Section Summary

Contrary to popular belief, trees and other woody perennials are an integral part of drylands, and are essential for maintaining ecosystem stability, resilience and biodiversity. Multiple studies document examples in recent history of environmental collapses caused by deforestation in drylands. Trees evaporate less water than they safeguard by improving soil hydrology, by providing soil litter cover and shade, and by dissipating heat into the atmosphere. As a consequence, more water remains stored in the soil and in the groundwater reserves of wooded dryland areas, and there is less runoff and evaporation. Thus, appropriate dryland tree species transform their own environment into highly fertile oases amidst otherwise barren landscapes. Dryland fruit and fodder trees are ideally suited for rehabilitation of degraded drylands, while restoring permanent, sustainable production potentials for fruit, fodder and biomass.

Project Wadi Attir has begun rehabilitating eroding degraded slopes by establishing agroforestry and permaculture systems in order to provide a wide range of goods and ecosystem services. Such plantations contribute to soil improvement and watershed protection, carbon sequestration and biodiversity conservation. Properly planned and maintained, such agroforestry plantations will evolve into true permaculture systems that require little care and input while providing a sustainable year-round supply of fruit, food, fodder, woody biomass and other products and services.

Trees in Drylands

Removal of trees and dryland forests induces irreversible environmental degradation since the conditions for trees and forests to reproduce and regenerate are lost. Twenty-three hundred years ago, the philosopher Plato observed the disastrous impact of deforestation on the mountainous Greek landscape. Similar effects have been observed in other dry environments around the world, whereby civilization collapses following the destruction of woody dryland vegetation. Dryland trees are masters at surviving and proliferating under harsh desert conditions, and are ideally suited for coping with climate extremes, floods and droughts. Many species evaporate less water than they safeguard by improving the soil and soil litter cover, providing shade, and dissipating heat into the atmosphere. As a consequence, more water remains stored in the soil and in the groundwater reserves of wooded dryland areas, and there is less runoff and evaporation. Where microclimatic conditions for proliferation and survival are upheld, dryland trees can transform their own environments to highly fertile oases amidst degraded desert landscapes.

Ecosystem Services of Dryland Trees

Trees, shrubs and other woody perennials provide a wide range of benefits to the environment and man, especially in drylands where their presence assures sustainability and ecosystem resilience. These benefits are called ecosystem services. Some of these services include:

  • Carbon Sequestration into soil and biomass;
  • Recovery of nutrients from deep soil;
  • Enrichment and protection of topsoils by plant litter;
  • Prevention of wind erosion;
  • Providing shade to animals and buildings;
  • Preventing water runoff and erosion;
  • Restoring natural habitats and biodiversity;
  • Providing animal fodder during the dry season;
  • Providing biomass energy;
  • Providing high value oils and fruit for economic development;
  • Pollen for bees year-round;
  • Modulation of microclimate;
  • Altering local temperature balance and precipitation.

Dryland Fruit Trees

A wide range of dryland trees, both wild and domesticated, have had a decisive role in the development of modern civilizations. Only trees display the necessary resilience to produce fruit and wood even in times of drought, and thus continue to guarantee survival in hunter-gatherer and pastoralist societies. Examples of such miracle trees can be found all around the world, providing essential food in good and bad times, among them carob (Fig. 1), Ziziphus, Propsopis, Moringa, marula and many others. A wide range of dryland fruit tree species have also been domesticated, such as olives, grapes, figs, almonds, and various species of Ziziphus. These trees have provided essential food to dryland inhabitants for thousands of years.

 Fig. 1: Example of Carob Pods

Fig. 1: Example of Carob Pods

Dryland Agroforestry and Permaculture

The above characteristics of dryland trees provide for the creation of sustainable, resilient and productive dryland agroforestry or dryland permaculture systems. And indeed, such systems have been in use for thousands of years, including in Mediterranean olive-carob woodlands intercropped with grains, or in other Mediterranean dryland orchards featuring grapes, figs, almonds and the like, all providing high-quality fresh food and long-term, storable survival food. Though such systems are initially more labor and cost intensive than conventional agriculture, the multitude of ecosystem services provided make such approaches more favorable for future sustainable dryland agriculture, applicable to huge areas of degraded dryland. Large-scale realization will contribute decisively to global food security, as well as climate protection and mitigation. In addition, such permaculture farming methods rapidly provide additional benefits like fresh livestock fodder, while enhancing soil quality and biodiversity (Fig. 2).

 Fig. 2: High yielding permaculture-pasture restored at project Wadi Attir

Fig. 2: High yielding permaculture-pasture restored at project Wadi Attir

Edible Forests

The expression “edible forests” or “edible forest gardens” relates to the establishment of mixed permaculture or agroforestry plantations based on perennial multipurpose trees and plants. Mediterranean woodlands based on olives, pomegranates, and figs have been at the heart of agriculture and economies of ancient civilizations around the Mediterranean Sea, and Project Wadi Attir has sought to replicate this example. The project is currently demonstrating this approach in a variety of layouts, with mixtures of Mediterranean and other dryland fruit and crop trees intercropped with other native trees for enhanced resilience and biodiversity.

