Over the course of his career, Roger has progressed from an interest in developing techniques to propagate tropical tree by the rooting of stem cuttings to the identification of general principles that determine the capacity to root. As a result of successful propagation, opportunities arise for clonal selection and cultivar development for the improvement of timber, wood and non-wood products. As long-lived plants, trees pose special challenges for genetic selection. These lead to the need to predict yield, identify the best combinations of genetic traits and evaluate clones in the field.
Clonal forestry and agroforestry then require wise deployment strategies for the expression of yield potential and the achievement of sustainable production. The latter also necessitates the maintenance of ecological function in the production system – whether farm or plantation. Cultivars of agroforestry trees open up opportunities to diversify and intensify farming systems for improved crop yields, the rehabilitation of degraded land, and the restoration of agroecological function. Together these benefits can be managed to promote enhanced livelihoods of the farmers through the reduction of poverty, malnutrition and hunger – especially in smallholder farming systems in the tropics.
Integrating agroforestry and tree domestication within rural development programmes leads to multifunctional approaches to agriculture which confer the environmental, social and economic sustainability that is much needed worldwide. To advance agriculture in this direction, Roger initiated what has become a global programme to start the domestication of wild fruit and nut trees that were the staple diet of people before the Green Revolution raised the profile of a few starch crops. This involved the development of some robust horticultural techniques that can be implemented in remote corners of the developing world, as well as some basic studies of the biology of potential new food crops that are important for the well-being of people in developing countries.