Australians know instinctively that the bush is adapted to burning. We see those tough, leathery-leafed eucalypts burned back to the stump and then a few weeks later there’s a‘beard’ of fine shoots that appear all over the trunk. They’re what is known as epicormic shoots – little reserve buds that live underneath the bark for just such an occasion as a bushfire.
I’ve had occasion to reflect on the role of fire in growing Australian plants in our gardens. That might seem a strange connection, but I recently had the wonderful Rural Fire Service onto my bushland property to conduct a hazard reduction burn and the pictures accompanying this blog will give you some idea of the intensity of the fire. It’s burned things back to the ground. It’s now a few weeks on and already that wonderful greening of the bush is happening. What really fascinates me is that when the bush does burn, there’s really intensive re-growth from the plants due to the nutrients that are released by the fire. All the ash that is on the ground not only fertilises it, but also triggers germination of all sorts of species. It’s recently become known fact that an active ingredient that has been isolated from smoke triggers seed germination.
So we see this profuse greening of the bush in the months after a fire which also triggers flowering in a wide range of species. I tend to come back to my bit of bush because one thing I do have in profusion is Gymea lily, Doryanthes excelsa, and that is one of the classic plants to be stimulated to flower by fire. I’ll be revisiting this in my bushland patch next spring so you can see the synchronisation of flowering that will happen from this hazard reduction burn.
In my experience with fire there are a couple of really important things that happen. There’s the release of large amounts of nutrients from the ash, as well as chemical triggers for germination, and the triggering of flowering, but I think the other thing that’s not often appreciated is that after a fire there’s a great reduction in the canopy. Suddenly there’s lots of light reaching the soil surface for a change, so a lot of plants at ground level that have been hiding underneath the leaf litter and bark that covers the soil in unburnt bush, are able to flower. A classic example of that is the Christmas bell, Blandfordia nobilis, or also Blandfordia grandiflora around Sydney – there are several other species around Australia as well.
So what does all this mean for you as a gardener wanting to grow these native plants? First, we can emulate the effect of increased nutrition by judicious fertilising. Plants like banksia, waratah and grevillea are notorious for being very phosphorus sensitive, but by giving them a low phosphorus fertiliser, you’re simulating the extra nutrients that come after a fire. By providing lots of light you are able to grow those pioneering ground-hugging species that appear after a fire like Christmas bell and fanflower, Scaevola species, which is a beautiful and colourful plant that comes up in profusion after a fire in its natural habitat. Gradually over the years these plants disappear as the forest grows back and there’s less light, and the nutrient levels decline again as nutrients are leached away through the soil. Nutrients are also stored in the leaf litter on the forest floor. In an unburnt forest, you’ve got years and years of organic matter that builds up and only breaks down very slowly, if at all. I think of a fire as a very rapid method of composting! A bit of wood ash, in moderation, will have a similar stimulatory effect on these species.
Get out into the bush to do your own observation, especially a year or two after a fire, as it’s a magnificent time to see all those low-growing plants that occur on the forest floor.
Happy gardening – you’ve been gardening with Angus!