Some 57% of Africa and 69% of Australia is either arid or semi-arid land. Rainfall is low and highly variable, and greatly exceeded by evaporation. Trees that grow under these harsh conditions play a vital role in providing shade and shelter for stock, preventing erosion and enhancing soil fertility. Trees also provide wood for fuel and construction. Fuelwood and charcoal supply more than 90% of the energy consumed for domestic purposes.

Population pressure and lack of sustainable management have severely degraded much of Africa's arid and semi-arid land. In Kenya, the population of arid and semi-arid regions is increasing by 4-5% per year, with about half the growth coming from migration from more populous, higher-productivity areas.

The need to control and reverse the degradation by replacing lost tree cover is imperative. However, poor seedling survival rates of zero to less than 30% have made attempts at reforestation largely ineffective.