop, Tzuk and Yakir2022). Beyond ecological insights, studying the adaptations of organisms in hyperarid drylands holds great promise for biotechnological and biodiversity applications (Bull and Asenjo, Reference Bull and Asenjo2013).
The Middle East accounts for over 30% of the world’s hyperarid drylands. This region hosts diverse biomes that have developed unique ecoevolutionary adaptations over thousands of years of biotic and abiotic interactions. They support more than 8,000 unique species of vascular plants (Hegazy and Doust, Reference Hegazy and Doust2016) and encompass a diverse range of ecosystems present in other regions, albeit under more favorable conditions. These ecosystems span from mangroves along the coastal fringes of the Red Sea to grasslands and shrublands extending across Turkey and Iraq (Box 1). Despite the geographic and historical interest the Middle East has generated, much of the research undertaken in this region has predominantly focused on the description of the flora in individual countries, such as Iran (e.g., Rechinger, Reference Rechinger1963–2005), Israel and Palestine (e.g., Danin, Reference Danin2004; Zohary, Reference Zohary1962), Lybia (e.g., Jafri and El-Gadi, Reference Jafri and El-Gadi1977–1993), Oman (e.g., Ghazanfar, Reference Ghazanfar1992; Ghazanfar and Fisher, Reference Ghazanfar and Fisher1998), Saudi Arabia (e.g., Mandaville, Reference Mandaville2013; Migahid, Reference Migahid1978), Turkey (e.g., Davis et al., Reference Davis, Mill and Tan1988, Reference Davis, Heywood and Hamilton1994) or Yemen (e.g., Brown and Mies, Reference Brown and Mies2012; Kilian et al., Reference Kilian, Hein and Hubaishan2002). Other studies described the vegetation of the Middle East from geobotanical and phytogeographical perspectives (e.g., Zohary, Reference Zohary1971, Reference Zohary1973). Similarly, the fauna of the Middle East has drawn significant interest due to the extreme environmental conditions these species endure, with several biodiversity hotspots in the region. For example, the Arabian Peninsula hosts a high number of endemic vertebrate species, 21.6% of which are unique to this region (Mallon, Reference Mallon2011). Additionally, the Middle East serves as an essential stopover for migratory bird species along major migratory routes that connect Africa, Asia and Europe (Schekler et al., Reference Schekler, Smolinsky, Troupin, Buler and Sapir2022). Countries like Israel have been extensively studied for their key role in bird migration routes for decades already (e.g., Leshem and Yom-Tov, Reference Leshem and Yom-Tov1996). However, except for Hegazy and Doust (Reference Hegazy and Doust2016), the life stories of many Middle Eastern species have not been comprehensively investigated and described while concurrently considering this region’s geography, plant evolution and ecology. Moreover, these studies have yet to integrate the complex interactions between human societies and ecosystems, particularly in the face of the additional pressures imposed by climate change.
Box 1. Hyperarid drylands in the Middle East are much more than barren landscapes.
The Middle East is home to diverse ecosystems that, while also found in other regions under more favorable conditions, can thrive in some of the driest environments on Earth. Gaining a deeper understanding of these ecosystems offers valuable insights into their functioning, restoration potential and relevance for addressing climate change, land degradation and desertification. For instance, mangroves (1) along the coasts of the Red Sea and Arabian Sea (Almahasheer, Reference Almahasheer2018; Blanco-Sacristán et al., Reference Blanco-Sacristán, Johansen, Duarte, Daffonchio, Hoteit and McCabe2022) are a key vegetation type in the Middle East. These ecosystems provide nursery grounds for marine life, support local communities through commercial species and protect coastlines from erosion. However, mangroves in this region endure extreme saline stress due to limited freshwater inputs and increasing groundwater extraction, on which they heavily rely (Adame et al., Reference Adame, Connolly, Turschwell, Lovelock, Fatoyinbo, Lagomasino, Goldberg, Holdorf, Friess, Sasmito, Sanderman, Sievers, Buelow, Kauffman, Bryan-Brown and Brown2021). Additionally, these mangroves face significant human pressures (Almahasheer et al., Reference Almahasheer, Aljowair, Duarte and Irigoien2016). Understanding how mangroves survive in such arid conditions offers a unique opportunity to predict how global mangrove ecosystems might respond to climate change, including the effects of human activities, sea-level rise and microclimatic shifts (Osland et al., Reference Osland, Enwright, Day, Gabler, Stagg and Grace2016). Similarly, the grasslands (2) of the Middle East, such as those in Iran’s Taftan mountains (Burrascano et al., Reference Burrascano, Naqinezhad and Fernández2018) and the southwestern Arabian Peninsula (Ghazanfar and Fisher, Reference Ghazanfar and Fisher1998), provide a valuable opportunity to study the