A guide to forest seed handling

with special reference to the tropics


compiled by
R.L. Willan

First printing 1985
Reprinted 1987

The designations employed and the presentation of material in this publication do not imply the expression of any opinion whatsoever on the part of the Food and Agriculture Organization of the United Nations concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries.

ISBN 92-5-102291-7

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying or otherwise, without the prior permission of the copyright owner. Applications for such permission, with a statement of the purpose and extent of the reproduction, should be addressed to the Director, Publications Division, Food and Agriculture Organization of the United Nations, Via delle Terme di Caracalla, 00100 Rome, Italy.


FAO and the DANIDA Forest Seed Centre have cooperated closely over the past two decades in the field of tree improvement and seed procurement. A representative of the Seed Centre has been a member of the FAO Panel of Experts on Forest Gene Resources since it was established in the sixties, while a representative of FAO's Forestry Department is a member of the Project Committee of the Seed Centre. This has ensured a high level of integration between the programmes of the two organizations. A particularly fruitful example of cooperation has been the series of training courses on tree improvement, seed handling and afforestation, jointly sponsored by FAO and DANIDA, and held successively in Denmark, Kenya, Thailand, Nigeria and Venezuela. Currently the Seed Centre is providing storage facilities for seed collected through FAO's project on Genetic Resources of Arid and Semi-arid Zone Arboreal Species for the Improvement of Rural Living.

The present publication is a further example of this cooperation. It gathers together information from a number of sources, including the FAO/DANIDA training courses mentioned above, Working Papers from FAO field projects, as well as technical leaflets and notes compiled by the Seed Centre. A draft edition of the Guide was published in 1983 in a limited number of copies, which were distributed for comments. The present edition has been revised in the light of comments from readers and illustrations have been added.

The increased rates of tree planting, which is apparent in so many countries today, emphasizes more than ever before the need for good seed. Seed quality has a critical effect on the quality of the trees established and on the economics of planting them. This is equally true whether planting is in large-scale commercial plantations or in small-scale diffuse farm woodlots or as scattered single trees. Seed quality comprises both the physiological viability and vigour of the seeds and their genetic quality - their ability to produce healthy offspring which are well suited both to the sites where they are planted and for the products or services which they are intended to provide. This Guide is concerned with the physiological quality of seeds and it is hoped that it will be useful especially to developing countries in the tropics, where publications on forest seed handling are few in comparison with those for the temperate zones.


The guide was compiled by R.L. Willan, consultant. The following specialists kindly submitted valuable, written comments on earlier drafts: H. Barner, F.T. Bonner, A.G. Gordon, S.K. Kamra, F. Ng, P.G. Pattanath, M. Robbins, M. Simak, B. Suszka, J.W. Turnbull and B. Wang.

Illustrations have been provided from a wide variety of sources; many have appeared in earlier publications. FAO and DANIDA are grateful to all who generously gave illustrative material and permission to reproduce it. The source of each illustration is shown in the individual credit lines. The line drawing on the cover is by M. Robbins.

Facilities and help given by all staff at the DANIDA Forest Seed Centre and by library staff at the Commonwealth Forestry Institute in Oxford are acknowledged with thanks.


Rome, 1985 © FAO

Hyperlinks to non-FAO Internet sites do not imply any official endorsement of or responsibility for the opinions, ideas, data or products presented at these locations, or guarantee the validity of the information provided. The sole purpose of links to non-FAO sites is to indicate further information available on related topics.

This electronic document has been scanned using optical character recognition (OCR) software. FAO declines all responsibility for any discrepancies that may exist between the present document and its original printed version.


Chapter 1     INTRODUCTION

Purpose and Content of this Guide

The Importance of Seed in Present-Day Forestry



Pollination and Fertilization

Angiosperm Seed Development

Angiosperm Fruit Development

Seed Dispersal in Angiosperms

Gymnosperm Seed Development

Gymnosperm Fruit Development

Seed Dispersal in Gymnosperms

Seed Germination


Hazards of Seed Production



Determining Species, Provenances and Stands




Determining Seed Quantities

Determining the Year for Collection

Effect of periodicity

Counting the fruit crop

Fruit crop rating methods

Estimating full seed content by cutting test.

