This past semester as a graduate student was challenging, but I learned so much from the professor and class, besides the readings and lectures. I wanted to bring some of what I had learned while living in Saudi Arabia to the class, as well as learn about what other areas of the world are doing to improve poor soils for cultivation, in arid and semi-arid high desert areas. What I had thought would be a somewhat straightforward paper, became more involved as many attributes including temperature, sand and dust storms (SDS), water scarcity and human health, are a part of the environment in these regions. I focused on the Southwest United States, as it was a Temperate Agroforestry class, and in the US the southwest has desert regions. There are many similarities to other deserts of the world, but also some unique attributes that are only found on the North American continent, such as native cactus plants and Indigenous peoples.
I hope this Review Paper will help disseminate knowledge that we all can use to help grow food more productively, while taking account of climate change issues, to promote ground cover systems like agroforestry and cover crops that help mitigate high surface temperatures, sand and dust storm damage to crops and human health, and promote water capture and retention in the soils of arid and semi-arid landscapes. Enjoy exploring what can be possible, to improve these parts of the world with agroforestry practices. It is a long paper, so brew a pot of coffee or tea!
What is a review paper? A review paper is taking scientific research papers, articles, videos, etc. that are published by other authors, and drawing on their knowledge and research to write about a topic. This paper has many useful reference articles, that you may want to read yourself. They contain figures and tables that are really helpful in illustrating points made here. There are 3 original photos that are referenced to me (author) in this paper, and if you want to use for yourself, just send me an email on the contact area of this blogsite.
At the very end of this post is a link to a new YouTube video, which I think does a great job showcasing worldwide efforts to plant desert landscapes, producing positive results.
Windbreaks and Related Agroforestry Practices in Arid and Semi-Arid Environments: Southwest USA
December 15, 2021
Table of Contents
3. Agroforestry Practices
3.1 Windbreaks and Shelterbelts
3.2 Alley Cropping
3.4 Windbreak and Shelterbelt Function
4. Arid and Semi-Arid Environments
4.1 Geographic Locations in the United States
4.2 Geographic Locations Worldwide
5. Issues in Arid and Semi-Arid Environments
5.1 Sand and Dust Storms (SDS)
5.2 Global Transport – SDS
5.3 Human Health
5.4 Wind and Vegetation Damage
5.5 Heat Level and Climate Change
5.6 Scarce Water Resources
6. History of the Dust Bowl, United States
6.1 Changes in Land Management
7. Southwest US High Desert Ecology
7.2 Sand Dunes
7.4 Dust and Wind Health Impact, US
7.5 Heat Level and Climate Change, US
8. Agroforestry Practices and Benefits
8.1 Windbreaks and Shelterbelts
8.3 Non-Living Windbreaks, Current and Future Trends
9. Southwest Desert Agriculture
9.1 Alley Cropping
9.2 Current Research of Native Plants
9.3 Indigenous Farming Practices
9.4 Date Palm in Agroforestry
10. Positive Dust Outcomes
10.1 SDS Decreasing in Future
11. Foreign Countries
12.1 Policy and Funding
12.2 Environmental and Societal
13. Conclusion 14. References
Windbreaks and Related Agroforestry Practices in Arid and Semi-Arid Environments: Southwest USA
“Bloom where you are planted”. This is usually something we say to someone going through a tough time in their life, or said in a way that is meant to empower the person to rise above the circumstances they find themselves in, and take advantage of their surroundings. While this analogy is drawn on nature, nature doesn’t work like it suggests. I would augment this common phrase and add, “Bloom where you are planted, when the conditions are right.” This is a much better reflection of how nature works. A seed or plant may have to wait years until the conditions are right for it to sprout, grow and bloom. One sustainable practice that combines agriculture and forestry is agroforestry. It endeavors to take all conditions of the landscape into account for actively engaging plants with the right environment. What do we do when the environment itself is challenging traditional knowledge of food production and changing to a warmer climate?
On the North American continent, the southwestern area of the United States is the most arid area in which life is challenging for plants, animals and people. High temperatures, dry conditions, and water scarcity characterize the desert landscape. The diverse ecological areas within this landscape can be agriculturally productive, while also benefitting wildlife, helping address climate change, support clean water, better air quality, and build the soil which sustains life. Agroforestry practices offer all of these benefits, as well as multifunctional landscape plans, customized for the farmer, and specific to the land. The United States and Canada fall under the region, North American Temperate Agroforestry (NATA) category (Gold and Garrett, 2022).
The priorities of adapting agroforestry practices throughout North America, are to diversify income of agricultural landscapes, environmental protection, wildlife habitat restoration, renewable energy production, aesthetics, and address challenges of climate change (Gold and Garrett, 2022). A good definition from Qureshi and Shoaib (2017); agroforestry is a deliberate integration of agricultural, and pastoral production, with woody components in the same spatial area, so that the interactions of ecology and economics occur simultaneously. Agroforestry as an intensive land-use management system, needs to cover four criteria that differentiate it from other practices; these being intentional, intensive, integrated and interactive (Gold and Garrett, 2022).
The objective of this review paper is to discuss the importance agroforestry practices offer, for a challenging future climate, in the southwestern US arid desert environments. Examining studies and experiments that have come from other arid desert areas around the world, it explores the importance of sand and dust storm (SDS) issues, climate change, desertification, and the use of agroforestry to sustain the health of soil, water, landscape, biodiversity, food, and people. There are new possibilities for food production based off traditional farming techniques that have been in use for hundreds of years. Combining the world’s knowledge and experience, and using new sustainable technology like solar power generation in the southwest US, agroforestry can help build resilience to climate change, drought, crop yield loss and desertification. The desert landscape in regards to water scarcity and water conservation measures for agroforestry will also be discussed. This paper will focus on three agroforestry practices for high desert areas of the southwest US; windbreaks, alley cropping and silvopasture.
3. Agroforestry Practices
The Center for Agroforestry at the University of Missouri, where the Association for Temperate Agroforestry is based, recognizes 6 land-use management practices within agroforestry. These are alley cropping, windbreaks, silvopasture, riparian and upland buffers, forest farming, and urban food forests (The Center for Agroforestry, 2021). The area of the southwestern United States is considered an arid and semi-arid environment, which has not been utilized to its full potential in agricultural and agroforestry terms (Nabhan et al., 2020). Many groups of Native Americans have lived and farmed the land for centuries, and currently scientists are studying the way these lands had been farmed traditionally (Nabhan et al., 2020; Southwest Agroforestry Action Network, 2020, 2021; Sandor and Homburg, 2015; Kuzdas, 2019; Murphree, 2017). The traditional knowledge of living within arid and semi-arid environments, adapted and maintained by traditional people groups, can be found in many places around the world. This paper looks at some of these as a comparable source of techniques that can be applied to the southwest US.
The agroforestry practices discussed in this paper, are windbreaks and shelterbelts, alley cropping, and silvopasture. Water retention similar to a riparian buffer will also be discussed, but within a flood plain instead of along a river. Windbreaks and shelterbelts are of ultimate importance to establish a wind barrier for dust storms and sand that affect landscape in a broad degree, impacting the environment, human health and vegetation in diverse ways. Alley cropping and silvopasture allow arid areas to be agriculturally productive within the limits of water scarcity, elevated temperatures, and poor soil quality. Along with these systems that incorporate trees, plants, crops, and livestock, there are ways to help maintain moisture level in the soil that makes agriculture possible.
3.1 Windbreaks and Shelterbelts
Windbreaks and shelterbelts are an agroforestry system that utilize trees, shrubs, grasses and cactus, as wind barriers (Brandle et al., 2022). They can be planted in single or multi-species arrangements that can diminish wind speed power on soil erosion, damage to foliage, reduction of odors, and change the deposit of sand, dust, and snow (Brandle et al., 2022; UNEP et al., 2016). Many windbreaks consist of trees and woody plants such as shrubs, perennial or annual crops, or grasses (Brandle et al., 2022; Rehacek et al., 2017; UNEP et al., 2016). The design arrangement can be a single, double, or triple-row configuration, that can be of monoculture species or mixed vegetation. Depending on the issue the windbreak is addressing, wind, snow, odor, or aesthetic, will determine what design is chosen for the desired effect.
3.2 Alley cropping
Alley cropping can be defined as planting perennial, and annual crops between widely spaced rows of trees, growing simultaneously (Garrett et al., 2022; Inglese et al., 2017). This agroforestry practice increases agricultural diversification of the land and economic opportunities, allowing the use of modern technology and large machinery for management and harvesting (Garrett et al., 2022). Shrubs, trees or cactus are grown in wide rows and the crop is grown in the interspace (Inglese et al., 2017). In temperate alley cropping, hardwoods, nuts and fruit trees are emphasized for production, more than leguminous for soil maintenance, as in the tropics (Garrett et al., 2022). In this way the farmer continues to cultivate the land for short-term food production, economic profit, while the trees can be harvested in the long-term and/or maintain soil quality, recycle nutrients and control erosion (Garrett et al., 2022; Inglese et al., 2017). Careful attention must be given to the design in alley cropping, as the crops, forage, trees/shrubs must be compatible in interactions for light, water, and root depth, to minimize competition and maximize return on input investments (Qureshi and Shoaib, 2017; Garret et al., 2022).
Silvopasture is a pasture and forest management system that brings livestock together within a treed environment. Establishment can be made by thinning an existing forest and managing the forage sources within. Trees can also be planted in the landscape so that shade, reduced winds, and organic leaf debris benefit livestock and forages, which in turn the livestock provide fertilizer and nutrient cycling back to the land. High-value trees like hardwoods may produce an economic benefit later on when managed for veneer and sawlog value (Jose et al., 2018; Pent et al., 2022). In the southwest, silvopasture is not a common practice like it is in more forested lands of the US, such as the northeastern and southeastern areas. The challenge in dry arid landscape is heat stress and water availability, both for plants and livestock, and where they could be successfully integrated without over competing for resources. One idea would be to invest in ecotourism and aesthetic appeal of silvopasture, in combination to produce economic and social benefits (Pent et al., 2022).
3.4 Windbreak and Shelterbelt Function
The external structure (width, height, shape, and orientation), and internal structure (leaf shape and size, branching matrix, and trunk(s)) determine the functional ability of the windbreak or shelterbelt (Brandle et al. 2022; Rehacek et al., 2017). Windbreaks work by breaking up the wind flow at the ground surface level, up to the height of the windbreak (Brandle et al., 2022). Also some wind travels through the windbreak, which decreases its speed and changes the flow pattern on the leeward side (Rehacek et al., 2017; Brandle et al., 2022).
Windbreaks and shelterbelts are an agroforestry system that utilize trees, shrubs, grasses and cactus, as wind barriers (Brandle et al., 2022). They can be planted in single or multi-species arrangements that can diminish wind speed power on soil erosion, damage to foliage, reduction of odors, and change the deposit of sand, dust, and snow (Brandle et al., 2022; UNEP et al., 2016). Windbreak aerodynamics are explained in Brandle et al. (2022);
A windbreak is a barrier on the land surface which obstructs the wind flow and alters flow patterns both up-wind of the barrier (windward) and down-wind of the barrier (leeward). As wind approaches a windbreak, some of the air passes through the barrier while the rest flows around the ends of the barrier or is forced up and over the barrier. (p. 4).
Diverting and changing the wind pattern, works to protect soil from erosion processes, creating a microclimate where temperature of air and soil, as well as moisture is affected (Coleman et al., 2022). Linear farm windbreaks provide protection and create a microclimate for leeward fields (Coleman et al., 2022). Structural characteristics and design arrangement of trees, shrubs, and grasses, affect the height, density, and orientation to the wind direction, in a successful windbreak (Coleman et al., 2022).
