The following is the established format for referencing this article:Cornejo-Denman, L., J. Romo-Leon, and A. Lutz-Ley. 2023. Traditional agricultural practices and their contribution to habitat quality and carbon storage in arid Northwest Mexico: a social-ecological approach in the Rio Sonora sub-watershed. Ecology and Society 28(1):18.
Along with environmental factors, agricultural activity is one of the main drivers of change in riparian landscapes of arid regions. Some agricultural practices are considered more sustainability-oriented than others. Despite this, their use is not widespread and their effect on the provision of ecosystem services is not clearly established. Thus, we propose an empirical framework for studying the effects of traditional agricultural practices on regulating ecosystem services in priority and spatially restricted ecosystems. Through spatial analysis and community field work, this study assesses changes in the use of two traditional agricultural practices: living fencerows and acequia irrigation systems and their effect on biodiversity and ecosystem service: habitat quality and carbon storage. Results show that the use of living fencerows promotes habitat quality and carbon storage, but their use is restricted by functional and socioeconomic factors. Acequia systems promote the provision of carbon storage but have a negative influence on habitat quality, and their use is changing mainly due to environmental and functional factors. The presence of obligate riparian vegetation in different configurations maintains the highest values for habitat quality and carbon storage, but it doesn’t provide the functional purpose of fencerows or acequias. We suggest that the expansion of voluntary and official conservation areas that promote regeneration of riparian vegetation adjacent and around agricultural areas could help mitigate floods, provide materials and suitable conditions for the maintenance of fencerows and acequias, enhance water and soil quality and many other services needed in agriculture. We consider our proposal to be useful for future assessments of ecosystem services tradeoffs and social-ecological dynamics in other understudied regions with predominantly agricultural activity.
Natural and human-driven changes in riparian landscapes have several ecological and social effects frequently interlinked. In arid environments, the loss of water-dependent riparian vegetation due to climate change processes and overexploitation of land and water resources compromises biodiversity, ecosystem services provision (Perry et al. 2012, Boulton 2014, Datry et al. 2017), and limits the access to materials (e.g. wood, sediments to use as fertilizers) that are useful for the development of some traditional agricultural practices (e.g., living fencerows, irrigation systems, natural fertilization techniques). In rural communities, where the local population depends mostly on agriculture, the loss of these practices can have important social-ecological effects and modify ecosystem services provision in the riparian landscape such as hydrological services, habitat and biodiversity, and carbon storage.
Biodiversity and ecosystem services support many of the benefits that people obtain from nature and are often used as indicators of the effect that land-use practices have on natural ecosystems (Martínez et al. 2009, Felipe-Lucia et al. 2020). Biodiversity has been recognized as crucial for the maintenance of ecosystem functions and services (Balvanera et al. 2006, Knapp 2019). Habitat quality is considered a biodiversity proxy and it indicates suitability of ecosystems to provide functions such as erosion regulation, water quality, and pollination; all of which are important for agriculture (MEA 2005, Sharp et al. 2020).
Ecosystem services are all the benefits that human beings obtain from natural resources and processes provided by healthy ecosystems. These are categorized as provisioning, regulating, cultural, and supporting services (MEA 2005). Regulating ecosystem services are those benefits obtained from the regulation of ecosystem processes and are sensitive to land-use change and anthropogenic climate change (Sutfin et al. 2016, Fu et al. 2015, Balvanera et al. 2016, Baessler and Klotz 2019, Hasan et al. 2020). Carbon storage is an example of a regulating ecosystem service, and it represents carbon stored in vegetation as part of its overall biomass (Schulze et al. 2019). Because terrestrial vegetation is one of the main carbon pools in the global carbon cycle and its modification contributes to the fluctuation of atmospheric carbon concentration, vegetation cover removal driven by land-use change is one of the main drivers of climate change (Lambin and Geist 2006, Chapin et al. 2011, IPCC 2019). Agricultural activities developed in arid riparian ecosystems greatly alter carbon storage by removing native vegetation and engaging in tradeoff cycles given the storage capacity of crops.
Biodiversity and regulating ecosystem services in arid riparian ecosystems can be compromised by conventional agriculture, however, not all agricultural practices are detrimental of habitat quality and carbon storage. Previous studies have documented that some traditional agricultural practices based on agroecological production systems can assemble sustainable productive landscapes along with maintaining biodiversity and ecosystem services (Liere et al. 2017, Palomo-Campesino et al. 2018). Therefore, some traditional agricultural practices may contribute to the conservation of biodiversity and ecosystem services at a regional scale, while providing benefits to the local environment and the people. Living fencerows and acequia systems are examples of these practices, and their use is widespread in several regions in the American continent and are linked to important natural elements in agroecosystems such as natural vegetation and water availability (Fernald et al. 2007, Garbach et al. 2010).
Living fencerows made of native trees are used to protect agricultural fields and are often associated with the provision of suitable habitat for wildlife in Neotropical regions (Martinez et al. 2007, Garbach et al. 2010), but their environmental effects haven’t been registered in arid regions. The use of this practice is common in riparian regions of northwestern México, but it has been scarcely studied or updated apart from a few studies conducted during the 80s (Nabhan and Sheridan 1977, Doolittle 1980, Sheridan 1988). Acequia irrigation systems are collective water management systems based on canals that distribute surface water through agricultural parcels (Rivera and Martinez 2009). Numerous benefits to the environment and human populations as well as beneficial responses to climate change are attributed to acequias, such as the rise of groundwater levels that help support riparian areas, which in turn, provide wildlife habitat and a landscape for recreational activities (Fernald et al. 2007, Fleming et al. 2014, Rupert 2017). Although highly documented for other regions, such as the southwest U.S. (Rivera and Martinez 2009, Cox and Ross 2011, Fernald et al. 2012, 2015), northeast México (Martinez 2005), central and south México (Harvey et al. 2004, Martinez Camillo et al. 2007, Garbach et al. 2010); their study in northwestern Mexico is scarce (Hernández-Rodríguez and Moreno-Vázquez 2018).
