Ecosystem services provided by dry river socio-ecological systems and their drivers of change

Dry rivers are a type of non-perennial river characterized by extreme dry conditions and dominance of terrestrial habitats. They are present in all continents, being especially abundant in arid and semiarid regions. Recent studies have shown their capacity to provide ecosystem services, although they are often undervalued and altered. This study is a literature review on the ecosystem services provided by dry rivers to human well-being. We apply the conceptual framework for the Millennium Ecosystem Assessment. First, we describe and exemplify the services provided by the natural system and its biodiversity. Second, we present the contributions of the local social system to service provision through co-production processes. Finally, the main drivers of ecosystem change that alter service provision are listed and discussed. We found that dry rivers and their biodiversity contribute to local human well-being. The ecological knowledge and culture of local human communities acquired over generations contribute to service provision maintaining the socio-ecological system’s sustainability and its resilience to disturbances. Among drivers of change, those of a social-cultural (e.g., sedentarization) and economic (e.g., globalization) nature affect dry rivers’ capacity to provide ecosystem services the most. Reconciling people and dry rivers requires a great deal of research and education.


Introduction
The ecological and management framework developed around the IRES concept (Intermittent Rivers and Ephemeral Streams) represents a main advance in knowledge of non-perennial rivers. The IRES concept includes all watercourses that cease flow at some point in time and space (Datry et al., 2017a, b). Recently, focus has been placed on an extreme type of non-perennial rivers characterized by a dominant dry phase, whose main habitat is terrestrial, defined as dry rivers (DRs) (Vidal-Abarca et al., 2020).
They only flow after sporadic heavy rainfall, are disconnected from groundwater and do not, therefore, harbor aquatic life. Given these conditions, the biodiversity (e.g., microorganisms, plants, invertebrates, vertebrates) and ecological processes of DRs (e.g., organic matter decomposition, biogeochemical cycles) are more closely linked with the terrestrial environment than to the aquatic environment. However, they remain part of the hydrological drainage network because they are generated by the erosive force of flash floods (García et al., 1999;Gordon et al., 2004). Understanding these rivers, therefore, requires merging terrestrial and aquatic sciences (Larned et al., 2010;Arce et al., 2019).
DRs are especially abundant in arid and semiarid regions worldwide (Mabbutt, 1977;Bull & Kirkby, 2002;Levick et al., 2008) but are present in all continents and climates (Stanley et al., 1997;Larned et al., 2010;Datry et al., 2014;Schneider et al., 2017), including humid and subhumid regions (Fritz et al., 2006;Buttle et al., 2012). Non-perennial rivers are estimated to represent more than 50% of the global river network (Raimond et al., 2013;Datry et al., 2014;Messager et al, 2021), but DRs representation at global scale is still unknown. The great variety of abiotic (e.g., frequency and intensity of flash floods) and biotic (e.g., riparian vegetation) factors that occur in the different climates and geographies where DRs are present, influence their geomorphology, stability, and sedimentation regime. Thus, DRs can range from narrow channels, rocky beds, and steep slopes to wide sand beds and slight slopes (García et al., 1999;Tooth & Nanson, 2011). Their disconnection with groundwater table is practically complete (Nanson et al., 2002) and flash floods only last a few hours (Shannon et al., 2002). Consequently, only after these sporadic events, the drainage network can be quickly but poorly connected (Knighton & Nanson, 1997).
Ecosystem services (ES) are the benefits that ecosystems and their biodiversity provide to human well-being (MA, 2005). These include provisioning (material products such as food, freshwater), regulating (benefits derived from the regulation of ecosystem processes such as climate regulation, water purification), cultural (non-material benefits people obtain from spiritual, cognitive, recreation, esthetic experiences), and supporting (processes such as photosynthesis and nutrient cycling which underpin the production of all the above ES) services. These benefits contribute to various components of human well-being: basic material for a good life (e.g., food, shelter, clothing), health (e.g., feeling well physically and mentally), good social relationships (e.g., social cohesion, mutual respect), security (e.g., secure access to natural resources, security from natural disasters), freedom of choice, and action to achieve what an individual values doing and being, equity, and fairness (MA, 2005).
Although research on the ES provided by nonperennial rivers is still limited, some studies have demonstrated their potential to provide benefits to human well-being. The current research focuses on describing the difference in ES provision between the three hydrological phases of these rivers: flowing, pool, and dry phase (Datry et al., 2017b;Koundouri et al., 2017;Kaletová et al., 2019;Magand et al., 2020;Stubbington et al., 2020). The flowing and pool phases provide more ES than the dry phase (e.g., Datry et al., 2017b) because water-dependent ES are altered during the dry phase, as surface water is lacking (Vidal-Abarca et al., 2020). However, this approach is not applicable to DRs because they remain almost entirely dry throughout the hydrological cycle. Hence, their services are sustained by the uninterrupted processes and functions of the terrestrial environment (Vidal-Abarca et al., 2020) and by the biodiversity that they harbor (Sánchez-Montoya et al., 2016a, b, 2017, 2020a, b, 2022. The lack of an integrative framework to assess DRs has led researchers to undervalue both their abiotic characteristics and biodiversity as ES providers, resulting in a poorly investigated ecosystem (Vidal-Abarca et al., 2020;Nicolás-Ruiz et al., 2021).
