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Feb. 23, 2015
 
 

Above: Ruins associated with a Byzantine farm near the ancient settlement of Shivta in the Negev Desert. This is an example of water harvesting techniques that have created a legacy effect on the desert landscape. Though long abandoned after reconstruction in the late 1950s, the ancient structures still capture runoff water as reflected by lush seasonal vegetation and trees.
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An international team of experts, including two BGU faculty members, Dr. Haim Goldfus (Department of Bible, Archeology and Ancient Near Eastern Studies) and Prof. Isaac A. Meir (Jacob Blaustein Institutes for Desert Research), have co-authored a paper that focuses on new paradigms aimed at understanding desertification processes and their impacts. The paper was published in the February 2015 issue of the prestigious journal Frontiers in Ecology and the Environment 

The paper proposes a new model to look at legacy effects in different timescales. A legacy effect refers to the impact of previous conditions on current processes or properties. Legacies have been recognized by many disciplines, from physiology and ecology to archaeology and geology. Within the context of climatic change, ecological legacies in drylands (e.g., vegetative patterns) result from feedback between biotic, soil, and geomorphic processes that operate at multiple spatial and temporal scales.  

“Understanding the magnitude of a historical phenomenon's effect on a specific environment in different time scales may provide better forecast tools for future actions and their projected outcomes,” say the researchers. 

The researchers explored the factors that influence the legacy effect, as follows:  (1) the magnitude of the original phenomenon, (2) the time since the occurrence of the phenomenon, and (3) the sensitivity of the ecological-soil-geomorphic system to change. The paper presents a conceptual framework for legacy effects at short-term (days to months), medium-term (years to decades), and long-term (centuries to millennia) timescales, which reveals the ubiquity of such effects in drylands across research disciplines. 

To illustrate the magnitude of such legacy effects, the co-authors, each coming from a different discipline, have demonstrated the impacts of different actions at different time scales. For example, geomorphic legacies at the long-term timescale can be seen in the stabilization of sand dunes by water-harvesting infrastructures built by ancient civilizations.  

The case study chosen and detailed by the BGU team is the Negev desert which, together with the broader Levant, witnessed a thousand year Classical continuum (ca. 300 BCE -700 CE), characterized by intense development of water collection and storage infrastructures. These infrastructures allowed commercial caravans composed of beasts of burden and people to travel along routes dotted by springs and water cisterns, fortresses and caravanserais. It also allowed the subsequent development of thriving settlements based, in part, on agriculture. Understanding the water and soil interaction brought the development of dry riverbed terracing that retained flood water long enough to allow its slow percolation underground. Where water flows, soil comes with it, which brought a gradual deepening of the terrace soil that allowed a diversification and transition from wheat and barley to vines and pomegranates, and then to trees with bigger root systems. By continuing to contain runoff water, the terraces acted as a flood control system, slowing erosion and gully incision processes. This also encouraged the continuous growth of dense vegetation which, in turn, prevented the intrusion of sand dunes into settlements, they explain.  

Understanding the mechanics and details of such processes becomes all the more relevant when the environment is under the combined stress of both climatic uncertainty and continuous population growth which, in turn, raises exponentially the ecological footprint due to both quantitative and qualitative pressure increases. This understanding, in turn, can have a decisive effect on our ability to ensure sustainable development, i.e. “development that meets the needs of the present without compromising the ability of future generations to meet their own needs” as stated in the Brundtland report, issued by the UN World Commission on Environment and Development, and published in 1987, by Oxford University Press as Our Common Future.