This statement, made by Le Houerou

This statement, made by Le Houerou (1980b) with particular reference to
grazing and husbandry problems in Africa, is applicable to most other aspects
of multipurpose woody perennials. But it is particularly true with regard to
data on productivity of this part of the plant community.
The scope of this paper does not permit a comprehensive literature review
on the productivity of multipurpose trees and shrubs. However, the screening
of a considerable number of those publications of various types which elaborate
not ordy on floristic and other aspects of plants, but also on uses, clearly
confirms that many authors provide interesting information on potential
and actual uses of woody perennials, but very little factual data on productivity.
Out of the many hundreds of species actually named and the thousands
mentioned as potentially useful, probably less than a hundred have been
subjected to yield measurements either per tree or per hectare. This state of
affairs actually matches the results of the qualified search of ICRAF's Multipurpose
Tree and Shrub Data Base, with only 16% of the uses mentioned
being accompanied by yield data.
Most authors of compendium-type publications, like, for example, von
Breitenbach (1963), Williams (1949), Burkhill (1935), Little (1980), Poynton
(1984), Schmutterer (1976), Palmer and Pitman (1972), Williamson (1975),
and Vickers and Plowman (1984), provide interesting and often detailed
information on taxonomy, phenology, morphology, and some on environmental
requirements also. However, even if the title of the publication
includes such adjectives as 'economic', as in the case of Burkhill's (1935)
Dictionary of Economic Products of the Malay Peninsula, yield data are not
included in the listed uses of woody perennials. Attributes, such as 'useful'
mentioned in association with the title also often do not fulfill the expectation
of obtaining data on actual productivity. Poynton (1984), Williamson (1975)
and Vickers and Plowman (1984) are apt examples.
What may sound like criticism is not meant to belittle the tremendous and
commendable efforts made by the authors mentioned in presenting in a
digested form the various aspects of plant biology and uses in qualitative
terms. It may not have been the intention, nor within the scope, of these