London — Smallholder farmers should use their indigenous knowledge of trees to boost incomes and drive social development, according to a new book by Roger Leakey, vice chairman of the International Tree Foundation and renowned tree biologist.

Leakey said his new book Living with the Trees of Life: Towards the Transformation of Tropical Agriculture is the world's first research-based guide for agroforestry - an agricultural practice that uses the interactive benefits of combining trees and shrubs with crops and/or livestock.

Leakey was speaking at the publication's UK launch, at the School of Oriental and African Studies, London, this month (17 September).

He has developed a three-step farming guide, which integrates agroforestry practices and technological interventions into sustainable farming. It aims to enhance trade and income, and to generate funds for reinvestment in education and local infrastructure.

The first step is to make soil more nitrogen-rich - and thus fertile - by planting leguminous trees and shrubs.

The second step is to encourage local farmers to select native crops for production. Using their indigenous knowledge, farmers select the most appropriate crops, which Leakey said are usually "traditional fruits, nuts and medicinal plants [which] they once gathered from the forest".

Farmers are then trained in rural resource centres (RRCs), where they learn low-tech methods for maximising the quality of fruits and nuts.

"By improving soil fertility and diversifying crops, we can generate income which will enhance livelihoods," Leakey said.

However, he believes that crop selection alone cannot drive social change. For this reason, his new model incorporates commercialisation: "If you don't have a market, you don't get anywhere," he warned.

The third step involves transitioning from the local to the global marketplace, and engaging with big businesses.

As well as selling crops, local artisans are also encouraged to start cottage industries using simple processing equipment, such as oil presses and nutcrackers, to package and store goods, thus adding important value to them.

In Cameroon, where the initial projects started, one RRC has seen its income rise from US$145 to US$28,350 per year in the ten years since its farmers were trained.

Leakey believes the three-step model will drive a "new wave" of social change, not only in West Africa, but across the continent and in Latin America and South-East Asia.

However, a pressing problem is ensuring that farmers are not exploited but supported by big businesses, said Albert Tucker, an international trade consultant and fair trade advocate.

Leakey agreed that there were still big question marks over how to protect farmers, and that years of international debate had so far failed to solve these issues.

His agroforestry ideas are supported by the International Tree Foundation and the World Agroforestry Center.

Meine van Noordwijk, chief science advisor at the World Agroforestry Centre, welcomed the new guide, saying it may be inspirational.

"Once the basic idea of farmer tree management is accepted and understood, selection of more productive trees and tree domestication can lead to substantial progress, while tree diversity contributes to risk management for uncertain futures," he told SciDev.Net.