Australian Seeds

A Guide to Their Collection, Identification and Biology

Luke Sweedman, David Merritt

• Publisher: CSIRO PUBLISHING
• Year: 2006
• Print ISBN: 9780643092983
• eBook ISBN: 9780643098602
• Topic: Scienze biologiche
• Subtopic: Ecologia

This is the first complete guide to the collection, processing and storage of wild collected seed. While the main focus is on Australian seeds, the procedures and protocols described within the book are of international standard and apply to users throughout the world.

The book provides a basic understanding to seed biology, evolution and morphology, and includes chapters on all aspects of harvesting, processing and storage of seeds. This will enable users to collect, process and store seed more efficiently, thus reducing loss of seed viability during the storage process with potentially huge savings in time, effort and expense in the rehabilitation and restoration industries.

With a strong emphasis on the species-rich Western Australian region, Australian Seeds features photographs of more than 1200 species showing clearly their size and shape. Comprehensive seed germination data enables users to know how long to allow for germination times and whether some form of pre-germination treatment is required and what this should be. This is of major importance to horticulturists and agriculturists planning crop and weed control programmes. It will also be a valuable resource to anyone interested in Australian flora.

CHAPTER 1

Introduction

Clare Tenner, Stephen Hopper, David Merritt,
Anne Cochrane and Luke Sweedman

Some 25 000 species of vascular plants – 10% of the world’s total – are found in Australia. At least 85% of these species are endemic, an outcome of 42 million years of isolation. Two-thirds of the Australian continent is arid, with less than 300 mm of rain a year. This area stretches from the Pilbara region of the north-west to the southern Nullarbor, where the desert meets the coast. Surrounding the arid zone on three sides are broad semiarid belts in which woodlands, mallee, and sclerophyll shrublands are prevalent. Salt lakes with uncoordinated drainage are common in broad valley floors, particularly in the west and south of the semi-arid zone, but the east is occupied by the bulk of Australia’s largest river system, the Murray-Darling. The wetter parts of Australia occupy less than a fifth of the continent, south and eastwards of the eastern highlands, across the tropical north and in a small isolated region of the south-west. Vegetation is complex, matching the topography and geology of these areas. The wettest places, often with deep fertile soils in eastern and northern Australia, are occupied by rainforests, while shallow soils in the highest rainfall areas have stunted woodlands and heaths. Wet sclerophyll forests occupy fire-prone sites and contain immense hardwoods such as mountain ash (Eucalyptus regnans) in the southeast and karri (Eucalyptus diversicolor) in the south-west. The highest mountains support alpine vegetation and stunted sclerophyll communities. Less fertile soils on rock outcrops throughout the wetter parts of Australia also have sclerophyll shrublands and stunted woodlands. Freshwater lakes and streams are strongly seasonal, as are coastal estuaries and bays into which the latter discharge. Coastal floras include mangroves and the usual cosmopolitan plants of dunes and strand, while adjacent Australian marine environments are noteworthy in the north for their coral communities of the Great Barrier Reef on the east coast and such places as Ningaloo Reef on the west coast.

Across Australia, there are three key floristic elements: woody evergreens, rainforests and the cosmopolitan plants. The bulk of the 25 000 species are endemic evergreen sclerophyllous plants of forests, woodlands, mallee, shrublands, sedgelands and grasslands. Particularly noteworthy is the dominance of three woody, evergreen genera: Eucalyptus/Corymbia (more than 900 species) and Acacia (more than 1100 species). Spinifex hummock grasses of the genus Triodia are prominent over vast desert areas. Species-rich families in Australia include the Proteaceae (banksias, grevilleas, etc.), Myrtaceae (eucalypts, melaleucas, etc.), Ericaceae (Epacridaceae – southern heaths), and Restionaceae (southern rushes). Occupying about 5% of the continent, the south-west of Western Australia is especially rich in the Gondwanan element of the Australian flora, with an estimated 8000 species, 50% of which are endemic to the region.

Tasmanian rainforest, a living Gondwanan museum.

In contrast, the extensive central Australian desert region, occupying one-third of the continent, has only 2000 species.

The ancient rainforest element covered only 1% of the Australian landmass at European colonisation. Rainforests occur in scattered sites from Tasmania to north Queensland and westwards across the tropical Northern Territory to the Kimberley region of Western Australia, and contain upwards of 2000 species, many endemic to Australia. The rainforests are living Gondwanan museums – fragmented and depleted relicts of vegetation that covered parts of the continent before the onset of Tertiary aridity after Australia drifted north from Antarctica, beginning 42 million years ago. These rainforest patches differ significantly in composition, with three major floristic groups recognised. There are cool-wet temperate rainforests of Tasmania, Victoria and New South Wales, hot-wet subtropical-tropical rainforests from near Sydney north to Queensland and the wettest parts of the Northern Territory, and hotdry semi-deciduous or deciduous rainforests and vine thickets extending from the Kimberley across to north Queensland and south into semi-arid New South Wales.

