Plant Resources of Arid and Semiarid Lands. A Global Perspective

338 Pages·1985·4.893 MB·English

by  J. R. Goodin and David K. Northington (Eds.)

Plant Resources of
Arid and Semiarid Lands
A GLOBAL PERSPECTIVE
Edited by
J. R. Goodin
Department of Biological Sciences
and International Center for
Arid and Semiarid Land Studies
Texas Tech University
Lubbock, Texas
David K. Northington
Department of Biological Sciences
Texas Tech University
Lubbock, Texas
1985
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United Kingdom Edition published by
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LIBRARY OF CONGRESS CATALOGING IN PUBLICATION DATA
Main entry under title:
Plant resources of arid and semiarid lands.
Includes bibliographies and index.
1. Botany, Economic. 2. Arid regions flora.
3. Arid regions. I. Goodin, Joe R. II. Northington,
David K.
SB107.P57 1985 630'.915'4 85-7385
ISBN 0-12-289745-5 (alk. paper)
PRINTED IN THE UNITED STATES OF AMERICA
85 86 87 88 987654321
CONTRIBUTORS
Numbers in parentheses indicate the pages on which the authors' contributions begin.
EDWARD S. AYENSU (1), Office of Biological Conservation and Department
of Botany, Smithsonian Institution, Washington, D.C. 20560
LOUTFY BOULOS (129), National Research Center, Cairo, Egypt
ROLANDO H. BRAUN W. (257), CONICET, Instituto Argentino de Investiga-
ciones de las Zonas Aridas (IADIZA), Mendoza (5500), Argentina
K. M. M. DAKSHINI (69), Department of Botany, University of Delhi, Delhi
110007, India
JUAN M. GASTÓ (257), Facultad de Agronomia, Universidad Católica de
Chile, Santiago, Chile
J. R. GOODIN (319), Department of Biological Sciences, and International
Center for Arid and Semiarid Land Studies, Texas Tech University, Lub-
bock, Texas 79409
HSIOH-YU HOU (233), Laboratory of Plant Ecology, Institute of Botany, Aca-
demia Sinica, Beijing, People's Republic of China
M. LAZARIDES (35), CSIRO Division of Plant Industry, Institute of Biological
Resources, Canberra City, A.C.T. 2601, Australia
C. M. McKELL (187), NPI, Salt Lake City, Utah 84108
N. T. NECHAYEVA (291), Desert Institute, Ashkhabad 744000, USSR
1
DAVID K. NORTHINGTON (319), Department of Biological Sciences, Texas
Tech University, Lubbock, Texas 79409
ALFREDO OLIV ARES E. (257), Facultad de Ciencias Agrarias y Forestales,
Universidad de Chile, Santiago, Chile
O. B. WILLIAMS (35), CSIRO Division of Water and Land Resources, Institute
of Biological Resources, Canberra City, A.C.T. 2601, Australia
1
Present address: National Wildflower Research Center, Austin, Texas 78725.
IX
PREFACE
It was our intent to develop a reference work that would assess the existing
native plant resources in all arid and semiarid regions of the world. This invento-
ry was to include potential food, forage, fiber, fuel, medicinal, and industrial
uses. No such inventory is currently available for the world as a whole, and since
the dry areas comprise one-third of the earth's land surface, such a resource
should provide a stimulating focal point for human developmental efforts in these
regions.
Every effort was made to have the chapters as uniform as possible in organiza-
tion and as complete as possible in content. Because of a lack of available
information in given areas, however, some of the authors were unable to include
parallel data on all topics. Nonetheless, the result is easily the most complete and
impressive compilation of worldwide plant resource data for the arid zone.
To provide the reader with an overview of the nature, scope, and organization
of information that each author attempted to provide, we include the following
outline that was used in the preparation of this book:
I. A general and short paragraph introducing the chapter.
II. Brief information about the total size and the amount of area treated as arid
2
and semiarid (km ), and the location of these dry areas, including stability and
rate and direction of change. Because of edaphic factors, seasonality, or other
factors, areas not classically considered "deserts" are included because of their
low productivity.
III. Annual precipitation, temperature, humidity; wind ranges and patterns;
and seasons in each of the dry areas described above, including discussion of
"effective" precipitation (that available to plants) and the total climatic pattern.
IV. Elevation, relief, aspect, and the effects of topography on water drainage
and loss.