4. Arid and Semi-Arid Environments
The southwestern area of the United States has climate and landscape diversity, in ecosystems that range from mountainous, forested and wet, to flat dusty plains, with sparse vegetation (Dosskey et al., 2017). The arid and semi-arid desert areas are the focus of this paper. Wikipedia (2021) defines arid and xeric areas as places of temperature extremes. High daytime temperatures and cold nights happen where there is no insulation from humidity and cloud cover (Dosskey et al., 2017). This harsh and diverse climate supports many habitats and unique species that minimize water loss (Dosskey et al., 2017). Woody-stemmed shrubs and small-leaved trees characterize the vegetation in a desert climate (Dosskey et al., 2017; Nabhan et al., 2020; Makkar, 2017; Dimmitt, 2021). Many desert habitats are ephemeral, such as wildflower blooms, and follow the seasonality of water resources. Animal biodiversity is also diverse and well suited to the changing extremes (Dosskey et al., 2017).
4.1 Geographic Locations in United States
Tong et al. (2017) states, “Climate model projections suggest a consistent trend toward an increasingly arid climate in the subtropics, including the southwestern United States” (p. 4305). As the southern area of the United States is nearer the equator, the states that contain arid environments are Arizona, California, Colorado, New Mexico, Nevada, and Utah (O’Neill et al., 2014; Dosskey et al., 2017). According to U.S. Global Change Research Program (2018), these states,
…occupy one-fifth of U.S. land area, extending across globally unique ecosystems from the Sonoran Desert to the Sierra Nevada to the Pacific Coast. The region is home to 60 million people, with 9 out of 10 living in urban areas and the total population growing 30% faster than the national average. The Nation depends on the region for more than half of its specialty crops such as fruits, nuts, and vegetables. (p. 1).
Tribal lands can be found in all states named above, and make up a significant portion of the southwest (U. S. Global Change Research Program, 2018). Dairy and livestock production are the main enterprises on rangelands, both Federal and private, and make up the largest land area in the Southwest US (U. S. Global Change Research Program, 2018). Different ecosystems comprise rangelands from savanna, steppe, scrubland, to arid grasslands (Dosskey et al., 2017). Water scarcity and limited accessibility is a desert characteristic (O’Neill et al., 2014; Dosskey et al., 2017).
4.2 Geographic Locations Worldwide
Globally there are many areas that are considered arid and semi-arid, where only drought tolerant and temperature extreme adopted plants and animals live. As well as the southwest USA, these areas are northern Sahara, east Africa, Mediterranean Europe, Middle East, west Asia and southern Australia (UNEP et al., 2016; Lal, 2001). They all have areas that are less arable due to extreme daytime heat and scare water resources. “Drylands of the world occupy 6.31 billion ha (Bha) or 47% of the earth’s land area distributed among four climates: hyper-arid (1.0 Bha), arid (1.62 Bha), semi-arid (2.37 Bha) and dry sub-humid (1.32 Bha)” (Lal, 2001, p. 35). It is estimated that along with climate change and predictions of increased world temperature, these areas will experience more desertification and will only become more of a concern, as people who live on the land or nearby, will be affected by dust, sand encroachment, and soil erosion, which affects agricultural productivity, agricultural employment, human health, and results in environmental degradation.
5. Issues in Arid and Semi-Arid Environments
5.1 Sand and Dust Storms (SDS)
Arid areas are places that naturally produce dust, and sand and dust storms (SDS) are common (Lal, 2001). “Sand storms occur within the first few meters above the ground surface…” (Middleton and Kang, 2017, p.1). “A dust storm is formally defined by the World Meteorological Organization (WMO) as the result of surface winds raising large quantities of dust into the air and reducing visibility at eye level (1.8 m) to less than 1000 m” (Middleton and Kang, 2017, p. 2). Similarly, Lancaster (2018) defines dust storms,
…as severe weather conditions in which visibility is reduced to 1 km or less by blowing dust. The frequency of dust storms is measured by the number of such events in a given time period. The magnitude of dust storms can be assessed by the duration of such conditions. Dust events (also known as dust haze) are conditions when visibility is reduced to 11.3 km or less by dust suspended in the air. Blowing dust is a situation where dust is raised to a height of 2 m or more by strong winds, but does not reduce visibility to less than 1 km. (p. 4).
Moving particles are characterized by the type they are; for example gravel and sand are known as creep and saltation, and in short-term and long-term suspension, as silt and clay (Opp et al., 2021). Dust is made of silt and clay particles (Opp et al., 2021).
Locations with soil dust particles that produce frequent SDS are located in the Northern Hemisphere, within a dust belt from North Africa, across the Arabian Peninsula, Mediterranean Europe, to northern India, north-western China, southern Mongolia and Northeast Asia, and in desert regions of Australia and the USA (WMO, 2019; Middleton and Kang, 2017). Middleton and Kang (2017) state,
Drylands in the Southern Hemisphere are much less active SDS sources, despite concentrations of activity in Central Australia, Southern Africa and the Atacama in South America. These sources have significant local impacts—as does the North American Great Basin—but remain relatively minor on the global scale. (p. 3).
In temperate regions of Europe, soil erosion by wind is a threat, due to unsustainable human mismanagement of agricultural soil and bodies of water (Middleton and Kang, 2017; WMO, 2019). Global impact of human activities and dust sources are hard to study, and most likely make up 25% of global emissions (UNEP et al., 2016). The area extending from Montana to southern Texas in North America, exhibits the highest dust activity, 60% of US wind erosion (UNEP et al., 2016). The US national maximum dust days per year is 50, occurring in the southern plains of Texas (Hagen and Woodruff 1973, as cited in UNEP et al., 2016).
Aeolian processes happen in a variety of environments, including cold and hot deserts, and agricultural fields, in which erosion, transportation and deposition by wind occur. Vegetation cover can be sparse, with clay, silt and sand particles making the soil surface easily erodible by strong winds. Aeolian processes mobilize dust and create areas of sand dunes (Lancaster, 2018). There are four phases of aeolian particle movement: abrasion, deflation, transport and deposition (Opp et al., 2021).
5.2 Global Transport – SDS
Often with SDS the source of the dust, and where it has an impact, is separated by large distances. Dust storms have both local and far reaching impacts because the particle size is smaller than sand, and finer dust can be transported much higher into the troposphere, out farther over land. This can result in a form of natural hazard that has international effects (Middleton and Kang, 2017). “There is no equivalent formal definition of sand storms, but storms dominated by sand tend to have limited areal extent and hence localized impacts, including sand dune encroachment” (Middleton & Kang, 2017, p. 2).
Different effects produced by and associated in similar desert landscapes, are currently termed as “syndromes”. For instance, the term “dust bowl” that we know in the US, is now applied to other areas of the world that experience dust from the plains on a wide scale. UNEP et al. (2016), cite Ludeke et al. (2004) in their delineation of the syndrome areas:
The Dust Bowl, Overexploitation and Aral Sea syndromes prevail in industrialized countries. …The Dust Bowl Syndrome dominates in Europe, the former Soviet Union and the United States, and is the most widespread syndrome in temperate as well as more arid zones in Spain and the Western USA. …The Sahel Syndrome is found throughout Sub-Saharan and North Africa, Asia, and Latin America. (p. 28).
Climate change can be a result of atmospheric dust loadings, as it affects earth’s radiative ability, either absorbing or scattering the solar radiation. It is thought that changing the earth’s radiative balance can have a number of negative effects including heating and cooling of the earth, and intensifying drought conditions (UNEP et. al., 2016). SDS are a serious threat to human health, air quality, agriculture, the transportation sector, energy sector including solar power, industry, and ecological systems both aquatic and terrestrial (WMO, 2019).
5.3 Human Health
We tend to think of dust storms affecting those who live in the areas where dust storms occur, but atmospheric and meteorological science has shown that dust storms that start in Africa, can travel over the Atlantic Ocean and over to North America. Similar aeolian processes take place in west Asia, with dust transported over the Pacific Ocean. There are many documented health studies on human health and dust exposure. Atmospheric dust aggravates and can cause many human health issues (Middleton and Kang, 2017; Lal, 2001). These include respiratory ailments such as asthma, bronchitis, emphysema and silicosis (lung fibrosis) (Middleton and Kang, 2017; UNEP et al., 2016; American Lung Association, 2020; Lancaster, 2018). UNEP et al. (2016) finds particle pollution affects more people than any other pollutant, including dust, using data from summary reports. It is very concerning as there is no level of safe threshold to exposure of organic and inorganic substances and chemicals (UNEP et al., 2016).
“The September 2009 dust storm in Sydney, Australia was significantly associated with a 23.0% increase in asthma-related emergency department presentations and a 14.1% increase of asthma hospital admissions compared to non-dust periods” (Merrifield et al., 2013, as cited in Zhang et al., 2016, p. 13). “Chronic exposure to fine dust is associated with premature death due to cardio-vascular and respiratory disease, lung cancer, and acute lower respiratory infections. Fine dust carries a range of pollutants, spores, bacteria, fungi, and potential allergens” (UNEP et al., 2016, p. 13).
When people move to, or visit areas that are arid and dry, they are at first unaware of some common irritants that are in the atmosphere, that can affect the moist linings of the eye, nose and throat. Most people are good at protecting their skin from heat and sun exposure that are high in a desert environment, as skin can become irritated and dry. Eye and sinus infections are common when dust and sand are blown about (UNEP et al., 2016). Many people who live within these desert areas have developed ways of dressing that can protect their skin, hair, eyes, nose, etc. from the effects of dust and sand. In the US, Valley fever is a common ailment in the southwest (UNEP et al., 2016).
Other human health problems from dust and sand storms are mortality and injuries related to poor visibility on the road while driving. Traffic and transport accidents and disruptions happen in train and airport service in other countries, especially the Middle East and China (UNEP et al., 2016; Middleton and Kang, 2017). Dust storms, where visibility is less than 1 km, have an immediate effect within the area on air quality and visibility (Lancaster, 2018). Downwind deposition of dust has an impact on soil nature and composition in arid regions, and where fine sediment is transported (Lancaster, 2018). UNEP et al. (2016) mentions “diseases associated with toxic algal blooms” as another human health concern. The America Lung Association (2020) has suggested measures for people living within high dust areas, such as wearing a face mask when outside, filtering indoor air using a HEPA filter, as well as keeping the windows shut and changing the filters often.
5.4 Wind and Vegetation Damage
Wind with fine dust particles and sand, can adversely affect vegetation and agriculture (Brandle et al., 2022; Lancaster, 2018). Wind blowing in arid environments kicks up particles of dust, soil, sand and other matter that actively abrade the ground and dislodge more particles. Lancaster (2018) describes the erosion process:
Erosion by wind involves two linked processes: abrasion (mechanical wearing of coherent materials, including playa crusts and clods created by tillage) and deflation (removal of loose material). Considerable attention has been devoted to the processes and rates of wind erosion because of their impact on agriculture, especially in semi-arid regions, and the implications of dust emissions for air quality. (p. 2).
Blowing dust and sand has a negative impact on the immediate environment by removing topsoil and exposing subsoil areas to erosion and desertification (Brandle et al., 2022). Plants that are sensitive to abrasion such as annual crops like lettuce and spinach do poorly in such conditions and whole fields can become damaged (Middleton and Kang, 2017; Lancaster, 2018, Brandle et al., 2022). Dust also accumulates on the leaves of plants and can inhibit the amount of sunlight being absorbed by the plants’ surface and congest the stomata (Middleton and Kang, 2017; Ikazaki, 2015; Opp et al., 2021). Wind erosion reduces soil nutrients in the top layer, usually thought to have the highest nutrient content, exposing the poorer subsoil structure which causes poor soil productivity and permeability (Brandle et al., 2022; Ikazaki, 2015). This is thought to be the one main cause of desertification in the Sahel region of Africa (Brandle et al., 2022). Wind erosion can also affect crop growth, burying crops under blowing sediment and producing abrasion injuries (Ikazaki, 2015).
According to Lancaster (2018), because wind erosion removes the topsoil, changes occur to the soil texture. Nutrients, organic matter and fertilizer are lost and impact the quality of the air and atmospheric radiative properties. Other chemicals that can be found in desert dust are aluminum, iron, calcium, magnesium, potassium, salts, pathogenic microorganisms, (fungi, bacteria and viruses) and pollutants created by manufacturing and industry (Middleton and Kang, 2017).
