Exploring Jordan’s Rangeland Transition: Merging Restoration Experiment with Modeling –A Case Study from Al Majdiyya Village
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Restoration of degraded rangelands in Jordan is essential to enhance and maintain the productivity and resilience of the fragile ecosystem. A balanced interaction between the rangeland’s hydrology and vegetation status is key for achieving long-term sustainability. Restoration of rangelands using mechanized water harvesting techniques, coupled with the out-planting of native shrub seedlings, has been introduced and recommended by researchers - and was lately adopted by different Ministries in Jordan. The impact of restoration on surface runoff and erosion, related to current state of ecosystem degradation, and the role of restoration techniques to recover the ecosystem’s function, need to be deeply investigated. This research aims to understand the rangelands’ water and sediment dynamics and the transition states of the ecosystem. The specific objectives are to evaluate the current (degraded) rangeland situation, to assess the micro-catchment water harvesting and the out-planting of native shrub seedlings approach on enhancing the degraded status (restored), and to investigate the long-term sustainability of the restoration approach compared with historical/native rangeland conditions (baseline). A sub-watershed close to Al – Majeddyeh village, located in the Middle Badia of Jordan, was used as a study site. The site was recently restored using the a mechanized micro-catchment technique (Vallerani) and out-planting of native species approach. In this study, the improved Rangeland Hydrological and Erosion Model (RHEM) was applied for simulating and evaluating the various rangeland states’ scenarios. RHEM is a process-based model that predicts the single rainfall event’s generated runoff and soil erosion rates at the hillslope scale and can predict the impact of plant growth and management practices on the rangelands’ hydrology. The model’s capability to capture the surface hydrological processes of the Jordanian research site was validated using local high temporal resolution rainfall data, top soil texture, topography (slope length and steepness) and plant and surface cover characteristics data from four runoff plots. The results indicate that the model is well capturing the runoff processes in the site - with an average coefficient of determination (R2) of 0.76 - comparing simulated with observed surface runoff obtained from the plots. Several scenarios of plant and ground cover were developed with experts, local community representatives and through protected site investigations to adequately represent the rangeland conditions during the past (baseline scenarios). In addition to detailed measurements of the plant and ground cover of the current condition (degraded states), and measurements at several restored sites (restoration states). Long-term weather data was used to estimate average annual surface runoff (mm/year) and soil erosion (ton/ha/year) rates for each state. The results show that average annual surface runoff rate (mm/year) range from (9.21 – 20.63), (19.86 – 27.76), and (17.47 – 20.51) for the baseline, degraded and restored scenarios respectively. The soil losses (ton/ha/year) range from (0.79-1.89), (1.05 – 4.65), (0.86 – 2.31) for the baseline, degraded and restored scenarios respectively. The most representative scenario (median) of each modeled status (baseline, degraded, and restored) was selected and the occurrence probability of soil loss (ton/ha) of certain events – related with a certain return period - was calculated using the long-term data series generated. The results indicate that a 20-year return period event (5% annual exceedance probability), for the baseline state, related with around 2.230 ton/ha soil loss, increases to a 60% chance of occurrence per year in the case of the degraded state, while it has a 10% chance of occurrence in the Restored state for any given year. The results of the modeling study indicate that restoration - using the Vallerani water-harvesting technique and out-planting of native shrub species - is a promising methodology to restore the degraded ecosystem and to approximate the environment’s historical hydrological conditions. This might also imply that a stable and balanced rangeland status can be achieved through the specific restoration approach. Restoration enhances the interception, storage and the efficient use of the rain water through plants, which will sustain a native cover and conserve the soil, and generally stabilize the rangeland ecosystem and improve its services. The results of the single-event based RHEM can be used in large-scale models to identify hot-spots for out-scaling of restoration taking into consideration the integrated watershed management approach and the upstream-downstream water balance. The model can be used by decision makers to develop ecological site descriptions that include the current eco-hydrological processes. Also, it can be used to develop ecosystem transition status, thus to estimate the impact of several disturbances such as changes in land management and climate. The plant cover changes simulated by RHEM can be used as a reference to assess the carrying capacities of the hillslopes areas, which provides essential information for sustainable livestock management - towards enhancing the livelihoods in the Jordanian Badia.