Determining the Best Dates for Collection

Laboratory methods

Field methods

Collection of Immature Seeds

Determining Which Trees to Collect From

Large-scale collections

Small-scale research collections

Single tree collections

Single clone collections

Collections for conservation

Assembling Resources for Seed Collection

Special Considerations for International Expeditions



Collection of Fallen Fruits or Seeds from the Forest Floor

Natural seedfall

Manual shaking

Mechanical shaking

Collection of seed after dispersal

Animal caches

Collection from the Crowns of Felled Trees

Collection from Standing Trees with Access from the Ground

By hand

Cutting, breaking and sawing

Use of rifle

Collection from Standing Trees with Access by Climbing

Climbing into the crown by way of the bole

Climbing into the crown directly

Climbing and picking fruits within the crown

Collection from Standing Trees with Other Means of Access

Productivity in Fruit Collection

Training and Safety



Maintaining Viability

Seed Extraction Close to the Collection Site

Maintaining Identity


Special Precautions for Recalcitrant Seeds in the Humid Tropics



Operations Prior to Extraction

Temporary storage at the processing depot



Methods of Extraction


Drying of Fruits without Artificial Heat

Drying under cover

Sun drying

Drying of Fruits with Artificial Heat

Types of Drying Kiln

Stationary tray kilns

Vertical progressive kilns

Horizontal progressive kilns

Rotating drum kilns

Portable kilns

Safety Precautions




Other Methods of Extraction

Operations after Extraction


Seed Cleaning Methods

Screening or sieving

Sorting according to length


Liquid flotation

Friction cleaning

Specific gravity separation

Other cleaning methods


Control of Moisture Content

Relationship of Seed Moisture Content to Atmospheric Humidity

Drying of Orthodox Seeds

Mixing before Storage

Chapter 7     SEED STORAGE


Natural Longevity of Tree Seeds

Hard-coated orthodox seeds

Orthodox seeds without hard seedcoats

Recalcitrant seeds

Factors Affecting Longevity in Storage

Seed condition

Storage conditions and ageing of seeds

Storage atmosphere

Seed moisture content

Storage temperature


Choice of Storage Method

Storage at ambient temperature and humidity

Dry storage with control of MC but not of temperature

Dry storage with control of both MC and temperature

Dry storage for long-term gene conservation

Moist storage without control of MC or temperature

Moist cold storage with control of temperature

Other methods

Storage Containers

Materials freely permeable to moisture and gases

Materials completely impermeable, when sealed, to moisture and gases

Materials resistant, but not completely impermeable, to moisture

Use of desiccants in containers

Choice and use of container

Design and Engineering of Seed Storage Facilities

Storage capacity

Design and equipment

Seed Shipment



Classification of Types of Dormancy

Treatments Designed to Break Seed-Coat Dormancy

Physical methods

Soaking in water

Acid treatment

Biological methods

Dry heat and fire

Special treatments for mechanical dormancy

Treatments Designed to Break Endogenous or Embryo Dormancy

Morphological dormancy

Overcoming physiological dormancy -cold stratification

Other moist prechilling methods

Chemical treatment of physiological dormancy

Other treatments for endogenous dormancy

Treatments Designed to Overcome Double Dormancy

Seed Dressing and Pelleting


Materials and methods

Other Types of Pretreatment

Chapter 9     SEED TESTING




Use of seed triers

Reducing the size of composite samples

Non-mechanical methods of dividing

Mechanical methods of dividing

Weight of sample

Purity Analysis

Seed Weight

Germination Testing

Germination equipment

Germination conditions

Germination conditions for selected species


Germination energy

Germination value

Germination testing in the nursery