5.5 Heat Level and Climate Change
Deserts are some of the hottest places on earth. Death Valley National Park, California, holds the world record high of 134°F (57°C). Summer temperatures by day in the region are 98°F (35°C) and above, similar to the Arabia Peninsula (U.S. Global Change Research Program, 2018). Along with rising temperatures worldwide, deserts can experience even hotter daytime temperatures and for longer periods. As heat intensifies in a desert landscape, water resources become less available. Research provided through the U. S. Global Change Research Program (2018) estimates,
Increases in temperature would also contribute to aridification (a potentially permanent change to a drier environment) in much of the Southwest, through increased evapotranspiration, lower soil moisture, reduced snow cover, earlier and slower snowmelt, and changes in the timing and efficiency of snowmelt and runoff.
Extreme heat advisories help humans to know when it is dangerously hot outside and to stay hydrated and seek shade. Animals and plants however will need to adapt or move out of an area that is no longer habitable for their species. From 1999-2004, Utah’s drought period saw a decline in cattle productivity, water and fodder, reported by 75% of ranch operations in that state (U.S. Global Change Research Program, 2018). U.S. Global Change Research Program (2018) looked at the elevated levels of CO2 in the atmosphere that change air quality:
Elevated levels of CO2 in conjunction with higher temperatures can increase the amount and potency of aeroallergens. These conditions may also lead to new cases or exacerbation of allergy and asthma. Mortality risk during a heat wave is amplified on days with high levels of ground-level ozone or particulate air pollution, with the greatest mortality due to cardiovascular causes.
When ecological areas that are already scarce in water heat up, they are at risk of desertification due to already dry soil matter. This links heat and dust again as two factors that will persist in future planning for transportation, urban planning and development, and expanded housing out to rural areas in the southwest. “Dust affects the climate system, possibly changing the earth’s radiative balance and modifying tropical cyclones, which can cause drought intensification” (UNEP et al., 2016, p.13). ”Episodes of extreme heat can affect transportation by reducing the ability of commercial airlines to gain sufficient lift for takeoff at major regional airports” (U.S. Global Change Research Program, 2018).
5.6 Scarce Water Resources
In working to plan an agricultural system, and/or livestock production area such as silvopasture in arid environments, one big challenge always exists. For the most part, many desert areas do not have underground aquafers and rely on rainfall and runoff from higher elevations. In agricultural and livestock production, and in supplying drinking water for a growing population, water in the southwest has already been an issue. “Agricultural irrigation accounts for nearly three-quarters of water use in the Southwest region, which grows half of the fruits, vegetables, and nuts and most of the wine grapes, strawberries, and lettuce for the United States” (U.S. Global Change Research Program, 2018). This is a reason that drought and water demands from agriculture, industry, and human population pose a risk for food security in the region (U.S. Global Change Research Program, 2018).
The southwestern states have many Native American groups that have lived and worked with sparse rainfall, and have evolved ways over generations, on how to deal with low precipitation and crop production. Between the US and Mexico, there are water laws that allocate among states, tribes, cities, industry, energy sector and agriculture. With higher temperatures, and variable precipitation, surface water and evaporation rates will diminish resources (U.S. Global Change Research Program, 2018).
Other research into desert systems and agricultural development have found water scarcity an issue when production systems are planned, because the amount of water the plants take out of the natural ecosystem is not accounted for. It is important to study the available water in the area, while matching plants to an arid, dry environment. Designing multiple plants to be grown in alley cropping or silvopasture systems will require perhaps a maximum limit on how many trees can be grown, depending on the soil and availability of water. The nature of desert rainfall and shallow groundwater resources make for a low recharge rate for water systems. Therefore, relying on groundwater for agriculture or agroforestry, will diminish natural resources further in an unsustainable manner (Wang and D’Odorico, 2019). The cycle is apparent for desert areas experiencing climate change, disturbed soil due to tilling, off road vehicles, and urban sprawl. Modifying landscape environment using agroforestry practices, like windbreaks, alley cropping and silvopasture can help to minimize the effects of climate change (Dosskey et al., 2017).
Water banking is one proposed way in which water can be captured and stored in groundwater aquifers. During high-precipitation years, excess water from streamflows on mountain ranges could be directed to an aquifer (U.S. Global Change Research Program, 2018). This water capture technology is employed in the Taklimakan Desert in Xinjiang, China. Newly planted native shelterbelts are drip irrigated when first planted, from the groundwater aquifers below the sand dunes (Opp et al., 2021). Lal (2001) research indicates,
…soil under vegetated cover is generally more porous, more organically rich, with a high infiltration rate. Therefore, with 50:50 surface area covered by vegetation, the effective rainfall received in the vegetated areas is twice the normal rain. Consequently, soils have different leaching rates, SOC content, salinity, and structural features within meters of each other. (p. 45).
“Desertification is formally defined by the UN Convention to Combat Desertification (UNCCD), as land degradation in arid, semi-arid and dry sub- humid areas resulting from various factors, including climatic variations and human activities” (UNEP et al., 2016). Desertification worsens and causes wind erosion and SDS, having expansive, open and exposed, dry surfaces in which wind has no obstructions (UNEP et al., 2016). Lal (2001) describes this definition in more detail at a functional level;
In this context, the term ‘land’ includes whole ecosystems comprising soil, water, vegetation, crops and animals. The term ‘degradation’ implies reduction of resource potential by one or a combination of degradative processes including erosion by water and wind and the attendant sedimentation, long-term reduction in the amount and diversity of natural vegetation and animals, and salinization. (p. 37)
As a result of desertification and drought occurring actively on a large scale, concerning many areas where people live, the United Nations had designated June 17th as “World Day to Combat Desertification”. It was on this day in Paris in 1994, that the Convention to Combat Desertification (UNCCD) was initiated (United Nations, 2019).
Globally, “desertification hotspots” are defined where the highest numbers of people are affected. Not surprisingly, the hotspots are the same regions affected by SDS, including North and South America and Australia (Intergovernmental Panel on Climate Change, 2019). These areas were identified because of the decline in vegetation from 1980 to 2000s, “affecting about 500 (+120) million people in 2015” (Intergovernmental Panel on Climate Change).
The soils where desertification occur, have poor water infiltration which leads to a reduction in water reserves within the soil layers, and in the production of biomass. Chang et al. (2015) discusses the general composition of desert soil in desertification, as a “decrease of inter-particle cohesion of soil” by loss of the clay particles. The soil surface becomes a crust that has low productivity, is nutrient poor, prone to erosion, and produces stunted plant growth and shallow roots (Lal, 2001; Lancaster, 2018). With increased surface exposure and a decrease in organic matter as plant litter, the decrease in vegetation leads to more desertification, which is a cycle. “Any management practice that removes or disturbs organic layers at the soil surface also increases surface exposure to wind. For example, ploughing for crop production or destruction of biological crusts through vehicular traffic disrupts the surface organic layer” (UNEP et al., 2016). In southwestern US, rangeland has been mismanaged by overstocking and overgrazing, reducing grasslands to shrub lands (UNEP et al., 2016).
6. History of the Dust Bowl, United States
Agricultural practices and livestock grazing on the Great Plains of the United States, in the years that led up to the 1930’s, had not considered soil health, native plant ecology, and landscape biology. Without regard to preserving soil health, the development of cultivating the drier grass plains area of the Midwest, along with overstocking rangeland, led to the Dust Bowl (UNEP et al., 2016). As the soil was tilled, fine particle size pieces were blown away by wind, which led to poor structure stability of the land, and loss of organic matter in a protective layer in which drought conditions worsened the process (UNEP et al., 2016). “Wind erosion from agricultural land in the North American Great Plains peaked in the Dust Bowl era of the 1930s, when a severe drought and poor land management resulted in significant soil losses and widespread economic hardship” (Middleton and Kang, 2017, p. 12).
The dust clouds produced were magnificent in height and width, like a blanket covering over the land. Travelling along the ground, the clouds blocked the sun and covered everything in a fine silt. The air quality and visibility was very poor, and had a negative effect on human and animal health. These type of storms still affect places in the southwest. For example in 1977, the San Joaquin Valley of California had high soil erosion and damage caused by high winds and drought. A 2,000 km2 area was affected in a 24-hour period, where 25 million tons of topsoil was lost (Goudie and Middleton 2006, as cited in UNEP et al., 2016).
6.1 Changes in Land Management
Learning from the Dust Bowl, land stewardship with a conservation mindset began in earnest. The government implemented a plan to plant acres of windbreaks and shelterbelts within the Great Plains area. The purpose was to stop the degradation of soil and organic matter, and to encourage practices that worked with nature on a large scale. This is one of the largest coordinated efforts in US history, for applying agroforestry at a government and regional model. Middleton and Kang (2017) discuss the creation of the new branch of ecological science;
Soil Conservation Service (SCS), created in the USA in 1935, identified areas in need of remediation using aerial photography surveys and detailed soil maps. The SCS acquired unoccupied and abandoned lands, significant dust storm sources, and used them for demonstration projects on terracing and contour plowing. (p. 12).
As much of the land was privately owned, shelterbelts, and methods for improved plowing were subsidized by governmental agencies (Middleton and Kang, 2017). On a large scale, farmers learned that sustaining agricultural production meant an obligation to protect their fields and crops from future ecological events, such as drought, wind, adverse weather conditions, and water scarcity. Modifying the way things were always done, helped bring balance back to the land. It also had a positive effect on biodiversity, as trees support wildlife and produce microclimates. Dosskey et al. (2017) believes that an effective climate strategy can be undertaken by the U. S. Government, similar to the effort made to create The Prairie States Forestry Project after the Dust Bowl. The management style was efficient and quick, using top-down government, and bottom-up landowner approaches. Lessons can be learned from this experience and the success of its work, and applied to the larger global problem of climate change (Dosskey et al., 2017).
7. Southwest US High Desert Ecology
The Sonoran, Mojave, Great Basin, and Chihuahuan Deserts are true deserts of the southwest. Desert plants are excellent at meeting their needs with little input and have reliable yields when drought conditions exist. Nabhan et al. (2020) suggests that these characteristics of desert plants not only give them resiliency in climate change, they provide a model with high potential for arid-adapted agriculture, and can help mitigate climate change. There is a wide variety of food crops that naturally grow in the arid southwestern climate. An example is the mesquite (Prosopis) tree, which can be managed in an agroforestry system for honey production, flour milled from their pods, soft drinks, bread, beer and tortillas (Gardea et al., 2011; as cited in Nabhan et al., 2020). Although they are mostly known regionally, they have growing market potential and produce value-added products. Nabhan et al. (2020) cites the local food and sustainable agriculture movement for arid-adapted grown food crops, like the growing market in Tucson, Arizona, “the first UNESCO City of Gastronomy in the United States”. In Indigenous dryland farming systems of the Hopi, crops such as corn, beans and squash were grown without irrigation, using conservation techniques, and still today these are grown along with melons and cotton (Johnson et al., 2021).
Dimmitt (2021) has studied the strategies of desert plants;
Aridity is the major and almost the only environmental factor that creates a desert, and it is this functional water deficit that serves as the primary limitation to which desert organisms must adapt. Desert plants survive the long rainless periods with three main adaptive strategies: succulence, drought tolerance, and drought evasion. Each of these is a different but effective suite of adaptations for prospering under conditions that would kill plants from other regions.
Saguaro cacti is a good example of being adapted to and only living in the Sonoran Desert, occupying elevations from sea level to 4,000 feet, and require drought and heat seasonally (Dimmitt, 2021).
Succulence is a characteristic of cactus plants. Cacti, family Cactaceae, grow at various altitudes from sea level in the deserts of California, to 4700 meters altitude in the Peruvian Andes. Tolerant of temperature extremes, they exist in tropical Mexico, and extending north to Canada with frozen temperatures to -40 degrees C/F (Makkar, 2017). However cactus species do not tolerate salinized soils (Makkar, 2017). In spite of development threats, “…the group has significant socioeconomic and cultural importance, with 57% of all known cactus species being utilized by people, and managed in wild and in anthropogenic created spaces (e.g. agricultural lands, pasture, and backyards)” (Correa-Cano et al., 2018, p. 2). Cactus is propagated using cladodes, also called cladophylls that are non-leafy parts of the plant (shoot systems). The genetic characteristics of the plant are preserved this way (Makkar, 2017).
