Strike Force Vulcan officers are investigating the deliberate ignition of nine grass trees on Gilmore Avenue near Darius Drive in Calista.
Department of Fire and Emergency Services crews attended at around 12.30am on Sunday and were able to extinguish the fires before they spread to nearby homes.
Investigators wish to speak to anyone who saw any suspicious people or activity, or has dash-cam vision of the area around the fires between 12.05am and 1am.
Anyone with information regarding these fires is asked to call Crime Stoppers on 1800 333 000 or make a report online at www.crimestopperswa.com.au.
Callers may remain anonymous if they wish.
Rewards of up to $50,000 are available for information that leads to the identification and conviction of an arsonist.
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