Additionally, there is no current documented evidence of the continuity or loss of these practices in the region. Considering the current and predicted effects of climate change in arid lands (IPCC 2013, Gay et al. 2015) and the sensitivity of riparian ecosystems, the assessment of sustainability-oriented practices (such as living fencerows and acequia systems) and their relation to biodiversity and ecosystem services is a regional priority.
The present study constitutes a first exploratory approach to the assessment of biodiversity and ecosystem services in relation to traditional agricultural practices in a spatially restricted hotspot ecosystem. Our study region is classified as a “region of environmental emergency” by the Mexican National Council on Science and Technology (CONACYT 2021) due to the severe social-environmental effects of increasing droughts, intensive and extensive use of water and soil for agriculture, cattle, and mining (including the recent mine spill from Buenavista del Cobre in Cananea in 2014). This has greatly affected the livelihoods and well-being of local communities by threatening economic activities, which rely directly on the ecosystem services provided by the riparian corridor, particularly agriculture. Despite this, the region continues to be understudied in several environmental and social respects, including biodiversity, ecosystem services, and agricultural practices. Assessments like the one we present can serve as a first step toward generating technical grounds for conservation, restoration, remediation, and environmental justice.
In this study, we combined pre-existing spatial information and empirical field data to develop knowledge about change mechanisms in traditional agricultural practices and their contribution to biodiversity and one ecosystem service. The main questions that guide our work are: how does the provision of habitat quality and carbon storage vary in agricultural places with fencerows and acequias compared to places with native riparian vegetation? And what are the main reasons for the continuity or loss in the use of fencerows and acequias?
To answer these questions, we used a social-ecological systems approach. As defined by Berkes et al. (2002), a social-ecological system is an adaptive complex system formed primarily by two domains: one socioeconomic and institutional and another ecologic-biologic. Thus, we propose a framework to empirically link the ecological elements (biodiversity and ecosystem service) and social elements (traditional agricultural practices) that represent instances of these two domains within the system (Herrero-Jáuregui et al. 2018). By combining remote sensing spatial analysis methodologies, participatory mapping, and community field work, this study offers a useful framework that can be implemented in future assessments of other understudied environments because it generates new information of unexplored social-ecological processes relevant to stakeholders and researchers interested in agricultural development and conservation alternatives in priority arid regions’ ecosystems.
This study combines mapping tools, field work, ancillary data, and expert knowledge for the assessment of habitat quality and carbon storage, and semi-structured interviews and participatory mapping for the assessment of traditional agricultural practices. We derived several points of interest from field work and participatory mapping and captured them in a GIS to perform a spatial overlap between these and the habitat quality and carbon storage models to compare the provision of these on each point. Finally, we developed causal loop diagrams, based on categories derived from discourse analysis of interviews with key informants, to explore relations between changes in traditional agricultural practices, habitat quality, and carbon storage provision.
The study area (Fig. 1) includes the riparian corridor defined by a seven-kilometer buffer east and west from the Sonora River (Río Sonora). The total area of the corridor is 2139 km². It is located in the Río Sonora sub-watershed in the central part of the northwestern Mexican State of Sonora. Climate in the region is semi-arid and average temperature ranges from 17°C to 31°C; the precipitation pattern is bimodal (summer and winter rainfall), with highest precipitation events occurring during the summer North American Monsoon and ranging from 268 mm to 542 mm (CONAGUA 2020).
The most extended land uses and vegetation types within the study area are: perennial agriculture (4359 ha), which includes cash crops for international export such as pecan trees, and grapes, and others for local commerce such as citruses; secondly, annual agriculture (3563 ha), which includes mostly crops for local consumption and commerce such as fodder crops, wheat, peanut, garlic, corn, and sugar cane; cottonwoods (752 ha), which compose most of the obligate riparian vegetation; human settlements (198 ha) represented mainly by rural communities; desert scrub (56,611 ha) and subtropical scrub (98,099 ha), which represent the most extended vegetation types adjacent to the riparian area; mesquite woodlands (15,836 ha), which are widespread in riparian areas and around; introduced grassland (15,474 ha), which represents areas with exotic forages (mostly buffelgrass Cenchrus ciliaris); and bare ground (19,046 ha), which represents areas with no apparent cover.
A total of 10 interviews were conducted with key informants in 7 different rural communities distributed in 4 municipalities: Ures (approximate population 8548), Baviácora (approximate population 3191), Banámichi (approximate population 1825), and Arizpe (approximate population 2788). Each of these municipalities represents the four sections of the sub-watershed. The south section (Ures) is characterized by agricultural activities and cattle raising and is 80 km away from the capital city of Hermosillo (approximate population 1 million). The central (Baviácora) and north-central (Banámichi) sections are areas with extensive agriculture (mostly forages), and the northern section (Arizpe) maintains subsistence agriculture and hosts intensive mining activities (the second largest copper mine in the world, Buenavista del Cobre, is located 100 km north of this section).
Biodiversity and ecosystem service assessment
We used the models provided by InVEST (integrated valuation of ecosystem services and tradeoffs; Sharp et al. 2020) to map habitat quality and carbon storage. Both models require a land use and vegetation map as main input, which we obtained from classifications previously generated from high spatial resolution satellite data for 2018 (Cornejo-Denman et al. 2020) and re-scaled at 10 meters using the nearest neighbor analysis.
The habitat quality assessment consists of a spatially explicit model that locates areas in which ecosystems preserve optimal characteristics for the maintenance of a particular group of species. In this study, we evaluated habitat quality of the riparian corridor based on the integrity of obligate riparian vegetation (i.e., plants that require stable groundwater levels to survive and are not well adapted to drought conditions), considering the importance of these communities as biodiversity hotspots (Riis et al. 2020, Rood et al. 2020) and keepers of several nature values. Areas with obligate riparian vegetation are appreciated because they provide cool and shaded spots for rest and recreation (cultural values), they also represent a healthy river because people relate them with the presence of water (societal values), and they characterize the riparian landscape, which supports and maintains the arid surrounding environments (intrinsic values; Webb et al. 2006, Burgos et al. 2015, Datry et al. 2017; L. Cornejo-Denman 2019, personal observation).