Dimmitt (2021) provides physiology information on succulents. They store water in all parts of their organisms; leaves, stems, roots. All cacti are succulents, and there are some plants that are non-cactus succulents such as agaves, aloes, elephant trees and euphorbias. Most have extensive shallow root systems which immediately react to light, brief rains which are characteristic in deserts. Root structures just below the surface take advantage of the few inches of topsoil that absorbs moisture in a short time, and under heat conditions. A saguaro is an example of shallow root system, radiating outward the length of its height.
Cactus pear, Opuntia ficus-indica is a CAM (crassulacean acid metabolism) plant, which opens stomata at night to fix CO2, and uses stored CO2 for photosynthesis during the day, thus preserving water loss during the day (Makkar, 2017; Dimmitt, 2021; Correa-Cano et al., 2018). This type of photosynthesis being slower, growth is also slower than C3 plants (Dimmitt, 2021). Highly efficient in water use, transpiration rate is 3-5 times lower than C3 and C4 plants who carry on transpiration during the daylight hours in different ways (Makkar, 2017). It’s ability to grow in poor and degraded soils, and being thornless or spineless, has attracted attention from researchers and farmers for its multi-uses (Makkar, 2017; Belgacem et al., 2017).
Agave deserti plants have the ability to switch from CAM to C3 photosynthesis and thus grow faster when there is more water present (Dimmitt, 2021). They have their own unique desert adapted design. The leaves form a rosette-shape, and channel rain to the base of the plant. A similar design is also found in the yucca plant, as both are in the subfamily agavoideae. The shallow root system is kept within the area, equal to the size of the above ground rosette (Dimmitt, 2021).
Desert shrubs and trees have a different rooting system than other temperate or tropical species. They tend to be more extensive and grow laterally out, extending two to three times the canopy diameter. The roots also extend farther down into the soil layers where the soil stays wet longer. There is a multi-strata of root systems that then take advantage of different levels of soil, nutrients, and intermix in competition for water resources. (Dimmitt, 2021) Most desert trees and shrubs have small leaves that are gray-green, blue-green and light in color, which helps them reflect light (heat) to keep them cool. The small leaf size and color avoid overheating and reduces water loss. (Dimmitt, 2021) Drought tolerant plants do not need to wait for saturated soil to survive, like succulents do. A creosote bush for example, “…can obtain water from soil that feels dust-dry to the touch. Similarly these plants can continue to photosynthesize with low leaf-moisture contents that would be fatal to most plants” (Dimmitt, 2021). Non-succulent desert plants that seem dead are actually in a dormant state like torpor in animals. This helps them survive months or years without rain and in dry seasons (Dimmitt, 2021).
In the southwest US, important grass species are black grama (Bouteloua eriopoda), blue grama (B. gracilis), and tabosa grass (Hilaria mutica). These have proven to enhance soil quality and vegetative cover. For establishing windbreaks and shelterbelts, Acacia spp is a native to the US. Neem has also been suggested, however it is a native of India. Populus (poplar) is good along river banks for riparian buffers. Leucaena and Acacia can be used for animal fodder. Prosopis is good for fuel wood, however it has become a pest plant in Texas rangelands (Lal, 2001).
Dosskey et al., (2017) discusses how landscapes can be managed for enhancing connection between existing fragments, that benefits gene flow and population support for animal and insect species. This can be done through corridor areas and mosaics of landscape to support biodiversity and habitat, and help mitigate or slow loss through decline in populations. Agroforestry systems can enhance biodiversity at local farm level to regional areas, as there is multi-level (from ground to the canopy), multi-species management, as well as reducing the clearing of natural habitats, and building soil health while controlling erosion (Coleman et al., 2022).
According to Nabhan et al. (2020) large branching cacti, long-lived woody shrubs, and perennial grasses have great capacity to control soil erosion. Underground water resources and biodiversity are enhanced by the support of legume trees that redistribute water and nutrients to neighbors. Legume trees also decrease the need for fertilizers, as they provide nitrogen fixation to the soil over years. Many native bee species are attracted to Prosopis, one of the many desert plants that support pollinators. Cacti are also extremely beneficial and enhance biodiversity. Inglese et al. (2017) discuss how their flowers attract pollinators and butterflies, and fruits attract birds and coyotes. Birds like the cactus wren, native of the southwest, nests in cactus plants, saguaro, cholla or yucca. In Arizona the American rat lives mostly beneath fallen cactus. Hundreds of species of ants use the cactus for food.
According to Dosskey et al. (2017) native bees are primarily solitary, (the female has her own nest, there is no hive) and are underground nesters. The undisturbed soils under trees and shrubs are perfect areas to nest. A smaller percentage (30%) make their nests in trees and shrubs, using the stems or tunnels left behind by other insects. Conventional agriculture tilling method decreases the habitat for native bees. Bumble bees are really effective pollinators and make ground-level nests, preferring hedgerows and windbreaks between fields. Here the nest density is twice that of grassland habitats. Bee flight patterns are affected positively and have higher pollination rates within calm, sheltered areas that are protected from strong winds (Brandle et al., 2022). Nabhan (1985) finds that bird species diversity increases with the presence of fencerows, such as in sites studied in the Sonoran Desert mesquite thickets. The trees provide microhabitats through shade and cooler temperatures. Microhabitats support aviary life cycle, and predator and prey interactions, at the edges of vegetative protection (Brandle et al., 2022).
Dimmitt (2021) emphasizes the importance of spatial specialization for annuals. Niche separation is beneficial to annual species of flora in desert environments. It limits competition when the conditions are right to produce flowers and seeds. Dune evening primrose and sand verbena like loose sand, while caterpillar weeds grow only in rocky soils. Dimmitt (2021) also addresses seed importance in deserts. In all the vacant looking sand and dry soil, there is a seed bank beneath. It is an extremely important food source for desert animals, and depository for future plants. “After a wet year there may be 200,000 seeds per square meter (square yard) of soil.” In dry years there is still enough to feed harvester ants, kangaroo rats and sparrows.
One factor that contributes to decrease in biodiversity of both flora and fauna, according to Correa-Cano et al. (2018) is artificial light at night (ALAN). Pollinating and foraging of desert plants like cacti, are becoming a challenge for some animals and insects. Light at night can influence the behavior of insects, birds, and bats, and reduce the time they spend in a certain area, or in which plants they choose. This in turn can modify the dispersal rates and pollination of cacti species. Ants and rodents disperse fruits fallen on the ground, and rats are another animal affected by ALAN.
Brandle et al. (2022) lists important ways in which agroforestry directly promotes biodiversity and strengthens the connections between flora and fauna. Agroforestry provides habitat space through plant interactions, preserves seeds and encourages growth of species sensitive to landscape changes, reduces the disturbance of soil and human environmental impact, and creates mosaics of habitat fragments that connect together to provide corridors where conservation can happen at a species level. It provides sustainable environmental non-market services like carbon sequestration, moisture suspension within soil layers, prevents erosion of topsoil, and encourages interactions within the landscape ecosystem.
7.2 Sand Dunes
Sand dune formation is a natural component of desert geology. Some arid areas have more aggressive sand dune drift than others, which is primarily caused by wind. Checkerboard or linear arrangements using non-living fences made of straw or tree branches are often used. Other engineering methods are covering the ground with nets, geotextiles, or stone mulch, chemical stabilizers, and crusting or wetting (UNEP et al., 2016). Vegetation cover does influence the sand cohesion around the plant and plays a large role in aeolian dynamics in semi-arid and coastal areas (Lancaster, 2018).
Mayaud and Webb (2017) discuss how vegetation affects sand transport. When sand and wind encounter short grasses, the sand is carried within and above the plant canopy, trapping sediment at ground level. Tall vegetation such as trees and shrubs, having spaces around the trunk and a distance to the crown, have sediment deposited within a wider range. Shade produced by desert trees and large branching cacti lowers ambient air temperature and relieves heat stress in animals, agricultural workers, and reduces energy costs near buildings (Nabhan et al., 2020). Dosskey et al. (2017) adds that soil temperatures, humidity, and wind speed are also altered using agroforestry systems, and the microclimates created provide environmental benefits as well as enhance productivity of fields and pastures. Sonoran farmers take advantage of the windbreak trees’ ability to shade crops and preserve soil moisture. This primarily takes place in spring fed oases and near floodplain areas (Nabhan, 1985).
7.4 Dust and Wind Health Impact, US
Tong et al. (2017) discusses how the climate in the southwestern US has seen a large increase in dust storms, changing over the years from 1988 to 2011, with a total of 2260 dust events recorded during that period. “On average, there are approximately 20 dust storms per year recorded at these sites in the 1990s, and 48 storms per year in the 2000s, representing an increase of 240% in two decades” (Tong et al., 2017, p. 3). As human population increases and urban land development spreads to outlying areas, public warning systems have been set in place to warn drivers and the transportation sector on Interstate routes in the Southwest (Middleton and Kang, 2017). Campaigns in the Southwest such as the website ‘pullasidestayalive.org’, have been made to inform the general public about dust storms and safety information (Middleton and Kang, 2017).
“Breathing in dust is particularly hazardous for children, the elderly, and those with respiratory conditions such as asthma” (Streiff, 2021). In the soil of some desert regions in the Western hemisphere, fungal pathogens Coccidioides immitis and C. posadasii spores cause Coccidioidomycosis, or Valley fever. This community-acquired disease is caused by inhaling spores that infect the lungs, which results in mild illness, to life-threatening pneumonia and tissue destruction (Zhang et al., 2016, Tong et al., 2017) “The incidence of Valley fever has increased eightfold from 1998 to 2011 in the endemic areas (Arizona, California, Nevada, New Mexico, and Utah)” (CDC, 2013, as cited in Tong et al., 2017, p. 6). “People of all ages in El Paso of Texas were 1.11 times more likely to be hospitalized by asthma on a dust event day than on a clear day” (Grineski et al., 2011, as cited in Zhang et al., 2016, p. 13). “Asian dust is shown to contribute to aerosol loadings in western North America. African dust transported to the Caribbean and Florida has triggered violations of US air quality standards and makes up about half the airborne particulates in South Florida’s air during the summer” (UNEP et al., 2016).
7.5 Heat Level and Climate Change, US
Climate change is a real concern for desert areas with little water resources, biodiversity and food production. There is a need to reconsider how we grow food both in the US and globally in arid and semi-arid areas. Yield stability of conventional annual crops, along with crops grown perennially may experience decline and failure (Nabhan et al., 2020). Concerning conventional crops such as olives, cotton, kiwi and oranges, they may replace others as the climate becomes hotter in some areas. Many southwest growers would need to have a new food system landscape designed to fit the higher temperatures, causing some to move, thus affecting rural communities (U.S. Global Change Research Program, 2018).
Heat stress can affect water competition among agriculture, municipal uses and energy generation. Livestock operations and farms will need to develop plans to keep animals cool during heat waves, and contend with drought conditions. When winter chill hours are reduced, some crops may fail, or drastically reduce in yield, affecting specific phases of the plant life cycle. Elevated temperatures also affect plant life cycle and have been linked to warm-season vegetable crop failure (U.S. Global Change Research Program, 2018). Worldwide, over the past 60 years, global food production has fallen 20% due to climatic conditions (Goldstein and Oken, 2021).
Particularly in regard to Native people living on reservation land in the Southwest US, droughts have shown to disrupt growing cycles for Indigenous staple foods; corn, pine nuts and acorns, which puts increasing pressure on food production and food security (U.S. Global Change Research Program, 2018). Additionally with predicted rise in illness related to climate change in rural and Indigenous communities, public health problems will affect the economies of this region (Nabhan et al., 2020). There are many studies of associated rise in hospital visits and human health problems directly related to high temperatures. U.S. Global Change Research Program (2018) illustrates the problem with heat waves in the southwest;
Exposure to hotter temperatures and heat waves has led to heat-associated deaths and illnesses in Arizona and California. In the unprecedented 2006 California heat wave, which affected much of the state and part of Nevada, extremely high temperatures occurred day and night for more than two weeks. Compared to non-heat wave summer days, it is estimated that the event led to an additional 600 deaths, 16,000 emergency room visits, 1,100 hospitalizations in California, and economic costs of $5.4 billion (in 2008 dollars).