V. Basic soil types and their origins in these dry areas, with special reference
to any unusual edaphic problems such as gypsum outcrops, high salinity or
alkalinity, or serpentine soils, as well as comments on water penetration, holding
capacity, runoff, and the physical features that control such factors.
xi
xii PREFACE
VI. The availability of surface and subsurface water in the dry areas, includ-
ing any past or planned modification of usage by humans, such as dam building,
irrigation from diverted and underground sources, and other factors, and com-
ments on water quality as well (including water resource projections).
VII. Current and projected growth rates for countries and for the dry areas,
within each continent. Some authors discuss one or a few countries; others
discuss many.
VIII. The current economic reliance on arid land productivity for each
country.
IX. Balance of trade, current resources and needs, and developing resources.
X. The fate of those countries with dry regions. Can the resource and eco-
nomic base be affected by the presence of these dry areas—positively and/or
negatively?
XI. Emphasis on the nature of the plants to be discussed: native, with signifi-
cant potential but presently not being developed as a "crop" plant. Introduced
plants are not included; if such plants have potential, they are discussed with the
continent of origin.
A. Food plants. Discussion of those plants native to the dry regions of a given
area that have demonstrated potential as a source of food for human
consumption. Herbs, spices, and beverage plants are included. As possi-
ble, there is commentary on the degree of usefulness, time scale of devel-
opment as a crop, and potential use of the plant that is more than local
(i.e., Could it become important as an exportable resource?).
B. Forage plants. Inventory of the herbs or shrubs that have potential as
forage plants for domestic animals, including information on palatability,
nutritional quality, potential problems (toxicity), and the potential degree
of intensification or development as a "crop" plant, if available.
C. Medicinal plants. Survey of the plants having known value in the treat-
ment of illness or ailments. This section does not include an exhaustive list
of all plants, especially those having only rumored or undocumented
value.
D. Industrial plants.
1. Fibers. An inventory of any plants useful as wood for building or for
macerating for paper, weaving, basket making, textiles, etc.
2. Fuels. Sources of firewood or biomass energy from methane or alcohol
production are considered, in addition to any potential sources of hydrocar-
bons for direct energy consumption.
3. Oils. A survey of those plants native to the dry areas that contain extracta-
ble oils, since industrial uses for extractable oils are very broad.
4. Waxes, resins, and latexes. An inventory of plants from which commer-
cially producible waxes, resins, and latex products (such as rubber) can be
extracted.
PREFACE xiii
E. Other plants. Plants that are not potential foods, forages, or medicinals,
and have no commercial or industrial value for their fibers or extractable
chemical compounds but might have value as ornamentals, or be useful in
dune stabilization or erosion control or land reclamation after mining or
other disturbances.
XII. Discussion of the degree of habitat stability, water availability, and other
factors that must be considered in developing native "crop" plants in arid and
semiarid regions.
XIII. A consideration of the balance among population pressures, ecological
stability, potential of the plant resources, and economic or local needs. What,
philosophically, should be our overview of arid land development?
XIV. A summary of the native plants having the greatest potential as new
resources from the dry regions of each continent or subcontinent. Economic
worth, local need, time scale for development, etc., are considered.
The need for this book became evident at the International Conference on Arid
and Semiarid Land Plant Resources, held in 1978 in Lubbock, Texas. Sponsored
by the International Center for Arid and Semiarid Land Studies at Texas Tech
University, this conference included 200 participants from 22 countries and
resulted in the publication of the proceedings, Arid Land Plant Resources. Plen-
ary talks summarizing specific geographic regions of the world were presented at
this conference, but because of the length of the proceedings the presenters
decided that a second publication would be appropriate.
We gratefully acknowledge the support of ICASALS and Texas Tech Univer-
sity, and especially thank Katina M. Clark for the preliminary editing of all the
manuscripts.
1
AFRICA
Edward S. Ayensu
Office of Biological Conservation
and Department of Botany
Smithsonian Institution
Washington, D.C.
