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24 Jan 2020

The impact of fire on plants

As intense bushfires cause devastation across the country, including at the Blue Mountains Botanic Garden, it is important to look at the loss of plant life and potential long-term effects of this crisis. 

A charred landscape 

The current fire season has had a devastating impact on the natural world across Australia. The extent of the bushfires has been of a scale that is very difficult to comprehend. Images and footage of the immense suffering of animals have been confronting and heartbreaking.

People often ask about the impact on plants. Charred landscapes of immense size are predominantly images of burnt plants – trees and the understorey species that comprise those ecosystems. But can we state how many plants have been killed?

Assessing the impact of fire on plants

It is difficult to estimate the number of plants impacted by fire. Published tree densities in different ecosystems are 500–1,200 trees per hectare. If we multiply this by the area burnt in the current fires (10 million hectares and counting), assuming 60 per cent was natural ecosystems, it could mean that 3–7.2 billion trees have been impacted, with as many understorey species (and this doesn’t even begin to take into account organisms such as fungi, lichens and algae). The impact on understorey species is usually much more dramatic, and final, as they are likely to be burnt completely.

However, the answer to this question is much more nuanced. The flora of Australian has evolved with fire. As the continent has become more arid, species such as eucalypts and wattles have come to predominate, and these plants have numerous adaptations to cope with fire.

In eucalypts, epicormic buds protected by bark spring to life after a fire with amazing haste, while seed of wattles and banksias are stimulated to germinate and grow once it rains enough for successful establishment. In some cases, we even see species of plants grow that have not been observed for a long time.

The impact on understorey plant species is usually much more dramatic, and final, as they are likely to be burnt completely
Chief Botanist & Director Research Dr Brett Summerell

Expected outcomes

The extent of recovery depends on the intensity of the fire. Lower-intensity, rapid fires do not substantially damage eucalypts, and stimulate germination of seed of a range of species. If the fire is high intensity – as it has been recently – we see trees killed and an almost sterilisation of the forest floor. In these situations, the loss of plant diversity may well be profound.

In ecosystems that are not adapted to fire, the losses can be much higher. Rainforests have not evolved to cope with dry conditions or fire. Trees in these forests are often thin-barked and easily killed by bushfire heat. Their seed is designed for dispersal by animals and not the stimulation of fire. When these habitats burn the outcome is poor.

The impact of fire on threatened species will be variable, depending on local conditions and the distribution and intensity of the fire. It will take a long time to assess the situation across ecological communities around the country. Monitoring the impacts and responses will be critical.

The expectation that climate change will continue to facilitate fires in the future highlights the importance of ensuring that we preserve plants in seed banks and botanic gardens, and understand the response of plants to a changing climate. We need to make a substantial inroad to collecting as many of Australia‘s 25,000 or so plant species, and their genetic diversity, as possible to be sure of preserving them into the future, and combine this with programs to recover threatened species and restore species in the wild.

Plants are vital for life. These fires highlight how much more research is needed to ensure their, and our, survival.

How you can help

Scientists the Botanic Gardens are working on real solutions to help ensure our plant life can withstand a changing climate. We are also restoring the Blue Mountains Botanic Garden Mount Tomah and working on water security solutions for our living collections. You can help support our efforts through the Foundation and Friends of the Gardens.

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