To generate a spatial representation and assessment of habitat quality, the model requires data related to land use, distribution, and impact of major threats. The model estimates the effect of anthropogenic land uses (threats) on natural vegetation by weighting the distance between vegetation location and multiple threats. Impact distance, relative threat impact, and relative sensitivity were derived from expert knowledge by applying a survey to 8 professionals (researchers and managers with experience in the region) asking them to indicate the impact of each threat on each natural habitat in a range between 0 and 10, and an estimate of the greatest distance in kilometers at which each threat ceases to influence natural habitats. Table 1 describes inputs and sources of model requirements.
Using the previous information, the model calculates habitat quality for each cell in the map representing the landscape, where the quality of habitat in cell x that is in land use land cover (LULC) class j is given by Qxj:
where Dxj is the total threat level in cell x, Hj indicates the habitat suitability of LULC class j, and k and z are constants (Sharp et al. 2020).
Results derived from this equation indicate the level in which threats affect natural vegetation in the region in terms of their capacity to maintain biodiversity (i.e., integrity of obligate riparian vegetation). Values of the habitat quality index are considered low when they are closer to 0 and high when they are closer to 1.
Threats (described in Table 2) represent the main human activities developed in the region, these have different effects on ecosystems depending on their extension and intensity, and they frequently modify vegetation through its total or partial removal.
Threats were identified and selected through field work and complemented with a literature review (Cervantes et al. 2007, Sánchez Colón et al. 2009, Castellanos-Villegas et al. 2010, Franklin and Molina-Freaner 2010, Moreno et al. 2010, Ruelas Monjardí et al. 2010, Chapin et al. 2011, Solís-Garzo et al. 2011, Marshall et al. 2012, Pérez Espejo 2012, Zárate Valdez 2012, Méndez-Estrella et al. 2016, De la Fuente et al. 2017, González-Gallina and Hidalgo-Mihart 2018). Additionally, these threats represent some of the main concerns of communities regarding their effects on soil quality and access to water, as well as water quality, and the direct consequences of these on their main economic activity (agriculture) and their health. We collected this information throughout two years (2017-2019) of exploratory and community field work and non-participant observation in the area. After threat identification and mapping, we used expert knowledge to derive variables for the habitat quality model.
The carbon storage model is generated through an aggregate of four main carbon pools: aerial biomass, belowground biomass, soil, and dead organic matter (Sharp et al. 2020). This aggregate is presented as a thematic map in which each cover type has a specific carbon storage. We estimated aerial biomass for each class through the application of allometric equations to several vegetation measurements taken directly in the field and from official data through the National Forestry Inventory (https://snif.cnf.gob.mx/), and then converted to total carbon using the 0.47 conversion factor (IPCC 2019). Belowground biomass and soil carbon values were obtained from the literature (Table 3). We did not include dead organic matter in the model because regional data for this carbon pool is scarce.
Interviews and assessment of traditional agricultural practices
To establish a spatial link between habitat quality and carbon storage provision and the main drivers of change in traditional agricultural practices in the region, we developed a data-gathering mixed instrument and applied it to key informants. The instrument includes a questionnaire, a semi-structured interview, and a participatory mapping section. This instrument is an exploratory tool and constitutes a complement to the assessment of biodiversity and ecosystem services based on spatial analysis.
We selected informants based on previous exploratory field work and non-participant observation during two years (2017-2019) of traveling through the region in which contact with different stakeholders allowed the identification of key informants, their activities and concerns about environmental issues threatening their livelihoods, and their willingness to participate in community organization by training and sharing information with others. Thus, the sample used in this study is represented in part by community leaders and key informants with vast knowledge of the landscape and current social and environmental issues in the region. We next selected informants based on their occupation (mainly agriculture) and by using a snowball sampling method (Miller and Brewer 2003). Additionally, we selected other potential informants based on their knowledge about specific points of interest, such as native cottonwood stands.
Key informants from 7 communities along the study area responded to a total of 10 semi-structured interviews: 4 interviews in 2 communities of the southern section (Ures), 3 interviews in 3 communities of the central section (Baviácora), 1 interview to a married couple in the north-central section (Banámichi), and 2 interviews in 1 community of the northern section (Arizpe). Informants included 10 men and 1 woman, with ages ranging from 36 to 76, whose main current occupation was small-scale agriculture. Some informants had other sources of income derived from cattle raising, recreational and ecotourism services, workshops, and touring.
We transcribed and analyzed all interviews through a standard categorization procedure for discourse analysis (Russell 2006, Denzin and Lincoln 2007) using a text processing software to extract information regarding perceived changes in the riparian landscape, changes in the use of living fencerows and acequias, and reasons for these changes. First, we asked interviewees if they were familiar with these practices and if these were common in their region; secondly, we asked if they directly engaged in the use of these practices and why. Based on this, we derived three explanatory categories that, according to interviewees, relate to changes in the use of acequia systems and living fencerows:
- Environmental category: observations related to vegetation changes and water quality and quantity.
- Socioeconomic category: observations related to technification of agricultural activities involving the use of other techniques and materials for the same purposes as traditional practices. These alternatives require a variable economic investment by either producers or the local government.
- Functional category: observations related to efficiency, either loss of it or additional benefits. It also includes observations related to management efficiency by users.
We used these categories to build two causal loop diagrams (Sterman 2000), one for each traditional agricultural practice. Each diagram includes the assessed practice, habitat quality and carbon storage, variables of change identified through discourse analysis (explained within each category), and some theoretical relations between elements.
We registered points of interest (Fig. 2) including traditional agricultural practices by previous exploratory and community field work in the area as well as through a participatory mapping approach (King 2002, Sletto et al. 2013). These points are indicators of change in the riparian landscape and ecosystem services provision. We used four maps (one for each municipality) in each corresponding interview and asked the interviewee to locate these points: large cottonwood stands, isolated cottonwoods, acequias, and living fencerows.
A) Large cottonwood stands: areas where obligate riparian vegetation has recovered either by voluntary conservation from managers or due to the abandonment of agricultural fields.
B) Isolated cottonwoods: remnants of obligate riparian vegetation represented by lines of large cottonwood trees bordering agricultural fields.