Single exposure or multiple exposures to ground-level ozone pollution, air allergens, extreme heat, and particulate air pollution (wildfires and dust storms), elevate the risk of respiratory and cardiovascular disease, and exacerbate pre-existing conditions. “Ground-level ozone is produced by chemical reactions of combustion-related chemicals (for example, from vehicles or wildfires) in a reaction that is dependent on ultraviolet radiation (that is, from the sun) and amplified by higher temperatures.” (U.S. Global Change Research Program, 2018)
8. Agroforestry Practices and Benefits
8.1 Windbreaks and Shelterbelts
Tree species that O’Neill et al. (2014) recommend for the southwest in northern New Mexico and Four Corners region are; poplar crosses, Rio Grande cottonwood (P. deltoides ssp. wislizeni) and Fremont cottonwood (P. fremontii). All these native species are found throughout this area (O’Neill et al., 2014). From studies of native trees found both in the Sonoran Desert and in urban landscapes in Arizona, Bang et al. (2010) found perennial species cholla cacti (Cylindropuntia spp.), palo verde trees (Parkinsonia spp.), and ironwood trees (Olneya tesota). Native shrub species are creosote bush (Larrea tridentata), bursage (Ambrosia deltoidea) and E. farinosa (Bang et al., 2010). In most places native trees have an adaptation advantage over non-native species, and also need to be resistant to pests and disease (Brandle et al., 2022). Mesquite is another important native tree that has multiple uses and benefits. It is a source of fuelwood, charcoal, feed for ruminants, and supplies poles and posts for fencing (Dosskey et al., 2017). A local industry relying on mesquite raw material has evolved within the Southwest US, thus producing more of a demand, but limiting sustainable management practice knowledge (Dosskey et al., 2017). Mesquite is known to have deep root systems that anchor the surrounding soil and can protect seedlings from drought (Lal, 2001). Trees in agroforestry systems reduce heat load on crops, providing shade which conserves soil moisture, increasing biological activities belowground, and aboveground microclimate for crops (Sharma, 2014; Brandle et al., 2022).
Lack of water and nutrients limits the production of biomass, which makes decision making important to include xerophytic plants along with water catchment technology for acquiring nutrients efficiently (Lal, 2001). To increase vegetation stabilization, shelterbelts are important to use within alley cropping and silvopasture where moisture levels permit (Bruno et al., 2018). Technology such as water jetting is a proven method to establish new plants using temporary irrigation (UNEP et al., 2016). Opp et al. (2021) report that it may not be feasible or desirable to have plantings in desert and semi-arid areas, as the heat, drought, and water scarcity produce challenges beyond reasonable inputs of seedlings, labor, temporary irrigation, etc. However research projects carried out by Bainbridge (Southwest Agroforestry Action Network, 2021, January) in which seeds were shown to possess drought evasion attributes, waiting out seasons or years until germination, and in Al Baydha, Saudi Arabia (Spackman, 2020) where a regenerative agriculture project was successfully implemented over years of drought, counters this assumption.
In combination with shrubs and layers of vegetation near ground level, tall vegetation such as trees, can be most effective in long range wind reduction (UNEP et al., 2016; Brandle et al., 2022). The height of the windbreak determines the distance of protection in the landscape from wind force, downwind up to 10 – 30 times windbreak height (UNEP et al., 2016; Middleton and Kang, 2017). As an example, Nabhan (1985) states that a 20 foot tall windbreak can reduce wind velocity at a distance of 4 H by 40% when windspeed is 20 mph, allowing for increase in pollination and reduction in evaporation. Length of the windbreak should be determined by the height, and be at least 10 times the height, to protect the field edges from higher wind velocity as windbreak ability decreases at the terminal ends, where wind flow picks up (Brandle et al., 2022). Miri et al. (2017) proposes a design using plants with greater porosity and a less streamlined windbreak effect at the edges of a windbreak area, because of the wind force, thus potentially protecting the surface beneath the edge of the windbreak in a more effective manner.
Porosity affects the pattern of the wind and 20% porosity has been found to maximize the distance of protection (UNEP et al., 2016). Brandle et al. (2022) states that the effectiveness of a wind barrier, is in its shape in 3D space, accounting for width, height and density, and at least 40% density to control wind speed. When choosing vegetation for maximum wind resistance Miri et al., (2017) has found that, “wind-resistant vegetation that presents low porosity, high frontal area and less deformation is highly recommended for providing maximum ground surface protection and thus producing the most efficient barriers to aeolian erosion” ( p.6). Living vegetation has potential benefits to catch or diminish air pollutants by filtering the air flow, depending on wind porosity of windbreak design, distance between plants, foliage density, and branching (Rehacek et al., 2017). Urban spaces contain higher levels of vehicle emissions and industrial air pollution, which is a reason that greening urban landscape using agroforestry practices, helps to clean the air and filter pollutants that affect human health (Middleton and Kang, 2017). Results from experiments conducted by Bang et al. (2010) confirm the advantages of wind protection on plant growth;
We have demonstrated that plants protected against wind in natural environments, such as the Sonoran Desert, increased twofold in biomass compared to unprotected plants. Consistent with our predictions, the sheltered plants in both desert and desert remnant habitats responded similarly to plants growing in urban areas. Also consistent with our predictions, extra wind protection in urban habitats did not have any effect on plant growth, because plants there are already sheltered by the structural design of the city. (p. 3).
Vegetation directly shelters soil from the wind, acting as a form of roughness that affects sediment deposits downwind (Mayaud and Webb, 2017). It also catches windborne particles and creates eddies, breaking the wind current (Mayaud and Webb, 2017). Vegetation also provides shade from solar radiation during the day and reduces nighttime cooling effects, helping to create ecological changes in the landscape (Dooskey et al, 2017; Nabhan, 1985). Eldridge et al. (2011) report that shrubs increase belowground carbon and nitrogen, no matter the species. It has been shown that maintaining cover crops, crop residue or mulch over soil in agriculture or rangeland, protects it from wind erosion, and in the same way shrubs, grasses and trees offer this service (Middleton and Kang, 2017; UNEP et al., 2016; Opp et al., 2021). By increasing the amount of drought-resistant trees that produce fruits, nuts and oils, an increased measure for food security and counter to desertification is provided (Qureshi and Shoaib, 2017).
Two types of windbreaks (field and livestock windbreaks) are recommended for agriculture, to increase production, yield, and decrease input of fertilizers, feed, and water (Brandle et al., 2009, 2022). Usually two or more rows of tall trees are planted for field windbreaks to increase density, sometimes requiring a design of additional windbreak perpendicular to the first, to cover all seasonal winds (Brandle et al., 2022). Additional rows within large field spaces should be planted 10 – 20 H apart to optimize wind protection coverage (Brandle et al., 2022). Wind erosion can be significantly reduced when the windbreak design accounts for wind speed near the soil surface (Dosskey et al., 2017; Miri et al., 2017). Inglese et al. (2017) finds cactus to be a functional windbreak choice in agroforestry application. Studies have shown results in improved fodder and grain yields. Prickly pear can be cultivated in rows and grows in large clumps, which allows livestock to graze in a silvopasture system with rotational grazing (Inglese et al., 2017).
In China, shrub communities planted repetitively as shelterbelts have been shown to be a cost effective way of fixing sand in arid areas, by increasing ground roughness (Cui et al., 2012). Many shrubs with lower individual effects can work in a design, in addition to larger shrubs or trees with stronger effects, and could function within rangelands if not overgrazed (Cui et al., 2012). Pardyjak et al. (2007) find similar outcomes in Sonoran desert experiments with wind simulation and dust deposit on nearby surfaces. They conducted research to improve air quality near vehicle generated dust disturbance, during different times of the day. The results showed that the canopy height had more effect on dust deposit, than adding multiple rows of artificial windbreaks. With limitations on projects such as financial, water availability, and the amount of land needed to be covered, this was a positive outcome.
Fences have been used as a cost effective measure in deserts to reduce sand deposition and wind erosion (Middleton and Kang, 2017). The only cost is in manufacturing, establishing and maintaining the fence, unlike living organisms that rely on water sources, etc. and are affected by climate conditions, requiring continual inputs and maintenance. The materials usually used in engineering a fence are, concrete, metal, plastic, wood, and stone (Middleton and Kang, 2017). Porosity and height determine the ability to trap sands and reduce wind effects (Middleton and Kang, 2017). Fences can also be made of living vegetation as in vines and shrubs.
Alghamadi and Al-Kahtani (2005) study sand drift and fence structures as a way to limit sand encroachment. Installing the fence perpendicular to the wind direction, causes sand to be deposited directly leeward (forward) of the fence (Alghamadi and Al-Kahtani, 2005; Middleton and Kang, 2017). The airstream pressure drops at the height of the fence and causes sand deposition forward. This technology has been used in areas of sand dune formation, transportation routes, and near habitation structures (Alghamadi and Al-Kahtani, 2005; Middleton and Kang, 2017).
Bruno et al. (2018) reviews studies of porous fence types, which have been in scientific literature since the 20th century. They have been used to control snow and sand in aerodynamic studies, however limited studies have been done with solid wall structures. This article suggests more research on the use of wall structures, understanding that constructing and using them can be cost prohibitive, as well as the overall gains in protection can vary depending on unique climate areas. Brandle et al. (2022) state that a solid barrier wall has 100% density. Proposed identification system for windbreaks: ‘layer system’; natural (sand crusting), oil-based, chemicals, ‘hedge system’; checkerboard and line-like obstacles using stones, straw, dried grasses, artificial vegetation, and live vegetation, ‘surface-like’; solid barriers like walls made of concrete, and porous fences (Bruno et al., 2018).
8.3 Non-Living Windbreaks, Current and Future Trends
Non-living plant windbreaks are useful in places of intense sand drift and in places where irrigation is not possible, area size to be covered is monumental, and with financial constraints (Opp et al, 2021). There are many designs that have proven, positive results around the world. Establishing areas or fields of ‘sand catchers’ by designing landscape barriers of straw, dead branches, dead plants, or stones, increases surface roughness and presents an obstacle that retains surface particles at lower wind velocity (Opp et al., 2021). Bruno et al. (2018) discusses the structure of these low surface windbreaks. Engineering an area in a grid pattern, or ‘checkerboard solution’ is the most widely adopted hedge system, tested first in China as constructed along the railway area in 1950 (Bruno et al., 2018). The pattern is designed in perpendicular orientation to the wind direction, fanning out in a matrix (Bruno et al., 2018). The non-living material is buried half way into the sand, and other half exposed to create roughness on the surface (Bruno et al., 2018).
Solutions for optimal design of non-living plant windbreaks for erosion control in arid and semi-arid environments, are still under research and experimentation stage (Pan et al., 2021). New polymerized anti-aging compound is used to make simulated shrubs based on the shape of Nitraria tangutorum, a low coverage shrub in the Ulan Buh Desert, in Mongolia and China (Pan et al., 2021). The polymer is an engineered wind-resistant material, currently under trial use in wind tunnel experiments in China (Pan et al., 2021). The results for optimal design of a non-living plant windbreak to control wind erosion at low surface height, so far show that “…hemisphere-shaped windbreaks should be applied as near-surface barriers, and the windbreaks of broom-shaped and spindle-shaped can be used as shelterbelts above the near-surface” (Pan et al., 2021, p. 10). Various polymer constructed foliage used in wind tunnel experiments, and shape configurations.