Social systems often co-operate with natural systems to maximize ES provision and foster synergies between them, a process known as co-production (Fischer & Eastwood, 2016;Bruley et al., 2021), which is widely recognized in perennial rivers (Palomo et al., 2016), but not in DRs (Nicolás-Ruiz et al., 2021). There is evidence of small local communities taking advantage of knowledge on DRs acquired over generations to promote ES production, although more research is required. The set of interactions between DRs (i.e., natural system) and their inhabitants (i.e., social systems), through a sustainable coproduction of ES for human well-being, is referred to in this study as a socio-ecological system (Partelow & Winkler, 2016;Partelow 2018), which operate on different spatial and temporal scales . For example, food and ecological knowledge from traditional farming benefits local people but can also be exported abroad or be useful for scientists.
However, the absence of a permanent water flow leads most of the society and water and land managers to consider DRs as useless, unproductive (DeLucio & Múgica, 1994;García-Llorente et al., 2012;Castro et al., 2018;Ghazi et al., 2018;Leigh et al., 2019), less valuable for their conservation (Rodríguez-Lozano et al., 2020), and dangerous when flash floods cause human and material damage (Di Baldassarre et al., 2010;Machado et al., 2017). This pejorative view of DRs may explain why they are one of the most impacted river ecosystems on the planet (Jacobson et al., 1995;Seely et al., 2003;Gómez et al., 2005;Levick et al., 2008;Acuña et al., 2017). The factors altering ecosystems and ES provision are known as drivers of change (e.g., land use change, freshwater depletion, socio-political processes) (MA, 2005).
This literature review aims to (i) describe the potential of DRs and their biodiversity to provide ES for human well-being according to the conceptual framework proposed by the Millennium Ecosystem Assessment (MA, 2005); ((ii) explore how the social system that inhabits DRs contributes to providing ES through nature-human cooperation processes; and finally, and (iii) analyze the main drivers of change that alter DRs' ability to supply ESs to society.

Dry rivers and their biodiversity as providers of ecosystem services
DRs and their biodiversity provide a wide variety of provisioning, regulating, cultural and supporting services to human well-being (Vidal-Abarca et al., 2020;2021;Nicolás-Ruiz et al., 2021) (Table 1). The provisioning services provided exclusively by the natural system and its biodiversity are several, such as food for humans in the form of plant (e.g., wild fruit and vegetables, such as asparagus; Fig. 1A) or wild animals (e.g., rabbits and partridges), and food for livestock consumption (e.g., natural grasslands, roots, shoots) ( Table 1). The growth of annual plants along DRs, which is favored by the higher amount of organic matter and moisture present in DRs compared to adjacent areas, has been used by local populations as pastures for livestock throughout history (Seely et al., 2003;Kihonge, 2017;Martinez-Yoshino et al., 2021). Regarding animals, edible insects, which are extremely nutritious with high fat, protein, and mineral contents depending on species (Durst & Shono, 2010;Van Houis et al., 2013), are traditional food for over 300 ethnic groups in 113 countries worldwide (MacEvilly 2000). For instance, the termites frequently found in DRs in Africa (Sánchez-Montoya et al., 2020a), among other world regions, are the second most eaten insect all over the world (Pal & Roy, 2014). Other terrestrial invertebrates, such as terrestrial snails, are common in DRs in the circum-Mediterranean region (Valverde, 1967). Terrestrial snails such as several species of the genera Otala, Eobania, Sphincterochila, and Iberus are eaten as food in arid environments of the Mediterranean Basin (García-Meseguer et al., 2017) (Fig. 1B), representing an important diet component highly consumed since the Late Pleistocene (Lubell, 2004). Similarly, vertebrates such as the European rabbits (Oryctolagus cuniculus (Linnaeus, 1758)), which are commonly observed in dry channels and their fringing riparian zones of Mediterranean semiarid DRs (Sánchez et al., 2004;Sánchez-Montoya et al., 2016b;, are still today a key Mediterranean diet component and played a key role in human subsistence, as evidenced by the large amount of rabbit remains of human origins in the Upper Paleolithic in archeological places in the Iberian Peninsula (Hockett & Bicho, 2000). Wild boars (Sus scrofa (Linnaeus, 1758)), which use dry channels as food resources (e.g., terrestrial plant roots) and movement corridors (Sánchez-Montoya et al., 2016a;Fig. 1C), are eaten in Europe and other world regions (Meng et al., 2009). In Africa, aardvarks (Orycteropus afer (Pallas, 1766)), an insectivore and nocturnal mammal which excavate in DR channels to create refuges (Melton, 1976;Sánchez-Montoya et al., 2017), have been persistently hunted for meat (Liebenberg, 2006). Similarly, kangaroos in Australia which have been traditional hunted in DRs by Aboriginal natives in north-western Australia (Withnell, 1901), are being increasingly incorporated into human diets in replacement of ruminant meat (Ratnasiri & Bandara, 2017).