C) Acequias: a fragment of one canal from a particular irrigation system.
D) Living fencerows: arrangements of planted and braided rows of native tree species (cottonwoods or willows) located between the river and agricultural fields.
We verified these four points of interest in the field and through satellite imagery analysis, digitized each into a GIS software, and used them to extract values from the habitat quality and carbon storage models.
Biodiversity and ecosystem service assessment and overlap of points of interest
Figure 3 shows both habitat quality and carbon storage models for the riparian corridor, along with points of interest represented as circles in different colors. The habitat quality model is assessed by an index from 0 to 1 in a colored thematic map, where places in blue indicate regions with values closer to 1 where habitat quality is high, and places in red indicate regions with values closer to 0 where habitat quality is low. The carbon storage model is represented by the resulting range of 0 to 73 tons of carbon per hectare in a colored thematic map, where places in blue indicate regions with values closer to 73 where carbon storage is high, and places in red indicate regions with lower carbon storage capacity. Table 4 presents the average habitat quality and carbon storage values for each point of interest in each section.
South section (Ures): isolated cottonwoods in this section of the riparian corridor are in the middle of the agricultural area and represent a remnant of obligate riparian vegetation. They hold the lowest habitat quality value for isolated cottonwoods in all sections (0.10), showing the degrading effect of agricultural activity on this service. The carbon storage value (59 tonC/ha) is also the lowest for isolated cottonwoods in all sections but is higher than the other points of interest in this section (probably due to the carbon storage provision of crops). Large cottonwood stands in this section represent areas with recreational activities, where riparian vegetation has been voluntarily preserved; these are located further from the agricultural areas and have high habitat quality values (0.78 and 0.84). Carbon storage in these points register the lowest values (46 and 54 tonC/ha) for large cottonwood stands in all sections.
Central section (Baviácora): acequias in this section show habitat quality values of 0.14, 0.42, 0.46, and 0.29. Large cottonwood stands hold different habitat quality values due to their location with respect to the agricultural area, i.e., the one located in the middle of the agricultural area holds the lowest habitat quality value (0.34), and the one located to the south, where the agricultural area narrows, holds the highest habitat quality value (0.74). Regarding carbon storage, the two cottonwood stands register similar values (57 and 56 tonC/ha).
North-central section (Banámichi): the only point of interest located in this section represents one acequia, which holds the lowest habitat quality value (0.08) for acequias in all sections. In this section, the agricultural valley is broader than in other sections of the corridor and the landscape stands out due to the total absence of obligate riparian vegetation. On the other hand, carbon storage value for this point (51 tonC/ha) is higher than the average carbon storage value for acequias in all sections due to the storage capacity of crops.
North section (Arizpe): isolated cottonwoods in this section are located along a dirt road, they register the highest habitat quality value (0.56) for isolated cottonwoods in other sections, and a high carbon storage value (63 tonC/ha). This is the only section in which interviewees reported the presence of living fencerows, and we were able to map two of them along the dirt road bordering the river. Both fencerows register habitat quality values (0.64 and 0.66) higher than the average for other points of obligate riparian vegetation in different configurations in all sections. Carbon storage values for living fencerows are 48 and 71 tonC/ha.
Categories of change in the use of acequias and living fencerows and causal-loop diagrams
The arguments that explain change in the use of acequias and living fencerows are stated in the interpretation of each causal-loop diagram presented. According to interviewees, main perceived reasons for change in the case of living fencerows are related to availability of resources, such as obligate riparian vegetation and to the loss of functionality. In the case of acequias, change relates to lack of surface water as well as management and maintenance difficulties.
Two diagrams are presented (Figs. 4 and 5), one per practice. Each diagram shows the traditional agricultural practices at the center inside a white elliptical shape, habitat quality and carbon storage at the top right corner inside white rectangle shapes, and variables of change (based on discourse analysis of interviews and literature review) are represented by rectangle shapes of different colors depending on the category they belong to (green for the environmental category, red for the socioeconomic category, and blue for the functional category). All elements in the diagrams are linked by arrows representing positive, negative, or feedback relations; continuous lines represent empirically observed relationships (based on discourse analysis of interviews, field work observations, and biodiversity and ecosystem service assessment), and the dashed lines are theoretical relationships (based on literature).
Living fencerows causal-loop diagram
Living fencerows are not very common in the region anymore. We only located them in the northern section of the sub-watershed.
Among the environmental factors that restrict the use of fencerows is the absence of obligate riparian vegetation composed of cottonwoods and willows because the vegetation provides the main material for building these fencerows, and informants clearly identified a decrease in this vegetation type in the region. As stated by three interviewees from the south (Ures) and central (Baviácora) sections:
These fences were made by cutting big branches of willows that were buried in the ground and then they were braided together, you needed big trees to cut these branches. There used to be a lot of willow in the river, now we don’t see any.
This is represented in the diagram by a negative relationship between “living fencerows” and “obligate riparian vegetation absence.” Inversely, the presence of this vegetation type is identified as a factor that promotes the use of fencerows, as stated by two interviewees in the north section (Arizpe):
There are many willow fencerows around here, you’ll see that they have different sizes, that means some are old and some are new, but my fields are not next to the river, so I don’t use them.
This is represented in the diagram by a feedback relationship between “living fencerows” and “obligate riparian vegetation presence.”
Among the socioeconomic factors that restrict the use of fencerows are those related to technification alternatives. These alternatives include the use of machinery to deviate the course of the river and the construction of wire and rock gabions, or fences made of wood poles and wire to protect the fields. This was stated by four interviewees in the south (Ures) and central sections (Baviácora):
These fences are known as ‘estacadas,’ they are not common here in Ures anymore, I remember them from when I was kid. Now the government offers help with machinery to deviate the river and protect crops.
This is represented in the diagram by a negative relationship between the variables “technification” and “living fencerows.” Additionally, there are negative theoretical relationships linking “technification” to “habitat quality” and “carbon storage.” The replacement of living fencerows by other inert materials could decrease the contribution of services previously provided by this practice because living trees in fencerows provide shelter for birds and other wildlife, thus promoting biodiversity and contributing to carbon storage due to their amount of aboveground biomass (Schulte et al. 2008, Snow and Snow 2017, Morantes-Toloza and Renjifo 2018).
