L A N D M A N A G E M E N T H A N D B O O K 30 A Guide to the Biology and Use of Forest Tree Seeds 1996 Province of British Columbia SPLENDOR OCCASU Ministry of Forests Research Program SINE A Guide to the Biology and Use of Forest Tree Seeds Carole Leadem Province of British Columbia SPLENDOR OCCASU Ministry of Forests Research Program SINE Canadian Cataloguing in Publication Data Leadem, Carole Louise Scheuplein, – A guide to the biology of forest tree seeds (Land management handbook ; ) Includes bibliographical references: p. --- . Seeds. Trees - British Columbia - Seeds. Gymnosperms - British Columbia - Seeds. Angiosperms - British Columbia - Seeds. Reforestation . I. British Columbia. Ministry of Forests. Research Branch. II. Title. III. Series. .. .’’ -- Prepared by Carole Leadem B.C. Ministry of Forests Glyn Road Research Station Glyn Road Victoria, BC for BC Ministry of Forests Research Branch Bastion Square Victoria, BC Published by B.C. Ministry of Forests Forestry Division Services Branch Production Resources 1205 Broad Street, 2 Floor Victoria, BC ©␣ Province of British Columbia Copies of this and other Ministry of Forests titles are available from: Crown Publications Inc. Fort Street Victoria, BC ACKNOWLEDGEMENTS I am grateful to Dr. D. George Edwards, Canadian Izard, Paul Nystedt, and Heather Strongitharm—and Forest Service, for his patience, guidance, and con- Anna Gamble for the publication’s design. structive criticism, and for giving so generously of his The efforts of the editorial team are most greatly wealth of knowledge about tree seeds. appreciated: Dr. Annette Walker, Fran Aitkens, and Thanks are extended to the many B.C. Ministry of Susan Bannerman. Andrew MacKinnon verified the Forests reviewers who shared their expertise and pro- tree species and scientific authorities mentioned in vided useful comments: Rob Bowden-Green, Heather this handbook. Rooke, and Dave Kolotelo of the Tree Seed Centre in I thank the following suppliers of the seed samples Surrey; Karen Yearsley of the Research Branch; Tony used for this publication’s photographs: Don Pigott, Willingdon of the Surrey Nursery; and Clare Hewson Yellow Point Propagation, Ladysmith; Peter Hellenius, of the Interior Seed Orchards in Vernon. Thanks also Silva Enterprises, Prince George; and the Ministry of to Joe Wong of Woodmere Nursey in Telkwa, and Forests Tree Seed Centre, Surrey. Tom Gore of the Candace Laird of the Silviculture Institute of University of Victoria’s Biology Department kindly British Columbia. made available his extensive photographic expertise Joanne Clark provided valuable technical support and facilities. Peggy Frank drew the illustrations for in producing the text and figures, and helped in figures and . Donald Gunn drew the illustrations countless other ways with the final manuscript. for figures and , and the cover topic indicator. I appreciated the work, suggestions, and enthusiasm D. George Edwards supplied the x-ray photos for of the Production Resources staff — especially David Figure . iii CONTENTS Acknowledgements . iii Introduction . The Basic Principles of Tree Seed Biology . . Seed Structure . . Development and Maturation . . Dormancy . . Germination . .. Hydration . .. Activation of growth processes . .. Emergence . .. Environmental factors . Applying the Principles of Tree Seed Biology . . Tree Seed Biology and Reforestation . . Seed Quality and Vigour . . Seed Collection and Storage . . Dormancy . . Germination . .. Hydration . .. Oxygen . .. Temperature . .. Light . .. Other factors . . Natural Regeneration . Conclusion . Appendix . Forest tree species occurring in British Columbia . Glossary . References . v Dormancy-release treatments for tree seeds . Stratification regimes commonly used for conifers grown in British Columbia . Moisture content guidelines for tree seeds . Forest tree seed anatomy (longitudinal sections) . Wings aid in the dispersal of seeds . Some trees contain resin vesicles in their seed coats . Seeds of the same genus can vary in size and shape . Typical development and maturation cycles of British Columbia conifer seeds . Comparison of the major steps in the natural and artificial regeneration sequences of forest tree seedlings . Stages of germinant development . Absorption of far-red light converts the pigment phytochromefar-red back to phytochromered . Vigorous seeds complete germination first . Mature and immature embryos of Douglas-fir . The longevity of seeds increases as seed moisture content and storage temperature decreases . Effects of stratification regime on the germination of western hemlock seeds . Effects of stratification regime on the germination rates of Pacific silver fir seeds . Respiration of subalpine fir seeds during stratification . Germination of a) lodgepole pine, b) Sitka spruce, and c) Douglas-fir seeds at different temperatures after stratification for , , , and weeks . X-rays are used to determine whether seeds are fully developed, damaged, or have been attacked by insects . A young whitebark pine seedling struggles to establish in a high alpine meadow . Photographic tableau of forest tree seeds . vi 1 INTRODUCTION The reasons for an interest in forest tree seeds vary widely. Nursery workers, silviculturists, seed orchard managers, cone collectors, and seed dealers have a very practical need for knowledge. But many others have developed a general interest in seed biology because they want to achieve a better under- standing of the natural world around them. Seed maturation, dormancy, and germination are still not completely understood. It remains somewhat of a mystery how a seed can remain viable for many years in the forest duff, then, responding to some cue, break through its woody seed coat and establish itself as an independent seedling. However, we know some of the factors critical to those processes, and we know that the effects of these factors may vary, depending on the physiological state of the seed. At the moment of natural seedfall, the potential quality of seeds is as high as it will ever be. To main- tain that quality and to produce the best seedlings for reforestation, knowledge of tree seed biology is essential. This handbook describes the basic principles that govern the biology of forest tree seeds and examines how these principles might apply to reforestation. Its intent is to give an overall picture of how and why seeds may germinate and to provide some understanding of a remarkable process. 2 THE BASIC PRINCIPLES OF TREE SEED BIOLOGY . Seed Structure A seed is a unique package containing the essential provides the energy supplies and structures of a new seedling and the nutrients to raw materials needed by the germinating embryo. support early growth. This package is constructed This tissue maintains the developing seedling until during a maturation period, after which the seed its photosynthetic and water uptake systems are undergoes a period of dormancy, followed by a able to support it. It contains vitamins, plant growth reactivation process referred to as germination. regulators, minerals, and many organic compounds, Each step in the sequence is critical to optimum all essential for normal embryo growth. seed performance. Nutritive tissues of conifer (gymnosperm) tree A fully developed seed consists of an embryo sur- seeds, and broad-leaved (angiosperm) tree seeds rounded by nutritive tissue, all of which is enclosed differ in several important respects, although both in a protective seed coat. The anatomy of several types of tissue perform the same function. tree.