The freshwater-provisioning service is naturally and occasionally provided from flash floods and scant springs occurring along DRs (Figs. 1D; 2). In addition, some terrestrial vertebrates that inhabit DRs Table 1 Evidence and examples of the four ecosystem service types provided by dry river according to MA (2005) Ecosystem service Renewable energy c The processing of many plants from dry rivers produces charcoal (e.g., mesquite: Prosopis sp.) Ríos Saucedo et al. (2013) Genetic resources The "Fertile Crescent" is an important center of diversity for many grains, particularly wheat and barley Teshome et al. (2010) Natural medicines Many plants that grow in dry riverbeds have medicinal uses Jacobson et al. (1995), Ahmad et al. (2004), Arenas (2012), and Martínez-Yoshino et al. (2021) Regulating Climate regulation Regional and local climatic regulation The residence time of organic carbon in dry riverbeds is much longer than in forest areas   Safriel and Adeel (2005) Local ecological knowledge In dry rivers (wadis) of Egypt and Sudan, "special gardening" is practiced maintaining tree plant populations that provide many ecosystem services Andersen (2007) 2007), and Cordell and Herbert (2002) Educational values Dry rivers (e.g., ramblas) are used to develop many educational and protection projects for threatened species https:// www. murcia. es/ medio-ambie nte/ medio-ambie nte/ publi cacio nes. asp; Anadon et al. (2005) Supporting Soil formation The vegetation that grows in dry rivers deposits organic matter that facilitates the formation of soil Abiotic material is a category not covered by MA (2005), but applicable to dry rivers c Renewable energy is an extend category and correspond to fibers (wood fuel) in MA (2005) worldwide significantly increase the water availability along this ecosystem by acting as landscape engineers. This is the case of some mammal species in Africa, such as chimpanzees (Pan troglodytes (Blumenbach, 1775)), baboons (Papio spp.), gemsboks (Oryx gazelle (Linnaeus, 1758)), plains zebra (Equus is among the most popular species for wildlife viewing, particularly for international tourists; O the bee-eater species that building nests in the banks of DRs, attract to bird watchers; P the presence of threatened species in DRs, such as the spurthighed tortoise (Testudo graeca graeca) is responsible for the development of educational projects; R dry rivers are spaces of social connection, and they communicate nearby villages; S: the decomposition of organic matter on dry riverbed facilitate soil formation and habitats for many plant species; T the latrines of European rabbits may constitute fertile islands in soils; U the use of DRs as preferential movement corridors for terrestrial vertebrates result in a significant source of nutrients via their excrements; V the red fox (Vulpes vulpes) frequently uses DRs in south of Spain acting as seed disperser for many plant species of the Mediterranean arborescent matorral. Photos: Courtesy E. Lundgren (E), and D. Carmona-López and J. Bautista (O) quagga (Boddaert, 1785)), and elephants (Loxodonta Africana (Blumenbach, 1797)). They dig wells in dry riverbeds (Hamilton, 1985;McGrew et al., 2007;Epaphras et al., 2008) as behavioral adaptation to survive water shortage periods, providing freshwater not only for themselves, but also for many other animals and humans (Naiman & Rogers, 1997;Ramey et al., 2013). Another interesting example is some introduced or feral equids that dig in dry channels to increase water availability where, seasonally, this resource is very limited (Lundgren et al., 2021). For instance, wild donkeys (Equus africanus asinus (Linnaeus, 1758)) in the North American deserts dig up to 2-m wells in groundwater along DRs (Fig. 1E), generating the only source of water along dry channels, or cutting distances between water bodies (Lundgren et al., 2021). DRs also provide biotic (e.g., fibers and resins as craft materials; Fig. 1F) and abiotic (e.g., salt, gravel, sand for building construction, gold for ornamental decoration; Fig. 1G) materials, renewable energies (e.g., firewood or charcoal), and natural medicines (Fig. 1H). It has been described that more than 50% of the plants from DRs of Spain´s southeast are used as natural medicines (Martínez-Yoshino et al., 2021). For instance, in Namibia, edible leaves, fruits, and roots of different species are used to headaches, asthma, colds and stomach problems, and rashes (e.g., Jacobson et al., 1995) ( Table 1).
The regulating services provided by DRs include freshwater regulation by water collection and drainage along DR channels. DRs are able to reduce and prevent flood damage to nearby crops and houses by quickly collecting and draining water  and, thus, contribute to the health and safety components of human well-being (Fig. 1I). Other regulation services comprise microclimate regulation by riparian vegetation (Roman, 2016), air-quality regulation by sequestering total nitrogen from the atmosphere (Scholz et al., 2002) and pest regulation (Table 1). For example, pods and seeds of some invasive alien trees of the genus Prosopis in DRs of Namibia constitute a significant part of the diet of a Muridae rodent species, limiting the spread of this invasive species (William et al., 2013).
