Desert bighorn sheep establish two desert areas in southwestern Arizona to help preserve the desert bighorn sheep: Cabeza Prieta National Wildlife Refuge and the Kofa National Wildlife Refuge. In 1941, the San Andres National Wildlife Refuge in New Mexico was added. Desert bighorn sheep populations have trended upward since the 1960s when their population was estimated at 6,700-8,100. The upward trend was caused by conservation measures, including habitat preservation. In 1980, desert bighorn sheep populations were estimated at 8,415-9,040. A state-by-state survey was conducted a few years later and estimated the overall US desert bighorn sheep population at 15,980. The 1993 estimate of
Thar Desert was conceived to halt spreading of the desert to fertile areas. There are few local tree species suitable for planting in the desert, which are slow growing. Therefore, exotic tree species were introduced for plantation. Many species of Eucalyptus, Acacia, Cassia and other genera from Israel, Australia, US, Russia, Zimbabwe, Chile, Peru and Sudan have been tried in Thar Desert. "Acacia tortilis" has proved to be the most promising species for desert afforestation and the jojoba is another promising species of economic value found suitable for planting in these areas. There are several protected areas in the Thar Desert. Stretches