interactions between abiotic and biotic factors across altitudinal and latitudinal gradients. As global aridity increases, understanding the dynamics of these grasslands – ranging from Mediterranean grasslands to semi-arid steppes – can offer crucial insights for improving grassland health in other dryland regions. This is particularly important given the extreme climatic conditions in which these grasslands exist, which mirror those in many other arid and semi-arid ecosystems globally, such as the grasslands in the Namib Desert (Evans et al., Reference Evans, Todd-Brown, Jacobson and Jacobson2020; Logan et al., Reference Logan, Jacobson, Jacobson and Evans2021) and Australia (Keast, Reference Keast2013). By studying how these Middle Eastern grasslands thrive, researchers can gain a deeper understanding of the resilience and adaptive strategies of grassland ecosystems, crucial for managing the effects of climate change on grasslands worldwide. Shrublands (3), which dominate much of the Middle East – such as the eastern Arabian Peninsula, parts of Jordan (e.g., Jebel Ajloun) and northern Israel (Upper Galilee) – also play a critical ecological role. They provide habitats for insects and small rodents and host biocrusts – communities of photo- and heterotrophic organisms living on the soil surface in large, unvegetated drylands. Biocrusts are essential for maintaining dryland ecosystem health by influencing soil respiration, nutrient cycling and runoff dynamics. While biocrusts have been extensively studied in regions like the Negev Desert and the Arava Valley in Israel (e.g., Galun and Garty, Reference Galun and Garty2003; Kidron and Tal, Reference Kidron and Tal2012), research across other Middle Eastern countries is limited. Studies from countries like Iran (Bashtian et al., Reference Bashtian, Sepehr, Farzam and Bahreini2019), Iraq (Hamdi et al., Reference Hamdi, Yousef, Al-Azawi, Al-Tai and Al-Baquari1978), Jordan (El-Oqlah et al., Reference El-Oqlah, Hawksworth and Lahham1986), Oman (Abed et al., Reference Abed, Al-Sadi, Al-Shehi, Al-Hinai and Robinson2013) and Saudi Arabia (Alotaibi et al., Reference Alotaibi, Sonbol, Alwakeel, Suliman, Fodah, Jaffal, AlOthman and Mohammed2020) suggest that biocrust composition is relatively uniform across the region (Galun and Garty, Reference Galun and Garty2003), but more research is needed to fully understand their distribution and composition in the Middle East. With its long history of land use and anthropogenic impacts under climate change (Kaniewski et al., Reference Kaniewski, Van Campo and Weiss2012), the Middle East offers valuable insights into how human activities shape biocrust communities under extreme environmental conditions. Studying the interactions between biocrusts and human-induced changes – such as grazing, agriculture and urbanization – can inform strategies for managing and mitigating these impacts, both regionally and globally. Leveraging remote sensing technologies (e.g., satellites, drones and eddy-covariance towers) alongside in situ data collection could enhance ecosystem surveys, providing timely insights into their functioning. This data could also support the establishment of new monitoring networks, such as eddy covariance flux networks, which remain underrepresented in hyperarid drylands worldwide (Smith et al., Reference Smith, Dannenberg, Yan, Herrmann, Barnes, Barron-Gafford, Biederman, Ferrenberg, Fox, Hudson and Knowles2019).
Here, we elaborate on how research on the biodiversity and ecology of Middle East hyperarid drylands can advance our understanding of dryland ecosystems globally while also contributing to the success of ongoing Saudi and Middle East Green Initiatives (https://www.greeninitiatives.gov.sa/). With an initial investment of more than USD 180 billion, these green initiatives aim to restore degraded marine and terrestrial environments, enhance biodiversity and mitigate the impacts of climate change throughout the Middle East. We argue that if these initiatives are successfully developed and implemented, they might serve as the foundation for further experimental and theoretical studies on the impacts of extreme climates on dryland ecosystems globally. Furthermore, the Saudi and Middle East Green Initiatives could establish the base for applied solutions aimed at preserving and/or rehabilitating the biodiversity and ecosystem services of global drylands, mitigating climate change and addressing land degradation and desertification.
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.
Open peer review
For open peer review materials, please visit https://doi.org/10.1017/dry.2024.6
Author contribution
J. B.-S. conceived the idea and wrote the initial draft; all authors contributed to the review and the final version of the manuscript.
Financial support
The work presented herein was funded by the King Abdullah University of Science and Technology’s Climate and Livability Initiative and Circular Carbon Initiative.
Competing interest
The authors declare that they have no conflict of interest.