Tropical Trees: Propagation and Planting Manuals
RAISING SEEDLINGS OF TROPICAL TREES
Written by K A Longman
Illustrated by Esther Dobson and R H F Wilson
Commonwealth Science Council
Tropical trees are increasingly seen as a valuable renewable natural resource. They maintain and improve soil fertility, and provide protection from sun, wind and heavy raindrops. Trees also yield a great range of important products, play a crucial role in many farming systems, and form the base of the food-chain for numerous animals. Their presence is clearly essential for the survival of people in the tropics.
Despite these many vital roles, tropical trees continue to disappear about ten times faster than they are replaced, which threatens the life-support systems of many human communities. Yet the forests and savannas, farmland and woodlands where they thrive could be managed sustainably, providing soil protection, supplies of products and other benefits in perpetuity.
Now tree planting projects are springing up all over the tropics, and manuals are needed because:
some agriculturalists thought that farmland should be completely cleared
foresters concentrated on a few introduced species, grown in pure plantations
economics was equated with maximising short-term gains
knowledge of tree biology did not underpin land-use
experience in one locality did not reach other regions
without trees, the land cannot support increasing human populations
and also because:
in the past, many kinds of trees just came up by themselves
information is still lacking about growing most local species
most of them are still ‘undomesticated’
seeds may not always be available
just one of a number of potential problems could lead to failure
Tropical Trees: Propagation and Planting Manuals provide practical, illustrated guide-lines, based on general scientific understanding and local experience. The main aim is to encourage the growing, planting and care of trees on any site, by anyone, at any scale. The series covers all stages from genetic selection through setting up a tree nursery to planting and successful establishment in the field (see inside back cover). Also included are sources of further information and examples of check-lists, record sheets and worked examples of calculations.
The Manuals are wiro bound so that pages can easily be photocopied for use in the field. We hope that the series will stimulate translations into other languages and the writing of sheets specifically for local use.
© Commonwealth Secretariat 2003
Published by the Commonwealth Secretariat
May be purchased from the
Commonwealth Secretariat Publications
Marlborough House, Pall Mall
London SW1Y 5HX
ISBN 0 85092 656 4
This manual may be reproduced in part for the purposes of education or to facilitate fieldwork
Prepared on behalf of the Commonwealth Science Council
Typeset in Plantin by the Commonwealth Secretariat.
Printed by SRM Production Services, Malaysia
This is the second volume (though actually the fourth to appear) in the series Tropical Trees: Propagation and Planting Manuals. It is about tropical tree seeds - choosing, obtaining, handling and germinating them. As with the previous manuals, it is based on the general biological principles that apply to woody perennials throughout the humid and semi-arid tropics. Thus, rather than listing instructions for individual species, it describes seed propagation environments and methods for raising good seedlings of most kinds of trees, provides advice on useful techniques and includes a check-list for trouble-shooting.
Planting tropical trees is frequently hampered by the difficulty of obtaining enough good seed of the desired species. This manual addresses the many facets of this problem in a practical way by starting from the processes of sexual reproduction in trees, typically both delayed and intermittent, except in relatively few species. The prospects for stimulating flower formation and for increasing the setting of fruits are discussed, and the vital and difficult questions of genetic selection explained in straightforward language. Collecting fruits and handling seeds are covered, with emphasis on avoiding losses at each stage, and on distinguishing non-storing seeds from those that are storable. Shading levels and germination media for successfully raising young seedlings are given considerable attention, together with techniques that can increase the proportion of them that survive. Other sheets deal with using ‘wildings’, crossing parent trees and doing seed experiments, and give sources of further information.
Like Volume 1 (Rooting Cuttings of Tropical Trees), this manual concentrates on a key stage in tree development. Readers should refer to Volume 3 (Growing Good Tropical Trees for Planting) for the later stages of handling and protecting nursery stock, as well as for information about the vegetative growth of trees and advice on setting up a tree nursery. The publication of Volume 2 completes the first section of the 5-part series, leaving the actual planting out and subsequent protection of the young trees for the final manual.
It is estimated that tropical ecosystems are currently still losing around a million trees a day, while planting and natural regeneration are together replacing less than 10 percent of these. Far from being simply a concern of conservation biologists, many other groups of people depend upon this serious shortfall in tree cover being made up, and then surpassed. For instance, farmers cannot go on indefinitely producing food off soil of declining fertility, yet a suitable admixture of soil-improving trees and shrubs Frequently allows a move towards sustainability. Villagers who now have to walk long distances to fetch firewood and water have often recognised that these two kinds of shortage go together. Town-dwellers who can no longer find previously common everyday articles in the market may be realising that the woodlands that used to provide a sustainable supply are no longer there. Administrators trying to provide enough goods and services for rising populations could appreciate that tree-planting might reclaim much of the one-fifth of tropical land which was degraded and rendered unproductive between 1945 and 1990.