9. Southwest Desert Agriculture
Desert agriculture in the Southwest US has challenges and opportunities unique to the landscape, ecosystems, and cultural heritage. Nabhan et al. (2020) defines arid-adapted agriculture in what they term ‘Aridamerica’, “… as a low-input farming system dominated by desert-adapted perennial plants (including succulents) and their soil microbes that produce higher and more reliable crop yields with less water than can most conventional annual crops” (p. 3). The challenges of growing plants for food, materials and fodder are ongoing in Africa, the Arabian Peninsula, and parts of Asia in particular, but the United States also has issues in these areas, despite technological advances in agriculture. Ribeiro-Barros et al. (2017) cite estimates that by the year 2050, food production needs to increase by 60% or more to feed the global population. Arid and semi-arid lands will need to be productive by using water harvesting and new advances in technology, to increase yield in those regions (Ribeiro-Barros et al., 2017).
Sandor and Homburg (2015) propose strategies focusing on watershed ecosystems of the southwest, capturing water resources on the land (water harvesting) to improve moisture levels and soil nutrient composition, working with small private landowners. As an example of a multi-story agroecosystem design from Nabhan et al. (2020), desert legume trees (mesquite) form the highest canopy, in which the understory is composed of cacti, herbaceous perennials and annuals, using active and passive rainwater harvesting. Biopolymer soil treatment could be another possible irrigation technique, improving germination and soil water retention of the soil layer (Chang et al., 2015). In a multistory agroforestry design, leaf fall, root decay and biomass is increased, producing higher fertility with trees and interconnected biological processes (Qureshi and Shoaib, 2017).
9.1 Alley Cropping
Alley cropping is another way to produce many benefits in agricultural, economic and environmental services. Two or more crops are cultivated which can have a mutually beneficial effect on growth, reduction in pests, conservation of moisture, increase biodiversity, attract pollinators, improve land fertility, while acting as a windbreak (Inglese et al., 2017; Garrett et al., 2022). Cactus as a native plant can be utilized in alley cropping as well as being a productive biomass generator, accumulating nutrient deposits from SDS and runoff (Inglese et al., 2017). Usually planted in hedgerows because of low-input costs and ease of management for pest control, cactus absorbs solar radiation on a large scale and has higher productivity (Inglese et al., 2017). Acacia, being a native legume tree of the southwest (Ribeiro‐Barros et al., 2017) would fit nicely in an alley cropping system, as would mesquite, helping fix nitrogen for crop production. Using a no-till system in alley cropping would control erosion, leaving the soil covered creating roughness, and store nutrients and moisture in the topsoil (Middleton and Kang, 2017).
Sustainable food production systems benefit from farming cactus along with livestock, as it helps in rangeland management by making fodder available with a high water content (90%), and in alley cropping systems (Makkar, 2017). Cactus needs to be fed along with other food sources, such as hay, grasses, etc., as it can produce diarrhea in ruminants, and lacks nitrogen. Makkar (2017) cites studies of cactus added to animal diets;
Studies that replaced 12, 25, 38 and 51% of cracked corn and Cynodon hay by cactus in the diets of dairy cattle showed that cactus can totally replace cracked corn and partially replace the hay (ca 40%) without any significant effect on milk production (ca 20 litres per day). When cladodes are fed to sheep or cattle with a protein-rich feedstuff, they may replace barley grains or maize silage without affecting body weight gains of the animals. (p. 5).
9.2 Current Research of Native Plants
Two current research projects at Utah State University, utilize native species of both the southwest peach and pinyon pine. The importance of these projects to utilize what already thrives within the local desert ecosystem, has potential to build a more resilient food system and incorporate this agroforestry practice in a mixed cropping design.
Reagan Wytsalucy’s work with Indigenous peoples of the Southwest, explores an important new crop within traditional food practices that can be developed to help improve areas of desert for food production in a multi-tiered system. The southwest peach, or Navajo Mountain fruit, is a peach tree introduced by the Spanish. They are now propagated by seed and grow into a multi-stemmed shrub. When nutrition analysis was performed, comparing the southwest peach to a standard USDA yellow peach, the southwest peach was higher in calories, calcium, fiber, carbohydrates and total fat. It was lower in protein and fatty acids, with no apparent difference in total minerals or sugars. When irrigated or watered, the peach takes up more water when available, and recovers at a faster rate, which makes it more drought tolerant than other species. With this understanding, the southwest peach could work within an agroforestry orchard system (Southwest Agroforestry Action Network, 2020).
Dr. Sun heads up the Pinyon Pine orchard project for nut production at the university. There are two species of native pinyon pine, Pinus edulis and Pinus monophylla which are being studied in an ongoing project, to develop cultivars that produce good quality nuts in a faster time frame. Using Pinus monophylla grafted onto the faster growing Pinus edulis root stock takes time, however they have had success with this method. The US imports 23% of all exported pine nuts worldwide, while native pine nuts sell for $40/lb. unshelled in New Mexico. The market exists in the US, and with grafted trees, could expand in production and quality in the future (Southwest Agroforestry Action Network, 2020).
Dr. Bainbridge’s work with the mesquite tree is especially important, highlighting the development of its deep root system, which makes mesquite an ideal native plant to use in arid areas, as it is drought resistant. Mesquite tree products are food (pods) including bean flour, wood, charcoal, honey (pollination), alcohol, smoke wood, and having medicinal properties. Services are windbreak, shade and shelter for livestock, dust control, ground water management and carbon sequestration. At 4 -6 meters down, is where nitrogen is fixed and where the most myrochozial roots exist. Mesquite forms compound leaves, which slow wind and capture sand and dust. They form mounds known as ‘nebka’ in sand, and are ecologically important but increasingly lost to development and off road activity. The tap root grows quickly, while the leaves remain small, with a root/shoot ratio 5:1. If there is groundwater roots will go down 20 – 30 feet, however they have been found at 46 meters if arid conditions. Ecological importance: habitat and food, moisture, biodiversity, nitrogen fixation, organic matter. (Southwest Agroforestry Action Network, January 12, 2021)
Scientific studies on O. ficus-indica L. (prickly pear) have been increasing worldwide, as evidenced at 123% increase in literature between years 2010 to 2015 (Bravo et al., 2016). It has potential phytochemical health benefits and many nutrients (Bravo et al., 2016). “In the Sonoran Desert, prickly pear (Opuntia) fruit are already harvested on large-scale and processed into syrups, jellies, candies, and probiotic fermented beverages” (Nabhan & Mabry, 2016; as cited in Nabhan, 2020, p. 9). Some of the human health benefits of cactus are listed.
9.3 Indigenous Farming Practices
Archaeological studies of the Southwest have found Native Peoples farming the desert lands for thousands of years, which can add to our current knowledge when designing and implementing an agroforestry project. With the aid of modern technology such as ‘Groasis’ (Groasis Ecological Water Saving Technolog, 2018), solar panels, etc., we can work with traditional knowledge creating a mosaic of agroforestry adoption. Gary Nabhan (Southwest Agroforestry Action Network, October 6, 2021) declares that arid North America is the laboratory of food production for the future. Nabhan states that, “Literally hundreds of our domesticated annual crops are now reaching their thermal thresholds in the kind of conditions we are regularly facing.” One strategy is to develop wild plants that have high desirable food value and heat adaption. “We constructed a list of candidate crops based on the diets of the Comcaac, O’odham, and Pima Bajo peoples of the Sonoran Desert. …over a third of which are water-use efficient crassulacean acid metabolism (CAM) succulents” (Nabhan et al., 2020, p. 627). Research needs to be directed to grow these crops with stable yields, as the antioxidants they contain, will help humans handle heat stress when eaten, as they mitigate dehydration.
In the University of Arizona lab, desert nurse plant guilds/models are being tested and planted out in arid environments (Southwest Agroforestry Action Network, October 6, 2021). The model consists of an overstory legume plant, with understory cacti and berry producing shrubs. Researching agrivoltaic perennial polycultures within desert environments for simultaneous energy and food production, positive outcomes were found in better working environments, and more efficient use of solar panels with green microclimate (Southwest Agroforestry Action Network, October 6, 2021). Nabhan et al. (2020) outline an optimal plan for arid food systems:
Biomimicry and traditional knowledge can aid in designing co-located food, water, and energy provisioning systems adapted to arid climates and scarce resources that improve agroecological and human health. Adopting such designs will require transdisciplinary integration of plant, environmental, social, and health sciences. (p. 628).
Native Peoples have used agricultural production systems based on natural ecosystems, passed on through generations of experience (Coleman et al., 2022; Sharma, 2014; Johnson et al., 2021). These systems have sustained agriculture production throughout drought periods, using water harvesting technology like locating fields near rocky outcrops where seasonal rains drain, and are channeled to the field (Johnson et al., 2021; Sandor and Homburg, 2015; Nabhan, 1985). Hopi farmers leave corn stalks in the field after harvest, which serves as guides to plant next year’s crop between the rows, using their own heritage seeds (Johnson et al., 2021). The corn stalks also catch snow and function as windbreaks for new corn seedlings, planted counter to wind direction (Johnson et al., 2021). Sandor and Homburg (2015) point out where research into native crops can increase scientific information that may help commercialized crops in heated environments. Zuni blue maize exhibits higher mycorrhizal fungi rates, possibly linked to soils, than hybrid corn has, which may give an advantage in arid climates (Sandor and Homburg, 2015). There is also an interesting question of crop and animal interaction in using a silvopasture approach, as Native Peoples did not use manure for fertilizer, as animals were not farmed (Sandor and Homburg, 2015).
Hopi agriculture is a holistic natural resource management system, which reflects the Hopi philosophical life approach for balance and service in nature (Johnson et al., 2021). Dr. Michael Kotutwa Johnson, a member of the Hopi people, discusses his indigenous culture’s agricultural practices:
Over time we’ve developed drought-tolerant varieties of beans — lima beans, tepary beans, string beans — and more than 21 different varieties of corn. This has helped us weather droughts. …Because our agricultural system is so old, we’re used to things like droughts and crop loss. We have psychological ways to overcome those challenges. The other thing is we don’t have a lot of money invested, so we don’t panic as much as other farmers. We don’t pay for the rain. We don’t put money into infrastructure. We manage with what we have (Kuzdas, 2019).
9.4 Date Palm in Agroforestry
Date Palm, although not a native species to North America, could be a good addition to agroforestry in arid American lands. In the US, California is the largest date producer, and smaller farms exist in Arizona, Texas, southern Utah, and Nevada (Agricultural Marketing Resource Center, 2021). “Date palm is traditionally found and cultivated in hot and dry areas of Southwest Asia and North Africa on large scale” (Younas et al., 2020, p. 1). “There are currently over 100 million date trees cultivated globally, most of which are in the Middle East (approximately 90%)” (Al-Shwyeh, 2019, p. 1). It is a low-cost food and can be used to overcome hunger and food insecurity (Younas et al., 2020). Fruiting begins at 5 years and plants are cultivated from the root system or suckers (Al-Alawi et al., 2017) (Figure 1). The trees can grow in clumps if not managed (Al-Alawi et al., 2017). Impressive characteristics which make date palm a good choice for increased agricultural production, are longevity and production over time, arid adaptation, and growing global market (Agricultural Marketing Resource Center, 2021; Younas et al., 2020). Trees can live for 80-100 years, and produce fruit 40-50 years (Agricultural Marketing Resource Center, 2021), even up to 60 years depending on the variety (Al-Alawi et al., 2017). Robust yield per tree is 400-600 kg/tree/year according to (Al-Alawi et al., 2017).
Establishing date palm plantation in AlUla, Saudi Arabia (author’s photo, 2021)
Dates have many nutritional health benefits for humans and livestock. In the US there is a growing demand for date products because of growing consumer awareness and education (Agricultural Marketing Resource Center, 2021). The nutritional benefits of dates are many; rich in carbohydrates, fatty acids, proteins, minerals (calcium, potassium, magnesium and phosphorus), vitamin B complex, Vitamin A, and dietary fiber (Al-Alawi et al., 2017; Younas et al., 2020; Qadir et al., 2020; Al-Shwyeh, 2019). According to Younas et al. (2020) dates are an excellent iron source, and supply almost 100% of RDI, dependent on the fruit maturation stage. They are also a good source of phytochemicals that have antioxidant potential, such as polyphenols and carotenoids, tannins and sterols (Al-Alawi et al., 2017; Qadir et al., 2020; Al-Shwyeh, 2019). They have potential benefits for treatment of diabetes in low amounts, as they have a low to medium glycemic value (Younas et al, 2020; Agricultural Marketing Resource Center, 2021). Dietary fiber in dates can be connected with heart protection by helping to minimize cholesterol absorption in the intestine (Younas et al., 2020).
