In order to understand how a wildfire spreads, its probabilities to do so and in which directions, it is important to take into account the layout of the place, as well as the kind of vegetation in the area. Ground fires are fed by roots and underground organic materials. They can burn even months with a slowest combustion. Surface fires are fueled by shrubbery, besides fuel that can be found on the ground, like leaves and sticks. Ladder fires allow the fire to pass from the ground to the canopy level. They develop thanks to trees that are smaller than the others, fallen logs, vines and invasive plants. Crown, or aerial, fires are those fires that develop at the canopy area, and they are fed on the crown of taller trees and the mosses and vines growing over them. The possibility for their development depends on the intensity and the diffusion of surface and ladder fires.
Wildfires spread very fast: they can reach the 10.8 Km per hour in woods and 22 Km/h in grasslands. They can advance, back, and spread through spotting: hot wood embers are "shot" from the fire to the surrounding vegetation and start other fires in further spots (in some cases, even 10 Km far). In this case, the fire can also go beyond natural barriers, like water streams, roads or firebreaks.