Increasing vegetation cover, water retention and biological productivity is therefore essential to ecosystem restoration in degraded drylands, whereby tree planting and increased water infiltration can enhance water retention and control water runoff. Ideally, a combination of these steps is required in profoundly degraded locations such as Project Wadi Attir in order to achieve rapid success.

Consequently, efficient restoration of degraded soils, erosion control and watershed protection must rely on detailed scientific understanding of both physical and biological processes in soil and soil surfaces. Any topographical changes must be performed with great care and minimal disturbance to the remaining intact soil structure and vegetation, while strictly avoiding the use of herbicides.

Fig. 3: Dense vegetation is the best way to control water runoff and thus soil erosion or desertification. Dry, dense woodlands (Mussery et al 2013) are the most efficient tool, as they also create a continuous layer of leaf litter that prevents runoff and promotes the growth of annual vegetation and soil rehabilitation. Dense and diverse shrublands are equally effective in runoff control and can be more biologically diverse (Leu et al 2014), though biological productivity is lower due to reduced water utilization efficiency (Fig. 4). Exposed large soil patches give rise to excessive water runoff, resulting in the erosion phenomena pictured in Fig. 2.

Dense vegetation is the most effective means to maximize water use efficiency and soil reclamation, not only in drylands, but in many types of ecosystems worldwide. Tree planting has therefore been widely applied for this purpose, with pine trees having been successfully applied to restore large stretches of Israel’s dry, hilly badlands.

Fig. 5: Soil water content during 2009 (left), within the A. victoria woodland (dark green line) is significantly higher than in conserved (brown) or overgrazed (bright green) shrubland. This significantly enhanced soil moisture content allowed the olive seedlings planted inside this woodland (shown to the right) to survive the summer with minimal irrigation.

The Project Wadi Attir site was heavily degraded, featuring many meter-deep erosion gullies, very low biological productivity and no perennial plant cover. Based on the above results, the restoration program was designed based on minimal soil movement, filling of major erosion structures, reducing water runoff by terracing all runoff channels, and rapid establishment of dense perennial and annual vegetation. Fig, 6 shows the major erosion hotspots before (2011) and after (2014) soil conservation work was performed and trees were planted.

Fig. 6: Erosion control and watershed protection at Project Wadi Attir: the two strongly eroding main gullies (left, in 2011) were partly filled and terraced, and densely planted with a wide variety of agroforestry trees (right, 2013) to stop soil erosion and water runoff, while establishing productive agricultural activities. Smaller gullies (bottom left) were terraced by building small dams in order to collect runoff for agroforestry purposes. A rocky slope was planted with about 300 olive trees (center right) that protects soil and prevents runoff while producing valuable oil.

Fig. 7: Watershed protection in record time: A small liman planted in 2013 with A. victoria and other tree species already provides full protection in 2014, thanks to rapid tree growth, litter production and soil improvement. The chopped weeds together with leaf litter already provide almost closed soil cover, enhancing water retention, infiltration, and nutrient availability and allowing for continued, self-sustained growing productivity in the absence of further irrigation.

Degraded slopes along the various side valleys are the source of significant runoff that threatens the whole water and soil conservation system in the event of sudden flash floods. Re-vegetation of such crusted bare soil areas was thus initiated using A. victoriae and Caparis seedlings, known for their ability to grow quickly under extremely dry conditions. The purpose was to provide 20 – 30% soil and plant litter cover within a few years, thereby enhancing water retention. So far, many of the seedlings established well without further irrigation, and thanks to good rainfall, we expect to achieve the above goals in many of the critical locations. Interesting and highly promising is the fact that A. victoriae has been able to establish in newly developing erosion gullies by exploiting the higher water availability, thus stabilizing them (Fig. 8).

Fig. 8: A. victoriae and Caparis spinosa are highly drought tolerant species that can rapidly cover large areas of degraded slopes, reducing runoff and restoring vegetation and soil quality.

Fig. 11: Natural mechanisms, such as recovering patches of perennial vegetation like Asphodelus ramosus, and digging animals and insects such as harvester ants, loosen and improve soil and create litter and soil dumps which enhance water infiltration and growth of annual plant life.