In traditional oasis farming, fodder, vegetables and some fruit trees are the main crops (Faci, 2019). Date palms are the upper strata, below which grow trees and shrubs, and lower strata crops such as fodder and vegetables (Faci, 2019). Date palms enhance the soil with organic matter and create a microclimate for more shade tolerant crops and livestock (Faci, 2019). In arid agroforestry it is possible to have mixed species of trees within date palm farms, such as citrus trees like orange and lemon. In Saudi Arabia, torounge, a hybrid cross between lemon and pomelo, is grown within date palm stands to diversify income, as irrigation must be provided for date palm and citrus production (Royal Commission for AlUla, 2021) (Figure 2). Silvopasture area is an added benefit of maintaining a date palm plantation, as animals like sheep, goats, and chickens take advantage of fodder production and recycle nutrients to the soil to fertilize the trees (Figure 3).
Young date palm farm with other tree species, AlUla, Saudi Arabia (author’s photo, 2021)
Farmer with goats and sheep in silvopasture area of date palm plantation, AlUla, Saudi Arabia (author’s photo, 2021)
Value-added products are plentiful for date palm fruit. Date palms produce date syrup, date juice, candies and sweets, confectionery, date sugar, drink products such as vinegar, wine and alcohol, and is a substitute for honey, maple syrup, and molasses (Younas et al., 2020; Qadir et al.2020; Agricultural Marketing Resource Center, 2021). “Currently, date seeds have also been used for the manufacturing of caffeine-free coffee; previously prepared by Arabs as a substitute for regular caffeinated coffee” (Younas et al., 2020, p. 6). In addition, damaged or unsaleable fruits can be used as an additional feed source for livestock, or as a supplement in the livestock feed industry. Younas et al. (2020) present research conducted in Saudi Arabia on improving sheep weight gain. “The results of the study suggest that it is economically feasible to feed lambs with 20% of low-quality date flesh for obtaining the desired well-being of animal without any adverse effects” (Younas et al., 2020, p. 6).
10. Positive Dust Outcomes
Positive outcomes from dust storms and sand transportation are naturally part of how the earth rejuvenates areas of the ocean and other depositions on land. When dust is deposited on the surface of ocean water, it adds phosphorus, which works in nitrogen and iron fixation to augment phytoplankton growth, which affects the carbon cycle (UNEP et al., 2016; WMO, 2019). Dust also positively affects precipitation levels by becoming an agent for droplets to form (UNEP et al., 2016). Terrestrial ecosystems, whether wet or dry climates, also benefit from the nutrients, especially phosphorus, that are vital to ecosystem cycling (UNEP et al., 2016; Lindsay et al., 2017; WMO, 2019). Data sets show that eroding mountain areas in temperate regions are somewhat reliant on dust deposits to strengthen their soil composition and ecosystem even though erosion occurs (Lindsay et al., 2017). Effects of dust on land ecosystems has positive and negative effects, both in source and deposit areas, for environment, ecosystems, human health and infrastructure (Opp et al., 2021). The cycle of dust transport is interconnected with natural atmospheric conditions, such as radiation, climate, ocean temperature, and ice cover (Opp et al., 2021).
10.1 SDS Decreasing in Future
Predicting future sand and dust storms is a science endeavor for NASA. Using computer models and information from global satellite images, a NASA research team used a model system based on data collected, compared to what they believe the atmosphere was like in the past. “The peak of Saharan dust transport to the eastern side of the Americas took place roughly between 12,000 to 17,000 years ago, at the end of the last Ice Age” (Streiff, 2021). As a result of climate change and increased temperature, NASA predicts that over the next 100 years, the dust clouds that occur in Africa will decrease to a 20,000-year minimum, and within the next 20 – 50 years, a 30% decline in activity (Streiff, 2021). From what we know about sand and dust deposits being vital to ocean and terrestrial ecosystem nutrient cycling, is the slowing down of sand and dust storms a mixed blessing? Dust from Asian sources has been studied in the US, both for the supply of beneficial plant nutrients and poor air quality effects (Middleton and Kang, 2017).
The trend in near-surface wind speeds in recent decades, has reported declines in the tropics and mid-latitudes both north and south of the equator. Higher wind speeds however are reported in latitudes greater than 70 degrees (UNEP et al., 2016). Streiff (2021) discusses the atmospheric cycle of dust;
Less dust in the air, which can reflect sunshine away from Earth’s surface like a sunshield, means more sunlight and heat reach the ocean, warming it further. All together this creates a feedback loop of warm sea surface temperatures leading to reduced dust, and reduced dust in turn contributing to additional warming, combining to impact climate, air quality, and storm and hurricane formation.
11. Foreign Countries
Agroforestry to mitigate SDS, climate change and desertification are happening on a global scale. Just a brief look at what some countries are doing in their regions of concern. This is not a comprehensive list, but is interesting as a comparison for further programs within the United States.
China: China’s rehabilitation of degraded drylands project Three Norths Forest Shelterbelt or Great Green Wall, has been developing for 40 years, and is ongoing for the long term, until completion in 2050 (Middleton and Kang, 2017). According to Officer (2021b) this project began as the Tarim Desert Highway Shelterbelt, built in the Taklamakan desert, between 1993 and 1995 to access large oil reserves. The history of sand engineering began first as a “sand catching checkerboard of straw”, followed by a single species shelterbelt that bordered the road, built under Three North Shelterbelt Program. Later additions in 2001 of more plant species, included two million rose willows, sacsaoul and buckthorn (Officer, 2021b).
There has been time to study both benefits and challenges throughout the years. “…a decade of experiments that showed that trees with small leaves and a maximum height of two meters proved the most suitable for life in the desert as they lose moisture slowly and are resistant to arid conditions” (Officer, 2021b). In planting “an area close to the size of Ireland in tree seedlings every year” (Wang and D’Odorico, 2019, p.1), some non-native species need more water, in which afforestation has caused a reduced flow in river and groundwater recharge rate. This unintended consequence impacts human water use and creates shortages (Wang and D’Odorico, 2019).
Pan et al. (2021) discusses how China has employed other forms of wind barriers that do not compete with water resources and are low cost. In engineering sand prevention projects for railway and transportation sectors, upright fences are made using bunches or reeds in the Taklimakan Desert. This is effective in preventing shifting sands from burying roads, by slowing down the air flow, in which the flow over the top of the barrier is accelerated so sand will deposit further out. Mobile sand dunes are a huge threat to villages, farmlands and infrastructure (Cui et al., 2012).
UNEP et al. (2016) reports on the Kubuqi Desert region of China, and the ecological restoration begun in the 1980’s to protect roads and infrastructure. A grid pattern of fences of straw, and shrubs bundled together were designed for sand control. The plants used were grasses and trees of Salix (willow), pea shrub and desert willow. The shelterbelt is 4 km wide. The challenge of growing trees, grasses and shrubs in such a large arid area, is water resources. A new innovation at the time was water jetting, which sped planting by creating a deep hole with a burst of water. This made irrigation possible and brought the survival rate up to 85% from 20%. A medicinal herbal enterprise was founded upon the mixed species forests and shelter belts. This transdisciplinary effort included governmental policies favoring private and community involvement, and stakeholder Elion Group, that incorporated business, ecological improvement and investment, where innovation and learning were keys to success (UNEP et al., 2016).
African Sahel: UNEP et al. (2016) reports on a similar measure in the Sahel region of Africa, called the Great Green Wall project. With the World Bank’s support, agroforestry practices using trees, grasses and shrubs will run along the southern boundary of the Sahara Desert. The goal is to grow a green belt 15 km wide from Dakar to Djibouti that will reinvigorate the soil, to teach sustainable land management practices to farmers, and produce food. One major goal is to prevent dryland degradation. In the West Africa Sahel, agroforestry is practiced using Faidherbia albida and Vitellaria paradoxa (shea) trees, both in agricultural settings and in silvopasture. These trees have an economic value for fuelwood and fodder. Sorghum and millet are interplanted, under 15 trees per hectare, and livestock can be fed the residues, which puts fertilizer back into the soil. This agroforestry practice reduces wind speed, soil erosion, fertilizes land, and supports social and economic goals.
Ikazaki (2015) presents a new wind erosion mitigation technique called “the fallow band system”. It was designed to overcome resistance to adoption of proven techniques by local farmers in the Sahel region, such as ridging, mulching fields, and planting windbreaks. The new system is low-input, requiring no cash input and minimal labor. The fallow band system uses fallow bands of earth (not seeded or weeded, so naturally occurring herbaceous cover), 5 m wide within the cultivated land, created at a right angle to sandstorm winds (easterly). These bands capture aeolian topsoil from dust storms that supply nutrients, preventing erosion even after the harvest of the field. The next rainy season, the fallow band is planted for that year’s crop, having acquired nutrients to improve yield, and a new fallow band is then created upwind (east) of the former area. The study suggests cowpea as a nitrogen fixer because it is drought and heat resistant for the area. This system works to utilize and take advantage of the natural cycle of sand storms/dust storms, without too much effort in resource poor areas.
Rosenstock et al. (2019) cites progress in the political climates of Sub-Saharan Africa, in favor of supporting nature-based solutions, agroecology, and climate-smart agriculture, which all promote agroforestry. Different systems for different areas in Africa, illustrate how agroforestry can fit case by case, farmer to farmer, depending on what needs are to be met, socially, economically, environmentally, and culturally.
Sudan: McNeish (2016) reports on new efforts in Sudanthat incorporate green technology in the energy sector that benefit agricultural production. Water pumps powered by solar energy allow for people to plant a wider variety of crops, not only relying on precipitation. Small nurseries grow tree seedlings which are planted around homes and fields as wind and sand protection, made possible by the new irrigation. Butane gas introduction has also altered the need to cut down trees, which people now know have a role in protecting and working with their farm environments.
Arabian Peninsula: Belgacem et al. (2017) reports that the Arabian Peninsula is one of the driest subcontinents in the world, with annual rainfall between 30 mm to 150 mm. This produces a severe water deficit throughout the year. Most of the countries are hyper-arid, the driest country being Oman with 62 mm/year on average. Belgacem et al. (2017) discuss the importance of using greywater and desalination in arid environments.
As reported by FAO in 2010, the Arabian Peninsula countries are the most advanced regarding non-conventional sources of water: desalinated water represents 8 percent and reused treated wastewater 2 percent of the total water withdrawal. Saudi Arabia and the United Arab Emirates account for 32% and 29% respectively of the use of desalinated water in the Middle East region. (p. 3).
Egypt also uses treated wastewater to irrigate new vegetation as a measure to conserve water resources (Middleton and Kang, 2017).
UNEP et al. (2016) reports on Kuwait and efforts to plant green belts with native Prosopis and Tamarix species. In two tested areas, “…dust deposition was 40% to 76% less in downwind areas than in upwind areas. Farm areas reduced deposition by 88%. Green belts reduced dust by 26%.” The positive results from agroforestry practices and managed farmland, recommend further implementation of green belts with native vegetation, and sustainable managed farms to mitigate dust problems.
Iran: Khojasteh and Asumadu-Sakyi (2021) report on a study of ridging technique used in Iran. Creating surface roughness to combat soil erosion and desertification has been one of the ways to mitigate these problems. Two-thirds of Iran’s surface area is easily eroded by wind, as the soil is loose and lacking moisture. Salt flats and desert make up 39% total land area. Over the last decade many techniques to manage dust storms and wind erosion have been tested. These include mulches, inorganic and organic polymers, and clay minerals, but the surface they produced was too stiff to allow plant propagation. The ridging device that the research team designed, needs further testing in actual landscape conditions, but the goal is to plant native species between the ridges, that would slow wind speed and capture aeolian deposits. Middleton and Kang (2017) also report that oil mulch is very effective as a sand stabilizer spray for the ground, and effectively helps seed germination in sand in Iran.
