The Role of Indigenous Fruit Trees in Sustainable Dryland Agriculture in Eastern Africa - Indigenous Fruit Trees in the Tropics: Domestication, Utilization and Commercialization - page 218

Brouard, 1995). A new model combining both approaches is actively being
developed for indigenous fruit trees of Africa (Leakey et al ., 2005a, b;
Tchoundjeu et al ., 2006).
11.4.3 Multiplication and distribution of improved varieties
In order to enhance farmers' participation in the planting of improved planting
stock of priority indigenous fruit trees, the farmers need good access to these
improved tree germplasms. The current systems of forest seed and seedling
distribution to farmers remain a major constraint (Simons, 1996). Many farmers
have planted trees, but the genetic quality of the material is often poor (there is a
risk of inbreeding because seeds are collected from very few trees), and many
farmers say that planting material of desired varieties of some species is
unavailable (Tripp, 2001; A. Raebald, personal communication). This is despite
the presence of large, well functioning tree seed centres in many African
countries, and it means that seeds and seedlings of improved high-quality and
high-yielding indigenous fruit trees cannot reach the farmers. If the domestication
of indigenous fruit tree species is to contribute to the improvement of rural
livelihoods, it requires that both knowledge and improved tree germplasm be
transferred to farmers. Research is therefore needed to develop and test
alternative (decentralized) ways in which seeds, seedlings and know-how can be
distributed efficiently.
11.4.4 Incorporation of improved varieties on farms
Domestication of trees in monoculture plantations has been known to result in
a loss of biological diversity, increased susceptibility to pests and diseases, and
rapid depletion of soil nutrient reserves (Pedersen and Balslev, 1990). However,
planting them in mixtures in the form of agroforestry parkland systems (widely
spaced trees) provides continuous tree cover and contributes to both the
productivity and the sustainability of farming systems by restoring the degraded
ecosystem, enhancing local biodiversity and creating a more favourable
microclimate for associated crops and livestock, in addition to supplying fruit
and fruit products that provide income and employment in rural areas, thereby
improving rural livelihoods. Research is therefore needed to determine the
appropriate spacing or density of trees in order to establish each species on
farms as widely spaced trees.
11.4.5 Management of trees on farms
Once a certain height is reached, some tree species tend to suppress associated
crop production, particularly in the dry subhumid zone. Jonsson et al . (1999),
during a year of exceptionally high rainfall, found no significant difference in
millet yield between crops in the shade and in the open. However, under