I. Introduction 1
II. Physiography 2
A. Size and Location 2
Β. Topography and Climate 2
C. Edaphic Factors 7
D. Hydrology and Water Resources 16
III. Demography 16
IV. Socioeconomic Factors 20
V. Plant Resources 22
A. Food Plants 25
B. Forage Plants 26
C. Medicinal Plants 28
D. Industrial Plants 29
E. Other Plants 31
VI. Summary 31
References 33
I. INTRODUCTION
This chapter is designed to provide a detailed perspective on the development
problems facing the arid and semiarid zones of Africa. Generally, in terms of
average family income, the countries that fall within these zones are among the
least prosperous. They include countries in the Sahelian zones that bound the
Sahara and large areas in eastern and southern Africa. The populations living in
these zones also experience poor dietary standards. Their caloric intake, more
than 70% of which is derived from cereals, is barely adequate; various studies by
the FAO and WHO indicate that in 13 of the 17-odd countries in Africa that fall
PLANT RESOURCS E 1 Copyright © 1985 by Academic Press, Inc.
OF ARDI AND SEMIARD ILANSD All rights of reproduction in any form reserved.
2 EDWARD S. AYENSU
within the semiarid tropical zone, the average caloric consumption is well below
acceptable levels. It is also known that because of uncertain and variable produc-
tion levels and inadequate storage facilities, caloric intake just before harvest is
generally 25-30% lower than it is immediately after harvest.
Regardless of cultural differences among the arid and semiarid countries of
Africa, these countries share enough natural characteristics that should enable
them to adopt similar policy frameworks to remedy some of the major develop-
ment problems that confront them.
II. PHYSIOGRAPHY
A. Size and Location
Second in size only to Asia, Africa is joined to the Asian continent by the
isthmus of Suez. Geologically, Africa was at one time also connected to Europe
at what are now the straits of Gilbraltar and Tunis. The continent stretches for
—35° on either side of the equator, and is also crossed by both the tropics of
Cancer and Capricorn. Thus, the bulk of the continent lies within the tropics.
Additionally, its shape is such that most of the continent lies in the northern
hemisphere.
B. Topography and Climate
Because its coasts are almost unbroken, Africa has been described as a com-
pact continent. Apart from the Atlas Mountains in the northwest of the continent,
Africa is mainly a plateau arising by steep escarpments from narrow coastal
plains. (See Fig. 1 for the topography of the continent.)
The UNESCO (1979) Map of the World Distribution of Arid Regions delimits
2
portions of Africa's 30 million km area as hyperarid, arid, or semiarid. The
division between arid and semiarid roughly follows the 400-mm annual rainfall
contour, but the criterion actually used to separate climatic zones is the ratio of
annual precipitation to évapotranspiration. The latter is estimated from insola-
tion, atmospheric humidity, and wind data. This ratio is preferred over precipita-
tion or the amount of available water (the difference, rather than the quotient,
between precipitation and évapotranspiration) because it approximates a water
balance parameter which governs vegetative dry-matter production, and does so
in spite of contrasting seasons in different regions to which is it applied.
Figure 2 has been redrawn from the UNESCO map; the subhumid zone shown
on the original has been omitted, and the description of temperature regimes to
2
aridity per se has been subordinated. The hyperarid zone, —6.5 million km ,
consists of the vast Sahara region, the north coast of Somalia, and the coast of
southwest Africa. Each of its parts is bounded by broad bands of less-desiccated
1. AFRICA 3
Fig. 1. Countries and topography of Africa.
2
land; together they make up the 6.1 million km arid zone. The semiarid zone,
2
—4.8 million km in area, surrounds drier lands and extends out from them to
varying distances, depending on the topography.
Aridity, defined in terms of atmospheric parameters such as rainfall, sunlight,
humidity, and the transport of air, represents a constraint on any plant-soil
system. Within an arid zone, however, different soil associations and vegetative
cover occur. Whereas climate is reasonably stable, vegetative change can lead to
irreversible destruction of the habitat by unskilled management, and is one of the
4 EDWARD S. AYENSU
MAGHREB
HYPERARID
ARID
SEMIARID 1 ]
COOL WINTER (0-IO°C)
WARM WINTER (20-30°C) H|
^KARROO
Fig. 2. Arid zones of Africa.
major and urgent problems facing the people of the continent. Soils erode be-
cause of vegetational changes or become saline through irrigation and long-term
accumulation of underground water. Thus, the inhospitality of an arid zone to
vegetative production increases and becomes widespread. For example, Le
Houerou (1970) estimated that on an annual basis, 100 km 2 of sandy soils lose
the capacity to support a Stipa tenacissima steppe in the four North African