"This is a fertilizer tree with reverse leaf phenology, which makes it become dormant and shed off its nitrogen-rich leaves during the early rainy season and at planting time when seeds need nitrogen," he said.
"And [then the tree] regrows the leaves at the beginning of the dry season, and thus does not compete with crops for light."
The tree species also acts as a windbreaker, provides wood for fuel and construction, and checks soil erosion by making the soil loose for water absorption during rainy season, Garrity added.
Acacia, iconic trees of the African landscape, are well adapted to a wide array of climates and soils, from the deserts to the humid tropics.
Scientists first observed farmers in Africa's Sahel region growing the trees in their sorghum and millet fields about 60 years ago.
Today the practice is still seen in Senegal, Mali, Burkina Faso, Niger, Chad, Sudan, and Ethiopia, and in parts of northern Ghana, northern Nigeria, and northern Cameroon. (See a map of Africa.)
In Zambia preliminary research has found that unfertilized maize yields in the vicinity of acacia trees averaged nearly three times those of crops grown nearby but beyond the trees' canopy.
Nobel Peace Prize laureate Wangari Maathai told the agroforestry conference that Africa must return to sustainable agriculture that embraces planting of "fertilizer trees" such as acacia.
(Related: "Food of the Future to Be More Diverse?")
"We have done great damage to the ecosystems through less sustainable agriculture practices like monoculture that has contributed to food insecurity in Africa," Maathai said.
"We need to encourage farmers to grow many food crops to reduce vulnerability of communities."
Acacia trees may also give small farmers benefits in the lucrative carbon-storage market, said Archim Steiner, executive director of the United Nations Environment Program (UNEP).
The World Agroforestry Center and UNEP are developing a standard method for measuring carbon storage on all types of landscapes, which could provide a basis for providing farmers with a financial incentive to increase tree cover on their farms.
Climate change talks scheduled later this year in Copenhagen will consider a new strategy that could include such a program.
SOURCES AND RELATED WEB SITES