Ecological restoration has increasingly shifted focus towards restoring ecosystem functions rather than attempting to recreate original, pre-disturbance conditions. This approach, known as functional restoration, prioritizes the rehabilitation of key processes that sustain ecosystems. Functional restoration is especially relevant in severely degraded landscapes, such as desertified regions, where full restoration to the original state is often unfeasible.

This study presents a conceptual model outlining the core processes that regulate ecosystem functions in water-limited ecosystems, derived from long-term research conducted in the Negev Desert (Dor-Haim et al. 2023). The model highlights the interconnections and feedback loops that drive the productivity and biodiversity of runoff-dependent dryland ecosystems. Hydrological processes, specifically rainfall-runoff dynamics, are central to the distribution of soil moisture, which, in turn, governs the system's functionality.

The model identifies two primary feedback loops:

1. The source feedback loop (biocrust-soil moisture interaction): Biological soil crusts (biocrusts) regulate water infiltration and runoff, capturing rainfall and redistributing it as runoff to other parts of the ecosystem. This process creates hydrological niches with varying moisture levels, which support adjacent patches of woody vegetation and herbaceous plants.
2. The sink feedback loop (woody vegetation-soil interaction): Woody vegetation improves soil properties by contributing organic matter and providing shade, reducing evaporation and maintaining soil moisture. This positive feedback enhances the productivity of vegetation and supports associated species.

The balance between the source feedback loop (biocrust) and the sink feedback loop (woody vegetation) is crucial for sustaining the system's overall productivity and biodiversity. Imbalances, such as excessive runoff without sufficient sinks, can lead to soil erosion, while inadequate runoff reduces water availability and productivity. Maintaining this balance is essential for ensuring the ecosystem's resilience to external pressures, including climate change and anthropogenic disturbances.

The Negev Desert serves as a compelling case study to test and apply this model in the field. A large-scale project known as "Savanization" employed this framework to create a human-designed landscape in desertified areas, leveraging source-sink feedbacks as a nature-based solution. This functional restoration approach resulted in a novel man-made landscape combining planted trees and natural vegetation, delivering a wide range of ecosystem services.

Based on this experience, we developed a set of guiding principles for the functional restoration of degraded landscapes, encompassing four key steps:

1. Identifying fundamental processes that regulate ecosystem functions in alternative states;
2. Detecting the drivers of degradation that disrupt these processes;
3. Implementing functional restoration by transitioning degraded landscapes into functional states;
4. Monitoring and assessing success through measurable impacts on ecosystem services.

Our case study in the Negev Desert offers valuable insights into reversing desertification in water-limited ecosystems by restoring source–sink networks. These principles provide a robust framework for guiding functional restoration efforts and enhancing ecosystem resilience, which is critical for addressing the challenges of the Anthropocene.

disturbance, ecosystem function, ecosystem, Negev desert, source-sink relationship, climate change, state change, management

Shayli Dor - Haim

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