In addition, DRs provide water quality regulation function as the water infiltration into aquifers (Suftin et al., 2014) allows for denitrification processes by microorganisms to take place (Whitford, 2002). This function may be enhanced by the digging behavior of some fauna along DRs (Fig. 1J). In this way, the proportion of high-quality water in landscapes grows and becomes available for different animal species. Finally, many invertebrate and vertebrate species contribute to DR regulating services acting as pollinators by being opportunistic nectar consumers (Herrera, 2020). For instance, thrips Haplothrips (order Thysanoptera) use Mollugo cerviana (Linnaeus, 1753) flowers, a native annual herb that usually grows in DRs in India, for breeding and feeding (Maddala & Aluri, 2019). This action effects not only self-pollination, but also cross-pollination since thrips could fly to migrate to the flowers of other closely spaced plants (Fig. 1K). Similarly, adult male lizards of Podarcis lilfordi (Günther, 1874) consume the nectar of Ephedra fragilis (Desfontaines, 1799) along dry channels located in the Western Mediterranean Basin (Garilleti et al., 2012) (Fig. 1L). These lizards have a more important role than insects in pollinating that particular Mediterranean shrub, frequently found in Mediterranean DRs (Celedón-Neghme et al., 2016;Fuster & Traveset, 2019).
Cultural services provided by DRs are referred as individual and collective subjective, physical and psychological experiences that people experience when they come into contact with nature. For instance, DRs have been a source of inspiration for writers, poets, painters, and other artists (Neruda 1976; Andreu-Lara & Ojeda-Rivera, 2019). They offer the opportunity to observe plant and animal species and learn about the ecological processes that occur in these ecosystems (Alberdi, 2011;Safriel & Adeel 2015;Hougha et al., 2018). In addition, DRs are also important natural areas where many recreational activities take place (Table 1, Fig. 1M). In these ecosystems, the mere presence of some vertebrate fauna provides cultural services like recreation and ecotourism. Mega-fauna inhabiting DRs, such as the African elephants that are a visually conspicuous ecosystems component especially during the dry season (Fig. 1N), is a popular attraction for international tourists (Lindsey et al., 2007). In fact, elephant conservation in savannah-protected areas brings comparable net positive economic returns to investments in sectors like education and infrastructure (Naidoo et al., 2016). Birdwatching, considered to be the most rapidly growing segment of naturebased tourism in the world (Cordell & Herbert, 2002), is also practiced in DRs. For instance, beeeater species that build nests on the banks of DRs (Fig. 1O) attract bird watchers to South African National Parks (Cumming & Maciejewski, 2017).
In addition, the presence of threatened species in DRs is responsible for education projects that focus on protecting target species. This is the case of the spur-thighed tortoise (Testudo graeca graeca (Linnaeus, 1758)) that inhabits DRs in southern Spain (Fig. 1P) (Anadon et al., 2005).
Besides, DRs are the center for leisure activities where to enjoy the beauty of natural and cultural landscapes (Seely et al., 2003;Andreu-Lara & Ojeda-Rivera, 2019), which promotes relaxation and healing (Teff-Seker & Orenstein, 2019) contributing to mental and physical health (Samakov, 2017;Arenas, 2012;Dan et al., 2021) and good social relationships. DRs are also places of social connection by communicating nearby villages (Gómez et al., 2005) (Fig. 1R) and generating feelings of belonging in people, which are linked with traditions, legends, rituals, or spiritual and religious experiences (Burmil et al., 1999;Kihonge, 2017).
Finally, supporting services in DRs are specially linked to soil formation and nutrient cycling, regulating part of biogeochemical cycles. For example, they participate in the carbon cycle by sequestering inorganic carbon in dry beds (Farage et al., 2003;von Schiller et al., 2017) and accelerating organic matter decomposition through processes like photodegradation (Del Campo & Gómez, 2016;Almagro et al., 2017). Hence, they facilitate soil formation and provide habitat for many plant (Martínez-Yoshino et al., 2021;Fig. 1S) and animal species (Sánchez-Montoya et al., 2016a; (Table 1). Some fauna contributes significantly to nutrient cycling and soil formation by providing supporting services in DRs. Some terrestrial vertebrates that commonly inhabit DRs supply primary producers with nutrients via decomposition and remineralization of their feces by microbes (e.g., Hansson et al., 1987). For instance, the latrines of European rabbits that are commonly observed in the riparian zone of Mediterranean semiarid DRs, (Fig. 1T) (Sánchez et al., 2004) may constitute fertile soil islands (Puigdefábregas et al., 1996), and facilitate plant growth (Delibes-Mateos et al., 2008). The use of DRs as preferential movement corridors by a wide variety of terrestrial wild and livestock vertebrates (Sánchez-Montoya et al., 2016b results in a significant source of nutrients via their excrements for instream primary producers. For instance, African elephant dung is frequently found on dry riverbeds in Namibia (Fig. 1U) as well as feces of livestock and domestic animals in Mediterranean DRs .
Finally, animal movement along DRs can have also important consequences for plant communities by acting as seed dispersal agents and providing supporting services (Table 1). This has been widely described for African elephants that disperse Acacia albida (Atchison 1948) seeds in their dung by occasional surface water along DRs, increasing the chances of germination (Nilsson & Dynesius, 1994). Similarly, the red fox (Vulpes Vulpes (Linnaeus, 1758)) which frequently uses DRs in southern Spain as movement corridors (Fig. 1V) (Sánchez-Montoya et al., 2022), acts as a seed disperser for many plant species of the Mediterranean arborescent matorral with a Ziziphus lotus (Linnaeus, 1753; Lamarck, 1789) habitat (Cancio et al., 2017). In North America, several snake species that inhabit DRs act as secondary seed dispersers by feeding on small rodents, which have specialized cheek pouches for transporting seeds from plant sources to larders (Reiserer et al., 2018).

