During the 2019/20 bushfire season in Australia more than 18.6 million hectares (46 million acres) of land was burnt. Almost 3000 homes, and thousands of businesses and other buildings were destroyed (according to the Centre for Disaster Philanthropy). It wasn’t the first high-consequence bushfire season and it certainly won’t be the last, so planning and preparation for bushfire resilient landscapes should remain at the forefront of designers and landscapers.
Fire agencies have long valued the role that turf (both in public spaces and in private lawns) plays in the strategic management of bushfire risk. However, little research has been undertaken to confirm the scientific importance of living turf for fire protection. Similarly, no work has been undertaken to understand whether synthetic grass has similar strategic properties. Until now.
Professional services company GHD was engaged by Hort Innovation to undertake a study on the benefits of living turf and its role as a bushfire retardant. The study confirmed that not only is living turf a natural bushfire-resilient retardant, but synthetic grass does not share those properties.
Samples of popular turf species, buffalo, couch and kikuyu were all subjected to ignition tests at varying fuel moisture levels to understand the combustibility of these turf types. The experiments were conducted at the high-tech Pyrotron facility at the CSIRO in Canberra, during the hot dry spring and summer conditions affecting major fires in eastern Australia at the time.
The varieties were tested according to different variables such as wind speed, length of grass and moisture levels. Different fuel sources were also tested. Ultimately, the experiments proved that living turf, even turf that was under severe moisture stress, was highly resistant to ignition, and had to be in a dead or near-dead state and desiccated to extremely low moisture content levels before it would sustain fire spread.
Live turf is known operationally within fire agencies to both mitigate fire spread and is a favoured means of providing defendable space near houses, to allow safe defence of properties. Lawns and walkways are a form of firebreak, which interrupt the path of surface fire spread – they can’t stop airborne embers, but they can provide defendable space from where such embers can be safely put out.
Designing and landscaping a garden in a bushfire prone area can significantly enhance the survivability of buildings during bushfires. The Victorian Country Fire Authority (CFA) provides detailed tips for landscaping in bushfire prone areas across the country, including the importance of a well-maintained lawn.
It is common in post-bushfire impacted areas to observe green, or partially green lawns remaining largely undamaged by fire surrounding either unburnt houses or burnt houses where airborne ember attack has directly impacted the house, but the surrounding lawn remains unburnt.
Synthetic grass is not a safe substitute for living grass. Synthetic grass comprises a mixture of combustible plastics, which are predisposed to melting and ignition. Separate to the risks around ignition and fire spread it should also be considered that if synthetic grass does ignite or melt, it results in the release of incredibly harmful toxins and chemicals.
The turf industry is continually developing new varieties to suit Australian conditions. There are more drought tolerant varieties requiring less maintenance now and talking with your local grower will determine what is suited to your climate and soils.
The full report on turf as a bushfire retardant is available on the Turf Australia website as well as details of local turf growers: www.turfaustralia.com.au