Among the functional factors that restrict the use of fencerows are those related to their functionality. It was frequently mentioned by informants that living fencerows are not solid enough to prevent the effects of flash floods caused by the erratic and intense precipitation events that characterize the North America Monsoon. This was stated by five interviewees across all sections:
The ‘estacadas’ are not useful if the river flow is big, these are more useful with small river flows, but if the rain is hard the flooding will wash away the fencerows. That’s why other structures work better.
This is represented in the diagram by a negative relationship between the variable “limited function” and “living fencerows.” On the other hand, there was also mention that, where present, living fencerows provide useful material such as wood; maintenance of fences requires pruning trees, thus it’s common that cut-up branches are used as wood in domestic labor. This was stated by one interviewee in the north section (Arizpe). This is represented in the diagram by a positive relationship between the variables “additional benefits” and “living fencerows.”
Based on our biodiversity and ecosystem service assessment, fencerows present average values for both elements. In the diagram, this is represented by two positive relationships linking “living fencerows” to “habitat quality” and “carbon storage.” Also, there are two positive relationships linking the variables “obligate riparian vegetation presence” to “habitat quality” and “carbon storage” because most points of interest containing cottonwoods had high average values for both. Finally, there are two negative relationships linking the variables “obligate riparian vegetation absence” to “habitat quality” and “carbon storage.”
Acequias causal-loop diagram
Acequia systems are common in the region, and we located them in all the communities visited. Many of these acequias are cement lined, but there are still dirt ones. At least two of the interviewees mentioned the longevity of these systems, dating them back to pre-Hispanic times.
Among the environmental factors that restrict the use of acequias is surface water decrease; these flows feed the acequia canals that came directly from the river. This was stated by two interviewees from the south section (Ures):
Years ago the river flowed all year long and field watering was done directly by channeling water from the river to the fields, those were our acequias, we don’t have them anymore.
Thus, in the diagram, the variable “surface water decrease” has a negative relationship with “acequias” and a positive relationship to “technification by wells and piped water.” Additionally, there are two positive theoretical relationships between the variables “technification by wells and piped water” and “groundwater decrease” and “obligate riparian vegetation absence.” Water extraction decreases groundwater levels and obligate riparian vegetation depends on a specific range of groundwater levels, thus, changes in these will promote the absence of obligate riparian vegetation (Poff et al. 2011, Patten et al. 2018).
Among the socioeconomic factors that restrict the use of acequias is the need for other water sources that respond to technification processes driven by two main factors: surface water decrease and a low willingness of users to maintain the acequia canals; in some cases, this has led users to build private wells. As stated by one interviewee in the south section (Ures):
It is very hard to agree among users for access to community water intakes, specially due to the maintenance these require, this is why I made my own well in my fields.
In the diagram this is represented by a negative relationship between “acequias” and the variable “ineffective acequia governance,” and this same variable holds a positive relationship with “technification by wells and piped water.” On the other hand, examples of successful management of acequias are also present in sections where users agree to participate in collective maintenance labor, have knowledge about the governing structure of the system, and high communication skills to change previously settled schedules for water use. This was stated by one interviewee in the central section (Baviácora):
And by one interviewee in the north-central (Banámichi) section, who mentioned that:
Our acequia comes from a spring near the river, we are many users and even when there is a formal schedule, we can have access to more water if our crops need it (if we are growing beans, for example), this requires a lot of observation and communication.
In the diagram, this is represented by a positive relationship between “acequias” and the variable “effective acequia governance.”
Based on our assessment, most acequias present a higher-than-average value for carbon storage (possibly due to their proximity to agricultural areas and the storage capacity of crops), and all acequias register a lower-than-average value for habitat quality. In the diagram, this is represented by a positive relationship between “acequias” and “carbon storage”, and a negative relationship between “acequias” and “habitat quality.” Also, there are two negative relationships linking the variable “obligate riparian vegetation absence” to “habitat quality” and “carbon storage” because most points of interest containing cottonwoods register high average values for carbon storage and habitat quality, thus their absence contributes negatively to their provision.
Biodiversity and ecosystem service assessment at the points of interest
Our results show considerable differences in the spatial distribution and provision of habitat quality and carbon storage. Habitat quality responds inversely to the presence of agricultural areas and thus, areas with the lowest values are located along the riparian corridor where agricultural activities are concentrated. Carbon storage provision is higher in general in the north section (Arizpe) and for the cottonwood living fencerow. This heterogeneity in the provision of habitat quality and carbon storage along the riparian corridor is explained by the unique characteristics of each section and by the presence of obligate riparian vegetation in its different configurations. Thus, the north section (Arizpe), which presents less intensive agricultural activities than the other sections and is the only section with obligate riparian vegetation in all its configurations, holds the highest average values for habitat quality and carbon storage. Previous ecosystem services assessments in watersheds also register a spatial heterogeneity in the provision of multiple ecosystem services (Duarte et al. 2016, Qiu and Turner 2013).
Highest habitat quality average values for our points of interest correspond to large cottonwood stands located in private lands in the south and central sections (Ures and Baviácora) of the sub-watershed. The first is La Chimenea (habitat quality 0.84), a horse-raising ranch with low impact recreational activity (not open to the general public) and where direct management actions (specifically, cattle removal) in the past 30 years have promoted the regeneration of native vegetation. This place is eight kilometers away from agricultural areas. The second is La Carrizosa (habitat quality 0.78), a small ranch with 10 years of recreational activity and open to the general public. This ranch has no direct management actions, but owners value riparian trees for their shade; it is located two kilometers away from agricultural areas. The third is El Herrero (habitat quality 0.74), composed of several agricultural parcels that were damaged by river floods and left without work for 30 years, leading to the regeneration of obligate riparian vegetation; this point has no direct management actions and is located within a small-scale agricultural area in a narrow section of the river valley. Although there are evident structural and compositional differences between these sites, results show the importance of voluntary conservation schemes in the restoration of native vegetation and highlight the resilience of riparian ecosystems.