Socio-cultural contributions to ecosystem service provision in dry rivers
All the benefits discussed in the previous section are produced solely by nature without human intervention, but there are many examples of how people-nature cooperation can generate ES. The success of social-ecological systems lies in the co-existence of the natural and social systems, which involves processes of adaptation and learning throughout history. For example, the lifestyles, ecological knowledge, and culture of the DRs' dwellers follow sustainable models of service coproduction coupled with natural rhythms (Fig. 2). When human populations use natural resources in a way that respects the spatial and temporal patterns of nature, ES provision is enhanced and the natural system becomes sustainable over time and resilient to disturbances (Tahmasebi, 2009;Balbo et al., 2016; Andreu-Lara & Ojeda-Rivera, 2019). However, social-ecological systems collapse when the social system overexploits the natural system and does not maintain its natural processes (see Drivers of change). One example of such is the different types of agriculture that are often practiced along DRs. Rain-fed crops or small traditional farms are integrated into both the landscape and the basin's natural processes and functions to promote the provision of services. However, irrigated, intensive, and monoculture agriculture tends to homogenize landscapes by altering negatively natural processes and services provision.
Co-produced provisioning services include crops, livestock, and water-harvesting systems managed by farmers and locals (Figs. 2, 3A). These co-production processes supplement the benefits provided by DRs and their biodiversity on their own, by covering all basic materials and health towards good quality of life. Local human communities take advantage of the higher degree of humidity and accumulation of organic matter in dry beds and their floodplains to grow cereals and fruit trees, such as almond, olive, and carob trees (Fig. 3B), and to obtain food for them and their livestock (Hans et al., 1999;Rodríguez Vaquero, 2007). They also practice "gardening particular," pruning and clearing the ground around the trees, to maintain tree plant populations that provide many benefits, and not only food. For example, the acacia forests (Acacia tortillis (Forssk.) Hayne, 1825) subsp. Raddiana (Savi) Brena, 1957) that grow in the channels of DRs (i.e., wadis) of Egypt and Sudan provide wood, charcoal, forage for the livestock, and shade for livestock and people (Andersen, 2007;Andersen et al., 2014).
Traditional livestock grazing has always been a solution to obtain food of animal origin in arid lands (Oteros-Rozas et al., 2013;Root-Bernstein et al., 2016) (Fig. 3C) and as a more sustainable alternative to vegetable production, which requires more water (Krätli et al., 2013). These systems imply a nomadic lifestyle (e.g., seasonal transhumance: Oteros-Rozas et al., 2014) coupled with the variability of environmental conditions (Coughenour, 2004). Such mobility maintains these ecosystems' resilience because shepherds adapt to change and uncertainty in the natural environment, combine different types of knowledge and learning, and generate opportunities for self-organization (Folke et al., 2005). The search of pasture for livestock is often linked with traditional routes that facilitate their movement (e.g., DRs: López Galán & Muñoz, 2008) and where to obtain freshwater (springs, wells, or livestock ponds attached to these rivers and groundwater: Vidal-Abarca et al., 2003;Martínez, 2004). Pastoralists' local ecological knowledge and their ability to manage scarce resources in stressed environments is a key for maintaining a flow of ES (Koocheki & Gliessman, 2005;Oteros-Rozas et al., 2012;Selemani, 2020).
Co-produced regulating services include erosion control through the building of crop terraces on floodplains , which slow the flow velocity during floods, together with riparian Fig. 3 Examples of ecosystem services co-produced by the socio-ecological system of dry rivers. A water-harvesting systems managed by farmers and locals; B carob tree cultivation in a dry riverbed; C traditional goat grazing in a dry river; D crop terraces laminate and reduce flow velocity, decreasing the damage caused by flash floods; E acequias in Spain help to regulate freshwater quality and local climate; F DRs are natural areas where many recreational and leisure activities are developed; G DRs generate feelings of belonging in people, which link to traditions, legends, rituals, or spiritual and religious experiences; H Painting of an arid landscape by Manuel Avellaneda, a painter from the arid Spanish southeast vegetation, reducing damage caused by flash floods (Fig. 3D). Similarly, traditional irrigation ditches, such as acequias, can help regulate freshwater quality and local climate (Iniesta-Arandia et al., 2014) (Fig. 3E). Freshwater regulation by the natural system and human management also supports other services, such as food, medicinal resources, local ecological knowledge, soil formation, primary production, or water and nutrient cycles.
