Australia is the driest flattest continent of earth which, due to its long-standing isolation, has led to some unique fauna, but also some extremely unique flora.
The Blue Mountains region, our most popular day trip, is just a couple of hours from Sydney. In the region we bear witness to the many types of Eucalyptus trees (around 100 of the 900 or so species that dominate Australia but are also scattered in to neighbouring Papua New Guinea and Indonesia).
Eucalyptus are evergreen and for many species we see in the Blue Mountains their unique attribute is that they lose their bark in yearly cycles rather than their leaves. The bark that trails off the tree and falls to the ground is welcome tinder when time comes – and it inevitably does – for Bushfire. Naturally occurring and man made fire is a fact of life in the bush-land environments of Australia.
Because fire is such a consistent force in the landscape of Australia certain trees and shrubs have evolved to resist and some even rely on fire to spread their seeds.
Banksia trees are a common tree we see in the region that do just that….
However, not all types of the 170 or so that exist. Some species of Banksia will release whatever seeds that are ripe when available, often helped along to new locations by flying foxes and birds. Others wait (sometimes years at a time) for the heat and smoke of a fire.
The fruits of the flowering Banksia are hard and woody, and the seed lies encased inside. Like all seeds they require water, oxygen and the right temperature to germinate – move from seed to seedling or, put another way, dormancy to life.
The right temperature and conditions for some Banksias is often due to fire. When a fire arrives a parent Banksia may be killed but the fruit will open from the follicle. The ready to go seeds fall and the fire clears any competitors and fertilises the top soil with ash.
However, there is one key ingredient required with several Banksia trees to ensure germination happens after fire – where there is fire, there is smoke!
It took until the year 2004 for scientists to nail down the process of smoke germination on several Australian trees and shrubs, including the Banksia. A team based in Western Australia deciphered that from the 4000 or so chemicals that reside in smoke a molecule they named karrikinolide (a local indigenous word for smoke), which is scientifically known as one of the butenolides molecules. These master molecules, as they have been labelled, are a by-product of the combustion of cellulose (fibres of the seed) together with other organic compounds in the plant tissues.
So there you have the unique story of the flowering Banksia, which loves the inevitable fire and the smoke that comes before and after it, as well as the flying foxes, birds and insects that live on their nectar and spread their seeds.
We should also mention that the famous botanist Joseph Banks, who travelled on the Endeavour expedition in 1770 with James Cook is where their name comes from.
Following are some pictures of flowering Banksia fruits in different states.
Come and see them in the flesh on a day trip or overnight experience to the Blue Mountains.