Belgacem et al. (2017) discuss the introduction of cactus Opuntia spp., which is spineless, to the Arabian Peninsula. Based on the success of this plant being farmed in North Africa through ICARDA, the Arabian Peninsula has similar environmental and food production needs which can be addressed by cactus. Cactus is drought-resistant and is a good source of water for livestock, and fruit production for human needs. It is an excellent alternative forage crop for pasture and rangeland improvement, and in a silvopasture system. Nurseries have been created in UAE, Qatar, Saudi Arabia and Yemen. Cactus is a good source of water, vitamin A and calcium (Belgacem et al., 2017).
Israel: Officer (2021a) reports on Israel’sprogress to combat erosion and desertification. In the 1950’s the World Bank helped fund a ravine project, whereby rainstorm flooding in the desert was diverted to ravines that were planted. In the natural landscape the ravines would erode. By manipulating the slope, depth and edges of the ravine areas using heavy machinery, flood water was caught and produced an area where trees could grow. The micro climates then created areas of biodiversity and reduction in soil erosion, mitigating desertification.
Korea: “The Republic of Korea has been much affected by dust blown from neighbouring countries and in response has developed the first Master Plan for Asian Dust Damage Prevention (2008-2012)” (UNEP et al., 2016).
According to Sharma (2014) not all technologies from one area of the world, work as well in another place. For example in India, using tractors for improvement in agriculture had a negative effect on regeneration of native Prosopis cineraria trees, increasing wind erosion. Some non-native plant additions have caused problems in decreased biodiversity, which is one factor in increasing desertification and fragmented ecosystems in arid zone agroforestry. It is a lesson in planning holistically and specifically regarding natural ecology in a landscape.
12.1 Policy and Funding
According to Griscom et al. (2017) Natural Climate Solutions (NCS) like agroforestry and other land-based sequestration efforts, have shown large potential for climate mitigation, however they are underfunded at only 2.5%, of all monies put toward solutions to climate change. Governmental and regional policies need to put priority on environmental issues and favor sustainable farming practices (agroforestry, cover crops, etc.), and apply these to commercial production, as well as native and perennial crops that are adapted regionally. “Shifting from input-intensive conventional agriculture to regenerative, arid-adapted agroecosystem designs has the potential to improve biodiversity and food security while promoting rural livelihoods” (Nabhan et al., 2020, p. 636).
Investment in research of Southwestern agriculture should be a priority in the United States. Research focus is to better understand soil biology, advance soil health, improve human impact, and food production for food security. Working knowledge of past indigenous systems, as well as current traditional ecological knowledge (TEK), and how they function with soil health, can help further research for more resilient soil production, by understanding nutrient cycling, nutrients in water runoff, biological crusts, animal interactions within agricultural Southwest systems, nitrogen-fixing wild plants and legumes, and underground root and mycorrhizae interactions. An example for further research is exploration of indigenous corn physiology, genetics, and environment studies. As most of the scientific literature is based on modern corn cultivars and mono-cropping, more testing and observational data need to be performed with indigenous corn varieties (Sandor and Homburg, 2015). The research findings may provide new answers in genetic adaptability to drought and heat conditions that could benefit commercial corn cultivars.
We need to develop nature-based, sustainable food systems that are more reliable in yield, and more adaptable in climate change, by using agroforestry products like nuts, fruits, berries, and leaves to address food security. Agroforestry with fruit trees and nut species will have more impact on human nutrition in the future, as going forward nuts are high in fats and protein, have positive effects on diet-related diseases, and are a healthier source of protein than animal meat sources (Rosenstock et al., 2019; Nabhan et al., 2020). Ribeiro-Barros et al. (2017) also advocate for more research in systems biology for perennial plants, as the focus has been mainly on annual crops. Discoveries in new bio-compounds could help the medical industry, as well as developing heat tolerant or drought tolerant crops, and disease and pest control (Ribeiro-Barros et al., 2017; Goldstein and Oken, 2021). Plant breeding is one tool to further advance resiliency in our food system for heat, water scarcity, drought, salinity and yield (Dosskey et al., 2017). Goldstein and Oken (2021) discuss the need for investments in technology for plant-based food products, research in alternative protein sources from plants, and high-tech farming approaches using GIS, sensors and monitors, hydroponics and aquaculture.
According to Kole et al. (2015) research and funding for technological advances in genomics, could increase biological capacity to handle heat, drought, and climate change through genetic diversity and plant breeding, while sustaining or increasing yield. Domestication of crops with a monoculture focus, and agricultural yield intensification due to the Green Revolution, have reduced genetic variability in staple crops worldwide, and affected pest, fertilizer and herbicide applications (Kole et al., 2015). An expansion in use of minor and specialty crops known to specific regions, possessing more dynamic nutritional function, can help in food security going forward with climate, disease and pest challenges (Kole et al., 2015). The science of genomics and plant breeding can further adoption of crops in hot environments, finding DNA markers for heat adaptation during the flowering and reproductive phase (Kole et al., 2015).
Ziegler et al. (2016) calls for the development of diverse markets and easier incorporation for carbon sequestration services, provided by agroforestry practices on farms. Ziegler et al. (2016) believes there is a need for guidelines and models for windbreaks, not based on forest models for carbon sequestration, as windbreaks can be multispecies, including native arid plants. Windbreaks, recognized by the U.S. Department of Agriculture Conservation Planning, as one tool for reducing soil erosion, need their own set of guidelines for how carbon is sequestered by species and region, making it easier for landowners and policy makers to access the environmental service (Ziegler et al., 2016). Farmers and land managers need to be compensated for working to reduce erosion, decrease pollutants and non-point source pollution, clean water, carbon sequestration and biodiversity growth (Lal, 2001).
Addressing issues with the USDA Natural Resource Conservation Service (NRCS) cost-share programs that could benefit Native American farmers, Johnson et al. (2021) points to problems within the application process, and low award percentages for Native American farmers in proportion to farms that could qualify. Johnson et al. (2021) identifies potential for program expansion under government programs such as NRCS, for indigenous conservation practices. Even though Indigenous conservation practices align with the goals of the NRCS, they are not fully recognized to qualify for EQIP and CSP contracts, which leaves farmers out (Johnson et al., 2021).
Reservation land in the Southwest makes up a significant portion of agriculturally available areas. According to Murphree (2017) the USDA Census of Agriculture, taken every 5 years, shows an increase in the percentage of farm acres in Arizona alone, due to ranches and subsistence farms on tribal lands being accounted for. In Arizona, out of the 20 American Indian nations, the Navajo Nation is the largest reservation in the US (17 million acres), and includes Utah and New Mexico areas, as mostly pasture land (Murphree, 2017). “Despite selling more than $92 million worth of agricultural products, 69% of the Navajo Nation farms reported total sales less than $1,000” (Murphree, 2017), as they are not commercially focused like other Indigenous Peoples. A unique socioeconomic aspect of the Navajo Nation farmers, is the large presence of female operators (Murphree, 2017). “Just under 50% of all Navajo Nation farms had a principal operator who was female while in the United States, 14% of all farms had a principal operator who was female, according to the 2012 Census of Agriculture.” (Murphree, 2017)
The need for public warning systems for SDS protection, and public health advisories are an ongoing project. One safety measure initiated as a coordinated international effort, the World Meteorological Organization’s Sand and Dust Storm Warning Advisory and Assessment System (SDS-WAS), began in 2007 (WMO, 2019). This international partnership of researchers and the global community, gives countries the ability to provide transboundary sand and dust storm forecasts and observations (WMO, 2019). Long-term sustainable land management for soil protection should be a global priority (UNEP et al., 2016). The World Meteorological Congress puts priority on investing in national, regional and global plans to mitigate negative effects caused by SDS, especially soil loss. Public health is at the forefront of this global operation (WMO, 2019).
12.2 Environmental and Societal
Designing any kind of agroforestry system takes into account the landscape, and landowner desires and viability of the plan to succeed in the ecological environment (Lovell et al., 2022). One of the most important considerations in arid environments is water source. Wang and D’Ordorico (2019) argue for comprehensive water assessment tools for use in a proposed project, taking into account plant water consumption and local water availability, as projects won’t be sustainable without this consideration. Branch and Wulfmeyer (2019) address the challenge of irrigation in desert agroforestry by use of desalinated-urban-waste water, as has been used in areas of the Middle East.
Chang et al. (2015) explore the results from the study on biopolymer supplements added in arid environments. Areas of China have vast expanses of sand and shifting dunes. To counter desertification, a new technology is being employed using biological materials (i.e., biopolymers). This requires spraying the ground which can be done in largescale operations. Biopolymers are organic materials as explained below by Chang et al. (2015);
Sugar based biopolymers (polysaccharides) produced by microorganisms are widely used in food (e.g., dairy products) and medical industries. …When a soil was mixed with even a little amount of biopolymer, we found that the presence of these hydrophilic biopolymers produced interesting soil characteristics, especially relevant in terms of anti-desertification. (p. 40).
Hydrophilic biopolymers adsorb water, hold it in the soil, prevent erosion, and make water available to seedling trees and crops in afforestation projects.
Regarding solar energy generation, Das (2018) discusses the difficulties of cleaning and maintaining solar panels, encountered in arid, dusty environments. Usually they require using deionized water due to little precipitation, however that is a drain on water sources (Das, 2018). New technology that could be utilized in places like Nevada, where solar plants may be a major option for power, involves generating an electrostatic current that would repulse dust particles on the panel, saving water inputs (Das, 2018).
Nabhan et al. (2020) provides examples of agroforestry practices incorporating solar panel systems for shade during the summer, and insulation during winter for warmer soil temperature, as well as sustainable energy production. To expand solar fields, this new technology would make these projects more cost-effective and environmentally friendly.
Investing in eco-tourism can be beneficial economically as well as environmentally, as it will bring awareness to areas with potential, for sustainability, aesthetics, agricultural production, and cultural heritage education (Sharma, 2014). Southwestern areas have large open spaces and spectacular beauty, diversity, and many parklands. Eco-tourism opportunities can be expanded and are important financially to the local economies, however working with knowledge of ALAN and its possible effects at nighttime in a desert ecosystem (Correa-Cano et al., 2018) will have to be investigated further.
Focusing on social capital as a driver in achieving larger impacts, Middleton and Kang (2017) highlight the necessity of engaging farmers in conservation efforts as active participants, not just adopting technology. The goal is to have economic, environmental and social benefits that reach beyond the focus of one landowner or property, and branch out to connect communities and regions.
Agroforestry practices provide many opportunities to balance land, livelihood, food production, food security, environmental health, soil health, sustain ecological functions and improve biodiversity, done in culturally appropriate ways. The Southwestern area of the US is experiencing what other arid and semi-arid, high desert areas around the world are. We don’t need to go to exotic places to see the effects of sand and dust storm damage in vegetation, agriculture, and health costs. Desertification is a current problem that we must have answers for, as topsoil layers are lost and redeposited elsewhere. Water scarcity along with rising heat indexes make the fear of drought conditions in the southwestern areas especially concerning.
As discussed within this paper, there are many good examples of systems that have been implemented around the world, to combat these above problems. We can learn from them and adopt what can work in the United States. As well we are in a unique position of employing and cultivating native plants that are adapted to heat stressed desert areas. For examples we have the mesquite tree, pinyon pine, southwest peach, and cactus Cactaceae family. Increasing markets to make larger scale production possible for such plant resources, need to happen both in researching nutrient qualities, and genomics for heat and drought adapted crop applications, and in education and knowledge dissemination to the general public to increase demand and supply. There is opportunity for new agroforestry systems involving cactus and date palms in both alley cropping and silvopasture systems.
With human population growing outside urban centers, and as land development competes for arable land, agroforestry positively addresses issues of food security along with greening spaces in urban food forests. The fact that Native Peoples have farmed arid agriculture systems for many generations, means we can learn from their knowledge and share new ways to adapt technology and native perennial crops. Sand and dust storms will persist for a while, however if we consider all the opportunities in agroforestry, the hope is that we can make plants bloom where they are planted.
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