ABSTRACT
Forage tree legumes benefit agriculture through their multipurpose contributions to livestock feeding, to productivity of farming systems, and to protection of the environment.
Of the several hundred forage tree legume species regarded as having potential for forage only about twenty are in significant use. These are listed, together with their agro-ecological range and tolerance of adverse environments, including acid soils, cool temperatures, low rainfall, poor drainage and high salinity. While some species have high nutritive value for livestock, other species are of limited value to ruminants because of low protein availability and low acceptability, caused principally by high condensed tannin content. Only 10 of the 20 species listed are considered to have a high nutritive value, namely Albizia lebbeck, Chamaecytisus palmensis, Cratylia argéntea, Desmodium rensonii, Desmanthus virgatus, Gliricidia septum, Leucaena leucocephala, Leucaena diversifolia, Sesbania grandiflora and Sesbania sesban.
The germplasm in commercial use worldwide is often inferior and with a narrow genetic base. The need is highlighted for farmers to have access to a greater diversity of planting material and improved varieties through better distribution systems. However, plant improvement is often limited due to taxonomic confusion in many genera, such as Albizia and Prosopis, and farmer access to new varieties is limited by lack of information and lack of resources to purchase high quality seeds. There is debate over whether to use fast growing exotic species, or slower growing native species. There are as many as 150-200 million people using Gliricidia septum worldwide, but there is minimal use in its native range. 82Conversely, native Acacia communities are overexploited in their native range, with minimal use elsewhere. Conservation of native range is critical, and in situ, ex situ and circa situm approaches are suggested. Issues of weediness potential are paramount when using exotic species, requiring greater care in the evaluation of risk factors.
Finally, the reasons for successes and failures in promotion of forage tree legume use in world farming systems are analysed, and suggestions made to extend the utilization of this important group of legume species to a greater number of farmers and environments.
