Assessing vegetation rehabilitation under restoration operations in arid rangelands (Case study: Bastak, Hormozgan province)

A large area of Iran rangelands is located in arid and semi-arid areas which a significant percentage of them have been degraded and are not in good condition. In these areas, vegetation restoration is not easy due to the water scarcity. Water harvesting operations are among the necessary management measures to restore and develop the rangelands of these areas. Water harvesting operations improve the rangeland restoration conditions by increasing the available moisture for plants. But not all water harvesting operations are equally effective and may not have the same effect on rangeland restoration in different areas. Therefore, it is necessary to compare such operations in different areas to be able to choose the best water harvesting operations. Therefore, this study investigates the efficiency of two water harvesting methods in the rehabilitation of arid vegetation in Hormozgan province.

In this study, three treatments have been considered: control area, area under microcatchment operation and area under water spreading system. Systematic-random sampling method was used to measure vegetation. Three 100 m transects were laid out in each area. Vegetation attributes were measured in ten 2×2 m plots located along each transect. In total 90 plots, the percentage of canopy cover and the number of the plant species were recorded. The biological form of plant species was determined based on the Rankier classification method. In addition, the percentage of rocks and pebbles, litter and bare soil were determined in each plot. To study the flora of the study area, all plant species in the region were sampled and identified using reliable references. To evaluate species composition in all three sites, plant functional types were used. One-way analysis of variance followed by LSD were used to compare control area, area under microcatchment operation and area under water spreading system in terms of vegetation attributes. The rate of vegetation attributes change was also determined. Detrended correspondence analysis was used to investigate the relationship between plant species and water harvesting operations and control areas.

The results showed that there was a significant differences between water harvesting operations and control areas in terms of bare soil, litter and vegetation (P <0.05) The water spreading system and microcatchment operation had a significant effect on vegetation canopy and litter cover in the region (P <0.05). Examination of plant functional types also showed that palatability classes II and hemicryptophytes had more chance to develop under water harvesting operations respectively. In terms of life form, water harvesting operations had the most positive effect on forbs and grasses, respectively (P <0.05). The results also showed that the families Poaceae, Chenopodiaceae and Fabaceae were successful families in the sites under water harvesting operations, especially the sites under water spreading system. The rate of vegetation attributes change was increasing in the area under water spreading system compared to the area under microcatchment operation, except for the bare soil. The highest and lowest positive changes belonged to litter and Simpson index with a mean of 9.07±0.62 and 0.48±0.25, respectively. The results of DCA showed that Cenchrus pennisetiformis،، ‏Tephrosia persica، ‏Atriplex leucoclada‏ ، ‏Cornulaca monacantha‏ ,‎ ‎Cynodon dactylon were the most important species related to water spreading system and microcatchment operation.

Both water spreading system and microcatchment operations improved the quality and quantity of vegetation in the region, but the effects of water spreading system were greater than microcatchment operation in restoring vegetation. According to the ecological indicators considered in this study, water spreading system is recommended to restore vegetation in arid and semi-arid regions. In the end, it is suggested that economic and social indicators such as the cost of implementing various water harvesting operations should be also considered in future studies, to combine all ecological, economic and social indicators to suggest the best water harvesting operations for rangeland restoration.