Testing homogeneity of germination results

Combining Purity and Germination Tests

Indirect Tests of Viability

Cutting test

Topographical tetrazolium test

Excised embryo test

Radiographic methods

Hydrogen peroxide

Testing Moisture Content

Other Tests


Damage, health

Calculation of Results


Seed weight


Indirect tests of viability

Moisture content

Interpretation of Results


Special Considerations for Recalcitrant Seeds of Tropical Rainforests

Appendix 1     Seed documentation

1 A   An example of an integrated system of seed recording forms as used in Sabah

Table 1Seed stands of forest research centre
Table 2Summary of forms and usage
Seed form  1Fruit collection demand note
"      "  2Fruit collection advice note
"      "  3Sack collection label
"      "  4Seed extraction record
"      "  5Register of seed stock and disposals
"      "  6Seed storage container label
"      "  7Purity and germination testing, seed sample transfer envelope
"      "  8Moisture content analysis, seed sample transfer form
"      "  9Sample test ledger sheet
"      "10Germination and purity test
"      "11Summary of test results
"      "12Seed demand/issue form
"      "13Seed order check list
"      "14Nursery germination record
"      "15Final germination test report

1 B   Selected examples of seed origin data sheets

1B1OECD (Certificate of Provenance)
1B2Tanzania Silviculture Research Station
1B3British Columbia Forest Service
1B4British Columbia Forest Service
1B5British Columbia Forest Service
1B6DANIDA Forest Seed Centre
1B7Petawawa Forest Experiment Station
1B8Thai-Danish Pine Project
1B9Commonwealth Forestry Institute
1B10Division of Forest Research, CSIRO, Canberra
1B11Banco de Semillas, ESNACIFOR, Honduras

1 C   Selected examples of other seed forms

1C1Cone Collecting Costs, British Columbia
1C2Register of identity numbers:
 I Index of serial identity numbers
1C3Register of identity numbers:
 II Index of species
1C4Seed extraction, Thai-Danish Pine Project
1C5Seed germination, Thai-Danish Pine Project
1C6Seed stock, Thai-Danish Pine Project
1C7Combined seed data card, Thai-Danish Pine Project
1C8Combined seed stock & data card, Denmark
1C9International seed lot certificate, ISTA
1C10Germination data sheet for replications of equal weight, Australia
1C11Cone crop survey and evaluation forms, British Columbia
1C12Sample seed testing ledger sheet
1C13Combined seed testing sheet, UK
1C14Standard consignment note and seed certificate, Australia

Appendix 2     Considerations in the design and equipment of long-term seed-storage facilities for genetic conservation (orthodox species).

Appendix 3     Long-term seed-storage facilities of the regional genetic resources project at Turrialba, Costa Rica. Construction details.

Appendix 4     The use of deep-freeze chests for longterm storage of small seed collections.

Appendix 5     Logistics of collecting 200 kg of Pinus caribaea seed

Appendix 6     Annotated list of equipment which may be needed for collection of seed, site information and herbarium specimens.

Appendix 7     Glossary

Appendix 8     Bibliography

Select Bibliography (some key references)

Appendix 9     Index

Latin names



1.1     Estimated total areas of forest plantations in Tropical Africa, Tropical America and Tropical Asia 1975–1985.

1.2     Estimated annual planting rates. Brazil, India and Tropical Africa.

1.3     Effect of species choice on quantity of seed required per unit area.

2.1     Longitudinal section through a typical pistil just before fertilization.

2.2     Longitudinal sections through ripe seeds of Paulownia tomentosa and Tectona grandis.

2.3     Examples of different types of fruits.

2.4     Longitudinal section through an ovule of Pinus during the period of pollen tube development preceding fertilization.

2.5     Examples of germination in two West African Sterculiaceae. Epigeal in Mansonia altissima and hypogeal in Cola nitida.