The co-production of cultural services is based on individual experiences, which interact directly or indirectly with the natural environment (Fig. 3F). This generates inherent cognitive responses to an individual, a process known as cognitive co-production (Palomo et al., 2016). Some examples are the development of a water culture in a place where it is scarce and difficult to obtain (Fig. 2), sustainable resource management models (e.g., nomadism: FAO, 2001) based on local ecological knowledge, equitable governance models to distribute water in solidarity and to minimize social conflicts (Navarro Sánchez, 2010), and even belief systems, (Sangha et al., 2018) are basic to maintain the resilience of these ecosystems (Balbo et al., 2016). In addition, this local ecological knowledge has generated a high diversity of cultural identities that are manifested in their own languages (according to Safriel & Adeel, 2005, 24% of global languages are associated with arid environments on the planet), parties and celebrations linked with DRs (e.g., pilgrimage of the Virgen de la Luz in the Rambla del Cañar: Sánchez Conesa, 2018; or the annual Henley-on-Todd regatta, which takes place on a DR in northern Australia: Steward et al., 2012), spiritual and religious beliefs (e.g., rain rituals: Abu-Zahra, 1988) (Hillel, 1998;Tejedor et al., 2019) (Fig. 3G), and artistic inspiration (Fig. 3H).

Drivers of change severely threaten the dry river socio-ecological systems
Although the social system can contribute to ES provision quite often, it also causes changes in DRs that alter service provision. The human factors that cause these changes are known as drivers of change. They are direct if they directly affect the natural system and service provision, or indirect if they operate by first enhancing direct drivers. According to the MA (2005), five direct drivers (i.e., land use change, overexploitation, invasive alien species, pollution, and climate change) and five indirect drivers (i.e., population change, change in economic activity, sociopolitical factors, cultural factors, and technological changes) of change can be distinguished (Fig. 4). We find many examples of them on all continents (Datry et al., 2017a;Vidal-Abarca et al., 2020), which are altering the capacity of DR socio-ecological systems to ES co-production (Fig. 4).

Direct drivers of change
Land-use change is currently the most altering driver of change of DRs' services, mainly for food provision. These changes can imply the total alteration of own channels (e.g., developing housing estates on DRs: Steward et al., 2012), such as the alteration of the natural flow regime (e.g., by water transfers from other permanent flow channels: Briggs et al., 1993), which may compromise local populations' water supply. In other cases, these modifications entail a lighter partial alteration, for instance the construction of walls to prevent damage caused by flooding, the building of dams to collect runoff water, or the transformation of dry channels into crop fields (Ito, 2005;Gómez et al., 2005). In many arid and semiarid regions, the use of dry riverbeds for dry land farming to cultivate cereals or some types of rain-fed trees is frequent (e.g., the carob tree) (Hernández-Hernández & Morales Gil, 2013), altering the substrate, natural vegetation, and its seed bank. More substantive changes are produced by intensive irrigated farming that imply groundwater extractions, compromising the provision of many ES (Skoulikidis et al., 2017).
The overexploitation of abiotic materials (e.g., groundwater, sands) alters the biophysical factors of DRs, such as biodiversity, by negatively affecting ES provision and enhancing trade-offs (i.e., one service, often a provisioning one, increases to the detriment of another one or more: Bennett et al., 2009;Datry et al., 2017b). For example, uncontrolled groundwater abstraction from DR-dependent aquifers compromises the maintenance of the natural vegetation that regulate air quality, soil temperature, seed collection, erosion control, silt retention, and energy dissipation during floods (Pulford et al., 1992;Levick et al., 2008). Martínez-Valderrama et al. (2020) pointed out how the overexploitation of groundwater until its current depletion in Saudi Arabia, turned different hyper-arid areas into green fields for wheat production. Likewise, the extraction of sands and gravels from dry riverbeds alter many ESs, such as erosion regulation, freshwater regulation (i.e., flow type, aquifer recharge), natural hazard regulation (i.e., flash floods), and habitat maintenance (e.g., destruction of the plant communities used by local communities as food, biotic materials, and natural medicines) (Madyise, 2013). A more recent report shows that the medicinal plants used by local communities are being overexploited by outsiders for their growing interest in traditional medicine (Ahmad et al., 2004).
DRs are often polluted by sewage discharges from wastewater treatment plants, industries and cities, agriculture water discharges, citizens dumping rubbish, and the dumping of debris related to construction, agriculture, and livestock activities (Hassan & Egozi, 2001;Gómez et al., 2005;Skoulikidis et al., 2017). When sewage or agricultural discharges are continuous over time, part of DR channels may become temporarily intermittent or perennial, which leads to changes in sedimentation processes and vegetation on banks (Hassan & Egozi, 2001;Skoulikidis et al., 2017). Sewage and agricultural discharges also contaminate DR-dependent aquifers and subsurface soil by diminishing the natural capacity to regulate water quality and endangering freshwater supplies for both local human populations and livestock (Seely et al., 2003).
