Table Of ContentAdvanced Series in Agricultural Sciences 23
Co-ordinating Editor: B. Yaron, Bet-Dagan
Editors: B. L. McNeal, Gainesville
F. Tardieu, Montpellier
H. Van Keulen, Wageningen
L. D. Van Vleck, Ithaca
Advanced Series in Agricultural Sciences
Volumes already published in the series
Volume 10 Volume 20
Saline and Sodic Soils (1982) Water Flow and Solute Transport
E. Bresler, B. L. McNeal, D. L. Carter in Soils (1993)
D. Russo, G. Dagan (Eds.)
Volume 11
A Theory of Feeding and Growth of Volume 21
Animals (1982) Production of Sugarcane:
J. R. Parks Theory and Practice (1993)
G. Hunsigi
Volume 12
Fertilization of Dryland and Volume 22
Irrigated Soils (1982) Management of Water Use
J. Hagin, B. Tucker in Agriculture (1994)
K. K. Tanji, B. Yaron (Eds.)
Volume 13
Agricultural Soil Mechanics (1983) Volume 23
A. J. Koolen, H. Kuipers Woody Plants in Agro-Ecosystems
of Semi-Arid Regions (1995)
Volume 14 H. Breman, J.-J. Kessler
Energy and Agriculture (1984)
G. Stanhill (Ed.) Volume 24
Soilless Culture Management (1995)
Volume 15 M. Schwarz
The Rhizosphere (1986)
E. A. Curl, B. Truelove
Volume 16
Population Genetics:
Basic Principles (1987)
D. P. Doolittle
Volume 17
Irrigation with Treated Sewage
Emuent (1991)
A. Feigin, 1. Ravina, J. Shalhevet
Volume 18
Advances in Statistical Methods
for Genetic Improvement of
Livestock (1990)
D. Gianola, K. Hammond (Eds.)
Volume 19
Electromagnetic Radiations in Food
Science (1992)
1. Rosenthal
Henk Breman J an-J oost Kessler
Woody Plants
in Agro-Ecosystems
of Semi-Arid Regions
with an Emphasis on the Sahelian Countries
With 55 Figures and 75 Tables
Springer-Verlag
Berlin Heidelberg New York
London Paris Tokyo
Hong Kong Barcelona
Budapest
Dr. HENK BREMAN
Ir. JAN-JOOST KESSLER
Research Institute for Agrobiology and Soil Fertility
Ministry of Agriculture, Nature Management and Fisheries
P.O. Box 14, 6700 AA Wageningen
The Netherlands
ISBN-13: 978-3-642-79209-0 e-ISBN-13: 978-3-642-79207-6
DOl: 10.1007/978-3-642-79207-6
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This book is dedicated to Paul Sciarone, a
graduate in law and in physics, whose insight
into the value of the studies on rangeland
dynamics in the Sahel region led to the
initiative of providing funds for subsequent
studies on the role and potential of woody
plants in this region.
Preface
This book provides a quantitative analysis of the role of woody
plants in semi-arid regions, for the aSSessment of their benefits
in agrosylvopastoralland-use systems with productive and sus
tainability objectives. The insights presented and conclusions
drawn allow the additional benefits of woody plants for specific
climatic and physical site conditions and land-use systems to
be estimated. The Sahel and Sudan zones in West Africa, on
which the book focusses, represent resource-poor conditions,
whose ecological dynamics have been relatively well studied.
The role of woody plants in this region, as assessed in this
book, is extrapolated to other semi-arid regions, leading to
general conclusions on agroforestry's potential as an option
for sustainable land use in semi-arid regions.
The origins of this book go back to 1982, when the Club du
Sahel requested that available data on woody plants in the
Sahel region be synthesised, to provide basic information to
enable better attention to be given to woody plants in rural
development programmes. We are grateful to the Club du
Sahel for this challenge.
Various people contributed to studies used in this book.
The preliminary inventory of the data available was made by
Frits Ohler; later his work was continued by Franciska Dekker.
Useful contributions were made by Chris Geerling and Frits
Penning de Vries. We thank Arnoud Budelman, Sjaak Conijn
and Meine van Noordwijk for their constructive criticism of
drafts of some chapters, Pieter Oostra for spending many
hours in correcting the list of references, and we are very
grateful to Peter Uithol for doing the simulation studies and
the layout. The Wageningen Agricultural University, Forestry
Department is acknowledged as having enabled the second
author to finalise this book.
The work involved in creating this book was supported
by the Research Institute for Agrobiology and soil Fertility
(AB-DLO) in Wageningen and, indirectly, by the Netherlands
VIII Preface
Ministry of Foreign Affairs, through their support to the
AB-DLO for research in Sahelian countries.
