When lightning or other forms of ignition start a fire in a forest, there is a chance of a wildfire. Wildfires may be started by a natural cause, such as lightning, or they may be started accidently by human activities or on purpose by an ill-meaning person. When houses are built close to trees, the trees provide the fuel that wildfires need to spread. The question the scientist wanted to answer was: How close must flames come to a house’s outside wooden walls before those walls catch fire? Note Topics: Active Forest Management, Fire, Wilderness, Convection, Defensible Space, Fire, Heat Transfer, Human Impacts.