Onion Cedar (Owenia Cepiodora) – Discovery and Recovery In Nightcap National Park

Onion Cedar (Owenia Cepiodora) – Discovery and Recovery In Nightcap National Park

Onion Cedar (Owenia Cepiodora) – Discovery and Recovery In Nightcap National Park

Contributed by Justin Mallee

First the discovery.

Marcel Proust wrote “The real voyage of discovery consists not in seeking new landscapes, but in having new eyes.” While the eyes in this story are not new, they have had a renewed focus as part of the Saving our Species (SoS) Onion Cedar project. The result … a 600% increase in the number of individuals known to occur in the Nightcap National Park.

Onion Cedar is a large rainforest tree with a glossy green crown that is renowned for both its smell (like an onion!) and, historically, for its timber quality (resembling Red Cedar). Despite years of botanical exploration in the area, Onion Cedar was considered extremely rare in the Nightcap with a total population of six individuals consisting of four adults, one sapling and one seedling. In the world of plant conservation, a population of six individuals is generally not good news. With numbers this low a storm event and associated tree falls could result in local extinction.

In 2017, SoS commissioned surveys to revisit the known individuals, assess the threats to them and, if opportunity allowed, look for more. The result was the discovery of a total of 37 individuals – 13 adults, 22 saplings and 2 seedlings. This is a major increase for the species and provides renewed hope for the future of the Nightcap population.

Now the recovery.

Historically, Onion Cedar would have occurred across the large tracks of forest that formed the Big Scrub. With less than 1% of its Big Scrub habitat remaining, the species is now confined to small isolated remnants including the aforementioned Nightcap population. Luckily, further to the west of Kyogle there are larger populations of Onion Cedar in the drier Hoop Pine dominated rainforest.

To address the low numbers in the Nightcap area, SoS is undertaking two main actions – assisted bush regeneration through the removal of competitive weeds and translocation planting of additional individuals into the existing populations.

The assisted regeneration works have removed large areas of weed dominated vegetation (Lantana) adjoining known populations. This first step in the regeneration cycle sets a ball in motion, stimulating the soil seed bank and creating opportunities for colonisation by wind, water or animal dispersed seeds. If left to their own devices the sites would likely grow as a mix of pioneering natives and weeds, but with ongoing assistance, through removal of germinating weeds, the sites will go on to become diverse and wonderous subtropical rainforests providing homes for hundreds of species of plants and animals.

In an ideal world Onion Cedar would be one of the native species colonising the bare ground following the initial weed removal. Unfortunately, this is unlikely to be the case as there are few trees of fruiting age and the dispersal mechanisms that limit the movement of seeds away from the parent trees are not known. To combat this SoS has collected seeds from the larger western populations and propagated them in a nursery. These nurseries grown plants will then be planted out into the regenerating lantana gaps, thus bolstering the wild populations.

If all goes to plan, more than 100 new Onion Cedars will be planted into the Nightcap. This will not only triple the current known population, but also introduce genetic material from the western populations. It is hoped that existing and new individuals will breed and that their progeny will have greater genetic diversity and resilience to future change. Projects such as this take years of research and detailed planning. Once implemented, these actions set a new trajectory for the site and the species that if maintained will have a legacy lasting hundred if not thousands of years.

Leave a Reply

Your email address will not be published.