So tree-planting is urgently needed; and it can be done by ordinary people without
great costs, and without having decades to wait for the many benefits and products. How is
the community to continue to offer sick children the medicinal products it knows about - let
alone one relevant to treating a world-wide disease - without maintaining a rich and diverse
resource of trees nearby? Rather than leaving tree planting only to the Forestry Department,
every branch of government and of education needs to encourage people to plant the trees
that could make a difference. This will not be easy for many tropical countries, perhaps
struggling with the effects of devastating floods or the extensive fires that ran out of control
- as well as great problems of price fluctuation, international debt and population structure
- yet it is crucial to their future stability.
The many important roles of tropical trees, covered in Volume 4 of this series (Preparing to Plant Tropical Trees), actually range from the global to the microscopic, and involve all of us, sometimes in unexpected ways. For instance, the capacity of trees to lock away carbon in their trunks, roots and the soil means that extra trees help to counterbalance global warming, whereas those net 300-odd millions of trees lost each year simply add to the problems being caused by the rate at which fossil fuels are being consumed. On a regional scale, there is even evidence that extensive deforestation has altered the very climate the site experiences. Or at the level of the close associations between soil micro-organisms and trees, how can we expect, without them, to enjoy the free and efficient nutrient recycling that underpins the sustainability of tropical land?
By shaking off some of the legacy of the past, perhaps the turn of the centuries will be remembered as a key stage in real human development in the tropics, after the disillusionment with projects that lacked local inspiration. Moreover, the last decades of the old millennium have been dominated by views which placed short-term profit above sustainable land-use. Essentially these doctrines prevailed by claiming pride of place for the market value of one out of a hundred products of tropical woodland, and playing down or ignoring all the other direct, indirect and ongoing benefits of tree cover. As such, its apparent logic evidently contained the seeds of its own destruction. But the deleterious results have been profound, the more so because many countries were thrust further into undermining their future prospects because of urgent present purposes. This set-back means that planting trees, within a fresh and positive vision for tropical development, will now require collaboration on a grand scale between all those who have a relevant part to contribute. This manual is an attempt to act along these lines.
I should like to thank the numerous colleagues and students who have contributed to my thinking over many decades.
The author, Dr Alan Longman, has worked in the West African tropics for 9 years, teaching plant physiology, doing research on trees and planning and developing a large tree nursery for vegetative propagation. He taught and supervised students at all levels, and his research into the growth and development of trees included studies of flowering and phase-change, rooting of cuttings and early genetic selection, and the effects of day-length and temperature on shoot growth and bud dormancy.
Starting as a forestry worker in 1949, Dr Longman was a Senior Lecturer in the University of Ghana, Principal Tree Physiologist of the U.K. Forestry Commission and a Charles Bullard Fellow at Harvard University. He began a research project on tropical trees at the Institute of Terrestrial Ecology near Edinburgh, Scotland, which has now been running for almost 25 years, with linked projects in several tropical countries.
Dr Longman felt that the practical knowledge and experience he gained during his time in West Africa could be of value to people throughout the tropics who are struggling to replace the 1 million tropical trees destroyed every day. On his retirement he embarked on the task of producing the five manuals in this series. He produced the manuscript for this second volume (the fourth to be produced) shortly before his untimely death.
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Raising Seedlings of Tropical Trees
|why grow tropical trees?||B 1|
|propagation by seed||B 2|
|overcoming seed problems||B 3|
|direct sowing||B 4|
|Sexual reproduction in trees|
|introduction: juvenility and maturity||B 10|
|from flower initiation to pollination||B 11|
|fruit and seed formation||B 12|
|seed viability and dormancy||B 13|
|stimulation of flowering||B 14|
|Choosing seed sources|
|introduction: biodiversity and domestication||B 20|
|provenance differences||B 21|
|which parent trees?||B 22|
|crossing trees with each other||B 23|
|reliable seed supplies||B 24|
|introduction to avoiding losses||B 30|
|fruit and seed collection||B 31|
|seed extraction and cleaning||B 32|
|drying and storing seeds||B 33|
|pre-sowing treatments||B 34|
|Germinating the seeds|
|introduction: favourable seed propagation environments||B 40|
|shelter and shading for germination||B 41|
|the seed germination medium||B 42|
|sowing and covering seeds||B 43|
|using wildings and germinating seeds||B 44|
|potting up and transplanting young seedlings||B 45|
|watering seeds and very young seedlings||B 46|
|checking and protecting seedlings||B 47|
|germination tests and other seed experiments||B 48|
|Check-lists, sources and records|
|check-list for seed and young seedling problems||B 50|
|some information on tree flowering and genetics||B 51|
|some information on seed handling and propagation||B 52|
|assessment of germination||B 53|