Wageningen, The Netherlands H. BREMAN
December 1994 1.-1. KESSLER
Contents
1 Introduction ............................... . 1
2 The Distribution and Canopy Cover
of Woody Species .......................... . 4
2.1 Introduction and Methodology ............... . 4
2.1.1 Introduction ............................... . 4
2.1.2 Climatic Zones ............................ . 4
2.1.3 Landscapes, Geomorphological Units
and Groundwater .......................... . 6
2.1.4 Land-Use Types ........................... . 8
2.1.5 Canopy Cover ............................. . 9
2.2 Distribution and Canopy Cover Data ......... . 12
2.2.1 1975-1982 ................................ . 12
2.2.2 Climatic Influences ......................... . 19
2.3 An Ecological Interpretation
of Woody Vegetation in the SSW A ........... . 25
2.3.1 Introduction:
Water Availability and Soil Texture .......... . 25
2.3.2 African Savannas .......................... . 27
2.3.3 The Sahel Zones ........................... . 28
2.3.4 The Sudan Zones .......................... . 32
2.3.5 Conclusions ............................... . 33
2.4 Human Influences on Woody Plants .......... . 34
2.4.1 Introduction ............................... . 34
2.4.2 Fire ...................................... . 35
2.4.3 Livestock Grazing and Browsing ............. . 39
2.4.4 Agriculture ................................ . 47
2.4.5 Wood Exploitation ......................... . 50
2.5 Conclusions ............................... . 51
3 Production of Woody Plants ................. . 54
3.1 Introduction ............................... . 54
3.2 Productivity and Biomass
of Woody Plant Communities ................ . 54
3.2.1 Gross and Net Productivity .................. . 54
x Contents
3.2.2 Biomass and Net Productivity ................ . 55
3.2.3 Conclusions ............................... . 59
3.3 Production of Woody Plant Components ...... . 60
3.3.1 Wood Production .......................... . 60
3.3.2 Foliage Production ......................... . 63
3.3.3 Flower and Fruit Production ................. . 66
3.3.4 Conclusions ............................... . 68
3.4 Estimating Woody Plant Production .......... . 69
3.4.1 Introduction ............................... . 69
3.4.2 Foliage Production and Canopy Cover ........ . 69
3.4.3 Methods to Estimate Woody Plant
Productivity ............................... . 71
3.4.4 Conclusions ............................... . 76
3.5 Phenology ................................ . 77
3.5.1 Introduction ............................... . 77
3.5.2 Phenological Data from the SSW A ........... . 77
3.5.3 Conclusions ............................... . 84
3.6 Nutrient Concentrations, Digestibility
and Palatability ............................ . 84
3.6.1 Introduction ............................... . 84
3.6.2 Nutrient Concentrations
of Woody Plant Components ................ . 88
3.6.3 Digestibility of Forage from Woody Plants ..... . 92
3.6.4 A Comparison with Herbaceous Foliage ....... . 94
3.6.5 Palatability of Forage from Woody Plants ..... . 94
3.6.6 Conclusions ............................... . 97
4 The Influence of Woody Plants
on Plant Production Factors .................. 98
4.1 Introduction ................................ 98
4.2 Interactions Between the Woody
and Herbaceous Layer ....................... 99
4.2.1 Introduction ................................ 99
4.2.2 Relationships Between the Woody
and Herbage Layer .......................... 100
4.2.3 Effects on Herbage Production
by Bush Clearing or Tree Felling .............. 107
4.2.4 Herbage Species Composition
in Relation to Canopy Cover ................. 109
4.2.5 Conclusions ................................ 113
4.3 Root Systems of Woody Plants ................ 114
4.3.1 Root Systems of Woody Plants
in Semi-Arid Regions ........................ 114
4.3.2 Root System Dynamics ...................... 121
Contents XI
4.3.3 Comparison with Herbaceous Root Systems .... 123
4.4 Influences of Woody Plants
on Water Availability ....................... . 124
4.4.1 Introduction ............................... . 124
4.4.2 Processes Influencing Water Availability ...... . 125
4.4.3 Water Availability and Water Use ............ . 146
4.4.4 Conclusions ............................... . 152
4.5 Influences of Woody Plants
on Nutrient Availability ..................... . 153
4.5.1 Introduction ............................... . 153
4.5.2 Patterns of Soil Fertility
in Relation to Woody Plants ................. . 154
4.5.3 Soil Fertility Changes During Fallowing ....... . 163
4.5.4 Woody Plant Processes
Influencing Nutrient Availability ............. . 167
4.6 Soil Organic Matter and its Functions
in Relation to Woody Plants ................. . 199
4.6.1 Introduction ............................... . 199
4.6.2 Effect of SOM on Soil Physical
and Chemical Properties .................... . 200
4.6.3 Decomposition Processes ................... . 201
4.6.4 Mineralisation Processes .................... . 204
4.6.5 SOM Contents in Semi-Arid Regions ......... . 205
4.6.6 Decomposition of Woody Litter
in Semi-Arid Regions ....................... . 209
4.6.7 A Quantified Example from the SSW A ....... . 213
4.6.8 Conclusions ., ............................. . 217
4.7 Influences of Woody Plants
on Light Availability ....................... . 219
4.7.1 Introduction ............................... . 219
4.7.2 Light Intensity and Plant Production .......... . 220
4.7.3 Distribution and Quality of Light
Under Woody Canopies .................... . 223
4.7.4 Light Availability Under a Closed Canopy ..... . 225
4.7.5 Light Availability
Under Isolated Woody Plants ................ . 227
4.7.6 Conclusions ............................... . 231
4.8 Potential Influences of Woody Plants
on Plant Production ........................ . 232
4.8.1 Introduction ............................... . 232
4.8.2 Net Production Limited by Light ............. . 234
4.8.3 Net Production Limited by Water ............ . 237
4.8.4 Actual Net Production, Limited by Water
and Nutrients .............................. . 248
4.8.5 Woody Plants and Plant Production Factors ... . 260
