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3 May 2020

Saving our rainforests after the fires

The devastating bushfires burnt over five million hectares in NSW alone, with rainforests amongst the most affected. Scientists are using 'plantbanking' to save vulnerable species in these important ecosystems. 

A shrinking biodiversity hotspot 

Perhaps as much as half of Australia’s biodiversity is found in our rainforests, including plants, animals, fungi and microbes. Many food and medicinal species, as well as crop wild relatives, are found in rainforests. For example, all Macadamias originated in eastern Australian rainforests and all four wild species are threatened.

Australian rainforests are also home to the world’s greatest diversity of wild citrus species, including the increasingly popular finger lime. The overall ‘ecosystem services’ provided by our existing rainforests are vital to the health of the planet and our survival.

Over the past 200 years, Australian rainforests have been reduced from four per cent of the landmass to now only occupy around 0.3 per cent of the country. More than 80 per cent of the Greater Blue Mountains World Heritage Area and 54 per cent of Gondwana Rainforests World Heritage Area were recently impacted by the fires

Chief Botanist Dr Brett Summerell says rainforests are not adapted to fire and have not had evolutionary drivers to adapt to extremely hot and dry conditions that come with fire.

"The trees in these forests are often thin-barked and easily killed by the heat of bushfires and the seed is designed for dispersal by animals and not stimulation by fire," says Dr Summerell. 

When these habitats burn, the outcome is usually poor and it is possible that entire species have been consumed by the fires
Chief Botanist & Director Research Dr Brett Summerell

Seedbanking to save species

Conserving species in the wild is critical and all our efforts are required to restore and manage their habitats. 

"With large scale-destructive events on the increase, it has never been more important to also conserve species ‘ex situ’, or ‘away from the site’ in botanic gardens, zoos and other safe havens, returning them to the wild when it is appropriate and safe to do so," says Dr Summerell.

Plants have been saved in cultivation and as seeds since humans first started foraging and farming. In recent years, as concerns over loss of biodiversity have increased, there has been a massive expansion in seed banking.

Most agricultural crops are held in seed banks such as the so-called ‘Doomsday’ seedbank under the arctic ice in Norway, which houses ‘back-up’ collections of many of the world’s crop species.

Seed banks for native species, such as the Australian PlantBank at the Australia Botanic Garden Mount Annan, are also found around the world.

"They're primarily in temperate regions, with few located in the tropics and areas of high rainforest diversity. These seedbanks are increasingly used as the source of plants for restoration of damaged ecosystems," says Dr Summerell.

Most fire adapted plants, like wattles (Acacia) and eucalypts, have seeds that can be banked and they are well represented in seed collections housed in the conservation repositories that make up the Australian Seed Bank partnership and the global backup collection at the Millennium Seed Bank in the UK.

"It is this ability to survive dry conditions that also means the seed of these species can be artificially dried and stored in a seed bank," says Dr Summerell. 

"Such seeds, in seedbanking terminology, are ‘orthodox’. In a seedbank freezer it’s predicted that the seeds of many Acacia species may last many centuries," Dr Summerell says. 

Plantbanking our rainforests

Global seedbanking efforts have conserved a huge proportion of the worlds dryland species and Senior Principal Research Scientist Dr Cathy Offord says it's now time to focus on those plant species that can’t be seedbanked.

"These species produce seed that will not survive drying or freezing, or they just don’t produce seeds at all," Dr Offord says.

"The highest proportion of such plants are found in rainforests and other wet habitats and for many of these species, we need to consider a process we call 'plantbanking'," says Dr Offord. 

Contrast dryland Acacias with Castanospermum australe, an Australian coastal rainforest species (Black Bean or Moreton Bay Chestnut). Both are from the same taxonomic family, Fabaceae, the pea family, yet their seed storage potentials are completely different. 

Black Bean seeds are typical of many rainforest trees in that they are large, with a thin seed coat. When mature, the seed is lime green and ready to germinate straightaway. 

"Unfortunately, the seed of this species dies when it is dried and cannot be frozen for long-term conservation in a seed bank," says Dr Offord. 

On the other hand, other rainforest species may be able to tolerate drying, but not freezing.

"Many seeds from rainforest species therefore cannot be conserved in a seed bank using traditional methods and they are generally termed ‘recalcitrant’," Dr Offord says. 

The conservation of recalcitrant rainforest species is complex, which is why it’s received relatively little attention. Traditionally, rainforest species have been conserved ex situ by growing them in a garden or plantation.

"This provides a source of material to propagate from, but the genetic diversity is generally low compared to seed bank collections that can hold thousands of individuals," says Dr Offord. 

Other techniques are available, such as tissue culture, which is labour intensive compared to seed banking and many fewer individuals can be conserved.

Cryostorage of shoots or embryos in liquid nitrogen at ultra-low temperature (less than -180 degrees Celsius) is another alternative and is similar to the storage of mammalian sperm, eggs and embryos.

"The technique shows great promise for recalcitrant plants, but its success varies from species to species and requires concerted research for rainforest species," says Dr Offord.

Plantbanking our rainforest species requires a mixture of these techniques to get effective conservation outcomes.

The Wollemi Pine: a plantbanking success story

A well understood example of plantbanking, which could be used for many threatened rainforest species, is the iconic Wollemi Pine (Wollemia nobilis) which was re-discovered in 1994.

Dr Cathy Offord's research has been vital in establishing the iconic Wollemi Pine as a global model for threatened species management. 

"Seed cones had to be initially collected by helicopter and we soon discovered that there were very few seeds in each cone," says Dr Offord. 

Wollemi Pine trees growing in their secret location in a canyon in the Blue Mountains, near Sydney.

It was almost impossible to collect Wollemi Pine seeds because of the 40 metre height of the trees and their location in a deep canyon
Senior Principal Research Scientist Dr Cathy Offord

From the wild, to the world

Dr Offord says the conservation program that has followed for the Wollemi Pine demonstrates the complexity needed, when comparing it to seedbanking alone. 

"The Wollemi Pine was brought into cultivation by cloning as many of the individual trees as possible, and over time releasing plants to other botanic gardens and eventually they became available to gardeners," says Dr Offord. 

"This dispersed collection means that living plants are now found in many parts of the world," Dr Offord says. 

To understand the environmental tolerances of this unique tree, Dr Offord has also co-launched the I Spy A Wollemi Pine citizen science survey which encourages people to report their sightings of the tree in parks or gardens.

Seed science and vital conservation reserach on the horizon

While some wild-collected Wollemi Pine seeds have been deposited in the seedbank at the Australian PlantBank, Dr Offord says they are thought to be short-lived.

"Representative collections of the majority of individuals in the wild are held in our botanic gardens and these plants are used to conduct studies on many aspects of the biology of this species, including fire response, climate adaptability, disease susceptibility, genetics and growth," says Dr Offord. 

"Using seeds from cultivated sources, we are now attempting to cryostore embryos, which offers the promise of greatly extended storage life," Dr Offord says.

Experimental translocations to the wild have also been made, which, although fire affected, will inform scientists about the possible return of this species to the wild if all else fails to protect this special tree in its natural habitat. 

Discover more about the Wollemi Pine with Dr Offord in our podcast 

Category: Science
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