Invasive plant and animal alien species are favored in DRs by altering natural conditions which facilitate their settlement and expansion (Milton & Dean, 2010;Williams et al., 2013;Zhang & Jiang, 2016). The introduction of these species responds not only to accidental but also to economic reasons. For example, the introduction of the tree Prosopis spp. in floodplains in Kenya and Ethiopia satisfy the increase forage for livestock (Linders et al., 2020), but causing the loss of valuable ES including reductions in natural pastures, drought resistance, livestock, and the pastoral cultural system associated with these ecosystems. Fig. 4 Examples drawn from the literature of direct and indirect drivers of change that alter the capacity of DR socioecological systems to ecosystem services co-production. The direct drivers of change result from underlying societal causes (i.e., indirect drivers) which are underpinned by societal values and behaviors that endanger the survival of these socio-ecological systems But however, positive impacts (e.g., increased availability of material for fuel, house construction, and fencing) have been identified for Prosopis juliflora ((Sw.) DC., 1825) on dry lands in Ethiopia which depends on users' perceptions (Tebboth et al., 2020).
Climate change, which will exacerbate extreme climatic conditions in DRs, acts as a direct driver. Because of rising temperatures and evapotranspiration, and decreased erratic rainfall, the arid regions will undergo longer dry periods (Larned et al., 2010;Mirzabaev et al., 2019). Both the decrease in rainfall and its uneven distribution compromise aquifer recharge (Squeo et al., 2006), which affect the freshwater provisioning service for local populations, and promote shrub encroachment that simplifies plant diversity and affects the provision of forage for livestock (Eldridge et al., 2011;Eldridge & Soliveres, 2015;Barbosa da Silva et al., 2016). The sporadic and rapid flash floods in DRs, which are becoming more intense, destroy the vegetation that grows in channels, affecting negatively to the agropastoral systems provide by DRs (e.g., in East Africa: Mude et al., 2007;Pricope et al., 2013). Climate change also affects many regulating and supporting ES, such as soil formation by decreasing organic matter input (Almagro et al., 2010) and increasing salinity in the riverbed, erosion regulation (Martínez-Mena et al., 2008), and habitat maintenance by changes in the geomorphology of channels (Larkin et al., 2020). Finally, it should be noted that, because of climate change, many perennial rivers are undergoing a desiccation process (Stokstad, 2021;Sedeño-Díaz & López-López, 2021), which contribute to increase the number of DRs in drainage networks worldwide.

Indirect drivers of change
The socio-ecological systems generated around DRs are generally made up of human populations that very much depend on the benefits co-produced with the natural system. The success of this co-existence lies in caring for the environment through practices, norms, values, and beliefs acquired throughout history, which have generated specific customs, wisdom, landscape diversity, and a holistic self-organization and governance system (Safriel & Adeel, 2005;Balbo et al., 2016;Sangha et al., 2018). When local resource management is embedded in a specific economic model (e.g., globalization: Safriel & Adeel, 2005) or is affected by political decisions designed on a large scale (Beck, 1998), local experience, and knowledge are overlooked, which leads to the loss of a system's resilience and great social inequity (Merçon et al., 2019). For example, wilderness conservation projects rarely include and involve the socio-cultural diversity of local populations. In Australia, the demands of 50 indigenous peoples have led their old rules being incorporated into the management plan of their territories based on the maintenance of the people-places-plants and animals' relationship (Davies et al., 2013).
The climate change, to which all the ecosystems of the planet are subjected (Mauser et al., 2013), can more intensely affect the local human populations that live around DRs (Balbo et al., 2016). Lack of water because of climate change will be the most determining driver of change, but the economic and socio-political drivers will probably have the strongest impact (Safriel & Adeel, 2005). Local communities' ability to self-organize is essential for maintaining the sustainability of these ecosystems (Balbo et al., 2016), which will only be possible if their traditional governance models are respected. The integration of these communities into globalization expands the biophysical limits on which the sustainability of a system is sustained, which leads to decoupling that implies changes in both social and natural systems (Balbo et al., 2016;Quintas-Soriano et al., 2022). For example, they may involve population changes like migrations or the rural exodus of part of the human population to disconnect from their knowledge, cultural roots, and beliefs (Fernández-Giménez et al., 2017). Hoole and Berkes (2010) found that the expulsion of northern Namibian communities from their lands brought about a decoupling process due to the loss of pastoralists' access to a range of environmental and cultural resources, such as freshwater, fodder, ancestral graves, edible and medicinal plants, and the traditional culture.
In the globalization context, socio-cultural factors are also altered, and women can be the main losers (Ahmed et al., 2016;Chiblow, 2020). In a study on the sedentarization of a nomadic pastoral community in Morocco, Steinmann (1998) showed how women lost their ability to supply their families with mushrooms, truffles, medicinal plants, and firewood. Additionally, opportunities to teach younger female generations about medicinal plants were limited. The disruption of migrations and changing environmental factors discouraged younger women from collecting and learning about medicinal plants from which they derived any economic benefit. Therefore, women's loss of access to natural resources increased their dependence on men.
Finally, science and technology advances have also had a significant impact on ES in recent decades. For example, agricultural production has intensified thanks to new irrigation techniques and industrial machinery. The increase in this service often entails the loss of other services like access to water or esthetics values (García-Llorente et al., 2012).