Carbon storage shows high average values for agricultural areas; this was expected given the storage capacity of some crops (IPCC 2019). Highest carbon storage average values for points of interest correspond to two traditional agricultural practices and one cottonwood stand. The first one is the cottonwood living fencerow (carbon storage 71) located in the north section (Arizpe) in a narrow area of the riparian corridor bordering a small agricultural parcel. The second one is the acequia (carbon storage 69) located in the central section (Baviácora) where the river valley expands and allows agricultural development. The third one is the large cottonwood stand (carbon storage 65) located in the north section (Arizpe), close to a small town surrounded by small-scale agriculture, and where the river valley is restricted by the steep landscape.
Obligate riparian vegetation in our study area registered the highest carbon storage average value (73 tonC/ha) of all cover types. Previous studies based on data from literature and site-specific data for aboveground biomass estimations in similar regions (Chan 2013, Mendez-Estrella et al. 2017) have also registered a higher carbon storage capacity for riparian vegetation compared to adjacent cover classes. The high carbon storage value (71 tonC/ha) presented by the cottonwood fencerows highlights the importance of the permanence of this practice for the sustenance of biodiversity and regulating ecosystem services.
Our study differs from other assessments due to the finer spatial resolution of our data. This resolution allowed us to have a better understanding of the dynamics of riparian ecosystems (e.g., specific values for living fencerows and acequias), which in arid regions have a very restricted distribution and are easily overlooked in coarser resolution assessments.
Traditional agricultural practices and the riparian landscape
Obligate riparian vegetation in the region has undergone progressive and historic degradation due to land use and water availability changes related to climate change and aquifer overexploitation (Van Devender et al. 2010, CONAGUA 2018). As seen in this study, obligate riparian vegetation’s presence in its different configurations (large stands, isolated individuals, living fencerows) is a priority for the provision of both services. Even when closeness to agricultural areas degrades obligate riparian vegetation, its presence around parcels might provide some benefits (infiltration, shade, habitat for beneficial species such as pollinators, etc.; Williams 2011, García-Martínez et al. 2015), which should be assessed under a “sustainable agricultural landscape” scope.
One observation that was frequently mentioned by interviewees in the south section (Ures) is the perception of degradation in the riparian landscape represented by the loss of greenness in vegetation, loss of edible plant species, and the disappearance of obligate riparian vegetation stands, which interviewees link to low water availability. In the whole region there is a general awareness of water quality and quantity loss, which people associate with long term drought events and mining activities. The 2014 mine spill from the Cananea copper mine is still fresh in people’s memory and discourse, and its environmental, socioeconomic and health consequences persist (Ibarra Barreras and Moreno 2017, Luque Agraz et al. 2019).
Although most of the interviewees do not consider obligate riparian vegetation’s presence as beneficial at a landscape scale, some of them express concern for how current agricultural and cattle-raising practices are damaging riparian vegetation, water quality, and crops. They also suggest the need to engage in healthier production systems, like diminishing the use of chemical fertilizers and pesticides and restricting cattle presence in riparian areas.
Living fencerows are associated with the presence of obligate riparian vegetation. In many areas where large natural stands of riparian vegetation are no longer present, fencerows are the only remnant of this vegetation type (L. Cornejo-Denman 2019, personal observation). However, living fencerows are scarce. Discourse analysis and field observations indicate a generalized loss in the use of fencerows, being present only in one of the four sections visited. Most interviewees barely remembered the use of this practice and didn’t recognize it as current. Living fencerows are a common practice in many agricultural landscapes throughout México; their main purpose is to serve as division and protection of productive areas. Besides their original purpose, several additional benefits are attributed to living fencerows. Economic benefits include low investments due to their low maintenance compared to conventional fences made with poles and wire that need to be replaced regularly (Cruz Léon et al. 2012). Fencerows are also a source of wood, food, and forage (Reyes Jiménez and Martinez Alvarado 2011). Ecological benefits may include habitat for rodents and birds (Nabhan and Sheridan 1977), carbon storage, soil improvement by mycorrhizal recruitment (which also prevents the overuse of chemical fertilizers), biodiversity conservation, landscape connectivity, and scenic beauty (Nabhan 2018, Reyes Jiménez and Martinez Alvarado 2011).
Replacement of traditional agricultural practices by alternatives based on technification implies the loss of habitat quality and carbon storage. It also could degrade local traditional knowledge (LTK), collective activities, and social cohesion (Brown and Kothari 2011, Parraguez-Vergara et al. 2018). Nabhan (2018) highlights the importance of living fencerows as a collective activity among farmers in the Río Sonora region, which is maintained by a diverse group of people who benefit from it, generating a beneficial cycle for the ecosystem and the people by improving crop productivity and maintaining local diversity. In their 1977 text about living fencerows, Nabhan and Sheridan discussed how this technique is a “great achievement” for rural farmers because it proves that agricultural productivity can be sustained without the need of “chemicals, concrete and fossil fuels,” especially in areas where technification and the use of machinery was uncommon in those years. Our results show living fencerows are being replaced by other techniques to reduce or divert river flows such as mechanical interventions, rock and wire gabions, or fences made with mesquite poles and wire.
The success of living fencerows was questioned by Doolittle (2003, 2006), stating that these cause geomorphic changes to the river channel, which can be detrimental to fields located downstream. He also described other forms of channel bank treatment, pointing to several geomorphic consequences that strongly transformed these sensitive landscapes. Other authors mention the limitations of fencerows when big floods occur (Bahre 1998). This limitation was mentioned by several interviewees in all sections of the riparian corridor as a reason for the change in this practice; some users mentioned that fencerows are useful in areas where agricultural parcels are not adjacent to the main river but instead near streams that feed the main river, to avoid the destructive force of floods.
Regarding the use of acequias, we found that these systems are still present throughout the Río Sonora region, even when most agricultural water currently comes from wells and piped infrastructure. Although acequias are a great example of collective water resource management, in our study, we found users who recognized the difficulties in their management and chose to build private wells; however, this option is not for everyone due to its high financial cost. Acequia systems are composed of dirt canals that must be frequently cleaned, weeded, and re-built. To improve their maintenance, currently many canals have been lined with cement, which also needs to be cleaned and coated. Other complications related to acequia management point out the importance of thoroughly knowing the governance structure of these systems because working around established rules is frequently needed because these do not always satisfy specific user needs.
