Document Type : Research Paper

Authors

• Javad Motamedi ¹
• Esmaeil Sheidai-Karkaj ²

¹ Associate Professor, Rangeland Research Division, Research Institute of Forests and Rangelands, Agricultural Research Education and Extension Organization (AREEO), Tehran, Iran

² Associate Professor, Range and Watershed Department, Faculty of Natural Resources, Urmia University, Urmia, Iran

Abstract

Background and objectives
Various indicators are used to assess, evaluate, and quantify the effectiveness of desertification control projects. One of the newer and more comprehensive indicators is the ecosystem multi-functionality index. Ecosystem multifunctionality emphasizes that ecosystems simultaneously provide multiple functions and services, and that their integrated, comprehensive assessment offers a much greater advantage than examining each function individually. This index reflects each ecological site's overall ability to sustain high levels of multiple ecosystem processes simultaneously. A higher numerical value for this index indicates that desertification control operations, particularly through the planting of different plant species, have produced an additive and synergistic effect on ecosystem functioning. The present study introduced and applied this index to assess the effectiveness of desertification control projects at different ecological zones located along the soil salinity gradient on the western margin of Lake Urmia.
Methodology
Initially, 12 sites across three ecological zones were selected along a 1500-meter gradient. At each site, fifteen 2-m² grid plots were established along a 150-meter transect at 10-meter intervals, and the canopy cover and aerial biomass of understory plants were measured within these plots. Additionally, along each transect, 15 stands of the species Nitraria schoberi, planted in 10-m² grids since 2013 as part of desertification control efforts, were identified, and their plant traits were recorded as ecosystem-related characteristics. Soil samples were also collected along each transect at the beginning, middle, and end points, from a depth of 20 cm, to evaluate the relationship between the distribution of understory vegetation and the plant traits of N. schoberi stands with soil properties. Redundancy Analysis (RDA) was then used to investigate the relationships between N. schoberi plant traits, understory vegetation attributes, habitat characteristics, and the spatial distribution of sites in the soil-parameter space. To calculate the ecosystem multi-functionality index, ecological data in all sites were normalized across all variables, and standardized scores were integrated and averaged to obtain the final multi-functionality value. After calculating the index for each site, its correlation with soil characteristics was examined, and the most influential variables determining the index values were identified. The index across the ecological zones were also compared to determine the superior zone in terms of ecosystem multi-functionality.
Results
According to the results, the values of plant traits in N. schoberi stands increased along the salinity gradient from the first zone (farthest from the salinity focus) to the third zone (closest to the salinity focus). However, the percentage of dry stands, the values of understory vegetation attributes, and the rangeland condition class were higher in the first zone than in the third zone. Consequently, the magnitude of the ecosystem multi-functionality index—derived from the magnitude of plant traits—increased progressively from the first to the third zone. As the salinity focus was approached, the values of Sand, Mg, and Ca increased, whereas Clay, N, OM, and Silt increased in the opposite direction. Bulk density (BD) and bicarbonate (HCO₃⁻) did not play a significant role in distinguishing sites along the salinity gradient. The ecosystem multi-functionality index exhibited the strongest positive correlation with the percentage of sand, sodium, sodium adsorption ratio, and exchangeable sodium percentage—variables aligned with the ecological requirements of N. schoberi. Therefore, N. schoberi grew more successfully in the third ecological zone, where soils were sandy and light-textured. The index showed the strongest negative correlation with percentages of silt, organic carbon, and available phosphorus. Thus, in the first and second ecological zones, where soils were clayey and heavy, N. schoberi exhibited reduced growth and smaller plant-trait values. As a result, the multi-functionality index in these zones was also lower than in the third zone.
Conclusion
The ability of ecological sites to maintain high levels of ecosystem processes in response to desertification control operations is not uniform across zones. The numerical value of the ecosystem multi-functionality index indicates that desertification control interventions using N. schoberi on the western edge of Lake Urmia had a greater positive effect on ecosystem functioning in the third ecological zone—closer to the salinity focus where soils are sandy and light—while this effect was markedly lower in the first and second zones, which are farther from the salinity source and characterized by heavy, clayey soils.

Keywords

• Desertification
• ecosystem multi-functional index
• plant traits
• salinity gradient
• soil properties