Originally published on cgiar.org by:Bioversity International on Mar 28, 2008
For immediate release
Rome, Italy
A 10-year study in eight countries has revealed that farmers maintain more diversity than previously thought, and do so in two distinct ways for two distinct reasons.

"Perhaps the most important result overall is that farmers who choose to grow traditional varieties are generally growing more than one variety, which is presumably a deliberate choice in favour of diversity" said Devra Jarvis, senior scientist at Bioversity, who coordinated the study.

The paper by Jarvis and her colleagues is published online this week in the Proceedings of the National Academy of Sciences (see details below). On more than 2000 small farms across five continents the team measured the richness and the evenness of the varieties farmers grow in their fields and gardens. Richness and evenness are two measurements of diversity that have long been used by ecologists. Richness refers to the number of different varieties, regardless of how common each may be. Evenness, by contrast, measures how common each variety is. If all the varieties are planted on roughly equal areas of land, then evenness is high, whereas if one or two varieties dominate the area planted to that crop, evenness is low.

"The point of these measures," said Jarvis "is that they let us compare different crops in different places and different cultures. They’re not often used in small-scale or single species studies."

The partnership studied 27 crops in 26 communities, representing about 63,600 hectares distributed across eight countries. Sites ranged from sea level, in the Yucatan Peninsula, Mexico, to above 3000 metres in Nepal. Environments included arid and semi-arid areas of Burkina Faso and Morocco, temperate areas in Hungary and Nepal, tropical highlands in Ethiopia, and tropical and subtropical lowlands in Mexico, Amazonian Peru and Vietnam. Farming systems were rain-fed or irrigated, stable or shifting cultivation.

"We wanted to be sure that we were covering different cultures and also different crop breeding systems," Jarvis explained. "We also had to concentrate on the major subsistence crops in each country, and on crops of global importance. And we wanted to develop tools that could be used anywhere to assess the diversity farmers are maintaining and using."

The results show that, despite the differences among crops, cultures and countries, there are consistent patterns to the ways farmers use and maintain diversity.

On any given farm, staple crops tend to have low evenness, so that one variety is dominant, while non staples are more even, with each variety occupying roughly the same area. Jarvis believes this reflects two different strategies. For staples, farmers are ensuring that they have diversity available for future use, for example to cope with environmental change or social and economic needs. For non-staples, they are growing different varieties that they currently need for different purposes. "The difference between the two situations has implications for the use and conservation of traditional variety diversity," Jarvis said.

Others have welcomed the results of the study. Jean-Louis Pham, at the French Institute of Research for Development in Montpellier, France, paid tribute to the painstaking efforts needed to assemble so much relatively simple data. He told a reporter that the results will no doubt be widely used as a reference, "providing us with a kind of state of the world of crop diversity at the beginning of the 21st century".

Reference: A global perspective of the richness and evenness of traditional crop-variety diversity maintained by farming communities PNAS published March 24, 2008, DOI: 10.1073/pnas.0800607105

For further information, contact Jeremy Cherfas.