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Reforestation projects in semiarid lands often yield poor results. Water scarcity, poor soil fertility, and structure strongly limit the survival and growth of planted seedlings in these areas. At two experimental semiarid sites, we evaluated a variety of low-cost planting techniques in order to increase water availability to plants. Treatments included various combinations of traditional planting holes; waterharvesting microcatchments; stone or plastic mulches; small waterproof sheets to increase water harvesting; dry wells; buried clay pots; and deep irrigation. Some of these treatments were also combined with addition of composted biosolids. Waterproof sheets significantly enhanced water harvesting (43%) and soil moisture in the planting hole (40%), especially for low-intensity rainfall events. Treatment effects on the survival and growth of Olea europaea seedlings varied between experimental sites. At the most water-limited site, clay pots, and dry wells improved seedling survival, while no treatment enhanced seedling growth. At the least water-stressed site, the application of composted sludge significantly improved seedling growth. We conclude that nutrient-mediated stress is subordinate to water stress in arid and semiarid environments, and we suggest modifications on the microsite scale to address these limiting conditions in Mediterranean drylands.

Citizen science has been gaining momentum in the UnitedPalabras Clave: conservación de suelo virgen, cooperación para el desarrollo, desarrollo de capacidad noacadémica, evaluación de la biodiversidad, investigación participativa, manejo de recursos naturales

The patchy distribution of semiarid ecosystems determines productivity and controls the retention of resources within the system. Resource fluxes depend on a number of biophysical and soil variables, besides the amount and intensity of particular rainfall events. At two Mediterranean experimental sites with contrasted composition and spatial vegetation arrangement, we evaluated a straightforward way to simplify some of these processes by using different planting techniques that modify the runoff generation threshold and redirect runoff towards the planting hole (M) and enhance the water infiltration and conservation in it (MDW). Traditional planting technique (H) and M were combined with the addition of composted biosolids. Soil moisture was increased with treatments during drought periods in the first 2 years after planting with mean values of 10·1, 8·9 and 6·9% in MDW, M and H, respectively. Lower landscape organization values at the site resulted in sinks being more efficient at retaining resources, with 3·68‐fold more organic matter accumulation on the soil surface of the planting hole, better growth of the Olea europaea‐planted seedlings and a better response to compost application in MDW than in H. At the site with better landscape organization, planting techniques only showed improvement in seedling survival (+20% in MDW than in H). We discuss ecosystem properties, such as plant composition and spatial arrangement, that determine the effectiveness of these techniques as dryland restoration tools and the hierarchy between water and nutrients as essential resources in these semiarid Mediterranean areas. Copyright © 2016 John Wiley & Sons, Ltd.

Drylands functioning depends on water fluxes and the retention of resources. The restoration of degraded areas should mimic the natural arrangement of vegetation in the landscape in a source-sink pattern.Reintroducing key woody seedlings through planting is a major concern in ecological restoration as these areas use to be overpassed degradation thresholds and ecosystem functions are limited. However, it is not clear how natural fluxes might determine seedlings performance of key shrub species. We have analyzed the microcatchment surface area of planting spots with and without water optimization treatment (waterproof surfaces with dry wells) and the survival and growth of Olea europaea seedlings during six years after planting in a semiarid degraded landscape. We recorded a positive effect of water optimization treatment in seedling survival and growth highlighting water limitation of these sites. We did not observe a clear and linear relationship between microcatchment collecting surface area and plant performance. The higher the collecting surface the lower the retention capacity of the planting pitch suggesting a loss of the integrity of the planting hole structure. Water optimization treatments were especially effective when collecting surface areas were low. These results might be useful for designing precision restoration actions in degraded landscapes.