The largest planted forest in Israel is Yatir Forest, located on the southern slopes of Mount Hebron, on the edge of the Negev Desert. It covers an area of 30,000 dunams (30 square kilometers). It is named after the ancient Levite city within its territory, Yatir, as written in the Torah: And unto the children of Aaron the priest they gave Hebron with its suburbs, the city of refuge for the manslayer, and Libnah with its suburbs, and Jattir with its suburbs, and Eshtemoa with its suburbs (Book of Joshua 21:13-14). In 2006, the JNF signed a 49-year lease agreement with the State of Israel which gives it control over 30,000 hectares of Negev land for the development of forests. Research on climate change is being carried out in Yatir Forest. Studies of the Weizmann Institute of Science, in collaboration with the Desert Research Institute at Sde Boker, have shown that the trees function as a trap for carbon in the air. Shade provided by trees planted in the desert also reduces evaporation of the sparse rainfall. Yatir Forest is a part of the NASA project FluxNet, a global network of micrometeorological tower sites used to measure the exchanges of carbon dioxide, water vapor, and energy between terrestrial ecosystem and atmosphere. The Arava Institute for Environmental Studies conducts research that focuses on crops such as dates and grapes grown in the vicinity of Yatir forest. The research is part of a project aimed at introducing new crops into arid and saline zones.