Relict olive trees at runoff agriculture remains in Wadi Zetan, Negev Desert, Israel

Olive (Olea europaea) trees in the arid Negev Desert of southern Israel are important relicts on the ancient agricultural landscape. Among them are a cluster of several trees located in Wadi Zetan, at the heart of the Shivta horticulture terroir, with its abundant agricultural runoff remains. Two isolated olive bearing trees stand in a sheltered beneath cliff in the upper part of the wadi. Radiocarbon dating of an internal part of the trunk of one of these living trees estimates its minimum age as the mid-16th – early 17th century CE (∼500 years old). Archaeological excavations conducted beneath the trees and the adjacent dam revealed OSL samples of loess accumulation dated to the Early Islamic period (8th-9th centuries CE). The stratigraphy and chronology of this sediment deposition indicate its rapid and short accumulation. Palynological analysis of the same OSL dated samples indicates that grapevines and olive trees were cultivated in the immediate vicinity of the site during the Early Islamic period. The lack of pollen of cultivated taxa from the latter part of the sequence points to cessation of the agricultural activity, probably a few hundred years later. Leaf samples for DNA profiling of the trees in comparison to other local old olive trees around the country, indicate that the trees in Wadi Zetan are genetically close to a known cultivar common among ancient olive trees. The trees have survived for at least a few hundred years, in an arid area, due to the local conditions and enhanced drainage from the man-made upper runoff system. These old olive trees bear a powerful and symbolic significance, indicating the endurance and sustainability of ancient desert runoff agriculture. Moreover, the survival of their relicts in Wadi Zetan suggests their potential as cultivars greater resilience to the harsh growing conditions of arid environments.