The cosmopolitan element of up to 3000 species occupies coastal habitats, saltlands, wetlands and alpine or mountainous areas. Typically, endemism is lower in this component of the flora.

The Australian flora is, indeed, extraordinary. And never has an appreciation of its seeds, and the need to conserve them, been greater.

SEEDBANKING IN CONSERVATION: THE INTERNATIONAL CONTEXT

An understanding of the role of seeds in conservation of the world’s biological diversity is necessary to appreciate the resources now dedicated to working with seeds. It is well recognised by the global community that biodiversity is being destroyed irreversibly by human activities and that a major effort is needed to better understand and conserve biodiversity. In January 2005, the Paris Declaration on Biodiversity noted that humans were altering the environment at unprecedented speed, with species being lost at a rate about 100 times faster than the average natural rate. The large-scale loss is irreversible, but the declaration calls for a major effort to discover, understand, conserve and use biodiversity sustainably.

In 2002 the Parties to the Convention on Biological Diversity (CBD) adopted a strategic plan with a mission to achieve by 2010 a significant reduction of the current rate of biodiversity loss. This was later endorsed by the World Summit on Sustainable Development. The CBD recognises that ex situ (off-site) measures – collecting seeds and then keeping them in seedbanks, for example – have an important role to play in the conservation of biodiversity. The CBD definition of biodiversity recognises diversity within species, between species and at the ecosystem level. Many studies have shown the threats that face biodiversity occur at all three levels. For example, at the ecosystem level, models suggest that by the year 2032 up to 48% of ecosystems could be converted to agricultural land, plantations or urban areas, compared to 22% today. At the species level it is thought that as many as two-thirds of the world’s plant species are in danger of extinction in nature during the course of the twenty-first century.

With regards to genetic diversity, it is estimated that 16 million populations are lost annually. In Australia alone, 2891 individual ecosystems have been identified as at risk, and 1595 native animal and plant species. The biggest direct cause of species loss is habitat loss and degradation – this affects 91% of all threatened plant species described in the 2000 IUCN red list. Habitat can be lost through conversion for, or intensification of, agriculture, urbanisation and infrastructure development, amongst other things. Protected areas can help safeguard habitat, but there are limits to the area of land that can be covered. It takes time to establish protected areas and it can be difficult to situate them for the optimal protection of plant species. Even in well-protected areas plants are subject to further threats including climate change, invasive alien species, over-exploitation by humans and manmade and natural disasters.

The Intergovernmental Panel on Climate Change predicts that the synergy between the stresses of climate change, habitat loss and fragmentation, and alien species will lead to extinctions. In Australia additional threats to biodiversity include dieback/disease, salinity, overgrazing, feral pests, and inappropriate fire regimes.

The root causes of biodiversity loss are, of course, more complicated to unravel, but include elements such as demographic changes, poverty and inequality, macroeconomic policies and trade practices and patterns of consumption. These will take time and political will to tackle. In the meantime seedbanks can play a significant role by conserving inter-species and intra-species diversity.

The collection and storage of seeds is not new. Many peoples have done this for millennia. Certainly, since the beginning of agriculture, most of the world’s food supply has relied on seeds that can be harvested and stored for a period of time. However, the establishment of native seedbanks for biodiversity conservation is a relatively recent occurrence, as is the use of stored seed in flora recovery projects. In some cases, ex situ conservation represents the only option available if the remaining natural populations are to be conserved in the face of destruction of their habitat. Actions to conserve individual species contribute in a fundamental way to broader conservation objectives, even if the species themselves are not highly threatened. Seedbanking cannot directly protect biological diversity of ecosystems, but it can ensure the protection of genetic diversity. Material can be provided for species and ecosystem recovery, and it has proved a cost-effective source of material for research. Investigations into seed germination and storage behaviour maximise the value of the material, and seedbanks have made an important contribution to education and public awareness.

Ex situ conservation is a critical component of an integrated global conservation programme, and seedbanking is one of the most valid and widespread methods used at present owing to its simplicity and economy in terms of technology, infrastructure, manpower and operating costs. It is possible to maintain large samples with wide genetic representation at an economically viable cost. Of the 9000 plant species whose storage characteristics are known, 92% have desiccation-tolerant seeds and are expected to remain viable in storage for at least 200 years.

Today there are around 150 seedbanks found within the world’s botanic gardens. In addition, many national crop and tree seedbanks are increasingly moving into conservation of wild plant species. In any case, seed collections are a readily accessible and cost-effective source of material for research. Material is quickly and easily accessible to researchers, without the need to carry out expeditions or to over-exploit wild populations. Terms and conditions can be attached to the supply of this material which ensure the fair and equitable sharing of any subsequent benefits.