3.1     Provenance Regions for Pinus caribaea and P. oocarpa in Honduras.

3.2     Cone crops of Douglas-fir, Vancouver Forest District, 1935–1974.

3.3     Example of a cone-cutter for seed crop estimation on a longitudinal section.

3.4     Seed content is estimated by counting good seeds on one surface of each of several sliced cones.

4.1     The Advanced Line Technique.

4.2     The Schaumann Tree Shaker.

4.3     Funnel for trapping Acacia aneura seed.

4.4     Net retrieval machine.

4.5     Use of vacuum seed harvester for acorns.

4.6     A selection of Acacia seed collecting equipment.

4.7     Saws, pruners, rakes and other hand tools for harvesting tree fruits.

4.8     The High Limb flexible chain saw.

4.9     Tree climbing spurs.

4.10   Two strut sectional ladder.

4.11   Single-strut sectional ladder.

4.12   Tree bicycle, tree gripper or baumvelo.

4.13   Tree bicycle in use.

4.14   Hand picking Larix cones. Tree bicycle.

4.15   Use of hand tools and safety line in picking fruits in the crown.

4.16   Climber controlling own descent by safety line locking method.

4.17   Use of extension platform for cone picking.

5.1     Interim cone storage racks.

5.2     Wire baskets used for temporary storage of cones.

5.3     Temporary cone storage in boxes.

5.4     Temporary frame for field drying eucalypt capsules.

6.1     Precuring sheds with open-air racks.

6.2     Top view of the Dybvig separator.

6.3     Solar drying of pine cones under clear polythene roofing.

6.4     Solar cone drying of Pinus kesiya and Pinus merkusii in rotatable drums.

6.5     Solar drying of pine cones.

6.6     Kiln seasoning. Stacked trays entering a kiln.

6.7     Interior view of a kiln with trays.

6.8     Rotating kiln.

6.9     Portable cone kiln.

6.10   Cone tumbler.

6.11   Double-storied tumbler room.

6.12   The Resilient Tapered Thresher.

6.13   CSIRO 15-cm Flailing Thresher.

6.14   Cement mixer used for dewinging.

6.15   Missoula dewinger for small seedlots.

6.16   Liriodendron tulipifera before and after dewinging.

6.17   Electrically operated laboratory seed blowers.

6.18   Locally made seed cleaner.

6.19   Air/screen seed cleaner.

6.20   Gravity seed separator.

6.21   Equilibrium moisture content of wheat seed, showing separate curves for desorption and absorption.

6.22   Moisture content percentages of fresh seed of Pinus palustris in equilibrium with air at various temperatures and relative humidities.

6.23   Equilibrium moisture contents for 3 orthodox species.

6.24   Equilibrium moisture contents for 4 recalcitrant species.

7.1     Airtight containers used for storing seed.

7.2     Interior view of cold storage room.

7.3     Examples of different types of container used for storage or shipment.

8.1     Effect of several presowing treatments on germination of black locust.

8.2     Benefits of cold stratification for speeding germination of loblolly pine.

8.3     The effect of various pretreatments on germination of Pinus elliottii.

8.4     The effect of pretreatment on germination of Acacia mangium.

8.5     A rinsing trough for washing acid from treated seeds.

8.6     One apparatus for treating large lots of seed with acid.

8.7     Outdoor stratification of Juglans nigra in sand.

8.8     Desired arrangement for stratification in a large barrel.

8.9     Loblolly pine seed prepared for stratification in a plastic bag.

8.10   Effects of several treatments to overcome double dormancy in eastern redbud.

8.11   The US Forest Service recommendation for preparing repellent and applying it to seed of Pinus elliottii.

8.12   Flow-scheme for the removal of mechanically damaged and filled-dead seeds according to PREVAC- and IDS- methods.

8.13   The germinating seeds of IDS/PREVAC-treated Pinus caribaea and P. oocarpa.

9.1     A seed trier.

9.2     Random cup divider.

9.3     Inverted cone dividers.

9.4     Seed dividers (a) Boerner (b) Gamet.

9.5     An opaque glass screen for purity tests and determinations of the number of seeds per kg.

9.6     Two types of weighing scales used in seed laboratories.

9.7     Counting board with seeds of Celtis laevigata.

9.8     Counting head on a vacuum seed counter.

9.9     Open seed germination cabinet and group of cabinets.

9.10   Conviron G 30 germinator.

9.11   Clear and black germination boxes developed for seed testing.

9.12   Copenhagen tank and rolled filter paper for germination tests.

9.13   Acorns of Quercus alba germinating on Kimpak.

9.14   Germination of Douglas-fir and lodgepole pine seeds.

9.15   X-ray radiograph of teak fruits showing the variation in the number of locules.

9.16   X-ray radiographs showing embryo and endosperm classes in coniferous seeds.

9.17   X-ray radiograph of Pinus caribaea seed.

9.18   Quercus seeds cut in halves for oven drying in moisture determination.

9.19   Dole electric seed moisture meter.

9.20   Electric moisture meters.