Reconciling people with dry rivers
It is striking how small local DR communities engage in the ES co-production for human well-being, while the rest of society does not seem to perceive or enjoy these benefits. Citizens, scientists, and administrators perceive them as ecosystems with low biodiversity, useless, unproductive, cryptic (Gómez et al., 2005;García-Llorente et al., 2012;Ghazi et al., 2018), and even degraded (Leigh et al., 2019). Recent studies have highlighted these different social perceptions and even conflicting emotions about non-perennial rivers and DRs. For example, Jorda-Capdevila et al. (2021), in a participatory and deliberative exercise with 16 researchers and managers to analyzing sociocultural values of non-perennial rivers, pointed out that the low freshwater supply during the non-flowing phase was the main reason why it was highly valued. Rodríguez-Lozano et al. (2020) analyzed the perception of the riverscape by students from three U.S. universities and they found that those living in arid and Mediterranean regions negatively perceived nonperennial rivers, even though they were the dominant river typology in these areas. Finally, Vidal-Llamas et al. (2021) through a survey to analyzing people´s perception on arid landscapes at Southeast of Spain, found that DRs arouse contradictory emotions (e.g., fun and fear).
These different perceptions could be, at least partially, explained by different educational (e.g., ecology studies, local ecological knowledge), socio-demographic (e.g., age, gender), cultural and experiential factors (e.g., living close to a river, frequency of visits, leisure activities), which influence the interests, priorities and values that people attribute to the natural environment (Díaz et al., 2015;Pascual et al., 2017;Rodríguez-Lozano et al., 2020).
Local communities are more knowledgeable about the benefits of DRs than the rest of society, which makes them more highly valued. Some authors point out that knowledge and learning, through education, both formal and non-formal, can contribute to changing attitudes towards these ecosystems. For example, specific university education on the ecology of nonperennial rivers increases recognition of their benefits to human well-being and conservation, although these changes in attitudes are less evident than for perennial rivers (Leigh et al 2019;Rodríguez-Lozano et al 2020). In fact, Suárez & Vidal-Abarca (2017), through a survey addressed to undergraduate students of Biology and Environmental Sciences at the University of Murcia (Spain) on the ES provision by arid zones, showed that less than 20% of students perceived regulating ES. In this context, it should be noted that the scientific community can promote contradictory social perception regarding DRs by generating uncertainties about their capability to generate ES (Datry et al., 2017b;Koundouri et al., 2017;Kaletová et al., 2019;Magand et al., 2020;Stubbington et al., 2020). For example, the loss of food resources (e.g., fish) provided by non-perennial rivers during the dry phase does not imply a loss of this ES because it can be replaced by food of terrestrial origin (e.g., rabbits, partridges, terrestrial snails, or edible insects).
Future research should deepen on social and cultural factors influencing the perception of DRs ecosystem services. In this sense, it would be useful to develop research that involves the participation of different social groups through surveys or interviews to demonstrate what ES really contribute to their wellbeing and how they are valued according to the interests and priorities of each social group. Understanding what kind of values (i.e., instrumental, intrinsic, relational) social groups attach to dry river services could contribute to a greater interest in these ecosystems (Díaz et al., 2015;Pascual et al., 2017). Reconciliation people with DR require greater knowledge not only of the biophysical processes that underlie the capacity of these ecosystems to provide ES but also to delve into the human dimension that perceives them in a polarized way according to their life experiences.

Concluding remarks
DRs provide a wide variety of ES that contribute to human well-being. The literature provides numerous examples of how the physical environment and its biodiversity supply provisioning, regulating, cultural, and supporting services. Besides, the involvement of the local human system through co-production processes intensifies the benefits provided. This production is engendered mainly by the ecological knowledge acquired throughout history by local human communities, which have led to the development of collaboration models between natural and social systems. This co-production of benefits is especially sensitive to political, economic, social, and environmental changes, such as climate change. The sociocultural contribution that these human communities make to the sustainable management of the resources provided by DRs can be especially interesting for addressing the environmental crises that affect a large part of the planet. One of the keys to the sustainability of DR socio-ecological systems lies not only in the recognition of the biophysical properties that prevail in these ecosystems, but also the social system's ability to adapt to them.
Acknowledgements This research was supported by the Spanish Ministry of Economy, Industry and Competitiveness, State Research Agency and ERDF (European Regional Development Fund) (Project ref: CGL2017-84625-C2-2-R), and the Spanish Ministry of Science, Innovation and Universities (Project ref: RTI2018-097950-B-C22). Néstor Nicolás-Ruíz was supported by a pre-doctoral grant from the Seneca Foundation (Science and Technology Agency of the Region of Murcia, Spain). Antonio Jose Garcia-Meseguer identified the species of terrestrial molluscs in Figure 1B. We also thank Helen Warburton for revising the English and the anonymous reviewers who helped us to improve this paper. We especially want to express our thanks to Tim Sykes whose comments have helped us to greatly improve this document.

Conflict of interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Ethical approval MRV-AG and MLSA conceived the original idea and structure of the manuscript and assumed the responsibility of the overall development. MRV-AG, NN-R, MMS-M, and MLSA carried out a bibliographic search. MRV-AG led the writing of the manuscript. MRV-AG, MMS-M, and MLSA were responsible for the art work. All authors contributed to the revising draft versions of the whole manuscript. All authors have read and agreed to the published version of the manuscript.