Aims: So far, no specific study has been conducted on the selection of suitable species in the floodwater spreading projects of the country. This research aims to achieve this goal for ecosystem restoration in a floodwater-spreading area in western Iran. In this regard, soil characteristics, plant biodiversity, growth status, and tree survival will be considered.
Materials & Methods: In the floodwater spreading area, three pure tree stands and a mixed tree stand, as well as a non-afforested area, were chosen; outside the floodwater spreading area, a non-afforested area (control) was considered. The afforested stands were 15 years old and included Eucalyptus camaldulensis, Prosopis juliflora, and Ziziphus spina-christi. At each location, tree growth, plant diversity, and soil properties (0–25 cm) were measured.
Findings: Fifteen years after planting, in the flood-spreading area, all pure and mixed stands improved organic matter (2-4 times), nitrogen (3-6 times), and phosphorus (1.5-2 times) compared to the control area. The biggest tree height was related to E. camaldulensis (5.8 m), and the highest standing volume was also observed for E. camaldulensis (16.5 m3.ha-1), followed by P. juliflora (3.2 m3.ha-1). The crown cover of E. camaldulensis and P. juliflora was 3-3.3 times larger than that of Z. spina-christi. The survival rate of P. juliflora (77%) was higher than that of E. camaldulensis (63%) and Z. spina-christi (69%). The seedling mortality could be due to inadequate soil moisture in some years. In pure tree stands under floodwater, the Diversity (0.25 times) and Richness indices (0.24 times) were higher than those in the control area. These two variables in the non-afforested area were greater (0.15 and 0.34 times, respectively) than in the control area. In the E. camaldulensis stand (0.88) and the P. juliflora stand (0.87), the evenness index did not significantly differ from that in the control area (0.84).
Conclusion: All three tree species were relatively successful in terms of survival and growth in the floodwater spreading area. Thus, for the restoration and development of afforestation, improvement of soil fertility, and vegetation cover in such dry, low-rainfall regions, the use of these three species, either pure or mixed, is recommended in floodwater-spreading areas.