The Millennium Seed Bank, Wakehurst Place, UK, is an example of a modern, well-equipped seedbank.

The CBD provides the international framework for activities on biodiversity. The overall objectives of the CBD are conservation of biological diversity, sustainable use of components of biological diversity, and fair and equitable sharing of the benefits arising from the use of genetic resources. As has been discussed above, seedbanks have a role to play in meeting all three of these objectives. The CBD emphasises that the fundamental requirement for the conservation of biodiversity is in situ (on-site) conservation, but that ex situ measures have an important role to play.

The Biodiversity Conservation Centre, Kings Park and Botanic Garden, Perth, Western Australia.

The CBD has been ratified by the governments of 187 countries, including Australia. It provides international political endorsement of the work of ex situ programmes, such as the Millennium Seed Bank Project, an international collaborative plant conservation initiative based in the United Kingdom. This worldwide effort aims to safeguard 24 000 plant species globally against extinction and has already successfully collected and stored seeds of virtually all the United Kingdom’s native flowering plants. This project is evidence of the resources now being directed into seedbanking for conservation. Even if species are lost in the wild, the work of seed collectors will ensure that plants will be available for use in future conservation and restoration efforts.

Botanists have been at the forefront of conservation developments, and led by example with the development of the Global Strategy for Plant Conservation (GSPC). The Strategy originates from a resolution at the 16th International Botanical Congress, held in St. Louis, USA, in 1999. It was developed by a globally representative group of botanical institutes, non-governmental organisations and inter-governmental organisations, and was adopted by the Parties of the CBD in 2002. The Global Strategy for Plant Conservation provides a framework for actions at global, national and local levels to understand and document plant diversity, conserve plant diversity, use plant diversity sustainably, promote education and awareness about plant diversity and build capacity for the conservation of plant diversity. The Global Strategy for Plant Conservation includes 16 targets to be reached by 2010. One calls for ‘60% of threatened plant species in accessible ex situ collections, preferably in the country of origin, and 10% of them included in recovery and restoration programmes.’ At a global level the lead organisations for this target are Botanic Gardens Conservation International (BGCI) and the International Plant Genetic Resources Institute (IPGRI).

Meeting this target is no simple task. At present we do not even know how many species there are, let alone which are threatened. The GSPC currently states that 10 000 threatened plant species are maintained in living collections (botanic gardens, seedbanks and tissue culture collections), representing 30% of known threatened species. This leaves another 10 000 to be collected and conserved by 2010. However, more recent figures suggest that the number of threatened species may be around three times those used in the GSPC.

The most important thing for seedbanks is to make information available on the species they hold, and to work together to avoid a duplication of effort. Some coordinated networks are already established. For example, the Millennium Seed Bank Project is working with partners from 17 countries worldwide to collect and conserve 24 200 species by 2010. Regional networks include the European Native Seed Conservation Network and the African Botanic Garden Network. There are also challenges regarding the quality of the collections. This will affect the usefulness of the collections for recovery and restoration programmes. There is little information at the moment on whether existing collections are genetically representative and attention also needs to be paid to the quality of storage. Finally, there is a challenge in ensuring that collections are held in their country of origin. This requires longterm commitment from the home governments but will also require technical support and assistance from established seedbanks. Australian seedbanks have a clear role to play here.

CHAPTER 2

Australian seeds through time

Stephen Hopper, Kingsley Dixon and Robert Hill

The evolution of seeds was a major step in enabling plants to colonise land beyond wetland habitats or their margins. Seeds provided an escape from the requirement for free water to ensure sexual reproduction. This requirement still applies to present-day mosses, liverworts, ferns and fern-allies, and explains why these plants are confined to habitats where water is prevalent when they reproduce.

The other advantages of seeds are the protection from desiccation, predators and pathogens they afford to the embryo, and the nutrients they provide for germination and early growth...

Table of contents

• Cover
• Title
• Copyright
• Dedication
• Contents
• Foreword
• Commendation
• Acknowledgments
• Preface
• Contributors
• 1. Introduction
• 2. Australian seeds through time
• 3. Seed and fruit structure
• 4. Seed biology and ecology
• 5. Seed collection in the field
• 6. Drying and cleaning seeds after collection
• 7. Seed storage and testing
• 8. Seedbanks and the conservation of threatened species
• 9. Australian seeds: a photographic guide
• 10. Collection guidelines for common Australian families and genera
• Appendix 1: Seed germination records
• Appendix 2: Specimen vouchers for the seed photographs
• Appendix 3: List of common names
• Appendix 4: List of botanical names
• Glossary
• References
• Index