Acequia systems in México are widely studied from a socio-historical perspective, however, the ecological contributions of acequias are poorly registered. Several elements of acequia management are shared in many parts of México, such as their importance in maintaining a water-based culture and community traditions (Martínez 2005), as well as some infrastructure characteristics, such as the location of the canal in densely vegetated areas to avoid evaporation, mostly in the northern arid regions (Martínez Saldaña 2009). On this point, many ecological contributions might be overseen given that vegetation associated with these systems can promote biodiversity, carbon storage, maintenance of riparian habitat, and provide edible plants for humans, such as quelites (i.e., edible greens) and others. These and other ecological contributions have been identified and associated with acequia systems in regions of the southwest U.S. (Fernald et al. 2007, 2012, 2015, Raheem et al. 2015), but are scarcely registered for México.
Although obligate riparian vegetation shows positive relations in the provision of the two mapped services, its presence alone doesn’t constitute an alternative to the use of fencerows or acequias because it doesn’t replace the function of either. In this respect, the expansion of voluntary conservation areas, such as recreational sites and private ranches that promote obligate riparian vegetation recovery could create a heterogeneous landscape in which agricultural areas were surrounded by large riparian vegetation stands while fencerows and acequias were used as corridors, connecting patches of native vegetation and providing their original agricultural function. Riparian vegetation around agricultural areas could maintain the functions and services of the riparian habitat, such as flood mitigation, which in turn might reverse some functional deficiencies attributed to fencerows promoting their widespread use.
We successfully achieved habitat quality and carbon storage mapping by using diverse sources of information including high spatial resolution data, targeting a spatially restricted and hotspot ecosystem. Spatial analysis was complemented and enriched by discourse analysis and participatory mapping, which helped us explain how and why living fencerows are being replaced in the region and how acequia systems are being modified.
Highest habitat quality and carbon storage provision is associated with the presence of obligate riparian vegetation in its different configurations. Lowest habitat quality is present in areas with intense agricultural activity and total absence of obligate riparian vegetation. The presence of obligate riparian vegetation in the form of fencerows or isolated individuals within agricultural areas increases habitat quality. In this study, the presence of fencerows was associated with high values of habitat quality and carbon storage. Although the presence of obligate riparian vegetation is necessary for the maintenance of the living fencerows practice, it is not a sufficient or determinant factor. The limited functionality of fencerows and the access to technification strategies that serve the original purpose of these are the most common causes of change in this practice.
According to our results, the two most common causes of change in the use of acequias identified by key informants are related to surface water decreases and collective management complications. However, the practice remains active throughout the region. In terms of their contribution to biodiversity and ecosystem services, acequia systems indirectly benefit carbon storage due to their proximity to agricultural areas but most of them register low habitat quality values.
Changes in traditional agricultural practices represent the adaptation of human populations facing environmental challenges and engaging in ecosystem services trade-off cycles. Future assessments should include cultural ecosystem services valuation and a plural conception and recognition of the several values of nature for a thorough diagnosis of how global change affects human and natural populations at a local scale. Even if traditional agricultural practices are replaced by alternatives that don’t contribute to the provision of some ecosystem services, conservation and restoration of obligate riparian vegetation around and in-between agricultural fields could still help maintain services that are important for agriculture; however, the social consequences of the loss of practices that promote collective values and community cohesion need to be considered.
Our study shows that combining spatial information and empirical field data is useful to develop new insights about change mechanisms in a semi-arid, riparian social-ecological system. The assessment is based on a clear and sound methodology that can be used by other researchers and decision makers interested in agricultural development using a sustainability approach. To overcome limitations, further research could increase the number of informants and locations for agroecological practices and expand the studied sector beyond the agricultural domain.
This study contributes relevant environmental data for an understudied region in a priority ecosystem; it also provides useful information for stakeholders (farmers and policymakers) regarding how biodiversity and ecosystem services can be enhanced by combining different agricultural and conservation practices. This information is valuable to decision makers in governmental agencies because decisions related to investments in natural habitats and ecosystems often face challenges conciliating conservation with agricultural development due to scarce knowledge regarding the social-ecological mechanisms in the region. Conservation, restoration, or remediation actions are difficult to plan and deliver without an information base regarding the condition of the ecosystems. In a region where resource extraction is privileged over conservation measures, and with a high inequity in the social access to resources, the social-ecological information of the riparian landscape presented in this study provides basis for further research, technical grounds for specific conservation actions, and alternative management proposals, and even arguments for local communities to defend their landscapes, territories, and resources.
RESPONSES TO THIS ARTICLE
Responses to this article are invited. If accepted for publication, your response will be hyperlinked to the article. To submit a response, follow this link. To read responses already accepted, follow this link.
LCD was the primary author, and all the other authors contributed to the writing and conceptualization of this paper. JRRL helped to set and discuss the research ideas and contributed/discussed all steps of the analysis and the development of the manuscript. ALL made important contributions during the development of the research project and commented and revised the manuscript.
The authors thank the National Council for Science and Technology of Mexico (CONACYT) for the support provided to LCD, through a postgraduate scholarship. JRRL thanks the support from the program "Apoyo a la incorporacion de nuevos PTC" (funded by SEP-PRODEP) and a grants from CONACYT (CB61865 and CB223525). LCD thanks the Posgrado en Biociencias at Universidad de Sonora, for the constant support of this work. Also, LCD thanks the Next Generation of Sonoran Desert Researchers for their support through a Student and Early Career Researchers scholarship.
Data/code sharing is not applicable. Parameters for models and qualitative data are reported within the manuscript.
