Overstory #31 - Tree Domestication

Editor's Note

Previous editions of The Overstory have covered the value of increased diversity (Overstory editions #14 and #21), using trees that do well in your area (Overstory #9) and tree seed selection (Overstory #19). In this edition, these topics merge in the subject of "tree domestication," bringing wild tree species into cultivation in agroforestry systems. Special guest author Dr. Roger R. B. Leakey , Head of Tropical Ecology, Institute of Terrestrial Ecology, Midlothian, UK, shares an excerpt adapted for The Overstory from his original work appearing in Agroforestry for Biodiversity. For more details about this publication, please see the reference below.

Domestication of Trees for Timber and Nontimber Forest Products

Throughout the tropics there are numerous perennial woody species that have provided indigenous peoples with many of their daily needs for millennia. Many of these people have now left the land for urban life, but they still demand traditional food, medicines, and other natural products. These traditionally important woody plants are virtually undomesticated. These neglected "Cinderella" species have great genetic diversity and also play a key role in biological, chemical, and hydrological cycles, protecting soils and providing ecological niches. The food-producing species are also important for food security, especially in the dry season, as well as a source of vitamins and minerals critical for the health and nutrition of children and pregnant women.

There are four groups of wild trees, shrubs, and vines which could be rapidly domesticated for agroforestry and which can be viewed as potentially important sources of income for farmers. These trees produce:

1. The traditionally important wild foods, mostly fruits, nuts and leaves for vegetables;
2. The traditionally important fibers;
3. Locally and industrially important pharmaceuticals and other extractives such as gums and resins;
4. Commercially important quality timbers and woods.

The domestication of tree species is a dynamic process which develops from deciding which species to domesticate and proceeds through background socioeconomic studies, the collection of germplasm, genetic selection and improvement to the integration of domesticated species in land-use. Domestication is an ongoing process in which genetic and cultivation improvements are continuously refined. In genetic terms, domestication is accelerated and human-induced evolution. Domestication, however, is not only about selection. It integrates the four key processes of the identification, production, management, and adoption of tree resources.

Strategies for tree domestication will vary depending on the value of the products, the extent of genetic variation within a species, and many other factors. For high-value species such as those producing marketable forest products the vegetative propagation of superior selections identified from within the existing wild populations will be appropriate. This is the approach generally followed in horticulture. Thus, an individual plant with superior yield, fruit flavor, stem form, or wood quality can be mass produced by vegetative propagation. In this way it is possible to select those clones likely to develop above-average characteristics in any given trait. By a series of ongoing selections and an ever-increasing intensity of selection, it is also possible to achieve rapid and substantial genetic improvements.

When identifying and selecting trees for cloning by vegetative propagation, there are two important criteria. It is important, 1) to ensure that those that are highly superior for the desired traits are chosen and, 2) to ensure that the selected individuals are unrelated and as genetically diverse in other traits as possible. This calls for strategy that allows intensive selection (e.g., 1 out of 100 to 10,000 trees) from among trees from different populations, ideally from throughout the range of the species. Furthermore, this should be an ongoing rolling program of multiple trait selection, in which more and more intensive selection is imposed through the addition of selection criteria for new traits while, at the same time, new sources of genetic stock are continually added as new genetic collections enter the program. These new collections should come from further exploration and from breeding programs and so continually broaden the genetic base of the planted trees. Molecular genetics techniques can be used to ensure that genetic diversity is maintained in the clones used for commercial production.

Selection procedures vary depending on the product and the situation. For example, for indigenous fruits, rapid progress will be made if indigenous knowledge can be used. Usually rural people know which are the best individual trees in their area for yield, fruit size, or flavor. Thus, as with temperate apples, pears, etc., people can be asked to report the existence of superior trees, so reducing the task of screening large numbers of trees. On the other hand, for medicinal trees, it is more likely that a chemical screening process will be required, but the magnitude of this task can probably be reduced by starting on a population basis, since it is likely that trees from certain environments will be richer in the required metabolites. Meanwhile, for timber trees, log size and straightness are the first selection criteria. Various forms of "plus-tree" (i.e., elite selection) provenance and progeny selection are well known. To these have recently been added some "predictive tests" which can be applied in the nursery as a procedure for mass screening from genetically diverse seedling populations. This involvement of farmers, however, has to be done for their ultimate benefit, in accordance with the Convention on Biological Diversity.

By capturing genetic diversity of a wide range of indigenous trees for growth in agroforestry systems, it is hoped the promises of agroforestry to alleviate poverty and to mitigate environmental degradation and the loss of biodiversity will be fulfilled.

Reference

Reprinted with permission from Roger R. B. Leakey, Agroforestry for Biodiversity in Farming Systems in Biodiversity in Agroecosystems, W. W. Collins and C. O. Qualset, Eds, Copyright CRC Press, Boca Raton, Florida ©1999. For order information call (800) 272-7727 (in the US).

Recent Publication

Domestication of Agroforestry Trees in Southeast Asia, 1999. Forest, Farm, and Community Tree Network (FACT Net), Winrock International, 38 Winrock Drive, Morrilton, AR 72110-9370 USA Tel: 501-727-5435, Fax: 501-727-5417 Email: forestry@winrock.org

Related Editions to The Overstory

• The Overstory #54--The Agroforester's Library, Part Two--Species References
• The Overstory #59--Choosing Species for Timber Production and Multiple Benefits
• The Overstory #43--Essentials of Good Planting Stock
• The Overstory #19--Selected Tree Seed
• The Overstory #16--Multipurpose Trees