Exactly, Fiber Lasers (i.e. 1064nm wavelength) pose a serious fire hazard when trying to work with wood. Because of its short wavelength, a 1024nm laser can partially transmit through organic materials like wood. However, because of the differences within the wood itself, this transmission is impossible to control and you'll get heat build up that can eventual cause the wood to ignite. Even if it doesn't burst into flame, you'll get a poor marking/engraving since it will be very inconsistent due to the variations in how the wood absorbs/transmits the 1024nm energy.