Saguaro and other cactus are not adapted to a fire regime, as fires did not regularly affect them in the past. Prior to the introduction of exotic grasses for cattle feed and landscaping, the native desert grasses were sparse and did not carry a fire far. Therefore a lightning strike would have caused only a small patch to burn before running out of fuel.
Other threats to the saguaro include vandalism, attempted transplant or theft of the cactus. The saguaro is one of many plants in Arizona protected by the Native Plant Protection Act, and within national park lands, the removal of any plant is illegal. Also, all land in the state is owned by somebody whether it is federal, state, tribal, or private.