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Table 1. Input requirements and source for the habitat quality model.
|Land use land cover map||Previously generated product (Cornejo-Denman et al. 2020), rescaled at 10 meters using the nearest neighbor analysis.|
|Threat impact distance||Variables were obtained through the elicitation method (Kuhnert et al. 2010) by surveys from eight professionals (researchers and managers) with previous experience in the region.|
|Relative threat impact weights||Variables were obtained through the elicitation method (Kuhnert et al. 2010) by applying surveys to eight professionals (researchers and managers) with previous experience in the region.|
|Relative sensitivity of habitats to threats||Variables were obtained through the elicitation method (Kuhnert et al. 2010) by applying surveys to eight professionals (researchers and managers) with previous experience in the region.|
|Form of threat decay function||Set by the researchers based on linear or exponential effects of each threat.|
|Threat maps||Elaborated by the researchers based on threat identification. Threats were selected based on a literature review and field observations.|
|Habitat suitability||Provided by the researchers based on study objective (all-natural vegetation is considered habitat).|
|Half saturation constant||Modified after running the model once under 0.5 value and recalculated it as half of the highest degradation value (Sharp et al. 2020).|
Table 2. Description of threats identified along the riparian corridor.
|Perennial agriculture||Perennial crops (pecan trees, citrus, grapes).||One of the main drivers of land-use changes globally, nationally, and locally. It also affects water quality and quantity (Sánchez Colón et al. 2009, Chapin et al. 2011, Pérez Espejo 2012, Méndez-Estrella et al. 2016).|
|Annual agriculture||Annual agriculture (forage, wheat, peanut, garlic, corn, sugar cane).||One of the main drivers of land-use changes globally, nationally, and locally. It also affects water quality and quantity (Sánchez Colón et al. 2009, Chapin et al. 2011, Pérez Espejo 2012, Méndez-Estrella et al. 2016).|
|Human settlements||Urban or rural settlements.||Urban expansion directly affects the landscape and modifies water availability through transfers, which enhances conflict among users (Díaz-Caravantes and Sánchez-Flores 2011, Díaz-Caravantes and Wilder 2014).|
|Highways and roads||Paved highways and dirt roads.||Paved and dirt roads promote habitat fragmentation, interrupt wildlife crossing, and reduce populations due to vehicle collision (González-Gallina and Hidalgo-Mihart 2018).|
|Pig farms||Pig farms.||Waste discharge cause air and water pollution with consequences to the environment and human health (Cervantes et al. 2007).|
|Mines (extraction)||Mines at active extraction stage.||Mining affects water quality and quantity, changes soil characteristics, and causes extreme landscape changes; consequences to local communities include decrease in crop productivity, water availability for agriculture and domestic use, and human health (Gómez-Álvarez et al. 2011, UNAM 2016, De la Fuente et al. 2017, León-Garcia et al. 2018, Luque Agraz et al. 2019).|
|Mines (exploration)||Mines at initial or advanced exploration stage.||Mining affects water quality and quantity, changes soil characteristics, and causes extreme landscape changes; consequences to local communities include decrease in crop productivity, water availability for agriculture and domestic use, and human health (Gómez-Álvarez et al. 2011, UNAM 2016, De la Fuente et al. 2017, León-Garcia et al. 2018, Luque Agraz et al. 2019).|
|Introduced grassland||Rangelands composed by exotic forages such as buffelgrass (Cenchrus ciliaris) or Johnson grass (Sorghum halepense).||Exotic rangelands decrease native diversity of plant communities, promote fire regimes and erosion, and associated overgrazing limits water infiltration (Franklin and Molina-Freaner 2010, Marshall et al. 2012, Zárate Valdez 2012).|
|Wells||Authorized wells (by the national water institution, CONAGUA).||Wells are the greatest source of water extraction. In an overexploited aquifer, high well density affects ecological water uses (Moreno et al. 2010, Ruelas Monjardí et al. 2010).|
Table 3. Values and source of main carbon pools used in the carbon storage model.
|Land use and vegetation||Aerial biomass carbon (ton/ha)||Source for aerial biomass carbon||Belowground biomass carbon (ton/ha)||Source for belowground biomass carbon||Soil carbon (ton/ha)||Source for soil carbon|
|Perennial agriculture||6.1||Méndez-Estrella et al. 2017||1.95||Méndez-Estrella et al. 2017||40.8||Méndez-Estrella et al. 2017|
|Annual agriculture||2.22||Méndez-Estrella et al. 2017||0.13||Méndez-Estrella et al. 2017||40.8||Méndez-Estrella et al. 2017|
|Cottonwoods||39.8||Field data (n 5)||10.72||Méndez-Estrella et al. 2017||22.95||Paz Pellat et al. 2016|
|Desert scrub||1.55||National Forest Inventory (n 16)||2.54||Méndez-Estrella et al. 2017||37||Paz Pellat et al. 2016|
|Subtropical scrub||2.84||National Forest Inventory (n 48)||1.64||Méndez-Estrella et al. 2017||24||Paz Pellat et al. 2016|
|Mesquite woodlands||5.78||National Forest Inventory (n 31)||3.7||Méndez-Estrella et al. 2017||33.26||Paz Pellat et al. 2016|
|Introduced grassland||0.74||Franklin et al. 2006||0.61||Méndez-Estrella et al. 2017||18.56||Paz Pellat et al. 2016|
|Bare ground||0||0||37.68||Paz Pellat et al. 2016|
Table 4. Average habitat quality and carbon storage values for each point of interest in the four sections of the riparian corridor.
|Watershed section||Points of interest||Habitat quality index average||Carbon storage average (tonC/ha)|
|South (Ures)||Isolated cottonwoods||0.10||59|
|Large cottonwood stands La Chimenea||0.84||54|
|Large cottonwood stands La Carrisoza||0.78||46|
|Central (Baviacora)||Acequia Sacomachi||0.14||46|
|Acequia El Alto||0.42||44|
|Large cottonwood stand Suaqui||0.34||57|
|Large cottonwood stands El Herrero||0.74||56|
|North-central (Banamichi)||Acequia Los Paredones||0.08||51|
|North (Arizpe)||Isolated cottonwoods||0.56||63|
|Willow living fencerow||0.64||48|
|Cottonwood living fencerow||0.66||71|
|Large cottonwood stand Bamori||0.69||54|
|Large cottonwood stand Bamori 2||0.72||65|