Dryland civilizations around the world have established their own sustainable dryland societies, utilizing dozens of multipurpose species for food and fodder production, and the production of other essential goods. Many such tree species have been planted at Project Wadi Attir as experimental or pre-commercial plantations, whereby each species is contributing to environmental sustainability in addition to providing specific goods and services.

Fig. 3: Edible forests, agroforestry, or Permaculture systems outperform all modern farming systems in maintenance, resilience, longevity and sustainability, as they are essentially self-sustaining while continuously providing food, fodder, wood, erosion control and additional services. Dryland fruit trees such as figs, olives, carob, almonds and pomegranates have been the key to long-term, sustained Mediterranean civilizations. Similarly, other edible dryland trees such as Moringa or Prosopis have historically provided essential food in Asia or the Americas, and are now being sustainably planted and utilized at Project Wadi Attir.

This includes a number of edible exotic forests established in liman plantations onsite: argan is a Moroccan species producing high value oil; marula is a Southern African dryland fruit tree; Prosopis seeds are edible and suitable for baking gluten-free cakes and bread; Moringa oleifera is a dryland tree producing huge amounts of protein and vitamin-rich leaves, and oil and protein-rich seeds useful as food or livestock/chicken feeds. A single 1000 m2 liman, such as the one shown in Figure 3, can provide several tons of food and other materials and thus contribute significantly to the food security of the local population.

More Tree Goods and Services

A number of dryland trees planted at Project Wadi Attir, including Eucalyptus, Prosopis and Albizia, also produce high-quality timber for furniture and construction. Many other tree species planted at the project site, including argan, marula and Moringa peregrina, produce high-value oils used in cosmetics and gourmet cuisine. Numerous tree species can be used to produce high-value resin, essential oils and medications. Another service of great value is the splendid flowering of many dryland species during the dry season, including Ziziphus, Eucalyptus and Acacia, which allow for year-round natural honey production.

Nitrogen Fixation and Litter Production

The additional litter provided by trees such as A. victoriae, especially during the dry season, enables effective control of desertification by maintaining or enhancing the soil litter layer. The nutrients provided are recovered from deep soil layers by the tree’s roots, which penetrate and saturate high volumes of soil. This process makes huge reserves of rare nutrients available to the thin topsoil layer. The higher biomass productivity achieved in such silvipasture systems allows for sustainable grazing, since the litter cover required for soil fertility is maintained even in drought years.

 Table 1: Nutrient content of A. victoria biomass. N, P, and K content were determined by the Ministry of Agricultures Gilat Service Unit.

Table 1: Nutrient content of A. victoria biomass. N, P, and K content were determined by the Ministry of Agricultures Gilat Service Unit.

A. victoriae appears unique in its capacity to promote growth of annual weeds. It produces large amounts of nutrient-rich plant litter (Table 1) that covers the soil and prevents evaporation, crusting and drying. This and other leguminous trees fix nitrogen at 100 – 300 kg per hectare, sufficient for the production of 800 – 2000 kg of protein, or more than 10 tons of biomass. Indeed, an A. victoriae woodland near the Project Wadi Attir site displays an annual biomass productivity of near 10 tons per hectare, a startling figure for an area generally considered to be a desert. Such productivity represents both a significant economic gain as well as an environmental gain, since synthetic ammonia production and its transport and application consume huge amounts of energy.

Carbon Sequestration and Climate Effects of Trees

Carbon sequestration is incorporation of CO2—a greenhouse gas released in excessive amounts by industrial activities, thereby causing global warming—into the biomass of growing trees. Tree leaves and roots of annual vegetation are transformed into organic material in the soil, called soil organic matter. Replanting trees and restoring vegetation thus binds significant amounts of greenhouse gases into the biomass and soil of degraded drylands. Various authors have estimated the amount of CO2 that could be sequestered by a global dryland rehabilitation program to 4 – 8 Gigatons of CO2 per year, corresponding to 10 – 20% of the amount of greenhouse gasses currently released by human activities.

At Project Wadi Attir, several thousand trees have been planted so far (Fig. 4). Over the next 50 years, those trees are expected to sequester hundreds of tons of greenhouse gasses into wood and soil, representing a significant percentage of the greenhouse gasses released by the project’s industrial activities.

Trees and other green vegetation have a host of other effects on weather, climate, hydrology and the environment. Albedo changes induced by dark vegetation would imply a warming effect, induced by the replanting of dryland forests (see chapter Desertification and Climate Change). However, additional impacts have to be studied and integrated in order to quantify the full climatic impacts of dryland forests (Leu 2010).

Fig. 4: The dryland trees planted in Project Wadi Attir’s terraces and limans will continue growing for decades, removing CO2 from the atmosphere. All trees planted will also provide additional services such as windbreak, erosion control, fruit production, nitrogen recovery and nitrogen fixation. They will also provide habitat for rare species.