Boosting seedling survival and growth under semi-arid Mediterranean conditions: Selecting appropriate species under rainfed and wastewater irrigation

Jordan has scarce and declining forest resources. Its low and variable rainfall has dictated the use of drought-tolerant species such as Pinus halepensis Mill. (Pinaceae) in rainfed forestation programs. We hypothesized that treated wastewater can be used to improve survival and growth of forest seedlings, and to diversify forestations. A split-plot experimental design was utilized to examine the effect of water regime (rainfed, municipal-treated wastewater, and freshwater) on seedlings’ survival and growth of eight forest species for 2 years. Irrigation improved survival rate of all evaluated species compared to rainfed conditions. Although irrigation was stopped during the second year, a lingering effect of irrigation treatment was observed. Moreover, wastewater irrigation resulted in comparable survival rates to those of freshwater, suggesting that wastewater can be used to improve forestation success. Survival rates under wastewater irrigation were noticed to vary by species. Seedlings growth and leaf N content were significantly greater under wastewater as compared to freshwater treatment, indicating that wastewater provided water as well as nutrients. Under rainfed condition, Juniperus phoenicea had the highest survival rate as compared to all other species, which suggests that forestation projects species diversity could be improved even under rainfed conditions.